Hsc chemistryModule 7

Organic chemistryStudent’s notes

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OutcomesA student:

› analyses and evaluates primary and secondary data and information CH11/12-5

› solves scientific problems using primary and secondary data, critical thinking skills and

scientific processes CH11/12-6

› communicates scientific understanding using suitable language and terminology for a

specific audience or purpose CH11/12-7

› analyses the structure of, and predicts reactions involving, carbon compounds CH12-14

Content Focus

Students focus on the principles and applications of chemical synthesis in the field of organic

chemistry. Current and future applications of chemistry include techniques to synthesise new

substances – including pharmaceuticals, fuels and polymers – to meet the needs of society.

Each class of organic compounds displays characteristic chemical properties and undergoes

specific reactions based on the functional groups present. These reactions, including acid/base

and oxidation reactions, are used to identify the class of an organic compound. In this module,

students investigate the many classes of organic compounds and their characteristic chemical

reactions. By considering the primary, secondary and tertiary structures of organic materials,

students are provided with opportunities to gain an understanding of the properties of materials –

including strength, density and biodegradability – and relate these to proteins, carbohydrates and

synthetic polymers.

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Content

Nomenclature

Inquiry question: How do we systematically name organic chemical compounds?

Hydrocarbons

Inquiry question: How can hydrocarbons be classified based on their structure and reactivity?

Students:

● construct models, identify the functional group, and write structural and molecular formulae for homologous series of organic chemical compounds, up to C8

– alkanes– alkenes– alkynes

Students:

● investigate the nomenclature of organic chemicals, up to C8, using IUPAC conventions, including simple methyl and ethyl branched chains, including:

– alkanes– alkenes– alkynes– alcohols (primary, secondary and tertiary)– aldehydes and ketones– carboxylic acids– amines and amides– halogenated organic compounds

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Introduction to Carbon Chemistry

Carbon (or Organic) chemistry is the study of compounds of carbon.

Hydrocarbons are compounds that contain only carbon and hydrogen.

Carbohydrates are compounds containing only carbon, hydrogen and oxygen.

There are 2 main types of carbon compounds:

1. aliphatic – straight chain carbon compounds

For example: Butane

2. Aromatic – specific cyclic carbon compounds

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Aliphatic Carbon Compounds

These are ‘straight chain’ hydrocarbons. For example:

propane

- C – C – C –

There are 3 types of aliphatic carbon compounds.

These compounds all belong to a homologous series.

A homologous series is a family of compounds which can be represented by one general

molecular formula.

Alkanes

Every carbon atom has four bonds around it.

Alkanes are carbon compounds that only have one bond between each carbon atom.

When naming alkanes the compound is named as a derivative of the hydrocarbon

having the longest carbon chain.

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Alkanes have the ending –ane on their name and are named according to the following

stems:

Stem No of

carbons

Name Formula Structure

Meth 1 Methane CH4

Eth 2 Ethane C2H6

Prop 3 Propane C3H8

but 4 Butane C4H10

Pent 5 Pentane C5H12

Hex 6 Hexane C6H14

Hept 7 Heptane C7H16

Oct 8 Octane C8H18

Non 9 Nonane C9H20

dec 10 Decane C10H22

Alkanes belong to the homologous series CnH2n+2

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Alkenes

There is at least one carbon – carbon double bond in the straight chain.

Alkenes have the ending -ene.

Naming Alkenes

Alkenes have the appropriate stem and where longer chains occur, numbers are used to

identify where the double bond is.

The double bond is always given the smallest possible number.

Stem Name Formula

Eth Ethene C2H4

Prop Propene C3H6

But Butene C4H8

Pent Pentene C5H10

Hex Hexene C6H12

Hept Heptene C7H14

Oct Octene C8H16

Non Nonene C9H18

Dec Decene C10H20

Alkenes belong to the homologous series CnH2n

Alkynes

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There is at least one carbon- carbon triple bond in the straight chain.

Alkynes have the ending -yne.

Naming Alkynes

Alkynes have the appropriate stem and where longer chains occur, numbers are used to

identify where the triple bond is.

The triple bond is always given the smallest possible number.

Stem Name Formula

Eth Ethyne C2H2

Prop Propyne C3H4

But Butyne C4H6

Pent Pentyne C5H8

Hex Hexyne C6H10

Hept Heptyne C7H12

Oct Octyne C8H14

Non Nonyne C9H16

Dec Decyne C10H18

Alkynes belong to the homologous series CnH2n-2

Branches (Side Chains)

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Branches are small aliphatic groups attached to an aliphatic chain.

Branches are named in alphabetical order, i.e. but, eth, hept, hex etc.

The compound must be named to give it the smallest numbers possible.

Branches are named by adding –yl to the stem, e.g. methyl, ethyl

For example: 2,3-dimethylbutane

Summary Tables for Naming Carbon Compounds

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TABLE 1: Prefixes for naming carbon chains Prefix meth eth prop but pent hex hept oct non dec

Number of Carbon atoms in the chain 1 2 3 4 5 6 7 8 9 10

TABLE 2: Hydrocarbons: compounds which contain only carbon and hydrogen

Type of Compound Prefix Suffix Functional Group Example Name

Alkyl group(side-chain or branch)

see TABLE

1-yl

Alkane less 1 terminal hydrogen

ethyl

Alkane see TABLE

1-ane

contains single bonds between carbon atoms

ethane

Alkene see TABLE

1-ene

contains a double bond between 2

carbon atomsethene

Alkyne see TABLE

1-yne

contains a triple bond between 2 carbon atoms

ethyne

Cyclic Hydrocarbons cyclo

-ane, -ene or -

yne(as

above)

carbon atoms form a ring cyclopropane

TABLE 3: Compounds containing carbon, hydrogen and oxygen

Class of Compound Suffix Functional Group

General Formula Example Name

Alkanol -ol(alkyl

alcohol)

-OH(hydroxyl)

R-OH ethanol(ethyl alcohol)

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(alcohol)

Alkanal(aldehyde)

-al(carbonyl)

R-CHO ethanal

Alkanone(ketone)

-one(carbonyl)

R-CO-R' propanone

Alkanoic acid

(carboxylic acid)

-oic acid

(carboxyl)

R-COOH ethanoic acid

Ester alkyl -anoate R-COO-R' methyl

ethanoate

Aldehyde Nomenclatures1. Aldehydes take their name from the parent alkane chain. The –e is removed from the

end and is replaced with –ol.

2. The aldehyde functional group is given the #1 numbering location and this number is

not included in the name.

3. For the common name of aldehydes start with the common parent chain and add the

suffix –aldehyde.

4. Compounds can also have the ending –al,. e.g. Ethanal (or Acetaldehyde)

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Summary of Ketone Nomenclature Rules1. Ketones take their name from the parent alkane chain. The ending –e is removed and

replaced with –one.

2. The common name for ketones is are simply the substituent groups listed

alphabetically + ketone.

3. Some common ketones are known by their generic names. For example propanone is

commonly called acetone.

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Worked Example 9.3and Try These Yourself p274

Amines

Amines are characterized by nitrogen atoms with single bonds to hydrogen and carbon.

Just as there are primary, secondary, and tertiary alcohols, there are primary, secondary,

and tertiary amines. Ammonia is a special case with no carbon atoms.

One of the most important properties of amines is that they are basic, and are readily

protonated to form ammonium cations. In the case where a nitrogen has four bonds to

carbon (which is somewhat unusual in biomolecules), it is called a quaternary

ammonium ion.

Do not be confused by how the terms 'primary', 'secondary', and 'tertiary' are applied to

alcohols and amines - the definitions are different.  In alcohols, what matters is how many

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other carbons the alcohol carbon is bonded to, while in amines, what matters is how many

carbons the nitrogen is bonded to.

Amides

The amide functional group has a nitrogen atom attached to a carbonyl carbon atom. If

the two remaining bonds on the nitrogen atom are attached to hydrogen atoms, the

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compound is a simple amide. If one or both of the two remaining bonds on the atom are

attached to alkyl or aryl groups, the compound is a substituted amide.

The carbonyl carbon-to-nitrogen bond is called an amide linkage. This bond is quite

stable and is found in the repeating units of protein molecules, where it is called

a peptide linkage.

Simple amides are named as derivatives of carboxylic acids. The -ic ending of the

common name or the -oic ending of the International Union of Pure and Applied

Chemistry (IUPAC) name of the carboxylic acid is replaced with the suffix -amide.

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N,N-dimethylethanamide

Halogenated Organic CompoundsWhen the carbon of an alkane is bonded to one or more halogens, the group is referred to as

an alkyl halide or haloalkane.

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IUPAC Rules for Alkane Nomenclature

 1.   Find and name the longest continuous carbon chain.

 2.   Identify and name groups attached to this chain.

 3.   Number the chain consecutively, starting at the end nearest a substituent group.

 4.   Designate the location of each substituent group by an appropriate number and name.

 5.   Assemble the name, listing groups in alphabetical order using the full name (e.g.

cyclopropyl before isobutyl).

    The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not

considered when alphabetizing.

There are two skills you have to develop in this area:

You need to be able to translate the name of an organic compound into its structural

formula.

You need to be able to name a compound from its given formula.

Cracking the code

A modern organic name is simply a code. Each part of the name gives you some useful

information about the compound.

For example, to understand the name 2-methylpropan-1-ol you need to take the name to

pieces.

The prop in the middle tells you how many carbon atoms there are in the longest chain (in

this case, 3). The an which follows the "prop" tells you that there aren't any carbon-carbon

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double bonds.

The other two parts of the name tell you about interesting things which are happening on

the first and second carbon atom in the chain. Any name you are likely to come across can

be broken up in this same way.

Counting the carbon atoms

You will need to remember the codes for the number of carbon atoms in a chain up to 8

carbons. There is no easy way around this - you have got to learn them. If you don't do

this properly, you won't be able to name anything.

Stem No of

carbons

Name Formula Structure

Meth 1 Methane CH4

Eth 2 Ethane C2H6

Prop 3 Propane C3H8

but 4 Butane C4H10

Pent 5 Pentane C5H12

Hex 6 Hexane C6H14

Hept 7 Heptane C7H16

Oct 8 Octane C8H18

Types of carbon-carbon bondsWhether or not the compound contains a carbon-carbon double bond is shown by the two letters immediately after the code for the chain length.

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code means

an only carbon-carbon single bonds

en contains a carbon-carbon double bond

For example, butane means four carbons in a chain with no double bond.

Propene means three carbons in a chain with a double bond between two of the

carbons.

Alkyl groupsCompounds like methane, CH4, and ethane, CH3CH3, are members of a family of

compounds called alkanes. If you remove a hydrogen atom from one of these you get an

alkyl group.

For example:

A methyl group is CH3.

An ethyl group is CH3CH2.

These groups must, of course, always be attached to something else.

Types of compounds

The alkanes

Example 1:  Write the structural formula for 2-methylpentane.

Start decoding the name from the bit that counts the number of carbon atoms in the longest

chain - pent counts 5 carbons.

Are there any carbon-carbon double bonds? No - an tells you there aren't any.

Now draw this carbon skeleton:

Put a methyl group on the number 2 carbon atom:

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Does it matter which end you start counting from? No - if you counted from the other end,

you would draw the next structure. That's exactly the same as the first one, except that it has

been flipped over.

Finally, all you have to do is to put in the correct number of hydrogen atoms on each carbon

so that each carbon is forming four bonds.

Example 2:  Write the structural formula for 2,3-dimethylbutane.

Start with the carbon backbone. There are 4 carbons in the longest chain (but) with no

carbon-carbon double bonds (an).

This time there are two methyl groups (di) on the number 2 and number 3 carbon atoms.

Completing the formula by filling in the hydrogen atoms gives:

Note:  Does it matter whether you draw the two methyl groups one up and one down, or both up, or

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both down? Not in the least!

Example 3:  Write the structural formula for 2,2-dimethylbutane.

This is exactly like the last example, except that both methyl groups are on the same

carbon atom. Notice that the name shows this by using 2,2- as well as di. The structure is

worked out as before:

Example 4:  Write the structural formula for 3-ethyl-2-methylhexane.

hexan shows a 6 carbon chain with no carbon-carbon double bonds.

This time there are two different alkyl groups attached - an ethyl group on the number 3

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carbon atom and a methyl group on number 2.

Filling in the hydrogen atoms gives:

Note:  Once again it doesn't matter whether the ethyl and methyl groups point up or down. You might also have chosen to start numbering from the right-hand end of the chain. These would all be perfectly valid structures. All you would have done is to rotate the whole molecule in space, or rotate it around particular bonds.

The cycloalkanes

In a cycloalkane the carbon atoms are joined up in a ring - hence cyclo.

Example:  Write the structural formula for cyclohexane.

hexan shows 6 carbons with no carbon-carbon double bonds. cyclo shows that they

are in a ring. Drawing the ring and putting in the correct number of hydrogens to

satisfy the bonding requirements of the carbons gives:

The alkenes

Example 1:  Write the structural formula for propene.

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prop counts 3 carbon atoms in the longest chain. en tells you that there is a carbon-

carbon double bond.

That means that the carbon skeleton looks like this:

Putting in the hydrogens gives you:

Example 2:  Write the structural formula for but-1-ene.

but counts 4 carbon atoms in the longest chain and en tells you that there is a carbon-carbon

double bond. The number in the name tells you where the double bond starts.

No number was necessary in the propene example above because the double bond has to

start on one of the end carbon atoms.

In the case of butene, though, the double bond could either be at the end of the chain or in

the middle - and so the name has to code for its position.

The carbon skeleton is:

And the full structure is:

Incidentally, you might equally well have decided that the right-hand carbon was the number 1 carbon, and drawn the structure as:

Example 3:  Write the structural formula for 3-methylhex-2-ene.

The longest chain has got 6 carbon atoms (hex) with a double bond starting on the

second one (-2-en).

But this time there is a methyl group attached to the chain on the number 3 carbon

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atom, giving you the underlying structure:

Adding the hydrogens gives the final structure:

Be very careful to count the bonds around each carbon atom when you put the

hydrogens in. It would be very easy this time to make the mistake of writing an H

after the third carbon - but that would give that carbon a total of 5 bonds.

Compounds containing halogens

Example 1:  Write the structural formula for 1,1,1-trichloroethane.

This is a two carbon chain (eth) with no double bonds (an). There are three chlorine

atoms all on the first carbon atom.

Example 2:  Write the structural formula for 2-bromo-2-methylpropane.

First sort out the carbon skeleton. It's a three carbon chain with no double bonds and a

methyl group on the second carbon atom.

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Draw the bromine atom which is also on the second carbon.

And finally put the hydrogen atoms in.

If you had to name this yourself:

Notice that the whole of the hydrocarbon part of the name is written together - as

methylpropane - before you start adding anything else on to the name.

Example 2:  Write the structural formula for 1-iodo-3-methylpent-2-ene.This time the longest chain has 5 carbons (pent), but has a double bond starting on the

number 2 carbon.

There is also a methyl group on the number 3 carbon.

Now draw the iodine on the number 1 carbon.

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Giving a final structure:

Note:  You could equally well draw this molecule the other way round, but normally where you have, say, 1-bromo-something, you tend to write the bromine (or other halogen) on the right-hand end of the structure.

Alcohols

All alcohols contain an -OH group. This is shown in a name by the ending ol.

Example 1:  Write the structural formula for methanol.

This is a one carbon chain with no carbon-carbon double bond (obviously!). The ol

ending shows it's an alcohol and so contains an -OH group.

Example 2:  Write the structural formula for 2-methylpropan-1-ol.

The carbon skeleton is a 3 carbon chain with no carbon-carbon double bonds, but a methyl

group on the number 2 carbon.

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The -OH group is attached to the number 1 carbon.

The structure is therefore:

Example 3:  Write the structural formula for ethane-1,2-diol.

This is a two carbon chain with no double bond. The diol shows 2 -OH groups, one on each carbon

atom.

Note:  There's no particular significance in the fact that this formula has the carbon chain drawn vertically. If you draw it horizontally, unless you stretch the carbon-carbon bond a lot, the -OH groups look very squashed together. Drawing it vertically makes it look tidier!

Check Your Understanding 9.4 page 279 3; 4Worked Example & Try These Yourself page 281- 283Check Your Understanding 9.5 page 285 3; 4

● explore and distinguish the different types of structural isomers, including saturated and unsaturated hydrocarbons, including: (ACSCH035) – chain isomers– position isomers– functional group isomers

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The empirical formula represents the simplest, integer (whole number) ratio of atoms in a

compound.

C2 H5

A molecular formula consists of the chemical symbols for the constituent elements followed by numeric subscripts describing the number of atoms of each element present in the molecule. Molecular formulas do not show bonding.

C4 H10

Structural formulas show the bonding within the molecule, i.e. their arrangement in space.

The condensed structural formula shows all the atoms, but it omits the bonds.

CH3CH2CH2CH3 or further condensed

CH3 (CH2)2 CH3

Structural IsomersStructural isomers have the same molecular formula but different structural formulas.

Some structural isomers of pentane:

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Positional Isomers

In hydrocarbons, isomers can occur through changing the position of double or triple

bonds, or different placement of substituents.

Positional isomers of Chloropentane

Chain isomers

Chain isomers involve rearrangement of the carbon skeleton.

Functional Group IsomersFunctional group isomers have the same molecular formulas, but different functional groups, hence different structural formulas.

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● conduct an investigation to compare the properties of organic chemical compounds within a homologous series, and explain these differences in terms of bonding (ACSCH035)

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● explain the properties within and between the homologous series of alkanes with reference to the intermolecular and intramolecular bonding present

The properties of these compounds differ due to:1. Chain length2. Type and number of intermolecular forces present which relate directly to the

functional groups.

SI Data book investigation to compare properties of straight chain hydrocarbons, alcohols and carboxylic acids.

AlkanesThe rule for alkanes is the longer the chain, the greater the degree of dispersion forces, the higher the boiling point.

Alcohols

There is one functional group that can form one hydrogen bond.

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Carboxylic Acids

There are two sites on the functional group that can form hydrogen bonds.

● analyse the shape of molecules formed between carbon atoms when a single, double or triple bond is formed between them

The following Table shows the geometric arrangement of bonds around carbon atoms.

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Chapter Review Questions 7; 8 a, c, f; 9; 10 a, c; 15

● describe the procedures required to safely handle and dispose of organic substances (ACSCH075)

● examine the environmental, economic and sociocultural implications of obtaining and using hydrocarbons from the Earth

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Students read and summarise Page 290 – 294

Steam Thermal Cracking

A process called steam thermal cracking is the main source of ethylene throughout the

world. In this process ethane (C2H6) gas from natural gas, or larger hydrocarbons in low

value petroleum fractions, are mixed with steam and passed through hot metal coils.

The steam removes carbon deposits from the metal coils.

The heat from the coils breaks bonds to change the ethane, or the larger hydrocarbons, to

ethylene.

Initial cracking required high temperatures.

A process called steam thermal cracking is the main source of ethylene throughout the

world.

Initial cracking required high temperatures.

Temperatures from 450°C to 700°C

Catalytic Cracking

Initial cracking required high temperatures. The use of catalysts in ‘catalytic cracking’

allows for much lower temperatures.

Many gas reactions are catalysed using solid inorganic catalysts onto which the gaseaous

reactants are adsorbed. This weakens their bonds and reduces the activation energy for

the reaction.

The main catalysts for catalytic cracking are a group of silicate minerals called ‘zeolites’.

Zeolites are crystalline substances composed of aluminium, silicon and oxygen. Zeolite

crystals have a three-dimensional network structure containing tiny pores. The reactant

molecules are adsorbed in these pores where the reactions are catalysed.

Catalysts are added to the feed stock as a fine powder that is circulated in the catalytic

cracker.

Example of a cracking reaction:

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Students read and do a brief summarise Pages 305 to 310

Products of Reactions Involving Hydrocarbons

Inquiry question: What are the products of reactions of hydrocarbons and how do they react?

Students:

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● investigate, write equations and construct models to represent the reactions of unsaturated hydrocarbons when added to a range of chemicals, including but not limited to:– hydrogen (H2)– halogens (X2)– hydrogen halides (HX)– water (H2O) (ACSCH136)

The chemistry of alkenes (ethene) is determined by its reactive double bond.

Reactions of Ethene

Ethene may undergo a large number of addition reactions to produce many useful

products:

1. Addition of hydrogen (hydrogenation)

Ethene is converted to ethane by heating it with hydrogen in the presence of a metal

catalyst such as nickel, platinum or palladium.

NiCH2=CH2(g) + H2(g) CH3-CH3(g)

2. Addition of halogens (halogenation)

When halogens are added to ethene the double bond opens out and the addition reaction

takes place.

These halogenation reactions are used to distinguish between alkanes and alkenes as

alkanes do not readily react with halogens whereas alkenes do.

When a solution of bromine in a non-polar solvent (it has a red-brown colour), the

solution discolours as the bromine adds across the double bond.

CH2=CH2-CH3 + Br2 CH2Br-CH2Br-CH3 (1,2-dibromopropane)

CH2=CH2-CH3 + HBr 2 possible produces as outlined below

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An aqueous solution of bromine, known as bromine water is also used to distinguish

between alkanes and alkenes. Bromine water is a yellow-brown solution which discolours

in the presence of alkenes.

CH2=CH2 + Br2(aq) CH2OH-CH2Br + HBr(aq)

2-bromoethan-1-ol hydrogen bromide

The addition of halogens to ethene produces some important products such as:

1,2-dichloroethane which is used to manufacture chloroethene which is used to produce

the plastic polyvinyl chloride, PVC.

3. Addition of hydrogen halides (hydrohalogenation)

Hydrogen halides such as HCl react with alkanes:

CH2=CH2(g) + HCl(g) CH3-CH2Cl(g)

4. Addition of water (hydration)

Ethene is used in the production of ethanol by adding water in the presence of a

sulfuric or phosphoric acid catalyst:

H2SO4 (dil)CH2=CH2(g) + H2O(l) CH3-CH2OH(l)

5. Oxidation of ethene

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The mild oxidation of ethene produces 1,2-ethanediol, (ethylene glycol) which is used

as antifreeze in cooling systems. Ethylene glycol lowers the freezing point and raises

the boiling point of water.

It is also used in the manufacture of magnetic tapes, photographic film and for making

synthetic fibres.

The oxidation of ethene can be achieved by reacting ethene with cold, dilute acidified

potassium permanganate (KMnO4) or with oxygen/water:

Cold, diluteH+/KMnO

4

CH2=CH2(g) + CH2OH-CH2OH(l)

O2/H2OCH2=CH2(g) + CH2OH-CH2OH(l)

● investigate, write equations and construct models to represent the reactions of saturated hydrocarbons when substituted with halogens

Substitution with Halogens

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In a substitution reaction, an atom of another element substitutes for a hydrogen atom

This reaction usually only occurs with chloride and bromine and will not occur unless

sufficient amounts of energy are supplied.

In the presence of UV light, methane will have one of its hydrogen atoms we placed by

chlorine, forming chloromethane and hydrogen chloride.

Substitution reactions can continue until all the hydrogen in the compound have been replaced by halogen atoms.Only one halogen atom can be replaced at a time.

Investigation 10.3

Investigation 10.4 modified

Combustion of fuels

Complete combustionFuels are substances that react with oxygen to release useful energy. Most of the energy

is released as heat, but light energy is also released.

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About 21 per cent of air is oxygen. When a fuel burns in plenty of air, it receives enough

oxygen for complete combustion.

Complete combustion needs a plentiful supply of air so that the elements in the fuel react

fully with oxygen.

Fuels such as natural gas and petrol contain hydrocarbons. These are compounds of

hydrogen and carbon only. When they burn completely:

the carbon oxidises to carbon dioxide

the hydrogen oxidises to water (remember that water, H2O, is an oxide of hydrogen)

In general, for complete combustion:

hydrocarbon + oxygen → carbon dioxide + water

Here are the equations for the complete combustion of propane, used in bottled gas:

propane + oxygen → carbon dioxide + water

C3H8 + 5O2 → 3CO2 + 4H2O

Incomplete combustion

Incomplete combustion occurs when the supply of air or oxygen is poor. Water is still

produced, but carbon monoxide and carbon are produced instead of carbon dioxide.

In general for incomplete combustion:

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hydrocarbon + oxygen → carbon monoxide + carbon + water

The carbon is released as soot.

Carbon monoxide is a poisonous gas, which is one reason why complete combustion is

preferred to incomplete combustion.

Gas fires and boilers must be serviced regularly to ensure they do not produce carbon

monoxide.

Carbon monoxide is absorbed in the lungs and binds with the haemoglobin in our red

blood cells. This reduces the capacity of the blood to carry oxygen.

Equations for the incomplete combustion of propane, where carbon is produced rather

than carbon monoxide:

propane + oxygen → carbon + water

C3H8 + 2O2 → 3C + 4H2O

Worksheets

Alcohols

Inquiry question: How can alcohols be produced and what are their properties?

Students:

● investigate the structural formulae, properties and functional group including:– primary– secondary

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– tertiary alcohols

Classification of Alcohols

The functional group of an alcohol is the hydroxyl, -OH group.

Some of the properties of alcohols depend on the number of carbon atoms attached to the

specific carbon atom that is attached to the OH group. Alcohols can be grouped into three

classes on this basis.

A primary (1°) alcohol is one in which the carbon atom (in red) with the OH group is

attached to one other carbon atom (in blue). Its general formula is RCH2OH. Where R

represent another carbon or carbon chain.

A secondary (2°) alcohol is one in which the carbon atom (in red) with the OH group is

attached to two other carbon atoms (in blue). Its general formula is R2CHOH.

A tertiary (3°) alcohol is one in which the carbon atom (in red) with the OH group is attached to three other carbon atoms (in blue). Its general formula is R3COH.

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Properties of Alcohols

The C – O and the H – O are polar bonds, hence, alcohols are polar compounds.

The properties of alcohols are dependent on two factors:

The presence of the –OH group, which forms hydrogen bonds with other alcohol

molecules and with water.

The size of the hydrogen chain.

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● explain the properties within and between the homologous series of alcohols with reference to the intermolecular and intramolecular bonding present

Students use SI Data books to produce a table of the properties of alcohols C2 to C8.Table is to include chain length, boiling point melting point and solubility in water.

Physical properties of alcohols

Boiling Points

The chart shows the boiling points of some simple primary alcohols with up to 4 carbon

atoms.

Notice that:

1. The boiling point of an alcohol is always much higher than that of the alkane with the

same number of carbon.

2. The boiling points of the alcohols increase as the number of carbon atoms increases.

3. The patterns in boiling point reflect the patterns in intermolecular attractions.

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Hydrogen bonding

Hydrogen bonding occurs between molecules where you have a hydrogen atom

attached to one of the very electronegative elements – fluorine, oxygen or nitrogen.

In the case of alcohols, there are hydrogen bonds set up between the slightly positive

hydrogen atoms and lone pairs on oxygen in other molecules.

In alkanes, the only intermolecular force is are dispersion forces.

Hydrogen bonds are much stronger than these and, therefore, it takes more energy to

separate the alcohol molecules than it does to separate the alkane molecules.

That’s the main reason that the boiling points are higher.

The effect of Dispersion Forces on the boiling points of alcohols.

The hydrogen bonding and the Dipole-Dipole interactions will be much the same for all

the alcohols, but the dispersion force is only increase as the carbon chain in the alcohol

gets bigger.

These attractions get stronger as the molecules get longer and have more electrons.

That increases the sizes of the temporary dipoles that are set up.

This is why the boiling points increase as the number of carbon atoms in the chains

increases. It takes more energy to overcome the dispersion force is, and so the boiling

points rise.

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https://www.chemguide.co.uk/organicprops/alcohols/background.html

● conduct a practical investigation to measure and reliably compare the enthalpy of combustion for a range of alcohols

Investigation 11.1

Worked Example 11.1 p317 & Try These Yourself p318

● write equations, state conditions and predict products to represent the reactions of alcohols, including but not limited to (ACSCH128, ACSCH136):

46

– combustion– dehydration– substitution with HX– oxidation

Combustion of alcoholsComplete combustion of alcohols produces carbon dioxide, water and energy, for example:

C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) + energy

Incomplete combustion of alcoholsThe incomplete combustion of alcohols produces carbon monoxide and/or soot plus less

energy then complete combustion, for example:

2C2H5OH(l) + 3O2(g) → 2CO(g) + 2C(s) + 3H2O(g) + energy

Dehydration of alcohols

Alcohols undergo dehydration reactions by losing water to form alkenes heated with

concentrated sulfuric acid or phosphoric acid.

Substitution with hydrogen halides (HX)

When alcohols react with hydrogen halons, like hydrogen chloride a substitution reaction

occur

This produces an alkyl halide and water.

The general reaction equation is:

For Example:

CH3 – CH2 – CH2OH + HCl → CH3 - CH2 – CH2Cl + H2O

● investigate the products of the oxidation of primary and secondary alcohols

47

Oxidation of primary alcohols

Alcohols readily undergo oxidation with strong oxidising agents such as acidified

permanganate ion (MnO4-) or dichromate ion (Cr2O7

2-) solutions.

Primary alcohols are oxidised to form aldehydes, which are the intern oxidised to form

carboxylic acids

The structural formula for the reaction:

Oxidation of secondary alcohols

Secondary alcohols are oxidised to form ketones, which cannot be further oxidised.

48

Acidified permanganate and dichromate ions both oxidise secondary alcohols.

Oxidation of tertiary alcohols

Tertiary alcohols cannot be oxidised without drastic conditions.

Check your understanding 11.2, 11.3 & 11.4 Q2, 3 & 7

● investigate the production of alcohols, including:– substitution reactions of halogenated organic compounds– fermentation

Production from Halogenated organic compounds

The addition of water to a haloalkane results in a substitution reaction where the halogen

is replaced by a hydroxyl functional group.

For example:

Fermentation

49

Fermentation is the process where carbohydrates are converted to ethanol and carbon

dioxide.

Carbohydrates are usually in the form of glucose, sucrose or starch.

The fermentation process depends on the presence of micro-organisms called yeasts. The

yeast produce enzymes that catalyse the conversion of sugars to ethanol.

The conversion of glucose to ethanol and carbon dioxide has the following equation:

yeast C6H12O6(aq) 2CH3CH2OH(aq) + 2CO2(g) + heat

Because the process is exothermic it is usually conducted under carefully controlled

temperature conditions.

The fermentation of sugars to ethanol is promoted by the following conditions:

The sugars being in solution (involving mashing of grain or fruit if necessary).

The presence of yeast (which contains certain enzymes).

A temperature of approximately 37°C (blood temperature).

The exclusion of air, which provides low oxygen concentrations.

Once the concentration of ethanol reaches 14-15% by volume, the yeast can no longer

survive, and the fermentation process stops.

The main steps in converting sugar cane to ethanol are:

1. The sugar cane crop is grown and then cut down ready for fermentation.

2. Crushed sugar cane is placed in fermentation tanks where bacteria act on it and, over

time, produce a crude form of ethanol.

3. The impure/crude ethanol is transferred to distillation stills where it is heated until it

vapourises. The vapour rises into the neck where it cools and condenses to pure

liquid ethanol.

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Investigation 11.3

51

● compare and contrast fuels from organic sources to biofuels, including ethanol

52

53

Reactions of Organic Acids and Bases

Inquiry question: What are the properties of organic acids and bases?

Students:

● investigate the structural formulae, properties and functional group including:– primary, secondary and tertiary alcohols

● explain the properties within and between the homologous series of carboxylic acids amines and amides with reference to the intermolecular and intramolecular bonding present

Notes pages 44 to 46

– aldehydes and ketones (ACSCH127)

Notes pages 12 to 13

– amines and amides

Notes pages 14 to 15

– carboxylic acids

Notes page 32

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● investigate the production, in a school laboratory, of simple esters

Esterification

Esterification is a naturally occurring process which can be performed in the laboratory.

An acid, containing the-COOH functional group, can react with an alkanol, containing

the-OH functional group, to produce an ester and water.

Esterification is a condensation reaction.

R-OH     +     HOOC-R!       R-OOC-R!     +     H2O alkanol            acid                     ester                water

Esterification is catalysed by the addition of a small amount of concentrated sulfuric acid.

The reaction is reversible and comparable quantities of alkanol, acid, ester and water are

present at equilibrium.

Common names, rather than systematic names, are often used to obtain the ester name:

                 CH3OH     +     HOOCCH3       CH3OOCCH3     +     H2O Common: methyl alcohol   acetic acid             methyl acetate       water Systematic: methanol     ethanoic acid         methyl ethanoate (not IUPAC preferred)                

                CH3CH2OH     +     HOOCH       CH3CH2OOCH     +     H2O Common: ethyl alcohol     formic acid                 ethyl formate            water Systematic: ethanol        methanoic acid         ethyl methanoate (not IUPAC

preferred) 

           

The naming of esters follows a straight forward pattern using IUPAC nomenclature.

The table below will give you a start. Copy it and attempt to complete it.

Note that the alkanol always forms the first part of the ester's name having its ending

changed from '...anol' to '...yl' and the alkanoic acid forms the second part of the ester's

IUPAC name with its ending changing from '...oic acid' to '... oate'?

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AlkanolAlkanoic acids

methanoic acid

ethanoic acid

propanoic acid

butanoic acid

pentanoic acid

hexanoic acid

heptanoic acid

octanoic acid

methanol

methyl methanoate

methyl ethanoate

methyl propanoate   methyl

pentanoate     methyl octanoate

ethanol

ethyl methanoate

             

propanol

propyl methanoate

             

butanol butyl methanoate   butyl

propanoate          

pentanol  

             

hexanol  

  hexyl propanoate          

heptanol  

             

octanol

 

    octyl butanoate       octyl

octanoate

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Check Your Understanding 12.1 & 12.2 p348 Q1, 2, 3 & 5a I, ii

57

● investigate the differences between an organic acid and organic base

Organic acids

Organic acids contain the carboxylic acid functional group.

Examples of organic acids are methanoic acid, Ethanoic acid, citric acid (citrus fruits),

fumaric acid (food additive) and malic acid (found in fruits and used as a food additive)

Organic basesOrganic bases are usually based around nitrogen compounds.

For example amines are common organic bases.

Some are the most important organic bases include the four nitrogenous DNA bases:

adenine, cytosine, guanine and thymine.

Acids-base properties in reactions

Organic acids and a bases have the same properties as inorganic acids and bases, for

example melting point and boiling point.

Organic acids and a bases react in the same manner as inorganic acids and bases.

For example: magnesium reacts with ethanoic acid

Investigation 12.2 page 351

58

● investigate the structure and action of soaps and detergents

Saponification

Background information:

Glycerol is an alkanol with 3 hydroxy groups and the formula CH2OHCHOHCH2OH. Its

systematic name is 1,2,3-propanetriol.

Esters are carbon compounds with the general formula RCOOR' where R and R' are alkyl

groups. Esters can be made by the reaction of an alkanol and an alkanoic acid.

alkanol   +   alkanoic acid                     ester   +    water 

Fats and oils are esters made from glycerol (1,2,3-propanetriol) and long chain fatty acids

such as stearic acid (CH3(CH2)16COOH). Different acids combined with glycerol produce

different fats and oils

Most soap is made from vegetable oils, especially olive, palm and coconut oils. Some is made from animal fats, called tallows.

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Saponification is the conversion in basic solution, of fats and oils to produce glycerol and

salts of fatty acids. This is one way of making soap.

Fat or oil+conc. NaOH glycerol+sodium salt of a fatty acid (soap)

One naturally occurring fat is glycerol tristearate. When this is heated with a base such as

sodium hydroxide, conversion occurs forming glycerol and a salt that is soap.

An emulsion is a mixture of two liquids that are dispersed and suspended in one another.

Neither liquid will dissolve in the other. The suspended particles are called colloids. For the

emulsion to be stable and emulsifier must be added.

A colloid is: A system in which finely divided particles, which are dispersed within a

continuous medium in a manner that prevents them from being filtered easily or settled

rapidly.

Examples of emulsions are: Emulsion Contents - emulsions of:

milk fat droplets in water. (Proteins are the natural emulsifiers in milk.  Additional emulsifiers can be added to milk to help keep the fat suspended and prevent it floating to the top as a cream layer.)

mayonnaise oil, water and vinegar, with egg added to prevent it separating into layers.

cosmetic creams oil and water (other chemicals added for perfume and colour).

paints pigments, solvents and polymers.

Cleaning Action of Soap and Detergents

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These two outcomes can be considered together.

The cleaning action of soap can be explained by its structure which allows it to act as an

emulsifier.

Most dirt is non-polar. Grease consists mostly of long chain, non-polar hydrocarbons.

However, water is polar, so it will not dissolve this non-polar dirt and grease.

When soap dissolves in water, the ions making up the soap dissociate:

RCOO–Na+ (s)           RCOO–(aq)   +   Na+ (aq)

The negative fatty acid ion is a surfactant (surface acting agent). The positive ion plays

no part in cleaning.

Surfactants lower the surface tension of water, by disrupting hydrogen bonds between water

molecules, and thus increase its ability to wet a surface.

Water does not wet grease very well. Water with surfactants spreads out over the grease, wetting it.

The fatty acid anions (surfactants) in soaps have a long, non-polar tail, consisting of a

hydrocarbon chain, and a polar, anionic (negatively charged) head.

The non-polar tail is hydrophobic, which

means that it prefers to be away from

water. The polar head is hydrophilic,

which means that it is attracted to water.

When surfactants are added to water, they do not spread evenly through the water, instead

they clump together, with the negative heads pointing outwards.

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The negative ends interact with polar water molecules and the whole clump stays suspended

in the water, forming an emulsion rather than a solution.

Surfactants clump together and stay suspended in water.

Non-polar grease molecules are taken into the non-polar centre of the clump.

Micelles are surrounded by negatively charged heads so they repel each other and do not aggregate in the wash water.

Surfactants help to remove the dirt.

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The tails dissolve in the greasy dirt and

the heads dissolve in water, drawing

water onto the dirt and fabric.

As the water is swirled around it pulls

the grease out of the fabric.

Surfactants keep the grease suspended in the water. Keeping the grease suspended means it

can be carried away by the water.

Soap, water and grease together form an

emulsion, with the soap acting as an

emulsifier, suspending the normally

incompatible grease in the water.

The word detergent means a cleaning agent. Detergents, like soaps, contain surfactants

(surface acting agents) which help to clean.

Soaps and synthetic detergents both have water soluble and oil soluble ends and both

clean in the same way (see above). They can be distinguished by the structure of their

molecules, their chemical composition and their effect in hard water.

  Soaps Detergents

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Made from fatty acids in animal and vegetable oils

hydrocarbon chain from petroleum

Composition sodium or potassium salts of long chain (alkanoic) fatty acids

usually hydrocarbons with a sulfate or sulfonate end

Structure ionic or polar head & long, non-polar hydrocarbon tail.

anionic

similar structure to soap - head & non-polar hydrocarbon tail may be anionic, cationic or non-ionic

Manufacture saponification - heating fats or oils (esters) with NaOH or KOH< - precipitation with sodium chloride

alkanol from petroleum is reacted with H2SO4 to form sulfonic acid this is reacted with NaOH to form sodium sulfonate

Reaction with hard water

do not lather well in hard water

soap anions form precipitates with

cations e.g. Ca2+ and Mg2+ in hard

water This forms a scum in the water

and on clothes, making clothes dull

and grey

lather in hard water

do not precipitate mineral salts in hard water

Biodegradability biodegradable biodegradable if hydrocarbon chain is straight. non-biodegradable if branched chain.

Phosphates no phosphates may be mixed with phosphates that pollute the environment.

Other cheaper to make

not very soluble

deteriorate with age.

more expensivesoluble in water do not deteriorate with age, very stable.

Detergents

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Surfactant molecules in detergents can be anionic, cationic or non-ionic.

Anionic Cationic Non-ionic

Anionic surfactants are the most widely used detergents.

They are used in dishwashing liquids and laundry detergents.

Their particles have a negatively charged head.

The most common ones have a long hydrocarbon end, obtained from petroleum, and

the ionic end is a sulfate (SO42–) ion or a sulfonate (SO3

–) ion.

The hydrocarbon end has a special ring structure made of 6 carbon atoms, called a

benzene ring, so they are called alkyl benzene sulfonates or sulfates.

Anionic surfactants are highly sudsing and have excellent cleaning properties,

especially for fabrics that absorb water readily e.g. cotton, wool and silk.

Cationic surfactants are detergents made of particles with a positively charged head.

They are usually ammonium compounds.

They are used as cleaners, fabric softeners (their positive charge adheres to fabrics that

usually carry negative charges, reducing static) and as germicides (ammonium ions

disrupt the cell walls of some pathogenic bacteria) in mouthwashes, nappy washes and

antiseptic soaps.

They are not used in dishwashers as glass has a negatively charged surface, which

attracts the positive heads, leaving the tails to make the glass slippery.

Non-ionic surfactants have a hydrophilic end with many oxygen atoms that form

hydrogen bonds with water. They do not ionise in water and are low sudsing. They are

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used as detergents for the laundry, for automatic dishwashers and for washing cars.

They are also used in cosmetics and froth flotation.

You might like to summarise this information in the form of a table.

Action in hard water

Hard water contains higher than normal levels of calcium and magnesium ions.

Concentrations greater then 20ppm of calcium and magnesium ions is said to be slightly

hard.

Very hard water can have concentrations to 180ppm of calcium and magnesium ions.

Calcium and magnesium ions bond with the carboxylate ions of soap to form a solid

precipitate known as scum.

Investigation 12.3 page 355Investigation 12.4 page 358

● draft and construct flow charts to show reaction pathways for chemical synthesis, including those that involve more than one step

66

Organic compounds and reactions

Complete this exercise:

Construct a flow chart exercise P362 Chemistry in Focus

Chapter Review Questions p366 1; 2; 3; 10 a, b, c &d;11c; 12c

Polymers

Inquiry question: What are the properties and uses of polymers?

Students:

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● model and compare the structure, properties and uses of addition polymers of ethylene and related monomers, for example:– polyethylene (PE)

A monomer is a repeating unit which reacts to form a long polymer chain

The reaction by which monomers become linked to form polymers is known as

polymerisation.

Addition polymerisation:

In addition polymerisation, the monomers simply add to the growing polymer chain in such

a way that all the atoms present in the monomer are also present in the polymer.

Polyethylene is called an addition polymer.

There are two types of polyethylene, these are:

1. Low density polyethylene (LDPE)

2. High density polyethylene (HDPE)

Ethylene is polymerised to polyethylene

During addition polymerisation, one of the carbon-carbon double bonds is broken under

the influence of a catalyst at higher temperatures and pressure.

A free radical initiator can also start the polymerisation process.

This leads to the following sequence of reactions:

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Breaking of this bond frees up one electron on each carbon atom for bonding.

This free electron is called a free radical. By definition a free radical is an unpaired and

unbonded electron. It is represented by a dot.

New carbon-carbon bonds form giving rise to the polymer chain.

High pressures produce soft, low density polyethylene (LDPE) consisting of tangled

chains (with molecular masses < 100 000); used in flexible plastic bags such as those

used to store food.

The production of LDPE produces significant chain branching.

Low pressures produce harder, high density polyethylene (HDPE) consisting of aligned

chains (with molecular masses > 100 000); used in crinkly plastic bags as used for heavy

duty garbage bags.

Production and uses of low density polyethylene (LDPE)

Temperatures range from 100 - 300°C

Pressures range from 1500 – 3000 atmospheres

Initiators such as diethyl ether or benzoyl peroxide.

The polymerisation process consists of three stages: initiation, propagation and termination.

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1. Initiation

The reaction is usually initiated with a catalyst, usually and organic peroxide. These

peroxides produce free radicals, a molecule with at least one unpaired electron.

2. Propagation

The free radical is electron deficient and attacks the double bond in the ethene molecule.

This then produces an ethyl group with a free radical which can then attack the double

bond of another ethene molecule.

R-O + CH2=CH2 R-O-CH2-CH2

R-O-CH2-CH2 + CH2=CH2 R-O-CH2-CH2- CH2-CH2

A branch occurs when a chain curls back on itself and the free radical removes a hydrogen

forming a free radical in the chain.

https://www.youtube.com/watch?v=dAuYCk8tiDI

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3. Termination

Termination occurs when two free radical polymers react to form a covalent bond. This is called a chain terminating reaction.

The difference in properties of the two forms are dependent on the degree of branching of

the polymer chains.

In LDPE the degree of branching is much greater and this reduces the dispersion forces

between strands. This results in soft, flexible, low density plastics with relatively low

melting points.

Branching in LDPE

Production of HDPE

The polymerisation of HDPE uses an ionic catalyst called the Ziegler-Natta catalyst. This

consists of mixtures of compounds such as TiCl4 and Al(C2H5)3.

The production uses low pressure, several atmospheres and around 60°C.

In this process ethene molecules are added to the growing polymer molecule on the surface

of the catalyst which reduces the amount of branching.

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– polyvinyl chloride (PVC)

https://www.youtube.com/watch?v=zCqeCU1pMFE

Vinyl Chloride

Vinyl chloride is the preferred IUPAC name

Chloroethene is the systematic name

The polymerisation of vinyl chloride is a free radical polymerization the same as LDPE.

Properties and Uses of PVC

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– polystyrene (PS)

Properties of polystyrene

1. High tensile strength (HIPS plastic) – can withstand high impact and stands the test of

time, so ideal for homewares such as shelving or electronic audio-visual equipment, sports

pitch surrounds, general protective purposes. This includes the housing of cigarettes and

alcohol in shops kiosks as it is a high-impact, protective material that ensures the products

are safe.

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2. Thermoplastic & malleability – easily moulded into different shapes so possible to make

hundreds of different products, ranging from children’s toys to home ware cutlery or

product prototypes/ 3D printing.

3. Recyclable – polystyrene doesn’t thermoset so can be melted and remoulded time and time

again, which is great for the environment!

4. Insulation – when aerated with CO2 to provide the ordinary polystyrene we see used to

package most high value parcels – this type of polystyrene has become a great insulator of

heat so can be used around the home or in food delivery processes.

 

– polytetrafluoroethylene (PTFE) (ACSCH136)

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Summary of Properties of Addition Polymers

75

Investigation 11.3 p383

● model and compare the structure, properties and uses of condensation polymers, for example:

76

A condensation polymer is formed by monomer molecules condensing out small molecules

(such as water) as the polymer chain forms.

– nylon

Nylon is a polyamide.

Proteins are one of the most important natural polyamide.

The amide linkage is when the carboxylic acid group bonds with an amine.

This forms an amide linkage.

Polyamides can form the trying molecules contain the carboxylic acid group at one end

of the molecule and an amine group at the other end of the molecule, or between a

dicarboxylic acid and a diamine.

The monomers polymerise through a condensation reaction between the carboxyl group

on one molecule and the amine group on another:

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Nylon-6 is made from on monomer containing 6 carbons with an amino group at one end

and a carboxyl group at the other end.

Nylon-6,6 is made from one monomer with 6 carbon atoms with an amino group at one

end and a carboxyl group at the other.

Properties of Nylon

Characteristics

The characteristic features of nylon 6,6 include:

Pleats and creases can be heat-set at higher temperatures

More compact molecular structure

Better weathering properties; better sunlight resistance

Softer "Hand"

High melting point (256 °C/492.8 °F)

Superior colourfastness

Excellent abrasion resistance

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Nylon 6 is easy to dye, more readily fades; it has a higher impact resistance, a more

rapid moisture absorption, greater elasticity and elastic recovery.

Variation of lustre: nylon has the ability to be very lustrous, semi-lustrous or dull.

Durability: its high tenacity fibres are used for seatbelts, tire cords, ballistic cloth and

other uses.

High elongation

Excellent abrasion resistance

Highly resilient (nylon fabrics are heat-set)

Paved the way for easy-care garments

High resistance to insects, fungi, animals, as well as moulds, mildew, rot and many

chemicals

Used in carpets and nylon stockings

Melts instead of burning

Used in many military applications

Transparent to infrared light

Some Uses of Nylon

Plastic Fasteners and Machine Parts

Nylon is used for making plastic machine parts as it is low cost and long lasting.  It is

often commonly used in the electronics industry for its non-conductivity and heat

resistance.  

It is used for screws, bolts, washers and nuts as well as circuit board hardware.  

Parts made of nylon are often used in mechanisms that rotate or slide due its low

coefficient of friction.

It is used to make bearings for the appliance industry because of its excellent abrasion

resistance.  

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Cookware

Nylon is used in cookware since it has a relatively high continuous service temperature.

These include spatulas, slotted spoons, turners, forks, tongs, brushes, etc.   

Easy to dye, nylon cookware can be colour co-ordinated with kitchen decor. 

Nylon cooking tools are gentle on non-stick surfaces. 

Companies such as OXO and Caphalon have used nylon for their cookware products.

Fabric

Perhaps the most important characteristic of nylon is that it can be made into strong

fibres.  When these are woven together a silky, lightweight fabric is produced.  

Nylon was introduced as a fabric during the 1939 New York World’s Fair and by 1940

was used to make women’s stockings. 

Nylon fabric became important as a synthetic substitute for silk in the manufacture of

parachutes when silk became scarce during WWII. 

Nylon is still used today to make parachute canopies due to its elasticity, strength, and

resistance to mildew, availability and price.  However, the use of nylon fibres does not

stop with the fabric. 

Harness straps and suspension lines are also made from nylon fibres as well as tents,

sleeping bags, sails, rope, tennis strings, fishing poles and lines, etc.

Students read Natural Polymers pages 393 to

Nylon rope demonstration

Check Your Understanding p392 Q2; 3; 4 & 7

– polyesters

An acid, containing the-COOH functional group, can react with an alkanol, containing the-

OH functional group, to produce an ester and water.

Note that esterification is a condensation reaction.

 R-OH     +     HOOC-R!       R-OOC-R!     +     H2O alkanol            acid                     ester                water

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The reaction is reversible and comparable quantities of alkanol, acid, ester and water are

present at equilibrium.

Common names, rather than systematic names, are often used to obtain the ester name:

                 CH3OH     +     HOOCCH3       CH3OOCCH3     +     H2O Common: methyl alcohol   acetic acid             methyl acetate       water Systematic: methanol     ethanoic acid         methyl ethanoate (not IUPAC             preferred)

                CH3CH2OH     +     HOOCH       CH3CH2OOCH     +     H2O Common: ethyl alcohol     formic acid                 ethyl formate            water Systematic: ethanol        methanoic acid         ethyl methanoate (not IUPAC preferred)                

Ester Linkage

81

Polyesters are formed through the polymerisation of a diol monomer and a dicarboxylic acid

monomer

82

Alkanol methanoic acid

ethanoic acid

propanoic acid

butanoic acid

pentanoic acid

hexanoic acid

methanol

methyl methanoate methyl

ethanoate methyl propanoate

 methyl pentanoate  

ethanol

ethyl methanoate

 

       

propanol

propyl methanoate

 

       

butanol

butyl methanoate

 butyl propanoate      

pentanol

   

       

hexanol     hexyl

propanoate      

heptanol  

  

     

octanol  

   octyl

butanoate    

The naming of esters follows a straight forward pattern using IUPAC nomenclature.

The table below will give you a start. Copy it and attempt to complete it.

There is no need to learn all the ester names. Just remember the naming pattern you used.

The alkanol always forms the first part of the ester's name having its ending changed from

'...anol' to '...yl' and the alkanoic acid forms the second part of the ester's IUPAC name with

its ending changing from '...oic acid' to '... oate'?

Esterification is catalysed by the addition of a small amount of acid. Esterification is called a

condensation reaction because a water molecule condenses out.

Only a few drops of concentrated acid needs to be added to a mixture of alkanol and

alkanoic acid to catalyse the reaction.

If concentrated sulfuric acid is added in large amounts, say 5% to 10% of the reaction

volume, it can have a significant effect on the position of equilibrium. Concentrated sulfuric

acid is a dehydrating agent, that is, it has a strong affinity for water. If a significant amount

of sulfuric acid is present, it will shift the equilibrium position to the right by absorbing

water.

 alcohol + acid  ester + water 

This increases the yield of ester. However using large amounts of sulfuric acid is wasteful,

uneconomic and complicates the separation of ester from the reaction mixture.

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Esterification requires heat for the reaction to reach equilibrium within an hour, rather than

after many days.

When the reaction mixture is heated, volatile components, such as the reactant alcohol and

the product ester, could escape.

This problem is overcome by refluxing the reaction mixture. This also increases the yield.

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85

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