Fractional distillation of crude oil (“Petroleum”)

This is where it all starts. Fossil fuels (coal, oil, natural gas (mainly methane)) are made up of molecules with carbon chains of different lengths.

14. Organic Chemistry

They burn in very exothermic reactions which is what makes them excellent fuels.

A hydrocarbon is a molecule made up of hydrogen and carbon.

Eg. Methane - molecular formula:

Structural (displayed) formula:

Propane - molecular formula:

Dot and cross diagram:

Structural formula:

Crude oil is a mixture of hydrocarbons which are separated by fractional distillation (which makes use of the fact that the H-Cs have different boiling points):

EC pp220-221

NB. Each of the collections of HCs on the right of the diagram are called “fractions”, eg. Refinery gases.

The fractions can be further processed to produce more useful and reactive molecules by the process of CRACKING

Eg. Heptane

Structural formula:

And

Possible products:

EC pp226-227

Cracking

When small alkanes are cracked, hydrogen can be produced:

Eg. Ethane

EQN:

Longer chain HCs are broken up using high temperatures, pressures and catalysts.

These are:

families of similar organic molecules with the same functional group

molecules with the same general formula

compounds with similar chemical properties

compounds with gradually changing physical properties, eg. melting points slowly increase as a chain gets longer.

We are going to look at the following homologous series:

I. AlkanesII. AlkenesIII. AlcoholsIV. Carboxylic acids

Homologous Series

EC pp214-215

HCs joined together by single covalent bonds.

General formula:

I. The Alkanes

Research: Find the boiling point for the first 10 alkanes, and add them to the table. Label them as solids (S), liquids (L) or gases (G) at room temperature.

The longer the chains, the stronger the intermolecular forces, so the higher the melting and boiling points.

Draw the structural formula for butane and octane:

1.Combustion

With plenty of oxygen, the products are carbon dioxide and water...

Eg. Pentane

The bonds in the alkanes are strong and hard to break, making them quite unreactive. There are 3 types of reaction than you must know...

Combustion is very exothermic, and explains why these compounds are used as fuels, eg. natural gas (mainly methane) in the home, and butane/propane as camping gases, octane and diesel in vehicles.

With limited oxygen, carbon monoxide and even carbon can be produced...

Alkanes react with halogens and their hydrogen atoms are slowly replaced. These are photochemical reactions. The classic and explosive example is...

Methane and chlorine (in UV light) EQNs:

The final mixture would contain all of the above compounds. These substitution reactions give multiple products (which means that they are not a good way to make a specific compound.

How would we separate the products from this type of reaction?What was the 3rd type of reaction that the alkanes undergo? EC pp224-225

2. Substitution reactions with chlorine (and other halogens)

Structural isomers are molecules that have the same molecular formula but a different structural formula.

eg. Pentane

Isomers

EC pp216-219

These are more reactive HCs, as they contain a Carbon-Carbon double bond. They are made by cracking (see earlier).

General Formula:

Draw the structural formulae for hexene (straight chain)

II. Alkenes

Draw the structural isomers of butene:

NB. Alkenes are called “unsaturated” molecules as they contain the C=C double bond (alkanes are “saturated”).

Note: Alkenes burn with a yellow flame due to incomplete combustion, but this is not an important reaction of the alkenes. They are not used as fuels.

Interesting reactions are…

1.Test for unsaturation

If the alkenes come into contact with bromine water, decolourisation results...

Eg. Ethene with bromine water

EQN:

Reactions of the alkenes (“addition” reactions)

Note the colour of reactants and products.

We say that the bromine is “added” to the double bond.

The hydrogen adds to the double bond, in the presence of a catalyst at high temperature producing the alkane...

Eg. Ethene with hydrogen

EQN:

2. With hydrogen (Nickel catalyst, 60-180ºC)

3. With Steam (with a H3PO4 catalyst at 300ºC and 70 atmospheres)

Here, an alcohol is produced...

This reaction is used to convert unsaturated vegetable oils into margarine.

Alkenes can join together to form long chains in a process called “polymerisation”.

Eg. Ethene at high temperature and pressure, and and oxygen catalyst.

EQN:

4. Polymerisation

Uses: “plastic” bags, bottles, bins, kettles,...

This is called “addition polymerisation” as many alkene undergo addition reactions to form the polymer. Other examples…

Monomer Polymerisation Uses

Propene

Chloroethene

Phenylethene

Tetrafluoroethene

Environmental problems and possible solutions

Read page 237 of EC and think about the following:

EC pp228-229/pp236-239

What can be done to overcome this problem?

Disposal of polymers is a problem. Why?

Listen to the podcasts about Plastics on the following webpage

https://chemistrybreeze.weebly.com/

Scroll down the first page you arrive at on the site

The functional group is -OH and the general formula is:

III. Alcohols

Write the formula and name for each of the following alcohols:

1.Fermentation

Glucose in the presence of yeast (an enzyme catalyst) and in the absence of air breaks down to make ethanol and carbon dioxide:

EQN:

2.The hydration of ethene:

We saw this reaction before. Steam will add the the C=C double bond.

EQN:

Making Ethanol

The first method produces a mixture of alcohol and water; the second, almost pure ethanol.

Watch this video that discusses the pros and cons of the 2 methods:https://youtu.be/9eXTDm4eIbs

1.Oxidation

In the presence of oxygen (from the air or otherwise), ethanol is oxidised to Ethanoic Acid:

EQN:

Reactions of Ethanol

Oxidation can also be achieved using the oxidising agent potassium dichromate(VI) which changes from orange to green in the process or potassium manganate(VII) which goes from purple to colourless.

Why is this oxidation?

Labelled diagram:

EQN:

2. Cracking of ethanol to make ethene

NB. Suck back

1.It is used as a solvent for organic substances that are insoluble in water, eg. in pens, paints, glues, aftershave, perfume,...

Use of Ethanol

2. It is used as a fuel for vehicles and can be produced on a large scale by the fermentation of sugar cane (sustainable energy). It burns in oxygen with a lovely blue flame

The combustion EQN:

3. In alcoholic drinks such as wines, beer and cider, and stronger beverages produced by distillation of fermented ethanol, eg. whisky, vodka and liquours.

EC pp230-231

The functional group:

IV. Carboxylic Acids

General formula:

Give the formula and name of the following:

Important reaction involving carboxylic acids:

1.They are all weak acids, as they are only partially dissociated when they dissolve in water:

EQN:

They react with alkalis and carbonates in the classic manner:

EQN:

2. As we saw before, they can be produced by oxidation of alcohols by atmospheric oxygen or potassium dichromate(VI).

3. They are used with alcohol to make ESTERS - “Esterification”

Esters are volatile, sweet or “fruity” smelling substances used in oils, perfumes and as flavourings in food.

They are produced when an alcohol and a carboxylic acid react:

Try to name the following:

This is called “ethyl ethanoate”

The ethyl part came from the alcohol, in this case ethanol

The ethanoate part came from the acid, in this case ethanoic acid

This part of the molecule is called an “ester link”

NB.1. Esterification is a reversible reaction.2. An acid is used as a catalyst (hydrochloric or sulphuric acid)3. These molecules contain an “ester link”. Identify it.

EC pp232-233

A bit more naming practice

Natural and Synthetic macromolecules

Macromolecules are very large structures made up of many small units connected by covalent bonds.In Year 10 we encountered graphite, diamond, silicon(IV)oxide but long chained polymers are also an example of macromolecules.

Synthetic polymersWe have already seen polyalkenes, which are an example of addition polymerisation.

Another example of polymerisation is “condensation polymerisation”.

Nylon (a polyamide)This synthetic polymer is formed by a condensation polymerisation reaction:

A molecule of water is “condensed every time an “amide link” is formed (unlike in polyalkenes).

Condensation PolymerisationThe monomers:

Nylon (a polyamide)The reaction can be abbreviated in the following way:

Condensation Polymerisation

Where is the amide link? http://www.youtube.com/watch?v=kLic5G5-vWM

Terylene (a polyester)

The monomers:

Which “link” is present in this polymer?

Yes, the ester link, so it is a polyester

Find out some uses of these polymers:

Nylon Terylene

The production of these polymers has a negative effect on the environment:

A significant percentage of the world’s fossil fuels is used to make them. This uses up a vital resource and adds to global warming.

Plastics are non-biodegradable - they last for many years, causing short and long term problems for land and sea animals.

Plastics cannot be burnt, as they produce toxic gases.

Problems caused by plastics (synthetic polymers) and possible solutions

EC pp236-241

Solutions:

Use sustainable energy sources in their production Use sustainable substances in their production (not fossil fuels) Recycle Use biodegradable polymers Use less plastic - develop alternative and more environmentally friendly materials

http://www.youtube.com/watch?v=LgP8Du7DZW8

There are 3 natural polymers that we need to be aware of:

•Starch (carbohydrates)•Proteins•Fats

Natural Polymers

Sugar molecules (produced by photosynthesis in plants) come together to form long chains in condensation polymerisation reactions to form complex carbohydrates

Abbreviation:

Carbohydrates

+ + …Etc

complex carbohydrate - polymer

Sugar units - monomers

The building blocks (monomers) used to make proteins are amino acids:Proteins

Using abbreviations, what would the chain look like?

The link is called an “amide link” in Chemistry and a “peptide link” in BiologyThis is a condensation polymerisation reaction.

Proteins are natural polyamides.

The word “hydrolysis” means “breaking up using water”.

Larger organic molecules are attacked by water, in the presence of acid (or alkali), and are broken into smaller pieces.

This is the reverse of the previous processes, and water is returned to the original molecules:

Starch Glucose (simple sugars)

Proteins Amino Acids

Hydrolysis of Natural Macromolecules

NB. Amino acids can be separated and identified using chromatography (see Year 10).

EC pp244-249

End of Chapter Question pp222-223pp234-235pp250-251