16.1 Intro to Alcohols

Learning Objectives:1. Know the general formula for alcohols.2. Be able to name alcohols.3. Describe the shape of alcohols.4. Classify primary, secondary, and tertiary

alcohols.5. Describe the physical properties of alcohols.

General Formula

• Alcohols have the functional group –OH.• The general formula is CnH2n+1OH.

• Example:• Ethanol = C2H5OH

Nomenclature

• Use the suffix –ol.• Use a number to designate the location of the

–OH group.

Nomenclature – Multiple OH groups

• Use numbers to designate the location of each hydroxyl group.

• Use the correct prefix to describe how many hydroxyl groups there are.

Primary, Secondary, or Tertiary

Physical Properties• The hydroxyl group means that hydrogen

bonding can occur between molecules.• This leads to higher melting and boiling

points than alkanes with similar chain lengths.

This is why vodka does not freeze in the freezer!

Solubility

• Hydrogen bonding also makes shorter chain alcohols soluble in water (hydrogen bonds form between OH and water).

16.3 Reactions with Alcohols

Learning Objectives:1. Describe the oxidation of alcohols to

aldehydes and ketones.2. Describe the structure of aldehydes and

ketones.3. Describe the chemical tests for aldehydes and

ketones.4. Describe elimination reactions of alcohols

(dehydration).

Combustion

• Alcohols will burn completely to carbon dioxide and water if enough oxygen present.

• Ethanol is used as a fuel.

Oxidation• Alcohols can also be oxidised gently and in stages.

Aldehydes• Contains a carbonyl group (C=O).• Aldehyde has the carbonyl at the end of the

chain (only one R group attached.• Named with the suffix –al (ie. methanal)

Ketones

• Has a carbonyl group in the middle of the carbon chain (two R groups attached).

• Named with the suffix –one (propanone).

Carboxylic Acids• Contains the functional group -COOH.• Named using the suffix –oic acid (ie. ethanoic acid).• Weak acids, only partially dissociate in water.

Ethanol to Ethanal (aldehyde)

• Dilute acid• Less potassium

dichromate [O]• Heated gently• Ethanal distils off

(BP 20o C), collected in iced container, cannot react further

• Ethanol (BP = 78o C) remains in reaction mix

Ethanol to Ethanoic Acid (Carboxylic Acid)

• Conc. sulphuric acid• Excess potassium

dichromate [O]• Reflux, vapourised

aldehyde or alcohol drips back into reaction mixture

• Until reaction goes to completion

Secondary Alcohols to Ketones• Secondary alcohols can be oxidised to form

ketones.• There is no further reaction.• Ketones CANNOT oxidise into carboxylic acids.

Tests for Aldehydes and Ketones

• Since aldehydes can be further oxidised to form carboxylic acids and ketones cannot, there are simply chemical tests to differentiate between the two.

OR

Tollen’s Test (the Silver Mirror)

• Add silver nitrate in aqueous ammonia (gentle [O])

• Aldehyde is oxidised, silver is reduced

• Produces solid silver metal (silver mirror)

Fehling’s/Benedict’s Test

• Add either reagent containing copper(II) complex ions (blue), gentle [O]

• Aldehyde is oxidized, copper is reduced to copper(I)

• Forms brick red copper(I) oxide

Cu2+ + e- Cu+

Elimination (Dehydration)

• Elimination reactions involve a small molecule being eliminated from the organic compound.

• In the case of alcohols water is eliminated so are called a dehydration reaction.

Dehydration Reaction

Products of Dehydration• A mixture of isomers is formed from dehydration

reactions.

Butan-2-ol

Butan-1-ene

Z But-2-ene E But-2-ene

16.2 Ethanol Production

Learning Objectives:1. Describe how ethanol is produced by

fermentation.2. Describe the pros and cons of fermentation.3. Describe what biofuels are.4. Explain what it means for a fuel to be carbon

neutral.

Ethanol is an important industrial product

Making Ethanol from Crude Oil• Ethene is produced from cracking crude oil.• Ethene can then be reacted with steam, using

phosphoric acid as a catalyst, to produce ethanol.

Fermentation• Ethanol can also be

made from the fermentation of carbohydrates (from plants) are broken down into sugars and then converted into ethanol by enzyme action by yeast.

Anaerobic Respiration

C6H12O6 2C2H5OH + 2CO2

• Rate affected by temperature (compromise 35o C)

• Air kept out to prevent oxidation to ethanoic acid (acid in vinegar).

• Once solution contains 15% ethanol, enzymes cannot function and fermentation stops.

Distillation

Ethanol as Biofuel

• Biofuel = fuel made from plant material (renewable)

• Being researched as an alternative to petrol so that we are no longer so reliant on crude oil, which is a non-renewable resource.

Carbon Neutral

• The combustion of ethanol produces the same amount of carbon dioxide as the plant absorbed while living, so ethanol is said to be a carbon neutral fuel.

• This is seen as a positive because CO2 is a greenhouse gas associated with global warming.

• However, this does not take into account other energy costs such as transportation or processing.

Production of Ethene

• Possible to produce ethene from ethanol made from fermentation.

• Renewable way to produce ethene which is an important industrial chemical.