CfE HigherChemistry

Unit 2: Natures Chemistry

Part 1: Alcohols, Carboxylic Acids and

EstersSummary Notes

Success Criteria

Learning Intention Completed?

1. I can identify the carboxyl group and draw the structures of carboxylic acids if told their names.

2. I can name carboxylic acids if shown their structure.3. I can predict the products formed when a carboxylic

acid reacts with a base.4. I can name and draw the structure of an ester if told the

parent alcohol and acid.

5. I can name and draw the alcohol and acid used to form an ester if told the name or shown the structure of an ester.

6. I can state some uses of esters and relate the use to the ester structure.

7. I can name and draw the structures for the products of hydrolysis of an ester.

8. I can explain the function of fats and oils in the human diet.

9. I can identify glycerol and identify its structure.10.

I know that fats and oils are tri-esters formed by reacting glycerol with 3 fatty acid molecules.

11.

I can look at the structure of a fat, oil or fatty acid and sate whether it is saturated or unsaturated.

12.

I can explain why oils have lower melting points than fats.

13.

I can draw the products of hydrolysis of a fat or oil.

14.

I know how soaps are produced from fats and oils.

15.

I can describe how soaps and detergents work.

16.

I can identify an emulsion and I know why they are used.

17.

I can identify addition reactions of alkenes and name the products of these reactions with: hydrogen, halogens and hydrogen halides.

Key Terms

Term DefinitionAlkanoic acid A homologous series of carboxylic acids, general

formula CnH2nO2. The first member is methanoic acid, HCOOH

Carboxyl group The functional group present in the carboxylic acid, -COOH. The name derives from the fact that the carboxyl group contains a carbonyl and a hydroxyl.

Condensation reaction

A reaction in which two (or more) molecules join to produce a single larger molecule, with water or another small molecule formed at the same time.

Esters Carbon compounds formed when alcohols react with carboxylic acids by condensation.

Hydrolysis The breaking down of larger molecules into smaller molecules by reaction with water.

Emulsion A mixture of liquids where small droplets of one liquid are dispersed in another. Emulsions of oil and water a frequently found.

Fatty Acid Carboxylic acids formed from the hydrolysis of fats and oils

Glycerol Propan-1,2,3-triol. Formed from the hydrolysis of fats and oils.

Hardening The process of hydrogenating an oil into a solid fat.Hydrophilic A term used to describe molecules, or parts of

molecules, which are attracted to water. For example the –OH group in alcohols is hydrophilic.

Hydrophobic A term used to describe a molecule, or parts of molecules, which repel and will not bond to water. For example the long chain carbons of fats and oils are hydrophobic.

Soap Salts of fatty acids e.g. sodium stearate. Soaps have an ionic head that is water soluble and a covalent tail which is soluble in oil.

Triglycerides The molecules found in fats and oils. They are formed from one glycerol molecule joining to 3 fatty acid molecules.

Addition Reaction A reaction that occurs when the double bond of an alkene is broken and a small molecule (such as H2, HCl or H2O) adds onto the alkene to make a saturated product.

1. Alcohols

Alcohols are chemical compounds which contain the hydroxyl functional group, -OH. Alcohols are characterised by their name ending in ‘-ol’, for example ethanol.

The hydroxyl functional group.

Alcohol StructureMethanol

Ethanol

Propanol

Butanol

Pentanol

Hexanol

Classifying Alcohols

Alcohols can be classified as either primary (⁰1), secondary (⁰2) or tertiary (⁰3).

To identify a primary alcohol you look to the carbon the hydroxyl group is attached to (carbon number 1). If this

This alcohol is a primary alcohol. Its systematic name would be propan-1-ol as the hydroxyl group is on the

carbon is attached to only one other carbon, then the alcohol is said to be primary.

To identify a secondary alcohol you again look to the carbon the hydroxyl group is attached to (in this case carbon number 2). If this carbon is attached to two other carbon atoms, then the alcohol is a secondary alcohol.

To identify a tertiary alcohol you once more look to the carbon atom attached to the hydroxyl group (in this case carbon number 2). If this is attached to 3 other carbon atoms then we can say that the alcohol is a tertiary alcohol.

1.

This alcohol is a primary alcohol. Its systematic name would be propan-1-ol as the hydroxyl group is on the

2.

This alcohol is a secondary alcohol. Its systematic name would be propan-2-ol as the hydroxyl group is on the second carbon.

2. This alcohol is a tertiary alcohol. Its systematic name would be 2 -methylpropan-2-ol as the hydroxyl group is on the second carbon and there is also a methyl branch on the second carbon.

Naming Alcohols

When naming alcohols there are rules we can follow.1. Identify the longest chain of carbon atoms (a chain can

bend so be careful!). This gives the name of the parent alcohol, in this case butanol.

2. Number the chain giving the carbon nearest the hydroxyl group the lowest number possible.

3. Identify the branch. –CH3 (methyl), -C2H5 (ethyl).4. Number the branch.

Making Alcohols

Alcohol can be made by 2 methods.1. Addition reaction of water to an alkene.

C CH

H

H

H

C C

H

H

H

OH

H

H

H+(aq)/H2O

2. Fermentation of glucose.

1. 2. 3. 4.

This alcohol is called…

3-methylbutan-2-ol.

The hydroxyl group is given the lowest number in priority over the branches. This is always the case when naming alcohols.

Ethene Ethanol

Dehydrating an Alcohol

Alcohols can be dehydrated via the following method.

C6H12O6 C2H5OH + CO2 Glucose Ethanol

C C

H H

OH

H

H

H

C C

H H

HH

H OH

ethanol

Aluminium Oxide

ethene

+

The product of this reaction is the corresponding alkene and water.

2. Carboxylic Acids

A carboxylic acid is characterised by its functional group, the carboxyl group. Carboxylic acids names always end in ‘-oic acid’, for example ethanoic acid.

Carboxylic Acid

Structure

Methanoic acid

Ethanoic acid

Propanoic acid

Butanoic acid

This is the carboxyl group -COOH

Pentanoic acid

3. Esters Esters are formed when an alcohol reacts with a carboxylic acid. The two molecules join together and eliminate a water molecule; this kind of reaction is known as a condensation reaction. The process can also known as esterification.

All esters contain the ester link, -COO.

Making EstersA small volume of alcohol is mixed with equal volume of carboxylic acid and a few drops of carboxylic acid is added to the mixture. The mixture is then heated in the water bath for several minutes.

The tube is then removed from the water bath and the contents added to a solution of sodium hydrogen carbonate. This solution neutralises the excess concentrated sulphuric acid. The ester can be seen as an immiscible layer on the surface. The ester can also be detected by its distinctive smell.

Naming EstersThe name of an ester depends on the alcohol and carboxylic acid that made it. The first part of the name, which ends in’ –yl’, comes from the alcohol. The second part of the name comes from the acid and ends in ‘-oate’.

For example an ester made from propanol and pentanoic acid will be called propyl pentanoate.

Uses of Esters

This part comes from the acidpentanoic acid, hence pentanoate.

This part comes from the alcoholpropanol, hence propyl.

Esters are associated with fruity aromas and as a result are frequently used within the fragrance and flavouring industry, making products such as:

Deodorants Aftershave Perfume Cosmetics Sweet flavourings Medicinal purposes (aspirin is an ester)

Some common esters used as flavourings is listed in the table below.Name Structural Formula FlavourPropyl ethanoate CH3CH2CH2OOCCH3 Pear3-methyl but-1-yl-ethanoate

CH3CH(CH3)CH2CH2OOCH3

Banana

Octyl ethanoate CH3(CH2)7OOCCH3 OrangeMethyl butanoate

CH3OOCCH2CH2CH3 Pineapple/apple

Pentyl butanoate CH3(CH2)4OOCCH2CH2CH3 Apricot

Esters can also be used as solvents. As esters are non-polar they can dissolve an array of compounds which would be insoluble in water. Ethyl ethanoate is used as a solvent in nail varnish. As it is a small molecule it evaporates quickly once it is painted onto the nail, leaving the dry varnish.

Hydrolysis of Esters

When an ester is hydrolysed it is broken up into a carboxylic acid and an alcohol. Hydrolysis can be carried out in the lab using the below reflux apparatus. Reflux apparatus ensure that the volatile reactants do not escape from the reaction vessel.

In practice water is rarely used to hydrolyse (break up) an ester as the reaction is reversible. This means the reaction will never go to completion with 100% conversion of ester to carboxylic acid and alcohol. To make an irreversible hydrolysis reaction chemists used sodium hydroxide (an alkali) to hydrolyse the ester. This produced a salt of the carboxylic acid, which can be separated from the alcohol through distillation. The salt can then be converted back into the carboxylic acid by reacting it with an acid.

4. Fats and Oils Fats and oils are an essential part of the human diet. They provide us with energy and warmth. Fats come from 3 main sources.

Animal Plant MarineLard (pork fat) Rapeseed oil Cod liver oilMutton fat Olive oil Whale oilBeef fat Coconut oil

Soya bean oil

Fats and oils get a bad reputation but they are an essential part of a healthy diet. Vitamin D is a fat soluble vitamin and so is found alongside fat in many foods. Vitamin D is made by our skin when it is exposed to sunlight, but in countries where sunlight is limited (Scotland being one of these countries) we must supply our body with enough vitamin D through what we eat.

The Structure of Fats and Oils

Ethyl propanoate + water

Propanoic acid + ethanol

Fats and oils are esters, more correctly triesters as each molecule contains 3 ester links within it. Since they are esters they are made from an alcohol and a carboxylic acid (fatty acids).The alcohol used to produce fats is called glycerol, or propan-1,2,3-triol.

Fatty acids can either be saturated or unsaturated. The table below gives the names of some common saturated and unsaturated fatty acid chains.

C

C

C

OH

OH

OH

H

H

H

H

H

Since glycerol contains 3 hydroxyl groups it will react with 3 fatty acid molecules. This is another example of a condensation reaction.

Melting and Boiling Points of Fats and Oils

Fats and oils have very similar structures - they are either triesters ( or triglycerides). They are made up of one glycerol molecule reacting with 3 molecules of a fatty acid. Physically, oils have lower melting points than fats and so are liquids at room temperature. Fats are solid at room temperature. The difference in melting and boiling points of an oil in comparison to a fat comes down to the degree of saturation within the fatty acid chain.Oils are esters made from largely unsaturated fatty acid chains. These chains contain carbon to carbon double bonds (C=C). These carbon to carbon double bonds repel one another and so the molecules cannot efficiently pack together (there are kinks in the chain), this weakens the intermolecular forces in-between the fatty acid chains.

In comparison, fats are made up of saturated fatty acid chains. This mean they contain more carbon to carbon single bonds (C-C) than an oil. Fats are able to pack together effectively, as they do not have the repulsion from the high proportion of C=C.

Structure of an oil.

Changing an Oil into a Fat

An oil can be converted into a fat via a process called hardening. During hardening hydrogen is added across the unsaturated C=C double bonds of the oil. The process can also be described as hydrogenation, as hydrogen is being added across the double bond.

The catalyst used for this process is a solid nickel catalyst. This is an example of a heterogeneous catalysis as the catalyst is in a different physical state to the reactants.

Hydrolysis of Fats

Structure of a fat.

Fats can be broken up via a hydrolysis reaction. The products of this reaction will be one glycerol molecule and 3 fatty acid molecules.

In practice water is rarely used to hydrolyse an ester as this reaction is reversible so alkalis are used instead, this is called alkaline hydrolysis.

The salts formed via the alkaline hydrolysis of fats and oils are known as soaps.

The Cleaning Action of Soaps

Soaps allow greasy residues to dissolve in water. The soap molecule must therefore be able to dissolve in both the water and the grease. Soaps have a very specific structure which allows them to do this:

Emulsions

Grease particles mixed with soapy water is an example of an emulsion. An emulsion is when small droplets of one liquid is dispersed within another. The grease and water would normally separate out to form two individual layers, but the soap acts as an emulsifier to bring everything together.Emulsifiers are found naturally in lots of products such as milk and mayonnaise. Emulsifiers have a hydrophobic part of the molecule (insoluble in water) and a hydrophilic part (soluble in water) which allows it to combine grease and water layers.