A functional group is a group of atoms in a molecule that cause it to react in a specific way. The functional group determines the main chemical and physical properties of a hydrocarbon

The functional group of alkenes is the double bond which is found within the molecule.

Alkanols or alcohols contain the hydroxyl functional group(-OH). Note: The hydroxyl group, -OH, should not be confused with the hydroxide group, OH^- (an anion). The hydroxyl group, -OH )covalent),  can be found anywhere within the molecule.

A primary alcohol has the hydroxyl or –OH group on the first carbon. Eg. Propan-1-ol, hexan-1-ol.

Alkanoic acids or carboxylic acids contain the carboxyl functional group (-COOH). This group is always terminal. Ie. The carboxyl group is always at the end of a molecule.

Esterification is a condensation reaction between an alkanol and an alkanoic acid. The two reactants combine to produce and alkyl alkanoate or ester. Water is produced as a by-product of the condensation reaction.

Refluxing is the process of heating a reaction mixture with a vertical condenser which is used to condense the vapours and return them to the reaction vessel.

The purpose of refluxing is to 1. speed up the rate of reaction by raising the reaction temperature and 2. stop the loss of volatile reactants and products by condensing the vapours.

Concentrated sulfuric acid, H2SO4, is used as a catalyst during esterification.

Concentrated sulfuric acid is used during esterification as

1. a catalyst. It increases the rate of reaction by lowering the activation energy of the reaction and

2. a dehydrating reagent. It removes water and forces the reaction to completion. i.e. the equilibrium position shifts to the right increasing the yield of ester.

Note: The role of sulfuric acid as a catalyst has NO effect on ester yield. Catalysts increase reaction rates (both forward and reverse) allowing equilibrium to be achieved more quickly.

An ester is a volatile compound formed from reaction between a carboxylic acid and an alcohol. It is often has a pleasant fruity or spicy odour.

Ethanol and butanoic acid.

Esters occur naturally in 1. fruits and in 2. fermentation products. They are responsible for giving fruits and fermentation products their distinctive odour. Often these natural flavours are a complex combination of esters. Eg. The fruity flavour in many wines.

Artificial esters are often cheaper to produce than natural extracts. When producing an ester, the first step is to identify what combination of esters makes up the desired flavour or smell. Eg. Ethyl butanoate is one of the esters in pineapple. The ester isoamyl acetate (3-methylbutyl ethanoate) has a very strong fruity aroma and is found in bananas and pears. Isobutyl propionate or 2-methyl-1-propyl propanoate is used in artificial rum essence.

Esters are used

1. in perfumes and cosmetics to provide pleasant aromas. Eg. Fruit flavoured lip balms.

2.in food flavourings since the odour of a food makes a significant contribution to its flavour. Eg. Banana ester used in banana lollies, isobutyl propionate is used in rum essence.

3. as solvents. Eg. Ethyl ethanoate in nail polish remover.

4. in PVC as a plasticiser to make it soft and pliable.

5. in scratch and sniff spots which are often found in magazines and stickers.

ALL molecules are attracted to one another by dispersion forces. The greater the molecule size the stronger the dispersion force.

The greater the intermolecular force the higher the boiling point.

Alkanol (alcohol) molecules are attracted to one another by

1. dispersion forces and

2. hydrogen bonding between the hydroxyl or –OH groups.

The stronger the intermolecular force the higher the boiling point. Alkanes are attracted to each by dispersion forces only. Alkanols are attracted to each other by dispersion forces AND hydrogen bonding. Since alkanols have a stronger intermolecular force they have a higher boiling point.

The stronger the intermolecular force the higher the boiling point. Alkanols are attracted to each other by dispersion forces and one hydrogen bond per molecule. Alkanoic acids are attracted to each other by dispersion force and two hydrogen bonds between molecules. Since alkanoic acids have a stronger intermolecular force they have a higher boiling point

Propan-1-ol and butanoic acid

The melting point of molecules is influenced by two factors, namely

1. the strength of the intermolecular bonds between the molecules and

2. the packing arrangement of the molecules in the solid state

The melting points alkanols of the follows a tick shape. The first two alkanols in the series, methanol and ethanol, have particularly effective hydrogen bonding in the packaging arrangement. The third alkanol, propanol, has the lowest melting point in the series due to ineffective hydrogen bonding in the packing arrangement. Dispersion forces then take over with the melting points continually increasing with molecular size.

1. Water always enters the bottom of the condenser. This drives out air bubbles which would reduce the efficiency of the condenser.

Note: In HSC diagrams the water inlet and outlet must be both drawn OPEN.

2. The top of the condenser also must be OPEN or the apparatus will explode! ie. DO NOT stick a thermometer in there.

Method: Preparation of methyl butanoate.

The ester was selected because it

a) has a fruity apple aroma

b) can be easily purified from the leftover reactants by distillation.

Boiling point data: Methanol(65°C), butanoic acid(163°C) and the ester methyl butanoate(102°C)

There are two stages in the preparation of the ester.

1. Refluxing: Reflux the following mixture for 30 minutes in a fume cupboard 10mL of methanol, 10mL of butanoic acid and 3 drops of concentrated sulfuric acid(catalyst) and boiling chips. DRAW a labelled diagram of the reflux apparatus.

2. Purification: After refluxing the reaction vessel contains a mixture of BOTH reactants and products. The ester is purified by the process of distillation which separates substances on the bases of differences in boiling points. The first fraction to come off at 65°C is the unreacted methanol. The second fraction at 102°C is the ester.

Safety precautions in refluxing a volatile mixture include

1. Prevent bumping by adding boiling chips

2. Avoid inhaling any vapours by doing the reaction in a fume cupboard

3. Wear safety goggles and protecting clothing (laboratory coat)-