Mark Riley 3107631608 Making Esters from Alcohols and Acids Chem 4 - Lesley Hirst 1

Making Scents of Esters

Mark Riley

Introduction Esters have a very sweet fruity smell. Naturally occurring esters are found in fruits.

An ester is a product of the reaction of an acid (usually organic) and an alcohol (the

hydrogen of the acid R-COOH is replaced by an alkyl group R'). Esters mainly result

from the condensation (a reaction that produces water) of a carboxylic acid and an

alcohol. The process is called esterification. This reaction can be catalyzed by the

presence of H+ ions. Sulphuric acid, H2SO4, is often used as a catalyst for this

reaction. Esters have the general formula R-COOR.

Task Practical Report

Aim Produce three different esters by using a range of carboxylic acids and alcohols.

Determine the ester formed by using the smell given off by the products and the

chemical equations for the three different reactions.

Details Ethanoic acid was used as the carboxylic acid for all three reactions. The alcohols

used were ethanol, methanol and propanol. The reaction of ethanoic acid with

ethanol will be discussed in detail and results and equations will be given for all

three reactions.

Mark Riley 3107631608 Making Esters from Alcohols and Acids Chem 4 - Lesley Hirst 2

THE EXPERIMENT

Procedure

1. Place 1 drop of concentrated sulphuric acid in a test tube 2. Add 10 drops of ethanoic acid (or propanoic acid) to the sulfuric acid in the tube. 3. Add 10 drops of ethanol (or other alcohol) to the mixture. 4. Put about 10 cm3 of water into the 250 cm3 beaker. Carefully lower the tube into the beaker so

that it stands upright. 5. Heat the beaker gently on a tripod and gauze until the water begins to boil, then stop heating. 6. Stand for 1 minute in the hot water. If the mixture in the tube boils, use the tongs to lift it out of

the water until boiling stops, then return it to the hot water. 7. After 1 minute, carefully remove the tube and allow it to cool. 8. When cool, pour the mixture into a test-tube half-full of 0.5 M sodium carbonate solution. There

will be some effervescence. Mix well by pouring back into the specimen tube – repeat if necessary. A layer of ester will separate and float on top of the aqueous layer.

9. Smell the product by gently wafting the odour towards your nose with your hand – do not put your nose near the top of the tube!

10. Repeat this procedure for up to three more different esters. Compare the odours of the different esters prepared by your group and by other groups. Write word equations for each reaction, and (for advanced students) chemical equations using structural formulae.

Equipment

Safety glasses

test tubes

dropping pipettes

250mL beaker

test tube rack

Bunsen burner

heat resistant mat

tripod

gauze

retort stand

chemicals.

Mark Riley 3107631608 Making Esters from Alcohols and Acids Chem 4 - Lesley Hirst 3

RESULTS

Test 1.

An ester is formed whenever a carboxylic acid reacts with an alcohol. In this first reaction, the alcohol used

was ethanol and the carboxylic acid used was Ethanoic Acid. A small amount of concentrated H2SO4

(Sulphuric Acid) was used as a catalyst. H2SO4 is a dehydrating agent and removes water from the

products. The alcohol (ethanol) loses OH and the carboxylic acid (ethanoic acid) loses a H. The method

used for this reaction is only suitable for preparing small amounts and the ester formed in this reaction

could only be characterised by odour.

Prior to mixing the solutions an equation was written for the reaction and ethyl ethanoate was predicted

as being the ester that would be formed.

Once this reaction was complete, the ester could not be determined as the strong odour given off by

unreacted ethanol made it impossible to smell the actual ester. The experiment was performed again with

much care given to the accuracy of measurements. This time the ester formed could easily be smelt and

group members agreed that the odour was very similar to nail polish remover. After some investigation, it

was confirmed that the aroma given off by ethyl ethanoate is of nail polish remover (although some

believe it to smell like pear).

ethanol + ethanoic acid → ethyl ethanoate + water.

C2H5OH(aq) + CH3CO2H(aq) → CH3CO2C2H5(aq) + H2O(l)

+ →

Mark Riley 3107631608 Making Esters from Alcohols and Acids Chem 4 - Lesley Hirst 4

RESULTS

Test 2.

Alcohol used- Methanol

Carboxylic Acid used- Ethanoic Acid

Smell- Paint/Glue (similar to ethyl ethanoate)

methanol + ethanoic acid → methyl ethanoate + water. CH3OH(aq) + CH3CO2H(aq) → CH3CO2CH3(aq) + H2O(l)

+ →

Test 3.

Alcohol used- Propanol

Carboxylic Acid used- Ethanoic Acid

Smell- Pear

propanol + ethanoic acid → propyl ethanoate + water. C3H7OH(aq) + CH3CO2H(aq) → CH3CO2C3H7(aq) + H2O(l)

+ →

Mark Riley 3107631608 Making Esters from Alcohols and Acids Chem 4 - Lesley Hirst 5

QUESTIONS

Question 1.

This method is only suitable for the preparation of small samples for characterization by odour. If you

wanted to prepare enough ester for characterization by boiling point you would need to use a different

technique.

Production of an ester on a larger scale.

1. Add ethanol, ethanoic acid and very small amount of sulphuric acid (dependent on the amount of carboxylic acid & alcohol used) to a flask and attach a Liebig condenser. See figure 1.

2. Bring the mixture to a boil under reflux for 1 hour using a suitable heat source such as a heat mantle or oil bath. (open flame not recommended) Using this boiling point to determine or confirm the ester is unreliable as alcohols (& even small chains of carboxylic acids) can have boiling points close to and sometimes even lower than esters (ethanol has a very low BP of 78.1°C vs ethyl ethanoate BP 77.1°C ), especially if the ester is very large (long chain).

3. Remove the heating source and allow mixture to cool to room temperature. 4. Pour the mixture into a separating funnel and add a small amount (Approximately the same volume

as the mixture) of cold water. Rinse the reaction flask with 5-10 mL of water and also add that to the separating funnel See figure 2.

5. Gently shake the separator funnel (attach stopper first), allow to rest, then remove the aqueous layer leaving only the organic layer.

6. Add sodium bicarbonate solution to the separating funnel which will extract any remaining acid and again form an aqueous layer which will then again be removed. Check that the aqueous layer removed is basic and if not repeat this step until it is.

7. Rinse again with a small amount of water and let separate. (adding aqueous sodium chloride can help in layer separation. Remove the lower aqueous layer and again discard it.

8. When the water has been removed, pour the ester from the top of the separating funnel into another reaction flask. See figure 3.

9. Assemble a distillation apparatus with a thermometer attached and distill the ester into a cooled receiver. Carefully watch the thermometer so the boiling point can be noted and the ester can be confirmed as ethyl ethanoate (Boiling point is approximately 77.1°C) or to determine the ester if the alcohol and carboxylic acid are unknown.

Figure 1. Figure 2. Figure 3.

Mark Riley 3107631608 Making Esters from Alcohols and Acids Chem 4 - Lesley Hirst 6

QUESTIONS

Question 2.

Which industries might use synthetic esters? Why? Food industry- Flavouring of food in particular of lollies & sweets. Also margarine & preservatives.

Cosmetic industry- Create nice smelling perfumes and add pleasant aromas to other products such as

shampoos and lotions such as

Beverage industry- To give drinks nice flavours such as cordials.

Alcohol industry- Again to add flavor. Most obviously the uses such as Propyl-2-methylpropanoate in

Rum.

Medicines- Especially children’s medicines to add nice fruity flavours.

Clothing industry- Synthetic fibres such as polyester.

Energy industry- Such as to make biodiesel fuels.

Mechanical industry- Such as use as lubricants on machinery.

Question 3.

Why do many living things produce esters?

Living things store much of their energy as esters, known as fats or oils. Many of the flavours and odours of

fruits are esters. The formation and breakdown of esters are reactions that occur frequently in living

things. Esters are part of the basic building blocks for all lipids and are a component of phospholipids and

fats. They assist in function and integrity of healthy skin, cholesterol metabolism, and prostaglandin

production. Esters help maintain resilience and lubrication of all cells. They break up cholesterol deposits

on arterial walls, thereby preventing hardening of and within the arteries. Esters are necessary for the

function of the thyroid and adrenal glands. Carnivorous plants (such as the Venus Fly Trap) produce esters

to attract pray as do many flowers produce esters to attract bees.

(Tutorvista 2009: Internet; HSC Online 2007: Internet)

Mark Riley 3107631608 Making Esters from Alcohols and Acids Chem 4 - Lesley Hirst 7

Bibliography

Bibliography

NSW HSC online., 2007, Estrification, [online], available from:

http://www.hsc.csu.edu.au/chemistry/core/acidic/chem935/chem935net.html [30 October 2009]

TutorVista., 2008, Esters, [online], available from: http://www.tutorvista.com/search/esters [31 October

2009]

Organic Chemistry Portal., 2007, Fischer Esterification, [online], available from: http://www.organic-

chemistry.org/namedreactions/fischer-esterification.shtm [30 October 2009]

Great site for drawing chemistry diagrams easily http://www.emolecules.com