Higher Chemistry Unit 2 – Natures Chemistry Section 5 - Alcohols, Carboxylic Acids and Esters

2.5 Alcohols, Carboxylic Acids and Esters Learning Intentions Learning Outcomes/Success Criteria Unit 2 CfE Higher Chemistry I can name, draw full structural formulae and write shortened structural formulae for alcohols. I can name, draw full structural formulae and write shortened structural formulae for carboxylic acids. I can name, draw full structural formulae and write shortened structural formulae for esters. I can name the functional groups in alcohols, carboxylic acids and esters I can describe how to prepare an ester I can name and predict the products produced and vice versa name and predict the esters in the reverse reaction. I can state describe characteristics and name uses of esters I can describe how esters are formed in a condensation reaction I can describe the process of hydrolysis of esters and predict the products of this.

Uses of Alcohols Ethanol can be produced on a large scale by catalytic hydration of ethene. This ethanol can be used as a fuel solvents, making medicines, printing inks and cosmetic products.

What makes a molecule an Alcohol? The chemical structure of an alcohol can be obtained by replacing one of the hydrogen atoms of an alkane with an –OH group, the hydroxyl functional group as shown below. ethane

Shortened Structural Formula Full Structural Formula Alcohols Alcohol (Carbon Atoms) Molecular Formula Shortened Structural Formula Full Structural Formula Boiling Point Methanol (1) CH3OH Ethanol (2) C2H5OH CH3CH2OH Propanol (3) C3H7OH CH3CH2CH2OH

Shortened Structural Formula Full Structural Formula Alcohols Alcohol (Carbon Atoms) Molecular Formula Shortened Structural Formula Full Structural Formula Butanol (4) C4H9OH CH3CH2CH2CH2OH Pentanol (5) C5H11OH CH3CH2CH2CH2CH2OH Hexanol (6) C6H13OH CH3CH2CH2CH2CH2CH2OH

Alcohol General Formula The number of Hydrogen atoms = 2 times the number of Carbon atoms plus 1 plus OH on the end General Formula for alcohols is CnH2n+1OH

What are Isomers? Isomers have the same molecular formula but different structural formula.

Questions Draw the full structural formula of: Hexan-2-ol Pentan-2-ol Draw as many isomers of hexan-2-ol

What makes a molecule a Carboxylic Acid? The chemical structure of a carboxylic acid can be obtained by removing all of the hydrogen atoms of an alkane and replacing it with the carboxyl functional group - COOH as shown below. ethane Ethanoic Acid

Shortened Structural Formula Full Structural Formula Carboxylic Acids Carboxylic acid (Carbon Atoms) Molecular Formula Shortened Structural Formula Full Structural Formula Methanoic Acid (1) HCOOH Ethanoic Acid (2) CH3COOH Propanoic Acid (3) C2H5COOH CH3CH2COOH

Shortened Structural Formula Full Structural Formula Carboxylic Acids Carboxylic acid (Carbon Atoms) Molecular Formula Shortened Structural Formula Full Structural Formula Butanoic Acid (4) C3H7COOH CH3CH2CH2 COOH Pentanoic Acid (5) C4H9COOH CH3CH2CH2CH2COOH Hexanoic Acid (6) C5H11COOH CH3CH2CH2CH2CH2COOH

Carboxylic Acid General Formula The number of Hydrogen atoms = 2 times the number of Carbon atoms plus 1 plus COOH on the end General Formula for carboxylic acids is CnH2n+1COOH

Learning Check Give names of the following: A. CH3COOH | B. CH3CHCOOH ethanoic acid (acetic acid) 2-methylpropanoic acid

Organic Chemistry Originally, chemical compounds were divided into 2 classes: Inorganic or Organic Organic compounds were derived from living things. It was believed that they contained a ‘vital force’ and could not be made from inorganic compounds (non-living sources). Organic chemistry is the study of carbon compounds

Organic Chemistry Organic chemistry is basically the study of compounds containing carbon (with the exclusion of oxides and carbonates). There are so many compounds containing carbon that a whole branch of chemistry is devoted to their study. Organic molecules may be as simple as methane, CH4 HO or as complicated as cholesterol

Esters

Esters Esterification, Alkanoic acids reacting with Alkanols. Alcohol + Carboxylic Acid  Ester + Water H+ Esters have sweet smells and are more volatile than carboxylic acids. They are responsible for sweet fruit smells. 280 aromas make up a strawberry smell!! 3-methylbutyl ethanoate in bananas. 2-aminobenzoate is found in grapes. We imitate these smells by manufacturing flavourings. Esters are also used in perfumes. Esters can also be used as solvents in glues. Polyesters are used to make plasticisers. Methyl ester is a biodiesel.

Naming Esters R-OH + R’-COOH  R’-COOR + Water ethyl propanoate R-yl R’-oate First, the 1st word comes from the alcohol. The name ends in –yl. Second, find the C=O in the carboxylate group, this gives the 2nd word with the ending –oate. This comes from the acid. Second First C2H5 C O CH3 CH2 COO CH2 CH3 Naming carboxylic acids and esters Advice from the BBC on naming organic compounds. ethyl propanoate

Learning Check Give the name of the following compound, which is responsible for the flavour and odour of pears. O  CH3 — C—O —CH2CH2CH3 propyl ethanoate

Naming esters. A B C D The ester in box D is made from ………………………… and …………………………………. acid and is called ………………………………………………… ethylmethanoate? Which box shows propylethanoate? methylethanoate? Box B Box A Box C methanol propanoic methylpropanoate

Making Esters One way of preparing esters is to condense an alcohol with a carboxylic acid: The reaction is slow at room temperature and the yield of ester is low. The rate can be increased by heating the reaction mixture and by using concentrated sulphuric acid as a catalyst. The presence of the concentrated sulphuric acid also increases the yield of ester. The aim of this experiment is to prepare an ester and to identify some of the characteristic properties of esters.

Ester formation Condensation Reaction + + CH3OH CH3COOH + Ester link H O + + R H O R C O H CH3OH CH3COOH + ethanoic acid methanol CH3COOCH3 + H20 methyl ethanoate The reaction is brought about by heating a mixture of a carboxylic acid and an alcohol with a little concentrated sulphuric acid. (which acts as a Catalyst and absorbs the water produced).

Making esters Procedure Decide which alcohol and carboxylic acid you need to make each ester in the table. 1. Before collecting the alcohol and carboxylic acid set up a water bath using the larger beaker and heat the water until it boils. Turn off the Bunsen. 2. Add the alcohol to a test tube to a depth of about 1 cm. To this add about the same volume of carboxylic acid. If the acid is a solid then use a spatulaful. 3.In the interests of safety your teacher/lecturer may carry out the next step. Add about 5 drops of concentrated sulphuric acid to the reaction mixture.

Making esters 4. Soak the paper towel in cold water, fold it up and wrap it round the neck of the test tube. Secure it with a rubber band. This arrangement acts as a condenser when the reaction mixture is being heated. 5. Place a loose plug of cotton wool in the mouth of the test tube. This will contain any chemicals which may spurt out of the reaction mixture when it is heated. 6.Place the test tube in the hot water bath

Making esters 7. While the reaction mixture is being heated add about 20 cm3 of sodium hydrogencarbonate solution to the small beaker. 8. After about 10 minutes, take the test tube from the water bath and remove the plug of cotton wool. Slowly pour the reaction mixture into the sodium hydrogencarbonate solution. This neutralises the sulphuric acid and any remaining carboxylic acid and so removes the smell of the carboxylic acid. 9. Gently swirl the contents of the beaker and look to see if there is any sign of the ester separating from the aqueous mixture. 10. To smell the ester with your nose at least 30 cm from the mouth of the beaker gently waft the vapour towards your nose and take just a sniff.

Uses of esters Esters are also used as non-polar industrial solvents. Esters are oily liquids with generally very pleasant fruity smells and have a range of uses. Many esters are used as flavourings and in perfumes. Natural fruit flavours contain subtle blends of some of the esters in the table below: Name Shortened Structural Formula Odour/Flavour CH3(CH2)4CH3 Banana CH3(CH)7CH3 Methyl Butanoate Pineapple 3-Methylbutyl Butanoate CH3(CH2)2(CH2)2CH(CH3)2 Apple CH3COOC3H7 Pear Methyl-1-butyl ethanoate CH3COOCH(CH3)C4H9 2-Methylpropyl methanoate Raspberry C3H7COOC5H11 Apricot, Strawberry Benzyl ethanoate CH3COOCH2C6H5 Peach, flowers Ethyl methanoate Methyl 2-aminobenzoate C6H4(NH2)COOCH3 Grapes Benzyl butanoate C3H7COOCH2C6H5 Cherry Esters are also used as non-polar industrial solvents.

Uses of esters Factors affecting perfume design e.g. using esters: Designing a perfume - several issues to address by way of design factors. The perfume needs to be a mixture of compounds to give a prolonged perfumery effect. The perfumer chemist has to design the mixture to give a particular fragrance which includes ...  the top note - the first fragrant molecule to be released, and the low note, the last molecule to be vapourised.

Uses of esters Esters are also used as non-polar industrial solvents. Some of the smaller esters are quite volatile and are used as solvents in adhesives, inks and paints – pentyl ethanoate is used in nail varnish for example.

Uses of esters Ethyl ethanoate is one of a number of solvents used to extract caffeine from coffee and tea. De-caffeinated products produced with ethyl ethanoate are often described on the packaging as "naturally decaffeinated" because ethyl ethanoate is a chemical found naturally in many fruits.

Uses of esters Caffeine (C8H10N4O2) is an example of a class of compounds called alkaloids which are produced by plants. The name alkaloid means “alkali-like”, where alkali is a base and hence refers to these basic properties. Carryout the experiment to extract caffeine from tea.

Uses of esters Caffeine is more soluble in the organic solvent ethyl ethanoate than in water, so we will extract caffeine into the organic solvent to separate it from glucose, tannins, and other water soluble compounds using a separating funnel. The ethyl ethanoate portions can be combined and the ethyl ethanoate removed by evaporation to leave the caffeine . https://www.youtube.com/watch?v=RIbff5iD0GQ

Hydrolysis of Esters Alcohol + Carboxylic Acid  Ester + Water Condensation Alcohol + Carboxylic Acid  Ester + Water Hydrolysis Alcohol + Carboxylic Acid  Ester + Water The ester is split up by the chemical action of water, hydrolysis. The hydrolysis and formation of an ester is a reversible reaction. R C O H + Bonds broken Ester + Water + R C O H Bonds formed Carboxylic Acid + Alcohol

Learning Check Draw the structure of the following compounds: 3-bromobutanoic acid Ethyl propanoate Br | CH3CHCH2COOH

Learning Check Write the equation for the reaction of propanoic acid and methanol in the presence of an acid catalyst. O O  H+  CH3CH2COH + HOCH3 CH3CH2COCH3 + H2O

Name the compound below Butyl butanoate

Learning Check What are the organic products when methyl ethanoate reacts with A. Water and an acid catalyst? B. KOH? O  CH3COH + HOCH3 O  CH3CO– K+ + HOCH3

Percentage yields CH3COOH + CH3CH2CH2OH <=> CH3COOCH2CH2CH3 + H2O 4.3 g of propyl ethanoate was produced when 6 g of ethanoic acid was reacted with propan-1-ol. What is the percentage yield of the ester? Percentage yield = actual yield/theoretical yield x 100%