Carboxylic Acids & Derivatives (CIE AS Chemistry)

A series of reactions based on propanoic acid is shown. 

Write an equation for reaction 1, using [H] to represent the reducing agent.

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Write an equation for the reaction of propanoic acid with calcium carbonate, CaCO₃.

An organic ester, B, has the empirical formula C₂H₄O. An experiment by a student in a college gave a value of 87.5 for M_r of B.

What is the molecular formula of B?

In the boxes below, draw the structural formulae of four isomers of B that are esters.

The student hydrolysed his sample of B by heating with aqueous mineral acid and then separating the alcohol, C, that was formed. He heated the alcohol C under reflux with acidified dichromate(VI) ions and collected the product D.

A sample of D gave an orange precipitate with 2,4-dinitrophenylhydrazine reagent. A second sample of D gave no reaction with Tollens’ reagent. 

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Which, if any of your esters, W, X, Y, or Z is chiral? Explain your answer.

Esters are compounds which provide the flavour of many fruits and the perfumes of many flowers.

The ester CH₃(CH₂)₂CO₂CH₃ contributes to the aroma of apples.

Leaf alcohol is a stereoisomer that can form when insects such as caterpillars eat green leaves.

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Describe a simple chemical test to distinguish between leaf alcohol and your product in part (c)(ii).

test ...................................................................................................................................


observation ......................................................................................................................

Fermentation of sugars by bacteria or moulds produces many different organic compounds.

One compound present in fermented molasses is 2-ethyl-3-methylbutanoic acid which gives a distinctive aroma to rum.

(CH₃)₂CHCH(C₂H₅)CO₂H

2-ethyl-3-methylbutanoic acid

A sample of 2-ethyl-3-methylbutanoic acid may be prepared in a school or college laboratory by the oxidation of:

A structural isomer of 2-ethyl-3-methylbutan-1-ol is 2-ethyl-3-methylbutan-2-ol, (CH₃)₂CHC(OH)(C₂H₅)CH₃.

What colour change would be seen if this were heated with the reagents you have given in part (b)(i)?

Explain your answer as clearly as you can.

An isomer of 2-ethyl-3-methylbutanoic acid which is an ethyl ester is a very strong smelling compound which is found in some wines. This ethyl ester contains a branched hydrocarbon chain and is chiral.

Draw the displayed formula of this ethyl ester.

Identify the chiral carbon atom with an asterisk (*).

Esters have important commercial uses, such as artificial flavourings in food. 

They can be prepared in several ways, including through the reactions of alcohols with carboxylic acids, as well as the carboxylic acid derivatives, acid anhydrides and acyl chlorides.

Ester S, CH₃CH₂COOCH₂CH(CH₃)₂ is used in rum flavouring. 

Outline how you could obtain a sample of ester S, beginning with a named alcohol and carboxylic acid.
 

Include any essential reaction conditions and write an equation for the reaction. 

You do not need to include details of the separation or purification methods involved. 

Ester S can undergo acid or alkaline hydrolysis. 

The products formed depends on the type of hydrolysis that has taken place.

Compare the two types of hydrolysis.

A second ester, Ester T is responsible for a raspberry scent and has the molecular formula C₅H₁₀O₂.

Ester T can be produced by the reaction of an acid with a branched primary alcohol.

Identify the acid and alcohol used to prepare ester T.

Draw and name ester T.

Lactic acid, 2-hydroxypropanoic acid, CH₃CH(OH)COOH occurs naturally in sour milk and in our muscles when we take hard exercise.

Lactic acid is chiral and shows stereoisomerism. 

Draw fully displayed structures of the two optical isomers of lactic acid. 

Circle the chiral carbon atom in the lactic acid molecule.

Lactic acid may be synthesised from ethanol by the following route. 

Give the reagent(s) and essential condition(s) for each step. 

step 1

reagent(s) .......................................................................................

conditions .......................................................................................

step 2

reagent(s) .......................................................................................

condition(s) .......................................................................................

step 3

reagent(s) .......................................................................................

condition(s) .......................................................................................

Lactic acid, CH₃CH(OH)COOH can be reduced by LiAlH₄. 

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Glycolic acid is commonly used in skin care products. 

The structure is shown in Fig. 3.1. 

Glycolic acid is added separately to each of the three reagents below.

Complete the table to show what you would observe.

If a reaction occurs, state the functional group of glycolic acid that is responsible for the reaction.

Two reaction sequences to produce glycolic acid are shown. 

Glycolic acid can also be made by reacting glyoxylic acid with NaBH₄.

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