Carbonyls

Reaction of acyl chlorides with phenol

RCOCl+C6H5OH → C6H5OCOR + HCl

Reaction of alcohols when heated with an acid catalyst

Alcohol → alkene + water

RCOH → RC=C + H2O

Reaction of acyl chlorides with alcohols

RCOCl + R’COH → RCOOCR’ + HCl

Reaction of acyl chlorides with water

RCOCl + H2O → RCOOH + HCl

Reaction of acyl chlorides with ammonia

RCOCl + 2NH3 → RCONH2 + NH4Cl

Reaction of acyl chlorides with amines

RCOCl + 2R’NH2 → RCONHR’ + R’NH3Cl

Oxidation of aldehydes with K2Cr2O7

RCOH + [O] → RCOOH

Oxidation of ketones

Ketones don’t undergo oxidation reactions, this can be used to distinguish between ketones and aldehydes.

What type of reaction is done across the C=O bond?

Nucleophilic addition.

Reaction of aldehydes with NaBH4

RCOH + 2[H] → RCH2OH

Reaction of ketones with NaBH4

RCOR’ + 2[H] → RCHOHR’

(secondary alcohol)

What is NaBH4 used as in reactions with carbonyl compounds?

NaBH4 is used as a reducing agent to reduce aldehydes and ketones to alcohols.

How does HCN react with carbonyl compounds?

HCN adds across the C=O bond of aldehydes and ketones.

Reaction of aldehydes with HCN

RCOH + HCN → RCHOHCN

Reaction of ketones with HCN

RCOR’ + HCN → RCOHCNR’

What can be used to supply HCN in a reaction?

H2SO4 and NaCN.

H2SO4/NaCN

What is used to detect the presence of the C=O group in aldehydes and ketones?

2,4-DNP can be used to detect the presence of the C=O group in aldehydes and ketones.

When the C=O group is detected by 2,4-DNP what happens?

A yellow or orange precipitate is formed.

What reagent/test can be used to distinguish between aldehydes and ketones?

Tollens’ reagent.

When Tollens’ reagent is added to an aldehyde what happens?

A silver mirror forms.

What is Tollens’ reagent contain?

A solution of silver nitrate in aqueous ammonia.

Why does Tollens’ reagent only react with aldehydes?

Tollens’ reagent contains Ag+ ions which act as an oxidising agent in the presence of ammonia.

In the reaction, silver ions are reduced to silver as the aldehyde is oxidised to a carboxylic acid.

How do you identify and aldehyde or ketones by melting point?

React the carbonyl with 2,4-DNP.

Filter the impure yellow/orange solid to separate it from the solution.

Leave to recrystallise.

Measure the melting point of these crystals and compare to a database.

Why are carboxylic acids soluble in water?

Carboxylic acids contain O-H and C=O bonds which are polar, allowing the carboxylic acid to form hydrogen bonds with water molecules.

Up to what carbon chain length are carboxylic acids soluble in water?

Up to 4 carbon atoms. Any more and the non-polar carbon chain has a too great effect on the overall polarity of the carboxylic acid.

Why are di-carboxylic acids more soluble than carboxylic acids?

Di-carboxylic acids have two polar carboxyl groups to form Hydrogen bonds, carboxylic acids only have one carboxyl group.

Redox reaction of carboxylic acids with metals.

carboxylic acid + metal → carboxylate salt + hydrogen gas

2RCOOH + Mg → (RCOO)2Mg + H2

Test for carboxyl group.

Carboxylic acids are the only common organic compounds to specifically react with carbonates.

How can you distinguish between carboxylic acids and phenols?

Phenols are not acidic enough to react with carbonates, however carboxylic acids can react with carbonates.

Reaction for the formation of an acid anhydride.

RCOOH + R’COOH → RCOOOCR’ + H2O

How do you name an asymmetric acid anhydride?

Remove acid from the parent carboxylic acid and replace with -anhydride.

State the two constituent carboxylic acids alphabetically.

Reaction for the formation of an ester (esterification)

RCOOH + R’COH → RCOOR’ + H2O

What is used as a catalyst in esterification?

Sulphuric acid.

H2SO4

How is acid hydrolysis of an ester carried out?

The ester is heated under reflux with dilute aqueous acid.

The ester is broken down by water with the acid acting as a catalyst.

The products are an alcohol and carboxylic acid.

What are the products of acid hydrolysis of an ester?

An alcohol and carboxylic acid.

Reaction for acid hydrolysis of an ester.

RCOOR’ + H2O → RCOOH + R’COH

How is alkaline hydrolysis of an ester carried out?

The ester is heated under reflux with a strong base supplying OH- ions.

The products are a carboxylate salt and alcohol.

Reaction for alkaline hydrolysis of an ester.

RCOOR’ + XOH → RCOOX + R’COH