Chemistry Chapter 26

Aldehydes can be oxidised

To carboxylic acids when refluxed with acidified Cr2O7 2+

Ketones will not

undergo further oxidation

Most common reaction for aldehydes and ketones

Nucleophilic addition

Forming Hydroxynitrile from carbonyl compounds

Use HCN (toxic so made in situ), useful for lengthening carbon chain.

Reducing Carbonyl compounds with NaBH4

warmed with compounds, Aldehyde = primary alcohol, Ketone = secondary alcohol. Hydride ion, :H- , acts as a nucleophile

Test for Carbonyl groups

Brady's reagent, 2,4-DNP, methanol and H2SO4. Orange/yellow precipitate. Can be filtered, recrystallised and tested for melting point to identify which.

Test for aldehydes

Tollens reagent, Silver nitrate in aqueous ammonia. Ag+ ions act as oxidising agent and reduced to silver metal - silver mirror. Aldehyde is oxidised to carboxylic acid. Ketones can't be oxidised to doesn't work.

Solubility of carboxylic acids

C=O and OH are polar so hydrogen bonds form with water. Soluble with less than 4 carbons. As carbon chain increases, non-polar chain has greater effect on overall polarity

Carboxylic acid hydrogen bonds

form diamers

derivative of carboxylic acid

A compound that can be hydrolysed to form the parent carboxylic acid

Esters

Named after salt of parent acid and alkyl chain.

Acyl chlorides

parent carboxylic acid + -oyl chloride; more reactive than carboxylic acid

Acid Anhydrides

Formed by removal of water from two carboxylic acid molecules.

Esterification - Condensation reaction

The reaction of an alcohol with a carboxylic acid to produce an ester and water. Warmed and c.H2SO4.

Hydrolysis of Esters

chemical breakdown of esters in the presence of water.

Acid hydrolysis of esters

Heated under reflux with dilute aqueous acid catalyst to form carboxylic acid and alcohol

Alkaline hydrolysis of esters

Heat under reflux with aqueous hydroxide ions (Irreversible). Forms a carboxylate ion and an alcohol.

How are acyl chlorides formed?

Reacting carboxylic acid with thionyl chloride, SOCl2

Why are acyl chlorides formed in a fume cupboard?

SO2 and HCl gases are formed

How do acyl chlorides react as nucleophiles

Loses the chloride ion whilst retaining the C=O

Why are acyl chlorides used in formation of esters (with alcohols)

Used in industry because it is a complete reaction with high atom economy. More reactive than COOH, so forms esters with phenol without a catalyst

Why are acyl chloride reactions done in anhydrous conditions?

Reacts violently with water to form COOH and HCl fumes.

Acid anhydrides react similarly to Acyl chlorides

but less reactive. When reacted with alcohol, forms an ester and COOH