Carbonyls (Aldehydes/Ketones/Carboxylic acids / Esters

What are carbonyls

Consist of carbon-oxygen double bond

• aldehydes and ketones

Describe nucleophillic addition reactions

Reduces carbonyls to alcohols

Reagent: NaBH4 or LiAlH4

→ BH4- ion a source of Hydride ion

Conditions: aqueous ethanol

→ produces primary alcohols + OH- ion

Why do we prefer NaBH4 to LiAlH4

• NaBH4 is less reactive than LiAlH4

• LiAlH4 reacts violently with water and alcohols

• LiAlH4 must use ether as a solvent

Why can nucleophillic addition reaction occur

• C=O bond is polar so the carbon attracts negatively charged lone pair of electrons from hydride ions

Why can aldehydes and ketones be reduced but not alkene

Hydride ion is a nucleophile attacks positive c in c=o

• hydride ion repelled by electron rich C=C

Why are enantiomers produced in carbonyl reduction

• carbonyl groups are planar due to C=O bond

• Can be attached from either side with equal probability of above or below attack

• Equal amounts of enantiomers are formed - racemic mixture ( not optically active)

Test for carbonyls

• Bradys reagent

• Red or orange ppt with carbonyl vs clear/no ppt

What is esterification and what are some uses

Carboxylic acid heated under reflux + alcohol + acid (H2SO4) catalyst → ester

• sweet smelling compounds for perfumes + flavourings

• Plasticisers

• Solvents for polar organic substances

• Solvent in glue→Volatile, evaporates easily leaving sticky glue substance

Why can esters be used in perfumes

• non-toxic

• Soluble

• Volatile

• Does not react with water

What are some properties of Carboxylic acids

• high boiling point → hydrogen bonding

• Very soluble in water → polar, form H-bonds

• Hydrocarbons chain size increases the solubility decreases as more of the molecule is non-polar

What are general reactions with Carboxylic acid

• Carboxylic acid + metal → metal salt + hydrogen

• Carboxylic acid + metal oxides → metal salt + water

• Carboxylic acid + metal hydroxide→ metal salt + water

• Carboxylic acid + metal carbonates → metal salt + water + CO2

Describe the formation of a triester

• Conditions: heat under reflux + acid catalyst (H2SO4)

• Formed from propan-1,2,3-triol (glycerol)

• Forms 3 water molecules

What is hydrolysis

Chemical reaction where water causes breaking of a chemical bond in a decomposition Reaction

Hydrolysis of esters in acidic conditions

• Esters are refluxed with catalyst of hot aqueous acids

• Decompose → Carboxylic acid + alcohol

• Water present in excess to favour products side of equilibrium

→ reversible reaction

Hydrolysis reaction of esters in alkaline conditions

• esters refluxed with hot aqueous alkali e.g KOH

• Decompose → alcohol + carboxylate salts

• Non-reversible products are easier to separate

→ makes soaps/ saponification

What is an Acyl chloride + how is it formed

• Contain function group R-COCL ,R is alkyl group

• Formed by reacting SOCl2 (thionyl chloride) + Carboxylic acid in dry conditions

• Acyl chloride separated by distillation

Properties of Acyl Chlorides

• polar + reactive

• Colourless liquids fume in moist air HCl

• Undergo addition-elimination

Describe Acyl Chloride nucleophilic addition-elimination

• Addition: carbon of C=O attracts lone pair of e- from nucleophile

• Pair of e- in C=O transferred to oxygen→ negatively charged

• Elimination: double bond reformed

• C-Cl bond breaks

• Cl reacts with hydrogen atom → HCL