What do carboxylic acids, aldehydes, ketones and esters have in common?
What is the functional groups of:
Carboxylic acids, Aldehydes, and Ketones all contain the carbonyl group (>C=O)
The functional group of:
Carboxylic acids is -COOH
Alcohols is -OH
Aldehydes is -CHO
Ketones is >C=O
Esters is -COOR
Oxidation of alcohols
Reagent: acidified potassium dichromate (IV) , K2Cr2O7
Orange-green colour change as dichromate ion is reduced to green Cr3+ cation
oxidant represented by [O] in eqn.
Primary Alc. is oxidised to an Aldehyde and then (if refluxed) a carboxylic acid
Secondary Alc. is oxidised to a ketone
Tertiary Alc. is not easily oxidised (but a stronger reagent eg acidified KMnO4 can break C=C bond, producing a mixture of compounds w. shorter carbon chains)
Tests to distinguish b/n aldehydes and ketones
These are redox reactions
both give ve tests for aldehydes
soln. turns from blue to brick red ppt.(precipitate)
as blue Cu 2+ ions are reduced to CuO which is brick red
silver mirror effect around test tube
as Ag+ ions are reduced to Ag
Reactions of Aldehydes and Ketones
Nucleophilic addition eg with Hydrogen Cyanide
The nucleophile ( CN:- remember the lone pair) attacks the slightly +ve charge on the C atom of the C=O grp
Reaction intermediate has an O: atom w. a -ve charge
an e pair from this atom forms a covalent bond w. a H ion, forming a hydroxynitrile
Reduction of acids/aldehydes and ketones to Alcoho
Oxidation reactions of alcohols to make acids/aldehydes/ketones can be reversed by reduction.
a strong reducing agent is needed eg NaBH4 in water, or LiAlH4 in non-aqueous solvent eg methanol
reducing agent represented as 2[H] in equation
acid/aldehyde reduced to primary alc.
ketone reduced to secondary alc.
These are also nucleophilic addition reactions
Esters are formed when an alcohol and a carboxylic acid react together in the presence of a strong, conc. acid catalyst eg H2SO4, with Na2CO3 soln to neutralize excess acid
Known as esterification
This is also a condensation reaction as a water molecule is released from where the acid and alcohol join.
names are eg methyl ethanoate (methanol + ethanoic acid)
Esterification reactions are reversible, low yield (therefore there is an equilibrium)
reverse reactions are hydrolysis (splitting with water) forming an Alc. and a carboxylic acid
Esters have a fruity smell/flavour
test for an alcohol by making an ester (+ve test = 'fruity smell')
USES: confectionery, solvents and as plasticisers (molecules that reduce rigidity eg in PVC)
Soaps are salts of long-chain carboxylic acids (fatty acids) produced by ester hydrolysis
Fatty acids are derived from lipids which are naturally occurring tri-esters
Fats and oils are hydrolysed to produce soaps by boiling w. NaOH (aq) (called saponification)
glycerol is a by-product of this and has uses in pharmaceutical/cosmetic industries
soaps are anionic detergents. They emulsify oils because the -vely charges carboxyl grp is hydrophilic (attracted to water) and the +vely charged hydrocarbon chains are attracted to oil, not water (hydrophobic). When soap is added to an oil-water mixture and this is then shaken, the oil is broken up into small droplets.