Edexcel Organic Chemistry Unit 4 Reactions

of aldehydes and ketones, carboxylic acids, esters and acyl chlorides

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Unit 4 Organic Chemistry Reactions
Aldehydes and Ketones
Oxidation of a primary alcohol, usually using potassium dichromate, distilled out before it can be
oxidized to a carboxylic acid.
The orange potassium dichromate will turn blue-green as chromium (III) ions are formed.
CH 3CH 2OH + [O] CH 3CHO + H 2O
Anything with a H2N group, such as 2,4-DNP, 2,4-dinitrophenylhydrazine.
The lone pair of electrons on the nitrogen acts as a nucleophile and forms a C=N bond with the +
carbon in the C=O group. A water molecule is eliminated, hence addition-elimination.
With 2,4-DNP, a yellow precipitate is formed when added to a simple aldehyde.
Nucleophilic Addition
The + carbon is attacked by nucleophiles. The methyl group is electron releasing, so the longer
the carbon chain of a carbonyl compound, the more + the carbon is, so the less reactive it is.
Reaction with HCN at pH8, a base is added to the HCN as it is a very weak acid, and produces
very few CN- ions. The base is added to react the H+ ions with the OH- ions to get water, so
shifting the position of equilibrium of the weak acid.
This happens by nucleophilic addition.

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Idodoform Reaction
Ethanal, and methlyl ketones undergo this reaction, forming a pale yellow precipitate of
Iodine is added to alkali solution, such as sodium hydroxide, to form iodate ions:
I 2 + OH -IO- + I -
These substitute into the CH3 group next to the C=O bond, forming a CI3C=O group. The electron
withdrawing effect of the three halogen atoms and the oxygen atom weaken the -bond, and
this breaks, forming iodoform, CHI3.…read more

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Potassium manganate reduces from purple to colourless in acidic solution, and from purple to
brown in neutral or alkali solution.
Potassium dichromate reduces from orange to green-blue.
Fehling's solution reduces from deep-blue solution to a red precipitate. Benedict's solution does
the same.
Tollen's reagent is reduced from colourless to form a silver mirror.
Carboxylic Acids
Oxidation of a primary alcohol or aldehyde usually using potassium dichromate, under reflux.
The orange potassium dichromate will turn blue-green as chromium (III) ions are formed.…read more

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The H- is added to the + carbon. This is carried out in ether solution because the reagents must
be kept dry. The H- ion in the AlH4- group is a powerful nucleophile.
Add aqueous acid, to protonate the O- formed in the first step.
Reduction of ethanoic acid to ethanol:
C H 3COOH + 4[H ]CH 3CH 2OH + H 2O
React with alchohols in the presence of concentrated sulphuric acid, as a catalyst.…read more

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Hydrolysis of an ester, heat an ester under reflux with an aqueous acid to form an acid and an
C H 3COOC 2H 5 + H 2O CH 3COOH + C 2H 5OH
Heat under reflux with aqueous alkali, which forms either the alcohol and the carboxylic acid salt.
Add strong acid to the salt to get the carboxylic acid.…read more

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To form an ester and misty fumes of HCl
C H 3COCl + CH 3OH CH 3COOCH 3 + HCl
The nitrogen atom in ammonia has a lone pair, used for nucleophilic attack on the C=O group. To
form an amide.
C H 3COCl + NH 3 CH 3CONH 2 + HCl
Amines also have a lone pair on the nitrogen used for nucleophilic attack to form a substituted
amide.…read more


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