(a) Exemplify the following reactions:

(i) Rosenmund reduction reaction.

(ii) Kolbe electrolysis reaction

(b) Arrange the following compounds in increasing order of their reactivity towards HCN:

Acetaldehyde, Acetone, Di-tert-butyl ketone.

OR

(a) Predict the products of the following reactions:

(i)

(b) Arrange the following compounds in increasing order of acid strength: Benzoic acid, 4-Nitrobenzoic acid, 4-Methoxybenzoic acid.

a(i)

In Rosenmund reduction reaction Acyl chloride (which is ClC=Oacid chloride) is hydrogenated on the catalytic reaction of palladium (Pd) in presence of barium sulphate.

a(ii)

• In Kolbe electrolysis reaction

The Kolbe electrolysis reaction mechanism involves a two-stage radical process.: electrochemical decarboxylation gives a radical intermediate, then two such intermediates combine to form a covalent bond.

(b)

• When HCN is attacking while in a reaction it is attacking as the nucleophile CN^- .

• Hence, as the negative charge on a species increases its reactivity towards HCN decreases.

• Amongst the given compounds, +I (electron releasing effect ) increases as

• Therefore the correct order of increasing reactivity of the given compounds towards HCN is: Acetaldehyde > Acetone> Di-tert-butyl ketone. This is due to the +I effect also for the increasing steric hindrance (therefore decreasing reactivity ) among the compounds.

OR

a(i)

• This is an example of Hell-Volhard-Zelinsky reaction , where the propanoic acid which has α-H atoms gets halogenated on reaction with chlorine and presence of small amount of phosphorus and forms corresponding

α-halocaboxylic acid, 2-chloropropanoic acid

Hence the product will be 2-chloropropanoic acid, .

a(ii)

This is an example of Etard reaction , where Chromyl chloride(CrO₂Cl₂)at first oxidises the methyl group of the given aromatic compound toluene to a chromium complex then by hydrolysis it gives corresponding benzaldehyde.

_.

(b)

• The correct increasing order of acid strength of the given acids 4-Methoxybenzoic acid< Benzoic acid<4-Nitrobenzoic acid.

• This is due to the nature (electron donating/withdrawing property) of the functional groups attached to the aromatic ring and as electron donating (such as –OCH₃) groups decreases the acidity of benzoic acids and ele ctron donatuiob groups ( such as NO₂) increases their acidity the order is justified.