A) i) Write the products formed when ethanal reacts with the following reagents:

a) and then

b)

c) in the presence of dil NaOH

B) Give simple chemical tests to distinguish between the following pairs of compounds:

i) Benzoic acid and Ethyl benzoate

ii) Propanal and Butan-2-one

OR

I) Account for the following:

i) is more reactive than towards the reaction with HCN.

ii) groups in semicarbazide (). However, only one is involved in the formation of semicarbazone.

II) Write the chemical equation to illustrate each of the following name reactions.

i) Rosenmund reduction

ii) Hell-Vohlard-Zelinsky reaction

iii) Cannizzaroreaction

A) i)

ii)

iii)

B) i)Benzoic acid and Ethyl benzoate can be distinguished by sodium bicarbonate test.

Acid reacts with to produce brisk effervescence due to the evolution of Carbon dioxide gas.Benzoic acid being an acid responds to this test, but Ethylbenzoate does not (in other words, Ethylbenzoate does not form Carbondioxide).

ii) Tollen’s test

Propanal is an aldehyde. Thus, it reduces Tollen’s reagent. But propanone being a ketone does not reduce Tollen’s reagent.

OR

I) i) ​The reaction of with HCN is a nucleophilic addition reaction. Aldehydes are more reactive than ketones this is because of 2 primary reasons:1) steric reason and 2) electronic reason.

 In the case of steric hinderances, the keto groups are more hindered because of the presence of 2 alkyl groups on both the sides of the carbonyl group. Thereby making it less reactive for the nucleophilic attack.

 In the latter case, the 2 bulky groups of the ketones reduce the electrophilicity of the ketones. Thus, is more reactive than towards the reaction with HCN.

ii) Though there are two groups in semicarbazide (). However, only one is involved in the formation of semicarbazone. This is because of the reason the group has lone pair of electrons which is delocalised. Therefore, the other available group which is not resonating with the carbonyl group takes part in the formation of semicarbazone.

II) i) Rosenmund Reaction

In this reaction the acyl chloride (like Benzoyl Chloride) gets hydrogenation using the catalyst Palladium in the presence of Barium Sulphate. Finally, it gets converted into benzaldehyde.

ii) Hell-Vohlard-Zelinsky reaction

The carboxylic acids which have alpha Hydrogen, when they are heated with halogens, they give alpha-halo acids. Such reactions are termed as Hell-Vohlard-Zelinsky reaction.

iii) Cannizzaro reaction

This is a disproportionation reaction in which aldehydes without α-hydrogens are used in presence of a strong base to yield an alcohol and a carboxylic acid is called Cannizzaro reaction. One molecule of aldehyde is reduced to yield the corresponding alcohol, while a second one is oxidized to the carboxylic acid.

Mechanism:

The reaction begins with the attack of a nucleophilic on the hydroxide ion of the carbonyl centre. This results in anion to attack another molecule of aldehyde, thereby transferring its hydride moiety.In the final step of the reaction, the acid and alkoxide ions formed exchange a proton. This reaction takes place in the presence of a concentrated base, the aldehyde first forms a doubly charged anion from which a hydride ion is transferred to the second molecule of aldehyde to form carboxylate and alkoxide ions. Subsequently, the alkoxide ion acquires a proton from the solvent.