Write the mechanism of esterification reaction of benzoic acid with ethanol in the presence of concentrated sulphuric acid.

The first step in the esterification is the protonation of a very small amount of the benzoic acid by the stronger sulphuric acid. Protonation of benzoic acid forms a resonance stabilized cation. Ethanol adds to the carbon of the cation. It looses a water molecule to form a tetrahedral intermediate and a proton. One of the hydroxyl group is protonated to remove water and loss of proton gives the ethyl benzoate.

An organic compound 'A' (molecular formula C 6 H 10 O ) forms hydrazone and reduces Tollens' reagent. When treated with CH 3 MgBr followed by hydrolysis 'A' gives a chiral compound 'B'. Compound ' B ' on oxidation with potassium dichromate/acid gives compound 'C'. Compound 'C' undergoes haloform reaction and gives cyclopentane carboxylic acid as oxidation product. Identify A,B,C and write the sequence of the reactions.

Aldehydes give positive Tollen's test while ketones do not give any reaction. When aldehyde is warmed with Tollen's reagent a silver mirror is formed. Aldehyde with molecular formula C 6 H 10 O reacts with CH 3 MgBr followed by hydrolysis to give alcohol. Alcohols undergo oxidation with potassium dichromate/acid to give ketones and carboxylic acids. Methyl ketones give cyclopentane carboxylic acid as oxidation product.

Why are ketones less reactive than aldehydes?

Ketones are less reactive than aldehyde because the positive charge of the carbonyl carbon is diminished by electron donating groups + I effect or by two alkyl groups.

An organic compound C 2 H 4 O gives red precipitate when warmed with Fehling’s solution. Give the IUPAC name of the compound and write the chemical equation for the reaction.

An organic compound with molecular formula C 2 H 4 O is acetaldehyde which gives red precipitate when warmed with Fehling's solution. Acetaldehyde is oxidised to corresponding carboxylate anion and the IUPAC name of acetaldehyde is ethanal. CH 3 CHO + 2 Cu 2 + + 3 OH − → CH 3 COO − + 2 Cu + + 2 H 2 O

Describe the following reaction. Rosenmunds reaction

Rosenmund reaction is a reaction for the preparation of aldehyde. In this reaction, acyl chloride or acid chloride is hydrogenated over palladium on barium sulphate to form aldehyde. The following reaction occurs,

Describe the following reaction. Cannizzaro reaction

Aldehydes without an α-hydrogen atom, undergo self oxidation and reduction reaction on heating with concentrated alkali. In this reaction, one molecule of the aldehyde is reduced to alcohol while another is oxidised to carboxylic acid salt. For example, when methanal is treated with concentrated potassium hydroxide, methanol and Potassium formate are produced.

Describe the following reaction. H.V.Z. reaction

Hell-Volhard-Zelinsky reaction is used for the preparation of α -halocarboxylic acids. In this reaction, carboxylic acids with an α -hydrogen are halogenated at the α -position on treatment with chlorine or bromine in the presence of a small amount of red phosphorus.

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - Aldehydes, Ketones and Carboxylic Acids>Manipur Board-2020>Q 9

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12th Manipur Board

IMPORTANT

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What is Aldol condensation? Describe it with suitable example each for the formation of aldol and ketol.

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