31.

(a) Write the structures of the main product when acetone ( CH₃-CO-CH₃) reacts with the following reagent:

(i) Zn-Hg/conc. HCl

(ii)  H₂N-NHCONH₂/H⁺

(iii) CH₃MgBr and then H₃O⁺

(a)  Arrange the following in the increasing order of their boiling point:

C₂H₅OH, CH₃-CHO, CH₃-COOH

(b)  Give a simple chemical test to distinguish between the following pair of compounds:

CH₃CH₂CHO and CH₃CH₂COCH₃

(i) Acetone undergoes clemmensen reduction in presence of zinc amalgam and conc.HCl to give propane.

(ii) Acetone reacts with semicarbazide to form semicarbazone.

(iii) Acetone reduces to form tertiary alcohol in the presence of Grignard reagent.

(b) Due to extensive hydrogen bonding, carboxylic acid has the highest boiling points an among the given compound. Alcohols, with a smaller number of the hydrogen bond, have a lesser boiling point. Aldehydes have least boiling point due to the absence of hydrogen bonding.

Hence the order of boiling point is:

CH₃-CHO < C₂H₅OH < CH₃COOH

(c) 2- Butanone has a methyl group attached to carbonyl carbon unlike propanal .hence , it can give iodoform test.

CH₃CH₂COCH₃  CH₃CH₂­COOH + CHI₃

                                              (Yellow ppt.)

CH₃CH₂CHO No reaction

Propanal