Question

a) Which named reaction is used to reduce CH₃COCI to CH₃CHO? 

b) Aldehydes and Ketones undergo reactions due to the presence of α – hydrogen atom. 

i) Write the name of the reaction of aldehyde which takes place only because of the presence of α – hydrogen atom. 

ii) How will you bring about the above reaction? 

c) i) CH₂CICOOH is a stronger acid than CH₃COOH Why? 

ii) How will you convert CH₃COOH to CH₂CICOOH

Answer 1

a) Rosenmund Reduction.

CH₃COCl \(\underset{Pd- BaSO_4}{\stackrel{H_2}{\longrightarrow}}\) CH₃CHO

b) i) Aldol condensation.

ii) Aldehyde or ketone containing at least one x-hydrogen undergo self-condensation reaction with dil. alkali

(e.g. dii. NaOH) as catalyst to form β – hydroxy aldehydes (atdol) or β – hydroxy ketones (ketol) respec travel.

c) i) Electron with drawing group or-leffect group ‘Cl’ stabilises the conjugate acid of the carboxylate anion through delocalisation of negative charge and strengthens the carboxylic acid.

CH₂CI COOH > CH₃ COOH

ii) When a carboxylic acid that contains α – hydrogen is treated with Cl₂ or Br₂ in the presence of small amount of red phosphorus the α – hydrogen atoms are replaced by chlonne or bromine atoms to give α – halo carboxylic acids. This reaction is known as the Hell-Volhard-Zelinsky (HVZ) Reaction.