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Chapter 5: Problem 55

A compound (A) gives an yellow precipitate with iodine and sodium hydroxide. On treating with a Grignard reagent, it gives (B). (B) gives a blue coloured pseudonitrole (C) in the Victor Meyer reaction which does not react with \(\mathrm{NaOH}\). (a) is (a) acetone (b) acetaldehyde (c) benzaldehvde (d) propanal

Short Answer

Expert verified
Answer: Compound A is acetaldehyde.

Step by step solution

01

Reaction with Iodine and Sodium Hydroxide

The presence of a yellow precipitate when reacting with iodine and sodium hydroxide indicates the presence of an aldehyde group. This narrows down our options to either acetaldehyde, benzaldehyde, or propanal as all of them have an aldehyde group (\(\mathrm{CHO}\)).
02

Reaction with Grignard Reagent

Grignard reagents add to aldehydes and ketones, resulting in the formation of a secondary or tertiary alcohol, respectively. In our case, compound (A) reacts with a Grignard reagent to give compound (B), which contains an alcohol group. This reaction does not provide clear differentiation among the options, so let's move to the next reaction.
03

Victor Meyer Reaction

The Victor Meyer reaction is used to identify aliphatic alcohols. In this reaction, alcohols are converted into pseudonitroles which exhibit different colors. A blue-colored pseudonitrole is formed by reacting primary or secondary alcohols. Since compound (B) gives a blue-colored pseudonitrole, it can be assumed that (B) is a primary or secondary alcohol, which implies (A) must be an aldehyde or ketone.
04

Reaction with Sodium Hydroxide

In the final reaction, we know that compound (C), the pseudonitrole, doesn't react with sodium hydroxide. This is an important piece of information because aromatic pseudonitroles react with sodium hydroxide while aliphatic pseudonitroles do not. This eliminates the option benzaldehyde as it is aromatic and would lead to the formation of an aromatic pseudonitrole.
05

Identify the Compound (A)

Based on the reactions we have analyzed, the remaining options are acetaldehyde and propanal. Both of these aldehydes would have similar reactions, but acetaldehyde would react more readily with Grignard reagents due to the presence of an hydrogen atom on the alpha carbon. Hence, the correct option for compound (A) is acetaldehyde. Therefore, the answer is (b) acetaldehyde.

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Most popular questions from this chapter

A compound, which is known as oil of bitter almonds is (a) acetaldehyde (b) acetone (c) acetophenone (d) benzaldehyde

Generally geminal diols are not stable. Account for the fact that the hydrates of the following carbonyl compounds are stable.

Hydroxyacetic acid (HOCH \(_{2}\) COOH ) is obtained by (a) the reduction of acetic acid by LiAlH (b) the hydrolysis of ethylene chlorohydrin, by aqueous alkali (c) the reaction of \(\mathrm{CH}_{3} \mathrm{CHO}\) with HCN followed by acid hydrolysis (d) Cannizzaro reaction of glyoxal.

Which of the following reactions will give acetophenone as a product? (a) Acid catalysed hydration of styrene followed by oxidation with hot alkaline \(\mathrm{KMnO}_{4}\). (b) Phenyl acetylene \(\stackrel{\mathrm{d} \mathrm{H}, \mathrm{SO}_{4}^{\prime} \mathrm{H}_{\mathrm{E}}^{2+}}{\longrightarrow}\) Aldehydes, Ketones and Carboxylic Acids (c) Reaction of benzoyl chloride with dimethyl cadmium. (d) Dry distillation of a mixture of calcium acetate and calcium benzoate.

The acylating species in the Friedel-Crafts acylation of benzene to give acetophenone is (a) \(\mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{O}^{\odot}\) (b) \(\mathrm{AlCl}_{4}\) (c) \(\mathrm{CH}_{3}-\stackrel{\oplus}{\mathrm{C}}=\ddot{\mathrm{O}}\) (d) \(\mathrm{CH}_{3}^{-\mathrm{C} \mathrm{C} \mathrm{Cl}}-\mathrm{O}-\mathrm{AlCl}\)
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