This is the organic chemistry question, which is based on word problem which usually comes for 5 marks in 12th board exam. This organic chemistry question was asked in Class 12 CBSE Board All India 2013.
Organic Chemistry Question Asked in Exam
An organic compound (A) which has characteristic odour, on treatment with NaOH forms two compounds (B) and (C). Compound (B) has the molecular formula C7H8O which on oxidation with CrO3 gives back compound (A). Compound (C) is the sodium salt of the acid. Compound (C) when heated with soda lime yields an aromatic hydrocarbon (D). Deduce the structures of (A), (B), (C) and (D). Write chemical equations for all reactions taking place.
Concept
This question talks about a compound (A) which has a characteristic odour. By the characteristic odour, we usually think about the ester. Let us suppose, compound (A) may be an ester.
Now, we read question further and found out that the compound (A) reacts with NaOH and gives compound (B) and (C) which usually a sodium salt carboxylic acid and an alcohol. It is mentioned in the question that one compound is sodium salt of acid and the other one oxidises to give back (A). This is not possible for an alcohol to give back ester on oxidation.
So, our assumption about (A) as an ester is wrong.
Now what to do? Is there any other compound which show a characteristic odour?
Yes, Benzaldehyde show characteristic odour.
So, here compound (A) is Benzaldehyde.
Benzaldehyde on treatment which NaOH show Cannizzaro reaction to form two compounds (B) and (C), i.e., Benzyl alcohol and Sodium salt of benzoic acid, respectively.
Compound B has the formula C7H8O. Yes the benzyl alcohol has the formula as mentioned earlier.
Now, compound B, i.e., benzyl alcohol, on oxidation with CrO3 give back compound A, i.e., benzaldehyde.
In last, compound C, i.e., sodium salt of benzoic acid on treatment with soda lime form a aromatic hydrocarbon D, i.e., benzene.
So, the concluded concept of this question is that, the benzaldehyde undergo Cannizzaro reaction which gives two compounds. One is benzyl alcohol which on oxidation with CrO3 gives back benzaldehyde. And the other is sodium salt of benzoic acid which on treatment with soda lime given a aromatic hydrocarbon, i.e., benzene.
Video Explanation
Check out other Solved Previous Year Organic Chemistry Questions
Read more: How Organic Conversions aren’t as Bad as You Think?