Identify the compound problem

Question:

In the following reaction sequence, the compound J is intermediate.

J (C₉H₈O₂) gives effervescence on treatment with NaHCO₃ and a positive Baeyer’s test. Indentify the compound I and K.

Options for I:

Options for K:

Solution:

Such question comes with multiple choices in a typical IIT JEE problem. The real solution may discover various options for I J and K. But remember you have to discover correct option from the option given only.

Although at first look it seems a tough question, this question can be solved with some basics on known Baeyer's test and some reasoning.

Step1: J gives brisk effervescence with sodium bicarbonate NaHCO_3. Now you must remember that when sodium bicarbonate reacts with an acid, it gives a brisk effervescence from the formation of CO2. This indicates the presence of carboxylic group in J.   

Step 2: Identify the concept tested in the question: J gives Baeyer’s test positive. Now recall basic rules of Baeyer's test. It tests for unsaturation (presence of double and triple bonds between C, C atoms). Only unsaturated compound gives a positive Baeyer's test; hence J is unsaturated acid.

Step 3:

 Now let’s identify I. I in the presence of acid anhydride (CH₃COO)₂O and sodium acetate (CH₃COONa) gives unsaturated acid. If you recall perkin reaction, you know that it is:

Aromatic aldehyde + acid anhydride + acid salt of the acid  = unsaturated aromatic acid

It means I must be an aromatic aldehyde. Now look at the options. Option 1 is aldehyde and correct.

Lets apply perkins reaction to option 1.

 Step 4:

 From here we found our J too. Now let’s find out K.

K

   Thus option 3 is correct for K.