Question:What products would be formed from the preceeding reaction if the carboxylic acid group were not protected?

Protection of a particular group in a compound leads to decrease in its yield. This is because protection and deprotection of a group adds two more steps in synthesis. So, there will be decrease in the yield of final product.

Following product will be formed, if the carboxylic acid group were not protected:

Preparation of 2-oxohexanedioic acid

In this reaction carboxylic acid group is not protected by any of reagents. In that case 4-hydroxybutanoic acid is treated with thionyl chloride gives a product in which Cl is substituted instead of OH groups.The synthesized product on reaction with CN gives 4-cycanobutanyol cyanide which on reaction with acid hydrolysis gets the final product 2-oxohexanedioic acid. Thus, both OH groups converted to COOH groups.