The correct order of acidic strength of the major products formed in the given reactions, is : Choose the correct answer from the options given below :
- C > A > D > B
- A > D > C > B
- A > D > B > C
- C > B > A > D
Answer
(1) C > A > D > B
Solution
A: PhNH2 PhN2+Cl- CuCN PhCN H3O+ PhCOOH (benzoic acid, pKa 4.19)
B: Tollens' reagent oxidises the aldehyde: CH3CH2CHO CH3CH2COOH (propanoic acid, pKa 4.87)
C: CH4 Mo2O3 HCHO Na2Cr2O7/H+ HCOOH (methanoic acid, pKa 3.75)
D: PhCH2MgBr + CO2 PhCH2COOMgBr H3O+ PhCH2COOH (phenylacetic acid, pKa 4.31)
HCOOH has no electron-donating group; the phenyl group (−I) in PhCOOH is directly on –COOH; in PhCH2COOH its −I effect is weakened by CH2; the ethyl group (+I) in propanoic acid decreases acidity.
Acidic strength: C > A > D > B
Answer: (1)