A white crystalline solid "X" gives the following chemical tests:

  1. It liberates $\ce{CO2}$ with $\ce{NaHCO3}$
  2. It forms a coloured dye in diazotisation and coupling with $\beta$-naphthol
  3. With $\ce{Br2}$/$\ce{H2O}$, it forms a white precipitate of 2,4,6-tribomoaniline.

"X" can be identified as:

Showing the four answer choices for the above question: (a) 3-aminobenzenesulfonic acid, (b) 4-aminobenzenesulfonic acid, (c) 4-acetamidobenzoic acid, and (d) 3-aminobenzoic acid.

I thought that (d) could be the answer as COOH releases $\ce{CO2}$ from $\ce{NaHCO3}$, but can sulphonyl group release $\ce{CO2}$ from $\ce{NaHCO3}$?

  • $\begingroup$ Aryl sulfonic acids are certainly acidic enough to release CO2 from bicarbonates. $\endgroup$ – Waylander Apr 13 '19 at 6:29
  • 1
    $\begingroup$ The title of the question is too broad. Please note that the title shall be as descriptive as possible. Generally, the wording of the title shall be established with great care; while being as concise as possible, it shall indicate, without ambiguity, the subject matter of the question in such a way as to distinguish it from that of other questions, without going into unnecessary detail. $\endgroup$ – Faded Giant Apr 13 '19 at 11:17

(i) indicates presence of 'strong' acidic group: -(SO3H) and -(CO2H) since both are strongly acidic to protonate NaHCO3 and yield CO2.

(ii) indicates presence of Primary Amine which can fully undergo diazotization reaction and then with beta-naphthol form azo dye (coloured dye).

(iii) excess of bromine water forming s-tribromoaniline directly indicates that Option 2(b) is correct.

An article on point (iii): journal_iisc

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