Question

An organic compound with the molecular formula \(C_8H_8O\) forms 2,4-DNP derivative, reduces Tollens’ reagent and undergoes Cannizzaro reaction. On vigorous oxidation it gives Benzene-1,2-dicarboxylic acid. Identify the compound and write the reactions of compound with 2,4-DNP and when it undergoes Cannizzaro reaction.

Hint:

Identification clues:

• 2,4-DNP test \(\Rightarrow\) Carbonyl compound.

• Tollens' test positive \(\Rightarrow\) Aldehyde.

• Cannizzaro reaction \(\Rightarrow\) Aldehyde without \(\alpha\)-hydrogen.

• Oxidation to phthalic acid \(\Rightarrow\) Ortho-substituted aromatic compound containing \(-CHO\) and \(-CH_3\) groups.
Hence, \[ \boxed{ o\text{-Methylbenzaldehyde} } \] is the only structure satisfying all the given conditions.

Answer 1

Concept: The identification of an unknown organic compound is based on the information provided regarding its molecular formula and characteristic chemical reactions. The given compound:

• Forms a 2,4-DNP derivative.

• Reduces Tollens' reagent.

• Undergoes Cannizzaro reaction.

• On vigorous oxidation gives Benzene-1,2-dicarboxylic acid (phthalic acid).
Each observation provides important information about the structure of the compound.

Step 1: Analysis of the molecular formula. Given molecular formula: \[ C_8H_8O \] The compound contains oxygen and has a high degree of unsaturation, suggesting the possible presence of an aromatic ring along with a carbonyl group.

Step 2: Inference from 2,4-DNP test. The compound forms a 2,4-dinitrophenylhydrazone derivative. This test is given by aldehydes and ketones. Therefore, the compound must contain a carbonyl group. \[ \boxed{\text{Aldehyde or Ketone}} \]

Step 3: Inference from Tollens' test. The compound reduces Tollens' reagent. Tollens' reagent is reduced by aldehydes but not by ordinary ketones. Therefore, the compound must be an aldehyde. \[ \boxed{\text{The compound contains } -CHO} \]

Step 4: Inference from Cannizzaro reaction. Cannizzaro reaction is shown only by aldehydes that do not possess an \(\alpha\)-hydrogen atom. Therefore, the aldehyde must not contain any \(\alpha\)-hydrogen. Aromatic aldehydes such as benzaldehyde and substituted benzaldehydes satisfy this condition. \[ \boxed{\text{Aromatic aldehyde without } \alpha\text{-H}} \]

Step 5: Inference from oxidation product. On vigorous oxidation, the compound gives Benzene-1,2-dicarboxylic acid which is \[ \boxed{\text{Phthalic acid}} \] Formation of phthalic acid indicates that the aromatic ring contains two oxidisable side chains at adjacent (ortho) positions. One side chain is the aldehyde group and the other must be a methyl group. During oxidation: \[ -CHO \rightarrow -COOH \] and \[ -CH_3 \rightarrow -COOH \] Thus the compound must be \[ \boxed{ o\text{-Methylbenzaldehyde} } \] or \[ \boxed{ 2\text{-Methylbenzaldehyde} } \] with structure \[ C_6H_4(CH_3)CHO \]

Step 6: Reaction with 2,4-DNP reagent. The aldehyde reacts with 2,4-dinitrophenylhydrazine to form the corresponding hydrazone. \[ C_6H_4(CH_3)CHO + H_2NNHC_6H_3(NO_2)_2 \] \[ \longrightarrow C_6H_4(CH_3)CH=NNHC_6H_3(NO_2)_2 + H_2O \] The product formed is the 2,4-dinitrophenylhydrazone derivative. \[ \boxed{ o\text{-Methylbenzaldehyde 2,4-DNP derivative} } \]

Step 7: Cannizzaro reaction. Since the aldehyde lacks \(\alpha\)-hydrogen atoms, it undergoes Cannizzaro reaction in the presence of concentrated alkali. Two molecules of the aldehyde react together. One molecule is oxidised to carboxylate ion and the other is reduced to alcohol. \[ 2C_6H_4(CH_3)CHO + NaOH \] \[ \longrightarrow C_6H_4(CH_3)COONa + C_6H_4(CH_3)CH_2OH \] On acidification: \[ C_6H_4(CH_3)COONa \longrightarrow C_6H_4(CH_3)COOH \] Thus the products are: \[ \boxed{ o\text{-Methylbenzyl alcohol} } \] and \[ \boxed{ o\text{-Methylbenzoic acid} } \]

Final Answer: The compound is \[ \boxed{ o\text{-Methylbenzaldehyde} } \] \[ \boxed{ C_6H_4(CH_3)CHO } \] Reaction with 2,4-DNP: \[ \boxed{ C_6H_4(CH_3)CHO + H_2NNHC_6H_3(NO_2)_2 \rightarrow C_6H_4(CH_3)CH=NNHC_6H_3(NO_2)_2 + H_2O } \] Cannizzaro reaction: \[ \boxed{ 2C_6H_4(CH_3)CHO + NaOH \rightarrow C_6H_4(CH_3)COONa + C_6H_4(CH_3)CH_2OH } \]