Question

An organic compound (A) gives violet colour with neutral \(\mathrm{FeCl}_{3}\). It answers Liebermann's test. This compound on catalytic reduction gives (B). The saturated compound (B) on oxidation with \(\mathrm{CrO}_{3}\) gives (C) of molecular formula \(\mathrm{C}_{6} \mathrm{H}_{10} \mathrm{O}\). (C) gives precipitate with 2,4 -dinitrophenylhydrazine. (C) can be obtained by reductive ozonolysis of (D). The other product of reductive ozonolysis, (E), undergoes Cannizzaro reaction with benzaldehyde to give (F) and HCOONa. Answer the following questions. Which of the statements about (F) is wrong? (a) (F) can have intermolecular hydrogen bonding. (b) (F) is produced by SN1 reaction of \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{Cl}\) with \(\mathrm{OH}^{\circ}\). (c) (F) undergoes facile dehydration. (d) (F) reacts with acetic anhydride to form a compound used in perfumery.

Short answer

Answer: (c) F undergoes facile dehydration.

Step-by-step solution

Identify compound A

Given that compound A gives a violet color with neutral FeCl3 and answers Liebermann's test, we can conclude that compound A is a phenolic compound. Liebermann's test typically gives a positive result with phenolic compounds. Step 2: Identify compound B and C

Identify compound B and C

Compound A undergoes catalytic reduction to give compound B, which, after oxidation with CrO3, gives compound C with molecular formula C_6H_{10}O. Both of these processes (reduction and oxidation) indicate the conversion of the phenol group in A to saturated alkane and then to a carbonyl group (aldehyde or ketone). Step 3: Identify compound C

Identify compound C

Compound C gives a precipitate with 2,4-dinitrophenylhydrazine, which is a test for the presence of an aldehyde or ketone carbonyl groups. Since the molecular formula of compound C is C_6H_{10}O and comes from phenol, we can conclude that compound C's structure is cyclohexanone. Step 4: Identify compounds D and E

Identify compounds D and E

Compound C can be obtained by reductive ozonolysis of compound D. This indicates that compound D has a carbon-carbon double bond, which yields compound C and another product (E) on ozonolysis. Here, we can understand that compound E undergoes Cannizzaro reaction with benzaldehyde to give compound F and HCOONa. Step 5: Identify compound F

Identify compound F

The Cannizzaro reaction involves the oxidation of an aldehyde and the reduction of another aldehyde, producing an alcohol and a carboxylic acid. Here, benzaldehyde undergoes reduction, and compound E is oxidized. The carboxylic acid generated must be sodium formate (HCOONa), indicating that compound F is the alcohol produced, \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{CH}_{2} \mathrm{OH}\) (benzyl alcohol). Step 6: Verify the statements about compound F

Verify the statements about compound F

a) F can have intermolecular hydrogen bonding: True. The hydroxyl group in benzyl alcohol can form hydrogen bonds with other molecules. b) F is produced by SN1 reaction of \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{CH}_{2}\mathrm{Cl}\) with \(\mathrm{OH}^{\circ}\): True. Benzyl alcohol can be formed by the nucleophilic substitution of benzyl chloride with hydroxide anion. c) F undergoes facile dehydration: False. Benzyl alcohol does not easily undergo dehydration to form an alkene due to resonance stabilization of the benzyl cation. d) F reacts with acetic anhydride to form a compound used in perfumery: True. Benzyl alcohol reacts with acetic anhydride to form benzyl acetate, which is commonly used in perfumes and flavorings. #Conclusion# Based on the analysis, the wrong statement about compound F (benzyl alcohol), in this case, is: (c) F undergoes facile dehydration.

Key concepts

Phenolic Compound Reactions

Phenolic compounds, which include a hydroxyl group directly attached to an aromatic ring, play an important role in organic chemistry. They exhibit distinct properties and undergo specific reactions, one of which is the ability to form colored complexes with iron(III) chloride, as noted in our original exercise where compound (A) gives a violet color with neutral \(\mathrm{FeCl}_{3}\). This reaction is a qualitative test indicating the presence of a phenol group.

Another noteworthy reaction is Liebermann's test, which involves the conversion of phenols to colored compounds when reacted with nitrous and sulfuric acid. These tests are valuable for identifying phenolic structures in unknown compounds. Their behavior under catalytic reduction is also essential, as it leads to the saturation of the aromatic ring and conversion into less reactive cyclohexane derivatives, setting the stage for subsequent chemical transformations.

Catalytic Reduction in Organic Chemistry

In organic chemistry, catalytic reduction refers to the addition of hydrogen (hydrogenation) to an organic molecule using a catalyst. Commonly employed catalysts include metals such as palladium, platinum, or nickel. The catalytic reduction of phenolic compounds can transform the aromatic ring into a cyclohexane ring, which is a saturated and less reactive species compared to its precursor. This process is an important step in our current problem as it helps to convert compound (A), a phenolic compound, into a saturated compound (B).

Oxidation Reactions with CrO3

Oxidation reactions are crucial for modifying the functional groups within organic molecules. Chromium trioxide (\(\mathrm{CrO}_{3}\)) is a powerful oxidizing agent that can convert primary alcohols to carboxylic acids and secondary alcohols to ketones. In the context of our textbook exercise, compound (B) undergoes oxidation with \(\mathrm{CrO}_{3}\) to form compound (C). Considering the molecular formula of compound (C) is \(\mathrm{C}_{6}\mathrm{H}_{10}\mathrm{O}\), and since it originated from a phenolic compound, it is likely oxidized to a ketone with a cyclohexane backbone, which is further confirmed by its reactivity with 2,4-dinitrophenylhydrazine.

2,4-Dinitrophenylhydrazine Test

The 2,4-dinitrophenylhydrazine (DNPH) test is used to detect the presence of carbonyl groups in aldehydes and ketones. When a carbonyl compound reacts with DNPH, it forms a yellow, orange, or red precipitate known as a hydrazone. This test is a strong indicator that compound (C) in our exercise contains a carbonyl group, which narrows down the structure to either an aldehyde or a ketone. Given the molecular clues and the reactions it has undergone, we can deduce that compound (C) is indeed a ketone.

Reductive Ozonolysis

Reductive ozonolysis is a reaction where an alkene is cleaved by ozone (\(\mathrm{O}_{3}\)) to form carbonyl compounds, and the reaction is followed by a reductive workup, usually involving zinc and acetic acid or dimethyl sulfide. This method effectively breaks the carbon-carbon double bond and can inform us about the molecular structure of the starting material. In the textbook problem, compound (D) undergoes reductive ozonolysis to yield compound (C), which has a ketone functional group, and another compound (E).

Cannizzaro Reaction

The Cannizzaro reaction is a redox reaction where an aldehyde is transformed into an alcohol and a carboxylic acid salt in the presence of a base, without an external oxidizing or reducing agent. Typically, this reaction occurs with non-enolizable aldehydes—those which lack an alpha-hydrogen. In our exercise, compound (E) is the aldehyde subjected to the Cannizzaro reaction with benzaldehyde, resulting in the production of compound (F) and sodium formate (\(\mathrm{HCOONa}\)). This identifies compound (F) as benzyl alcohol, which is consistent with the other information we have previously deduced.