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Chapter 26: Problem 643

Give for each of the following pairs of compounds a chemical test, preferably a test-tube reaction, that will distinguish the two compounds. Write a structural formula for each compound and equations for the reactions involved: (a) \(\mathrm{m}\) -niltrotoluene and phenylnitromethane (b) \(\mathrm{p}\) -nitrotoluene and benzamide (c) hydrazobenzene and benzidine (d) \(\mathrm{p}\) -methoxyazobenzene and \(\mathrm{p}\) -methylazoxybenzene (e) aniline and cyclohexylamine.

Short Answer

Expert verified
(a) Hydrolysis with sodium hydroxide (\(\mathrm{NaOH}\)): m-nitrotoluene → m-aminotoluene + \(\mathrm{NaNO}_{2}\); Phenylnitromethane → benzylamine + \(\mathrm{HNO}_{2}\). (b) Reaction with ammonia: Benzamide → \(\mathrm{C}_{6}\mathrm{H}_{5}\)-\(\mathrm{CONH}_{4}\) (crystalline product). (c) Oxidation reaction: Hydrazobenzene → azobenzene. (d) Acid-catalyzed hydrolysis with \(\mathrm{HCl}\): p-methylazoxybenzene → \(\mathrm{C}_{6}\mathrm{H}_{4}\)-\(\mathrm{N}_{2}\)-\(\mathrm{C}_{6}\mathrm{H}_{4}\)-\(\mathrm{OH}\) + \(\mathrm{CH}_{3}\mathrm{Cl}\). (e) Reaction with bromine water: Aniline → \(\mathrm{C}_{6}\mathrm{H}_{5}\)-\(\mathrm{N}\mathrm{Br}_{2}\) (white precipitate).

Step by step solution

01

Draw the structural formulas

The structural formulas are as follows: - m-nitrotoluene: \(\mathrm{C}_{6}\mathrm{H}_{4}\mathrm{NO}_{2}\)-\(\mathrm{CH}_{3}\) - phenylnitromethane: \(\mathrm{C}_{6}\mathrm{H}_{5}\)-\(\mathrm{CH}_{2}\mathrm{NO}_{2}\)
02

Find a suitable chemical test

A suitable chemical test that can distinguish between m-nitrotoluene and phenylnitromethane is a hydrolysis reaction, which will yield different products for each compound. The hydrolysis can be carried out in alkaline conditions using a solution of sodium hydroxide (\(\mathrm{NaOH}\)).
03

Write the chemical equations

The chemical equations for the chosen test are: m-nitrotoluene + \(\mathrm{NaOH}\) → hydrolysis → m-aminotoluene + \(\mathrm{NaNO}_{2}\); Phenylnitromethane + \(\mathrm{NaOH}\) → hydrolysis → benzylamine + \(\mathrm{HNO}_{2}\). (b) p-nitrotoluene and benzamide
04

Draw the structural formulas

The structural formulas are as follows: - p-nitrotoluene: \(\mathrm{C}_{6}\mathrm{H}_{4}\mathrm{NO}_{2}\)-\(\mathrm{CH}_{3}\) - benzamide: \(\mathrm{C}_{6}\mathrm{H}_{5}\)-\(\mathrm{CONH}_{2}\)
05

Find a suitable chemical test

To distinguish p-nitrotoluene and benzamide, we can use the reaction of ammonia with the compound. Benzamide will react with ammonia to form a crystalline product while p-nitrotoluene will not react.
06

Write the chemical equations

The chemical equation for the chosen test is: benzamide + ammonia → \(\mathrm{C}_{6}\mathrm{H}_{5}\)-\(\mathrm{CONH}_{4}\) (crystalline product) (c) hydrazobenzene and benzidine
07

Draw the structural formulas

The structural formulas are as follows: - hydrazobenzene: \(\mathrm{C}_{6}\mathrm{H}_{5}\)-\(\mathrm{N}_{2}\)-\(\mathrm{C}_{6}\mathrm{H}_{5}\) - benzidine: \(\mathrm{C}_{6}\mathrm{H}_{4}\)-\(\mathrm{NH}_{2}\)-\(\mathrm{C}_{6}\mathrm{H}_{4}\)-\(\mathrm{NH}_{2}\)
08

Find a suitable chemical test

For hydrazobenzene and benzidine, we can use oxidation reaction. Hydrazobenzene on oxidation will form azobenzene (\(\mathrm{C}_{6}\mathrm{H}_{5}\)-\(\mathrm{N}_{2}\)-\(\mathrm{C}_{6}\mathrm{H}_{5}\)) and benzidine will not participate in oxidation.
09

Write the chemical equations

The chemical equation for the chosen test is: hydrazobenzene + oxidizing agent → azobenzene (d) p-methoxyazobenzene and p-methylazoxybenzene
10

Draw the structural formulas

The structural formulas are as follows: - p-methoxyazobenzene: \(\mathrm{C}_{6}\mathrm{H}_{4}\)-\(\mathrm{N}_{2}\)-\(\mathrm{C}_{6}\mathrm{H}_{4}\)-\(\mathrm{OCH}_{3}\) - p-methylazoxybenzene: \(\mathrm{C}_{6}\mathrm{H}_{4}\)-\(\mathrm{N}_{2}\)-\(\mathrm{C}_{6}\mathrm{H}_{4}\)-\(\mathrm{O}\)-\(\mathrm{CH}_{3}\)
11

Find a suitable chemical test

We can use acid-catalyzed hydrolysis to distinguish between p-methoxyazobenzene and p-methylazoxybenzene. p-methylazoxybenzene will react with dilute aqueous hydrochloric acid (\(\mathrm{HCl}\)) while p-methoxyazobenzene will not.
12

Write the chemical equations

The chemical equation for the chosen test is: p-methylazoxybenzene + \(\mathrm{HCl}\) → \(\mathrm{C}_{6}\mathrm{H}_{4}\)-\(\mathrm{N}_{2}\)-\(\mathrm{C}_{6}\mathrm{H}_{4}\)-\(\mathrm{OH}\) + \(\mathrm{CH}_{3}\mathrm{Cl}\) (e) aniline and cyclohexylamine
13

Draw the structural formulas

The structural formulas are as follows: - aniline: \(\mathrm{C}_{6}\mathrm{H}_{5}\)-\(\mathrm{NH}_{2}\) - cyclohexylamine: \(\mathrm{C}_{6}\mathrm{H}_{11}\)-\(\mathrm{NH}_{2}\)
14

Find a suitable chemical test

To distinguish aniline and cyclohexylamine, we can use bromine water. Aniline will react with bromine water, producing a white precipitate, while cyclohexylamine will not.
15

Write the chemical equations

The chemical equation for the chosen test is: aniline + Br₂(aq) → \(\mathrm{C}_{6}\mathrm{H}_{5}\)-\(\mathrm{N}\mathrm{Br}_{2}\) (white precipitate)

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Most popular questions from this chapter

Suggest the syntheses of (a) \(\beta\) -naphthol from naphthalene (b) Orange II from \(\beta\) -naphthol and sulfanilic acid.

Devise a synthesis of "Diamine Green B" based on nitrobenzene, aniline, phenol, and H-acid.

During the heat of an important Organic Chemistry examination, a student proposed the following route for the synthesis of p-bromocumene from p-aminocumene. The professor, upon seeing the student's synthesis, laughed and gave the chagrined student half credit, promising full credit if the student could carry out the experiment in good yield in the lab. Try as he might, the student continued to obtain a mixture of products. What went wrong, and what is the nature of the mixture?

(a) Besides destabilizing the anilinium ion, how else might a nitro group affect basicity? (b) Why does the nitro group exert a larger base-weakening effect from the para position than from the nearer meta position?

Diazotization of \(2,4-\) dinitroaniline in aqueous solution is accompanied by some conversion to phenols in which a nitro group is replaced by a hydroxy group. Give a reasonable mechanism for this reaction.
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