91Ó°ÊÓ

Explain the observation that attempted Fischer esterification of 2,4,6-trimethyl benzoic acid with methanol and HCL is unsuccessful. No ester is obtained, and the acid is recovered unchanged. What alternative method of esterification might be successful?

Treatment of 5- aminopentanoic acid DCC(dicyclohexylcarbodiimide) yields a lactam. Show the structure of the product and the mechanism of the reaction.

Outline methods for the preparation of acetophone(Phenyl methyl ketone) starting from the following:

d) Benzonitrile e) Styrene

When ethyl benzoate is heated in methanol containing a small amount of HCL, Methyl benzoate is formed. Propose a mechanism for the reaction.

The step-growth polymer nylon 6 is prepared from caprolactam. The reaction involves the initial reaction of caprolactam with water to give an intermediate open-chain amino acid, followed by heating to form the polymer. Propose a mechanism for both steps, and show the structures of nylon 6.

21-68 When a carboxylic acid is dissolved in isotopically labeled water, thelabel rapidly becomes incorporated into both oxygen atoms of the carboxylic acid. Explain.
$\text{R}−\stackrel{\text{O}}{\stackrel{âˆ\yen }{\text{C}}}−\text{OH}\stackrel{{\text{H}}_{\text{2}}\text{O}}{→}\text{R}−\stackrel{\text{O}}{\stackrel{âˆ\yen }{\text{C}}}−\text{OH}$

21-70 Treatment of a carboxylic acid with trifluoroacetic anhydride leads to anunsymmetrical anhydride that rapidly reacts with alcohol to give an ester.
$\mathbf{\text{R}}\mathbf{−}\stackrel{\mathbf{\text{O}}}{\stackrel{\mathbf{âˆ\yen }}{\mathbf{\text{C}}}}\mathbf{−}\mathbf{\text{OH}}\stackrel{{\mathbf{\left(}{\mathbf{\text{CF}}}_{\mathbf{\text{3}}}\mathbf{\text{CO}}\mathbf{\right)}}_{\mathbf{\text{2}}}\mathbf{\text{O}}}{\mathbf{→}}\mathbf{\text{R}}\mathbf{−}\stackrel{\mathbf{\text{O}}}{\stackrel{\mathbf{âˆ\yen }}{\mathbf{\text{C}}}}\mathbf{−}\mathbf{\text{O}}\mathbf{−}\stackrel{\mathbf{\text{O}}}{\stackrel{\mathbf{âˆ\yen }}{\mathbf{\text{C}}}}\mathbf{−}{\mathbf{\text{CF}}}_{\mathbf{\text{3}}}\stackrel{{\mathbf{\text{R}}}^{\mathbf{\text{'}}}\mathbf{\text{OH}}}{\mathbf{→}}\mathbf{\text{R}}\mathbf{−}\stackrel{\mathbf{\text{O}}}{\stackrel{\mathbf{âˆ\yen }}{\mathbf{\text{C}}}}\mathbf{−}{\mathbf{\text{OR}}}^{\mathbf{\text{'}}}\mathbf{+}{\mathbf{\text{CF}}}_{\mathbf{\text{3}}}{\mathbf{\text{CO}}}_{\mathbf{\text{2}}}\mathbf{\text{H}}$
(a) Propose a mechanism for the formation of the unsymmetrical anhydride.
(b) Why is the unsymmetrical anhydride unusually reactive?
(c) Why does the unsymmetrical anhydride react as indicated ratherthan giving a trifluoroacetate ester plus carboxylic acid?

21-71 Butacetin is an analgesic (pain-killing) agent that is synthesized commercially from p-fluoronitrobenzene. Propose a synthesis.