Chapter 18

Make atomic-orbital models of ethanoic acid and ethanol and of the ethanoate anion and ethoxide anion. Show how these models can be used to explain the greater acidity of ethanoic acid relative to ethanol.

Which acid in each of the following pairs would you expect to be the stronger? Give your reasoning. a. \(\left(\mathrm{CH}_{3}\right)_{3} \stackrel{\oplus}{\mathrm{NCH}}_{2} \mathrm{CO}_{2} \mathrm{H}\) or \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NCH}_{2} \mathrm{CO}_{2} \mathrm{H}\) b. \(\left(\mathrm{CH}_{3}\right)_{3} \stackrel{\mathrm{N}}{\mathrm{N}} \mathrm{H}_{2} \mathrm{CO}_{2} \mathrm{H}\) or \(\left(\mathrm{CH}_{3}\right)_{2} \stackrel{\oplus}{\mathrm{N}}(\stackrel{\ominus}{\mathrm{O}}) \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}\) c. \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCO}_{2} \mathrm{H}\) or \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\) d. \(\mathrm{CH}_{3} \mathrm{OCH}_{2} \mathrm{CO}_{2} \mathrm{H}\) or \(\mathrm{CH}_{3} \mathrm{SCH}_{2} \mathrm{CO}_{2} \mathrm{H}\) e. \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}\) or \(\mathrm{HC} \equiv \mathrm{C}-\mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}\)

Predict the outcome of an attempted esterification of ethanoic acid with tert- butyl alcohol in the presence of dry HCl.

What would you expect to happen to the \({ }^{18} \mathrm{O}\) label in a mixture of ethanoic acid, hydrochloric acid, and \(\mathrm{H}_{2}^{18} \mathrm{O}\) ? Explain.

Benzoic acid is not esterified by the procedure that is useful for \(2,4,6\) -trimethylbenzoic acid because, when benzoic acid is dissolved in sulfuric acid, it gives the conjugate acid and no acyl cation. Explain why the acyl cation, 11 of \(2,4,6\) -trimethylbenzoic acid might be more stable, relative to the conjugate acid of benzoic acid.

Predict the product of decarboxylation of 2 -methyl-3-butenoic acid.

At higher voltages than normally used in the Kolbe electrolysis, salts of carboxylic acid in hydroxylic solvents produce (at the anode) alcohols and esters of the type \(\mathrm{ROH}\) and \(\mathrm{RCO}_{2} \mathrm{R}\). Explain how this can occur.

Optically active sodium 2-bromopropanoate is converted to sodium 2-hydroxypropanoate in water solution. The product has the same stereochemical configuration at \(\mathrm{C}_{2}\) as the starting material and the reaction rate is independent of added \(\mathrm{OH}^{\ominus}\) at moderate concentrations. At higher concentrations of \(\mathrm{OH}^{\ominus}\), the rate becomes proportional to the \(\mathrm{OH}^{\ominus}\) concentration and the 2-hydroxypropanoate formed has the opposite configuration to the starting material. Write appropriate mechanisms to explain these facts. Give your reasoning.

The following substances have boiling points as indicated: ethyl ethanoate \(\left(77^{\circ}\right)\) ethanoic anhydride \(\left(140^{\circ}\right)\) ethanoic acid \(\left(118^{\circ}\right)\) ethanamide \(\left(221^{\circ}\right)\) Account for these differences on the basis of molecular weight and hydrogen bonding.

Why is a carboxylate anion more resistant to attack by nucleophilic agents, such as \(\mathrm{CH}_{3} \mathrm{OH}\) or \(\mathrm{CH}_{3} \mathrm{O}^{\ominus}\), than is the corresponding ester?

a. Develop a mechanism for ester interchange between ethanol and methyl ethanoate catalyzed by alkoxide that is consistent with the mechanism of base- induced ester hydrolysis. b. Why doesn't it matter whether one uses methoxide or ethoxide as the catalyst? c. If one used \(D\) -2-butyl ethanoate as the starting ester and methanol as the exchanging alcohol, what would be the configuration fo the 2 -butanol formed with methoxide as a catalyst?

Explain why the base-induced hydrolysis of methyl 2,4,6-trimethylbenzoate is unusually slow. Write a mechanism for the hydrolysis of methyl \(2,4,6\) -trimethylbenzoate that occurs when the ester is dissolved in concentrated sulfuric acid and the solution poured into a mixture of ice and water (see Section 18-3A):

Grignard reagents add to \(\mathrm{N}, \mathrm{N}\) -dialkylalkanamides, \(\mathrm{RCONR}_{2}^{\prime}\), to give ketones after hydrolysis. With esters or acyl chlorides, a tertiary alcohol is the usual product. Explain why, on the basis of the stability of the \(\mathrm{RR}^{\prime} \mathrm{CZ}(\mathrm{OMgX})\) intermediate, the amides may be expected to be less likely than esters or acyl chlorides to give tertiary alcohols. How could you use an N,N-dialkylalkanamide to prepare an aldehyde with the aid of a Grignard reagent?

Explain why 2,4-pentanedione can be expected to contain much more enol at equilibrium than does ethyl 3oxobutanoate. How much enol would you expect to find in diethyl propanedioate? In 3-oxobutanal? Explain.

Write structures for all of the Claisen condensation products that reasonably may be expected to be formed from the following ester mixtures and sodium ethoxide: a. ethyl ethanoate and ethyl propanoate b. diethyl carbonate and 2 -propanone c. diethyl ethanedioate and ethyl 2,2-dimethylpropanoate

What advantages and disadvantages may sodium hydride \((\mathrm{NaH})\) have as the base used in the Claisen condensation?

Would you expect 3 -butenoic acid to form a lactone with a five- or a four- membered ring when heated with a catalytic amount of sulfuric acid?

Explain why the Michael addition of diethyl propanedioate to 3-phenylpropenoic acid is unlikely to be successful.

Show how the following substances can be prepared by syntheses based on Michael additions. In some cases, additional transformations may be required. a. 3-phenylpentanedioic acid from ethyl 3 -phenylpropenoate b. 3,5-diphenyl-5-oxopentanenitrile from 1,3-diphenylpropenone (benzalacetophenone) c. 4,4 -(dicarbethoxy)heptanedinitrile from propenenitrile (acrylonitrile)

The cis- and trans-butenedioic acids give the same anhydride on heating, but the trans acid must be heated to much higher temperatures than the cis acid to achieve anhydride formation. Explain. Write a reasonable mechanism for both reactions.

Write reasonable mechanisms for each of the following reactions: a. \(\mathbf{b}\). c. \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{CH}_{3}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H} \stackrel{\mathrm{H}^{\oplus}}{=} \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{CH}_{3}+\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\) The order of reactivity for \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{R}\) is \(\mathrm{R}=\mathrm{CH}_{3}->\mathrm{CH}_{3} \mathrm{CH}_{2}-\gg\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\).

Write equations for a practical laboratory synthesis of each of the following substances from the indicated starting materials (several steps may be required). Give reagents and conditions. a. 2 -chloroethyl bromoethanoate from ethanol and/or ethanoic acid b. 2 -methoxy-2-methylpropanamide from 2 -methylpropanoic acid c. 3,5,5-trimethyl-3-hexanol from 2,4,4-trimethyl-1-pentene (commercially available) d. 3,3-dimethylbutanal from 2,2-dimethylpropanoic acid e. \(2,3,3\) -trimethyl-2-butanol from 2,3-dimethyl-2-butene