# 18.E: Carboxylic Acids and Their Derivatives (Exercises)


Exercise 18-1 Explain why the proton line position of the acidic hydrogen of a carboxylic acid, dissolved in a nonpolar solvent such as carbon tetrachloride, changes much less with concentration than does that of the $$\ce{OH}$$ proton of an alcohol under the same conditions (Section 9-10E).

Exercise 18-2 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.

Exercise 18-3 The $$K_a$$ for the first ionization of carbonic acid, $$\ce{O=C(OH)_2} + \ce{H_2O} \rightleftharpoons \ce{O=C(OH)O}^\ominus + \ce{H_3O}^\oplus$$, is about 1000 times smaller than $$K_a$$ for ethanoic acid. Show how this fact can be rationalized by considering the expected relative stabilization energies of carbonic acid and the hydrogen carbonate ion compared to those of ethanoic acid and ethanoate anion.

Exercise 18-4 Which acid in each of the following pairs would you expect to be the stronger? Give your reasoning.

a. $$\ce{(CH_3)_3} \overset{\oplus}{\ce{N}} \ce{CH_2CO_2H}$$ or $$\ce{(CH_3)_2NCH_2CO_2H}$$

b. $$\ce{(CH_3)_3} \overset{\oplus}{\ce{N}} \ce{CH_2CO_2H}$$ or $$\ce{(CH_3)_2} \overset{\oplus}{\ce{N}} \overset{\ominus}{\ce{(O)}} \ce{CH_2CO_2H}$$

c. $$\ce{(CH_3)_3CCO_2H}$$ or $$\ce{CH_3CO_2H}$$

d. $$\ce{CH_3OCH_2CO_2H}$$ or $$\ce{CH_3SCH_2CO_2H}$$

e. $$\ce{CH_2=CH-CH_2CO_2H}$$ or $$\ce{HC \equiv C-CH_2CO_2H}$$

Exercise 18-5* Simple electrostatic considerations suggest that the acidities of carboxylic acids of the type $$\ce{(CH_3)_3} \overset{\oplus}{\ce{N}} \ce{(CH_2)}_n \ce{CO_2H}$$ should decrease much more slowly with increasing $$n$$ than the acidities of the type . Explain why this should be so.

Exercise 18-6* The chloro acid $$3$$ is a stronger acid than the acid without the chlorine, whereas the chloro acid $$4$$ is a weaker acid than the corresponding acid with no chlorine. Explain why this can be expected from simple electrostatic theory. (Models may be helpful.)

Exercise 18-7* Fluoroethanoic acid is only about twice as acidic as chloroethanoic acid, even though fluorine is much more electronegative than chlorine (Section 10-4B). The lengths of aliphatic $$\ce{C-F}$$ bonds are about $$1.38 \: \text{Å}$$, whereas those of $$\ce{C-Cl}$$ bonds are $$1.78 \: \text{Å}$$. How could this difference in bond lengths tend to compensate for the differences in electronegativity between chlorine and fluorine and make the acids similar in strength?

Exercise 18-8 Explain why the equilibrium of Equation 18-5 is less favorable than that of Equation 18-4.

Exercise 18-9 Use bond energies and the stabilization energy of ethanoic acid ($$18 \: \text{kcal mol}^{-1}$$, Section 18-2A) to calculate $$\Delta H^0$$ for the addition of water to ethanoic acid to give 1,1,1-trihydroxyethane. Compare the value you obtain with a calculated $$\Delta H^0$$ for the hydration of ethanal in the vapor phase. Would you expect the rate, the equilibrium constant, or both, for the hydration of ethanoic acid in water solution to be increased in the presence of a strong acid such as sulfuric acid? Explain.

Exercise 18-10 Predict the outcome of an attempted esterification of ethanoic acid with tert-butyl alcohol in the presence of dry $$\ce{HCl}$$.

Exercise 18-11 What would you expect to happen to the $$\ce{^{18}O}$$ label in a mixture of ethanoic acid, hydrochloric acid, and $$\ce{H_2^{18}O}$$? Explain.

Exercise 18-12 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. (Among other factors, consider the geometries of the various species involved.)

Exercise 18-13 Predict the product of decarboxylation of 2-methyl-3-butenoic acid.

Exercise 18-14 Explain why decarboxylation of 2,2-dimethyl-3-oxobutanoic acid, $$\ce{CH_3COC(CH_3)_2CO_2H}$$, in the presence of bromine gives 3-methyl-3-bromo-2-butanone, $$\ce{CH_3COC(CH_3)_2Br}$$.

Exercise 18-15 What information would you need to calculate $$\Delta H^0$$ for the reaction $$\ce{CH_3CO_2} \cdot \rightarrow \ce{CO_2} + \cdot \ce{CH_3}$$?

Exercise 18-16 Why does Kolbe electrolysis not give $$\ce{RH}$$ by the reaction $$\ce{RCO_2} \cdot \overset{\ce{-CO_2}}{\longrightarrow} \ce{R} \cdot \overset{\ce{H_2O}}{\longrightarrow} \ce{RH}$$?

Exercise 18-17* 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 $$\ce{ROH}$$ and $$\ce{RCO_2R}$$. Explain how this can occur.

Exercise 18-18* Write a sequence of mechanistic steps that embody the suggestions given for conversion of $$\ce{HO_2C(CH_2)_6CO_2H}$$ to $$\ce{CH_2=CH(CH_2)_4CO_2H}$$ with $$\ce{Pb(O_2CCH_3)_4}$$ and $$\ce{Cu(OCH_3)_2}$$ as a catalyst. Complete the steps necessary to give all of the products and regenerate the catalyst. The role of $$\ce{Cu}$$(II) in the oxidation of radicals is discussed briefly in Section 23-10B.

Exercise 18-19 Write the steps in the phosphorus-catalyzed bromination of propanoic acid and explain why propanoyl bromide is expected to undergo acid-catalyzed bromination more readily than propanoic acid. (Review Section 17-1.)

Exercise 18-20* Optically active sodium 2-bromopropanoate is converted to sodium 2-hydroxypropanoate in water solution. The product has the same stereochemical configuration at $$\ce{C_2}$$ as the starting material and the reaction rate is independent of added $$\ce{OH}^\ominus$$ at moderate concentrations. At higher concentrations of $$\ce{OH}^\ominus$$, the rate becomes proportional to the $$\ce{OH}^\ominus$$ concentration and the 2-hydroxypropanoate formed has the opposite configuration to the starting material. Write appropriate mechanisms to explain these facts. Give your reasoning. (It may be helpful to review Sections 8-5 and 15-11.)

Exercise 18-21 The following substances have boiling points as indicated:

ethyl ethanoate $$\left( 77^\text{o} \right)$$

ethanoic anhydride $$\left( 140^\text{o} \right)$$

ethanoic acid $$\left( 118^\text{o} \right)$$

ethanamide $$\left( 221^\text{o} \right)$$

Account for these differences on the basis of molecular weight and hydrogen bonding.

Exercise 18-22 Why is a carboxylate anion more resistant to attack by nucleophilic agents, such as $$\ce{CH_3OH}$$ or $$\ce{CH_3O}^\ominus$$, than is the corresponding ester?

Exercise 18-23

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?

Exercise 18-24 Ester interchange also can produce (but more slowly) with an acidic instead of a basic catalyst. Write a mechanism for this reaction consistent with acid-catalyzed ester formation (Section 18-3A).

Exercise 18-25 By analogy with the reaction mechanisms already discussed, propose a mechanism for each of the following reactions:

a. $$\ce{C_6H_5CO_2CH_3} + \ce{C_2H_5OH} \overset{\ce{H}^\oplus}{\longrightarrow} \ce{C_6H-5CO_2C_2H_5} + \ce{CH_3OH}$$
b. $$\ce{CH_3COCl} + \ce{CH_3CH_2OH} \rightarrow \ce{CH_3CO_2CH_2CH_3} + \ce{HCl}$$
c. $$\ce{CH_3CO_2O} + \ce{CH_3OH} \overset{\ce{H}^\oplus}{\longrightarrow} \ce{CH_3CO_2CH_3} + \ce{CH_3CO_2H}$$
d. $$\ce{CH_3CONH_2} + \ce{H_3O^+} \overset{\ce{H_2O}}{\longrightarrow} \ce{CH_3CO_2H} + \ce{NH_4^+}$$
e. $$\ce{CH_3CONH_2} + \ce{OH^-} \rightarrow \ce{CH_3CO_2^-} + \ce{NH_3}$$
f. $$\ce{CH_3COCl} + 2 \ce{NH_3} \rightarrow \ce{CH_3CONH_2} + \ce{NH_4Cl}$$
g. $$\ce{CH_3CO_2CH_3} + \ce{CH_3NH_2} \rightarrow \ce{CH_3CONHCH_3} + \ce{CH_3OH}$$

Exercise 18-26 What can you conclude about the mechanism of acid-catalyzed hydrolysis of oxacyclobutan-2-one ($$\beta$$-propiolactone) from the following equation:

Exercise 18-27 Write a plausible mechanism supported by analogy for the following reaction:

Exercise 18-28 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):

Exercise 18-29 Grignard reagents add to $$\ce{N}$$,$$\ce{N}$$-dialkylalkanamides, $$\ce{RCONR'_2}$$, 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 $$\ce{RR'CZ(OMgX)}$$ intermediate, the amides may be expected to be less likely than esters or acyl chlorides to give tertiary alcohols. How could you use an $$\ce{N}$$,$$\ce{N}$$-dialkylalkanamide to prepare an aldehyde with the aid of a Grignard reagent?

Exercise 18-30 Explain why 2,4-pentanedione can be expected to contain much more enol at equilibrium than does ethyl 3-oxobutanoate. How much enol would you expect to find in diethyl propanedioate? In 3-oxobutanal? Explain.

Exercise 18-31 Arguing from the factors that appear to regulate the ratio of $$\ce{C}$$- to $$\ce{O}$$-alkylation of enolate anions (Section 17-4), show how you could decide whether the reaction of the sodium enolate salt of ethyl 3-oxobutanoate with a strong acid would give, as the initial product, mostly the enol form, mostly the keto form, or the equilibrium mixture.

Exercise 18-32 When a small amount of sodium ethoxide is added to ethyl 3-oxobutanoate, the proton NMR peaks marked a, b, and c in Figure 18-6 disappear. Explain why this should be so. (You may wish to review Section 9-10E.)

Exercise 18-33 Possible byproducts of the Claisen condensation of ethyl ethanoate are

Explain how these products may be formed and why they are not formed in significant amounts.

Exercise 18-34 Ethanol has a $$K_a$$ of $$10^{-18}$$ and ethyl 3-oxobutanoate has $$K_a = 10^{-11}$$. Calculate $$\Delta G^0$$ for the reaction of sodium ethoxide with the ester as per Equation 18-13. (See Section 4-4A.)

Exercise 18-35 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

Exercise 18-36 Show how the following substances may be synthesized by Claisen-type condensations from the indicated starting materials. Specify the reagents and reaction conditions as completely as possible.

a. ethyl 2-methyl-3-oxopentanoate from ethyl propanoate
b. ethyl 2,4-dioxopentanoate from 2-propanone
c. diethyl 2-phenylpropanedioate from ethyl phenylethanoate
d. 2,4-pentanedione from 2-propanone
e. 2,2,6,6-tetramethyl-3,5-heptanedione from 3,3-dimethyl-2-butanone
f. ethyl 2,2-dimethyl-3-phenyl-3-oxopropanoate from 2-methylpropanoate

Exercise 18-37 What advantages and disadvantages may sodium hydride $$\left( \ce{NaH} \right)$$ have as the base used in the Claisen condensation?

Exercise 18-38 Why does the following reaction fail to give ethyl propanoate?

Exercise 18-39 Show a synthesis of 3-ethyl-2-pentanone from ethyl 3-oxobutanoate. What advantage would this route have over alkylation of 2-pentanone with sodium amide and ethyl iodide? (Section 17-4A.)

Exercise 18-40 How could you prepare diethyl methylpropanedioate that is free of diethyl propanedioate and diethyl dimethylpropanedioate? (Review Section 18-8B to find an alternative synthesis not involving alkylation.)

Exercise 18-41 Show how one could prepare cyclobutanecarboxylic acid from diethyl propanedioate and a suitable dihalide.

Exercise 18-42 Write a mechanism based on analogy with other reactions in this chapter that will account for the strong alkali-induced cleavage of ethyl 2-methyl-3-oxobutanoate in accord with Equation 18-21.

Exercise 18-43*

a. In the formation of $$\ce{LiCH_2CO_2C_2H_5}$$ (Equation 18-22), would it be better to add the ester to the solution of the base in oxacyclopentane, or the reverse? Give your reasoning.

b. Suppose a solution formed in accord with Equation 18-23 were allowed to stand (before adding acid and water) until equilibrium is established between the various possible Claisen, mixed-Claisen, and aldol-addition products described in Sections 18-8B and 17-3C. What products would you then expect to be formed on hydrolysis with dilute acid and water? Which would be expected to predominate? Give your reasoning.

c. Show how you could synthesize methyl 2-(1-cyclohexenyl)ethanoate from cyclohexanone by the reactions described in Section 18-8E.

Exercise 18-44* The formation of an acyl coenzyme A, $$\ce{RCO-S} \textbf{CoA}$$, from coenzyme A and a carboxylic acid is coupled to a cleavage reaction of ATP to give AMP:

$\ce{RCO_2H} + \text{ATP} + \textbf{CoA} \ce{-SH} \rightleftharpoons \ce{RCO-S} \textbf{CoA} + \text{AMP} + \ce{PP}$

Write the possible steps involved in this esterification reaction. (Review Section 15-5F.)

Exercise 18-45 Write a mechanism for the base-catalyzed equilibration of $$\alpha$$,$$\beta$$- and $$\beta$$,$$\gamma$$-unsaturated esters. Which isomer would you expect to predominate? Why does this type of isomerization proceed less readily for the carboxylate anions than for the esters? Would $$\gamma$$,$$\delta$$-unsaturated esters rearrange readily to the $$\alpha$$,$$\beta$$-unsaturated esters? Why, or why not?

Exercise 18-46 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?

Exercise 18-47 Explain why the Michael addition of diethyl propanedioate to 3-phenylpropenoic acid is unlikely to be successful.

Exercise 18-48* The Michael-addition product that results from ethyl 3-phenylpropenoate and diethyl propanedioate, in principle, also can be formed by sodium ethoxide-catalyzed addition of ethyl ethanoate to ethyl (2-carbethoxy)-3-phenylpropenoate. Work out the course of this reaction along the lines of Equations 18-25 and 18-26 and explain why it is less likely to be successful than the addition of diethyl propanedioate to ethyl 3-phenylpropenoate. It will be helpful to compare the various possible acid-base equilibria involved in the two possible routes to the same Michael-addition product.

Exercise 18-49 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)
d. from and 3-butene-2-one

Exercise 18-50 Explain how steric hindrance would lead one to expect that the proton-transfer product in the addition of $$\ce{N}$$-(1-cyclohexenyl)azacyclopentane to methyl 2-methylpropenoate would have the structure shown in Equation 18-27, rather than the following:

Exercise 18-51 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.

Exercise 18-52 Write equations for a practical laboratory synthesis of the following substances from the indicated starting materials (several steps may be required). Give reagents and conditions:

a. butanoic acid from 1-propanol
b. 2,2-dimethylpropanoic acid from tert-butyl chloride
c. 2-methylpropanoic acid from 2-methylpropene
d. 2-bromo-3,3-dimethylbutanoic acid from tert-butyl chloride
e. cyclobutylmethanol-1-$$\ce{^{14}C}$$, $$\ce{(CH_2)_3CH^{14}CH_2OH}$$, from cyclobutanecarboxylic acid and $$\ce{Ba^{14}CO_3}$$
f. 4-pentenamide from 3-chloropropene
g. 2,2-dimethylpropyl 2,2-dimethylpropanoate from tert-butyl chloride

Exercise 18-53 Write reasonable mechanisms for each of the following reactions:

a. cis-$$\ce{CH_3CH=CHCO_2H} \underset{2. \: \ce{H}^\oplus}{\overset{1. \: ^\ominus \ce{OH}, \: 100^\text{o}}{\longrightarrow}}$$ trans-$$\ce{CH_3CH=CHCO_2H}$$

b.

c. $$\ce{CH_3CO_2CH_3} + \ce{CH_3CH_2CO_2H} \overset{\ce{H}^\oplus}{\rightleftharpoons} \ce{CH_3CH_2CO_2CH_3} + \ce{CH_3CO_2H}$$

The order of reactivity for $$\ce{CH_3CO_2R}$$ is $$\ce{R} = \ce{CH_3}- > \ce{CH_3CH_2}- \gg \ce{(CH_3)_2CH}-$$.

Exercise 18-54 4-Bromobicyclo[2.2.2]octane-1-carboxylic acid (A) is a considerably stronger acid than 5-bromopentanoic acid (B). Explain. (Hint: Consider the possible conformations and modes of transmission of the electrical effect of the $$\ce{C-Br}$$ dipole.)

Exercise 18-55 tert-Butyl ethanoate is converted to methyl ethanoate by sodium methoxide in methanol about one tenth as fast as ethyl ethanoate is converted to methyl ethanoate under the same conditions. With dilute $$\ce{HCl}$$ in methanol, tert-butyl ethanoate is rapidly converted to 2-methoxy-2-methylpropane and ethanoic acid, whereas ethyl ethanoate goes more slowly to ethanol and methyl ethanoate.

a. Write reasonable mechanisms for each of the reactions and show how the relative-rate data agree with your mechanisms.

b. How could one use $$\ce{^{18}O}$$ as a tracer to substantiate your proposed mechanisms?

Exercise 18-56 It has been reported that esters $$\left( \ce{RCO_2R'} \right)$$ in $$\ce{^{18}O}$$ water containing sodium hydroxide are converted to in competition with alkaline hydrolysis. The rates of both exchange and hydrolysis reactions are proportional to $$\ce{OH}^\ominus$$ concentration. Explain what these facts mean with regard to the mechanism of ester hydrolysis.

Exercise 18-57 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
f. the 1,2-ethanediol ketal of cyclopentanone, , from hexanedioic acid

Exercise 18-58 For each of the following pairs of compounds give a chemical test, preferably a test-tube reaction, that will distinguish between the two substances. Write an equation for each reaction.

a. $$\ce{HCO_2H}$$ and $$\ce{H_3CCO_2H}$$
b. $$\ce{CH_3CO_2C_2H_5}$$ and $$\ce{CH_3OCH_2CO_2H}$$
c. $$\ce{CH_2=CHCO_2H}$$ and $$\ce{CH_3CH_2CO_2H}$$
d. $$\ce{CH_3COBr}$$ and $$\ce{BrCH_2CO_2H}$$
e. $$\ce{BrCH_2CH_2CH_2CO_2CH_3}$$ and $$\ce{CH_3CH_2CHBrCO_2CH_3}$$
f. $$\ce{(CH_3CH_2CO)_2O}$$ and
g. and
h. $$\ce{HC \equiv CCO_2CH_3}$$ and $$\ce{CH_2=CHCO_2CH_3}$$
i. $$\ce{CH_3CO_2NH_4}$$ and $$\ce{CH_3CONH_2}$$
j. $$\ce{CH_2=CH-CH_2CH_2CO_2H}$$ and $$\ce{CH_3CH_2CH=CHCO_2H}$$
k. $$\ce{(CH_3CO)_2O}$$ and $$\ce{CH_3CO_2CH_2CH_3}$$

Exercise 18-59 Explain how you could distinguish between the pairs of compounds listed in Exercise 18-58 by spectroscopic means. Be specific about what would be observed.

Exercise 18-60 Suppose you were given four bottles, each containing a different isomer (2-, 3-, 4-, or 5-) of hydroxypentanoic acid. Explain in detail how you could distinguish the various isomers by chemical reactions.

Exercise 18-61 Compound A $$\left( \ce{C_4H_8O_3} \right)$$ was optically active, quite soluble in water (giving a solution acidic to litmus), and, on strong heating, yielded B $$\left( \ce{C_4H_6O_2} \right)$$, which was optically inactive, rather water-soluble (acidic to litmus), and reacted much more readily with $$\ce{KMnO_4}$$ than did A. When A was oxidized with dilute chromic acid solution, it was converted to a volatile liquid C $$\left( \ce{C_3H_6O} \right)$$, which did not react with $$\ce{KMnO_4}$$, and gave a yellow precipitate with $$\ce{I_2}$$ and $$\ce{NaOH}$$ solution.

Write appropriate structures for the lettered compounds and equations for all of the reactions mentioned. Is Compound A defined by the above description? Explain.

Exercise 18-62 Name each of the following substances by the IUPAC system:

a.
b. $$\ce{CH_3COCH[CH(CH_3)_2}CO_2C_2H_5}$$
c. $$\ce{CH_3CH_3COC(CH_3)_2CON(CH_3)_2}$$
d. $$\ce{HOCH=CHCO_2C_2H_5}$$
e. $$\ce{C_2H_5OCOCOCH_2CO_2C_2H_5}$$
f. $$\ce{C_2H_5O_2CCH_2CH(CO_2C_2H_5)COCO_2C_2H_5}$$
g.
h.
i. $$\ce{CH_3CH_2COCH(CH_3)CH_2CH_2CH(CH_3)_2}$$
j. $$\ce{CH_3CH_2CH_2CH(CH_2CH=CH_2)CO_2H}$$
k. $$\ce{CH_3COCH(CO_2C_2H_5)_2}$$
l. $$\ce{C_6H_5CH=CH-CH(OH)CH_2CO_2C_2H_5}$$

Exercise 18-63 Write equations for the synthesis of each of the substances in Exercise 18-62 a-l from compounds with fewer carbon atoms, using the type of reactions discussed in Sections 18-9 and 18-10. You may wish to review Sections 13-6 to 13-9 before beginning.

Exercise 18-64 Direct reduction of aldehydes with 2,3-dimethyl-2-butylborane proceeds rapidly and gives the corresponding alcohol. Nonetheless, reduction of carboxylic acids with the same borane (Section 18-3C) proceeds slowly and gives high yields of aldehydes. Explain why the reaction of $$\ce{RCO_2H}$$ with the 2,3-dimethyl-2-butylborane produces $$\ce{RCHO}$$ instead of $$\ce{RCH_2OH}$$.

## Contributors

John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."

18.E: Carboxylic Acids and Their Derivatives (Exercises) is shared under a not declared license and was authored, remixed, and/or curated by John D. Roberts and Marjorie C. Caserio.