B. V. Tronov and N. Kh. Sibgatullin.

On the Preparation of Esters by the Action of Acetic Anhydride on Alcohols

To determine the strength of the bond between various hydrocarbon radicals and oxygen in esters, we prepared a series of esters of acetic acid. In the literature, rather inconvenient or expensive methods are often given for obtaining these compounds, for example through the silver salt, organomagnesium compounds, etc.; moreover, in many cases even the yield of the product is not indicated. We used a simpler reaction—the interaction of alcohols with acetic anhydride—long known, but little studied from the preparative standpoint.

The experiments were always carried out with an excess of acetic anhydride (4–8 times), which considerably improves the yield, if calculated on the alcohol. After the addition of anhydrous sodium acetate and 1–2 drops of concentrated sulfuric acid (cooling is necessary here), the mixture was left for from 70 to 720 hours at ordinary temperature (18–20°); then the ester formed was distilled off. After washing with water and drying over calcium chloride, it was subjected to fractional distillation, the portion boiling within a range of 1–3° being taken.

In the first distillation there were usually observed constantly boiling mixtures, which sometimes boiled above, sometimes below the ester.

For the experiments we used pure Kahlbaum acetic anhydride. The alcohols, also from Kahlbaum, were previously distilled (within 1°). The sodium acetate was taken freshly fused and carefully powdered.

We obtained the following esters:

\[ \mathrm{CH_3 \cdot COO \cdot CH_2 \cdot CH_2 \cdot CH_3} \]

\[ \mathrm{CH_3 \cdot COO \cdot CH(CH_3)_2} \]

\[ \mathrm{CH_3 \cdot COO \cdot CH_2 \cdot CH_2{=}CH_2} \]

\[ \mathrm{CH_3 \cdot COO \cdot CH_2 \cdot CH_2 \cdot CH_2 \cdot CH_3} \]

\[ \mathrm{CH_3 \cdot COO \cdot CH_2 \cdot CH(CH_3)_2} \]

\[ \mathrm{CH_3 \cdot COO \cdot CH(CH_3) \cdot CH_2 \cdot CH_3} \]

\[ \mathrm{CH_3 \cdot COO \cdot C(CH_3)_3} \]

\[ \mathrm{CH_3 \cdot COO \cdot CH_2 \cdot CH_2 \cdot CH_2 \cdot CH_2 \cdot CH_2 \cdot CH_3} \]

\[ \begin{array}{c} \mathrm{CH_3 \cdot COO \cdot CH - CH_2 - CH_2} \\ \phantom{\mathrm{CH_3 \cdot COO \cdot}}\ | \qquad\qquad | \\ \phantom{\mathrm{CH_3 \cdot COO \cdot}}\mathrm{CH_2 - CH_2 - CH_2} \end{array} \]

\[ \mathrm{CH_3 \cdot COO \cdot CH_2 \cdot CH_2 \cdot C_6H_5} \]

Acetic-propyl ester. According to the literature, it was prepared from potassium acetate, propyl alcohol, and sulfuric acid by heating in a sealed tube¹, from propyl iodide with

with silver acetate at \(100^\circ\)¹); or by the catalytic action of \(ZrO_2\) on a mixture of acetic acid and propyl alcohol at \(240^\circ\)²). Yields are not given.

We took 40 g of propyl alcohol, 160 g of acetic anhydride, and 40 g of sodium acetate; the mixture stood for 72 hours. On distillation, the greater part passed over at \(150^\circ\). Of pure ester (b.p. \(99^\circ\)—\(102^\circ\)) 51 g was obtained, i.e. 75% of the theoretical amount.

Acetic acid isopropyl ester. The methods of preparation indicated in the literature are: isopropyl iodide and silver acetate³); isopropyl alcohol, potassium acetate, and sulfuric acid in a tube at \(130—140^\circ\)³); or, finally, acetic acid and isopropyl alcohol with \(ZrO_2\) catalyst at \(240^\circ\)²). Yields are not indicated.

We took 60 g of alcohol, 240 g of anhydride, and 60 g of sodium acetate. Duration of the experiment: 115 hours. The greater part of the liquid distilled over at \(105—107^\circ\). Yield of ester, b.p. \(89—92^\circ\), 79 g, i.e. 78% of theory.

Acetic acid allyl ester. In the literature a method is given for preparation from allyl iodide with silver acetate⁴); there are also indications of the formation of this ester on reduction (N-methylphenylhydroxylamine) of allyl ester with zinc in acetic acid⁵). Yields are not given.

In our experiments, for 60 g of allyl alcohol, 208 g of acetic anhydride and 70 g of sodium acetate were taken. The mixture stood for 384 hours. The greater part distilled over at \(104—105^\circ\). Ester was obtained, with b.p. \(102—103^\circ\), 48 g, i.e. 46%.

Acetic acid n-butyl ester. It was obtained by the reaction of butyl iodide or bromide and silver acetate in acetic acid medium⁶). Yield with the iodide, 94%; with the bromide, 88%.

In our work, a mixture of 45 g of alcohol, 180 g of anhydride, and 45 g of sodium acetate stood for 72 hours. On distillation, the greater part boiled at \(118—120^\circ\). Of pure ester (b.p. \(123—124^\circ\)) 59 g, corresponding to 85% of theory, was obtained.

Acetic acid isobutyl ester. According to the literature, it was isolated after the reaction of ethylmagnesium bromide, isobutyl alcohol, and acetic anhydride in ethereal solution⁷). The yield was theoretical.

We took 40 g of alcohol, 200 g of anhydride, and 40 g of sodium acetate. The mixture stood for 216 hours. The greater part distilled over at \(126—128^\circ\). Yield of ester, with boiling point \(114—115^\circ\), 64 g, i.e. 97%.

Acetic acid secondary-butyl ester. It was prepared by the interaction of the corresponding iodide with silver acetate⁸), or from secondary butyl alcohol with acetyl chloride on heating⁹).

In our work, a mixture of 30 g of alcohol with 160 g of anhydride and 30 g of sodium acetate, after standing for 652 hours, gave 38 g, i.e. 81%, of ester, b.p. \(112—114^\circ\). During the first distillation a halt was observed at \(123—125^\circ\).

Acetic acid tertiary-butyl ester. It was prepared by the reaction of isobutylene with acetic acid in the presence of zinc chloride—

¹) A. Rossi. Lieb. Ann. 159, 81; E. Linnemann. Lieb. Ann. 161, 31.
²) A. Maiche. Chem. Zbl. 1921 I, 488.
³) C. Friedel. Lieb. Ann. 124, 327.
⁴) N. Zinin. Lieb. Ann. 96, 361.
⁵) J. Meisenheimes. Ber. 52, 1675, Chem Zbl. 1919. III, 816.
⁶) A. Lieden, A. Rossi. Lieb. Ann. 158, 170.
⁷) J. Houben. Ber. 39, 1738.
⁸) V. Luyines. Ann. de Chimie et de Phys. [4] 2, 422.
⁹) Norris, Green. Amer. Chem. Journal. 26, 310.

…or by the action of acetic anhydride on the reaction product of tertiary butyl alcohol with magnesium bromomethyl\(^2\). There are no yields.

There are also indications for obtaining this ester through tertiary butyl iodide with silver acetate\(^3\). After rather unsuccessful attempts to prepare the substance by the first and third of the indicated methods, we mixed 60 g of trimethylcarbinol with 300 g of acetic anhydride and 43 g of sodium acetate, and, after standing for 640 hours at ordinary temperature, heated it for another 26 hours on a water bath. No constant-boiling mixture was obtained on distillation. Of the ester, b.p. 97–98°, 40 g were obtained, i.e. 42%.

Acetic hexyl ester. It was prepared from hexyl iodide and potassium acetate in alcoholic solution\(^4\). The yield is not indicated.

We took 25 g of normal hexyl alcohol, 50 g of acetic anhydride, and 25 g of sodium acetate. Duration of the experiment: 126 hours. A constant-boiling mixture with b.p. 145° was observed. Yield of ester (b.p. 167–179°): 24 g, i.e. 69%.

Acetic cyclohexyl ester. In the literature methods are indicated for obtaining it from cyclohexene with acetic acid\(^5\), and by heating cyclohexanol for two hours with acetic anhydride\(^6\). Yields are not given.

We set up the reaction of cyclohexanol (60 g) with acetic anhydride, 150 g, in the presence of sodium acetate, 60 g, at ordinary temperature for 720 hours. On distillation, the thermometer was observed to stop at 140–142°. Ester obtained: 55 g, i.e. 65%.

Acetic β-phenylethyl ester. It was prepared by heating the corresponding alcohol with acetic anhydride\(^7\) (but the yield is not indicated), and also by prolonged boiling of phenylphenetol with acetic acid and 70% sulfuric acid, with a yield of 65% of theory\(^8\).

We took 25 g of β-phenylethyl alcohol, 40 g of acetic anhydride, and 25 g of sodium acetate. The mixture stood for 130 hours. During distillation the temperature rose continuously. Yield of ester with b.p. 230°: 25 g, i.e. 75%.

In general it may be said that the reaction with acetic anhydride, in the case of saturated primary and secondary alcohols, leads to very good yields of esters. It is interesting that the greatest yield was given by isobutyl alcohol, with a branched chain; it also reacted more vigorously than all the other alcohols we took when added to the anhydride (so that at first cooling was necessary). Alcohols with large radicals—hexyl and cyclohexyl—gave somewhat poorer yields of esters. β-Phenylethyl alcohol, the only one with a benzene ring, reacted again somewhat better. A poor yield was given by the unsaturated allyl alcohol, and an even worse one by tertiary butyl alcohol. However, for the latter this method is nevertheless apparently the most convenient method of preparation. By the action of acetic anhydride on tertiary amyl alcohol, no ester could be obtained at all, despite the mixture standing for 720 hours.

1) I. Kondakov. Zh. f. kh. o. 25, 451.
2) L. Henri. Chem. Zbl. 1907. II, 584.
3) A. Butlerov. Lieb. Ann. 144, 7.
4) Franchimont, Zincke. Lieb. Ann. 163, 197.
5) L. Brunet. Ann. de Chimie et de Phys. [8] 6, 216.
6) A. Baeyer. Lieb. Ann. 278, 99.
7) Radziszewski. Ber. 9, 373.
8) A. Wohl and E. Berthold. Ber. 43, 2183; Chem. Zbl. 1910. II, 642.

1. J. Pierre, E. Puchot. Lieb. Ann. 153, 262. ↩