L. N. D’yakonova-Shul’ts and A. S. Klokova.

From the Laboratory of Organic Chemistry of the Siberian Technological Institute.

Study of the Reaction Products of Esters of Mineral Acids with Tertiary Amines

The aim of the present work was to elucidate the mechanism of the interaction of esters of mineral acids with tertiary amines.

On this question one can point to only a very small number of works: F. Ullmann¹ obtained addition products of dimethyl sulfate with dimethyl-o-toluidine, quinoline, quinaldine, phenylacridine, and 2,3-diaminophenazine. R. Wolffenstein² prepared the addition product of dimethyl sulfate with the methyl ester of nicotinic acid:

\[ \begin{array}{c} \mathrm{CH}\\ \mathrm{HC}\quad \backslash\ \mathrm{C{-}COOCH_3}\\[4pt] \mathrm{HC}\quad \mathrm{CH}\\ \mathrm{N{-}OSO_2OCH_3}\\ \mathrm{CH_3} \end{array} \]

A. Angeli³, studying the reaction of pyridine with certain nitric-acid esters (nitrates of glycerol and cellulose), found that the nitrate decomposes into an aldehyde and nitric acid:

\[ \mathrm{R{-}CH_2ONO_2} \;\longrightarrow\; \mathrm{R{-}C(=O)H + HNO_2}, \]

while the amine only serves as a catalyst. On the other hand, according to the observation of Ya. I. Mikhailenko and N. A. Kudryasheva,⁴ nitric-acid esters can react with tertiary amines also normally, giving the corresponding ammonium salts:

\[ \mathrm{C_9H_7N + C_6H_5{-}CH_2ONO_2} \;\longrightarrow\; \begin{array}{c} \mathrm{C_9H_7N{-}ONO_2}\\ \vert\\ \mathrm{CH_2{-}C_6H_5} \end{array} \]

We took the following amines and esters:

The experiments were carried out in the following manner.

Into a flask connected by means of a stopper with a vertical tube, the ester was introduced, and then the tertiary amine was gradually added in a molar ratio of \(1:1^{1/2}\) or \(1:2\). In the case of strong self-heating, the synthesis was conducted with constant shaking and cooling in a water bath. On standing of the mixture in a desiccator, two layers are formed: the lower, oil-like one—the reaction product—and the upper one, the unreacted portion of the substances taken; the two layers are separated by means of a separatory funnel. The compounds formed were immediately tested for solubility, and, depending on this, a suitable washing liquid was chosen for removing traces of ester and amine that had not entered into reaction. In most experiments the products obtained were washed with absolute ethyl ether. Washing was carried out with vigorous shaking, and sometimes by grinding the obtained substance with the washing liquid. If this did not achieve its purpose, as was found already in the analysis, the substance was dissolved in alcohol or acetone and precipitated with absolute ether. Crystalline compounds were recrystallized for purification. After washing and recrystallization the products were dried in a desiccator for 10 to 20 hours and weighed. After the operations listed, analyses of the salts obtained were performed.

The analysis was carried out by two methods:

1) Salts obtained with esters of sulfuric acid:

\[ (\mathrm{CH}_3)_2\mathrm{SO}_4,\; (\mathrm{C}_2\mathrm{H}_5)_2\mathrm{SO}_4 \text{ and } \mathrm{C}_6\mathrm{H}_5\mathrm{SO}_2\mathrm{OC}_2\mathrm{H}_5 \]

were decomposed by the Carius method.

2) Salts obtained with esters of nitric and nitrous acids were analyzed in the form of chloroplatinates.

To obtain the latter,\(^{1}\) the prepared salts were precipitated with an alcoholic solution of chloroplatinic acid in the presence of 2–3 drops of conc. hydrochloric acid—a yellow crystalline precipitate fell out.

The precipitate was filtered off, washed 3 to 4 times with alcohol, and dried in a desiccator over \(\mathrm{H}_2\mathrm{SO}_4\).

\(^{1}\) On complex platinum compounds with amine derivatives one may cite: A. Edinger, journ. f. pr. Ch. (2) 41, 345. Anderson, Lieb. Ann. 96, 200.

The results of the experiments are given in the following tables.

Experiments with dimethyl sulfate.

SYNTHESIS.

ANALYSIS.

Experiments with diethyl sulfate.

SYNTHESIS.

ANALYSIS.

The results of the analyses show that the reactions proceed according to the equation:

\[ \begin{array}{c} \text{pyridine} \end{array} \;+\; \begin{array}{c} \mathrm{R{-}O} \\[0.4em] \mathrm{R{-}O} \end{array} \!\!>\mathrm{S}\!\!< \begin{array}{c} \mathrm{O} \\[0.4em] \mathrm{O} \end{array} \;\longrightarrow\; \begin{array}{c} \text{\(N\)-R-pyridinium} \\ \mathrm{OSO_2OR} \end{array} \qquad \begin{array}{l} \text{where \(R\) is a} \\ \text{hydrocarbon} \\ \text{radical} \end{array} \]

and likewise with the other amines listed in the tables.

Syntheses with tribenzylamine by the method described above did not succeed.

On heating on a water bath for 100 hours, formation of an addition product was likewise not observed. Further, on heating in sealed tubes at \(150^\circ\) for 100, 150, 200, 250, 300, and 350 hours, dimethyl sulfate reacted only partially. A substance insoluble in water was obtained. After decomposition in sealed tubes for 100 hours at \(150^\circ\), the sulfur found was less than theory by \(3.7\%\), if it is assumed that the reaction proceeds according to the usual type:

\[ \begin{array}{c} \mathrm{CH_3{-}O} \\ \mathrm{(C_6H_5{-}CH_2)_3N{-}CH_3{-}O} \end{array} \!\!>\mathrm{S}\!\!< \begin{array}{c} \mathrm{O} \\ \mathrm{O} \end{array} \;\longrightarrow\; \mathrm{(C_6H_5CH_2)_3N^{+}\!\left(\begin{array}{c}\mathrm{CH_3}\end{array}\right){-}OSO_2OCH_3} \]

Analysis: sample \(0.2033\) g; obtained \(0.1109\) g \(\mathrm{BaSO_4}\).

\[ \begin{array}{rcl} \text{Calculated sulfur for the formula } \mathrm{(C_6H_5CH_2)_3N\!\left(\begin{array}{c}\mathrm{CH_3}\end{array}\right){-}OSO_2OCH_3} &—& 11.16\% \\ \text{Found} &—& 7.46\% \end{array} \]

On interaction of the ethyl ester of benzenesulfonic acid with triethylamine, colorless crystals separated, with m.p. \(68\text{–}69^\circ\); they dissolve readily in water and alcohol, and do not dissolve in ether and benzene. They were separated from the reaction mixture, washed with ethyl ether, and kept in a desiccator over \(\mathrm{H_2SO_4}\).

The substance obtained was analyzed by two methods:

1) by Carius, and
2) by calorific combustion.

Analysis by Carius:

\[ \begin{array}{ll} \text{Sample}—0.1897\ \text{g} & \\ \mathrm{BaSO_4}—0.1594\ \text{g} & \begin{array}{l} \text{Calculated sulfur for the formula:} \\[0.3em] \mathrm{(C_2H_5)_3N{-}OSO_2C_6H_5} \left(\begin{array}{c} \\[-0.6em] \mathrm{C_2H_5} \end{array}\right) —11.16\% \\[0.3em] \text{found}—11.54\% \end{array} \end{array} \]

On fusion with potassium nitrate:
Sample—0.4409 g; obtained 0.3727 g of $\mathrm{BaSO_4}$.
Found sulfur—11.59%.

The analyses indicate that the reaction proceeds according to the equation:

\[ (\mathrm{C_2H_5})_3\mathrm{N} + \mathrm{C_6H_5SO_2OC_2H_5} \rightarrow \begin{array}{c} \mathrm{C_2H_5}\\[-0.2em] \big/\\[-0.2em] (\mathrm{C_2H_5})_3\mathrm{N}\\[-0.2em] \big|\\[-0.2em] \mathrm{OSO_2C_6H_5} \end{array} \]

Experiments with esters of nitric and nitrous acids.

SYNTHESIS.

The compounds obtained were converted into chloroplatinates, which were subjected to analysis.

The chloroplatinates are yellow crystalline precipitates, which do not dissolve in ether, alcohol, or acetone, but dissolve in hot alcohol.

ANALYSIS

Thus here also, according to the data obtained, as with the esters of sulfuric acid, the addition of one molecule of ester to one molecule of amine takes place.

The formation of chloroplatinates proceeded according to the equation:

\[ 2\,\mathrm{C_5H_5N} \begin{matrix} \mathrm{CH_3}\\[-2pt] \diagup\\[-6pt] \diagdown\\[-2pt] \mathrm{ONO_2} \end{matrix} +\mathrm{H_2PtCl_6} \rightarrow 2\,\mathrm{HNO_3}+(\mathrm{C_5H_5N{-}CH_3})_2\mathrm{PtCl_6} \]

Conclusions:

On the basis of certain literature data and experimental data obtained by us, it may be accepted that, in the interaction of esters of mineral acids with tertiary amines, addition of the ester molecule to the amine molecule occurs, with formation of a salt according to the scheme:

\[ \mathrm{RN}+\mathrm{R_1OX} \rightarrow \mathrm{R{-}N} \begin{matrix} \mathrm{R_1}\\[-2pt] \diagup\\[-6pt] \diagdown\\[-2pt] \mathrm{OX} \end{matrix} \]

The addition reaction proceeds more rapidly with esters of sulfuric acid and slowly with esters of nitric acid, and still more slowly with esters of nitrous acid.

Among the esters of sulfuric acid, dimethyl sulfate reacts most rapidly; after it, in rate of reaction, follows diethyl sulfate. The ethyl ester of benzenesulfonic acid is inferior to them.

Under our conditions (with not too strong heating), only one molecule of amine adds to the molecule of sulfates. According to their activity, the esters of nitric acid may be arranged in the following order: methyl nitrate, ethyl nitrate, isobutyl nitrate, and isoamyl nitrate; i.e., the shorter the carbon chain, the greater the rate of combination with tertiary amines.

Among the amines, triethylamine and pyridine reacted most rapidly; then followed dimethylaniline, quinoline, diethylaniline, and tribenzylamine. Decomposition analogous to that observed by A. Angeli was not observed with the esters used in our work.

1. F. Ullmann, Lieb. Ann. 327, 104. ↩

2. R. Wolffenstein, Deut. Pat. Nr. 343.054. ↩

3. A. Angeli, C. 4, 762 (1921). ↩

4. Ya. I. Mikhailenko and N. A. Kudryasheva, Communications 6, 60. ↩