INTERACTION OF AMINES WITH VINYL ETHERS

III. VINYLATION OF DIPHENYLAMINE WITH VINYL ACETATE AND SYNTHESIS OF POLY-\(N\)-VINYLDIPHENYLAMINE

V. P. LOPATINSKII, E. E. SIROTKINA, Yu. P. SHEKHIREV

(Presented by the scientific seminar of the organic chemistry section)

\(N\)-Vinyldiphenylamine was first obtained by Wold in 1935 during the vinylation of diphenylamine with acetylene in the presence of metallic potassium or caustic potassium in xylene or without a solvent [1]. Later the synthesis process was accelerated by using pyridine as solvent at a temperature of \(180^\circ\) under a pressure of 20–25 atm [2]. A similar synthesis was also carried out by A. E. Favorskii and M. F. Shostakovskii [3]. It was noted that the monomer is very unstable, sensitive to oxidation by oxygen, and readily turns red in air, especially on heating. As a result, its polymerization is very difficult to carry out, and the polymers are usually obtained colored and insufficiently pure [1, 4].

In the present work we attempted to obtain \(N\)-vinyldiphenylamine by vinylating diphenylamine with complex vinyl ethers, i.e., under the conditions of the vinyl-exchange reaction [5, 6]. Vinyl acetate was used by us as the vinylating agent.

It turned out that the interaction of diphenylamine with vinyl acetate in the presence of mercury(II) sulfate proceeds analogously to the previously described reaction of carbazole with vinyl acetates under the same conditions [7] and leads to the formation of the polymer of \(N\)-vinyldiphenylamine in one stage. Monomeric \(N\)-vinyldiphenylamine is apparently formed here as an intermediate product and polymerizes under the reaction conditions.

A study of the influence of various factors on the reaction showed that the quantitative conversion of diphenylamine into poly-\(N\)-vinyldiphenylamine occurs when equimolecular amounts of diphenylamine and vinyl acetate are used in acetone solution in the presence of the above-mentioned catalyst. In dioxane the reaction gives an insignificant yield of polymer (8%), while in diethyl ether, pyridine, and nitrobenzene no interaction is observed. With an increase in the amount of catalyst, the yield of polymer and the degree of conversion of diphenylamine increase. In the presence of 5% mercury(II) sulfate, based on the weight of diphenylamine, diphenylamine reacts completely in 10 hours at \(20^\circ\), and the yield of the polymer fraction insoluble in methanol reaches 73%.

Changing the temperature from 0 to 20°C leads to a noticeable increase in the yield of the polymer fraction insoluble in methanol. The best yields of this fraction were achieved at 20°C and a reaction time of 10 hours (Table 1). With further increases in the temperature and duration of the process, the yields of the indicated polymer fraction decrease.

Table 1

Results of some experiments on the interaction of diphenylamine with vinyl acetate

In all experiments, the completeness of conversion of vinyl acetate was monitored by the amount of acetic acid released during its decomposition. Under optimal conditions, with complete conversion of vinyl acetate, unreacted diphenylamine is not detected in the reaction products. It should be noted that the reaction between diphenylamine and vinyl acetate proceeds most effectively in the presence of freshly prepared mercury(II) sulfate, formed directly in the reaction medium.

The polymer of \(N\)-vinyldiphenylamine was isolated from the reaction products by precipitation with methanol. The polymer fraction insoluble in methanol had molecular weights from 800 to 1050 (determined cryoscopically) and was a white amorphous powder with a softening temperature of 115–130°C (in a capillary), soluble in aromatic hydrocarbons, chlorobenzene, dioxane, chloroform, and pyridine. The polymer is poorly soluble in methanol and ethanol and insoluble in water. On storage in air and under the action of light, the polymer gradually acquires a pink color and subsequently becomes orange. Preliminary studies of the dielectric properties of the polymer gave the following results: volume resistivity \(10^{15}\ \Omega\cdot\text{cm}\), dielectric constant 2.8 (at a frequency of \(10^5\) cycles), dielectric loss tangent: 0.05 (at a frequency of 126 cycles) and 0.015 (at a frequency of \(10^5\) cycles). The structure of the polymer as poly-\(N\)-vinyldiphenylamine is proved by the fact that it does not give a nitroso derivative.

Experimental Part

The work used diphenylamine of “chemically pure” grade with a melting point of 52°C and freshly distilled vinyl acetate with a boiling point of 73°C.

Into a three-necked flask equipped with a stirrer, thermometer, and dropping funnel and placed in a thermostat are charged 1.072 g of mercury acetate \((\mathrm{CH_3COO})_2\mathrm{Hg}\) and 22 ml of acetone. With stirring, 0.18 ml of sulfuric acid (specific gravity 1.84) is added. As a result of the exchange reaction, the catalyst—mercury(II) sulfate—is formed. Then 20 g of diphenylamine is introduced into the flask, and 11 ml of vinyl acetate is added dropwise over the course of an hour with continuous stirring. The reaction mixture is kept at a temperature of \(20 \pm 2^\circ\mathrm{C}\) for 10 hours with stirring. After the reaction is complete, the solution is filtered from the catalyst, and the polymer is isolated by precipitation in 300 ml of methanol with stirring. The isolated fraction is washed with water to neutral reaction and dried. The yield of the fraction (molecular weight 1030 by the cryoscopic method) is 73.1%. Softening temperature \(115—130^\circ\mathrm{C}\) (in a capillary).

Found, %: \(N\) 7.03; 7.06; \((\mathrm{C}_{14}\mathrm{H}_{13}\mathrm{N})_n\).
Calculated, %: \(N\) 7.18.

The amount of acetic acid formed as a result of the reaction of diphenylamine with vinyl acetate, excluding the acid formed from mercury acetate: found 7.10 g; calculated 7.11 g.

Conclusions

1. The possibility has been demonstrated of obtaining the polymer of \(N\)-vinyldiphenylamine in one stage by the interaction of diphenylamine with vinyl acetate in the presence of mercury(II) sulfate.

2. The optimal conditions have been established under which quantitative conversion of diphenylamine into poly-\(N\)-vinyldiphenylamine is achieved, and the yield of the fraction with a softening temperature of \(115—130^\circ\mathrm{C}\) reaches 73%.

References

1. W. Wolf, German patent 636213, 1935, Fridländer, 23, 94.
2. E. Keyßner, W. Wolf. German patent 642424, 1935; Fridländer, 23, 273.
3. A. E. Favorskii, M. F. Shostakovskii, A. I. Zitser. Scientific Research Works of Chemical Institutes and Laboratories of the USSR Academy of Sciences for 1940, USSR Academy of Sciences, Moscow–Leningrad, 1941.
4. C. E. Schildknecht. Vinyl and Related Polymers, N—Y, 1952.
5. R. L. Adelman. J. Org. Chem., 14, 1957, 1949.
6. W. Watanabe, L. Conlon. J. Am. Chem. Soc., 79, 1669, 1957.
7. V. P. Lopatinskii, E. E. Sirotkina. Proceedings of the Tomsk Polytechnic Institute, vol. 111, 44, 1961.