RESEARCH IN THE FIELD OF THE CHEMISTRY OF CARBAZOLE DERIVATIVES

47. Synthesis of Acrylates of 9-(β-hydroxyethyl)carbazoles

V. P. Lopatinskii, I. P. Zherebtsov

(Presented by the scientific-methodological seminar of the Faculty of Chemical Technology)

9-(β-hydroxy)ethylcarbazole has been used for the synthesis of 9-vinylcarbazole [1, 2, 3]. Recently, Natta and co-workers showed that methacrylate of 9-(β-hydroxy)ethylcarbazole is capable of stereospecific polymerization, with the formation of a polymer having very high heat resistance [4].

It was to be expected that acrylates of 9-(β-hydroxy)ethylcarbazoles would also be interesting monomers, and therefore we set ourselves the task of synthesizing them.

The two most commonly used methods for obtaining acrylates of various alcohols are their esterification with acrylic acid or transesterification of the methyl ester of acrylic acid [2, 5]. We chose the first method for the synthesis of acrylates of 9-(β-hydroxy)ethylcarbazoles, since the available data [6] indicated that esterification of 9-(β-hydroxy)ethylcarbazoles with acids proceeds effectively. At the same time, we sought to avoid side reactions that usually occur during transesterification and consist in the addition of the alcohol at the double bond of acrylates [2, 5], especially in the presence of basic catalysts.

Table 1

Dependence of the yield of acrylate of 9-(β-hydroxy)ethylcarbazole on the amount of acrylic acid

The reaction was carried out in an aromatic hydrocarbon medium in the presence of the catalyst—para-toluenesulfonic acid—with simultaneous removal of water in the form of an azeotrope, in the presence of hydroquinone in the system as a polymerization inhibitor. Preliminary experiments showed that, when benzene is used as the solvent, esterification does not proceed to any appreciable extent in 4 hours. Therefore xylene was used as the solvent. As a result of a series of experiments presented in Table 1,

(the remaining conditions are given in the description of the synthesis of 9-(β-hydroxy)ethylcarbazole acrylate) and intended to determine the minimum amount of acrylic acid necessary to obtain a satisfactory yield of acrylate, conditions were found that make it possible to obtain acrylates of 9-(β-hydroxy)ethylcarbazoles in good yield. Increasing the reaction time beyond 45 min, as well as decreasing the duration of the process, leads to a lower yield, which can be explained by increased losses due to polymerization in the first case and by insufficient time in the second. Simultaneously occurring polymerization also lowers the acrylate yield when large amounts of acrylic acid are used, greater than 2 mol per mole of 9-(β-hydroxy)ethylcarbazole. When 9-(β-hydroxy)ethylcarbazole is replaced by 3,6-dichloro-9-(β-hydroxy)ethylcarbazole, the corresponding acrylate is likewise obtained in good yield.

9-(β-Hydroxy)ethylcarbazole acrylate readily polymerizes in the presence of radical-type initiators, for example benzoyl peroxide, diazoaminobenzene, and azodiisobutyric acid dinitrile. The polymer of 9-(β-hydroxy)ethylcarbazole acrylate has good dielectric properties: the dielectric constant (in the frequency range from 20 to \(10^3\) Hz) depends little on temperature and is about 5.5; the dielectric loss tangent (in the same frequency range at 20–100°C) depends little on temperature and is \(5 \cdot 10^{-4}\).

Experimental Part

Starting materials. 9-(β-Hydroxy)ethylcarbazole was obtained by the method described earlier [3], mp 80–81°C.

3,6-Dichloro-9-(β-hydroxy)ethylcarbazole was obtained by the method described in [7], mp 157–158°C.

Acrylic acid, xylene (a mixture of three isomers), and p-toluenesulfonic acid were “pure” grade reagents; hydroquinone was “photo” grade.

9-(β-Hydroxy)ethylcarbazole acrylate

A mixture of 21.1 g (0.1 M) of 9-(β-hydroxy)ethylcarbazole, 100 ml of xylene, 2 g of p-toluenesulfonic acid, and 11.1 ml (0.15 M) of acrylic acid is boiled with a reflux condenser equipped with a Dean–Stark trap for 45 min. After cooling to room temperature, the mixture is washed three times in a separatory funnel with a 5% potassium hydroxide solution, and the xylene solution is dried over calcium chloride. The xylene is removed by heating the mixture under reduced pressure (10 mm Hg) in the presence of 0.1 g of hydroquinone, and the residue is recrystallized from methanol. This gives 17.7 g (66.3%) of the substance as fine needles with mp 73–74°C. After three recrystallizations from methanol, the yield of 9-(β-hydroxy)ethylcarbazole acrylate with mp 77–79°C is 12.5 g (47% of theory). Evaporation of the filtrates regenerates a small amount of 9-(β-hydroxy)ethylcarbazole.

Analyses, %: N found: 5.33; \(C_{17}H_{15}O_2N\); calculated: 5.28.

Polymerization of 9-(β-Hydroxy)ethylcarbazole acrylate

1.6 g of 9-(β-hydroxy)ethylcarbazole acrylate is thoroughly mixed with 0.01 g of benzoyl peroxide, the mixture is placed in a test tube and carefully melted in a water bath, after which the sealed test tube is kept for 3 h at a temperature of 125°C. A transparent, colorless, glassy polymer is formed.

3,6-Dichloro-9-(β-oxy)-ethylcarbazole acrylate

To a mixture of 29 g of 3,6-dichloro-9-(β-oxy)-ethylcarbazole, 150 ml of xylene, 3 g of p-toluenesulfonic acid, and 0.2 g of hydroquinone, 23 ml of acrylic acid is added, and the mixture is boiled for one hour with a reflux condenser fitted with a Dean–Stark trap. The hot solution is washed with water and with a 5% aqueous solution of caustic potash, after which, on cooling, a precipitate of 3,6-dichloro-9-(β-oxy)-ethylcarbazole acrylate separates from the solution. After removal of the solvent by distillation under reduced pressure and recrystallization of the residue from a mixture of methanol with acetone, 22.5 g of substance is obtained, mp 139–140°C (65% of theoretical). Analyses, %: found: Cl 20.92; N 4.17; 4.27. C\(_{17}\)H\(_{13}\)O\(_2\)NCl\(_2\). Calculated: Cl 21.37; N 4.20.

3,6-Dichloro-9-(β-oxy)-ethylcarbazole acrylate also polymerizes in the presence of benzoyl peroxide, forming a glassy polymer. The properties of the polymer are under investigation.

Conclusions

1. Acrylates of 9-(β-oxy)-ethylcarbazoles have been synthesized.
2. It has been shown that the acrylates obtained polymerize under the action of radical-type initiators.

Literature

1. G. S. Kolesnikov. Synthesis of Vinyl Derivatives of Aromatic and Heterocyclic Compounds. Academy of Sciences of the USSR, 1960.
2. Monomers. Collection 2, Foreign Literature Publishing House, 1953.
3. V. P. Lopatinskii, E. E. Sirotkina, I. P. Zherebtsov. Izvestiya TPI, 112, 42, 1963.
4. G. Natta, P. Longi, E. Pellino. Macr. chem. 71, 212, 1964.
5. P. Vatsulik. Chemistry of Monomers, vol. 1, Foreign Literature Publishing House, 1960.
6. V. P. Lopatinskii, I. P. Zherebtsov, L. S. Shelkovnikova. Izvestiya TPI, 163, 1970.
7. V. P. Lopatinskii, E. E. Sirotkina, I. P. Zherebtsov, S. K. Vereshchagina. Izvestiya TPI, 136, 11, 1965.