STUDY IN THE CHEMISTRY OF CARBAZOLE DERIVATIVES

57. SYNTHESIS OF ANIONITES BASED ON A COPOLYMER OF STYRENE WITH 3-VINYL-9-ALKYLCARBAZOLES

V. P. Lopatinskii, E. E. Sirotkina, M. P. Grosheva, L. S. Sizova

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

At the Department of Technology of Basic Organic Synthesis of TPI, work has been carried out for a number of years on the use of vinyl derivatives of carbazole for the synthesis of ion-exchange materials.

As was reported earlier [1], for the synthesis of anionites we used cross-linked copolymers of 3-vinyl-9-alkylcarbazoles and divinylbenzene. However, when carrying out the chloromethylation reaction of these copolymers, which is an intermediate stage in the synthesis of anionites, additional cross-linking of the chloromethylated copolymer was found to occur; as a result, the chlorine content in the product decreases and, consequently, the exchange capacity of the anionite obtained is reduced.

In this connection, it was of interest to use linear copolymers of 3-vinyl-9-alkyl derivatives of carbazole with styrene, which would be cross-linked during the chloromethylation reaction and could subsequently be used for the synthesis of insoluble ion-exchange materials.

In the present work, the influence of various factors on the process of chloromethylation of linear copolymers of 3-vinyl-9-alkylcarbazoles with styrene and on the process of cross-linking of the chloromethylated copolymer was studied. For the investigation, a copolymer obtained by emulsion copolymerization of styrene with 3-vinyl-9-alkylcarbazoles according to the procedure described earlier [2] was used. The results of the synthesis of linear copolymers are presented in Table 1. The copolymers obtained are transpar—

Table 1

Characteristics of copolymers of 3-vinyl-9-alkyl derivatives of carbazole with styrene
(Reaction temperature — 80°C; reaction duration 6 hours. Initiator — Diniz in an amount of 1% of the weight of the monomer charge)

... as colorless granules, insoluble in aliphatic alcohols and hydrocarbons, but soluble in aromatic hydrocarbons. The chloromethylation process was studied on a copolymer obtained by copolymerizing 20% 3-vinyl-9-ethylcarbazole with 80% styrene.

Chloromethylation of the Linear Copolymer

Chloromethylation of the copolymer was carried out using monochlorodimethyl ether in the presence of a catalyst—anhydrous zinc chloride. The reaction was conducted in a three-necked flask equipped with a reflux condenser, stirrer, and thermometer. A weighed portion of zinc chloride and the required amount of monochlorodimethyl ether were placed in the flask, and stirring was begun to dissolve the catalyst in the ether. Then, with the aid of a funnel, a weighed portion of the copolymer was introduced and the mixture was kept, with the stirrer operating, for 1–2 hours at room temperature. The temperature was then raised to the required value and maintained for a specified time with stirring.

After completion of the chloromethylation reaction, the granules were thoroughly filtered on a Büchner funnel, and the chloromethylated copolymer was washed with methanol, then with a 5% solution of hydrochloric acid and distilled water until the wash waters were neutral. The chloromethylated copolymer was dried at room temperature to an air-dry state, and the content of total and active chlorine, as well as the swelling of the chloromethylated copolymer, was determined by the usual method [3]. In the course of the study, the following factors affecting the degree of chloromethylation of the linear copolymer of 3-vinyl-9-ethylcarbazole and styrene, as well as its crosslinking, were examined:

a) duration of swelling of the copolymer in monochlorodimethyl ether;
b) amount of monochlorodimethyl ether;
c) temperature of the chloromethylation reaction;
d) amount of catalyst (zinc chloride);
e) amount of 3-vinyl-9-ethylcarbazole in the copolymer.

The chloromethylation process was monitored by analysis for total and active chlorine, and the crosslinking process by the swelling of the chloromethylated copolymer in xylene.

Studies of the swelling of linear copolymers in monochlorodimethyl ether at 20°C showed that the copolymers are soluble in it. However, after 5–6 hours a jelly-like mass, insoluble in aromatic hydrocarbons, formed in the reaction flask, which indicates the formation of a crosslinked product. Consequently, chloromethylation and crosslinking of the copolymer occur already at room temperature and without catalyst. To increase the rate of the crosslinking process, preliminary swelling was carried out in monochlorodimethyl ether containing zinc chloride. Carrying out the chloromethylation process without preliminary swelling of the copolymer in monochlorodimethyl ether showed that the granules of the chloromethylated copolymer have large cavities. Such a copolymer has reduced mechanical strength and may be destroyed both during subsequent amination and during use of the finished anion exchanger. As can be seen from Table 2, increasing the duration of swelling of the copolymer in monochlorodimethyl ether to 10 hours does not lead to an increase in the chlorine content in the chloromethylated copolymer, nor to a change in the degree of crosslinking of the product. Evidently, to improve the mechanical strength of the chloromethylated copolymer, two-hour swelling of the copolymer in monochlorodimethyl ether at room tem-

literature. Therefore, all further studies were carried out with swelling of the copolymer in monochlorodimethyl ether for 2 hours.

Table 2

Effect of the duration of swelling of the copolymer in monochlorodimethyl ether (MCDME)
(Amount of ZnCl₂—25% of the weight of the copolymer, MCDME : copolymer = 10 : 1, reaction temperature—60°C)

Fig. 1. Effect of the amount of monochlorodimethyl ether on the chloromethylation process.
—●— MCDME : copolymer = 8 : 1,
—△— MCDME : copolymer = 10 : 1, ZnCl₂—50% of the weight of the copolymer,
—×— MCDME : copolymer = 15 : 1,
—□— MCDME : copolymer = 20 : 1, reaction temperature—60°C.

As is evident from Fig. 1, the optimum amount of ether is 8–10 parts by weight per 1 part by weight of copolymer, which is apparently determined by its adsorption by the copolymer during the swelling process.

The greatest percentage of chlorine is introduced over a short period of time when the process is carried out at 60°C (Fig. 2); at this temperature, within 3–4 hours the theoretically possible degree of crosslinking is reached, as indicated by the straight portion of the curve and by the constant degree of swelling of the products obtained. From Fig. 3 it is evident that at

Axis labels: \( \% \) chlorine; \(t\), h.

Fig. 2. Effect of temperature on the chloromethylation process. —●— \(30^\circ\mathrm{C}\), —×— \(40^\circ\mathrm{C}\), —△— \(50^\circ\mathrm{C}\), —□— \(60^\circ\mathrm{C}\). Amount of \(\mathrm{ZnCl_2}\): 20% of the copolymer weight; MKhDME : copolymer \(= 10 : 1\).

Axis labels: \( \% \) chlorine; \(t\), h.

Fig. 3. Effect of the amount of \(\mathrm{ZnCl_2}\) on the chloromethylation process. —●— 20% \(\mathrm{ZnCl_2}\), —×— 25% \(\mathrm{ZnCl_2}\), —△— 50% \(\mathrm{ZnCl_2}\), —□— 100% \(\mathrm{ZnCl_2}\); MKhDME : copolymer \(= 10 : 1\), reaction temperature \(60^\circ\mathrm{C}\).

With 50% catalyst, a larger percentage of chlorine is introduced during the chloromethylation process. A decrease in the amount of catalyst leads to a decrease in chlorine in the chloromethylated product and to a decrease in the exchange capacity of the finished anion exchanger; in addition, the rate of crosslinking of the chloromethylated copolymer is probably reduced, which leads to its partial dissolution during the reaction, and cavities are formed on the surface of the beads, reducing their mechanical strength.

It is known from the literature that polystyrene does not crosslink under mild chloromethylation conditions [4]. This proposition was verified under our conditions; the chloromethylated polystyrene obtained dissolved in aromatic hydrocarbons (xylene, benzene), whereas chloromethylation of 9-ethylcarbazole, even in the presence of catalytic amounts of Friedel–Crafts catalysts, leads to the formation of a crosslinked insoluble product [1]. Consequently, crosslinking of the copolymer during chloromethylation proceeds through the carbazole nuclei. This is clearly seen from Table 3. Increasing the con—

Table 3

Effect of the amount of 3-vinyl-9-alkylcarbazole derivative in the copolymer on the chloromethylation process
(Amount of catalyst — 50%, reaction temperature — 60°C, MKhDME : copolymer — 10 : 1, reaction time — 6 h)

Table 4

Effect of the amount of ZnCl₂ catalyst on the chloromethylation process
(Reaction temperature — 60°C, reaction time — 6 h, MKhDME : copolymer — 8 : 1)

Note. KhMS — chloromethylated copolymer.

content of the vinyl carbazole derivative in the copolymer; upon chloromethylation of the latter, a more highly cross-linked product is obtained, since its swelling in xylene decreases.

By aminating the resulting chloromethylated copolymers with a 36% aqueous solution of trimethylamine at a temperature of 40°C for 8 hours, anion exchangers were obtained, the characteristics of which are given in Table 4.

Conclusions

1. The process of chloromethylation of linear copolymers of 3-vinyl-9-alkylcarbazoles with styrene was studied, and it was shown that the final products of the chloromethylation reaction are cross-linked resins insoluble in aromatic hydrocarbons.

2. The optimum conditions for the chloromethylation reaction and for cross-linking of the copolymer in the presence of a zinc chloride catalyst were determined.

3. It was shown that the degree of cross-linking in the chloromethylation process can be controlled by the amount of the vinyl carbazole derivative in the initial copolymer.

4. By amination of the chloromethylated copolymer, an anion exchanger was obtained with an exchange capacity of \(3.6\text{–}3.8\,\frac{\text{mg-eq}}{\text{g}}\).

Literature

1. V. P. Lopatinskii, E. E. Sirotkina, M. P. Grosheva. Izv. TPI (in press).

2. V. P. Lopatinskii, E. E. Sirotkina, S. I. Kudinova. Izv. TPI (in press).

3. K. M. Olshanova, M. A. Potapova. Handbook of Ion-Exchange, Distribution, and Precipitation Chromatography, 1965.

4. K. Paper, H. Paisley and M. Joung. J. Chem. Soc., 1953, 4097.