[CONTRIBUTION FROM
THE
CHEMICAL LABORATORY OF THE STATE COLLEGEOF WASHINGTON]
T H E INTERACTION O F SELENIUM TETRACHLORIDE AND BENZENE I N T H E PRESENCE OF ANHYDROUS ALUMINUM CHLORIDE* W. E. BRADTt
AND
JOHN FRANKLIN GREEN
Received July 6, 19%; revised November SO, 195'6 INTRODUCTION
Between 1888and 1894 M. C. Chabriel presented the results he obtained by the interaction of SeCL and benzene in the presence of anhydrous A1C13. He reported the following four products. (a) Chlorobenzene. (b) A yellow liquid boiling at 227-8"/50-60 mm. which he stated was diphenyl selenide, (CsH&3e. This substance, Chabrie said, reacted with aqueous bromine to form di-(bromophenyl) selenide, (C6H4Br)2Sewhich crystallized from alcohol in white hexagonal prisms melting at 112". ( c ) 9 red oil boiling at 245-50"/50-60 mm., to which he assigned the formula (C6H6)3(C6H4C1)Se~. ( d ) Yellow crystals (m.p. 60") stated to be phenylselenol, CdLSeH, which were precipitated from alcoholic solutions by salts of mercury and silver. In 1894 F. Krafft and R. E. Lyons2expressed the opinion that Chabrie's phenylselenol was diphenyl diselenide, (CsH&Sez. Later F. Krafft and A. Kaschau3repeated the interaction of SeCll and benzene in the presence of anhydrous aluminum chloride and reported the three products to be (a) chlorobenzene, (b) diphenyl selenide, and (c) diphenyl diselenide. They found that alcoholic solutions of diphenyl diselenide gave precipitates with metallic salts, but that these precipitates differed from those obtained from phenylselenol prepared by a method other than that under discussion. They established in this way that Chabrie had not prepared phenylselenol. This has been verified by later investigat0rs.l
* Presented a t the Regional Meeting of the Pacific Division of the American Association for the Advancement of Science a t Seattle, Washington, June, 1936. t Present address, University of Maine, Orono, Maine. 1 CHABRIE, Bull. SOC. chim., [2], 60, 133-7 (1888); [3], 2, 796 (1889); [3], 11, 1080-3 (1894); Compt. rend., 109, 182-5 (1889); Ann. chim. phys., 161, 20, 202-86 (1890). KRAFFTAND LYONS,Ber., 27, 1761-8 (1894). KRAFFTAND KASCRAU, ibid., 29, 429-35 (1896). 4 BRADT AND CROWELL, Proc. Ind. Acad. Sci., 41, 227-33 (1931); BRADT AND GREEN, ibid., 41, 215-25 (1931). 540
SELENIUM TETRACHLORIDE AND BENZENE
54 1
EXPERIMENTAL*
Fifty grams of pure SeClr,t with 136.5 g. of benzene, was placed in a flask, and 30 g. of anhydrous AICls,$ was added in four equal parts during the reaction period.
After heating for one hour and allowing to stand a t room temperature for 60 hours no further reaction was observed. The products then were carefully hydrolyzed by the addition of 100 cc. of cold water, made strongly acid by the addition of 50 cc. of concentrated hydrochloric acid and separated into a brown benzene and a cloudy aqueous layer. The benzene layer was washed, dried and distilled under reduced pressure. The three products identified were: (a) chlorobenzene, previously reported both by Chabrie and by Krafft with his coworkers (b.p. 130-1"/700 mm.), ( b ) diphenyl selenide, (CeH&Se, reported previously both by Chabrie and by Krafft and coworkers (b.p. 30143"/700 mm.; product concentrated "03, followed by HC1 -+diphenylselenonium dichloride; m.p. 183"), and (c) diphenyl diselenide (CBH.&S~Z previously reported by Krafft and co-workers and considered by Chabrie to be phenylselenol. The latter product was obtained in the form of golden-yellow crystals from alcohol, melting a t 63". The melting point was not depressed by the presence of diphenyl diselenide prepared either by the method of Krafft and Lyons2 or that of Lyons and Bradt.5 No product corresponding to Chabrie's (CsH6)s(C6H4C1)Se~ was present. No phenylselenol resulted from the reaction. Diphenylselenonium dibromide.-Diphenyl selenide was treated with cold bromine water for two hours in an effort to duplicate Chabrie's work; the product of this reaction was identified as diphenylselenonium dibromide: m.p. (recrystallized from rtlcohol) 141"; the melting point of a mixture with diphenylselenonium dibromide prepared according to the method of Krafft and Vorstere was not depressed; color, orange-red. Qi-p-bromophenyl selenide.-The diphenylselenonium dibromide described above was heated over a flame, cooled, and purified, and the resulting products were identified as diphenyl selenide and di-p-bromophenyl selenide : m.p. (from 95% alcohol) 115". The mixture melting point with di-p-bromophenyl selenide prepared according to the method of Edwards et al.7 was not depressed. Chabrie had reported the formation of dibromophenyl selenide, melting a t 112", without indicating that the bromine atoms were in the para positions. Mercuric chloride addition compound.-The addition of aqueous mercuric chloride rsolution to an alcoholic solution of diphenyl diselenide caused the formation of a white precipitate. This compound, after purification by washing with hot water, then with alcohol, followed by recrystallization from acetone, was identified as the inercuric chloride addition compound of diphenyldiselenide, (C6H&Se~.2HgC1~. Anal. Calc'd for C12H10C14Hg2Se2: C, 16.83; H, 1.18; C1, 16.58; Hg, 46.89; Se, 18.51. Found: C, 17.07; H, 1.13; C1, 16.46; Hg, 46.74; Se, 18.43.
+
* The selenium used in this work was supplied in stick form by the courtesy of the Baltimore Copper Smelting and Rolling Company, Baltimore, Maryland. t Prepared according to the method of BELLAND GIBSON,J. Chem. SOC.,127, 1880 (1925). $ Commercial aluminum chloride purchased from the J. T. Baker Chemical Company. 6 LYOSSA N D BRADT, Ber., 60, 60-63 (1927). KRAFFT A N D VORSTER, i b i d . , 26, 2813-22 (1893). 7 EDWARDS et al., J. Chem. SOC., 1928, 2293-2303.
542
W. E . BRADT AND JOHN FRANKLIN GREEK
The mercuric chloride addition compound of diphenyldiselenide is very slightly soluble in water, alcohol, ether, benzene, and may be crystallized from acetone as a white powder melting a t 187-8" (corr.). An analogous compound has been prepared by the action of silver nitrate on diphenyl diselenide. This, however, was not completely analyzed. Xrafft and KaschauS stated that alcoholic solutions of diphenyl diselenide formed precipitates with metallic salts, but did not establish their structure. It is the (MX). are identical opinion of the authors that these addition compounds (CbH6)2Se2. with those reported by Chabrie as selenomercaptides (CsH6Se.h!). No trace of the red oil described by Chabrie as corresponding to the formula (CeH6)3(CsH4C1)Se2 (b.p., 24550") was detected. It was noted, however, that mixtures of crude diphenyl selenide and diphenyl diselenide exhibited a red oily appearance and that, as Chabrie observed, the latter compound separated upon standing. Zinc chloride addition compound of triphenylselenonium chloride.-Only one watersoluble organoselenium compound was found as a product of the interaction of selenium tetrachloride and benzene in the presence of anhydrous aluminum chloride. An excess of aqueous 20% zinc chloride was added to the water-soluble reaction products, and a very heavy white precipitate was obtained. After washing and repeated crystallization from hot water this was identified as the zinc chloride addition compound of triphenylselenonium chloride, [(C&) 3SeCl]~.ZnC1~; m.p. 274". Anal. Calc'd for CIGHa~C14Se2Zn: C, 52.17; H, 3.66; Se, 19.13; Zn, 7.89; C1, 17.13. Found: C, 52.40; H, 3.69; Se, 19.10; Zn, 7.7. The melting point was not depressed by the presence of the zinc chloride addition compound of triphenylselenonium chloride prepared by the method of Bradt and Crowell.8 Addition of silver nitrate to the water solution precipitated as silver chloride 74.7y0 of the chlorine in the addition compound. The ZnClp addition compound crystallizes from water in short rhombic crystals. In the presence of hydrochloric acid its solubility in water decreased to a sufficient extent to make possible its easy isolation. It is sparingly soluble in alcohol and less so in chloroform, ether, benzene, carbon disulfide and nitrobenzene. This zinc chloride addition compound is quite stable even a t high temperatures. Treatment with concentrated potassium hydroxide solution decomposed it, forming a crystalline product and a dark brown oil. The approximate yields of the crude products isolated are given by the following data, which represent the average values from two duplicate reactions in which 50 g. of selenium tetrachloride was used as previously described: chlorobenzene, 1 g. ; diphenyl selenide, 20 g. ; diphenyl diselenide, 5 g. ; triphenylselenonium chloride ZnC12, 20 g.
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SUMMARY
Chabrie reported that the interaction of selenium tetrachloride and benzene in the presence of anhydrous aluminum chloride formed: (a) chloand robenzene, ( b ) diphenyl selenide, (c) a compound, (CCHJ3(C6H4C1)Se2, (d) phenylselenol. He also reported the preparations of selenomercaptides of the type CeH5SeAgand a dibromophenyl selenide in which the position of the bromine on the benzene ring was not specified. Krafft and his co-workers in criticism of Chabrie's results established the 8
BRADTAND CROWELL, J. Am. Chem. Soc., 66, 1500-2 (1933).
543
SELENIUM TETRACHLORIDE AND BENZENE
fact that the phenylselenol reported was diphenyl diselenide and that the supposed selenomercaptides were not derivatives of phenylselenol but of diphenyl diselenide. They, however, did not identify the latter derivatives. No investigator of this reaction has reported the presence of any watersoluble products. The products of this reaction have been shown to be: (a) chlorobenzene, (b) diphenyl selenide, (c) diphenyl diselenide, and (d) triphenylselenonium chloride. It has also been shown that the compounds reported by Chabrie as selenomercaptides are addition compounds of metallic salts with diphenyl diselenide. The pure mercuric chloride addition compound (C&)zSez. 2HgCL has been prepared. The preparation of the dibromophenyl selenide reported by Chabrie has been repeated and the compound identified as di-p-bromophenyl selenide. The following equations are proposed to explain these facts. Identified organic products are underlined.
I. SeCld + 3CsH6
!!!z) (C6H5)3SeC1 + 3HC1
11. ( C G H ~ ) & ?b2 C ~ (CsH5)zSe + c6115c1
111. (CeH&Se + Se heat (CsH5)zSe~ ITT.(CeH5)2Se+ Br2 --+ (C6H&SeBrz V. (CeH5)zSeBrz !?$ (p-BrC6H&Se (C6H6)?Se 2HBr VI. (CsH5)zSez+ 2HgCl2 (C6H5)2Se2.2HgC1~ T’II. 2(C6H5)&C1 + ZnCL -+ [(C&)sSeCl]z* ZnClz
+
--f
+
