MATTHEWS : BENZENE HEXABROMIDE. 243 XX.-Benzene Hexabromide. By FRANCIS EDWARD MATTHEWS, Ph.D. IN the course of work on the halogen hexa-additive compounds of benzene and its derivatives, the author has had occasion to prepare the hexabromide of benzene in considerable quantity. R 2244 hlATTHEtVS : BENZENE HEXABROMIDE. As benzene hexachloride exists in two isomeric forms, the existence of two modifications of the hexabromide was to be expected, but, although carefully looked for, no indication of the second modification was obtained. As the hexabromide prepared by the method described in a former paper (Trans., 1892,61,p. 110) seemed homogeneous, its further investi- gation was abandoneduntil a paper was published by Orndorf and Ho welIs ( A m y . Chem. J., 1896,18, pp.312-319), who succeeded in isolating a very small quantity of a second modification from the hexabromide prepared by the method suggested in my paper, but not from that prepared by other methods. Having a considerable amount of crude material on hand, I once more attempted t o obtain the second modification, but in the course of a series of fractional extractions with chloroform performed on some half-pound of substance, I could find no evidence of the more insoluble modification, as the crystals obtained from the final extract had the same crystalline form, melting point, and solubility as those from earlier portions. I n the method of preparation adopted by Orndorf and Howells there was, however, one slight difference from that which I used, and this may account for the difference in the result.After exposure to sunlight, they evaporated the mixture of bromine, water, and benzene t o dryness, and subsequently made extracts of the residue ; my crude material consisted solely of the solid precipitated during the action of sunlight, which was roughly freed from the mother liquor by filtration through coarse muslin, and by subsequent washing with benzene, so that it seems probable that the second modification, although very insoluble, is produced in such small quantity as not to precipitate spontaneously from the mother liquor, which consists of benzene, a considerable quantity of bromobenzene, and a small amount of para- dibromobenzene. Bromobenzene does not appear t o be capable of forming a hexabro- mide under the conditions in which benzene hexabromide is produced, the bromine displaces hydrogen in the nucleus, and paradi bromobenzene is almost exclusively formed.Bromobenzene also could not be made to form a hexachloride; on mixing bromobenzene with water and passing in chlorine, bromine is liberated, rapidly in sunlight, more slowly in diffused daylight, and on continuing the action a complex mixture of halogen compounds is formed. In all its reactions save one, benzene hexabromide behaves as has been described by previous investigators; the sole difference is the action of alcoholic alkali hydroxides on it. According t o previous work, benzene hexabromide is decomposed by alcoholic solutions ofMATTHEWS : BENZENE HEXABROMTDE. 245 alkalis, similarly to the hexachloride, quantitatively into 1 : 2 : 4 tri bromobenzene with the removal of 3 mols.HBr. This I have found not to be the case, as on boiling the pure recrystallised hem- bromide with alcoholic soda, more bromine is removed than is required by the equation C,H,Br, + 3NaOH = C,H3Br, + 3NaBr + 3H,O. Some pure benzene hexabromide, recrystallised from chloroform, and which gave on analysis 85.44 per cent, of bromine (Theory 86.02) was decomposed with excess of alcoholic soda free from chlorine, and the amount of bromine in solution was determined. 0.2298 gram C,H,Br, gave 0.2707 gram AgBr. Br = 50.1. 0.2154 ,, C,H,Br, ,, 0.2444 ,, AgBr. Br = 48.3. Theory for removal of Br, = 43.0, of Br,= 57.3 per cent. From the above it follows that 1 mol. C,H,Br, parts with about 3& atoms of bromine to alcoholic soda, and, in order to identify the products, the reaction was carried out on a much larger scale.After the hexabromide had been boiled with excess of alcoholic soda for some time and everything had gone into solution, excess of water was added, and the semi-solid precipitate extracted with ether ; the solu- tion was dried, the ether distilled off, and the residue fractionally distilled, when the whole came over between 210' and 280°, two principal fractions being obtained, the first distilling at 220-230°, and the other at 260--270°. Both of these portions solidified on stand- ing, and the fraction 260-270°, after recrystallisation from benzene, gave the following figures on analysis, 0.2820 gave 0.5070 AgBr. Br = 76.5. C,H,Br, requires Br = 76.2 per ct.It was identified as unsymmetrical tribromobenzene from the above figures by its boiling point and melting point (43'). The other chief fraction, 220--230°, was freed from oily matter on a porous plate and recrystallised from benzene, in which it was very soluble, by spontaneous evaporation. It was then found t o melt at 86-87'', and gave the following figures on analysis. 0.1036 gave 0.3094 AgBr. 0.2744 ,, Br = 68.0. 0.3096 CO, and 0.0490 H,O. C = 30.8 ; H = 2.0. C,H:,Br2 requires Br = 67.8 ; C = 30*5 ; H = 1.7 per cent. The substance is therefore a dibromobenzene, and from its melting point and from the melting point of its nitro-derivative (83') it appears to be the para-compound. Between 230' and 260°, small fractions of liquid substances were obtained, but as the small amount precluded their separation by fractional distillation, an attempt was made to 0,1032 9 , 0.1160 CO, ,, 0.0180 H20. C = 30.6 ; H = 1.9.246 SHENSTONE AND EVAh’S : OBSERVATIONS ON THE separate them by fractional crystallisation of their nitro-derivatives ; the presence of orthodibromobenzene was suspected, but the results obtained did not completely substantiate its presence. Tribromobenzene yields no trace of dibromobenzene, neither does it part with bromine when acted on by boiling alcoholic soda; the formation of the dibromobenzene, therefore, takes place during the decomposition of the benzene hexabromide . Benzene hexabromide, on reduction with nascent hydrogen in acid alcoholic solution, yields benzene. The benzene thus obtained was found to yield both modifications of benzene hexachloride on treatment with chlorine. ROYAL INDIAN ENGINEERING COLLEGE, COOPERS HILL.