The Complexes of Benzene with Halogens and Interhalogens in Carbon Tetrachloride* **
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Daehan Hwahak Hwoejee Volume 9, Number 4, 1965 Printed in Republic of Korea. The Complexes of Benzene with Halogens and Interhalogens in Carbon Tetrachloride* ** by Sang Up Choi, Suck Joo Chang and Shoon Ja Kwon Department of Chemistry, Hanyang University (Received September 17, 1965) 벤젠과 할로겐 또는 할로겐間化合物 사이의 錯物에 관한 연구 漢陽大學校 化學科 崔相案 -張石柱 -權純子 （1965. 9. 17 受理 ） 要 糸勺 벤젠과 요오드 , 브롬 , 염소 또는 일브롬화요오드 와의 각 系를 사염화탄소 용액에서 分光光度法 에 의하 여 연구한 결과 C6H6.X2 또는 C&H6-IX형의 錯物이 형성됨을 알았다 （X 는 할로겐 原子를 표시 함 ） . 이들 錯物의 생성에 대한 25。에서의 평형상수 는 다음과 같다 . C6H6.I2 0.173 I mole-i, C6HS-Br2 0.137 I mole-\ C6H6-CI2 0.0643 I mo!e-\ C6H6-IBr 0. 341 I mole-L 이 결과와 다른 사람들의 결과를 종합 하면 벤젠과의 錯物의 상대적 안정도가 다음 순서로 감소함을 알 수 있다 . lCl>IBr>I2>Br2>Cl2 이 순서는 그들의 상대적 산도를 의미하며 할로겐 분자의 편극율 및 할로겐 원자의 전기음성도의 차이 에 의하여 설명할 수 있다 . Abstract Ultraviolet spectrophotometric investigations have been carried out on the systems of benzene with iodine, bromine, chlorine and iodine monobromide in carbon tetrachloride. The results reveal the formation of one to one molecular complexes of the type, CgHe* X2 or CgHg, IX (X denotes halogen atoms). The equilibrium constants obtained at 25° for the complex formation are 0.173, 0.137, 0. 0643 and 0- 341 / mole-1 for *Br2CeH6 t CgHg-C^ and CeHg'IBr, respectively. These results combined with those obtained by other workers indicate that the relative stabilities of the benzene complexes decrease in the order, lCl>IBr>I2>Br2>Cl2. This order may be a measure of their relative acidities toward benzene, which is explained in terms of the relative polarizabilities of halogen molecules and the relative electronegativities of halogen atoms. * The Molecular Complexes. III. Introduction '• Based partly on M. S. thesis submitted by Suck Joo Chang . and by Shoon Ja Kwon to the Graduate School of Seoul After Benesi and Hildebrand ° 鱼沒 demons- National University. Bated the formation of the one to one molecular 153 154 崔相橐 •張石柱 •標純子 大韓化學會誌 complex between benzene and iodine in carbon iodine in carbon tetrachloride. tetrachloride solution, studies were extended to Keefer and Andrews evaluated also the equil other systems by a number of workers.2,3) ibrium constants, KXf for the formation of the com Among the various experimental techniques plexes of benzene with bromine2fI), chlorine & used,心 spectrophotometric measurement was one and iodine monochloride 2b) in carbon tetrachlo of the most common methods. Utilizing spectr ride. ophotometric data, the equilibrium constants for The Kx values obtained ar 25° were as follows: the formation of the molecular complexes were Benzene------------- K『=1. 04. calculated by the method proposed by Benesi and Benzene—chlorine, Kx—0. 33. Hildebrand 15 or the methods modified by other Benzene---------- monochloride, 瓦 =4. 76. investigators. 5) The relative magnitudes of the Kx values may Benesi and Hildebrand 15 observed that the be a measure of relative stabilities of the comp solution of a mixture of benzene with iodine lexes. Since all of the complexes mentioned in carbon tetrachloride had the maximum absor above are the benzene-complexes, the relative ption at 2970 A, and attributed it to the form complexing power of the halogens and the ation of the one to one molecular complex, interhalogen with benzene presumably decreases CgHs- I2, in solution. They determined both the in the order, molar absorptivity, at of the complex at 2970 A, ICl>I2>Br2>Cl2. ancl the corresponding equilibrium constant *, It then appeared of interest io extend the studies Kx, in which the concentration of benzene was to the system of benzene— monobromide in expressed by mole fractions and the concentrat carbon tetrachloride, in order to determine the ions of other species by molar concentrations. relative complexing power of iodine monobromide The values obtained at room temperature were with benzene. Thus, the present study involved as follows: the spectrophotometric investigations of the sys & = 15400, 政 = 1.72. tems of benzene with iodine, bromine, chlorine, As the results of similar studies, however, and iodine monobromide in carbon tetrachloride. Keefer and Andrews 2d) observed the absorption maximum of the benzene---------- complex at Experimental 2920 A, and determined both the molar absorp Materials, —Benzene (reagent grade, Wako, tivity of the complex at 2920 A and the corres Japan) was treated with concentrated sulfuric ponding equilibrium constant **, K, in which acid, and washed successively with water, 10% the concentrations of all species were expressed aqueous solution of sodium carbonate, and again in terms of molar concentrations. The values water.6) It was then dried over metallic sodium, obtained at 25° were as follows: and distilled through a 100-cm. distillation 4=16400, K=Q. 15 I mole-1. column packed with glass helices. The reflux Thus, the results reported by the two groups ratio was controlled at approximately 1：15. The of authors did not agree well with each other. middle fraction of the distillate was c이 lected It appeared of interest, therefore, to reinvestigate and the boiling point observed was 80. 2°. spectrophotometrically the system of benzene一 Carbon tetrachloride(reagent grade, Katayama, • This equilibrium constant has no dimensions and will be Japan) was dried over calcium chloride and referred to as Kx hereafter in this paper. distilled through a 100-cm. distillation column This equilibrium constant has the dimensions of I mole-1, and will be referred to as K hereafter in this paper. at the reflux ratio of about 1：15. The mid시 e Vol. 9 (1965) The Complexes of Benzene with Halogens and Interhalogens 155 portion of the distillate was collected and the by placing in a thermostat prior to the spectrop boiling point observed was 76. 8°. hotometric measurements. The temperature of Iodine (reagent grade, Merck, Germany) was the thermostat was kept at 25±0. 5°. purified by sublimation of a mixture of iodine The Spectrophotometric Measurements.— with potassium iodide (about 3-1 by weight), The absorbancies of the stock solutions of iodine, followed by resublimation of the product.7) It bromine, chlorine, iodine monobromide or be was stored over phosphorus pentoxide in a nzene in carbon tetrachloride were measured desiccator. over the region of wave lengths from 2700 to 6000 A, using the pure solvent, carbon tetrach Bromine (Wako, Japan) was used without further purification. loride, as the blank. Chlorine was prepared by dissolving potassium Then, the stock solution of benzene was mixed at various ratio with the solutions of the halo dichromate into hydrochloric acid. The evolving gens or the interhak^en*. The absorbancies of chlorine gas was washed successively with water the resultin용 solutions were immediately measu and concentrated sulfuric acid in order to remove contaminated hydrogen chloride. red. The prolonged keeping of the mixture solutions was avoided for otherwise slow chemical Preparation of Stock Solutions.—The sol changes might have occurred. The blank in ution of iodine in carbon tetrachloride was this case was the carbon tetrachloride solution prepared by weighing an appropriate quantity of iodine into a volumetric flask, and adding of benzene with the same concentrations as those carbon tetrachloride solvent to make up to vol of the solutions containing the halogens or the ume. The solution thus prepared was diluted interhalogen. further to suitable concentrations. A Beckman DU Spectrophotometer and a set of 1-cm. quartz cells were used for the absorb The solutions of bromine or chlorine in carbon ancy measurements. tetrachloride were perpared by pipetting a small amount of bromine or bubbling chlorine gas Results and Discussion into ca놔 xm tetrachloride in volumetric flasks. The concentrations of the solutions were then Calculation of Equilibrium Constants for deterimined by titration with 0.1 normal sodium the Complex Formation, —The absorption spe thiosulfate solution in the presence of excess ctra of the individual stock solutions of iodine, potassium iodide.8) After the concentrations bromine, chlorine, iodine monobromide or be were determined, the solutions were diluted to nzene in carbon tetrachloride did not indicate appropriate concentrations. the presence of maximum absorption peaks in The solution of iodine monobromide in carbon the vicinity of 2900 A. When the absorption tetrachloride was prepared by dissolving an spectra of the solutions of a mixture of benzene equivalent quantity of elemental iodine into with iodine, bromine, chlorine or iodine mon- bromine solutions whose concentrations had obromide in carbon tetrachloride were measured, already been determined. however, absorption maxima were observed in The solution of benzene in carbon tetrachloride the region of wave lengths near 2900 A. was prepared by weighing an appropriate quantity The maximum absorptions observed are attri- of benzene into a volumetric flask and adding * The total v이 ume after mixin응 the two solutions was assu carbon tetrachloride to make up to volume. med to be the sum of those of the two solutions in the All the stock solutions were brought to 25° calculation of concentrations of the resulting solutions. 156 崔相業 •張石柱 •權純子 大韓化學會誌 buted to the formation of the complexes of 1 ; 1_ A—a0 — a—a0 L ” ' (^a — a0)K (6). benzene with the ha!o흉 ens or the interhalogen in solution. The complexes of this type are This assumption (equation 5) was found to be assumed to be the one to one molecular compl reasonable from the values of K, a, aQ, A and exes, as was first proposed by Benesi and Hild 〔B] “ obtained on all the systems in the present ebrand for the system of benzene---------- in study. (Tables H, and M) carbon tetrachloride.。 After the values of a0 were determined expe D + B 二 =C (1), rimentally, the quantities of J.{A~ where D denotes the benzene molecules, B the a0were plotted against〔D〕“ The plots molecules of iodine, bromine, chlorine or iodine indicated good linearity between the two quant monobromide, and C the one to one molecular ities in all the systems examined.