View Article Online / Journal Homepage / Table of Contents for this issue 5 28 CALDWELL AND WERNER : DERIVATlVES OF L 11.-Dewha t ives o,f Mul t ivalen t lodine. Part 111. The Action of Heat on Ioclobenxene Diclzloride, und on the ni- and p- Nitro- and p- Chloy*o-dcrivcctives. By WILLIAMCALDWELL and EMILALPHONSE WEHNER. IN his original paper on the preparation of iodobenzene dichloride (J.pr. Chem., 1886, [ ii], 33, 154) Willgerodt states that the compound decomposes at 115-120" with evolution of all the chlorine in the free state, leaving iodobenzene. The same change, he states, takes place when the substance is kept over sulphuric acid. Published on 01 January 1907. Downloaded by Universitat Politècnica de València 29/10/2014 12:21:21. Later (Ber., 1893, 25, 3494) he remarks that the dichloride, when exposed to ti,oist air, decomposes with evolution of hydrogen chloride. More recently (Bey., lS9S, 31, 1136) F. Keppler has shown that the compound when kept in sealed tubes, even in the dark, decomposes with formation of p-chloroiodobenzene. The iesults which we have obtained from a study of the action of heat on the three isomeric iodotoluene dichlorides have induced us to re-examine the behaviour of the iodobenzene derivative. We find that the dichloride, when heated, undergoes sudden decom- position at temperatures varying from 110-136", according to the rate of heating, and the main change takes place in accordance with the equation : C,H,*ICl, = C,H,ClI( 1 : 4) + HC1. The amount of chlorine evolved in the free state does not exceed 27 per cent. OE the theoretical. Rapid heating favours the formation View Article Online MULTlVALENT IODINE. PART 111. 529 of p-chloroiodobenzene, which is the sole substitution derivative produced. When iodobenzene dichloride is kept in a closed vessel or over sulphriric acid, no chlorine is evolved in the free state. It has already been shown (Werner, Trans., 1906, 89, 1632) that o-iodonitrobenzene dichloride when heat,ed loses all its chlorine in the free state, and this we fiud is also true in the case of the p-derivative; nz-iodonitro- benzene dichloride, on the other hand, decomposes at 103' with formation of a substitution product to the extent of 27 to 28 per cent. of the theoretical, p-Chloroiodobenzene forms a dichloride which decomposes at 112O, a substitution derivative being formetl in this case also to the extent of about 27 per cent. of the theoretical. Thus, whilst the nitro-group in 0- and p-positions completely prevents the forniation of a substitution product, its presence in the m-position has the same inhibiting effect as the chlorine atom in the p-position. E x P E it IME N TA L. Action of Heat 092 Iodobenxene Dichloride, C,H,*ICI,.-The results OF two experiments in which 2 grams of this substance were heated in the manner described in our previous paper are as follows : Sudden decom- Per- Percentage position centage of of the First traces of Cl+HCl Free C1 theoretical C1 evolved. evolved. evolved. for CI,. Experiment I. Heated slowly ... 102" 124" 6.97 27-0 ,, 11. ,, rapidly.. 87" 136-137" 5 '99 23.2 The numbers in the last column represent the percentage decom- position in accordance with the equation : Published on 01 January 1907. Downloaded by Universitat Politècnica de València 29/10/2014 12:21:21. C,H,*IClz = C,H,I + Cl,, proving that a large proportion of a substitution product is formed. In order to examine the products of decomposition, 112 grams of iodobeozene dichloride were decomposed by heat. The liquid product obtained was shaken with potassium hydroxide solution and finally dried over the solid hydroxide. It weighed 90 grams, and after several distillatiors was ultimakely separated into four fractions. Fractions I, 180--195O, and 11, 195-210°, consisted of iodobenzene, 26 and 21 grams respectively. Fraction 111, 210--225°, consisted of a mixture in equal proportions of iodobenzene and chloroiodobenzene, 7 grams. Fraction IV, 225-236", solidified on cooling to a crystalline mass, and was p-chll)roiodobenzene, m. p. 55*Eio, 20 grams. The composition of fractions I1 and III was determined by chlorina- tion and subsequent analyses of the dichlorides, Allowing for the View Article Online 530 DERIVATIVES OF MUL'I'IVALEXT K)T)INE. PART 111. loss accompanying the distillations, the proportion of p-chloroiodo- benzene produced was much less than when small quantities of the iodobenzene dichloride were decomposed. Action of C'hlovine on p-C7hZoroiodobenxene.-Twelve grams of 23-chloroiodobenzene were dissolved in chloroform, and chlorine was passed into the cold solution. There was no liberation of iodine. The tlichloride separated in pale yellow, microcry Ftalline needles. It was filtered by the aid of the pump, washed with chloroform, and dried in the air. Ten grams were obtained. 0 5 gave, on trituratioii with potassium iodide solution, C1, 0.11733 = 23'46. C,H,C1*ICl2 requires C1= 22.91 per cent, Action of Heat on. p-C?LZoroiodobenxene Dichlovide, C,H,CI -ICI,. -T wo grams were heated in the manner already described. At 83" the first trace of chlorine was evolved, and at 113' decomposition took place with effervescence, some hydrogen chloride being evolved. C1 evolved, 0.331 45 = 16.57 per cent. This corresponds to 72.32 per cent. of the theoretical decomposition in accordance with the equation : C,H,Cl*ICl, = C6H,ClI + C1,. A substitution product is formed to the extent of 27 to 28 per cent. of the theoretical. Action of Heat on m-Iodonit~obsnzeneDich7ode, N02*C6H,~~Cl,.- The m-iodonitrobenzene was puiified by distillation in steam. It was obtained in pale yellow crystals melting at 38*5O.* The dichloride forms glistening plates, resembling iodoforin in appearance. Two grams heated with the previously described precautions evolved chlorine at 65-46". At 103O sudden decomposition took place with Published on 01 January 1907. Downloaded by Universitat Politècnica de València 29/10/2014 12:21:21. effervescence, some hydrogen chloride being evolved. C1 evolved, 0.3233 = 16,165 per cent, which corresponds to 72-88 per cent. of the theoretical decomposition in accordance with equation : N0,*C6H,*ICl, = NO;C6H,I + C1, ; consequently a substitution product is also formed, in this rase to the extent of 27 to 28 per cent. of the theoretical. Action of Heat on p-Iodonitrobenxene Ilichloride, NG,*C6H,*IC12.- Two grams were heated as above described. Evolution of chlorine commenced at 106O, and continued gradually up to 173") at which temperature the product melted without any effervescence. C1 evolved, 0.4431 = 22.15. Theory for the loss of two atoms of chlorine = 22.18 per cent. * The melting point is recorded as 34" (Griess) and 36" (Korner). View Article Online DEPEEYSION OF FItEE%IK(; POINT OF HY1)ROGEN PEROXIDE. 531 The decornpositiou in this instance is therefore complete, and confirms the result obtained by Willgerodt. During the heating the p-iodo- nitrobenzene sublimes in beautiful, long, slender, pale yellow needles. U N I VEI~SITYCIIIWIC A I, T,.~RORATORY, TIUNITYCOI,I,I~GIS, DUELIN. Published on 01 January 1907. Downloaded by Universitat Politècnica de València 29/10/2014 12:21:21..