GB661806A - Improvements in or relating to the production of dichlorobutenes - Google Patents

Abstract

Dichlorobutenes are made by the vapour phase reaction between preheated butadiene and preheated chlorine, the chlorine and at least one mol. of butadiene per mol. of chlorine are introduced into an unpacked initial reaction zone wherein the reactants are thoroughly and rapidly mixed during a relatively short contact time, the temperature in said zone being controlled at a level somewhat above that required to insure a completely vaporous reaction system and the resultant gaseous mixture is subjected in a final reaction zone and during a relatively longer contact time, to a temperature appreciably higher than that of the initial reaction zone but below that at which substantial substitution chlorination of the butadiene takes place. The latter temperature is defined as that temperature at which more than about 5 per cent of the reaction takes place via substitution. 1,4-Dichlorobutene-2 and 3,4-dichlorobutene-1 are the primary products. At pressures of 0.5-2.0 atmos. the mol. ratio of butadiene to chlorine may be 1 : 1 to 16 : 1, temperatures 140-220 DEG C. in the initial and 200-450 DEG C. in the final zones, space velocities of 1500-100,000 and 30-300 vols. of gas at N.T.P. per vol. of initial and final reaction zones per hour respectively and a volume ratio of initial to final reactor of 1 : 10 to 1 : 1000. Preferably the mol. ratio of butadiene to chlorine is 3 : 1 to 6 : 1, initial and final temperature ranges of 160-190 DEG C. and 250-350 DEG C. respectively, and of initial to final reactor volume of 1 : 50 to 1 : 300. The mixing of the preheated reactants must not result in a temperature higher than that to be used in the initial zone. Inert diluents may be used to absorb heat. Products may be isolated by fractional distillation, approximately equal amounts of the two specified compounds being obtained. Unreacted butadiene may be recycled after removal of hydrochloric acid. Elongated or tubular reactors are preferred and the connections between vessels should be conical or graduated to avoid dead spaces. Water should be absent. Chlorination catalysts and packing or contact materials may be used in the final zone. Downflow operation is preferred. Chlorine may be injected at several points in the system including the final reactor. In examples: (1) butadiene at 140 DEG C. and chlorine at 124 DEG C. are thoroughly mixed by means of a tee mixer and reacted at 175 DEG C. in the initial and 250 DEG C. in the final zones to yield dichlorobutadienes, and examples (2)-(8) illustrate the effect of varying the temperatures and space velocities in the reaction of (1).