Patented May 13, 1947 2,420,623 UNITED STATES PATENT of FICE 2,420,623 PROCESS FOR PRODUCING THONY, CE LORDE Water H. Salzenberg, Wilmington, Del, and Michael Sveda, Cleveland, Ohio, assignors to E. I. du Pont de Nemours & Company, Wilming ton, Del, a corporation of Delaware No Drawing. Application November 25, 1943, Serial No. 511,684 4. Claims. (C. 23-203) 1. 2 This invention relates to the manufacture of single tube to a point below the liquid level and thionyl chloride and is more particularly directed introduced in the body of liquid. The gases could to processes involving the reaction of sulfur tri be introduced through separate tubes though it oxide, chlorine, and sulfur monochloride at a would be advisable to have some means of effect temperature above about 100° C. 5 ing agitation or of requiring the gases to pass Thionyl chloride has heretofore been produced upward through the liquid in a circuitous route. by batch processes and with only a poor yield. Instead of using gaseous chlorine and Sulfur tri It is an object of the present invention to pro oxide, these materials could be added as liquids. vide a process for the reaction of sulfur trioxide The reaction of sulfur monochloride with Sul and chlorine with sulfur monochloride to produce 10 fur trioxide and chlorine may be Summed up as thionyl chloride with a high yield. It is a further follows: object of this invention to provide a continuous process for the production of thionyl chloride. It is a still further obejct to provide processes for According to this equation two mols of Sulfur the production of thionyl chloride using sulfur 5 trioxide are required for each mol of chlorine but trioxide, chlorine, and sulfur as raw materials. it is preferred that an excess of chlorine be main Still further objects will become apparent here tained. Thus from about 1.5 to 2 mols of sulfur in after. trioxide should be used for each mol of chlorine. The foregoing and other objects of the inven In the beginning of a batch operation or a Con tion are attained by reacting sulfur trioxide and 20 tinuous operation according to the invention the chlorine with sulfur monochloride at a tempera reactor should be partly, say about two-thirds ture above about 100° C. For a continuous proc filled with sulfur monochloride. The sulfur ess the Sulfur monochloride is contained in a heel monochloride may conveniently be prepared in which also contains a small amount of thionyl situ by putting molten sulfur into the reaction chloride, the equilibrium composition of the heel 25 vessel and passing chlorine through it to produce being maintained by withdrawing thionyl chloride sulfur monochloride. It will also be understood as it forms and by supplying sulfur monochloride that in a continuous process of the invention the to the heel to replace any which is reacted or sulfur monochloride content of the heel may be Withdrawn. increased by the addition of sulfur and by the use Typically then, sulfur trioxide and chlorine are 30 of the necessary extra, chlorine. run in gaSeOUIS form into a liquid body contain In a batch process operated according to the ing Sulfur monochloride. The liquid is main present invention the sulfur monochloride is con tained at a temperature above about 100° C. as verted to thionyl chloride and the product to more particularly described hereinafter and a gether with some unreacted Sulfur monochloride mixture of thionyl chloride, sulfur monochloride, 35 is removed by vaporization at the temperature sulfur dichloride, and sulfur dioxide pass from of reaction. the reaction vessel to a condenser. The sulfur In a continuous process according to the in dioxide together with some unreacted sulfur tri vention the sulfur monochloride will soon reach a Oxide and chlorine pass through the condenser constant composition and will form a heel to while thionyl chloride, sulfur monochloride and 4:0 which chlorine, sulfur trioxide and sulfur mono Sulfur dichloride are removed as a liquid mixture. chlorine and, if desired, sulfur may be added as The mixture is treated with sufficient sulfur to required. convert sulfur dichloride to sulfur monochloride The heel composition in a given process will and then thionyl chloride is distilled from the depend upon the temperature of Operation. At sulfur monochloride after which the sulfur mono 45 relatively low temperatures the thionyl chloride chloride may be returned to the reaction heel. content of the heel will be greater than at rela The thionyl chloride from the distillation is the tively higher temperatures. The reaction vessel product of the process and it will be found to be should be provided with suitable heating and of high purity and will represent a high yield on cooling means to adjust the temperature so that the basis of the reactants used. the heel will contain from about 3 to 15 per cent As has been noted above, sulfur trioxide and of thionyl chloride. More specifically, under pre chlorine are introduced into a liquid body of sul ferred conditions of operation, the heel will con fur monochloride. The gases are preferably tain from about 6 to 10 per cent of thionyl chlo mixed before they are introduced into the sulfur ride. The heel Will also contain. Some Sulfur monochloride and they are passed through a pentoxydichloride which, if desired, can be recoy 2,420,628 3 4. ered from time to time from the heel. The face of the liquid. The liquid was preheated to amounts of sulfur pentoxydichloride will be larg 100 C., and gaseous chlorine and Sulfur trioxide est when relatively low temperatures are used. were continuously premixed in a molar ratio of Generally it will be found that a temperature 1.79SO3: iCl2, and led beneath the surface of the of about 100° C. to 138° C. may be used for the Sulfur monochloride at a rate of 24.3 pounds batch or continuous processes of the present in (0.304 pound-mols) of sulfur trioxide... and 12.1 vention. The higher temperature is the boiling pounds (0.171 pound-mols) of chlorine per hour. point of sulfur monochloride and of course a ten Simultaneously, but through a separate inlet perature somewhat below this should crdinarily tube, sulfur monochloride was added continuous be used. It will generally be found most desir O ly at a rate of 51.7 pounds (0.383 pound-mols) able to use a temperature from about 105 to per hour. The heat of reaction was sufficient to about 110° C. maintain the liquid in the vessel at 107 C., a Catalysts may be used in the reaction and temperature 30° C. above the boiling point of there may be employed, for instance, a small thionyl chloride, and a mixture of thionyl chlo amount of antimony trichloride. There may be: ride and Sulfur monochloride containing some used, say, 0.1 per cent to about 3 per cent of sulfur dichloride was continuously distilled off. antimony trichloride. Instead of antimony tri The condensate, 225.5 pounds, containing about chloride any other catalyst for the reaction may 40 per cent thionyl chloride, 10 per cent dissolved be used and there may be employed, for instance; Sulfur dioxide, 10 per cent sulfur dichloride, and mercuric chloride or such chlorides of heavy 20 about 40 per cent sulfur monochloride, was dis metals as bismuth:trichloride. tilled. Over elemental Sulfur in order to convert The vapors, leaving the reaction Wessel Contain low-boiling Sulfur dichloride to. high-boiling sul relatively; large, amounts of thionyl chloride and fur monochloride, resulting in a thionyl chloride sulfur monochloride and a Small amount of Sul fraction of high purity. By distilling the crude fur dichloride. The gases, also: contain. Sulfur fraction Collected during a 3-hour run, as out dioxide and if the rate of flow of Sulfur trioxide lined above, 95.9 pounds (0.766 pound-mols) of and chlorine:is high then some of these may paSS thionyl chloride was obtained, corresponding to through unreacted. There Will. Of course. always 92 per cent yield based on a combined sulfur and be. a. Small. excess of chlorine. The vapors, as chlorine output. they leave the reaction Wessel, can be condensed 30 Eacample II directly and distilled, or they may be partially condensed, as, in a reflux. Condenser, and the A process of the invention was: carried out, as Sulfur monochloride-rich condensate returned to in Example I at a temperature of about 107 to the: reaction. Preferably the: vapors may go, di 10° C. but differs largely from Example I in tak rectly to a fractionating column for complete 35 ing the effluent gases from the reaction vessel and separation of Sulfur monochloride. passing them through molten sulfur and then Instead; of adding sulfur or sulfur mono-chlo through a plate column fractionating tower. The ride: to the reaction vessel, it may be found most Sulfur monochloride obtained from the bottom of advantageous to pass the effluent gases from the the fractionating column was returned to the re reaction through molten sulfur. This, can be 40 action vessel and the thionyl chloride product done; for example by passing the gases through Was of excellent purity. The yields. were sub a packed tower over which molten. Sulfur is stantially the Same as in Example I. flowed. Fine chlorine and the Sulfur dichloride in While certain illustrative processes have been the effluent gases will, of course, react with the ShoWin it will be understood that the invention is sulfur" to form sulfur monochloride. Following 45 not to be limited thereby but that various proc the Sulfur treatment the gases: can be passed to eSSes may be employed reacting sulfur trioxide, a, plate, column fractionating tower or eise con chlorine, and sulfur monochloride without de densed for later distillation. parting from the spirit of this invention. The relatively low boiling gases such as sulfur We claim: dioxide and some of the sulfur trioxide may be 50 1. In a continuous process for the production recovered in various Suitable Ways and One may, of thionyl chloride, the steps comprising passing if desired. Oxidize: the Sulfur dioxide to. Sulfur tri Sulfur trioxide and chlorine at the rate of 1.5 oxide; and use; the mixture after a suitable addi to 2 mols of sulfur trioxide to each mol of chlo tion of chlorine for reaction with sulfur mono rine into a heel of liquid sulfur monochloride chloride, 55 which contains about 3 to 15 per cent of thionyl If the vapors leaving the reaction vessel are chloride and which is maintained at a temper simply condensed the condensate can be boiled ature of about 105 to 110° C., removing vapors to distill off the thionyl chloride from sulfur from the reaction Zone through a partial con monochloride and the sulfur monochloride may denser, condensing the vapors withdrawn but be returned to the reaction heel. If the effluent 60 permitting Sulfur dioxide, Sulfur trioxide, and vapors were not treated with sulfur then sulfur chlorine to be separated therefron, treating the may be used before the distillation of the con condensate with sulfur to convert any sulfur di densate to; effect conversion of the Sulfur dichlo chloride to Sulfur monochloride and distilling ride to Sulfur anonochloride. thionyl chloride from the condensate, separating In order that, the invention may be better un 65 the sulfur monochloride from any unused sulfur, derstood reference should be had to the follow and returning it to the said heel, ing illustrative. examples: 2. In a continuous process for the production of thionyl chloride the steps comprising passing Eacample I Sulfur trioxide and chlorine at the rate of 1.5 to Eighty pounds: (0.592 pound-mols); of sulfur 70 2 nos of Sulfur trioxide to each mol of chlorine monochloride, and 0.8-pound of antimony trichlo into a heel of liquid Sulfur monochloride which ride, were placed in a cylindrical, iron reaction contains about 3 to 15 per cent of thionyl chlo vessel, 12' internal diameter and 36' high, fitted ride and Which is maintained at a temperature with a heating and cooling jacket, a condenser, of about 105 to 110° C., removing vapors. from and a gas inlet. tube. extending 10' below the Sur 75 the reaction zone, treating the vapors, with sui 2,420,623 S 6 fur, fractionating the vapors to separate the Zone, treating the product thus withdrawn with thionyl chloride product from sulfur monochlo Sulfur to effect conversion of Sulfur dichloride ride, and returning sulfur monicchloride to the to sulfur monochloride. Said heel. WALTER, H. SATZENBERG. 3. In a process for the production of thionyl MICHAE SWEDA. chloride the steps comprising passing Sulfur trioxide and chlorine into a heel of liquid sulfur REFERENCES CEO monochloride which contains thionyl chloride and which is maintained at a temperature of ihe following references are of record in the about 105° to 110° C., removing vapors from the file of this patent: reaction zone, treating the product thus with FOREIGN PATENTS drawn with sulfur to effect conversion of sulfur Number Country Date dichloride to sulfur monochloride. 4. In a process for the production of thionyl 139,455 Germany ------June 21, 1902 chloride the steps comprising passing sulfur tri 5 OTHER REFERENCES oxide and chlorine into a heel of liquid sulfur Inorganic and Theoretical Chemistry, Mellor, monochloride which contains thionyl chloride and which is maintained at a temperature above vol. X; Longmans, London, pages 657 and 658. about 100° C., removing vapors from the reaction (Copy in Div. 59.)