Sept., 1922
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
sulfide. The second class either contains carbosulfhydryl groups or forms them by reactions during vulcanization. This class includes mercaptans, dithiocarbamates, thioureas, xanthates, etc., and is said to function through the formation of the metallic salts which are described as forming mercaptide polysulfides that contain per-sulfur sufficiently active to react with rubber a t ordinary temperatures. I n support of this general theory there has been prepared an active type of zinc sulfide4 which forms polysulfides and is an active accelerator. Thiocarbanilide is comparatively inactive in the absence of zinc oxide and has been found to form zinc and lead mercaptides through its tautomeric mercapto form. Twiss21energetically disagrees with this theory of the action of zinc mercaptides, dithiocarbamates, xanthates, etc., calling attention to the fact that the zinc salts still need the presence of zinc oxide to bring out their full vulcanizing power. Bedford and SebreIlz2found that their action was also increased, in rubber cements, by the presence of aniline, and Cadwellen22 finds the same action of aniline and other amines, not only on zinc dithiocarbamates, xanthates, etc., but also on thiuram disulfides and xanthic disulfides : (R2N-CS-S-S-CS-NR2 and RO-CS-S-SCS-OR) BruniI8 offers a second theory for the action of zinc oxide, which parallels the above-mentioned theory up to the formation of the zinc salt of the thio acid or mercaptan. H e states that sulfur reacts with the zinc salt to form a disulfide and zinc sulfide according to the equation: (R~N-CS-S-)Z Zn S = (RzN-CS-S)~ f ZnS
+
This disulfide is then believed to vulcanize the rubber by reverting to the monosulfide, which in turn reacts with elemental sulfur to reform the disulfide. TwissZ3again calls attention to the need of zinc oxide for bringing out the full effect of the disulfide, even when the disulfide is formed outside the rubber mix and compounded as such, under which conditions Bruni’s theoretical need or zinc oxide should be absent. Twiss believes that there is some reaction product common to disulfides, dithiocarbamates, zinc oxide, and sulfur, which forms the true accelerator or vulcanizing agent. Further in regard to the thiuram disulfides, it has been shown that they do not vulcanize rubber-sulfur-zinc oxide mixes a t room temperature as do the zinc salts described below, while the action of hydrogen sulfide14even at ordinary temperatures, changes the disulfide to a dithiocarbamate, and in the presence of zinc oxide starts the process of rapid vulcanization without the application of heat. The abovementioned action of aniline in causing thiuram disulfides to vulcanize rubber at ordinary temperatures may be explained in the same manner according to Fromm24 who showed that aniline and other primary amines easily react with these disulfides to form dithiocarbamates. Thiuram disulfides as well as dithiocarbamates, derived from secondary amines, are found b y Twiss to be much more active than those from primary amines. I n general, the study of the mechanism of vulcanisation seems to be concentrating on the action of accelerators which need tho aid of zinc oxide. Little has been published on the effect of litharge, lime or magnesia. The action of aniline, aldehyde ammonia, para nitroso-dimethyl aniline, and many other accelerators still remains practically untouched. The important factor of temperature, the nonactivity of certain accelerators a t temperatures where others are violently active, has been commented on as due to the relative stability or instability of the reaction products, but a satisfactory explanation has not yet appeared. 18
Brit. Patent Application 177,493 (1922).
*a
J . SOC.Chem. Ind., 61 (1922), 81T.
24
Ann., 848, 144.
857
This, in brief, is the present status of the chemistry of rubber vulcanization. The advent of the organic accelerator has furnished the rubber chemist definite chemical compounds for use in vulcanization and provided a means of throwing some light on the mechanism of the process. I n general, the polysulfide theory is fairly well accepted; in detail there are many differences of opinion and many unsolved problems. History, in connection with rubber chemistry, is being made a t a rapid rate and we await with extreme interest the developments of the immediate future.
D. H. Killeffer Succeeds R. T. Stokes Following the sudden death of the former secretary of the Biscuit and Cracker Manufacturers’ Association, the position was offered to and accepted by Mr. R. T. Stokes who had but JOURNAL. recently become associate editor of THIS Mr. D. H. Killeffer has been appointed associate editor to succeed Mr. Stokes. Mr. Killeffer is a graduate of the University of North Carolina. After graduation he became a member of the staff of the Brown Laboratories of Nashville and served in the department of tests of the Nashville, Chattanooga, and St. Louis Railway. Subsequently he was research chemist on plant development for the Calco Chemical Co., and since January 1920 has been a member of the editorial staff of Drug and Chemical Markets. Mr. Killeffer will have head. quarters in New York but our readers will meet him frequently in other Darts of the countrv. particularly in industrial chemi: D . H . KILLEFFER cal fields. Meeting of Chemists at U t r e c h t At Utrecht on June 21 to 23 there was held the first gathering since the war at which chemists from Germany and Austria have met chemists from England, America, and other countries. America: L. M. Dennis, D. A. MacInnes, W. A. Noyes. Austria: E. Abel, J Billiter, F. Emich, A. Kailan, A. Klemenc, F. Pregl, A. Skrabal, R. Wegecheider. Czechoslouakia: J. V. Dubsky, A. Simek. Denmark: N. €3. Bjerrum, J. N. Bronsted, J. Petersen, Chr. Winther. England: E. C. C. Baly, F. G. Donnan, W. C. McLewis. Germany: M. Bodenstein, G. Bredig, 0. Hahn, P. Pfeiffer, R. Schenck, W. Schlenck, A. Stock, P. Walden, H. Wieland. Holland: J. Backer, J. J. Blansma, Ernst Cohen, A. F. Holleman, F. M. Jaeger, H. R. Kruyt, W. Reinders, P. van Romburg. Lithuania: M. Centnerschwer. Russia: N. Schilow. Switzerland: J. Piccard.
The original suggestion of the meeting was made by Professor Donnan of London, and the preliminary plans were made a t a meeting in the home of Professor Cohen of Utrecht in June 1921. The details were carried out by Professor Cohen. The following scientific papers were read and discussed: E. C. C. BALY. Photochemical Catalysis. P. WALDEN. Free Radicals. W. A. NOYES.Positive and Negative Valences. W. SCHLENCK.Contributions to the Chemistry of Free Radicals and the Varying Affinity of Carbon Compounds. M. BODENSTEIN.The Photochemical Structure of Phosgene. I,. M. DENNIS. The Preparation and Properties of Metallic Germanium. H. WIELAND. Free Radicals. N. SCHILOW,Distribution Equilibria. J. PICCARD.Absorption Colors of the Second Class. E. ABEL. Direct and Indirect Esterification in Absolute and Aqueous Glycerol, According to Experiments of Karl Heidrich. A. KLSMENC. Vapor Pressures of Isometric Benzol Derivatives. A Proposal for the Introduction of a Small Unit of M. CENTNERSCHWER. Measure (Radion).
A t a reception in Hotel Pays-Bas on Wednesday afternoon, there were addresses of welcome by G. L. Voerman, President of the Chemical Society of Holland; Professor Went, President of the Royal Academy of Science of Amsterdam, and a response by W. A. Noyes. [W.A . Noyes, Urbana, Ill.]
