The Thermal Decomposition of Dimethyl Disulphide

Abstract

The thermal decomposition of dimethyl disulphide has been stitdied in the gaseous state by a static method. The primary reaction, which follows a reproducible induction period, produces one mole of methyl rnercaptan per mole of disulphide, together with a product of low volatility believed to be a thioformaldehyde polymer:There is also a competing reaction producing a large quantity of hydrogen sulphide. 'The remaining volatile products, hydrocarbons of two or more carbon atoms (believed to be chiefly ethylene), free sulphur, polysulphides, and carbon disulphide are formed either by the latter reaction or by the extensive decomposition of products. The decomposition is catalyzed by hydrogen sulphide, and more strongly by the complete reaction mixture. A mechanism is proposed for the main reaction.The present investigation was undertaken as a contribution to our fragmentary understanding of the mechanisms of reactions i~lvolvi~lg the carbonsulphur bond system in organic sulphur compounds. The C-S-S-C bond system of dimethyl disulphide was of special interest. Little is known about the thermal deconlposition of the alkyl disulphides, although the thermal decompositio~l of aryl disulphides has received some study. The work of Schonberg, Mustafa, and Askar (10) suggests that diphenyl disulphide dissociates a t the S-S bond into two free aryl thial radicals. In an early investigation Otto and Rossing (8) found that on distillation a t atmospheric pressure diamyl disulphide (b.p. 248" C.) gradually decomposes into sulphur or sulphur-rich substances and a tarry residue. Bezzi (3) reported that dioctyl disulphide decomposes a t its boiling point of 190" C. a t 15 mm. Faragher, Morrell, and Comay (7) found that decomposition of vaporized naphtha solutio~ls of various alkyl disulphides a t 496" C. produces the corresponding alkyl mercaptan, hydrogen sulphide, free sulphur, alkyl sulphides, thiophenes, and saturated and unsaturated hydrocarbons.In some preliminary experiments in this laboratory it was found by Patrick (9) that dimethyl and diethyl disulphides decompose above 300" C. yielding co~nplex pressure-time curves. The homogeneous decomposition of dimethyl disulphide was found to produce large amounts of mercaptan and hydrogen sulphide. E X P E R I M E N T A L ReagentsT h e dimethyl disulphide, obtained from Eastman I<odak Co., Rochester, New York, gave negative tests for mercaptans, hydrogen sulphide, free 'Manuscript

Hydrogen Peroxide, Part Three. Chapter 7: Chemical Properties. Chapter 8: Decomposition Processes

“…Furthermore, the individual reactions have been studiod separatel)y, and tha kinetics elabi3ihed in t'arms of concentration dependence, reaction rate constants, frequency factorooand ac.tivation e0ergies (73, 115,116), and upon the basis of this knowledge the rate of the catalysis may be predicted for a given set of conditions. It is obvious that the rates of the two reactions must be equal if one form t the catalyst is not to become exhausted.…”

Gas‐phase thermolysis of aryl tert‐butyl disulphides

“…I t is unlikely that the two reaction products in equation (1) are formed by the intervention of radicals originating from homolytic C-S or S-S bond fission. A unimolecular mechanism, involving a four-centre cuadropolar cyclic transition state, l3 similar to that proposed for homologous sulphides and ethers,' seems to be the most likely path for product formation in equation (1). The fact that the mass spectra of these disulphides clearIy show the peak of rn/z corresponding to the aryl disulphane [C~HSSSH, m / z = 142, 96%; 48%; p-N02C6H4SSH, m/z 187, 9.2%; base peak, C4Hy m/z 57; 70eV) confirms that the 1-3 hydrogen trariser ,mechanism bccurs also' under electron impact c~fldltious ' ' Table 8 shows Table 7 gives the rate coefficients, calculated at 390 and 450°C by using the respective Arrhenius parameters, for the aryl tert-butyl disulphides, and also those for di-tert-butyl disulphide.…”

10.1007/s10975-008-2013-2

“…In the case of DMDS, this process yields methanethio groups (ëç 3 S). DMDS decomposition can yield thioformaldehyde, which can partially polymerize into (CH 2 S) n [5]. For example, basic sites can abstract a proton from the methanethio fragment to form an OH group and a ëç 2 S group.…”