Atomization monosulphides

Figure 11.15. Typical chemical groupings in a sulphur-vulcanised natural rubber network, (a) Monosulphide cross-link (b) disulphide cross-link (c) polysulphide cross-link (j = 3-6) (d) parallel vicinal cross-link (n = 1-6) attached to adjacent main-chain atoms and which have the same influence as a single cross-link (e) cross-links attached to common or adjacent carbon atom (f) intra-chain cyclic monosulphide (g) intra-chain cyclic disulphide (h) pendent sulphide group terminated by moiety X derived from accelerator (i) conjugated diene (j) conjugated triene (k) extra-network material (1) carbon-carbon cross-links (probably absent)...

In an attempt to prepare a phosphathiosemicarbazide (159) the diphosphine monosulphide (160) was obtained instead. This surprising result was explained by attack of the jhlorophosphine at sulphur instead of at nitrogen as shown. Another unexpected result was the attempted Staudinger reaction of trimethylsilyl azide with (161) which gave (162) the reaction is probably initiated by azide attack at the thiocarbonyl group in preference to the phosphorus atom. 

The monosulphide and polysulphides are formed by burning the metals in sulphur vapour, by the action of sulphur on the metals dissolved in liquid ammonia, and by the action of the molten metals on sulphur dissolved in toluene. Hydrates or alcoholates and, in some cases, the anhydrous compounds may be prepared by dissolving sulphur in hot solutions of the hydrosulphides or monosulphides. Potassium, rubidium and caesium give all the sulphides where = 1, 2, 3, 4, 5, or 6 sodium only up to the pentasulphide, and lithium only those for which x = 1, 2 and 4 (Pearson and Robinson, 1931). All the metals form two polysulphides of relatively outstanding stability one is invariably the disulphide, and the other tetrasulphide in the case of lithium or sodium, and pentasulphide in the case of potassium, rubidium or caesium. The amount of water of crystallisation and the solubility decrease with increase in atomic number of the metal, the gradation being most marked between sodium and potassium. 

The monosulphides occur as hexagonal crystals which always show a deficiency of metal atoms without heterogeneity of structure (Fig. 260),... 

Apart from the extreme compounds TiS3 and TijS the sulphides of Ti include TiS2 and TiS, with the simple (h.c.p.) Cdl2 and NlAs structures, and a series of phases with compositions intermediate between those of the disulphide and monosulphide (Table 17.8). These phases have structures based on more complex c.p. sequences in which Ti atoms occupy octahedral interstices. Certain layers of metal atom sites are fully (or almost fully) occupied while others are only partially occupied (at random)-contrast the Cr sulphides Cr7Sg, CrgSg, and Cr3S4, in which the packing of the S atoms remains the same (h.c.p.). 

Because it is well established that radical cations of monoamines and monosulphides have substantial h)q5erfine couplings only for the protons at carbon atoms adjacent to the radical centre, " nitrogen-centred Cys can develop polarizations only for of the substrate, while sulphur-centred Cys must cause both... 

The structure of ebonite is basically similar to that of a soft vulcanizate prepared by the use of a low accelerator to sulphur ratio (see Fig. 18.2) although, of course, there are far more sulphur-containing structures per unit volume and the material is essentially saturated. When ebonite is pyrolyzed, various 2-methylthiophens are obtained this suggests that a substantial proportion of the sulphur is present in cyclic monosulphide groups attached to the tertiary carbon atom in the main chain ... 

It is now possible to introduce a second parameter E which measures the cross-link efficiency after treatment with the triphenyl phosphine. On the assumption that treatment causes all cross-links to become monosulphidic the term (E -l) provides a measure of the combined sulphur not in cross-links , e.g. in pendent groups or in intra-chain cyclic sulphides. If the reaction does not proceed beyond the disulphide stage then this measure is given by (E - 2). Whilst it is tempting to use E - (E - 1 or 2) as a measure of the average value of the number of sulphur atoms in a cross-link, Jc, there is a possible error due to the removal of sulphur from cyclic sulphides and pendent sulphides by the triphenyl phosphine. 

The use of sulphur donors in place of elemental sulphur has been practised since the early 1920s when it was found that the accelerators tetramethyl thiuram disulphide and tetraethyl thiuram disulphide in conjunction with zinc oxide gave vulcanizates with improved ageing properties when compared with conventional accelerated sulphur systems. For many years it was believed that vulcanization was brought about by the abstraction of one sulphur atom from the disulphide to yield the corresponding monosulphide... 

Monosulphides with keto substituents in one alkyl side chain are inactive except where the CO-group is in the y-position to the sulphur atom, i.e. to form the grouping SCH2CH2CO when substantial activity results. More branched alkyl substituents enhance this activity. 

The reaction of sodium polysulphide with dihalides containing 4-5 carbon (or carbon + oxygen) atoms in the main chain may produce monosulphidic ring structures in addition to some linear polymer. This reflects the well-known stability of five- and six-membered ring structures and is illustrated in Table 15.2 (Berenbaum, 1%2). 

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