DiSulphides, alkyl

The ease with which the hydrogen atom is detached from the sulphur is noteworthy (analogy with H2S) even atmospheric oxygen gradually converts the mercaptans into aryl or alkyl disulphides, and mild oxidising agents do so at once ... 

Carbon-sulphur bond homolysis has been shown to be, in addition to sulphur-sulphur bond homolysis, a primary process in the photolysis of disulphides in solution. Sulphur-sulphur bond homolysis is, however, responsible for the establishment of an equilibrium between various alkyl disulphides on irradiation." Other liquid-phase studies of the photodecomposition of acyclic alkyl disulphides have been reported," -and the quantum yield for the formation of methyl ethyl disulphide from methyl disulphide and ethyl disulphide has been determined. ... 

Simple alkyl disulphides, in contrast to monosulphides, show considerable inhibitory activity, which diminishes on passing to more complex aryl and alkyl analogues. 

The facile cleavage of alkyl disulphides by silver nitrate and sodium methanesulphinate provides a new route to thiolsulphonate esters (Scheme 161). 

RCO2H + RSTI + (Et0)aP(0)Cl] i acid chlorides (RCOCI + Bu STI) aldehydes (R CHO + R SSR R COSR by irradiation)and ketones [R COR converted into the tosylhydrazone, TosNHN=CR R + HCN + EtSH + HCl TosNHNHCR R C(SEt)=NH2+ Cl" -> RiR2CHC(0)SEt on pyrolysis] [R COR + R R CClCOCl + HCHO + Bu gBSPh -> R R C-(OH)CR R C(0)SPh]. The conventional route to thiol-esters from metal thio-carboxylates has been extended to t-amino-alkyl-Bunte salts as the source of the 5-substituent (primary and secondary amino-alkyl-Bunte salts, however, yield acylamido-alkyl disulphides). ... 

Low substrate selectivity accompanying high positional selectivity was also found in isopropylation of a range of alkyl and halogenobenzenes by /-propyl bromide or propene in nitromethane, tetramethylene sulphone, sulphur dioxide, or carbon disulphide, as indicated by the relative rates in Table 86. The toluene benzene reactivity ratio was measured under a wide range of conditions, and varied with /-propyl bromide (at 25 °C) from 1.41 (aluminium chloride-sulphur... 

Few racemic alkyl p-tolyl sulphoxides were prepared in rather low yields (16—40%) by the reaction of Grignard reagents with mixed anhydrides 108, 109 and compound HO formed in situ from p-toluenesulphinic acid and 3-phthalimidoxy-l,2-benzoisothiazole 1, 1-dioxide167 (equation 59). The mixed anhydrides 109 or 110 when reacted with cyclopen-tene and cyclohexene enamines 111 gave the corresponding a-ketocycloalkyl sulphoxides 112 in low yields (10-41%) along with small amounts of several by-products such as disulphides and thiosulphonates167 (equation 60). 

Rajanikanth and Ravindranath44 have recently published a deoxygenation reaction for sulphoxides that uses metallic lithium in refluxing dimethoxyethane. Dialkyl and alkyl phenyl sulphoxides were reduced cleanly in yields around 70%, even if sterically hindered, but benzyl sulphoxides gave mixtures of products. For example, benzyl phenyl sulphoxide gave frans-stilbene (33%), benzyl phenyl sulphide (20%) and diphenyl disulphide (47%). These products can be rationalized by reaction pathways such as in equation (17) ... 

Carbon disulphide methanol phenol n-hexane methyl n-butyl ketone organophosphorus compounds tetra-alkyl lead compounds. 

Allyl propyl disulphide a-Alumina, see Aluminium oxide Aluminium as Al Metal dust Pyro powders Welding (umes Soluble salts Alkyls (NOC)... 

MDHS 14 General method for the gravimetric determination of respirable and total dust MDHS 15 Carbon disulphide MDHS 16 Mercury vapour in air Laboratory method using hopcalite adsorbent tubes, and acid dissolution with cold vapour atomic absorption spectrometric analysis MDHS 17 Benzene in air Laboratory method using charcoal adsorbent tubes, solvent desorption and gas chromatography MDHS 18 Tetra alkyl lead compounds in air Continuous on-site monitoring method using PAC Check atomic absorption spirometry... 

Propiolactone is one example. It will alkylate amino, imino, hydroxyl and carboxyl groups, all of which occur in proteins, and react also with thiol and disulphide groups responsible for the secondary structure of proteins and the activity of some enzymes. 

Another approach was developed by Scott in the 1970 s (7.8) which utilises the same mechanochemistry used previously by Watson to initiate the Kharacsh-type addition of substituted alkyl mercaptans and disulphides to olefinic double bonds in unsaturated polymers. More recently, this approach was used to react a variety of additives (both antioxidants and modifiers) other than sulphur-containing compounds with saturated hydrocarbon polymers in the melt. In this method, mechanochemically formed alkyl radicals during the processing operation are utilised to produce polymer-bound functions which can either improve the additive performance and/or modify polymer properties (Al-Malaika, S., Quinn, N., and Scott, 6 Al-Malaika, S., Ibrahim, A., and Scott, 6., Aston University, Birmingham, unpublished work). This has provided a potential solution to the problem of loss of antioxidants by volatilisation or extraction since such antioxidants can only be removed by breaking chemical bonds. It can also provide substantial improvement to polymer properties, for example, in composites, under aggresive environments. 

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