Sulphenamides

Sulphenamides.—A variety of bivalent sulphur compounds act as sulphenyl-ating reagents towards amines, giving sulphenamides, and most routes to these compounds are of this type. The copper(i)-catalysed reaction of azides with alkanethiols gives sulphenamides, in addition to the corre sponding primary amine and disulphide arenethiols give only amine and disulphide, the sulphenamide being entirely converted into these products. 

Transamination reactions of sulphenamides provide convenient access to particular derivatives a useful source of sulphenyl compounds is a thiophthalimide (148), - whose use is advocated for 

Kumamoto, S. Kobayashi, and T. Mukaiyama, Bull. Chem. Soc. Japan, 1972, 45, 866. 

4- amino-diphenyl sulphides is accounted for in terms of homolysis of the 

Preparations of Thiocyanates.—Syntheses from metal thiocyanates have been described involving aryl thallium(iii) acetate perchlorates and cop-per(n) thiocyanate, and the Se analogue using KSeCN with alkyl 

Uridine or 2 -deoxyuridine give the 5-thiocyanato-derivatives by substitu-ticm with thiocyanogen chloride, opening a route to biologically active 5-mercaptopyrimidines through dithiothreitol reduction of the thiocyanate. 

A novel ring-cleavage reaction involving mesoicmic 1,3,4-thiadiazoles leads to S-cyanothioimidates R N=CR SCN.  

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The Goodyear vulcanization process takes hours or even days to be produced. Accelerators can be added to reduce the vulcanization time. Accelerators are derived from aniline and other amines, and the most efficient are the mercaptoben-zothiazoles, guanidines, dithiocarbamates, and thiurams (Fig. 32). Sulphenamides can also be used as accelerators for rubber vulcanization. A major change in the sulphur vulcanization was the substitution of lead oxide by zinc oxide. Zinc oxide is an activator of the accelerator system, and the amount generally added in rubber formulations is 3 to 5 phr. Fatty acids (mainly stearic acid) are also added to avoid low curing rates. Today, the cross-linking of any unsaturated rubber can be accomplished in minutes by heating rubber with sulphur, zinc oxide, a fatty acid and the appropriate accelerator. 

Figure 8.5 Chemical transformation of omeprazole to the corresponding sulphenamide under add conditions and the subsequent modification of an enzyme cysteine residue by the sulphenamide.

However, the conversion of omeprazole to the active sulphenamide does not result in formation of a reversible enzyme inhibitor, but rather results in in situ formation of a powerful affinity label. Hence we can consider omeprazole to be a unique example of quiescent affinity labeling in which selectivity results from the unique environment of the target enzyme. 

Abbreviation for cyclohexylbenzothiazole sulphenamide, the first of the sulphenamide range of delayed action accelerators. 

A non-sulphur vulcanising agent for natural rubber and some types of synthetic rubber. One trade name is Dicup. /V,A/-Dicyclohexyl-2-benzothiazole sulphenamide... 

Abbreviation for the organic accelerator cyclohexylbenzothiazole sulphenamide, also abbreviated to CBS. 

Abbreviation for A-isopropylthio-A-cyclohexylbenzothiazyl-2-sulphenamide, a prevulcanisation inhibitor. 

Abbreviation for Nigerian Standard Rubber. A/-terf-Butyl-2-Benzothiazole Sulphenamide... 

Organic accelerators of the thiazole class having delayed action and finding particular application in tyre compounds containing furnace blacks. Sulphenamides are manufactured from mercaptobenzothiazole by reaction with an amine, the nature of which determines the degree of delayed action. 

Benzothiazole sulphenamide accelerators are suitable for semi-efficient and efficient vulcanisation systems. 

Addition of bis-(3-triethoxysilylpropyl)-tetrasulphide plus accelerator and sulphur can counter loss of crosslinking. Accelerator systems which respond to this antireversion agent are the thiazoles and the sulphenamides. Thiurams do not respond. For cure state equilibrium to be maintained the proportions of the three constituents (sulphur, accelerator and antireversion agent) are adjusted to give a constant modulus. 

Mono- or di-sulphenamides of pentachlorothiophenol are claimed to provide reversion resistance. 

Dithiophosphates such as zinc dibutyl dithiophosphate used with a sulphenamide can give improved reversion resistance. 

TV-Cyclohexylthiophthal i m idc (CTP) functions as an effective retarder of vulcanisation for accelerators in the sulphenamide classes. It produces scorch retardation without effect on compound modulus. It is not effective, however, in other classes of vulcanisation systems, notably those based on thiazoles, thiurams and dithiocarbamates. 

General.—Triethyl phosphite has been used to achieve stepwise O-ethylation of phosphoric and benzylphosphonic acids.5 The disulphide linkage in bis(phosphinyl) disulphides is cleaved by ammonia in a suitable solvent to yield the phosphinyl-sulphenamides (l).6... 

Oxophosphoranesulphenamides, obtainable with difficulty from oxophosphoranesulphenyl chlorides and amines, are readily obtained from the amine and bis-(dialkoxyphosphinyl) disulphides 88 deoxygenation and desulphurization of the sulphenamides has been observed (Scheme 6).87... 

The nitrophenylsulphenimine 71 is formed from the sulphenamide 70 and N-chlorosuccinimide in the presence of triethylamine. The imine reacts with Grignard compounds RMgBr to yield sulphenamides 72, which are cleaved by trifluoroacetic acid to the amino acids 73. Hence 71 functions as an electrophilic glycine equivalent84. 

A general method for the generation of aminyl radicals is by treatment of sulphenamides 340, prepared from secondary amines and A-benzenesulphenylphthalimide, with tributyltin hydride in the presence of AIBN (2,2/-azobisisobutyronitrile). The cyclopropyl derivative... 

Similarly to the sulphenamides, the photochemistry of isothiazole is initiated by the fission of the weakest S—N bond192 (equation 137 and 138). 

Kodama and co-workers [58] have reported TG-DSC curves for the analysis of the interaction between vulcanisation accelerators (tetramethylthiuram disulphide, dibenzothiazolyl disulphide, diphenylguanidine and N-cyclohexyl-2-benzothiazolyl-sulphenamide) and fillers (carbon black, white carbon, hard clay and CaC03). The initial melting point (MP) of the accelerators was largely influenced by the fillers. The higher the surface activity of the filler is, the lower and wider the melting range becomes. 

A TG-DTA study of the thermochemical processes occurring at vulcanisation temperatures with N-oxydiethylene-2-benzthiazyl sulphenamide and N-cyclohexyl-2-benzthiazyl sulphenamide and their mixtures with sulphur showed the formation of high molecular weight polysulphides [73]. The influence of metallic oxides (Fe203, Sn02) on hot air ageing of one-pack room temperature vulcanised fluorosilicone rubber has been studied by means of TG-DTA [74, 75]. TG-DTA and TG were both applied to study the thermal characteristics of room temperature vulcanised silicone rubber [76]. 

The direct amination of other nitroaromatics using organo sulphenamides such as N,N-tetramethylenethiocarbamoylsulphenadmide or N-phenyl-benzenesulphenadmidehas been demonstrated (3). 

Barnes et al developed an LC-MS method to identify vulcanisation agents and their breakdown products in food and drink samples. A large sample of 236 retail foodstuffs were analysed for the presence of 2-mercaptobenzothiazole (MBT) and its breakdown product mercapto-benzothiazole (MB). The accelerators 2-mercaptobenzothiazyl (MBTS) and A-cyclohexyl-2-benzothiazole sulphenamide (CBS), which are commonly used in food contact rubbers, were also looked for. MBT and MB are also known to be breakdown products of these two compounds. The detection limit for these species was found to depend on the food product type and ranged from 0.005-0.043 mg/kg. No MBT, MB, MBTS or CBS were detected in any of the samples above these levels. 

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