Formation of Mercaptides

Decomposition with HsS liberates sulfuric acid which may be harmful on evaporation. Among others, Cd also forms a fairly insoluble mercaptide with GSH. Ag forms highly insoluble precipitates with nearly all mer-captans. The foregoing reaction and also the one using Hg ions have been used for an amperometric titration of GSSG (41, 42). Disulfides suffer hydrolysis in aqueous solution expressed in the following way by Cecil (43)  

As you know, cleavage of the S—S bond also may be achieved by CN or SOs, one S-atom being converted into the mercaptan. 

In dealing with the effects of mercuriorganic compounds I only want to mention p-chloromercuribenzoate and Sal5Tgan. Colored compounds of this type are used for histochemical detection of thiols (cf. paper of Barnett and discussion remarks of Seligman in this volume). 

Metalloids too are able to form compounds with SH-groups. Concerning GSH among others the following arsenic compounds have been described (GS)3As from the reaction of AsjOj + GSH in methanol (40) (GS)2AsPh from PhAsCh or PhAsO 4- GSH (44) (GS)As(Ph)2 on reacting Lewisite and GSH (45). 

H2SeOs and HsTeOs form, with GSH in aqueous solution, yellow mer-captides, precipitating Se or Te in the elementary state when made alkaline (46). Alcohol precipitates from the yellow solution the Se compound which can be decomposed by alkali as follows (47)  

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Formation of mercaptides. It has been mentioned already that GSH is isolated as a slightly soluble Cu or Hg salt. The composition of the mercaptide formed with Hg sulfate in aqueous sulfuric acid is as follows (40) ... 

Another source of thermal instability arises from metal incorporation in the polymer via reaction of mercaptan with metal oxides. Formation of mercaptide groups can be minimized by incorporation of small amounts of sulfur. 

The efficiency of mercaptan removal is highest for light mercaptans (i.e R is a light hydrocarbon radical) and concentrated caustic solutions. The circulating caustic solution contains a dispersed Merox catalyst udiich promotes the conversion of mercaptans to disulfides at a relatively low tenoperatuie without ptmooting otho reactions and does not affect the formation of mercaptides. 

Di(thiocyano)thiophene also presents a different behavior at a mercury-dropping electrode and in the case of treatment by dipotassium salt of cyclooctatetraene dianion THF is the same solvent for both cases (Todres et al. 1979). The reaction between di(thiocyano) derivative and CjHgKj taken in equimolecular amounts leads to the formation of potassium salt of 2-mercapto-5-thiocyanothiophene (potassium mercaptide), potassium cyanide, and cyclooctatetraene (see Scheme 2.17). Potassium mer-... 

The interaction of alkyl halides with mercaptans or alkaline mercaptides prodnces thioalkyl derivatives. This is a typical nncleophilic substitution reaction, and one cannot tell by the nature of products whether or not it proceeds through the ion-radical stage. However, the version of the reaction between 5-bromo-5-nitro-l,3-dioxan and sodium ethylmercaptide can be explained only by the intermediate stage involving electron transfer. As found (Zorin et al. 1983), this reaction in DMSO leads to diethyldisulfide (yield 95%), sodium bromide (quantitative yield), and 5,5 -bis(5-nitro-l,3-dioxanyl) (yield 90%). UV irradiation markedly accelerates this reaction, whereas benzene nitro derivatives decelerate it. The result obtained shows that the process begins with the formation of ethylthiyl radicals and anion-radical of the substrate. Ethylthiyl radicals dimerize (diethyldisulfide is obtained), and anion-radicals of the substrate decompose monomolecularly to give 5-nitro-l,3-dioxa-5-cyclohexyl radicals. The latter radicals recombine and form the final dioxanyl (Scheme 4.4). 

The addition of a mercaptide to a nitrile provides the key reaction to the preparation of a thiazolidinone that shows diuretic activity. The hrst step in the reaction of ethyl 2-mercaptoacetate (105-2) with ethyl cyanoacetate (105-1) thus probably leads hrst to the formation of the addition product (105-3). The imino... 

The kinetics of the carbon disulfide elimination reaction were studied using PMR and visible spectroscopy (16). This spontaneous reaction was found to be first order in the M(RSXant)2 complexes (M = Ni, R = Et, r-Bu, Bz M = Pd, R =/ -Bu), both in the disappearance of the starting material and in the formation of the mercaptide-bridged species in CHC13 and THF. The pseudo-first-order kinetics observed in CS2 are attributed to an equilibrium between the M(RSXant)2 complexes and this solvent. Rate constants for the reaction are of the order of 10 3 to 10"1 min"1 depending on solvent, temperature, alkyl... 

In 1959, the coordinated mercaptide ion in the gold(III) complex (4) was found to undergo rapid alkylation with methyl iodide and ethyl bromide (e.g. equation 3).9 The reaction has since been used to great effect particularly in nickel(II) (3-mercaptoamine complexes.10,11 It has been demonstrated by kinetic studies that alkylation occurs without dissociation of the sulfur atom from nickel. The binuclear nickel complex (5) underwent stepwise alkylation with methyl iodide, benzyl bromide and substituted benzyl chlorides in second order reactions (equation 4). Bridging sulfur atoms were unreactive, as would be expected. Relative rate data were consistent with SN2 attack of sulfur at the saturated carbon atoms of the alkyl halide. The mononuclear complex (6) yielded octahedral complexes on alkylation (equation 5), but the reaction was complicated by the independent reversible formation of the trinuclear complex (7). Further reactions of this type have been used to form new chelate rings (see Section 7.4.3.1). 

Formation of disulfides From mercaptides Thioglycolic acid Fe3+. Cul+... 

Formation of a symmetrical sulphide (a) (e.g. dipropyl sulphide, Expt 5.204), is conveniently effected by boiling an alkyl halide (the source of carbocations) with sodium sulphide in ethanolic solution. Mixed sulphides (b) are prepared by alkylation of a thiolate salt (a mercaptide) with an alkyl halide (cf. Williamson s ether synthesis, Section 5.6.2, p. 583). In the case of an alkyl aryl sulphide (R-S Ar) where the aromatic ring contains activating nitro groups (see Section 6.5.3, p. 900), the aryl halide is used with the alkyl thiolate salt. The alternative alkylation of a substituted thiophenol is described in Section 8.3.4, p. 1160. The former procedure is illustrated by the preparation of isobutyl 2,4-dinitrophenyl sulphide (Expt 5.205) from l-chloro-2,4-dinitrobenzene and 2-methylpropane-1-thiol. 

A range of metal catalysts can be employed with peroxygen species for the effective oxidation of sulfur compounds. For example, branched-chain high molecular weight mercaptans are difficult to oxidize with hydrogen peroxide. However, this difficulty is overcome if the reaction is conducted with hydrogen peroxide in the presence of a copper(II) salt.395 The formation of a copper(I) mercaptide followed by its oxidation are believed to be the key steps. 

Halomercaptans are converted to thietanes by treatment with a as exemplified by the formation of 3-hydroxythietane 21 from 3-chloro-l-mercapto-2-propanol 20 4-thiocyano-2-pentanol 22 is converted to a mixture of cis- and trans-2,4-dimethylthietane 23 by treatment with sodium hydride. The latter reaction involves displacement of cyanate ion by the mercaptide ion. 2,2,4-Trimethylthietane was also prepared by this method. 

Weight loss and hardening of polymer Loss of compression set resistance and some polymer volatihsation Formation of a trace amount of acidity Formation of lead mercaptide segment in the polymer chain when PbOj is used as a curing agent... 

The two possible reactions of organotin mercaptide stabilizers, both ending in the formation of dialkyltin dichloride, are shown in Schemes 3.3.1 and 3.3.2. 

Nucleophilic attack by this species at the a-carbon atom will also be governed by the same steric considerations as in thermal decomposition and hence the inverse relationship of thermal stability and resistance to nucleophilic attack, and anti-wear activity and ease of nucleophilic attack. Further thermal processes involve olefin elimination from alkyl groups and lead to the formation of phosphorus acids. Nucleophilic substitutions of one phosphorus species by another leads to P-O-P structures and zinc mercaptide Zn(SR)2 as a reaction intermediate. Reaction of this mercaptide with dithiophosphate leads to trithiophosphates and eventually tetrathiophosphates. Finally, an oil-insoluble deposit is formed of a mixture of zinc thiophosphate and zinc pyro- and polypyrothiophosphates. 

The formation of a quaternary salt (7) upon heating 2,3-0-isopropylidene-5-0-(p-tolylsulfonyl)adenosine, observed by Clark, Todd, and Zussman and referred to elsewhere in this review, accounts for the low yield, since this monomolecular quaterni-zation takes place much more rapidly than bimolecular displacement of the p-tolyl-sulfonyloxy group by the methyl mercaptide ion. Recently, this difficulty has been overcome and a good yield of L-2-amino-4-(5-thioaden-5-yl)butyric acid obtained by the reaction of (9b) with the disodium salt of homocysteine in liquid ammonia. This compound had also been prepared enzymically. ... 

Although a conventional initiation of anionic polymerization by alkyl lithiums involves their addition to a C=C bond, an exceptional mode of initiation associated with ring-opening polymerization was reported by Morton and Kammereck186). Ethyl lithium seems to initiate polymerization of propylene sulphide, but the reaction involves first a desulphuration of the monomer, leading to the formation of lithium mercaptide ... 

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