Thiol thiolate ions from

A kinetic study of the acid-catalysed loss of alkoxide and thiolate ions from alkoxide and thiolate ion adducts, respectively, of benzylidene Meldrum s acid, methoxy-benzylidene Meldrum s acid, and thiomethoxybenzylidene Meldrum s acid has been reported. The reactions appear to be subject to general acid catalysis, although the catalytic effect of buffers is weak and the bulk of the reported data refers to H+ catalysis. a-Carbon protonation and, in some cases, protonation of one of the carbonyl oxygens to form an enol compete with alkoxide or thiolate ion expulsion. This scenario rendered the kinetic analysis more complex but allowed the determination of p/fa values and of proton-transfer rate constants at the a-carbon. In conjunction with the previously reported data on the nucleophilic addition of RO and RS ions to the same Meldmm s acid derivatives, rate constants for nucleophilic addition by the respective neutral alcohols and thiols could also be calculated. ... 

TABLE 3. Second-order rate constants for the reaction of alkyl nitrites with the thiolate ions derived from three thiols in water at 25 °C... 

Sec. 18.8) from thiols by Sn2 reaction of thiolate ions with primary alkyl halides... 

As shown in Scheme 8.4, the resulting disulfide anion radical dissociates into a thiolate ion R-S and a thiyl radical R-S. Proton transfer from the tryptophan cation radical to the thiolate ion leads to the tryptophan radical Trp and the thiol RSH. The final stage of the process is governed by radical coupling, which may result in sulfenylation of the Trp moiety yielding Trp-S-R, or in inter-molecular cross-linking, i.e. in the formation of enzyme dimers or trimers. 

There have been several studies reporting equilibrium and rate measurements for reactions of TNB with thiolate ions. Values of the equilibrium constants measure the thermodynamic affinity of the nucleophile for the carbon center, a quantity usually known as the carbon basicity. This is distinct from nucleophilicity, which reflects the rate constant for nucleophilic attack. The results show that in comparison with oxygen bases, the polarizable sulfur bases have higher carbon basicities and nucleophilicities than expected from the values of the parent thiols [84, 161,162]. 

Sulfides can be prepared from thiols in a process that is essentially the sulfur analog of the Williamson ether synthesis, involving a thiolate ion, rather than an alkoxide. 

Harder nucleophiles often react with thiirans to give a predominance of attack at carbon, with consequent cleavage of the weak carbon-sulphur bond. This strategy has been used to prepare 7-oxa-4-thia-alk-l-enes from alkoxides, thiiran, and allyl chlorides, yS-mercaptoethyl sulphides from thiiran and thiolate ions, thiazines by the CujO-catalysed cyclization of the adducts of a-lithio-isocyanides with thiirans, tautomeric mixtures of (18) and (19) or (20) from thiiran and hydrazones, 7V-methylpyrrolidines from bis(epithio)linoleic acid and methylamine, and 2,4-dimethylhex-5-ene-2-thiol by addition of the Grignard reagent derived from 3-chlorobut-l-ene with 2,2-dimethylthiiran. Methylthiiran has been found to open... 

The tricyclic sulphides (11) were formed by intramolecular opening of an epoxide by a thiolate ion that was generated in situ. The precursors (12) were readily obtained by reduction and brosylation of the Diels-Alder product of cyclopenta-1,3-diene (cyclohexa-1,3-diene) and ethyl acrylate. Various reactions of (11), including conversion into the parent heterocycle, were described. The dilithio-salt (13), obtained from toluene-a-thiol and two... 

Estimated from Eq. (3) and parameters in Tables I and II. c These ions are reduced by thiols. Since Cu(II) forms less stable complexes with thiols than Cu(II), this will always occur in an environment of thiols alone. However, log Ki for Fe(III) with thiols is larger than for Fe(II), and so log p4 for Fe(III) with ME should be proportionately much larger them with Fe(II). Thus, coordination of four thiolate groups, as occurs in electron transfer proteins, will lead to a very stable Fe(III) complex, which is much less easily reduced to Fe(II) than when only a single thiolate is coordinated. 

Thiolates are strong ligands and a rich coordination chemistry with cobalt(III) exists. Normally, thiols are employed directly in synthesis, and this is the usual entry into their coordination chemistry. However, alternative approaches do appear from time to time, and recently the cobalt-mediated direct thiolation of an aromatic ring in bidentate phenyl(2-pyridyl)diazene using dithiocarbamate ion to produce a coordinated tridentate thiolate has been reported.1034... 

Probably the aspect of primary importance for the catalytic activity of cysteine proteases is the high nucleophilicity of the active-site thiol group. It is now generally accepted that the active form of papain and of cysteine proteases in general consists of a thiolate-imidazolium ion-pair, built from Cys25 and Hisl59. 

The formation of complexes of l,2,3,4-thiatriazole-5-thiol has been well described in CHEC-II(1996) 1,2,3,4-thiatriazole-5-thiol can form complexes with various metals such as palladium, nickel, platinum, cobalt, zinc, etc. <1996CHEC-II(4)691>. These complexes can be prepared either by cycloaddition reactions of carbon disulfide with metal complexes of azide anion (Equation 20) or directly from the sodium salt of l,2,3,4-thiatriazole-5-thiol with metal salts. For instance, the palladium-thiatriazole complex 179 can be obtained as shown in Equation (20) or it may be formed from palladium(ll) nitrate, triphenylphosphine, and sodium thiatriazolate-5-thiolate. It should be noted that complexes of azide ion react with carbon disulfide much faster than sodium azide itself. 

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