Mono thiol

National Institute for Occupational Safety and Health Criteria for a Recommended Standard. .. Occupational Exposure to n-Alkane Mono Thiols, Cyclohexanetbiol, Benzenethiol. DHEW (NIOSH) Pub No 78-213, Washington, DC, US Government Printing Office, 1978... 

Cys(StBu) with phosphines only a slight excess of tributylphosphine is required for this purpose. Under these conditions reduction of the diselenide does not occur at all, and subsequent air oxidation of the two cysteine residues at high dilution leads in a highly selective manner to the diselenide- and disulfide-bridged peptides. The selectivity of the disulfide bridging is assured by the complete absence of thiol/diselenide exchange reactions even at alkaline pH values due to the very low reactivity of the diselenide toward mono-thiols as a result of their highly differentiated redox potentials. ... 

If we copy Nature rather more exactly, the Claisen ester condensation can be carried out under neutral conditions. This requires rather different reagents. The enol component is the magnesium salt of a malonate mono-thiol-ester, while the electrophilic component is an imidazolide—an amide derived from the heterocycle imidazole. Imidazole has a pK of about 7, Imidazolides are therefore very reactive amides, of about the same electrophilic reactivity as thiol esters. They are prepared from carboxylic acids with carbonyl diimidazole (CDI). 

Mono-thiol ester version of the Dieckmann-type condensation ... 

The importance of controlling the direction of ring closure for the unsymmetrical di-ester condensation has prompted researchers to introduce different chemoselective methods for this reaction. The mono-thiol version of the condensation was first developed for that particular purpose by Yamada, Hosaka, and co-workers in 1981. An example is the ring formation of compounds 22. The ring closure occurs using an appropriate base such as lithium diispropylamide (LDA) in dry THF at -30 °C in the case of X = CH2 or sodium hydride at room temperature in case of X = N (or S) to form the corresponding carbocyclic or heterocyclic rings 22a-c in 74-77% yields. 

We have noted that this derivative is readily oxidized (either by air or iodine) to disulfide 36 which can be converted back to 35 by reduction with LiAlH4. Sucrose mono-thiol 37, prepared from the monosilylated at the C6 ( fructose end ) derivative 24, was used for construction of C2-symmetrical disulfide 38. It could be readily oxidized to di-sulfide 38 (Scheme 8). °... 

Lewisite (CICH CH AsCl2)5 the most vesicant of the arsenical war gases, produces lesions in man that are not reversed or even averted by any mono-thiol. The work done by Peters and his colleagues at Oxford from 1923 onwards led to the discovery that lewisite injures the skin and exerts widespread toxicity by blocking - SH- groups of pyruvate oxidase (Peters, 19365 1948). Injuries caused by lewisite can be completely reversed by those dithiols which have two -- SH - groups close together (Peters, Stocken,... 

Mono-substitution occurs most readily in the stepwise replacement of the halogen substituents of 2,4,6-trichloro-s-triazine with aqueous methanol and sodium bicarbonate (30°, 30 min), the monomethoxy derivative (324) is obtained on heating (65°, 30 min), the disubstitu-ted derivative is formed and on brief heating (65°) with the more basic sodium carbonate or methanolic sodium hydroxide (25°, 3 hr) complete methoxylation (320) occurs. Ethanolic ethoxide (25°, 1 hr) or sodium carbonate (35°) is sufficient to give complete ethoxy-dechlorination. The corresponding phenoxy derivatives are obtained on treatment with one (0°), two (15°, 1 hr), or three equivalents (25-70°, 3 hr) of various sodium phenoxides in aqueous acetone. The stepwise reaction with phenols, alcohols, or thiols proceeds in better yield in organic solvents (acetone or chloroform) with collidine or 2,6-lutidine as acid acceptors than in aqueous sodium bicarbonate. ... 

The most common procedure previously employed to effect the elimination of thiols from thioacetals has been heating in the presence of a protic acid. For example, propionaldehyde diethyl thioacetal is converted to 1-ethylthio-l-propene on heating at 175° in the presence of phosphoric acid. The relatively high temperature and acidic conditions of such procedures are, however, distinct disadvantages of this method. Another approach consists of oxidation of a thioacetal to the mono S-oxide and thermal elimination of a sulfenic acid at 140-150°. ... 

A preparation of 3-substituted thiete dioxides takes advantage of the commercial availability of the parent four-membered thietanes. The latter is oxidized to the sulfone, which in turn is photochemically mono- or di-chlorinated in the 3-position. The 3-chlorothietane dioxide (239a) can be easily transformed into the thiete dioxide, whereas the 3,3-dichloro homolog is transformed into the 3-chloro-2H-thiete 1,1-dioxide (240b) (equation 91). 240b reacts with carbanions, amines, alcohols and thiols to give the corresponding 3-substituted thiete dioxides. ... 

The use of tetraoctylammonium salt as phase transfer reagent has been introduced by Brust [199] for the preparation of gold colloids in the size domain of 1-3 nm. This one-step method consists of a two-phase reduction coupled with ion extraction and self-assembly using mono-layers of alkane thiols. The two-phase redox reaction controls the growth of the metallic nuclei via the simultaneous attachment of self-assembled thiol monolayers on the growing clusters. The overall reaction is summarized in Equation (5). 

Malonic half thiolesters are prepared in good yields from magnesium mono-methylmalonate with CDI under C-acylation and subsequent addition of a thiol.[179] Benzyl- and allylmalonic half thiolesters are prepared analogously. 

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