Aliphatic thiols, protonation

Primary Sulfonium Ions. Aliphatic thiols are completely protonated in HS03F-SbF5 diluted with S02 at -60°C [Eq. (4.30)].149... 

Under aprotic conditions, prototropic transformations of thiols are relatively slow, so one can observe distinct waves of the oxidation of the protonated form and of its parent base [19, 20]. Normally, the oxidation of thiols (aliphatic, aromatic, and heteroaromatic) affords diorganyl-disulfides. So various aliphatic and aromatic thiols are easily converted into the corresponding disulfides upon oxidation in MeOH/MeONa with the yields ranging... 

The thiophene ring is opened and sulfur extruded as hydrogen sulfide when 3,4-dinitrothiophene is reacted with piperidine. The product contains two nitroenamine units coupled to each other (Scheme 140). Other secondary amines react similarly (69CC549). Secondary aliphatic amines also react with 2-nitrothiophene to form the nitrodienamines (426) in 50-80% yield. It is believed that the reaction involves addition of the amine at position 5, followed by proton transfer and ring opening to give the thiol which, in the presence of air, oxidatively dimerizes to (426) (Scheme 141). In one case the thiol has been trapped as the silver salt and methylated (74JCS(P1)2357). 

Fluorogenic labelling of pesticides. The subject has been reviewed earlier by Lawrence and Frei (27). Labelling consists in replacing a proton or other atom of a pesticide with a so-called labelling compound such as dansyl chloride (V) or fluores-camine (VI). The former reacts with primary and secondary amines, phenols, some thiols and aliphatic alcohols. The latter reacts very selectively with primary amines. 

Similar to alcohols, aliphatic ethers [54], thiols [55], and sulfides are also protonated on oxygen or sulfur, respectively, at -60 °C in magic acid carbocations are subsequently formed upon raising the temperature. Promoted sulfides, excluding tertiary alkyl, are resistant to cleavage up to -i-70 °C [56]. 

Alkanesulfonic acids can be prepared from the thiols or disulfides and air using cocatalytic DMSO and HBr.f The use of aqueous DMSO in the absence of air, but in the presence of a halogen or hydrogen halide catalyst, readily converts most aliphatic, aromatic, and heterocyclic thiols or disulfides to the corresponding sulfonic acid. In effect, DMSO oxidizes the hydrohalide to the molecular halogen, which then reacts with the organosulfur substrates. Water serves as a proton and oxygen source, and inhibits the Pummerer-type decomposition of the DMSO. 

Similar to alcohols, aliphatic ethers, thiols, and sulfides are also protonated on oxygen or sulfnr, respectively, at — 60 °C in... 

In simple aliphatic systems this protonated form of the disulfide radical anion is usually not detectable because of its fast decay into freely diffusible thiyl and thiol components, reaction (32) ... 

Other Physical Properties.—Conformational information for thiols and sulphides can be obtained from enthalpy of formation data. Proton-transfer of benzyl-mercaptan (protonation at sulphur with CF3SO3H, and de-protonation by imidazole) has been studied. Thermodynamic parameters for acidity constants of substituted benzenethiols, and for hydrogen-bonding interactions between alkanols and di-n-octyl sulphide and the analogous ether and N-methylamine, reveal a dominant electronic influence of the orM<>-substituent, and substantially higher hydrogen-bond acceptor ability for the aliphatic sulphide than is generally assumed. ... 

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