Of sulfinic acids

Salts of thiols (170) or of sulfinic acids (171) react like the alkoxides, giving 4-alkylthio- or 4-alkylsulfono-substituted butyrates. Alkali cyanides give 4-cyanobutyrates (172), hydroxylamine gives a hydroxamic acid (173), and hydra2ine a hydra2ide (174). 

Sulfinyl chlorides may be prepared from the corresponding thiols or disulfides by oxidative reactions rather than by reductions of sulfonyl compounds. A recent example, which improves the earlier procedure of Douglass, is given by equation (3)50. The chemistry of sulfinic acids and their derivatives has been reviewed51 52,53. 

Addition of sulfinic acids (or salts) to unactivated C=C double bonds 172... 

Addition of sulfinic acids to polar C=C double bonds.173... 

Additions of sulfinic acids to polyenes ( hydrosulfonylation ), however, proceed with very strong acids80 or under catalysis of Pd complexes81 (equation 17). With copper(II) arenesulfinates, azulene has been oxidatively sulfonylated in the 1- and 2-positions of the five-membered ring82 (equation 18). The sulfonylmercuration has also been applied with success to conjugated dienes83 (equation 19). 

An inverse addition of sulfinic acid to a thiocarbonyl group could have taken place with the reactive intermediate 8, which should arise from thiophosgene and methanesulfmic acid (sodium salt)106 (equation 28). The first step of this reaction represents an S-acylation... 

The total yield of sulfinic acid from the mixed sulfoxides is higher than that from diphenyl sulfoxides (31%) but lower than that from the corresponding dialkyl sulfoxides, and accounts for about 45% of the OH radicals (Table 1). 

The total yield of OH radicals is 6.0 and hence the yield of sulfinic acid of G = 2.7 indicates that 45% of the OH radical produced in the radiolysis attack the sulfinyl group of MTMSO. The authors48 said that the residual 55% attack the sulfide S—C bond, but this claim ignores completely other routes, such as hydrogen abstraction, which was found for other sulfoxides45. 

Alkyl halides or alkyl sulfates, treated with the salts of sulfinic acids, give sulfones. A palladium catalyzed reaction with a chiral complexing agent led to sulfones with modest asymmetric induction. Alkyl sulfinates (R SO—OR) may be side products. Sulfonic acids themselves can be used, if DBU (p. 1337) is... 

This reaction type has been intensely studied °. The application of highly polar solvents, catalysis with tertiary amines" or with acids mesomeric stabilization of intermediate carbenium ions " (allylic and benzylic systems propargylic systems" ) as well as derivatives of sulfinic acids with increasing acidity - usually indicate an ionic pathway (intra- and/or inter-molecular) ... 

Zwanenburg and Wagenaar have reported the rather unusual rearrangement of sulfone 81 to 82, after standing overnight at 0°, and suggested an elimination-addition mechanism, via initial isomerization of A to the A -thiazoline-oxide with subsequent elimination and readdition of sulfinic acid, followed by spontaneous loss of water in a Pummerer-type aromatization reaction. 

In a way analogous to sulfonic esters, sulfinic esters are available quite readily and in very good yield. As usually the first step is the activation of sulfinic acid by CDI to the corresponding imidazolide which then reacts with alcohols [12H14]... 

Scheme 36. Elimination of sulfinic acid from 2-deoxy-2-C-p-tolylsulfonyl-/i-D-ara moHexopyranosyl p-tolyl sulfones promoted by silica.

Methyl methanethiosulfonate (MMTS) is a small reversible blocking agent for sulfhydryl groups (Thermo Fisher, Toronto Research). It reacts with free thiols to form a dithiomethane modification with release of sulfinic acid (Figure 1.122). The sulfinic acid component decomposes into volatile products, which don t affect the disulfide formed from the MMTS reaction Alkylthiosulfonates react rapidly with thiols under mild conditions at physiological pH. The MMTS compound is a liquid at 10.6 M concentration and is conveniently added to a reaction medium by pipette. Complete thiol modifications of available cysteine residues in proteins can... 

Structure, acidity and basicity 100 Oxidation of sulfinic acids 101 Disproportionation 102 Reactions with alkyl sulfides and disulfides 103 Desulfonylation 106... 

Nucleophilic substitution reactions of sulfinate ions 106 Addition of sulfinate ions to multiple bonds 108 Radical reactions of sulfinic acids 110... 

The acidity of sulfinic acids is quite substantial. Benzenesulfinic acid has a pAg-value of 1.2 in water (Ritchie et al., 1961). Aliphatic sulfinic acids are somewhat weaker (p/fa = 2.2-2.3) (Rumpf and Sadet, 1958 Wudl et al., 1967). For the ionization of a series of arenesulfinic acids ArS02H in water pis +0.97 (Ritchie et al., 1961). 

---