Thiolsulfonic----- from

Heterolytic scission of the -S-S- bond in which only electrophilic assistance is involved is the exception rather than the rule in reactions involving bond fission of this type. Kice et a/.165,166 have demonstrated that a variety of S-S bond cleavages involve concomitant electrophilic and nucleophilic catalysis including (a) the formation of aryl thiolsulfones from aryl thiolsulfinates and aryl sulfinic acids and (b) the hydrolysis (acetic acid—1% water and 60%... 

Sodium hydroxide Thiolsulfonic from sulfinic acids... 

These acids are less stable, less soluble and less acidic than the corresponding sulfonic acids. The common impurities are the respective sulfonyl chlorides from which they have been prepared, and the thiolsulfonates (neutral) and sulfonic acids into which they decompose. The first two of these can be removed by solvent extraction from an alkaline solution of the acid. On acidification of an alkaline solution, the sulfinic acid crystallises out leaving the sulfonic acid behind. The lower molecular weight members are isolated as their metal (e.g. ferric) salts, but the higher members can be crystallised from water (made slightly acidic), or alcohol. 

The basic reactions of thiolsulfonates have been known for sometime (Field et al., 1961, 1964), but more recently, they have been applied to the study of protein interactions by site-directed modification of native cysteines or through modification of cysteines introduced at particular points in proteins by mutagenesis. Such studies have yielded insights into the structure and binding site characteristics of proteins (Kirley, 1989). Pascual et al. (1998) used AEAETS to probe the acetylcholine receptor from the extracellular side of the membrane in order to investigate the molecular accessibility and electrostatic potential within the open and closed channel. 

We will defer consideration of the particular pattern of nucleophile reactivity observed until Section 9. There we will compare it with what is found for the same group of nucleophiles reacting with (a) an aryl rr-disulfone ArS02S02Ar, a substitution that involves the same leaving group as in (139) but which takes place at a sulfonyl ( S02) rather than a sulfinyl ( S=0) sulfur, and (b) an aryl thiolsulfonate, ArSSOzAr, a substitution where ArSO is displaced from a sulfenyl ( S) sulfur. 

Although not as good a leaving group as a sulfonate (ArSOj) or a halide ion (X ), a sulfinate ion (ArSOj) is still sufficiently good that it can be displaced from sulfenyl sulfur by a wide variety of nucleophiles. As a result the chemistry of thiolsulfonates is dominated by reactions of the general type shown in (167). 

The reactions of thiosulfonates shown in general form in (167), and which constitute the majority of their chemistry, are, of course, substitution reactions at a dico-ordinate, or sulfenyl, sulfur. Substitutions of this type occur widely and with great frequency in the chemistry of all types of sulfenyl compounds. Because of their extreme importance in the chemistry of both thiolsulfonates and other sulfenyl derivatives, it is appropriate that we now review some of the major features regarding their mechanism that have emerged from the study of such reactions with various sulfenyl derivatives. 

Thiolsulfonates decompose thermally according to first-order kinetics with the production of sulfides, sulfur dioxide, hydrocarbons and other products resulting from secondary decompositon of a thioaldehyde... 

Sulfinic acids probably have the structure (1) rather than (2), and certainly any equilibrium between (1) and (2) lies on the side of the hydroxy isomer (1) (Figure l).la The free sulfinic acids are rather unstable and tend to disproportionate into the thiolsulfonate and the sulfinic acid hence, they are generally used as the stable sodium salts. Owing to their instability, few sulfinic acids occur naturally, but they may exist as intermediates in the oxidation of thiols thus, cysteinesulfinic acid is an intermediate in the oxidation of cysteine and 2-aminoethanesulfinic acid has been isolated from molluscs. 

Thioethers from thiolsulfonic acid esters Replacement of C-formyl by alkylthio groups... 

Sulfinic acids from thiolsulfonic acid esters SO2SH SOgH... 

Disulfides from thiolsulfonic acid esters S SOgR S SR ... 

Potassium acetate a-Diketone monothioketals from a-hydroxymethyleneketones Spiro-1,3-S,S-heterocyclics from bis(thiolsulfonates)... 

Thiolsulfonic add esters from sulfonic acid dilorides via K-thiolsulfonates... 

Thiolsulfonic acid esters from 2 sulfenyl nitrate molecules... 

This work was subsequently extended to other benzene thiols2 and to 6- and 7-mercapto-2-aminobenzothiazoles which cleanly underwent the conversion to the mixed thiolsulfonates, with pyridine as the base, with no observed formation of sulfonamide from competing sulfonylation of the 2-amino group.2 ... 

Without additional reagents Ar. thiolsulfonic acid esters from ar. sulfinic acids and ar. sulfenylchlorides... 

Thiolsulfonic acid esters from sulfinic acids and disulfides... 

Thiolsulfonic acid esters from sulfonic acid chlorides SOgGl- SOgSR... 

Without additional reagents Disulfides and thiolsulfonic acid esters from thiolsulfinic acid esters... 

Thiolsulfonic acid esters from diazo compounds s.ll, 676 CiNa- GHSOgSR... 

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