Sulfinic acid

[4]: 679  The formal anhydride of a sulfinic acid has not joining oxygen atom, but is instead a sulfinyl sulfone (R–S+(–O−)–S2+(–O−)2–R′),[5] and disproportionation is believed to occur through the free-radical fission of this intermediate.

[4]: 682  Sulfinates react with Grignard reagents to give sulfoxides, and undergo a variant of the Claisen condensation towards the same end.

[4]: 686 Cobalt(III) salts can oxidize sulfinic acids to disulfones, although yields are only 30–50%.

These salts are generated by reduction of sulfonyl chlorides with metals,[8] although thiolates also reduce sulfonate thioesters to a sulfinate and a disulfide.

Sulfones may eliminate in base, particularly if a strong nucleophile is present; thus for example sodium cyanide causes bis(2‑butanone-4‑yl) sulfone to split into levulinonitrile and 3‑oxobutane 1‑sulfinic acid:[4]: 681 The nitrile presumably forms through conjugate addition of cyanide to the corresponding enone.