Thiols, especially in the presence of base, are readily oxidized by reagents such as bromine and iodine to give an organic disulfide (R−S−S−R).
: 2 R−SH + Br → R−S−S−R + 2 HBr
Oxidation by more powerful reagents such as sodium hypochlorite or hydrogen peroxide can also yield sulfonic acids (RSOH).
: R−SH + 3 HO → RSOH + 3 HO
Oxidation can also be effected by oxygen in the presence of catalysts:
: 2 R–SH +  O → RS−SR + HO
Thiols participate in thiol-disulfide exchange:
:RS−SR + 2 R′SH → 2 RSH + R′S−SR′
This reaction is important in nature.