Tetramethylazodicarboxamide
Tetramethylazodicarboxamide (also known as TMAD and diamide) is a reagent used in biochemistry for oxidation of thiols in proteins to disulfides. It has also been used as a reagent in the Mitsunobu reaction in place of diethyl azodicarboxylate.

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Further reading

Azo compounds
Reagents for organic chemistry