Hans Freiherr[a] von Pechmann (1 April 1850 – 19 April 1902) was a German chemist, renowned for his discovery of diazomethane in 1894.

[5] He also first prepared 1,2-diketones (e.g., diacetyl), acetonedicarboxylic acid, methylglyoxal and diphenyltriketone; established the symmetrical structure of anthraquinone.

Von Pechmann also produced the first example of solid polyethylene serendipitously in 1898, via the decomposition of diazomethane.

Von Pechmann was born in Nürnberg, the only son of a doctor, who was also named Hans.

The von Pechmanns had distinguished themselves as soldiers; in 1702, von Pechmann's ancestor Martin Günther von Pechmann, a general of artillery in the Bavarian army, had been raised to the rank of a baron of the Holy Roman Empire by Leopold I.