Sebastian Moiseevich Tanatar

Sevast'ian (or Sebastian) Moiseevich Tanatar (; 7 (19) October 1849, Odesa – 30 November (19 December) 1917, Odesa) was a Russian chemist.

He was born into a family of Karaite merchants in Odesa. When he was 14, his family moved to Simferopol, Crimea, where he graduated from the Simferopol gymnasium three years later. In 1867, he returned to Odesa to attend Novorossiyskiy University (now Odesa University), from where he graduated in 1872. In 1873–1874 he studied abroad. He later returned to Odesa University, where he achieved the rank of a Full Professor in 1896.

Tanatar made several pioneering contributions to chemistry. In 1880, he showed that fumaric and maleic acid, upon oxidation, yield two isomeric hydroxycarboxylic acids, later shown to be racemic and mesotartaric acids. In 1895, he accomplished the transformation of cyclopropene into propylene at high temperature. In 1898–99 he produced perborates and percarbonates by electrolysis. Tanatar also discovered compounds of hydrogen peroxide with (1899), (1901), and other salts and with urea (1908). He also made significant contributions to nitrogen chemistry, such as industrial manufacturing of ammonia, nitrous acid and nitric acid, determination of the heat capacity and the atomic mass of beryllium, and the invention of gas mask.