Willy Marckwald (1864, Jakobskirch, Germany – 1942, Rolândia, Brazil) was a German chemist. He was nominated for the Nobel Prize in Chemistry in 1922 by Gustav Tammann and again in 1929 by Niels Bohr, Dirk Coster and George de Hevesy.
Marckwald studied at Berlin's Friedrich-Wilhelms-Universität and received there from the First Chemical Institute in 1886 his Promotierung under A. W. Hofmann with a dissertation on organic chemistry entitled Beitrag zur Kenntniss der Thialdehyde und Thialdine.
By his research on furans, Marckwald received his Habilitation in a very short time in 1889 under the supervision of A. W. Hofmann at Friedrich-Wilhelms-Universität Berlin. In 1899 Marckwald became one of the department heads at the Second Chemical Institute. He held this Privatdozent-level position until his age-related retirement in 1930.
From 1928 to 1931 he was the board chair of the German Chemical Society.
In 1890 Marckwald married Margarete Salomon (1871–1908). Their marriage produced two sons, Friedrich (1892–1917), who died in World War I as a naval aviator, and Johann (1902–1986). In 1936 Willy Marckwald, with his son Johann and his daughter-in-law Prisca, became immigrants in Brazil.
From the starting point of his Promotierung dissertation and Habilitation, Marckwald developed a wide interest in all the fields of chemistry of his era. In heterocyclic chemistry, building upon the research done on Gabriel synthesis, he developed a method for synthesis of aziridines from β-halogen-amines. This ring closure method, known as the Gabriel-Marckwald reaction, allows the preparation of heterocyclic amines that are n-membered, where n=3,4,5,6, or 7. In so far as possible, Marckwald sold the patent rights for use in industry. On this topic, he also wrote monographs of general interest.