Born near Wiesbaden in Germany, Erlenmeyer studied at Giessen and practiced at first as a pharmacist. In 1855 he became a private pupil of August Kekulé at Heidelberg and later was appointed professor at the Munich Polytechnic (1868–83). He synthesized guanidine and was the first to give its correct formula (1868). He also synthesized tyrosine and formulated the Erlenmeyer rule, which states the impossibility of two hydroxy groups occurring on the same carbon atom or of a hydroxy group occurring adjacent to a carbon–carbon double bond (chloral hydrate is an exception to this rule). His son F. G. C. E. Erlenmeyer introduced the Erlenmeyer synthesis of amino acids and synthesized cystine, serine, and phenylalanine.