A mixture comprising 2.6 g. of 4-methyl-10-(methylthio)-4H-thieno[3,4-b][1,5]benzodiazepine (U.S. Pat. No. 3,951,981 -- Ex. 7), 8.6 g. of piperazine, 3 drops of acetic acid and 15 ml. of xylene is stirred and refluxed for 4 hours. The reaction mixture is evaporated, washed with water and the residue is dissolved in 50 ml. of 2N acetic acid. The solution is filtered, the filtrate is made alkaline with ammonium hydroxide and extracted with benzene. The extracts are dried over magnesium sulfate, filtered and evaporated producing an amber oil. This oil is dissolved in 20 ml. of ethanol and a mixture of 2.1 g. of fumaric acid in 40 ml. of ethanol is added. The solid is collected and recrystallized from 125 ml. of methanol giving the desired product as the fumarate salt, m.p. 205°-206° C. (dec.).
