A mixture of 80 g. (93.2 ml., 1.14 moles) of crotonaldehyde (b.p. 102–103°), 120 g. (1.15 moles) of malonic acid (m.p. 134–135°), and 120 g. (122 ml., 1.52 moles) of pyridine (b.p. 113–115°) is heated for 3 hours in a 1-l. flask on a steam bath under a reflux condenser. At the end of this period the evolution of carbon dioxide will have practically ceased. The flask and contents are then cooled in ice, and a solution of 42.5 ml. (0.76 mole) of concentrated sulfuric acid in 100 ml. of water is added with shaking. Most of the sorbic acid separates at once; the remainder is obtained by chilling the solution in an ice bath for 3 hours. The crude acid is filtered by suction and washed once with a small amount of ice water; it is recrystallized at once from 250 ml. of boiling water. The purified acid, which separates on standing overnight in the ice chest, is filtered; it melts at 134°. The yield is 36–41 g. (28–32%) (Note 1), (Note 2), and (Note 3).