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).