Manufacture of beta-ionone by cyclising pseudo-ionone - by sulphuric acid in sulphur dioxide

摘要

Pseudo-ionone is cyclised by 90-98% H2SO4 in the presence of liquid SO2 at temps. between the b.pt. of SO2 and room temp., pref. -10 to +10 degrees. The SO2 evaporates during the reaction and maintains a low reaction temp., which must not exceed +10 degrees. in order to keep the beta: alpha-ionone ratio high. The SO2 also dissipates the heat of hydration producing during working up of the reaction mixture by pouring into water. Yields of beta-ionone are 10% and alpha-ionone contents are 1%.