Microwave Assisted Synthesis of Diosgenin Esters of Maleic and Itaconic Acids

Abstract

Diosgenin monomaleate and diosgenin monoitaconate were prepared by the esterification of diosgenin with maleic and itaconic anhydride, respectively, in toluene using p-toluenesulphonic acid as catalyst. A domestic microwave oven was modified and used for the synthesis of both products. The reaction time for consuming all the diosgenin according to thin-layer chromatography (TLC) was reduced by around 90% in the synthesis of monomaleate of diosgenin as well as in the synthesis of monoitaconate of diosgenin in comparison with conventional heating, whereas the monomaleate of diosgenin yield increased from 43 to 80–85% and the monoitaconate of diosgenin yield from 34 to 95% under the same experimental conditions. It was easier to purify the diosgenin monoitaconate than the diosgenin monomaleate. Both products were characterized by NMR and FTIR spectroscopy.

Keywords:

• Diosgenin
• Modified microwave reactor
• Monoitaconate
• Monomaleate

Notes

^a Δt_r (%) = (t_r conv. heat. − t_r MW irradiation) × 100/t_r conv. heat.

^b Boiling point of toluene.

^c Boiling point of pyridine.

Note. The reaction time (t_r) corresponds to the diosgenin exhaust according to TLC.