In
Chem. Pharm. Bull., 1979, 27(1), 198-203
(
http://www.angelfire.lycos.com/scifi2/lego/journals/13.djvu) the reduction of the double bond of phenylnitropropenes is described.
Formic acid reduction of beta-nitrostyrenes
General procedure
A mixture of Ia - f and 5.2 g (0.06 mol based on HCOOH) of TEAF in 40 ml of DMF was stirred at appropriate temperature. Dry air free from CO2 was introduced in order to check evolution of CO2 by saturated Ba(OH)2 solution. After CO2 evolution almost ceased, DMF and excess TEAF were destilled off under reduced pressure. The residue was dissolved in benzene. The benzene solution was washed with water and dried over anhyd. MgSO4. Evaporation of benzene under reduced pressure gave the crude reaction product. Recrystallization or distillation under reduced pressure gave pure reduction product. In the run with If, the production was purified was purified by passing through a basic column using benzene-ethyl acetate as an eluent. Physical and analytical data of the reduction products are summarized in Table III.
Yield for P2NP (phenylnitropropene): 70%, reaction time: 6.0 h, reaction temp: 120-122 °C
Note: This will not work for nitrostyrenes!
Preparation of TEAF (adopted from Chem. Pharm. Bull., 1977, 25, 135-140):
A mixture of 80% formic acid and trialkylamine (triethylamine), roughly in the azeotropic molar properties, was carefully distilled under a reduced pressure. After removal of a lower boiling distillate, a fraction at constant higher boling temperature was collected. This distillate was dried over anhydrous MgSO4 an redistilled.
In the above reaction 5.2 g of the azeotrope are used, equal 0.06 mol HCOOH (2.76 g). Therefore 2,44 g of TEA should be added carefully to 2.76 g of pure formic acid or a solution in water containing 2.76 g of pure formic acid.
A formic acid:triethylamine 5:2 solution is commercially available.