Experiment 6.136

β-Nitrostyrene

Ph-CHO + Me-NO₂ -NaOH-> PhCH=CHNO₂

Equip a 1500-ml three-necked flask with a thermometer, mechanical stirrer and a dropping funnel. Place 61 g (54 ml, 1 mol) of nitromethane (1), 106g (101 ml, 1 mol) of purified benzaldehyde and 200 ml of methanol in the flask and cool it with a mixture of ice and salt to about -10°C. Dissolve 42g of sodium hydroxide in 40-50 ml of water, cool and dilute to 100 ml with ice and water; place this cold solution in the dropping funnel. Add the sodium hydroxide solution, with vigorous stirring, to the nitromethane mixture at such a rate that the temperature is held at 10-15°C. Introduce the first few ml cautiously since, after a short induction period, the temperature may rise to 30°C or higher; check the rise in temperature, if necessary, by adding a little crushed ice to the reaction mixture. A bulky white precipitate forms; if the mixture becomes so thick that stirring is difficult, add about 10 ml of methanol. After standing for about 15 minutes, add 700 ml of ice-water containing crushed ice; the temperature should be below 5°C. Run the resulting cold solution immediately from a dropping funnel and with stirring into 500 ml of 4 M hydrochloric acid contained in a 3-litre flask; adjust the rate of addition so that the stream just fails to break into drops. A pale yellow crystalline precipitate separates almost as soon as the alkaline solution mixes with the acid. The solid settles to the bottom of the vessel when the stirrer is stopped. Decant most of the cloudy liquid layer, filter the residue by suction and wash it with water until free from chlorides. Transfer the solid to a beaker immersed in hot water; two layers form and on cooling again, the lower layer of nitrostyrene solidifies; pour off the upper water layer. Dissolve the crude nitrostyrene in 85 ml of hot ethanol. (CAUTION: nitrostyrene vapours are irritating to the nose and eyes, and the skin of the face is sensitive to the solid.) Filter through a hotwater funnel and cool until crystallisation is complete. The yield of pure nitrostyrene, mp 57-58°C, is 125 g (85%).

Note 1:
The commercial material may be redistilled and the fraction having bp 100-102°C collected.

Cognate preparations

3,4-Methylenedioxy-β-nitrostyrene

In a 250-ml round-bottomed flask mix 30g (0.20 mol) of 3,4-methylenedioxybenzaldehyde (piperonal), 13.4 g (0.22 mol) of nitromethane, 7.8 g (0.1 mol) of ammonium acetate and 50 ml of glacial acid. Attach a reflux condenser, and boil the mixture under gentle reflux for 1 hour. Pour the reaction mixture with stirring into a large excess of ice-water (about 1 litre). When all the ice has melted, filter off the crude product under suction and recrystallise from a mixture of absolute ethanol and acetone (about 2:1 v/v). Almost pure yellow crystals of the nitrostyrene, mp 161°C, are obtained. The yield is 23.3 g (60%). Further recrystallisation from the same solvent yields the pure compound, mp 162°C.

2,4-Dimethoxy-β-nitrostyrene

Follow the above procedure, but use 33.2g (0.20 mol) of 2,4-dimethoxybenzaldehyde as the starting material. The yield of recrystallised product (yellow crystals, mp 103°C) is 28.5 g (68%). Further recrystallisation gives pure product of mp 105°C.