Preparation of Nitroethane from Ethyl bromide and Sodium Nitrite
32.5 grams of ethyl bromide (0.3 moles) was poured into a stirred solution of 600ml dimethylformamide and 36 grams dry NaNO2 (0.52 mole) in a beaker standing in a water bath keeping the solution at room temperature as the reaction is slightly exothermic. Always keep the solution out of direct sunlight. The stirring was continued for six hours. After that, the reaction mixture was poured into a 2500 ml beaker or flask, containing 1500 ml ice-water and 100 ml of petroleum ether. The petroleum ether layer was poured off and saved, and the aqueous phase was extracted four more times with 100 ml of petroleum ether each, whereafter the organic extracts were pooled, and in turn was washed with 4x75ml of water. The remaining organic phase was dried over magnesium sulfate, filtered, and the petroleum ether was removed by distillation under reduced pressure on a water bath, which temperature was allowed to slowly rise to about 65°C. The residue, consisting of crude nitroethane was distilled under ordinary pressure (preferably with a small distillation column) to give 60% of product, boiling at 114-116°C.
Ethylene glycol also works as solvent, but the reaction proceeds pretty sluggishly in this medium, allowing for side reactions, such as
CH3CH2-NO2 + CH3CH2-ONO -> CH3CH(NO)NO2 + EtOH.
KNO2 can also be used instead of NaNO2.
If NaNO2 is used in DMF, 30g of urea can also be added as nitrite scavenger to minimize side reactions, as well as simultaneously increasing the solubility of the NaNO2 and thereby significantly speeding up the reaction.
If the ethyl bromide is substituted with ethyl iodide, the required reaction time is decreased to only 2.5 h instead of 6 h. In case ethyl iodide is employed, a slight change in the above procedure needs to be done. The pooled pet ether extracts should be washed with 2x75ml 10% sodium thiosulfate, followed by 2 additions of 75ml water, instead of four of 75ml water as above, to remove trace leftover I2.
