Nitroethane Simplest Syntheses
Introduction
I present to you the three simplest syntheses of nitroethane:
- From sodium ethyl sulfate and a metal nitrite.
- From ethyl halide and silver nitrite.
- From ethyl bromide (iodide) and sodium nitrite.
This list allows to select a suitable reagent that can be purchased in your country. According to local prices for reagents, prices for final product and reagents availability, you can choose a more reasonable synthesis way.
- Appearance: oily liquid, fruity odor
- Boiling Point: 112.0 to 116.0 °C/760 mmHg
- Melting Point: -90 °C
- Molecular Weight: 75.067 g/mol
- Density: 1.054 g/ml (20° C)
- Refractive Index: 1.3917 at 20 °C/D; 1.39007 at 24.3 °C/D
Nitroethane Synthesis From Sodium Ethyl Sulfate and Metal Nitrite
To synthesize nitroethane, combine 1.5 moles of sodium nitrite (103.5 g) with 1 mole of sodium ethyl sulfate (158 g) and 0.0625 moles of potassium carbonate (8.6 g). Heat the mixture steadily to a temperature range of 125–130 °C. As the reaction proceeds, nitroethane will begin to distill off immediately upon formation. Once the rate of distillation decreases significantly, stop the heating process. The collected crude nitroethane should then be washed with an equal volume of water, dried over calcium chloride (CaCl₂), and, if necessary, treated with a small amount of activated carbon for decolorization. Finally, purify the product by re-distillation, isolating the fraction that boils between 114–116 °C. This method typically yields 42–46% based on theoretical values.
A more comprehensive procedure for this synthesis is available elsewhere, originally intended for nitromethane production. However, it can be easily adapted for nitroethane synthesis by replacing dimethyl sulfate with diethyl sulfate. Be sure to recalculate the quantities of all reagents accordingly to match the chemical differences and ensure proper reaction stoichiometry.
Nitroethane Synthesis From Ethyl Halide and Silver Nitrite
Begin by cooling 100 grams (0.65 mol) of silver nitrite in 150 ml of anhydrous ether to 0 °C using a 500 ml three-neck flask. Perform this step under low-light conditions—preferably in a dark room or under yellow lighting—to avoid light-sensitive reactions. Slowly add 0.5 moles of ethyl halide (either 78 g of ethyl iodide or 55 g of ethyl bromide) dropwise over a span of two hours, maintaining constant stirring and a stable temperature of 0 °C throughout the addition. After the addition is complete, continue stirring the reaction mixture for 24 hours at 0 °C. Then, if ethyl bromide is used, allow the mixture to stir for an additional 24–48 hours at room temperature to ensure full conversion to nitroethane.
Nitroethane Synthesis From Ethyl Bromide (Iodide) and Sodium Nitrite (DMF)
To carry out this nitroethane synthesis, add 32.5 grams of ethyl bromide (0.3 mol) to a well-stirred solution of 36 grams of dry sodium nitrite (0.52 mol) dissolved in 600 ml of dimethylformamide (DMF). Maintain the reaction vessel in a water bath at room temperature, as the reaction is mildly exothermic. It is important to keep the entire setup away from direct sunlight to prevent decomposition or side reactions. Stir the mixture continuously for six hours. Once the reaction is complete, pour the mixture into a large container (approximately 2.5 liters in volume) containing 1500 ml of ice-cold water and 100 ml of petroleum ether. Separate the upper petroleum ether layer and save it. Then, extract the aqueous phase four more times with 100 ml portions of petroleum ether. Combine all organic extracts and wash them with four portions of 75 ml water each. Dry the resulting organic layer over anhydrous magnesium sulfate, filter it, and carefully remove the petroleum ether via distillation under reduced pressure on a water bath, gradually increasing the bath temperature to around 65 °C. The remaining crude nitroethane is then purified by distillation under atmospheric pressure using a small distillation column. Collect the fraction boiling at 114–116 °C, which represents a 60% yield of the target product.
The ethyl bromide reacts with NaNO2, forming nitroethane and ethyl nitrite.
Substituting ethyl bromide with ethyl iodide also affects the process: the reaction time drops from 6 hours to just 2.5 hours. However, when using ethyl iodide, a slight adjustment to the post-reaction workup is necessary. Instead of washing the pooled petroleum ether extracts with four portions of water, wash them with two 75 ml portions of 10% sodium thiosulfate solution followed by two 75 ml water rinses. This extra step effectively removes any residual free iodine that may be present.
Conclusion
To sum up, nitroethane can be prepared using several simple methods, each offering different benefits based on reagent availability, cost, and yield. The synthesis from sodium ethyl sulfate and a metal nitrite is easy to perform, while the method using silver nitrite and ethyl halide provides a higher yield but requires more care and expensive materials. The process using sodium nitrite in DMF or DMSO offers a good balance between simplicity and effectiveness, with optional adjustments like urea addition to improve results. Depending on your local access to chemicals and equipment, you can choose the most suitable method for producing nitroethane efficiently and reliably.
Sources
- Audley, Gary J., Donald L. Baulch, and Ian M. Campbell. "A new method for the synthesis of nitroethane, ethyl nitrite, and ethyl nitrate." Journal of the Chemical Society, Chemical Communications 18 (1982): 1053-1055. https://pubs.rsc.org/en/content/articlelanding/1982/c3/c39820001053/unauth
- Kabalka, George W., and Rajender S. Varma. "Syntheses and selected reductions of conjugated nitroalkenes. A review." Organic Preparations and Procedures International 19.4-5 (1987): 283-328.
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