Nitromethane
From Wikipedia, the free encyclopedia
| Nitromethane | |
|---|---|
 |
 |
| IUPAC name | nitromethane |
| Other names | nitrocarbol |
| Identifiers | |
| CAS number | [75-52-5] |
| RTECS number | PA9800000 |
| SMILES | C[N+]([O-])=O |
| Properties | |
| Molecular formula | CH3NO2 |
| Molar mass | 61.04 g/mol |
| Appearance | colorless liquid |
| Density | 1.138 g/cm³, liquid |
| Melting point |
−29 °C (244.15 K) |
| Boiling point |
100–103 °C (373-376 K) |
| Solubility in water | ca. 10 g/100 mL |
| Acidity (pKa) | 10.2 |
| Viscosity | 0.61 mPa·s at 25 °C |
| Hazards | |
| MSDS | External MSDS |
| MSDS | MainHazards = Flammable, harmful |
| NFPA 704 |
 3
2
4
|
| R-phrases | R5 R10 R22 |
| S-phrases | S41 |
| Flash point | 35 °C |
| Related compounds | |
| Related nitro compounds | nitroethane |
| Related compounds | methyl nitrite methyl nitrate |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
|
Nitromethane is an organic compound with the chemical formula CH3NO2. It is the simplest organic nitro compound. It is a slightly viscous, highly polar liquid commonly used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, and as a cleaning solvent. As an intermediate in organic synthesis, it is used widely in the manufacture of pharmaceuticals, pesticides, explosives, fibers, and coatings. It is also used as a racing fuel.
Contents |
[edit] Preparation
Nitromethane is produced industrially by treating propane with nitric acid at 350–450 °C. This exothermic reaction produces the four industrially significant nitroalkanes: nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane. The reaction involves free radicals, including the alkoxyl radicals of the type CH3CH2CH2O., which arise via homolysis of the corresponding nitrite ester. These alkoxy radicals are susceptible to C-C fragmentation reactions, which explains the formation of a mixture of products.[1]
Although inexpensively available, nitromethane can be prepared in other methods that are of instructional value. The reaction of sodium chloroacetate with sodium nitrite in aqueous solution produces this compound:
- ClCH2COONa + NaNO2 + H2O → CH3NO2 + NaCl + NaHCO3
Nitromethane is distilled from the reaction and then dried over a mild desiccant.[2]
[edit] Uses
The principal use of nitromethane is as a stabilizer for chlorinated solvents, which are used in dry cleaning, semiconductor processing, and degreasing. It is also used most effectively as a solvent or dissolving agent for acrylate monomers, such as cyanoacrylates (more commonly known as "super-glue").[1]
[edit] Derivatives
In organic synthesis nitromethane is employed as a one carbon building block. Its acidicity allows it to undergo deprotonation, enabling condensation reactions analogous to those of carbonyl compounds. Thus, under base catalysis, nitromethane adds to aldehydes in 1,2-addition in the nitroaldol reaction. Some important derivatives include the pesticides Chloropicrin, Cl3CNO2 and tris(hydroxymethyl)nitromethane, (HOCH2)3CNO2. Reduction of the latter gives tris(hydroxymethyl)aminomethane, (CH2OH)3CNH2, better known as “tris,” a widely used buffer.
In more specialized organic synthesis, nitromethane serve as a Michael donor, adding to α,β-unsaturated carbonyl compounds via 1,4-addition in the Michael reaction.
[edit] As an engine fuel
In a minor application, nitromethane is used as a fuel in racing, particularly drag racing, as well as for rockets and RC Models. In car racing, nitromethane is commonly referred to as "nitro" or just "fuel". The oxygen content of nitromethane enables it to burn with much less atmospheric oxygen in comparison to hydrocarbons such as gasoline:
- 4CH3NO2 + 3O2 → 4CO2 + 6H2O + 2N2
14.6 kg of air is required to burn one kg of gasoline, but only 1.7 kg of air for one kg of nitromethane. Since an engine’s cylinder can only contain a limited amount of air on each stroke, 8.7 times more nitromethane than gasoline can be burned in one stroke. Nitromethane, however, has a lower energy density: Gasoline provides about 42–44 MJ/kg whereas nitromethane provides only 11.3 MJ/kg.
Nitromethane can also be used as a monopropellant, i.e., a fuel that burns without added oxygen. The following equation describes this process:
- 4 CH3NO2 → 4 CO + 4 H2O + 2 H2 + 2 N2
Nitromethane has a laminar combustion velocity of approx. 0.5 m/s, somewhat higher than gasoline, thus making it suitable for high speed engines. It also has a somewhat higher flame temperature of about 2400 °C. The high heat of vaporisation of 0.56 MJ/kg together with the high fuel flow provides significant cooling of the incoming charge (about twice that of methanol), resulting in reasonably low temperatures.
Nitromethane is usually used with rich air/fuel mixtures because it provides power even in the absence of atmospheric oxygen. When rich air/fuel mixtures are used, hydrogen and carbon monoxide are two of the combustion products. These gases often ignite, sometimes spectacularly, as the normally very rich mixtures* of the still burning fuel exits the exhaust ports and out through the exhaust pipes. [* the very rich mixtures are necessary to reduce the temperature of combustion chamber hot parts so to control Pre-ignition and subsequent Detonation]
Note: The proceding three Paragraphs refer to conditions where the volume of Nitromethane blended with Methanol => 80%.And with a typical 500 cu.in. Drag Racing Engine producing now* in excess of 8000 HP. *Aug. 2007.
A small amount of hydrazine blended in nitromethane can increase the power output even further. With nitromethane, hydrazine forms an explosive salt that is again a monopropellant. This unstable mixture poses a severe safety hazard.
In model aircraft and car glow fuel, the primary ingredient is generally methanol with some nitromethane (0% to 65%, but rarely over 30% since nitromethane is expensive compared to methanol) and 10–20% lubricants (usually castor oil and/or synthetic oil). Even moderate amounts of nitromethane tend to increase the power created by the engine (as the limiting factor is often the air intake), making the engine easier to tune (adjust for the proper air/fuel ratio).
[edit] Explosive properties
Nitromethane was not known to be a high explosive until the 1950s when a railroad tanker car loaded with it exploded. After much testing it was realized that nitromethane was a more energetic high explosive than TNT, although TNT has a higher velocity of detonation and brisance (shattering power against hard targets). Both of these explosives are oxygen poor and some benefits are gained from mixing with an oxidizer, such as ammonium nitrate. Pure nitromethane is an insensitive explosive with a VoD of approximately 6200 m/s, but even so inhibitors may be used to reduce the hazards. The tank car explosion was speculated to be due to adiabatic compression, a hazard common to all liquid explosives. This is when small entrained air bubbles compress and superheat with rapid rises in pressure. It was thought that an operator rapidly snapped shut a valve creating a 'hammer-lock' pressure surge. Nitromethane can be sensitized by adding a base to raise the pH.
Nitromethane can also be mixed with ammonium nitrate, which is used as an oxidizer, to form an explosive mixture known as ANNM. One graphic example of this was the use of nitromethane and ammonium nitrate on the Alfred P. Murrah Federal Building at Oklahoma City.
[edit] Purification
Nitromethane is a popular solvent in organic and electroanalytical chemistry. It can be purified by cooling below its freezing point, washing the solid with cold diethyl ether, followed by distillation.[3]
[edit] See also
- Adiabatic flame temperature, a thermodynamic calculation of the flame temperature of nitromethane
[edit] References
- ^ a b Sheldon B. Markofsky “Nitro Compounds, Aliphatic” Ullmann's Encyclopedia of Industrial Chemistry 2002 by Wiley-VCH, Wienheim, 2002. DOI: 10.1002/14356007.a17_401.
- ^ Cohen, Julius B. Practical Organic Chemistry, Macmillan 1930, preparation 32
- ^ Coetzee, J. F. and Chang, T. H. (1986). "Recommended Methods for the Purification of Solvents and Tests for Impurities: Nitromethane". Pure Appl. Chem. 58: 1541-1545.
