Nitromethane

Nitromethane
IUPAC name nitromethane
Other names nitrocarbol
Identifiers
CAS number	75-52-5 Y
PubChem	6375
ChemSpider	6135 Y
KEGG	C19275 N
ChEMBL	CHEMBL276924 Y
RTECS number	PA9800000
Jmol-3D images	Image 1
SMILES C[N+](=O)[O-]
InChI InChI=1S/CH3NO2/c1-2(3)4/h1H3 Y Key: LYGJENNIWJXYER-UHFFFAOYSA-N Y InChI=1/CH3NO2/c1-2(3)4/h1H3 Key: LYGJENNIWJXYER-UHFFFAOYAW
Properties
Molecular formula	CH3NO2
Molar mass	61.04 g/mol
Appearance	colorless liquid
Density	1.1371 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
R-phrases	R5 R10 R22
S-phrases	S41
Main hazards	Flammable, harmful
NFPA 704	3 2 4
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
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Not to be confused with methyl nitrate.

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 in Top Fuel drag racing, and as an important component in the fuel for the miniature internal combustion engines used, for example, in radio-controlled models.

Preparation

Nitromethane is produced industrially by treating propane with nitric acid at 350–450 °C (622–842 °F). 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:^[2]

ClCH₂COONa + NaNO₂ + H₂O → CH₃NO₂ + NaCl + NaHCO₃

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]

Derivatives

In organic synthesis nitromethane is employed as a one carbon building block.^[3][4] Its acidity 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, (HOCH₂)₃CNH₂, better known as “tris,” a widely used buffer.

In more specialized organic synthesis, nitromethane serves as a Michael donor, adding to α,β-unsaturated carbonyl compounds via 1,4-addition in the Michael reaction.

As an engine fuel

Nitromethane is used as a fuel in motor racing, particularly drag racing, as well as for rockets and Radio Control models (such as cars, planes and helicopters) and is commonly referred to in this context as "nitro". The oxygen content of nitromethane enables it to burn with much less atmospheric oxygen.

4CH₃NO₂ + 3O₂ → 4CO₂ + 6H₂O + 2N₂

14.7 lb (6.7 kg) of air is required to burn 1 lb (0.45 kg) of gasoline, but only 1.7 lb (0.77 kg) of air for 1 lb 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. This analysis indicates that nitromethane generates about 2.3 times the power of gasoline when combined with a given amount of oxygen.

Nitromethane can also be used as a monopropellant, i.e., a fuel that burns without added oxygen. The following equation describes this process:

2 CH₃NO₂ → 2 CO + 2 H₂O + H₂ + 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 2,400 °C (4,350 °F). The high heat of vaporization 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. Very rich mixtures are necessary to reduce the temperature of combustion chamber hot parts in order to control pre-ignition and subsequent detonation. Operational details depend on the particular mixture and engine characteristics.

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, and is forbidden for use in model aircraft fuels.

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).

Explosive properties

Nitromethane was not known to be a high explosive until a railroad tanker car loaded with it exploded on June 1, 1958.^[5] 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. 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 6,400 m/s (21,000 ft/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 in the Oklahoma city bombing.

It is also miscible with concentrated nitric acid, forming an explosive composition with similar power and sensitivity to nitroglycerin.

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.^[6]

See also

• Top Fuel
• Adiabatic flame temperature, a thermodynamic calculation of the flame temperature of nitromethane

References

1. ^ ^{a b} Sheldon B. Markofsky “Nitro Compounds, Aliphatic” Ullmann's Encyclopedia of Industrial Chemistry 2002 by Wiley-VCH, Weinheim, 2002; doi:10.1002/14356007.a17_401.
2. ^ F. C. Whitmore and Marion G. Whitmore (1941), "Nitromethane", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0401 ; Coll. Vol. 1: 401 
3. ^ Hyp J. Dauben, Jr, Howard J. Ringold, Robert H. Wade, David L. Pearson, Arthur G. Anderson, Jr, Th. J. de Boer, and H. J. Backer (1963), "Cycloheptanone", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv4p0221 ; Coll. Vol. 4: 221 
4. ^ Wayland E. Noland (1963), "2-Nitroethanol", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv5p0833 ; Coll. Vol. 4: 833 
5. ^ Interstate Commerce Commission: Ex Parte No 213. “Accident Near Mt. Pulaski, ILL”
6. ^ Coetzee, J. F. and Chang, T. H. (1986). "Recommended Methods for the Purification of Solvents and Tests for Impurities: Nitromethane" (PDF). Pure Appl. Chem. 58 (11): 1541–1545. doi:10.1351/pac198658111541. http://www.iupac.org/publications/pac/1986/pdf/5811x1541.pdf. 

External links

• WebBook page for nitromethane
• History of Nitromethane