Nitromethane

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Nitromethane
Nitromethane Nitromethane
Identifiers
CAS number 75-52-5 YesY
PubChem 6375
ChemSpider 6135 YesY
KEGG C19275 N
ChEMBL CHEMBL276924 YesY
RTECS number PA9800000
Jmol-3D images Image 1
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
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 4: Readily capable of detonation or explosive decomposition at normal temperatures and pressures. E.g., nitroglycerin Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 35 °C (95 °F; 308 K)
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 (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Nitromethane is an organic compound with the chemical formula CH
3
NO
2
. 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 miniature internal combustion engines that are used in radio-controlled models.

Preparation[edit]

Nitromethane is produced industrially by treating propane with nitric acid at 350–450 °C (662–842 °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[edit]

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[edit]

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[edit]

Nitromethane is used as a fuel in motor racing, particularly drag racing, as well as for rockets and radio-controlled 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

The amount of air required to burn 1 kg (2.2 lb) of gasoline is 14.7 kg (32 lb), but only 1.7 kg (3.7 lb) of air is required for 1 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. 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 approximately 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%, 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[edit]

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 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.

Purification[edit]

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[edit]

References[edit]

  1. ^ a b Markofsky, S. B. (2000). "Nitro Compounds, Aliphatic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_401.pub2. 
  2. ^ Whitmore, F. C.; Whitmore, M. G. (1941), "Nitromethane", Org. Synth. ; Coll. Vol. 1: 401 
  3. ^ Dauben, H. J. Jr.; Ringold, H. J.; Wade, R. H.; Pearson, D. L.; Anderson, A. G. Jr.; de Boer, T. J.; Backer, H. J. (1963), "Cycloheptanone", Org. Synth. ; Coll. Vol. 4: 221 
  4. ^ Noland, W. E. (1963), "2-Nitroethanol", Org. Synth. ; Coll. Vol. 4: 833 
  5. ^ Interstate Commerce Commission. "Accident Near Mt. Pulaski, ILL" (PDF). Ex Parte No 213. 
  6. ^ Coetzee, J. F.; Chang, T.-H. (1986). "Recommended Methods for the Purification of Solvents and Tests for Impurities: Nitromethane" (PDF). Pure and Applied Chemistry 58 (11): 1541–1545. doi:10.1351/pac198658111541. 

External links[edit]