Chemistry:Nitromethane

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Nitromethane
Structural formula of nitromethane
Nitromethane
Names
IUPAC name
Nitromethane
Preferred IUPAC name
Nitromethane[1]
Other names
Nitrocarbol
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
KEGG
RTECS number
  • PA9800000
UNII
Properties
CH3NO2
Molar mass 61.04 g/mol
Appearance colorless, oily liquid[2]
Odor Light, fruity[2]
Density 1.1371 g/cm3 (20 °C)[3]
Melting point −28.7 °C (−19.7 °F; 244.5 K)[3]
Boiling point 101.2 °C (214.2 °F; 374.3 K)[3]
Critical point (T, P) 588 K, 6.0 MPa[4]
ca. 10 g/100 mL
Solubility miscible in diethyl ether, acetone, ethanol[3]
Vapor pressure 28 mmHg (20 °C)[2]
Acidity (pKa)
-21.0·10−6 cm3/mol[7]
Thermal conductivity 0.204 W/(m·K) at 25 °C[8]
1.3817 (20 °C)[3]
Viscosity 0.63 cP at 25 °C[8]
3.46[9]
Thermochemistry[10]
106.6 J/(mol·K)
171.8 J/(mol·K)
-112.6 kJ/mol
-14.4 kJ/mol
Hazards
Main hazards Flammable, health hazard
GHS pictograms GHS01: Explosive GHS02: Flammable GHS06: Toxic GHS08: Health hazard
GHS Signal word DANGER
H203, H226, H301, H331, H351
P210, P261, P280, P304+340, P312, P370+378, P403+233
NFPA 704 (fire diamond)
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. gasolineHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazards (white): no codeNFPA 704 four-colored diamond
3
2
3
Flash point 35[9] °C (95 °F; 308 K)
418[9] °C (784 °F; 691 K)
Explosive limits 7–22%[9]
20 ppm[9]
Lethal dose or concentration (LD, LC):
940 mg/kg (oral, rat)
950 mg/kg (oral, mouse)[11]
750 mg/kg (rabbit, oral)
125 mg/kg (dog, oral)[11]
7087 ppm (mouse, 2 h)
1000 ppm (monkey)
2500 ppm (rabbit, 12 h)
5000 ppm (rabbit, 6 h)[11]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 100 ppm (250 mg/m3)[2]
REL (Recommended)
 none[2]
IDLH (Immediate danger)
 750 ppm[2]
Related compounds
Related nitro compounds
 nitroethane
Related compounds
 methyl nitrite
methyl nitrate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is ☑Y☒N ?)
Infobox references

Nitromethane, sometimes shortened to simply "nitro", is an organic compound with the chemical formula CH3NO2. It is the simplest organic nitro compound. It is a 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 pesticides, explosives, fibers, and coatings.[12] Nitromethane is used as a fuel additive in various motorsports and hobbies, e.g. Top Fuel drag racing and miniature internal combustion engines in radio control, control line and free flight model aircraft.

Preparation

Nitromethane is produced industrially by combining propane and nitric acid in the gas phase 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.[12]

Laboratory methods

It 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:[13]

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-glues").[12] It is also used as a fuel in some forms of racing. It can be used as an explosive, when gelled with several percent of gelling agent. This type of mixture is called PLX. Other mixtures include ANNM and ANNMAl – explosive mixtures of ammonium nitrate, nitromethane and aluminium powder.

As an organic solvent, it is considered to be highly polar (εr = 36 at 20 °C and μ = 3.5 Debye) but is aprotic and possesses very low Lewis basicity. Thus, it is a rare example of a polar solvent that is also weakly coordinating. This makes it useful for dissolving positively charged, strongly electrophilic species. However, its relatively high acidity and explosive properties (see below) limit its applications.

Reactions

Acid-base properties

Nitromethane is a relatively acidic carbon acid. It has a pKa of 17.2 in DMSO solution. This value indicates an aqueous pKa of about 11.[14] It is so acidic because the anion admits an alternate, stabilizing resonance structure:

Resonance with the aci form.

The acid deprotonates only slowly. Protonation of the conjugate base O2NCH2−, which is nearly isosteric with nitrate, occurs initially at oxygen.[15]

Organic reactions

In organic synthesis nitromethane is employed as a one carbon building block.[16][17] 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), beta-nitrostyrene, 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 radio-controlled model power boats, cars, planes and helicopters. In this context, nitromethane is commonly referred to as "nitro fuel" or simply "nitro", and is the principal ingredient for fuel used in the "Top Fuel" category of drag racing.

The oxygen content of nitromethane enables it to burn with much less atmospheric oxygen than conventional fuels. During nitromethane combustion, nitric oxide (NO) is one of the major emission products along with CO2 and H2O.[18] Nitric oxide contributes to air pollution, acid rain, and ozone layer depletion. Recent (2020) studies[19] suggest the correct stoichiometric equation for the burning of nitromethane is:

4 CH3NO2 + 5 O2 → 4 CO2 + 6 H2O + 4 NO

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, 8.6 times as much nitromethane as gasoline can be burned in one stroke. Nitromethane, however, has a lower specific energy: gasoline provides about 42–44 MJ/kg, whereas nitromethane provides only 11.3 MJ/kg.[citation needed] This analysis indicates that nitromethane generates about 2.3 times the power of gasoline when combined with a given amount of oxygen.[citation needed]

Nitromethane can also be used as a monopropellant, i.e., a propellant that decomposes to release energy 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.[citation needed]

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.[citation needed]

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. The National Hot Rod Association and Academy of Model Aeronautics do not permit its use in competitions.[20]

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

Nitromethane was not known to be a high explosive until a railroad tank car loaded with it exploded on June 1, 1958.[21] After much testing, it was realized that nitromethane was a more energetic high explosive than TNT, although TNT has a higher velocity of detonation (VoD) 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.[citation needed]

If mixed with ammonium nitrate, which is used as an oxidizer, it forms an explosive mixture known as ANNM.

Nitromethane is used as a model explosive, along with TNT. It has several advantages as a model explosive over TNT, namely its uniform density and lack of solid post-detonation species that complicate the determination of equation of state and further calculations.

Nitromethane reacts with solutions of sodium hydroxide or methoxide in alcohol to produce an insoluble salt of nitromethane. This substance is a sensitive explosive which reverts to nitromethane under acidic conditions and decomposes in water to form another explosive compound, sodium methazonate, which has a reddish-brown color:

2 CH3NO2 + NaOH → HON=CHCH=NO2Na + 2 H2O

Nitromethane's reaction with solid sodium hydroxide is hypergolic.

Nitromethane exhaust

Exhaust gas from an internal combustion engine whose fuel includes nitromethane will contain nitric acid vapour, which is corrosive, and when inhaled causes a muscular reaction making it impossible to breathe. The condensed nitric acid-based residue left over in a glow-fueled model engine after a model-flight session can also corrode their internal components, usually mandating use of a combination of kerosene to neutralize the residual nitric acid, and an "after-run oil" (often the lower-viscosity "air tool oil" variety of a popular preservative oil) for lubrication to safeguard against such damage, when such an engine is placed into storage.

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.[22]

See also

References

  1. ↑ "Front Matter". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 662. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 NIOSH Pocket Guide to Chemical Hazards. "#0457". National Institute for Occupational Safety and Health (NIOSH). https://www.cdc.gov/niosh/npg/npgd0457.html. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Haynes, p. 3.414
  4. ↑ Haynes, p. 6.69
  5. ↑ Haynes, p. 5.94
  6. ↑ Reich, Hans. "Bordwell pKa table: "Nitroalkanes"". http://www.chem.wisc.edu/areas/reich/pkatable/. 
  7. ↑ Haynes, p. 3.576
  8. ↑ 8.0 8.1 Haynes, p. 6.231
  9. ↑ 9.0 9.1 9.2 9.3 9.4 Haynes, p. 15.19
  10. ↑ Haynes, p. 5.20
  11. ↑ 11.0 11.1 11.2 "Nitromethane". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH). https://www.cdc.gov/niosh/idlh/75525.html. 
  12. ↑ 12.0 12.1 12.2 Markofsky, S. B. (2000). Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_401.pub2. ISBN 978-3527306732. 
  13. ↑ Whitmore, F. C.; Whitmore, M. G. (1941). "Nitromethane". Organic Syntheses. http://www.orgsyn.org/demo.aspx?prep=cv1p0401. ; Collective Volume, 1, pp. 401 
  14. ↑ Bordwell, F. G.; Satish, A. V. (1994). "Is Resonance Important in Determining the Acidities of Weak Acids or the Homolytic Bond Dissociation Enthalpies (BDEs) of Their Acidic H-A Bonds?". Journal of the American Chemical Society 116 (20): 8885–8889. doi:10.1021/ja00099a004. 
  15. ↑ Kramarz, K. W.; Norton, J. R. (2007). "Slow Proton-Transfer Reactions in Organometallic and Bioinorganic Chemistry". Progress in Inorganic Chemistry. pp. 1–65. doi:10.1002/9780470166437.ch1. ISBN 9780470166437. 
  16. ↑ 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". Organic Syntheses. http://www.orgsyn.org/demo.aspx?prep=cv4p0221. ; Collective Volume, 4, pp. 221 
  17. ↑ Noland, W. E. (1963). "2-Nitroethanol". Organic Syntheses. http://www.orgsyn.org/demo.aspx?prep=cv5p0833. ; Collective Volume, 4, pp. 833 
  18. ↑ Shrestha, Krishna Prasad; Vin, Nicolas; Herbinet, Olivier; Seidel, Lars; Battin-Leclerc, Frédérique; Zeuch, Thomas; Mauss, Fabian (2020-02-01). "Insights into nitromethane combustion from detailed kinetic modeling – Pyrolysis experiments in jet-stirred and flow reactors". Fuel 261: 116349. doi:10.1016/j.fuel.2019.116349. ISSN 0016-2361. https://hal.archives-ouvertes.fr/hal-02320515/file/2020%20Fuel%20CH3NO2.pdf. 
  19. ↑ Shrestha, Krishna Prasad; Vin, Nicolas; Herbinet, Olivier; Seidel, Lars; Battin-Leclerc, Frédérique; Zeuch, Thomas; Mauss, Fabian (2020-02-01). "Insights into nitromethane combustion from detailed kinetic modeling – Pyrolysis experiments in jet-stirred and flow reactors". Fuel 261: 116349. doi:10.1016/j.fuel.2019.116349. ISSN 0016-2361. https://hal.archives-ouvertes.fr/hal-02320515/file/2020%20Fuel%20CH3NO2.pdf. 
  20. ↑ "AMA Competition Regulations 2015–2016 Part 7. Fuels". Academy of Model Aeronautics. February 15, 2016. p. 24. https://www.modelaircraft.org/files/2015-2016General.pdf. 
  21. ↑ Interstate Commerce Commission. "Accident Near Mt. Pulaski, ILL". Ex Parte No 213. Archived from the original on 1 November 2020. https://web.archive.org/web/20201101034350/http://www.blet602.org/Historic_accidents/Mt.%20Pulaski_6.1.1958.pdf. 
  22. ↑ Coetzee, J. F.; Chang, T.-H. (1986). "Recommended Methods for the Purification of Solvents and Tests for Impurities: Nitromethane". Pure and Applied Chemistry 58 (11): 1541–1545. doi:10.1351/pac198658111541. http://www.iupac.org/publications/pac/1986/pdf/5811x1541.pdf. 

Cited sources

  • Haynes, William M., ed (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 978-1439855119. 

External links



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