Nitromethane

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Structural formula
Valence structural formula of nitromethane
General
Surname Nitromethane
other names

Nitrocarbol

Molecular formula CH 3 NO 2
Brief description

colorless liquid with a fruity odor

External identifiers / databases
CAS number 75-52-5
EC number 200-876-6
ECHA InfoCard 100,000,797
PubChem 6375
Wikidata Q407733
properties
Molar mass 61.04 g mol −1
Physical state

liquid

density

1.14 g cm −3

Melting point

−29 ° C

boiling point

101 ° C

Vapor pressure
  • 36.4 h Pa (20 ° C)
  • 61 hPa (30 ° C)
  • 155 hPa (50 ° C)
  • 280 hPa (65 ° C)
pK s value
solubility
Dipole moment

3.1 D

Refractive index

1.38056

safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
02 - Highly / extremely flammable 08 - Dangerous to health 07 - Warning

Caution

H and P phrases H: 226-302 + 332-351-361d
P: 210-308 + 313
MAK

Switzerland: 100 ml m −3 or 250 mg m −3

Toxicological data

940 mg kg −1 ( LD 50 ,  rat ,  oral )

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Nitromethane
Brief description Petrol for racing and high-performance engines
properties
Physical state liquid
calorific value

11.3 MJ kg −1

Flash point

36 ° C

Ignition temperature 415 ° C
Explosive limit 7.1-63 vol%
Temperature class T2
Explosion class IIA
safety instructions
UN number 1261
Hazard number 33
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Nitromethane , CH 3 NO 2 , is the simplest organic nitro compound . The compound is the monosubstituted representative of the series of nitromethanes with nitromethane, dinitromethane , trinitromethane and tetranitromethane . It is a nitroalkane and a constitutional isomer of carbamic acid .

Presentation and extraction

In the laboratory, the reaction of sodium chloroacetate with sodium nitrite or of bromomethane with silver nitrite produces nitromethane. Industrial production takes place by nitration of methane or by gas-phase nitration of propane , about 25% of which is contained in the resulting nitroalkane mixture.

properties

Nitromethane is a colorless, slightly smelling, highly flammable liquid with a melting point of −29 ° C and a normal pressure boiling point of 100.8 ° C. Nitromethane can only be mixed with water to a limited extent. With increasing temperature, the solubilities of nitromethane in water and of water in nitromethane increase.

Solubilities between nitromethane and water
temperature ° C 0 9.5 19.7 31.0 40.4 50.0 60.5 70.5 80.2 89.8
Nitromethane in water in% 9.0 9.7 10.4 11.7 12.8 14.8 15.1 17.1 19.6 20.8
Water in nitromethane in% 1.10 1.44 1.91 2.50 3.65 5.8 6.13 7.92 8.18 10.42

The 1 H-NMR spectrum shows only a single signal at 4.28 ppm for the CH function. This is a significant shift from methane at 0.23 ppm. Two tautomeric structures can be formulated for the compound . In addition to the nitrotautomer, there is also a nitronic acid tautomer. However, the equilibrium is practically on the side of the nitrotautomer. Quantum chemical calculations show a difference between the free enthalpy of 59.8 kJ mol −1 and the nitric acid structure. The formation of salts in the presence of alkaline solutions such as sodium hydroxide solution leads to the corresponding nitronic acid salts.

Nitromethane tautomerism.svg

The vapors act on the central nervous system, prolonged exposure or ingestion lead to liver and kidney damage .

Thermodynamic properties

The vapor pressure function according to Antoine is given by log 10 (P) = A- (B / (T + C)) (P in bar, T in K) with A = 4.11350 B = 1229.574 and C = -76.221 in the temperature range from 404.9 to 476 K or with A = 4.40542, B = 1446.196 and C = −45.633 in the temperature range from 328.86 to 409.5 K.

Compilation of the most important thermodynamic properties
property Type Value [unit] Remarks
Standard enthalpy of formation Δ f H 0 liquid
Δ f H 0 gas 		−113 kJ mol −1
−81 kJ mol −1 		as a liquid
as a gas
Enthalpy of combustion Δ c H 0 liquid −709.6 kJ mol −1 as a liquid
Heat capacity c p 105.98 J mol −1 K −1 (25 ° C)
1.74 J g −1 K −1 (25 ° C) 		as a liquid
Critical temperature T c 588 K
Critical pressure p c 63.1 bar
Critical density ρ c 5.77 mol·l −1
Enthalpy of fusion Δ f H 0 9.703 kJ mol −1 at the melting point
Enthalpy of evaporation Δ V H 0 33.99 kJ mol −1 at normal pressure boiling point

The temperature dependence of the evaporation enthalpy can be calculated according to the equation Δ V H 0 = Aexp (−βT r ) (1 − T r ) β (Δ V H 0 in kJ / mol, T r = (T / T c ) reduced temperature) with Describe A = 53.33 kJ / mol, β = 0.2732 and T c = 588 K in the temperature range between 318 K and 374 K.

Vapor pressure of nitromethane plotted against temperature
Heat of vaporization of nitromethane plotted against temperature

Safety-related parameters

Nitromethane forms highly flammable vapor-air mixtures. The compound has a flash point of 36 ° C. The explosion range is between 7.1% by volume (180 g / m 3 ) as the lower explosion limit (LEL) and 63% by volume (1600 g / m 3 ) as the upper explosion limit (UEL). A correlation of the explosion limits with the vapor pressure function results in a lower explosion point of 33 ° C and an upper explosion point of 86 ° C. The limit gap width was determined to be 1.11 mm. This results in an assignment to explosion group IIA. The ignition temperature is 415 ° C. The substance therefore falls into temperature class T2. The electrical conductivity is rather low at 5 · 10 −7 S · m −1 .

Safety rules must be observed when handling, as nitromethane is capable of detonation. Although the mechanical sensitivity is very low, in the impure state or as a mixture with other substances, for example amines , the sensitivity can be increased. Important explosion indicators are:

Mixtures of nitromethane with methanol are also capable of detonation. The detonation speed decreases linearly with an increasing proportion of methanol and drops to 5.08 km / s with a proportion of 35% methanol.

Detonation speed of nitromethane- methanol mixtures, plotted against the mass fraction

use

Nitromethane is used as a solvent for spectroscopy and high-performance liquid chromatography , for the production of rocket fuels , explosives ( PLX , ANNM ), insecticides and as an additive for petrol .

It is a useful reagent in organic chemistry because it can be easily deprotonated and, in this form, undergoes reactions such as the nitro- aldol reaction , also known as the Henry reaction , through which aliphatic nitro compounds can easily be produced.

Its use as a racing fuel is the most important use both historically and currently.

Historical use

Nitromethane found its first documented use as a performance-enhancing fuel additive for internal combustion engines in 1950, when Rodger Ward , an American racing driver, achieved a series of surprising racing victories. Vic Edelbrock, responsible for engine tuning, had achieved a considerable increase in engine performance in a series of tests with different nitromethane levels in gasoline. However, they required lengthy adjustments in order to survive the race distance on this fuel.

Usage today

In model construction , glow-igniter engines with a methanol / nitromethane mixture are mostly used for RC cars and flight models . Nitromethane improves the performance of the engines and at the same time has a cooling effect, whereby the cooling of the engine is weaker than the heating caused by the increase in performance.

In motorsport, a mixture of methanol with up to 85% nitromethane is used as fuel for the top-fuel dragster vehicle class. Passenger car gasoline engines are used, for which the modification effort is comparatively low. Further adjustments of the characteristic, such as with pure methanol firing, are not necessary here. With pure nitromethane, about twice the performance of a gasoline-powered engine is possible, with correspondingly higher thermal and mechanical loads.

Individual evidence

  1. ↑ a b c d e data sheet nitromethane (PDF) from Merck , accessed on January 19, 2011.
  2. ↑ a b c d e f g h i j k l m n o Entry on nitromethane in the GESTIS substance database of the IFA , accessed on January 8, 2020(JavaScript required) .
  3. ^ FA Carey, RJ Sundberg: Organic Chemistry . VCH, Weinheim 2004, ISBN 3-527-29217-9 .
  4. ^ WS Matthews et al: Equilibrium Acidities of Carbon Acids. VI. Establishment of an Absolute Scale of Acidities in Dimethyl Sulfoxide Solution. In: J. Am. Chem. Soc. 97, 1975, pp. 7006-7014 (see also Bordwell pKa Table (Acidity in DMSO) ).
  5. ↑ a b c Entry on nitromethane. In: Römpp Online . Georg Thieme Verlag, accessed on November 11, 2014.
  6. ↑ Entry on nitromethanes in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  7. ↑ Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for 75-52-5 or nitromethane ), accessed on November 2, 2015.
  8. ^ Richard van Basshuysen: Handbook Internal Combustion Engine. 5th edition. Vieweg + Teubner, Stuttgart 2010, ISBN 978-3-8348-0699-4 . ( limited preview in Google Book search).
  9. ^ S. Hauptmann, J. Grafe, H. Remane: Textbook of Organic Chemistry . German publishing house for basic industry, Leipzig 1980, p. 480 .
  10. ↑ a b Brockhaus ABC chemistry . tape 2 . FA Brockhaus Verlag, Leipzig 1971, p. 951 .
  11. ^ A b R. M. Stephenson: Mutual Solubilities: Water-Ketones, Water-Ethers, and Water-Gasoline-Alcohols. In: J. Chem. Eng. Data . 37, 1992, pp. 80-95, doi: 10.1021 / je00005a024 .
  12. ↑ a b W. Hofmann, L. Stefaniak, T. Urbanski, M. Witanowski: Proton Magnetic Resonance Study of Nitro Alkanes . In: Journal of the American Chemical Society . tape 86 , no. 4 , 1964, pp. 554–558 , doi : 10.1021 / ja01058a005 .
  13. ^ H. Brand, JF Liebman, A. Schulz: Cyano-, Nitro- and Nitrosomethane Derivatives: Structures and Gas-Phase Acidities . In: European Journal of Organic Chemistry . tape 2008 , no. 27 , 2008, p. 4665-4675 , doi : 10.1002 / ejoc.200800583 .
  14. ↑ HA Berman, Ed West: Density and Vapor Pressure of Nitromethane 26 ° to 200 ° C . In: Journal of Chemical & Engineering Data . tape 12 , no. 2 , 1967, p. 197-199 , doi : 10.1021 / je60033a011 .
  15. ^ JP McCullough, DW Scott, RE Pennington, IA Hossenlopp, G. Waddington: Nitromethane: The Vapor Heat Capacity, Heat of Vaporization, Vapor Pressure and Gas Imperfection; the Chemical Thermodynamic Properties from 0 to 1500K . In: Journal of the American Chemical Society . tape 76 , no. 19 , 1954, pp. 4791-4796 , doi : 10.1021 / ja01648a008 .
  16. ↑ a b N. D. Lebedeva, VLR Ryadenko: Enthalpies of Formation of Nitroalkanes . In: Russian Journal of Physical Chemistry (Engl. Transl.) . tape 47 , 1973, p. 1382 .
  17. ↑ Yu. K. Knobel, EA Miroshnichenko, Yu. A. Lebedev: Heats of Combustion of Nitromethane and Dinitromethane; Enthalpies of Formation of Nitromethyl Radicals and Energies of Dissociation of Bonds in Nitro Derivatives of Methane . In: Bulletin of the Academy of Sciences of the USSR, Chemical Science Division . tape 20 , no. 3 , 1971, p. 425-428 , doi : 10.1007 / BF00852023 .
  18. ↑ a b c W. M. Jones, WF Giauque: The Entropy of Nitromethane. Heat Capacity of Solid and Liquid. Vapor Pressure, Heats of Fusion and Vaporization . In: Journal of the American Chemical Society . tape 69 , no. 5 , 1947, pp. 983-987 , doi : 10.1021 / ja01197a001 .
  19. ^ A b c D. N. Griffin: The Critical Point of Nitromethane . In: Journal of the American Chemical Society . tape 71 , no. 4 , 1949, pp. 1423-1426 , doi : 10.1021 / ja01172a079 .
  20. ^ A b V. Majer, V. Svoboda: Enthalpies of Vaporization of Organic Compounds: A Critical Review and Data Compilation . Blackwell Scientific Publications, Oxford 1985, pp. 300 .
  21. ↑ a b c d e E. Brandes, W. Möller: Safety-related parameters. Volume 1: Flammable Liquids and Gases. Wirtschaftsverlag NW - Verlag für neue Wissenschaft, Bremerhaven 2003.
  22. ↑ Technical rule for hazardous substances TRGS 727, BG RCI leaflet T033 Avoidance of ignition hazards due to electrostatic charges , status August 2016, Jedermann-Verlag Heidelberg, ISBN 978-3-86825-103-6 .
  23. ↑ a b c d e J. Köhler, R. Meyer, A. Homburg: Explosivstoffe . 10th edition. Wiley-VCH, Weinheim 2008, ISBN 978-3-527-32009-7 .
  24. ↑ SA Koldunov, AV Ananin, VA Garanin, VA Sosikov, SI Torunov: Detonation Parameters of Nitromethane / Methanol Mixtures . In: Central European Journal of Energetic Materials . tape 6 , no. 1 , 2009, p. 7-14 ( waw.pl [PDF]).
  25. ↑ Nitromethane: Top-Fuel Drag Racing's Soup of Choice. DragTimes, accessed May 29, 2012 .
  26. ^ Jeff Hartmann: High-Performance Automotive Fuels & Fluids . ISBN 0-7603-0054-2 .
  27. ↑ Helmut Hütten: Fast engines dissected and coiffed . 6th edition. Schmidt, Braunschweig 1977, ISBN 3-87708-060-X .

literature

  • A. Makovky, L. Lenji: Nitromethane - Physical properties, thermodynamics, kinetics of decomposition, and utilization as fuel. In: Chem. Rev. 58, 1958, pp. 627-643, doi: 10.1021 / cr50022a002 . (Review article)