Nitropropane

1 1-Nitropropane As mentioned in Section 4.13, most open-chain compounds—barring severe steric hindrance—are conformationally mobile at room temperature, and protons in each set average out and become practically magnetic equivalent. Thus a 300-MHz, room-temperature spectrum of 1-nitropro-pane is described as an A3M2X2 system rather than A3MM XX, and first-order rules apply (Fig. 4.45). 

The X2 protons are strongly deshielded by the N02 group, the M2 protons less so, and the A3 protons very slightly. There are two coupling constants, JAM and /MX, that are very similar but not exactly equal. In fact, at 300 MHz, the M2 absorption is a deceptively simple, slightly broadened sextet ( A + nx + 1 = 6). At sufficient resolution, 12 peaks are possible (nA + 1) ( x + 1) = 12. 

The A3 and X2 absorptions are triplets with slightly different coupling constants. The system is described as weakly coupled, and we can justify mentally cleaving the system for analysis. 

Data were last reviewed in lARC (1982) and the compound was classified in lARC Monographs Supplement 7 (1987). 

Name 2-Nitropropane lUPAC Systematic Name 2-Nitropropane Synonyms Dimethylnitromethane isonitropropane 

2 Structural and molecular formulae and relative molecular mass 

13 600 tonnes. 2-Nitropropane is reportedly produced by two companies in the United 

According to the 1981-83 National Occupational Exposure Survey (NOES, 1997), as many as 10 000 workers in the United States were potentially exposed to 2-nitropropane (see General Remarks). Occupational exposures may occur in its production and use as a solvent. 

National Toxicology Program Nitromethane. National Toxicology Program executive summaries, pp 1-12, 1983 

Stokinger HE Aliphatic nitro compounds, nitrates, nitrites. In Clayton DG, Clayton FE (eds) Patty s Industrial Hygiene and Toxicology, 3rd ed, rev, Vol 2C, Toxicology, pp 4153-4155. New York, Wiley-Interscience, 1982 

Machle W, Scott EW, Treon J Physiological response of animals to some simple mononi-troparaffins and to certain derivatives of these compounds. J Ind Hyg Toxicol 22 315-332, 1940 

Lewis TR, Ulrich CE, Busey WM Subchronic inhalation toxicity of nitromethane and 2-nitropropane. J Environ Pathol Toxicol 2 233-249, 1979 

National Tjxicology Program Toxicology and Carcinogenesis Studies of Nitromethane (CAS No. 75 52 5) in F344/N Rats and B6C3F1 Mice (Inhalation Studies). NTP TR 461, NIH Pub No 97-3377, US Department of Health and Human Services, 1997 

The problem is that the B2, C2, and D2 methylene groups are strongly coupled to one another they 

FIGURE 3.52 1-Hexanol in CDClj (A) 600 MHz, (B) 300 MHz. Inserts have same ppm scales, hence, the 600 MHz data has twice the number of Hz per ppm verses the 300 MHz. 

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The simpler nitrop>arafIins (nitromethane, nitroethane, 1- and 2-nitroproj)ane) are now cheap commercial products. They are obtained by the vapour phase nitration of the hydrocarbons a gaseous mixture of two mols of hydrocarbon and 1 mol of nitric acid vapour is passed through a narrow reaction tube at 420-476°. Thus with methane at 476° a 13 per cent, conversion into nitro methane is obtained ethane at 420° gives a 9 1 mixture of nitroethane (b.p. 114°) and nitromethane (b.p. 102°) propane at 420° afifords a 21 per cent, yield of a complex mixture of 1- (b.p. 130-6°) and 2-nitropropane (b.p. 120°), nitroethane and nitromethane, which are separated by fractional distillation. 

In this preparation, phenyi-2-nitropropene is reduced to phenyl-2-nitropropane with sodium borohydride in methanol, followed by hydrolysis of the nitro group with hydrogen peroxide and potassium carbonate, a variety of the Nef reaction. The preparation is a one-pot synthesis, without isolation of the intermediate. 

Nitroethane and 1-(3,4 methylenedioxy) 2- nitropropane This method of producing the above mentioned nitro compounds is by far the best Ritter has come across yet The problem with standard nitroethane synthesis is that the -NO2 source most commonly used is silver nitrite (a la Merck Index citing). Needless to say, this is going to be an expensive compound to make as it is not available commercially but must be synthesized from costly silver nitrate. The other methods mentioned in Vogels 5th masterpiece... 

A solution of gramine (87,3 mg, 0,50 mmol) and 2-nitropropane (33.7 mg, 0.38 mmol) in CHjCN (3 ml) was treated with -Bu3P (18.6 mg, 0.l4mmol). The mixture was refluxed for 4 h. The solvent was removed in vacuo and the residue was acidified with 0.5N aq. HCl and extracted with 95 5 CHjClj-MeOH. The extract was washed with brine and dried (Na2S04). The solvent was removed in vacuo and the residue purified by TLC to yield 138.5 mg (99% yield) of the product. 

Only 20—40% of the HNO is converted ia the reactor to nitroparaffins. The remaining HNO produces mainly nitrogen oxides (and mainly NO) and acts primarily as an oxidising agent. Conversions of HNO to nitroparaffins are up to about 20% when methane is nitrated. Conversions are, however, often ia the 36—40% range for nitrations of propane and / -butane. These differences ia HNO conversions are explained by the types of C—H bonds ia the paraffins. Only primary C—H bonds exist ia methane and ethane. In propane and / -butane, both primary and secondary C—H bonds exist. Secondary C—H bonds are considerably weaker than primary C—H bonds. The kinetics of reaction 6 (a desired reaction for production of nitroparaffins) are hence considerably higher for both propane and / -butane as compared to methane and ethane. Experimental results also iadicate for propane nitration that more 2-nitropropane [79-46-9] is produced than 1-nitropropane [108-03-2]. Obviously the hydroxyl radical attacks the secondary bonds preferentially even though there are more primary bonds than secondary bonds. 

Nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane are produced by a vapor-phase process developed ia the 1930s (2). 

Oxidation. Nitroparaffins are resistant to oxidation. At ordinary temperatures, they are attacked only very slowly by strong oxidi2ing agents such as potassium permanganate, manganese dioxide, or lead peroxide. Nitronate salts, however, are oxidi2ed more easily. The salt of 2-nitropropane is converted to 2,3-dimethyl-2,3-dinitrobutane [3964-18-9], acetone, and nitrite ion by persulfates or electrolytic oxidation. With potassium permanganate, only acetone is recovered. 

Ttinitroparaffins can be prepared from 1,1-dinitroparaffins by electrolytic nitration, ie, electrolysis in aqueous caustic sodium nitrate solution (57). Secondary nitroparaffins dimerize on electrolytic oxidation (58) for example, 2-nitropropane yields 2,3-dimethyl-2,3-dinitrobutane, as well as some 2,2-dinitropropane. Addition of sodium nitrate to the anolyte favors formation of the former. The oxidation of salts of i7k-2-nitropropane with either cationic or anionic oxidants generally gives both 2,2-dinitropropane and acetone (59) with ammonium peroxysulfate, for example, these products are formed in 53 and 14% yields, respectively. Ozone oxidation of nitroso groups gives nitro compounds 2-nitroso-2-nitropropane [5275-46-7] (propylpseudonitrole), for example, yields 2,2-dinitropropane (60). 

O-Acylation of 2-nitropropane occurs on reaction with either ketene or acetic anhydride (61) in the presence of dry sodium acetate at 70—80°C. Ketovinylation of 2-nitropropane at the 1-position occurs on treatment of sodium 2-propanenitronate with a chlorovinyl ketone (62). 

The preparation of polynitroparaftins has been reviewed (75). 2,2-Dinitropropane has been produced ia pilot-plant quantities by Hquid-phase nitration starting from either propane or 2-nitropropane (76,77) (see Nitration). 

High performance Hquid chromatography (hplc) may be used to determine nitroparaffins by utilizing a standard uv detector at 254 nm. This method is particularly appHcable to small amounts of nitroparaffins present, eg, in nitro alcohols (qv), which caimot be analyzed easily by gas chromatography. Suitable methods for monitoring and deterrnination of airborne nitromethane, nitroethane, and 2-nitropropane have been pubUshed by the National Institute of Occupational Safety and Health (NIOSH) (97). Ordinary sorbant tubes containing charcoal are unsatisfactory, because the nitroparaffins decompose on it unless the tubes are held in dry ice and analyzed as soon after collection as possible. 

Inhalation is the chief route of worker exposure. Comparative data from acute or subchronic inhalation exposures with rats (98) indicate that nitromethane and nitroethane are the least toxic of the nitroparaffins by this route and do not induce methemoglobin formation. The nitropropanes are less well tolerated 2-nitropropane is more toxic than 1-nitropropane and is more likely to cause methemoglobinemia. 

A comprehensive study of the tolerance of laboratory animals to vapors of 2-nitropropane was reported in 1952 (100). In a study pubHshed in 1979, rabbits and rats survived exposure to nitromethane for six months at 750 and 100 ppm, respectively, with no unexpected findings (101). Similarly, no compound-related effects were found for rabbits exposed to 2-nitropropane at 200 ppm or for rabbits or rats exposed at 27 ppm. Liver damage was extensive in male rats exposed at 207 ppm for six months, and hepatocellular carcinomas were observed. Subsequendy, the International Agency for Research on Cancer (lARC) found that there is "sufficient evidence" to conclude that 2-nitropropane causes cancer in rats but that epidemiologic data are inadequate to reinforce the conclusion in humans (102). The National Toxicology Program also concluded that it "may reasonably be anticipated to be a carcinogen" (103). 

Environmental Concerns. Few data on the environmental effects of the nitroparaffins are available. However, they are known to be of low toxicity to the fathead minnow (109). Based on their uv spectra, the nitroparaffins would be expected to undergo photolysis in the atmosphere. The estimated half-life of 2-nitropropane in the atmosphere is 3.36 h (110). Various values have been determined for the half-life of nitromethane, but it is similar to 2-nitropropane in persistence (111). Reviews of the available data on the environmental effects of nitromethane and 2-nitropropane have been pubhshed by the U.S. Environmental Protection Agency (112,113). 

When disposed of, all the nitroparaffins are considered to be hazardous waste. AH have the characteristic of ignitabHity however, 2-nitropropane also is a Hsted hazardous waste (U171) because of its toxicity. The preferred method of disposal is by incineration. GeneraHy, the nitroparaffins must be... 

Nltropropane. As much as 9100 t of 2-nitropropane once were consumed for use in coatings annually. Concern about toxicity and a general movement to low volatile organic compound (VOC) coatings have resulted in almost the complete disappearance of this use for 2-nitropropane. However, derivatives such as 2-meth5l-2-nitro-l-propanol (used in tire cord adhesive) and 2-amino-2-methyl-l-propanol (a pigment dispersant and buffer), have served as an outlet for 2-nitropropane production. 

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