Nitration of Propane

Nitrating propane produces a complex mixture of nitro compounds ranging from nitromethane to nitropropanes. The presence of lower nitroparaffins is attributed to carbon-carbon bond fission occurring at the temperature used. Temperatures and pressures are in the range of 390°-440°C and 100-125 psig, respectively. Increasing the mole ratio of propane to nitric acid increases the yield of nitropropanes. Typical product composition for 25 1 propane/acid ratio is  

Nitropropanes are good solvents for vinyl and epoxy resins. They are also used to manufacture rocket propellants. Nitromethane is a fuel additive for racing cars. 

Nitropropane reacts with formaldehyde producing nitroalcohols CH3CH2CH2NO2 -h HCHO CH3CH2CH(N02)CH20H These difunctional compounds are versatile solvents, hut they are expensive. 

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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. 

The only method utilized commercially is vapor-phase nitration of propane, although methane (70), ethane, and butane also can be nitrated quite readily. The data in Table 5 show the typical distribution of nitroparaffins obtained from the nitration of propane with nitric acid at different temperatures (71). Nitrogen dioxide can be used for nitration, but its low boiling point (21°C) limits its effectiveness, except at increased pressure. Nitrogen pentoxide is a powerful nitrating agent for alkanes however, it is expensive and often gives polynitrated products. 

Table 5. Effect of Temperature on the Nitration of Propane with Nitric Acid...

F. SI sol in w (1.4ml/100ml) 0.5ml w dissolves in 100ml of 1-Nitropropane misc with many org solvents. Prepd by the vapor-phase nitration of propane (Refs 1 a 3)... 

Accdg to Hibshman et al (Re f 4), vapor-pbase nitration of ethane produces a mixture of C2H.5NO with CH8N02- In the lab method of prepn by Desseigne Giral (Ref 8), pure NEt xs produced starting from ethanol, oleum and Na nitrate. It is stated, however, that the method is not suitable for industrial purposes because it cannot compete with vaivirahhasp nitration of propane which renders... 

Nitromethane was first prepared in 1872 by Kolbe, and is produced commercially by high-temperature vapour-phase nitration of propane. The process, which uses nitric acid as the nitrating agent, is based on a free-radical reaction in which the active species is the NO2 radical (Markofsky, 1991 Angus Chemical Co., 1998). 

All four compounds are produced by the vapor-phase nitration of propane.197-199 Nitroalkanes are important as solvents and intermediates.199... 

The nitration of propane is operated at 370-450 C and at about 10 atm. The use of about a fourfold excess of propane, 60-70% nitric acid, and short residence time ensures good temperature control.199 The conversion of nitric acid to nitroalkanes is less than 50% (the balance are nitrogen oxides). Excess propane is usually recycled to achieve about 60-80% yield of nitroalkanes. Under these conditions nitropro-panes are the main products. 

All available evidence points to a radical mechanism for nitration, but many aspects of the reaction are not fully understood. Mixtures are obtained nitration of propane gives not only 1- and 2-nitropropanes but nitroethane and nitromethane ... 

Exercise 24-20 Show how the following compounds can be prepared from the commercially available nitroalkanes obtained from the nitration of propane. (It may be desirable to review the material on aldol and Michael additions in Chapters 17 and 18.)... 

Levy and Rose [68] reported that nitration of propane with nitrogen dioxide at 360°C under 10 atm gave a 75-80% yield of nitroparaffins. The mixture of products was composed of 20-25% nitromethane, 5-10% nitroethane, 45-55% 2-nitropropane, 20% 1-nitropropane and 1% 2,2-dinitropropane. Geiseler [69] nitrated paraffins under 4 atm at 190°C. Grundman and Haldenwanger [70] nitrated cyclohexane with nitrogen dioxide at 120-125°C under 4-5 atm and obtained both mono- and di-nitroproducts. 

FIG- 31. Oijgram oT nitration of propane by Commercial Solvents Corp.,... 

Albright ct al (971 examined the inlluence of gamma radiation upon Ihc vapour phase nitration of propane with nitric acid at 400 450°(. There was a slight effect of irradiation on the yield of nitro products, in agreement with the above finding (Ob). The increase of the yield o nitro alkanes was of the order of onlv 10 15%. 

The industrial method for the nitration of propane is based mainly on the description by Dole2el (4] in the German edition of the book by the author of the present monograph. Some detaUs can also be found in the review article by Shechter and R. B. Kaplan [6b. ... 

Derivation Nitration of propane and other paraffin hydrocarbons under pressure. 

The development of the preparation of nitroparaffins from laboratory scale through pilot-plant to full-scale operation covered a 20-year-long effort by Commercial Solvents Corporation. A full-scale plant with a capacity of more than 10,000,000 lb per year went on stream in 1955. By a process of nitration of propane, the main production of nitroparafl5ns includes nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane. The nitration is done in the vapor phase. A flow diagram illustrating the process is shown in Fig. 4-17. There are five process sections in the nitroparaffin preparation. These involve (1) nitration, (2) products recovery, (3) products purification, (4) products separation, and (5) reactants recovery. A report by Schecter and Kaplan states that conditions for the nitration of propane are 770 F (410 C) at pressures of 115-175 psi. Initially the vapor-phase... 

Show how the following compounds might be prepared from the commercially available nitroalkanes obtained from the nitration of propane. 

Lee, Chung and Albright [57] examined the nitration of propane with nitric acid vapours at 425-430°C when propane to nitric acid ratios were 6 1 and... 

Albriglit a al. [h7] examined the influence ot gamma radiation iipor the vapour phase nitration of propane wnfi nitric acic at 400 450°C. H ero was a slight effect of irradiation on the >ield of nitro products, in agreement with t ic above finding [ >bj. The incieasc of the yield ot nitro alkanes was of llic order of only 10 S7. 

The nitroparaffins produced by the vapor phase nitration of propane or ethane are available from two United States production facilities Angus Chemical Company (Sterling, LA) and W. R. Grace and Company (Deer Park, TX). This chapter discusses the naming nomenclature for the nitroparaffins, their physical properties, the various industrial uses, possible environmental concerns, and the safe handling of the nitroalkanes. 

Data obtained for the nitration of propane with NO in the gas phase at <300 "C in the presence of oxygen shows [3] that a rise in oxygen concentration in the reaction zone by increasing the opportunities for radical formation appreciably increases the yield of nitroalkanes. If the same process is carried out at 350 C, there is a sharp fall in the yield and extent of conversion, and there is an appreciable increase in the carbon monoxide (CO) content of the exit gases. It would appear that, in the high-temperature nitration of alkanes, conditions are created under which the rate of the reaction ... 

In the course of gas-phase nitration of alkanes with NO, increase in the yield of nitroalkane can be attained by increase in the rate of radical formation and retardation of oxidative reactions in which the free radicals take part. It is probable that the catalytic effect of molecnlar iodine on the nitration of propane with NO is associated mainly with the tendency of inactive iodine atoms to retard the oxidation of hydrocarbons [11]. In the presence of 0.15% I, the CO content of the reaction products is reduced from 22.1 % to 5.2%. Simultaneously, the yield of nitro compounds is increased by 10%. 

The effect of NO is particularly notable in the nitration of propane with nitric acid at 420 °C [10]. Being a powerfnl inhibitor of chain reactions (Chapter 3), NO reduces the rate of radical formation and the rate of recombination of radicals with NO. On the other hand, the increase observed in the content of CO and Cp of the exit gases indicates the development of processes of hydrocarbon breaking. The addition... 

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