Nitric acid vapour

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. 

Although no chemical reaction occurs, measurements of the freezing point and infra-red spectra show that nitric acid forms i i molecular complexes with acetic acid , ether and dioxan. In contrast, the infrared spectrum of nitric acid in chloroform and carbon tetrachloride - is very similar to that of nitric acid vapour, showing that in these cases a close association with the solvent does not occur. 

A zinc/potassium chlorate mixture is explosive on impact or friction. With potassium superoxide the metal glows. The same thing happens when a mixture of zinc and titanium oxide is heated or when nitric acid vapour is in contact with melted zinc ( 400°C). 

A jet of ammonia will ignite in nitric acid vapour. 

The fluoro compound is resistant to nitration and an operating temperature of 90°C is necessary to ensure formation of the 5-nitro derivative. Under these conditions, the atmosphere (containing the fluoro compound, its nitro derivative and nitric acid vapours) in the nitration vessel is explosive and above the flash point. An unknown ignition source led to an explosion and rupture of the 3 cu. m vessel, and a maximum explosion pressure of 50 bar was confirmed experimentally. Such explosive atmospheres are not found in low temperature nitration reactions. 

Nitric acid vapour pyrolyzes at a measurable rate above 100 °C, decomposition proceeding in accordance with the stoichiometric equation... 

Because anhydrous nitric acid is of low thermal stability even at room temperature, very few photochemical and radiolytic studies have been carried out with it. A flash photolytic study of nitric acid vapour by Husain and Norrish250 has provided evidence for a primary photochemical split into OH and N02, viz. 

Ammonium nitrate mixed with litharge expels ammonia from the solid salt at ordinary temp. T. J. Pelouze found that when ammonium nitrate is treated with a little sulphuric acid, ammonium sulphate and nitric acid are formed the same result obtains with the dried salt in fifty times itB weight of sulphuric acid provided the temp, is below 120° but at 150°, nitrous oxide mixed with a little nitric oxide and nitric acid vapour is evolved, and sulphuric acid and water remain. If the salt be mixed with ten times its weight of sulphuric acid, about 75 per cent, of the. salt forms nitric acid and ammonium sulphate, and 25 per cent, forms nitrous... 

Nitric acid is a strong oxidizing agent. Organic substances may ignite when reacted with the concentrated acid (fuming and anhydrous). Nitric acid vapour irritates the respiratory tracts. If nitric acid gets on one s skin, it causes serious... 

Research on the nitric acid vapour pressure in the ternary system... 

Similar conclusions have been reached by Champetier and Foex [70] and by Trombe, Foex and Champetier [71]. Wilson and Miles also studied the kinetics of nitration in nitric acid vapour. On the basis of these investigations they concluded that two molecules of nitric acid take part in the reaction with one OH group ... 

During World War II, a method of two-stage cellulose nitration was used in Germany on a semi-plant scale (10 tons a month). Cellulose was first treated with air saturated with nitric acid vapours, and then the partially nitrated cellulose was immersed in 98% nitric acid. The initial treatment of the cellulose with vapours of nitric acid prevents the surface gelatinization that ordinarily occurs if cellulose is introduced direct into concentrated nitric acid. The product obtained in this way... 

The main drawback of these methods consists in the difficulty of maintaining constant composition of the mixed acid, hence there is liable to be a significant lack of uniformity in the resulting nitration product. A more uniform product can be obtained by using nitric acid vapour [24],... 

If concentrated sulfuric acid is heated with a metal nitrate such as sodium nitrate, nitric acid vapour is produced. 

Thus Badger and Bauer [7] examined the spectrum of 100% nitric acid vapour alone and in dioxane solution in the region near 1 p. Dalmon [8,49], Dalmon and Freymann [9], and Freymann [66] have studied the spectra of nitric acid and its solutions in dioxane, carbon tetrachloride and water. 

In favour of the view, that postulates the formation of an addition product during the first stage of nitration this fact should be known to all who are practically engaged in nitration of aromatic hydrocarbons. Immediately before contacting the nitrating acid (HN03 or nitric and sulphuric acids mixture), benzene and toluene give brown coloured products amid nitric acid vapours. On dissolution in the acid these products decolourize at once. It is quite possible they arc addition products formed by nitric acid vapours with the hydrocarbon. 

The nitration of aliphatic hydrocarbons may be accomplished in the vapour phase, at 410-430°C, using nitric acid vapour. A number of papers describing this method of nitration were published by Hass and co-workers [29] between 1936 and 1940. 

McCleary and Degering [36] present a different mechanism for the nitration of paraffins with the nitric acid vapour, although like Titov they also assume the formation of free radicals ... 

A number of explosions in French TNT factories which occurred during 1917-18, in particular the one at Neuville-sur-Saone (1917) which caused the destruction of the whole plant, were presumably due to the decomposition of the products of reaction of metals, such as lead or iron, with TNT under the conditions described in a paper by Kovache and Thibon [31]. Products readily decomposed, and sensitive to friction and impact, were formed in various parts of the plant where contact between these metals and the TNT could occur in the presence of dilute nitric acid, for example in the TNT washing tank and granulators. Similar compounds were found in a nitrator where part of the TNT in close contact with metals was subjected to the action of nitric acid vapours, for example around the seals at the stirrer shaft bearings. 

Nitrogen oxides, as well as nitric acid vapours, generated in the reaction, flow via the ventilating pipe to a system of jars, coolers and absorption towers, where they are absorbed. 

Nitromethane, CH3N02, is a volatile liquid. It may be obtained by direct vapour phase nitration of paraffinic hydrocarbons either with nitric acid vapours (Hass et al. [1-8]) or with nitrogen dioxide (T. Urbanski and Slebodzinski [9]). It may also be prepared by the action of sodium- or potassium nitrite on chloroacetic acid... 

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