Nitration temperature

Both vapor-phase and Hquid-phase processes are employed to nitrate paraffins, using either HNO or NO2. The nitrations occur by means of free-radical steps, and sufftciendy high temperatures are required to produce free radicals to initiate the reaction steps. For Hquid-phase nitrations, temperatures of about 150—200°C are usually required, whereas gas-phase nitrations fall in the 200—440°C range. Sufficient pressures are needed for the Hquid-phase processes to maintain the reactants and products as Hquids. Residence times of several minutes are commonly required to obtain acceptable conversions. Gas-phase nitrations occur at atmospheric pressure, but pressures of 0.8—1.2 MPa (8—12 atm) are frequentiy employed in industrial units. The higher pressures expedite the condensation and recovery of the nitroparaffin products when cooling water is employed to cool the product gas stream leaving the reactor (see Nitroparaffins). 

Process (3) may be slow, hence under industrial conditions it may be broken off before equilibrium is established. This means that chemical reaction (3) is not completed. As a final product, a not very homogeneous nitrocotton is obtained. The higher the nitrating temperature, the more rapid the denitration process, the sooner the reaction balance is established, and hence the more uniform the product ... 

Treatment of DPT (239) with dinitrogen pentoxide in pure nitric acid leads to the isolation of the nitrate ester (249), an unstable explosive which is highly sensitive to impact and readily undergoes hydrolysis. A low nitration temperature favours the formation of (249) and its presence during the nitrolysis of hexamine is clearly undesirable. The nitrolysis of DPT (239) with one equivalent of pure nitric acid in an excess of acetic anhydride yields 1-acetomethyl-3,5,7-trinitro-l,3,5,7-tetraazacyclooctane (251), a useful starting material for the synthesis of other explosives. ... 

C-Nitration of 1,2,3-triazole and 1,2,4-triazole rings can be achieved with either mixed acid or solutions of nitric acid in acetic anhydride. V-Nitration is usually achieved with nitric acid in acetic anhydride at ambient to subambient temperatures. Thermal rearrangement of the N-nitro product to the more stable C-nitro product often occurs at higher nitration temperature. 

The formation of this substance is favoured by a low nitration temperature. It is unstable and highly sensitive to impact hence its presence in cyclonite is very undesirable. 

Fig. 17. Temperature changes during the nitration of hexamine with nitric acid, according to Dunning, Millard and Nutt [50], 7—Anhydrous acid, nitration temperature 20°C 2—anhydrous acid, nitration temperature —35.5°C 3—96% acid, nitration temperature 20°C 4—96% acid, nitration temperature —35.5°C 5—90% acid, nitration temperature 20°C 6—90% acid, nitration temperature —35.5°C 7—85% acid, nitration temperature 20°C —85% acid, nitration temperature —35.5°C.

Nitrating temperature Residual acid content Heat test... 

A nitration temperature within the limits 30-35°C should not be considered dangerous and is often applied in some factories (e.g. Gyttorp [7]). However, should any irregularity occur which may be accompanied by an increase in temperature, obviously less time will be available to lower it than if the working temperature is lower (e.g. 20-25°C). 

The most reliable method of determining the quality of glycerine is the laboratory nitrating test. This should be carried out under conditions that correspond as closely as possible to those prevailing in the plant. During the laboratory nitration, temperature, the rate of separation of the nitroglycerine and the add layers, the contact surface of phases and so on should be recorded. 

Nobel invented a radically new design of nitrator for the manufacture of nitroglycerine. Originally it was made of sheet lead and equipped with a cooling coil supplied with water, (Fig. 15, p. 65) and later a water-cooled jacket made of wood was added (Fig. 28). In later versions of the Nobel nitrator the cooling jacket was omitted in favour of a four-fold cooling coil with which it was easier to control the nitration temperature. 

The exact setting of the acid and glycerine rotameters is adjusted by means of the corresponding valves and the nitrating temperature is checked. It should be 40-45°C higher than the temperature of the incoming mixed add. 

The Mikolajczak process is usually safer than nitroglycerine manufacture. It is necessary, however, to maintain a low nitrating temperature and to use acid free from oxides of nitrogen which favour oxidation reactions. Local overheating should be carefully avoided, because dilute acid is specially prone to produce oxidation processes. 

The relation between the chemical stability and nitrating temperature observed by Ropuszynski [29] in the instance of nitroglycerine (p. 43) and nitroglycol (p. 148) has been also confirmed with dinitrodiglycol. Diglycol nitrated at a higher temperature demonstrates improved stability owing to its lower content of residual acids. The relevant data are shown in Table 23. 

Effect of the conditions of nitration. The conditions under which the nitration was carried out exert an appreciable influence on the viscosity of nitrocellulose solutions. Thus a high nitrating temperature produces low viscosity nitrocellulose... 

Nitration temperature °C Nitrogen content % Viscosity sec Solubility in ether-alcohol %... 

Lunge et al. [15] examined the effect of the composition of mixed add, and the influence of the nitration temperature within the range from 0 to 80°C on the nitrogen content of nitrocellulose, the content of non-nitrated cellulose, the yield, the solubility of the products in ether-alcohol mixture and the viscosity of the acetone solution. Cotton linters were used. From these experiments it has been established that nitrocellulose containing more than 13.5% N is unstable and decomposed readily, as mentioned before. 

In principle the viscosity of nitrostarch is affected by the same factors which cause a change of viscosity in nitrocellulose. Thus a high nitrogen content in the product, an elevated nitration temperature, or an intensive stabilization boiling of the nitrated product lowers the viscosity of the nitrated substance. However, in the case of nitrostarch the changes in viscosity under the influence of these factors are insignificant. 

Recently extensive investigations on the nitration of starch, mainly by using mixed nitric and sulphuric acid have been carried out by Kunz and T6th [46]. Their object was to determine the effect of the ratio of the components in the nitrating mixture and the activity of nitric acid in the mixtures on the nitrogen content of the nitrostarch, the heat of esterification, and the relation between the nitration temperature and the viscosity of the product. Their observations concerning the time of reaction are of special interest. This varies as a linear function of the nitration temperature. In the graph (Fig. 169) the relationship is shown for two mixed acids ... 

Crystalline form of ammonium nitrate Temperature °C Change of volume cm3/g Thermal effect cal/g... 

The influence of the nitration temperature on the orientation of a nitro group is in certain cases rather marked When nitrating toluene with a mixture of nitric and sulphuric acids at -5°C, Pictet [56] observed that more para-isomer was obtained than at the temperature of 0°C. 

The procedure of Bradfield and B. Jones was applied later by W. W. Jones and Russel [58] to their experiments on the nitration of toluene (their work will be further discussed later on p. 274). The results they obtained established the rule a lower nitration temperature causes an increase in the quantity of para- nitro-toluene formed and reduces the amounts of ortho- and meta- isomers. 

Nitration temperature °C Quantity oT phenylnitromethane obtained g Quantity of phenyldinitromethane obtained g... 

Thus, p- xylene yielded 2,5-dichloro-p-xylene. The principal reaction with anisole was also chlorination and with phenol nitration when nitration temperature was low (-80°C) both o- and p- nitrophenols were formed. At room temperature chlorination also occurred yielding 2,4-dichloro-6-nitrophenol and 3,6-dichloro-2-nitro-phenol. 

The Leverkusen (I. G. Farbenindustrie) process differs in that it uses a slightly different mixed acid and a rather lower nitration temperature. 

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