Temperature of nitration

The safety limit of temperature depends on the chemical structure of the compound being nitrated. For exMnple, in the nitration of dinitrotoluene to trinitrotoluene or of phenol to picric acid, temperatures neM 120°C Mid over are considered dangerous. In the nitration of dimethylaniline to tetiyl, a temperature higher than 80°C must be considered dangerous. Esterification with nitric acid should be carried out at a temperature close to room temperature or lower. 

There are three methods of mixing organic substances to be nitrated with nitrating mixtures  

Insufficient mixing may easily result in a low nitration rate owing to the small interfacial area. It can also lead to a non-uniform nitration process. Owing to inadequate construction of the stirrer, too low a speed of rotation, or an interruption in stirring, so-called dead spaces may easily be formed in which non nitrated or not fully nitrated substances accumulate. If a rather large quantity of the mixture is stirred suddenly, rapid extension of the interfacial area takes place, followed by the generation of large amounts of heat and a rise in temperature. This may cause a spontaneous decomposition of the reaction mass in the nitrator, and then an explosion. 

Such an accident, well known in the history of the chemical industry, happened at the Rummelsburg factory in 1914 during the nitration of benzene. The transmission belt slipped off and caused the stirrer to stop. In spite of this benzene continued to flow into the nitrator. When the fault was noticed, the stirrer 

A few workers have investigated recently the problem of the influence of stirring on the rate of nitration and the yield of the reaction. McKinly and White [7] reported that the rate of nitration of toluene to nitrotoluene increased by 3% only when the stirring speed was increased from 1327 to 2004 r.p.m. 

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A lower temperature of nitration favours the formation of m-nitrotetryl, e.g. when dimethylaniline is nitrated at 65 and 0°C the corresponding percentages of m-nitrotetryl are 11 and 30%, respectively. 

Nitration is usually carried out in such a way that the solution of dimethylaniline in sulphuric acid is introduced into a nitrating mixture rich in nitric acid. The nitration reaction proceeds vigorously, and it is therefore most important to control the reaction temperature. Formerly it was believed that for safety s sake the lowest possible temperature of nitration should be maintained. Later it became clear that at such a temperature nitration is not brought to completion and a large quantity of incompletely nitrated products accumulates, which may lead to an... 

The reaction is able to take place without destroying the fibrous structure of the cellulose. The extent of nitration of the —OH groups is dependent on the reaction conditions, particularly the composition of the acid, the time and temperature of nitration. 

The relation between the temperature of nitration and the yield of nitroglycerine is especially marked if less concentrated mixed acids are used. According to Naoum s data, nitrating glycerine in mixed acid containing... 

The discrepancy has been explained by the experiments of T. Urbanski and Kwiatkowska [28] who found that by dissolving sorbitol in a five-fold quantity of concentrated nitric acid (d = 1.52) at 0°C followed by precipitating the product with the help of a ten-fold amount of 20% oleum at +5°C, hexanitrate only slightly contaminated with pentanitrate was formed. When, however, the temperature of nitration and precipitation is -10°C an oily mixture of sorbitol hexa- and pen-tanitrates was produced. Most probably it was a mixture of this kind that Davis described, as sorbitol pentanitrate exists under normal conditions in the form of an oil. The explosive properties of nitrosorbitol resemble those of nitromannitol. 

On varying the temperature of nitration from 0 to 80°C, Lunge observed that ... 

Temperature of nitration °C Nitrogen content of nitrostarch % Relative viscosity (water = 100) Solubility in alcohol %... 

The formation of the small amount of meta nitro-toluene is explained thus by Holleman (2) It is apparent that there is an opposition between the ortho and para derivatives on one hand, and the meta derivatives on the other. Either the first two are the chief products, or the last. Concerning the temperature of the reaction, it has been proved that the quantity of the by-products is the smaller, the lower the temperature of nitration. This statement of Holleman is based on earlier work by himself, and in a paper he gives this tabulation (3)... 

Ogilvie B. G., Rutter M., and Nedwell D. B. (1997b) Selection by temperature of nitrate-reducing bacteria from estuarine sediments species composition and competition for nitrate. FEMS Microbiol. Ecol. 23, 11 —22. 

Temperature of Nitration. Total Yield. 7-Isomeride. 5-Isomeride. 

Some efforts have been made to reduce the proportion of undesirable m-nitrotoluene. A general rule is that the lower the temperature of nitration the smaller the proportion of meta isomer (Vol. I, p. 273). Also the use of nitric acid acetic anhydride mixture at 0 C can assure a lower proportion of m-nitro toluene, for example to reduce it to 1.6% [22]. This is in agreement w ith former findings (Vol, I, p. 274). 

Anthraquinonc was nitrated to 1,5 dinitro-antluactuinone by T. Urbahski and Zyiowski 165). The temperature of nitration was U0-120 C for hour and the yield 67%. 

The influence of the temperature of nitration of 4-alkyl-phenol acetates was examined by the same authors [40] and simultaneously and independently by Schofield and associates [41]. The latter examined the thermal migration of the nitro group ... 

It seems that the high temperature of nitration applied by Hess and coworkers (Vol. I, p. 86) 410 430 C was too high for dinitro compounds and they decomposed. 

The temperature of nitration for benzene may vary within moderate limits. When no cycle acid is used, it is inadvisable to exceed 50 C when fortified spent acid is employed, the nitration temperature may be kept between 50 and 55°C. The efficiencies of agitation and of heat exchange are also important considerations, which affect not only the control of temperature but also the rate of feed. 

Diagrams - Fig. 14a—c — shows that substitution can occur not only in meta, but also in ortho and para positions. According to the diagrams it should be expected that the proportion of ortho isomer should be superior to that of the p-dinitrobenzene. Indeed this is in agreement with the experiment the proportion of o-dinitrobenzene is larger and at high temperature of nitration much larger than that of p-dinitrobenzene (Vol. 1, p. 243, Tables 38 and 39). 

Weight ratio Temperatures of nitration fC) Time o nitration (min)... 

Calculation of acid mixtures Temperature of nitration Solubility of nitrocompounds Design of nitrators Heat exchange devices Stirrers... 

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