Nitric esters decomposition

The decomposition of powder at an elevated temperature does not differ greatly from that of the nitric esters themselves, i.e. nitrocellulose and nitroglycerine (the decomposition of nitrocellulose at various temperatures was discussed earlier in Vol. II, p. 310). The higher the temperature, the more actively the decomposition of the powder proceeds, with total loss of nitrogen, as NO and N02, and carbon as CO and C02. Hydrogen is evolved chiefly as water, the amount of water decreasing with increase in the temperature of decomposition of the powder (Sapozhnikov s investigations). 

Strong bases have an adverse effect on the stability of smokeless powder as described above. Moreover, Angeli [59] found that pyridine and its homologues cause decomposition of nitrocellulose. (On the action of pyridine on other nitric esters see Yol. II.) At an elevated temperature (e.g. 110°C) pyridine can produce an intense denitration of esters which may even lead to an explosion. 

The majority of the stability tests for smokeless powder are much the same as the methods used to determine the stability of nitric esters, in particular nitrocellulose (Vol. II). They are based on heating samples of the powder, thus starting decomposition processes or hastening processes already initiated within the powder. The value of such methods is comparative, since at an elevated temperature different reactions occur than those which would arise under normal conditions of storage. Nevertheless experiments over many years have shown that certain interrelations may be established for the stability of powder at various temperatures. Vieille [61] reports that the heating of a sample of powder for 1 hr at a temperature of 110°C involves approximately the same decomposition as ... 

PETN (2.13), also known as pentaerythritol tetranitrate (C5H8N4012), is the most stable and the least reactive of the explosive nitric esters. It is insoluble in water, sparingly soluble in alcohol, ether and benzene, and soluble in acetone and methyl acetate. It shows no trace of decomposition when stored for a long time at 100 CC. It is relatively insensitive to friction but is very sensitive to initiation by a primary explosive. 

Hydrolytic decomposition has already been discussed. A different type of decomposition of nitric esters occurs at elevated temperatures. More detailed information concerning this type of decomposition will be included in the descriptions of the individual esters properties, in particular those of nitroglycerine and nitrocellulose. 

A number of authors have tried to express the decomposition rate of nitric esters in mathematical formulae. Thus Berthelot [77] expressed the relation between the decomposition rate of nitric esters and the temperature as ... 

It is necessary to take into consideration the fact that the decomposition of nitric esters has an autocatalytic character water and nitrogen dioxide formed during the decomposition lead to the formation of nitric and nitrous acids which accelerate the reaction of decomposition of the nitric ester. The influence of nitric acid on the rate of decomposition of nitroglycerine was studied by Roginskii [79] and is described below. 

It is known and has been demonstrated by several authors (by Sapozhnikov et al. [80] for nitrocellulose by Lukin [81] for nitroglycerine) that change of temperature alters the composition of the reaction products. As the result of numerous experiments, particular temperatures were chosen for definite nitric esters. Thus, owing to the greater ease of decomposition of nitroglycerine as compared with nitrocellulose the high temperature heat test for nitroglycerine is carried out at a temperature lower than that for nitrocellulose (120 and 132° C respectively). 

T. Urbanski, Malendowicz and Dybowicz [68] examined the behaviour of nitroglycerine (and of other nitric esters) exposed to ultra-violet rays and established that nitroglycerine irradiated once for a short period with a quartz lamp started to undergo slow decomposition which stopped only after an interval of 2-3 days. A sample of 3 g nitroglycerine was irradiated for 1 hr with rays from quartz lamp passing through a filter permeable to rays of 3200-4100 A whilst maintained at a temperature of 15°C. In order to test the decomposition of the specimen, from time to time 0.25-0.5 g sample of the substance were removed, shaken with water and the pH values determined. The following results have been obtained immediately after irradiation pH = 6.86 after 6, 24, 48 and 72 hr—6.12, 4.66,4.48 and 5.22 respectively. 

Due to its symmetrical structure, pentaerythritol tetranitrate is characterized by high resistance to many reagents. Thus PETN, differing from the majority of nitric esters, is not readily decomposed by sodium sulphide at 50°C. On the other hand, it is decomposed quite quickly by boiling in a ferrous chloride solution. Boiling with a 2.5% solution of sodium hydroxide causes very slow decomposition, whereas nitrocellulose rapidly decomposes under these conditions. 

Trimethylene glycol occurs in the glycerin which is produced by fermentation. There is no harm in leaving it in glycerin which is to be used for the manufacture of explosives. It may however be separated by fractional distillation. When pure it is a colorless, odorless, syrupy liquid, specific gravity (x°/4°) 1.0526 at 18°. It mixes with water in all proportions and boils at atmospheric pressure at 21 i° without decomposition. At temperatures above 15° or so, it is oxidized rapidly by nitric acid or by mixed acid. It is accordingly nitrated at 0-10° under conditions similar to those which are used in the preparation of ethyl nitrate and other simple aliphatic nitric esters (except methyl nitrate). 

Nitrocellulose, like all other nitric esters with the possible exception of PETN,.is intrinsically unstable, even at ordinary temperatures. Yet the decomposition of a thoroughly purified sample is remarkably slow. Koehler and Marqueyrol100 have made a careful study of the decomposition of nitrocellulose at various temperatures in the vacuum of a mercury pump. They found that it evolved gas at the rate of about 0.7 cc. per gram per day at 100°, 0.01 cc. per gram per day at 75°, and 0.0001 cc. per gram per day at 40°. 

There are many other variations of the heat test.101 They are sometimes called stability tests, but most of them, it will be noted, involve the self-catalyzed decomposition of the sample in an atmosphere of air or of red fumes. They indicate the comparative stability only 6f materials which are physically alike. True indications of the stability of nitric esters are to be secured only by studying the decomposition of the substances in vacuum. For this purpose the 120° vacuum stability test is most generally preferred. 

Pentaerythrite tetranitrate is the most stable and the least reactive of the explosive nitric esters. It shows no trace of decomposition if stored for a very long time at 100°. While nitrocellulose... 

Symmetrical diethyl- and dimethyldiphenyl-urea are known as Centralite I and II respectively. They are used as stabilisers, as they absorb the oxides of nitrogen, formed by the decomposition of nitric esters. 

Nitric esters undergo gradual decomposition on storage. Stalulity tests are therefore necessary as a control of the safety of e q>l< ivcs of this type. The tests are applied during manufacture and to the finished explosive and they may also be applied at intervals during storage, especially in hot climates. 

This depends upon the action of nitric peroxide on colloidal silver oxide. A current of air is passed over the powder and into a colloidal solution of silver oxide. The nitric peroxide reacts with the silver oxide and decreases the amount of light diffused by the colloid. The decrease forms a measure of the decomposition of the nitric esters. 

The thermal decomposition of methyl nitrate has been studied by Phillips [5], who suggested that the reactions occurring at the initial stages of decomposition of methyl nitrate and of other simple nitric esters are as follows ... 

Nitrated cellulose acetate has been prepared, and nucleophilic replacement of nitrate groups of cellulose nitrate with halides has been performed. Oxidative decomposition of cellulose nitrate into a water-soluble material may be brought about by aqueous digestion at high temperature and high pressures, and this finds particular application in the determination of small proportions of the sulfate in cellulose nitrate. A route for the replacement of nitric ester groups in cellulose nitrate by sulfuric ester groups has been reported. ... 

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