Picric acid melting temperature

Since picric acid melts at high temperature, shells are loaded by pouring it in. mixed with various nitro compounds dinitrophenol, mono- and di-nitronaph-thalenes, TNT, TNX etc. (Vol. El). 

Picric acid was adopted all over the world as the basic explosive for military uses. The major problems of picric acid are corrosion of the shells in the presence of water and high sensitivity of its salts. Also, picric acid melts only at a very high temperature. 

The greenish yellow plates, which separate as the solution is cooled to room temperature, are filtered, washed 3 times with 150- to 200-ml. portions of water, and air-dried. The filtrate and first washings are combined and heated, 10 g. of picric acid is added, and the mixture is cooled and filtered. This process is repeated, using 10-g. portions of picric acid, until the air-dried picrate fraction so obtained melts below 195° (Note 5). 

As early as 1873, picric acid was detonated to produce explosion. Subsequently, it was found to be a suitable replacement for black powder. From 1888 into World War I, it was used as a basic explosive for military purposes. Because it required prolonged heating at high temperatures in order to melt and because it also caused shells to corrode in the presence of water, an active search for better explosives continued. 

Picric acid was used in grenade and mine fillings and had a tendency to form impact-sensitive metal salts (picrates) with the metal walls of the shells. The filling of mines and grenades was also a hazardous process, since relatively high temperatures were needed to melt the picric acid. Some of the properties of picric acid are presented in Table 2.9. 

Tetryl is a pale yellow, crystalline solid with a melting temperature of 129 °C. It is moderately sensitive to initiation by friction and percussion, and is used in the form of pressed pellets as primers for explosive compositions which are less sensitive to initiation. It is slightly more sensitive than picric acid, and considerably more sensitive than TNT. Tetryl is quite toxic to handle and is now being replaced by RDX and... 

RDX has a high chemical stability and great explosive power compared with TNT and picric acid. It is difficult to dissolve RDX in organic liquids but it can be recrystallized from acetone. It has a high melting point which makes it difficult to use in casting. However, when it is mixed with TNT, which has a low melting temperature, a pourable mixture can be obtained. Some of the properties of RDX are presented in Table 2.15. 

Belyaev s experimental studies related to liquid secondary explosive materials—methylnitrate, nitroglycol, nitroglycerine—and to secondary explosive materials which are solid at room temperature, but which melt when ignited—trotyl, picric acid, etc. 

Pure hexanitrocarbanilide crystallizes from acetone-ligroin in pale yellow rosettes which soften and darken at 204° and melt at 208-209° with decomposition. It yields picric acid when warmed with dilute sulfuric acid, and trinitroaniline when boiled with strong ammonia water. A deep ruby-red color is developed when hexanitrocarbanilide is allowed to stand at ordinary temperatures in contact with strong ammonia water. Tetranitrocarbanilide, dinitroaniline, trinitroaniline, picric acid, and dinitro-phenol do not give this color. 

Tetranitrobenzene is a crystalline substance, melting at 129-130°C. In the presence of moisture it is readily decomposed to form picric acid. When boiled with water it is fully converted to picric acid. It reacts with ammonia even at room temperature, forming picramide ... 

When heated to a temperature above its melting point, picric acid can react with sulphur. Addition of sulphur lowers the ignition temperature of picric acid (see below). 

Tucholski determined the dehydration temperatures of picric acid salts hydrates, their melting points, initiation temperatures and temperatures preceding explosion. T. Urbanski and Sion determined their sensitiveness to impact and flame. 

It is prepared by nitration of m-cresoldisulfonic acid. During the First World War, 60 40 mixtures of trinitrocresol and picric acid were used (under the name of Kresylith) as grenade fillings, since they melt at a temperature as low as 85 °C (185 °F). 

Nitro groups also increase the reactivity of phenols, but replacement of the hydroxyl by an amino group still needs temperatures of 150-200° and thus usually the use of pressure vessels.1054 Primary amines can be obtained at normal pressures from di- and tri-nitrated phenols and naphthols by melting them with urea 1055 1056 picramide, m.p. 188°, for instance, was formed in 88% yield by heating picric acid with 3 equivalents of urea at 173° for 36 h.1056... 

Picric acid did have its problems in the presence of water it caused corrosion of the shells, its salts were quite sensitive and prone to accidental initiation, and picric acid required prolonged heating at high temperatures in order for it to melt. 

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