Picric acid decomposition

Identification of Amines. Picric acid combines with many amines to give crystalline picrates, of general formula B,(NO )aCeHjOH, where B is a molecule of a monacidic base. These picrates have usually sharp melting- or decomposition-points, and serve to characterise the amines concerned. They may be formed either by (a) direct union of the acid and the base in a suitable solvent, or (6) by the interaction of sodium picrate and a salt of the amine in aqueous solution. 

Dissolve 0 01 mol of the phenohc ether in 10 ml. of warm chloroform, and also (separately) 0 01 mol of picric acid plus 5 per cent, excess (0 -241 g.) in 10 ml. of chloroform. Stir the picric acid solution and pour in the solution of the phenohc ether. Set the mixture aside in a 100 mb beaker and ahow it to crystallise. Recrystahise the picrate from the minimum volume of chloroform. In most cases equahy satisfactory results may be obtained by conducting the preparation in rectified spirit (95 per cent. CjHgOH). The m.p. should be determined immediately after recrystallisation. It must be pointed out, however, that the picrates of aromatic ethers suflFer from the disadvantage of being comparatively unstable and may undergo decomposition during recrystaUisation. 

The salt is nearly as shock-sensitive as picric acid. When pure it does not explode on heating, but traces of nitrate cause explosive decomposition. 

The substance is exceptionally sensitive to the action of acids. When mixed with picric acid, for example, it undergoes violent decomposition after 2 hours heating at 60°C. At 100°C decomposition ensues in 10-15 minutes. A mixture with trinitrotoluene is decomposed at 85°C. 

For every 10 °C increase in temperature, the rate of decomposition is approximately doubled, but may increase as much as 50 times if the explosive is in the molten state. The rates of decomposition depend on the condition of storage and the presence of impurities which may act as catalysts. For example, nitroglycerine and nitrocellulose decompose at an accelerated rate due to autocatalysis, whereas the decomposition rate of TNT, picric acid and tetryl can be reduced by removing the impurities which are usually less stable than the explosive itself. With many of the explosives the presence of moisture increases the rate of decomposition. 

The result a are compared to a standard expl, such as picric icid, gunpowder or mercury fulminate, and expressed as a ratio known as figure of insensitiveness. This ratio represents the relative energies of the impact required to produce explosions of equal degrees of completeness from initial decomposition to complete detonation. Picric Acid is taken as 100, and explosives giving higher numbers are less sensitive while those giving lower numbers are more sensitive than picric acid. Ref R.Robertson, JCS 119 1,15(1921)... 

Di-m-tolyl methyl tellurium iodide,3 (C7H7)2(CH3)TeI, is obtained in quantitative yield from its components. It crystallises in four-sided columns, soluble in chloroform, insoluble in ether. It melts at 121° to 122° C.s splitting up again into its components. When boiled with water and silver oxide and the solution treated with picric acid, a picrate is formed this separates from alcohol with five molecules of solvent of crystallisation, and melts at 114° to 115° C. The platinichloride melts with decomposition at 154° to 155° C. 

Tri-p-tolyl tellurium iodide1 melts with decomposition at 232° to 233° C., dissolves readily in methyl alcohol or chloroform, less readily in benzene or ether, and is insoluble in water. Tri-p-tolyl tellurium bromide occurs when the iodide or chloride is boiled with silver bromide. It melts at 265° to 266° C. with decomposition, and dissolves in alcohols or chloroform, but is insoluble in benzene or ether. Tri-p-tolyl tellurium chloride is prepared from the bromide in the usual way. It melts at 260° to 261° C. and gives precipitates with the chlorides of mercury, tin and gold, picric acid and platinic chloride. The hydroxide is a resin, melting at about 110° C., and yielding a pier ate, consisting of long prisms, M.pt. 194° to 195° C.a... 

Guanidine picrate is procured as a yellow, finely crystalline precipitate by mixing warm solutions of guanidine nitrate and ammonium picrate. It is even less sensitive to blow and to shock than ammonium picrate it is not detonated by fulminate and is used with a picric acid booster. The pure material, recrystallized from alcohol or from water, in both of which solvents it is sparingly soluble, melts with decomposition at 318.5-319.5°. 

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. 

Fig 2 Kinetic gas-evolution curves in the decomposition of Tetryl with the addition of Picric Acid at 150° 1) Tetryl alone 2) 0.62 mole of Picric Acid per mole of Tetryl 3) 1.26 moles of Picric Acid per mole of Tetryl 4) 2,57 moles of Picric Acid per mole of Tetryl... 

Tait24 was determined as 189°C by adiabatic Dewar tests, with an apparent energy of activation of 144 kJ/mol. Dinitrophenol is now classified as an explosive in the UK, and is normally available from laboratory suppliers wetted with 15% water, as is picric acid. See entry THERMOCHEMISTRY AND EXOTHERMIC DECOMPOSITION (reference 2). 

Some of the authors had drawn attention to the explosive character of picric acid salts, but it was not until 1830 that Welter [3] suggested the possibility of applying picrates as explosives. At that time picric acid was obtained solely by acting with nitric acid on indigo. Marchand [7] expressed the view, which proved to be true, that it was aniline, formed as mi intermediate product in the process of decomposition of indigo, silk Mid other organic matter, which yielded picric acid under the influence of nitric acid. 

Violent boiling of picric acid with a concentrated solution of sodium hydroxide may bring about decomposition of the former ... 

Based on effects observed in water (Navy 1984b), tetryl released to soil is expected to be susceptible to slow hydrolysis in acidic and neutral soils and to relatively rapid hydrolysis in highly alkaline soils (HSDB 1994). Samples of water collected from lysimeters containing tetryl-contaminated soil indicated that the major transformation products were picric acid (5-14%) and other polar, water- soluble decomposition products no tetryl was detected in the water, or in the soil at the end of the study, suggesting complete hydrolysis (Kayser and Burlinson 1988 Navy 1982). The specific reaction leading to these products was not determined. Because tetryl is subject to photolysis in water, it may be susceptible to photolysis on sunlit soil surfaces (HSDB 1994). 

Evidently the a-H is likely to be involved in the early stages of the decomposition process [16], perhaps moving to an adjoining nitro group to form a nitronic acid tautomer, 4 [35,45,46]. These are known to be reactive and unstable [47], The transfer or loss of a proton to yield a nitronic acid or a nitronate (aci) anion has also been invoked as the initial step in the decompositions of other energetic molecules, e.g. picric acid [35,48] and amine-sensitized nitromethane [49-51]. 

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