Picric acid general

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. 

Picrates, Picric acid combines with amines to yield molecular compounds (picrates), which usually possess characteristic melting points. Most picrates have the composition 1 mol amine 1 mol picric acid. The picrates of the amines, particularly of the more basic ones, are generally more stable than the molecular complexes formed between picric acid and the hydrocarbons (compare Section IV,9,1). 

VIII. Explosive Characteristics. Picric Acid is generally considered to be a relatively insensi tive but brisant expl. On a qualitative sensitivity scale of comparing common expls, PA would be judged to be more sensitive than TNT but appreciably less sensitive than Tetryl. Its power and brisance are also similar to those of TNT (112% TNT in the Ballistic Mortar 101% of TNT in the Trauzl Block and 107% in the plate dent test (Ref 48). In this section we will consider the steady detonation parameters. initiation characteristics and potential hazards of PA... 

Picric acid, in common with several other polynitrophenols, is an explosive material in its own right and is usually stored as a water-wet paste. Several dust explosions of dry material have been reported [1]. It forms salts with many metals, some of which (lead, mercury, copper or zinc) are rather sensitive to heat, friction or impact. The salts with ammonia and amines, and the molecular complexes with aromatic hydrocarbons, etc. are, in general, not so sensitive [2], Contact of picric acid with concrete floors may form the friction-sensitive calcium salt [3], Contact of molten picric acid with metallic zinc or lead forms the metal picrates which can detonate the acid. Picrates of lead, iron, zinc, nickel, copper, etc. should be considered dangerously sensitive. Dry picric acid has little effect on these metals at ambient temperature. Picric acid of sufficient purity is of the same order of stability as TNT, and is not considered unduly hazardous in regard to sensitivity [4], Details of handling and disposal procedures have been collected and summarised [5],... 

Secondary explosives (also known as high explosives) are different from primary explosives in that they cannot be detonated readily by heat or shock and are generally more powerful. Secondary explosives can be initiated to detonation only by a shock produced by the explosion of a primary explosive. Widely used secondary explosives include trinitrotoluene (TNT), tetryl, picric acid, nitrocellulose, nitroglycerine, nitroguanidine, cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranit-... 

In general laboratories there are some compounds that are potentially explosive, e.g. picric acid. It is important that such substances are stored under suitable conditions, e.g. under water, and that they are regularly inspected in order to maintain these conditions. The use of such substances should be carefully controlled and only small amounts used. 

Chloroprene is available commercially on a restricted basis in the United States as crude P-chloroprene with a minimum purity of 95% (Lewis, 1993 DuPont Dow Elastomers, 1997). The principal impurities are dichlorobutene and solvents, with smaller amounts of 1-chlorobutadiene (a-chloroprene), chlorobutenes and dimers of both chloroprene and butadiene. Due to its reactivity, chloroprene is stored at 0°C or below under nitrogen and contains significant quantities of inhibitors, such as phenothiazine, tert-butylcatechol, picric acid and the ammonium salt of A -nitroso-N-phenylhydroxy lamine, to prevent degradation and polymerization (Stewart, 1993). Generally within six weeks of manufacture, crude chloroprene is distilled to produce polymerization grade, which is used within approximately 24 h of distillation. 

Picrates.1 At one time organic bases were isolated and identified as the pic-rates, which are often highly crystalline. Picric acid is generally supplied as a moist solid containing water, which hinders crystallization of picrates. The water can be replaced by ethanol for storage. Picrates can be prepared by reaction in acetone, in which picric acid is fairly soluble and then allowed to crystallize by addition of ether. 

The ability to form addition compounds, especially with aromatic hydrocarbons composed of condensed rings, is one of the specific properties of aromatic poly-nitro compounds. For example, compounds of trinitrobenzene or picric acid with naphthalene, as well as with other hydrocarbons with condensed rings, are very characteristic. Generally they are intensely coloured. 

Molecular addition compounds are readily formed and decomposed, e.g. by acting with a suitable solvent, which would dissolve one of the components and extract it. For example addition compound formed between picric acid and a hydrocarbon can be split into its components by extracting the picric acid with alcohol while the hydrocarbon remains undissolved. Another fact also indicative of the instability of the addition products is that those of picric acid may be decomposed by treating their solutions with saturated solution of potassium chloride. Potassium picrate is then precipitated, while the other component remains in solution (Taben and Kosak [117]). Generally speaking, the organic addition compounds... 

Fig. 117. General view of nitrators for the production of picric acid [8].

Generally the use of lead as a material for construction of a picric acid plant is avoided, except in Great Britain and in the U.S.A. where it is used for the parts of installation which are also in contact with inorganic acids. The latter, being strong acids, are assumed to inhibit the formation of lead picrate. 

A first requirement for a substance to produce a taste is that it be water soluble. The relationship between the chemical structure of a compound and its taste is more easily established than that between structure and smell. In general, all acid substances are sour. Sodium chloride and other salts are salty, but as constituent atoms get bigger, a bitter taste develops. Potassium bromide is both salty and bitter, and potassium iodide is predominantly bitter. Sweetness is a property of sugars and related compounds but also of lead acetate, beryllium salts, and many other substances such as the artificial sweeteners saccharin and cyclamate. Bitterness is exhibited by alkaloids such as quinine, picric acid, and heavy metal salts. 

Although picric acid is already a colouring matter, in general the colouring matters are more complicated compounds. Of the many thousands of colouring matters we shall only discuss the triphenylmethane derivatives further here. 

The aliphatic amines are, in general, volatile liquids soluble in water. They are strong bases which turn litmus blue, and react with mineral acids to form neutral salts. The reaction to litmus — apart from the physical form — shows immediately whether the base or a salt is at hand. For the isolation and identification of aliphatic amines, the salts formed with picric acid and similar acids are of value. These salts are usually nicely crystalline and have characteristic melting points. 

In the presence of picric acid, the reaction products were the same, but general acid catalysis could be observed. The solvent isotope effect was determined using a mixture of 82.5 % ethanol and 17.5 % water. If 38 % of the mobile (O-bonded) hydrogen of the solvent was replaced by deuterium the reaction rate was decreased by a factor of 1.45. Linear extrapolation to 100% deuteration led to an approximate result of kH/kD 2.2. Similar experiments referring to general catalysis and solvent isotope effects have been done for the ethanolysis of 9-diazo-fluorene, and similar results have been obtained [215]. 

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