Picric acid salts with amines

Picric acid combines with amines to yield salts (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 9.6.3, p. 1238). 

The reagent has been used for the cleavage of picric acid salts of amines. The finely divided yellow picrate is shaken with a mixture of ether and a concentrated aqueous solution of ethanolamine, and the ether solution is drawn off and extracted repeatedly with ethanolamine solution until it is no longer colored. Hiinig and Baron studied the velocity of splitting of quaternary ammonium salts on refluxing with ethanolamine. ... 

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. 

Picric acid forms ionic salts with amines, picrates, which are solids of characteristic melting point even though the parent acids are liquids for example, the picrates of m-anisidine, N,N-diethylaniline, and N-methylaniline melt at 169, 142, and 144°. 

A great number of organic acids yielding crystalline salts with amines have been proposed. The best known acids are 3,5-dinitrobenzoic (I) (54) 2,4-di-nitrobenzoic (II) (55) 3,5-dinitro-o-toluic (III) (56) 3,5-dinitro-p-toluic (IV) (57) picric (V), picrolonic (VI), styphnic (VII), imidazoledicarboxylic... 

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],... 

Negative substituents enhance the acidic properties of phenols, an effect opposite to that produced with aromatic amines. o and p-Chloro-phenols are considerably stronger acids than phenol itself, and o- and p-nitrophenols are still stronger. Trinitrophenol, picric acid, is a strong acid whose salts are neutral and not decomposed by carbonic acid or by ammonium salts. These salts of picric acid can be salted out of neutral solutions by sodium or potassium chloride. With negatively substituted phenols, it may be possible to separate the phenolate from solutions which are neutral or weakly alkaline to litmus. In doubtful cases, just as with the amines, the precipitated material must be studied to determine whether it is the free phenol or one of its salts. The color of the precipitate gives an indication in the case of the nitrophenols, since the free phenols have only a weak yellow color, whereas the alkali salts are deep yellow. Solubility tests with indififerent solvents may be used in the case of uncolored compounds. Only the free phenol can be separated from acidic solutions. 

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. 

Amines (weak base) form salts with picric acid (trinitrophenol), and all amine picrates exhibit an absorption maximum at 359 nm with a molar absorptivity of 1.25 X 10 . A 0.200-g sample of aniline, C6H5NH2, is dissolved in 500 mL water. A 25.0-mL aliquot is reacted with picric acid in a 250-mL volumetric flask and diluted to volume. A 10.0-mL aliquot of this is diluted to 100 mL and the absorbance read at,35, nm in a 1-cm cell. If the absorbance is 0.425, what is the percent purity of the aniline -... 

Wieland, 1907 Wieland and Wecker, 1910). Oxidation was carried out in an inert solvent such as benzene, from which the salt precipitated. The easier and more reliable preparation of perchlorate salts by the iodine-silver perchlorate method (Weitz and Schwechten, 1926, 1927), to which we have referred earlier (p. 168), allowed a much clearer understanding of the nature of triarylaminium ions to be obtained. Isolation of perchlorates permitted chemical studies, and easy reduction to the triarylamine by iodide ion, ferrous ion, etc., was consistent with the cation-radical view that was developed. The name aminium ion was coined by Weitz. Other salts were prepared such as tritolylaminium picrate (by oxidation of the amine with lead dioxide in the presence of picric acid), and it was also recognized that conjugate anions in salts obtained by oxidation with antimony pentachloride, phosphorus pentachloride and ferric chloride had to be complex anions rather than simple anionic radicals. This is a particularly pertinent point in antimony pentachloride oxidations (p. 165). 

Picric acid and the picrate salts of amines absorb at 380 nm with a molar absorptivity of 13,400. An accuracy of +2% was obtained for the spectrophotometric determination of molecular weights of amines [30]. Molecular-weight determinations have been reported of sugars from the absorption spectra of their osazones... 

Many amines, including th( terti.ary typo, form doubUi salts with such reagents as chloro-platinic acid, picric acid, ( tc. rh( S( ... 

In certain cases the solution of the salt may be alkalized and the liberated amine can be separated, for example, in a separatory funnel or by steam distillation, or by extraction with ether or benzene. In other cases a more complicated procedure needs to be chosen the bases are liberated from picrates by triturating the picrate with cone. HCl, and the liberated picric acid is filtered off on a sintered glass filter. The filtrate is evaporated, preferably in vacuo, and the hydrochloride obtained is converted to the free base according to the procedure given above. 

Inhibitors are compounds, which inhibit the polymerization process during the initiation and growth of the chain. Typical inhibitors include hydroquinone, pyrocatechol and its derivatives, aromatic p-phenylenedi-amine amines, N-phenyl-2-naphthylamine, and also trinitrobenzene, picric acid, copper salts, and others. The reaction of free radical with a monomer molecule depends on the reactivity of double bonds of Ihe latter. 

Walden and Birr showed that for isomeric picrates the thermal expansion coefficients of the primary, secondary, and tertiary ammonium salts are greater than for the quaternary salts. Presumably the larger expansion coefficients occur in sustems which are less ionic because of the dissociation of the salt into amine and picric acid. This explanation is in agreement with the comparison of the isoelectronic salts and hydrocarbons in Section 2.2. For them the nonelectrolyte has the greater thermal expansion coefficient when the comparison is made at constant pressure and temperature, in agreement with Walden and Birr, while for a comparison at constant volume and temperature the salt has a greater coefficient. Thus nonelectrolyte components are in equilibrium with the primary through tertiary ammonium salts and the shifts in this equilibrium will be reflected in the thermal expansion coefficient and produce unreasonable estimates of the surface tension. 

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