Bases picrates

Argemone alba Lestib. Berberine base, picrate, m.p. 232-5°. ... 

Platinum Base Picrates. Some compds contg Pt and PA are expl, for example ... 

JV-Methylmescaline was isolated by Spath and Bruck (125) from the mother liquors from the crystallization of the nonphenolic bases of mescal-buttons. The identity of this base was established by comparison with synthetic iV -methylmescaline which was obtained by the condensation of mescaline with benzaldehyde, followed by methylation of the benzal derivative with methyliodide, and hydrolysis of the quaternary base picrate, m.p. 177.6-178 trinitro-m-cresolate, m.p. 189.5-190.5 p-nitrobenzoyl derivative, m.p. 142-143 . 

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. 

The dibromohydrate is first produced, and treatment with ammonia gives the free base, which after recryslallization in nitrobenzene gives brown crystals (m.p. 215°C). The picrate decomposes around 254°C. 

Representative Method Although each chemical kinetic method has its own unique considerations, the determination of creatinine in urine based on the kinetics of its reaction with picrate provides an instructive example of a typical procedure. 

Creatinine The most widely used creatinine methods are based on reaction between creatinine and picrate ions formed in an alkaline medium. 

Specifications, Analysis, and Toxicity. Dicyandiamide is identified quaHtatively by paper chromatography and quantitatively by ultraviolet spectrometry of the chromatogram. More commonly, total nitrogen analysis is used as a purity control or the dicyandiamide is converted by hydrolysis to guanylurea, which is determined gravimetrically as the nickel salt (50). Methods based on the precipitation of silver dicyandiamide picrate are sometimes used (51). Dicyandiamide can also be titrated with tetrabutylammonium hydroxide ia pyridine solution. Table 4 gives a typical analysis of a commercial sample. Dicyandiamide is essentially nontoxic. It may, however, cause dermatitis. 

The most versatile derivative from which the free base can be readily recovered is the picrate. This is very satisfactory for primary and secondary aliphatic amines and aromatic amines and is particularly so for heterocyclic bases. The amine, dissolv in water or alcohol, is treated with excess of a saturated solution of picric acid in water or alcohol, respectively, until separation of the picrate is complete. If separation does not occur, the solution is stirred vigorously and warmed for a few minutes, or diluted with a solvent in which the picrate is insoluble. Thus, a solution of the amine and picric acid in ethanol can be treated with petroleum ether to precipitate the picrate. Alternatively, the amine can be dissolved in alcohol and aqueous picric acid added. The picrate is filtered off, washed with water or ethanol and recrystallised from boiling water, ethanol, methanol, aqueous ethanol, methanol or chloroform. The solubility of picric acid in water and ethanol is 1.4 and 6.23 % respectively at 20°. 

It is not advisable to store large quantities of picrates for long periods, particularly when they are dry due to their potential EXPLOSIVE nature. The free base should be recovered as soon as possible. The picrate is suspended in an excess of 2N aqueous NaOH and warmed a little. Because of the limited solubility of sodium picrate, excess hot water must be added. Alternatively, because of the greater solubility of lithium picrate, aqueous 10% lithium hydroxide solution can be used. The solution is cooled, the amine is extracted with a suitable solvent such as diethyl ether or toluene, washed with 5N NaOH until the alkaline solution remains colourless, then with water, and the extract is dried with anhydrous sodium carbonate. The solvent is distilled off and the amine is fractionally distilled (under reduced pressure if necessary) or recrystallised. 

If the amines are required as their hydrochlorides, picrates can often be decomposed by suspending them in acetone and adding two equivalents of ION HCl. The hydrochloride of the base is filtered off, leaving the picric acid in the acetone. Dowex No 1 anion-exchange resin in the chloride form is useful for changing solutions of the more soluble picrates (for example, of adenosine) into solutions of their hydrochlorides, from which sodium hydroxide precipitates the free base. 

Chloromethyl)pyridine hydrochloride [1822-51-1] M 164.0, m 170-175°, 172-173°, pK , -5.6. Purified by recrystn from EtOH or EtOH-dry Et20. It melts between 171° and 175° and the clear melt resolidifies on further heating at 190° and turns red to black at 280° but does not melt again. The picrate-hydrochloride (prepared in EtOH) has m 146-147°. The free base is an oil, [Mosher and Tessieri J Am Chem Soc 73 4925 1951.]... 

The crude base is purified by converting 2g of base in toluene (3.3mL) into the acetate salt by heating at 65-70 with 0.46g of AcOH and the crystals are collected and dried (0.96g from two crops m 141-143 ). The acetate salt is dissolved in warm H2O, basified with aqueous NaOH and extracted with C6H6. The dried extract (MgS04) is evaporated in vacuum leaving a viscous oil which crystallises and can be distd. [Gottstein and Cheney J Org Chem 30 2072 1965.] The picrate has m 234-236 (from aq MeOH), and the formate has m 147-148° (from heptane). 

Other purification procedures include the formation of the picrate, prepared in benzene soln and crystd to constant melting point, then decomposed with warm 10% NaOH and extracted into ether the extract was washed with water, and distd under reduced pressure. The oxalate has also been used. The base has been fractionally crystd by partial freezing and also from aq 80% EtOH then from absolute EtOH. It has been distd from zinc dust, under nitrogen. 

Dried with Linde type 5A molecular sieves or Na2S04 and fractionally distd at reduced pressure. Alternatively, it was refluxed with, and distd from, BaO. Also purified by fractional crystn from the melt and distd from zinc dust. Converted to its phosphate (m 135°) or picrate (m 223°), which were purified by crystn and the free base recovered and distd. [Packer, Vaughn and Wong J Am Chem Soc 80 905 1958.] The procedure for purifying via the picrate comprises the addition of quinoline to picric acid dissolved in the minimum volume of 95% EtOH to yield yellow crystals which are washed with EtOH and air dried before recrystn from acetonitrile. The crystals are dissolved in dimethyl sulfoxide (previously dried over 4A molecular sieves) and passed through a basic alumina column, on which picric acid is adsorbed. The free base in the effluent is extracted with n-pentane and distd under vacuum. Traces of solvent are removed by vapour phase chromatography. [Mooman and Anton J Phys Chem 80 2243 1976.]... 

Crystd as its picrate (m 191°) from EtOH, then the free base was liberated, dried at 78°/8mm over P2O5 and crystd from pet ether (b 80-100°). [Cumper, Ginman and Vogel J Chem Soc 1188 1962.] It can be purified by zone melting. Also crystd from hexane, benzene/pet ether (b 40-60°) or sodium-dried benzene, dried and stored over H2SO4. The monohydrate is obtained by crystn from aqueous EtOH or ethyl acetate. It has been crystd from H2O (300 parts) to give the monohydrate m 102-103° and sublimes at lO mm [Fielding and LeFevre J... 

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