Picrate heterocycles

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°. 

Oxazines can form salts with strong acids. The salts vary with regard to their solubility and stability. Some of the hydrochlorides are hydrolyzed by water. Some less common salts are known e.g., dichromates and ferrocyanates, " chloroplatinates and chloroaurates. Sometimes the picrates can also be used to identify the 1,3-oxazine derivatives. " In some instances a special procedure is required to form the picrates, as the heterocyclic ring can open under the action of picric acid. " ... 

The reaction of aminoguanidine bicarbonate (84) with sodium nitrite in the presence of excess acetic acid produces 1,3-ditetrazolyltriazine (89), another nitrogen-rich heterocycle (C2H3N11 = 85 % N) which readily forms explosive metal salts. The reaction of aminoguanidine bicarbonate (84) with sodium nitrite in the presence of mineral acid yields guanyl azide (90), of which, the perchlorate and picrate salts are primary explosives. Guanyl azide (90) reacts with sodium hydroxide to form sodium azide, whereas reaction with weak base or acid forms 5-aminotetrazole. ... 

I, 8-Naphthyridine [254-60-4] M 130.1, m 98-99 , pK 3.36. Purify 1,8-naphthyridine through an AI2O3 column and elute with toluene and pet ether, evaporate the eluate, crystallise the residue from pet ether (b 60-80°), and sublime it at 80°/13mm. The picrate [15936-16-0] has m 207-208° (from EtOH), and the methiodide has m 180-181° (from EtOH). [Hawes Wibberley J Chem Soc (C) 1564 1967, UV Armarego Physical Methods in Heterocyclic Chemistry (Ed Katritzky, Academic Press) Vol III 134 1971, Beilstein 23 II 178,23 III/IV 1237.]... 

H2SO4, anhydrous dication), pK " with 3,4-hydrated species), pKl 12.1 (hydrated anion). Purify quinazoline by passage through an activated alumina column in C6H6 or pet ether (b 40-60"). Distil it undar reduced pressure, sublime it undo-vacuum and crystallise it from pet ether. The.picrate has m 188-189" (from MeOH). [Armarego J Appl Chem 11 70 1961, Armarego Quinazolines, Fused Pyrimidines Part I Brown Ed, Wiley-Interscience 1967, Brown Quinazolines Supplement 1 Taylor Ed, Wiley-Interscience 1996, ISBN 0-471-14565-3 for covalent hydration see Albert Armarego Adv Heterocycl Chem 4 1 1965, Beilstein 23 H 175, 23 II 177, 23 III/IV 1221.]... 

Dichloropyrido[3,2- /]pyrimidine is dehalogenated by Adams catalyst in ethanol at room temperature and 1 atmosphere of hydrogen pressure, but the parent heterocycle appears to be unstable a picrate (mp 191 C) was isolated.77... 

If nitrogen heterocycles have basic properties, the preparation of picrates, chloroplatinates, or the quaternization of the heterocyclic nitrogen with methyl iodide (see p. 326) is recommended this is true especially for pyridine-, pyrroline-, and quinoline-type bases. Tetraphenylboranates (111) are also suitable for the identification of nitrogen heterocycles. For their preparation see p. 331. The preparation of quinoline picrate is described on p. 330. 

For the identification of piperazine derivatives powder X-ray diffraction of their picrates has been proposed (113) for gas chromatography of heterocyclic nitrogen compounds on columns with inorganic salts see (114). 

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