Quinoline, picrate

With amines, picric acid yields picrates. Some of them such as quinine or quinoline picrates, are very difficult to dissolve in water and this may be utilized for quantitative determination of picric acid or these bases. 

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. 

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.]... 

The phenylation of quinoline with dibenzoyl peroxide has been reported to give a mixture of 4- and 5-phenylquinoline which can be separated by the fractional recrystallization of their picrates, In a later investigation, the other five phenylquinolines have also been identified among the products, the relative reactivities of the nuclear positions being 8- > 4- > 3-, 5- > 2-, 6-, 7-... 

Pyridine, the quinoline and acridine AT-oxides readily form salts e.g. hydrochlorides (27) and picrates) which have been used for their characterization. Basic salts of the type (ArNO)2HX are also known the structure (28) is indicated for 2-picoline 1-oxide hemihydro-bromide based on IR evidence. A list of these salts has been compiled (b-71MI20500). 

A convenient synthesis of thieno[2,3-6]quinoline (Scheme 111) (76ZN(B)1297,76ZN(B)1685, 77JCS(P1)2024) utilizes the readily available methyl 2-oxo-3-vinyl-l//-quinoIin-4-carboxylate (380) as starting material. Treatment of (380) with phosphorus oxychloride yields the chloroquinoline which on addition of bromine gives a trihalo compound. The cyclization to (381) is effected with thiourea in boiling ethanol. Elimination of the methoxycarbonyl group yields thieno[2,3-6]quinoline as colorless needles with m.p. 107-108 °C, which can be characterized as the picrate with m.p. 213-214 °C. 

The azametallocenes, such as 206 and 208, are less stable than their cyclopentadienyl analogs.158 The pKa for azaferrocene (206) is similar to that of quinoline, whereas the manganese compound was a much weaker base.158 Azaferrocene yields a picrate and a methiodide, but, as might be expected, it does not undergo electrophilic substitution.158 The mass spectra of azametallocenes have been discussed.1636 The preparation of cyclopentadienyliodobis(imidazole)cobalt(III)iodide has been reported.1630... 

Melinonine H, formulated as C20H21-23N2O+ from analyses of the picrate, mp 290°-292°, and perchlorate, has one A-methyl and one O-methyl group. Its UV-spectrum shows that this alkaloid is the only quinoline derivative so far isolated from calabash curare or Strychnos species. It is not identical with the quaternary Ab-metho derivatives of cinchonine or cinchonidine (40). 

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