Dipicrate salts

In 1937 Hunter and Hlynka were able to reduce a methanolic solution of 4(5)-nitroimidazole (27 R = H) with sodium amalgam and trap the 4(5)-aminoimidazole (25 R = H) with cyanic acid giving the urea derivative (31) (37BJ488). Other reducing agents gave inferior results. Subsequently, 4(5)-aminoimidazole (25 R = H) was obtained as either its dihydrochloride (30%) or dipicrate salt but the isolation procedures were lengthy and difficult (41 Mil). 

Table 5. Free energies of binding of diammonium dipicrate salts to hosts at 298 K in CHCI3 saturated with H2O...

Methylene bis(guanidinomethane), CH2(.CH2.NH.C( NH).NH2)2 mw 158.21, N 53.16% hygr crysts, mp 135° sol in ale w. Prepd by treating methylene bis(aminomethane) with s-methyl isothiourea sulfate. More recently isolated as the dipicrate salt by heating a mixt of cyanamide, methylene bis(aminomethane), and methylene bis (aminomethane p-toluene-sulfonate), then treating with PA for the dipicrate mw 616.42, N 27.27%, OB —77.9%, mp 242°. Their expl props were not investigated... 

Table 11 Physical characteristics and thermochemical data of picrate and dipicrate salts...

The purity of SF was determined by gas-liquid chromatography as described by Hagler and Behlow (1981) using a Varian 3700 gas chromatograph with dual flame ionization detectors (Varian Instrument Co., Sunnyvale, CA). Slaframine samples and a SF standard regenerated from the dipicrate salt were derivatized in 2 ml vials with open-top cap and Teflon-silicon septa. One ml of each sample or standard was pipetted into a vial and the CH2CI2 evaporated under a stream of IM2. Each sample was derivatized with 100 yl TriSil BT (Pierce Chemical Co., Rockford, IL) for 30 min at room temperature. The reaction mixture was diluted with 900 yl CH2CI2. 

A stock solution of SF regenerated from the dipicrate salt was diluted to 2 mg/ml and 0.5 ml was placed into 16 vials. The CH2CI2 was evaporated with gentle heat and either a stream of N2 or dry, filtered air. The vials were allowed to sit for 0, 0.5, 1, or 2 hr before the SF residue was redissolved in 0.5 ml CH2CI2 or 0.85% saline. One y 1 from... 

Crystd from aqueous ether as dipicrate. For mono K salt see entry in Chapter 5. 

Attempts to convert M into a crystalline salt were unsuccessful. However, an amorphous dipicrate could be purified by repeated precipitation and could also be converted into a clean though equally... 

In the dihydrochloride (602), the second molecule of acid is not firmly bound because of protonation of the second basic site by internal hydrogen bond formation. This would suggest that in the dipicrate, one mole of picric acid participates in salt formation, and that the second mole of picric acid is added to the hydrogen-bonded cation (LXI) forming a molecular complex. The existence of a monopicrate might thus serve to point out structures with steric inhibition of hydrogen bonding. 

The first synthesis of a derivative of 2,8-phenanthroline was reported by Merz, Weidlich, and Fink13 in 1964. They prepared 5,6-dimethoxy-2,8-phenanthroline (34) (isolated as the dipicrate) in very low yield by conducting a double Pomeranz-Fritsch isoquinoline synthesis on 4,5-dimethoxyisophthalaldehyde. The parent compound was prepared 2 years later12 in 25-35% yield, along with 1,9-phenanthroline (4%), by the photocyclization of trans-1 (3-pyridyl)-2-(4-pyridyl)ethylene in benzene. This reaction was used by Hiinig and his colleagues15 to prepare an N,N -dimethyl diquaternary salt of 2,8-phenanthroline by methylating the crude product from the irradiation reaction. 

Aqueous zinc nitrate similarly treated gave the colorless crystalline bis (triaminopropane) zinc di-iodide (X) (20). An aqueous solution of sodium tetrachloroplatinate(II), Na2[PtCl4], when treated with two equivalents of the triamine, heated until clear, and then concentrated and added to aqueous sodium bromide and iodide gave the colorless bis(triamino-propane)-platinum(II) dibromide (XI X = Br), m.p. 270-271°C., and the di-iodide (XI X = I), m.p. 266-267°C., respectively. The fact that in these salts (which were sufficiently stable for recrystallization from hot water) the divalent platinum was showing the exceptional coordination number of 6—i.e., that it was coordinated to all six amino groups of the two triamine molecules, was shown by the addition of the dibromide to an excess of sodium picrate, both in cold aqueous solution, whereby only the dipicrate (XI X = C6H2N3O7) was precipitated had any amino groups remained uncoordinated, they also would have formed picrates (1928) (19). 

Nicotyrine, C10H10N2, a base found in tobacco (384, 392, 385), is a colorless oil, b.p. 280-281°, 150°/15 mm., 1.124. It forms a dipicrate, m.p. 170-171°, a chloroplatinate, m.p. 160° (dec) and a methiodide, m.p. 211-213°. It had been prepared synthetically long before its occurrence in tobacco was discovered. 3, 2-Nicotyrine is an intermediate in Pictet s synthesis of Z-nicotine (365). The methylation of the potassium salt of nornicotyrine yields nicotyrine (366), which is 2-(3 -pyridyl)-iV-methyl-pyrrole. It is obtained as the product of the dehydrogenation of nicotine with silver oxide (330). The dehydrogenation of nicotine with sulfur in boiling toluene yields thiodinicotyrine and 2,5% of nicotyrine (386). Nicotine when passed over platinized asbestos at 320° yields a mixture of nicotyrine and dihydronicotyrine (387). 

Convolvicine, as its hydrochloride, is recovered from the mother liquors from the isolation of convolvine and convolamine. When liberated from its salt it is an oily base which turns yellow on standing. By titration it appears to be a monoacidic base but it forms a dipicrate. 

The resolution of synthetic di-sparteine was achieved by Leonard and Beyler (278, 279) by means of i- and d-jS-camphorsulfonic acid, and both optically active forms of sparteine were obtained. The free bases were not isolated but each enantiomorph was identified through the formation of two known derivatives. The derivatives used to identify Lsparteine were the d-jS-camphorsulfonate and the dipicrate. The former salt was characterized by melting point, mixed melting point with an authentic sample, and specific rotation. The latter salt was characterized by melting point and mixed melting point with authentic I-sparteine dipicrate. d-Sparteine i- 3-camphorsulfonate had a specific rotation equal and opposite to its enantiomorphic Z-sparteine d-/3-camphorsulfonate. Characterization of d-sparteine was accomplished by conversion of the camphor-sulfonate salt to the dipicrate and monoperchlorate, both of which were... 

The acid is soluble in Et20 and crystallises from Et20/petroleum ether (m 183-183.5 ), or H2O as the dihydrate which dehydrates in a desiccator over cone H2SO4 in a vacuum. The dipicrate crystallises from aqueous ether. For the mono K salt see entry in Metal-organic Compounds , Chapter 5. [Abbott et al. Org Synth Coll Vol II10 1943, Huntress et al. Org Synth Coll Vol IV 329 1963, Beilstein 2 H 801, 2 I 317, 2 II 670, 2 III 1991, 2 IV 2290.]... 

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