Compounds, colored pyrimidines

A solution of pyrimidine-4,5-diamine (2 g, 18 mmol) in TFAA (10 mL) was refluxed for 2 h under a stream of COj. The temperature then was raised and the anhydride removed by distillation. The residue was kept at 210 "C for 45 min under an atmosphere of CO. The last traces of anhydride were eliminated by distillation in vacuo at 210 C. The crystalline residue weighed 2.8 g (82%), mp 192 C. For purificiition, the compound was extracted with boiling EtOH (40 mL) to which CaCOj (0.5 g) and charcoal were added and the mixture filtered through diatoniaeeous earth. The extraction with EtOH was repeated. The combined filtrates, concentrated to 15 mL, were kept in the refrigerator for 5 h and cream-colored needles obtained yield 1.2g (35%) rap 192 C. 

Dodecyl- and 2-ethylperhydropyrido[l,2-c]pyrimidines were patented as fading prevention compounds for colored photographic material [88JAP(K)88/149643],... 

Hydroxyl groups substituted at positions 2- and 4-(6-) of the pyrimidine nucleus exist mainly in the pyrimidone form [1-4]. The only true hydroxyl position on this ring system is position 5. This hydroxyl group is of phenolic character and all 5-hydroxypyrimidines give a positive (blue-violet coloration) test with ferric chloride. Because of the relative difficulty in synthesis of all but a few compounds, most 5-hydroxypyrimidines have not been extensively studied. 

In solid-state inorganic chemistry. MCD is an important technique for the determination of color centers in alkali-metal halide crystals, rare earths, and highly symmetric compounds such as hexaha-lides of platinum or ruthenium. In organic chemistry, MCD is observed with, e,g.. metal poiphy-rins, pyrimidine ba.ses, and nucleoside derivatives. 

The optical spectrum of platinum—a-pyridone blue, as with the pyrimidine analogues, varies with pH, counteranions, temperature and time. Polarized single-crystal spectra in conjunction with a SCF-X Sw calculation have elucidated the major features of the electronic structure [67]. The blue color has been attributed to transitions from the inner Pt—Pt bonding o orbital to an antibonding one (a ) and from the outer Pt—Pt 7t bonding orbital to outer Pt—Pt a. The effect of alteration of the Pt—Pt distances in the platinum—ethylenediamine—pyridone blue was correlated with the optical spectrum. The delocalization of the unpaired spin density classes the pyridone blue as a Robin—Day Class III-A compound [68]. 

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