Citrazinic acid

Citrazinic acid (2,6-dihydroxyisonicotinic acid) [99-11-6] M 155.1, m >300°, pK] 3.0, pK2 4.76. Yellow powder with a greenish shade, but is white when ultra pure and turns blue on long standing. It is insoluble in H2O but slightly soluble in hot HCl and soluble in alkali or carbonate solutions. Purified by precipitation from alkaline solutions with dilute HCl, and dry in a vacuum over P2O5. The ethyl ester has m 232° (evacuated tube) and a pKa of 4.81 in MeOCH2CH20H [IR Pitha Coll Czech Chem Comm 28 1408 1963]. 

There has been considerable interest in hydroxy-3,3 -bipyridines and 3,3 -bipyridinones. Following from some very early work on the oxidation of citrazinic acid (2,6-dihydroxypyridine-4-carboxylic acid), which was considered to give some polyhydroxy-3,3 -bipyridines, it has been shown that the 3,3 -bipyridinone 59, a product of the hydrolysis of a natural blue pigment from Corynehacterium insidiosum, is obtained by oxidation of 2-hydroxy-5-aminopyridine (60) or 2,6-dihydroxypyridine-4-carboxylic acid 61) 80,83 similar oxidation of 2,6-dihydroxy-3-aminopyridine-4-carboxylic acid affords the natural product indigoidine (20). Numerous related oxidative condensations have been reported subsequently. Cyano-acetamide condensations analogous to those discussed in the synthesis of 2,3 -bipyridines afford, for example, the cyano-substituted 3,3 -bipyridinone 62 588 v, lereas condensation of 3-pyridylacetonitrile with ethyl phenyl-propiolate and ethanol affords compound 63. To complete the section on... 

SUver(n) forms stable complexes with a variety of nitrogen donor ligands such as pyridine, substituted bipyridine, phenanthrohne, or citrazinic acid. They are usually obtained by reaction of a silver(I) salt with peroxodisulfate in the presence of the ligand. ... 

Fig. 3-89. Separation of citrazinic acid. - Separator column IonPac AS5 eluent 0.0028 mol/L NaHC03 + 0.0022 mol/L Na2C03 + 100 mg/L p-cyanophenol flow rate 2.0 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations 20 ppm each of thiocyanate and citrazinic acid.

Citrazinic acid 1,2-Dihydro-6-hydroxy-2-oxo-4-pyridinecarboxylic acid C8H8N04 99-11-6 166.109 ye pow >300 dec s HjO, alk si HCI... 

Figure 5.7. Coupling reactivity as a function of sur-face-to-volume ratio (proportional to the specific surface area) for the coupler M prepared as an NS dispersion. This coupling reactivity is expressed as pczA in units of g CZA per litre. Both the coupler M and CZA (citrazinic acid) are four-equivalent. The specific surface-to-volume ratio for monodisperse spheres is 6 d. The average diameters < c > for the various dispersions were measured by disc centrifugation with turbidity detection. (Data by courtesy of Dr Andrew Sierakowski)...

M.p. 210-15° with blackening. Sol. hot B2O. Insol. EtOH, EtjO. Heated with HCJ —> citrazinic acid. 

Citric acid pC-1) when treated with ammonia or urea at 130 to 200° or with p-toluenesulfonic acid under autoclaving conditions affords citrazinic acid (X-2, X = OH) or its amide (X-2, X = NHa) in yields exceeding 60% of theory.f... 

Citrazinic acid can be converted in high yield to 2,6-dichloroisonicotinic acid (X-3, X = Cl) with POCI3. The latter is easily reduced catalytically to isonicotinic acid (X-3, X = H). ... 

Infrared studies have ruled out XII490a and XII490b as structures for crystalline citrazinic acid. Esters of citrazinic acid exist in form XII-490c in... 

Triphenyl-2-pyridone and 5-phenoxy-4,6-diphenyl-2-pyridone are reported to be 0-alkylated by diazomethane. Citrazinic acid and its methyl ester (xn-514) give mixtures of the products of 0- and //-methylation. 4Carbomethoxy-6-methoxy-l-methyl-2-pyridone (XII-515) can be prepared from citrazinic acid by dimethyl sulfate to give methyl A-methylcitrazinate (Table XII-13/ which is then treated with diazomethane. 

Bifunctional calatysis, 845 2, 2 -A -Siglutaconimide, 860 from 3-amir o-2-pyridona, 860 from citrazinic acid, 860 from the 3,3 -dipyridyl, 860 from nitrosocitranzinic acid, 860... 

Figure 3.172 Separation of citrazinic acid. Separator column lonPac ASS eluent ...

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