Acid form, azinic acids

The nitro form is much more stable than the aci form in sharp contrast to the parallel case of nitroso-oxime tautomerism, undoubtedly because the nitro form has resonance not found in the nitroso case. Aci forms of nitro compounds are also called nitronic acids and azinic acids. 

Pyrazolotroponehydrazones like 580a, on treatment with carboxylic acid derivatives or aliphatic carbonyl compounds, are cyclized to fused [l,2,4]tri-azine derivatives (e.g., 580b,c) with aromatic carbonyl compounds, they form azines (79BCJ1972 80JHC1057, 80S331). 

Azine approach. Reissert compounds such as (222) on treatment with acid form transient cyclic intermediates containing the 3,4-fused oxazole ring. When the acid is tetrafluoroboric acid, the Reissert salt (223) can be isolated (73JA2392). 

Methods for the preparation of hydrazones and oximes differ little from those used for the synthesis of imines from ketones and aldehydes in that the appropriate nitrogen species and the ketone are mixed. However, the equilibrium for the majority of reactions of ketones and aldehydes with hydrazines and hy-droxylamine favor the product hydr nes and oximes and removal of the water formed by the condensation is not required. 8(> Acid catalysis is complicated by the basicity of the reagent and, for example, the maximum rate of oxime formation is at approximately pH 4. Complicating reactions can occur such as the 1 2 combination of hydrazine with two ketones or aldehydes to form azines but this is not a problem with the substituted hydrazines that are used for asymmetric induction. 

Methylthio-l,2,4-triazin-5(2//)-ones (209) have been converted into 3//-[l,2,4]triazino[3,2-i]quinoxaline-3,10(4//)-diones (212) upon cyclocondensation with anthranilic acid (210) (Scheme 40). A-Methylanthranilic acid (211) with (209) afforded the 5-methyl-3/f-[l,2,4]triazino[3,2- )]quin-azoline-3,10(5//)-diones (213) (Scheme 40). Reaction of 2-methyl-3-methylthio-6-phenyl-l,2,4-tri-azin-5(2//)-one (214) with anthranilic acid (210) gave 1-methyl-3-phenyl-47/-[l,2,4]triazino[3,4-i]quinazoline-4,6(l//)-dione (216) via the intermediate (215) (Scheme 41) <84CB1077, 84CB1083). 3-Alkylthio-4-amino-l,2,4-triazin-5(4//)-ones (217) with anthranilic acid formed l-amino-3/f-... 

Treatment of the acid vith mercuric chloride or sulphur dioxide oxidises it to phenylphosphinic acid. The following derivatives are formed by the combination of equimolecular proportions of the component substances Phenylphosphinous acid phenylliyd azine, long, colourless prisms, M.pt. 135° C., soluble in hot water, sparingly soluble in cold water, and eliminating the acid portion of the molecule vath. excess of mineral acid phenylphosphinous acid p-tolylhydrazine, fine needles, M.pt. 148° C. phenylphosphinous acid benzylhydrazine, colourless prisms, M.pt. 108° C. 

Acid catalysis increases reactivity both para and ortho to the site of protonation. Coulombic attraction of an anionic nucleophile to the vicinity of the positive center will to some extent remove the proton (65), forming the less reactive azine and the nucleophile s... 

Alkylthio, arylthio, and thioxo. The thioxo group in pyrimidine-2,4-dithione can be displaced by amines, ammonia, and amine acetates, and this amination is specific for the 4-position in pyrimidines and quinazolines. 2-Substitution fails even when a 5-substituent (cf. 134) sterically prevents reaction of a secondary amine at the 4-position. Acid hydrolysis of pyrimidine-2,4-dithione is selective at the 4-position. 2-Amination of 2-thiobarbituric acid and its /S-methyl derivative has been reported. Under more basic conditions, anionization of thioxo compounds decreases the reactivity 2-thiouracil is less reactive toward hot alkali than is the iS-methyl analog. Hydrazine has been reported to replace (95°, 6 hr, 65% 3deld) the 2-thioxo group in 5-hexyl-6-methyl-2-thiouracil. Ortho and para mercapto- or thio- azines are actually in the thione form. ... 

Chlorophthalazine is quite reactive to many basic nucleophiles but reacts sluggishly with aqueous or alcoholic alkali. In contrast, it is very rapidly hydrolyzed by warm, concentrated hydrochloric acid as are its diazine isomers. In hydrolysis with very dilute acid or with water, it forms some phthalazinone but mostly the self-con-densation product which hydrolyses to give 2-(l -phthalazinyl)-phthalazin-l-one (70% yield). Such self-condensations in diazanaph-thalenes and in monocyclic azines are always acid-catalyzed (Sections II, C and III,B). With methanolic methoxide, 1-chlorophthalazine (65°, few mins), its 7-methoxy analog (20°), and 1,6- and 1,7-dichlorophthalazines (20°) readily undergo mono-substitution. 

Hydrazine is hypergolic with cone, nitric acid [1]. Of a series of hydrazones and azines derived from aldehydes and ketones, only those which decomposed when heated alone were hypergolic with the acid when heated at 12.5°C/min [2], Solid hydrazones formed from various aldehydes with dimethylhydrazine or phenylhydrazine are hypergolic with the acid [3],... 

Reaction of azines 86 with nitriles in the presence of alkyllithium and subsequent treatment of the formed product with sulfuric acid gave the pyrazolo[l,5-u]pyrimidine 87 (82CC454). 

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