Pyrazolones special

Kocevar et al. investigated the reactivity of 3-hydrazinopyridazines 386 in the presence of the oxazolone compound 387 <2001H(54)1011 >. In some special cases (mostly when R8 = Me), formation of 388 in high yields was observed, while in other cases an entirely different transformation (formation of a pyrazolone ring as a substituent instead of the hydrazine group) was experienced. 

With regard to heterocyclic compounds as coupling components, the importance of the formerly widespread pyrazolone-, aminopyrazole-, and 4-hydroxy -quinolone-based yellow azo dyes has greatly diminished with the advent of the tinctorially superior and therefore more economical pyridone azo dyes. Only a few examples have survived and then only for special applications such as for dyeing of acetate fibers. Examples are C.I. Disperse Orange 56 and C.I. Disperse Yellow5. (for structure, see Section 3.2.5). 

Numerous cationic azo dyes are prepared by the action of /V-hydroxymcthyl-chloroacetamide on azo dyes in sulfuric acid medium, followed by displacement of the reactive chloro substituent by pyridine or trialkylamine. Of special significance for dyeing paper are dyes that are prepared by coupling of diazotized 2-(4 -aminophenyl)-5-methylbenzothiazole to acetoacetaiylides, pyrazolones, naphthols [143], or barbituric acid derivatives [144], followed by reaction with N-hydroxymethylchloro-acetamide and pyridine. The azo dye obtained by oxidative dimerization of 2-(4 -aminophenyl)-5-methylbenzothiazole may also be subjected to this conversion [145], Dye 51 colors paper yellow. 

This reaction was first reported by Knorr in 1883. It is the preparation of pyrazole derivatives from 1,3-dicarbonyl compounds and hydrazines. Similarly, pyrazole derivatives can also be prepared from hydrazines and equivalent molecules of 1,3-dicarbonyl compounds, such as a-ethoxymethylene a-phenylacetone. In a special case, -carbonyl aldehyde reacts with a simple hydrazine to afford tautomers of 3- and 5-substituted pyra-zoles, of which the proton oscillates rapidly back and forth between two nitrogen atoms. These two tautomers are distinguishable only at sufficiently low temperatures." It should be pointed out that the reaction of hydrazine with j8-carbonyl ester leads to the formation of pyrazolone. ... 

Asthmatic attacks due to non-narcotic analgesics, mostly occur in patients with so-called intrinsic or idiosyncratic asthma (often associated with nasal polyposis, sinusitis and eosinophilia of the blood) (McFadden and Austen 1977). About 10% of patients with this kind of asthma show severe reactions to aspirin, methyl-salicylate, pyrazolone derivatives, indomethacin, ibuprofen, diclofenac and sometimes even phenacetin and paracetamol. (Sodium salicylate is often tolerated.) The special reactivity may appear only in later life and concerns a number of chemically unrelated drugs. In some of these patients analgesic therapy with a morphine derivative such as pentazocine (Fortalgesic) or hyoscine butylbromide (Buscopan) may be necessary. However, in other patients, those with aspirin urticaria rather than asthma, the reaction may also rely on a drug-specific allergic mechanism (de Weck 1971). 

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