PYRAZOLONE DYESTUFF

The class of 2-amino-4H-pyrans has been known for several decades. The first representatives 1 and 2 are from the late 1950s to the early 1960s. Spiro-conjugated pyranopyrazole 1 was obtained in studies on pyrazolone dyestuffs (56ACS587), while pyranopyranone 2 served as a precursor for the blood anticoagulant warfarin (62JOC3086). 

See also PYRAZOLONE DYESTUFF PREPARATION, SULFUR BLACK... 

Pyrazolone dyestuff preparation, 350 Pyrophoric alloys, 350 Pyrophoric catalysts, 350 Pyrophoric iron—sulfur compounds, 351 Pyrophoric materials, 352 Pyrophoric metals, 354 Pyrotechnics, 355... 

Phenylhydrazine condenses with acetoacetic ester to give a pyrazolone derivative which on methylation gives phenazone. The sulphonic acid similarly gives rise to the tartrazine dyestuffs. It is used to make indole derivatives by the Fischer process. 

Dyestuffs. The use of thiophene-based dyestuffs has been largely the result of the access of 2-amino-3-substituted thiophenes via new cycHzation chemistry techniques (61). Intermediates of type (8) are available from development of this work. Such intermediates act as the azo-component and, when coupled with pyrazolones, aminopyrazoles, phenols, 2,6-dihydropyridines, etc, have produced numerous monoazo disperse dyes. These dyes impart yeUow—green, red—green, or violet—green colorations to synthetic fibers, with exceUent fastness to light as weU as to wet- and dry-heat treatments (62-64). 

In mordant dyes, phenols, naphthols, and enolizable carbonyl compounds, such as pyrazolones, are generally the couplers. As a rule, 2 1 metal complexes are formed ia the afterchroming process. A typical example of a mordant dye is Eriochrome Black T (18b) which is made from the important dyestuff iatermediate nitro-l,2,4-acid, 4-amiQO-3-hydroxy-7-nitro-l-naphthalenesulfonic acid [6259-63-8]. Eriochrome Red B [3618-63-1] (49) (Cl Mordant Red 7 Cl 18760) (1, 2,4-acid — l-phenyl-3-methyl-5-pyrazolone) is another example. The equiUbrium of the two tautomeric forms depends on the nature of the solvent. 

The reaction is very common in pyrazolone chemistry. Since alkoxypyrazoles and tautomerizable pyrazolones undergo this reaction and 3-pyrazolin-5-ones, like antipyrine, do not, it is assumed that the reaction takes place at C-4 of the OH tautomer. Pyrazolone diazo coupling is an important industrial reaction since the resulting azo derivatives are used as dyestuffs. For instance, tartrazine (Section 4.04.4.1.3) has been prepared this way. 3,5-Pyrazolidinediones react with aryldiazonium salts resulting in the introduction of a 4-arylazo group. As has been described in Section 4.04.2.1.4(v), diazonium salts couple in the 3-position with indazole to give azo compounds. 

Schetty related his rules only to diarylazo dyestuffs and demonstrated that o-carboxyarylazo-pyrazolones formed both facial and meridional complexes. He attributed this to the greater distance between the two oxygen donor atoms in these compounds than in the corresponding... 

Heterocyclic coupling components have, in a similar manner as heterocyclic diazo components (sect. 2.1.4), recently become very important and are used in large scale industrial production of dyestuffs and chemicals. A recent review deals with the industrial um of pyrazolones 75, iminopyrazoles 76, pyridones 77, amino-pyrimidines 78, aminopyridines 79, hydrochinolines 80 and aminothiazoles 81 as coupling components. 

We have published a series of updates on the chemistry of pyrazol-3-ones, derivatives important particularly in the chemistry of pharmaceuticals and dyestuffs. Part I, which was published in 2001 in Volume 80, describes syntheses of pyrazol-3-ones. Part II (Volume 87, 2004) summarizes reactions at ring atoms at pyrazol-3-ones. Part III (Volume 95, 2008) discusses the reactivity of ring substituents of pyrazol-3-ones. Chapter 2 covers more recent syntheses and a variety of applications of pyrazol-3-ones. Together this four-part series updates the major work on pyrazolones that was published by Wiley in the series of monographs The Chemistry of Heterocyclic Compounds back in 1964. All the four parts of this mini series are authored by George Varvounis of the University of Ioannina, Greece. 

The reactivity of the 3- and 5-azolones centres mainly on their ability to react with electrophiles such as halogens (giving 4,4-dihalo-derivatives with excess reagent), or to nitrate, or undergo Vilsmeier formylation the example shown below is the formylation of Antipyrine , once used as an analgesic. Many dyestuffs have been synthesised via coupling of aryldiazonium cations with 5-pyrazolones at C-4 - tartrazine is such an example. 

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