Formaldehyde reaction with 3-pyrazolin-5-ones

Pyrazolones show a great variety of reactions with carbonyl compounds (B-76MI40402). For instance, antipyrine is 4-hydroxymethylated by formaldehyde and it also undergoes the Mannich reaction. Tautomerizable 2-pyrazolin-5-ones react with aldehydes to yield compound (324) and with acetone to form 4-isopropylidene derivatives or dimers (Scheme 8 Section 4.02.1.4.10). 

Bis(3-pyrazolin-5-ones) in which the linking chain is not attached to the pyrazolinone nucleus by functional groups are listed in Tables XVI and XVII. Most of these compounds have as the linking chain an arylidene group and are prepared by the reaction of 3-pyrazolin-6-ones with aryl aldehydes,B66 e68,569,807,1001,1133 as shown in eq. 117 (p. 50). Some aliphatic aldehydes have also been used in this reaction.409 3-Pyrazolin-5-ones react with formaldehyde or formamide to form the corresponding bis compounds (eq. 142).910-1192 Under basic conditions... 

Presumably the linking group is >NCH—N<. Bisamides of l-(amino-phenyl)-2-pyrazolin-5-ones and of 3-amino-2-pyrazolin-5-ones have been used. l-(3-Aminophenyl)-3-methyl-2-pyrazolin-5-one reacts with many aldehydes and ketones to form polymers.964 Probably condensation occurs at C-4 and the amino group. The product of reaction of p-cresol with formaldehyde has been found to react with 1-(4-hydroxy -phenyl)-3-methyl-2-pyTazolin-5-one to give a polymer that must have the aromatic and pyrazolinone rings connected by ether linkages.1269... 

---