4-Nitroso-3-pyrazolin-5-ones

Methyl-l-phenyl-3-pyrazolin-5-one gives a green-black dye (736) with 4-nitroso- or 4-amino-dimethylaniline and silver chlorides in the presence of light, a process of great importance in colour photography (B-76MI40403). 

The organisms Pyricularia oryzae, which causes rice blast, and Helminthosporium oryzae, which causes brown leaf spot, can be controlled with complexes of the ligands 1-phenyl-3-methyl-4-nitroso-2-pyrazolin-5-one (36) and 3-methyl-4-nitroso-2-pyrazolin-5-one (37). The complexes were of the type ML Xj (L = 36, 37 X = C1-, Br, N03 ) or [ML2]Y2 (Y = C104 ). The former were assigned an octahedral or distorted octahedral structure and the latter are tetrahedral. The most active nickel complex was (38).92... 

Ridi1185 has reported that the reaction of 2,3-dimethyl-l-phenyl-4-nitroso-3-pyrazolin-5-one with phenylhydrazine gives 4-phenylazo-3-methyl-l-phenyl-2-pyrazolin-5-one. This may occur by replacement of the methylphenylhydrazine moiety in the 3-pyrazolin-5-one by phenylhydrazine. The 4-oximino-2-pyrazolin-4-one could then react with phenylhydrazine to give the reported product. 

Most syntheses of tertiary amino-3-pyrazolin-5-ones are based on an alkylation by one means or another of the primary or secondary amino analogs. In some cases simultaneous reduction of a nitroso or nitro compound or of a Schiff base and alkylation of the amine so formed is carried out. 4-Dimethylamino-3-pyrazolin-o-ones (amino-... 

Reduction of 4-nitroso-2,3-dimethyl-l-phenyl-3-pyrazolin-5-one with zinc or iron and acid554,550 915 or catalytically561 in the presence of formaldehyde also gives aminopyrine. The analogous 4-nitro compound can also be reduced catalytically in the presence of formaldehyde... 

Extremely good yields have been reported in these halogenations.1605 4-Alkyl-2-pyrazohn-5-ones react with halogens readily, but even with an excess only monohalogenated products have been obtained.1605 Smith and co-workers1309 have found that l,3-dimethyl-2-pyrazolin-5-one reacts with bromine to give both the expected 4-bromo product and also l-bromo-3-methyl-2-pyrazolin-5-one. This same compound was obtained by bromination of 3-methyl-2-pyrazolin-5-one with A-bromo-succinimide.1309 4-Bromo-2-pyrazolin-5-ones have been prepared by bromination of 2-nitroso-3-pyrazolin-5-ones1209 (eq. 205) with... 

Although the compounds obtained by introduction of a nitroso group at C-4 in 2-pyrazolin-5-ones are considered as 4-nitroso-2-pyrazolin-5-ones for purposes of classification in this discussion, they actually exist as the oximino isomers (eq. 208) and are usually so... 

Knorr 809 first prepared 4-oximino-2-pyrazolin-5-ones by treatment of 2-pyrazolin-5-ones with nitrous acid (eq. 208) and this has remained the standard method of preparation.25,413,446 818 1004,1549 If an excess of nitrous acid is used, the nitroso substituent introduced is oxidized further to a nitro substituent.992 Amyl nitrite9 and nitrogen trioxide355,406 have also been used as nitrosating agents, though not extensively. 

Treatment with nitrous acid of a 4-substituted-2-pyrazolin-5-one having no substituent on N-l gives the 1-nitroso derivative.262... 

The 4-nitroso-3-pyrazolin-5-ones are always prepared by nitrosation of 3-pyrazolin-5-ones with nitrous acid.99,103,145,647,781,807 809,854,888, 972,978.984 Only one 3-nitroso-3-pyrazolin-5-one has been reported.972 This was prepared by nitrosation of 3-pyrazolin-5-one having a 4-methyl substituent and no substituent at C-3. 

The reduction of 4-nitroso-3-pyrazolin-5-ones has already been discussed in connection with the synthesis of 4-dialkylamino-3-pyra-zolin-5-ones. This reduction occurs readily to give the corresponding amine when catalytic hydrogenation or various chemical combina-tions461,092,1174 1175 are used. Oxidation of nitroso to nitro occurs in the presence of excess of nitrous acid or by use of nitric acid.984-992... 

The 4-nitro-3-pyrazolin-5-ones are listed in Table XXVIII. They have been prepared most frequently by direct nitration of 3-pyrazolin-5-ones, usually with concentrated nitric acid.807,809,880,888,1001,1320 The oxidation of 4-nitroso-3-pyrazolin-5-ones to give the 4-nitro compounds has been mentioned in connection with reactions of the 4-nitroso compounds. Nitration of 3-pyrazolin-5-ones with nitrogen tetroxide has been accomplished.1491... 

In the presence of sulfuric acid 1-nitroso-3-pyrazolidinones lose nitrous acid by elimination, giving 2-pyrazolin-5-ones which are then nitrosated at C-4.335,1028 The amino group in 4-amino-3-pyrazol-idinones is diazotizable and the resulting diazonium salt undergoes coupling.12... 

There has been a great deal of interest in 4-amino-3-pyrazolin-5-ones because of their pharmacological activity. These compounds are closely related to antipyrine and aminopyrine and a great many of them have considerable antipyretic and analgesic activity. By far the most widely used method of preparation of 4-amino-3-pyrazolin-5-ones has been reduction of the corresponding nitroso compounds (eq. 250). 

Owing to the active hydrogen atoms at C-4 in 3,5-pyrazolidinediones various substitutions at C-4 can be accomplished. Reaction with acid chlorides in the presence of aluminum chloride gives 4-acyl-3,5-pyrazolidinediones.919,976 However, if two groups are already present at C-4, the enolic form of the dione is acylated on the oxygen atom to give 3-acyloxy-2-pyrazolin-5-ones.998 Treatment of 3,5-pyrazolidinediones with nitrous acid gives nitrosation at C-4.976 The nitroso... 

These are listed in Table XLVIII. The nitrosation of 3,5-pyrazoIi-dinediones has already been mentioned (Section 2). A second method of preparation of the 4-nitroso-3,5-pyrazolidinediones (which are usually considered to have the tautomeric oximino form) has been used by Michaelis and Kirstein.981 This involves treatment of 3-chloro-3-pyrazolin-5-ones with nitrous acid (eq. 260). A third method of syn-... 

TABLE XXVIII. 3-Pyrazolin-5-ones. Nitroso and Nitro Substituted Derivatives... 

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