Nitric oxide 1-pyrazoline

Pyrazolin-5-ones react with concentrated nitric acid809,880,888, 992.1001 or an excess of nitrous acid984,992,1001 to form 4-nitro-3-pyxazolin-5-ones. Presumably the excess of nitrous acid first nitrosates and this product is oxidized to the nitro compound. 

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... 

Only half-a-dozen of these compounds are known (Table XLI) and at least this number of methods of preparing them have been reported. Borsche and Manteuffel125 have found that 2-pyrazolin-4,5-diones are formed as the by-products when oc-ketoesters are treated with aryl-diazonium salts. The principal products are 4-arylazo-2-pyrazolin-5-ones. Nitric acid oxidation of 3-methyl-l-phenyl-2-pyrazolin-5-one forms the corresponding 4,5-dione.809 Wislicenus and Gtiz1842 heated 4 -bromo - 4 - nitro -1 - (4 - bromophenyl) - 3 - methyl - 2 -pyrazolin - 5 - one in water and obtained the analogous 4-oxo compound. Acid hydrolysis of rubazonic acids, which are 4-imino-2-pyrazolin-5-ones, leads to 2-pyrazolin-4,5-diones.424 809 Oxidation of 4,4 -bis(2-pyrazolin-5-ones) or of rubazonic acids with nitric acid809 forms the 4,5-diones. 

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