4-Imino-2-pyrazolin-5-ones

Imino-2-pyrazolin-5-ones of the type (XXIX) have become very important in the field of color photography and will be discussed in... 

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. 

VII), since Glauert and Mann578 found no imino or hydroxyl absorption in the infrared spectra of l,4-diaryl-2-pyrazolin-5-ones. Recently366a the infrared spectra of 3-methyl-, 3-trifluoromethyl-,... 

Alphen1513 it is also obtained by the reductive cyclization of a crotonic ester (eq. 56). The replacement of a 4-imino function in a 2-pyrazolin-5-one by a 2-pyrazolin-5-one lacking a 4-substituent also leads to a... 

Several methods for the synthesis of 5-imino-2-pyrazolines depend upon the amination of a pyrazole ring. 5-Chloropyrazoles react with aniline to give the corresponding 5-amino compound.826,1002 The chloropyrazoles can be prepared and amination accomplished in one... 

A few bis(2-pyrazolin-5-ones) having one or both 5-oxo groups replaced by imino groups have been prepared. The preparation of those having one imino group is shown in eqs. 99 and 100. Those linked... 

Pyrazolin-5-one hydrochlorides react with hydrazines at about 100° to form 5-imino compounds (eq. 155).983 A similar reaction has... 

All of these derivatives of 2-pyrazolin-5-ones have a nitrogen atom substituted at the 4-position as the 3-nitrogen-substituted-2-pyrazolin-5-ones are tautomeric with the 5-imino-3-pyrazolidinones and are considered as such in this discussion. The 4-nitrogen-substituted-2-pyrazolin-5-ones are not usually prepared by cyclization directly to the desired pyrazolinone ring but rather by modification of already formed pyrazolinones. The methods used are usually those employed in... 

Amino-3-pyrazolin-5-ones (4-imino-3-pyrazolidinones) react with nitrous acid as do ordinary aromatic amines to form diazonium salts.426,984,1353 These then couple readily with aromatic amines,1017,1018,1060 phenols992,1323 and aliphatic compounds having active hydrogen atoms,428,1017 such as acetoacetic esters. The products are 4-azo-3-pyrazolin-5-ones (eq. 200). The diazonium salts also couple... 

Two 4-nitro-5-imino-2-pyrazolines are listed in Table XII. One of these was prepared by permanganate oxidation of the 4-oximino compound1010 and the other by direct nitration.1656 These compounds were believed to be aminopyrazoles rather than 5-imino-2-pyrazolines. 

The 5-imino-2-pyrazolines having no N-l substituents can be acylated with acetic anhydride to form the 1-acyl derivatives,301,342,391 as can their 5-oxo analogs. Compounds of this type having a 3-acetoxy substituent have been prepared by reaction of 3-amino-2-pyrazolin-5-ones (5-imino-3-pyrazolidinones) with acetic anhydride (eq. 237).594,1598 Cusmano and Sprio343,344 have treated a-benzylidene-j8-ketonitriles... 

The reaction of 5-imino-3-pyrazolidinones with acetic anhydride forms 2-acetyl-3-acetoxy-5-acetimido-3-pyrazolin-5-ones as well as the 5-imino-2-pyrazoline derivatives already mentioned.594-1599... 

For purposes of classification the 4-aminopyrazoles are considered to be 4-imino-2-pyrazolines and analogs of 2-pyrazolin-4-ones. These compounds are listed in Table XL. Such compounds can be prepared by direct cyclization using ethyl diazoacetate and ethyl cyanoacetate.92 This is the same as eq. 243, except that the malonic ester is replaced by ethyl cyanoacetate. Purines can be hydrolyzed to 4-imino-2-pyrazolines by using strong acid.1210 1846 By far the most frequently used preparation is reduction of appropriately substituted pyrazoles, such as 4-nitro,368,812,819,1015,1019,1049 4-nitroso1165 or 4-aryl-azo.671 974,995 The hydrolysis of the carbethoxy 4-imino-2-pyrazolines derived from ethyl cyanoacetate and ethyl diazoacetate forms 4-imino-2-pyrazolin-3-carboxylic acid which is readily decarboxylated to the parent compound.92... 

For purposes of classification, 4-hydroxy-, 4-mercapto- and 4-amino-3-pyrazo in-5-ones, except 4-amino having no hydrogen on the nitrogen, have been considered to be 3,4-pyrazolidinediones or derivatives thereof. These compounds could theoretically exist as the 4-oxo, 4-thiono or 4-imino forms but do exist largely, if not exclusively, as the hydroxy, mercapto and amino isomers. The amino compounds will be named as 4-amino-3-pyrazolin-5-ones. They are listed in Table XLIV. 

Synthetic methods involving conversion of other, but similar, ring systems to 3,5-pyrazolidinediones have been reduction of 1,2-diphenyl-3,4,5-pyrazolidinetrione with tin and hydrochloric acid63 and hydrolysis of 5-imino-3-pyrazolidinones (3-amino-2-pyrazolin-5-ones) with acid.1339,1596... 

One of the most widely used methods for the preparation of 5-imino-3-pyrazolidinones is from 5-oxo-3-pyrazolin-3-carboxylic acids or their derivatives by use of the Hofmann167,697 or Curtius167,1387,1395 rearrangements (eq. 264). A similar synthesis is from the analogous... 

In compounds which have no substituents at N-l or N-2 nuclear acylation also occurs and under some conditions acylation occurs at C-4. The use of 2-alkyl- or aryl-5-imino-3-pyrazolidinones, which exist as the 3-amino-2-pyrazolin-5-one isomer, with an equivalent of acid chloride, either aliphatic or aryl, leads to 3-acylamides (eq. 266),14,67,594,695,1247,1594,1595 although in some cases a side-reaction gives both N- and O-acylation.1595 Under the same conditions 3-hydroxy-5-imino-2-pyrazolinones give O-acylation.1599 The reaction of... 

The reactions undergone by 5-imino-3-pyrazolidinones are in general very similar to those of 2-pyrazolin-5-ones. The hydrogen atoms at C-4 are active and this position is the reactive center in the nucleus of these molecules. Condensation with aldehydes and ketones occurs with formation of benzylidene644,1083 or 4,4 -benzylidenebis... 

TABLE XVII. Miscellaneous Bis(3-pyrazolin-5-ones) and Bis(5-imino-3-pyrazolines)... 

TABLE XXIV. 3-Pyrazolin-5-ones. Imino, Amino, Amido, Azo, Aminoazo, and Hydrazido Substituents... 

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