Bis 2-pyrazolin-5-ones

The most widely used synthesis of 4,4 -bis(2-pyrazolin-5-ones) is mild oxidation of monocyclic 2-pyrazolin-5-ones, which has already been discussed in the section devoted to reactions of 2-pyrazolin-5-ones (eq. 45). These compounds can also be synthesized by reaction of a,a -diacylsuccinic esters with hydrazines (eq. 54).357.807.8i5 a number... 

Only a very few 4,4 -bis(2-pyrazolin-5-ones) linked by a double bond have been prepared. The parent compound of this series, 4-(3-methyl -1 -phenyl - 5 - oxo - 2 - pyrazolin - 4-ylidene)-3-methyl-l-phenyl-2-pyrazolin-5-one (XXII-D), is known as pyrazole blue.323,807,809,816, 1090,1091 was so nameci by Knorr because of its great resemblance to indigo blue. All these compounds are strongly colored. The usual synthesis is by ferric chloride oxidation of monomeric 2-pyrazolin-5-ones (eq. 61)296,809 or by oxidation of the corresponding bis compounds... 

A few 4,4 -bis(2-pyrazolin-5-ones) are known in which the linking chain contains nitrogen atoms. These are Schiff bases and amides. 5-Oxo-2-pyrazolin-4-carboxaldehydes react with diamines having two primary amino groups to form 4,4 -bispyrazolinones.U9° The amides are synthesized by reaction of bisisocyanates with 2-pyrazolin-5-ones... 

The 3,3 -bis(2-pyrazolin-5-ones) in which the rings are connected by carbon chains (Table VIII) are usually prepared by condensation of a hydrazine with an appropriate / ,/ -dioxodiester (eq. 84).419,462,1222,1225 Such bispyrazolinones linked by a carbonyl group have been prepared by pyrolysis of the calcium salt of 5-oxo-2-pyrazolin-5-one.1549... 

The l,l -bis(2-pyrazolin-5-ones) (Table IX) have been prepared by three methods. Two of these are variants on the familiar / -ketoester condensation with hydrazines but in these cases compounds having two hydrazine moieties are used.116,212,255,459,1037 These two methods are illustrated in eq. 85. The R in the hydrazines used in the direct con-... 

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... 

Only a very few 4,4 -bis(3-pyrazolin-5-ones) are known in which the rings are linked directly. These are prepared by methylation of 4,4 -bis(2-pyrazolin-5-ones)807>809 or by treatment of the methiodides of 4-(5-chloropyrazol-4-yl)-3-pyrazolin-5-ones with alkali.991 These compounds are listed in Table XV. 

A few bis(2-pyrazolin-5-ones) having alkoxy substituents are known and are listed in Table III. These are prepared by addition of alcohols to the double bond connecting the pyrazolinone rings in pyrazole blue. 

Amino-substituted bis(2-pyrazolin-5-ones) have been prepared in which the rings are linked by carbon chains or by nitrogen atoms. The former are listed in Tables VIII and IX and the latter in Tables VII and VIII. In most of those cases in which carbon chains link the two rings the amino substituents are introduced as they are in mono-pyrazolinones.255 494 Eisner, Elvidge and Linstead419 have prepared some amino bis(2-pyrazolin-5-ones) by direct cyclization (eq. 190). 

Some l,r-bis(4-arylideneamino-2-pyrazolin-5-ones) have been prepared by Furuya and Ueno494 by treating bis(2-pyrazolin-5-ones) with oxidizing agents in the presence of arylamines. 

The 4,4-dichloro-2-pyrazolin-5-ones are reduced with hydriodic acid to the corresponding monochloro compound.1605 The 4-mono-halogenated-2-pyrazolin-5-ones react readily with another mole of the same compound or with unhalogenated 2-pyrazolin-5-ones to give bis(2-pyrazolin-5-ones). In the former case the two rings are linked by a double bond,1307 and in the latter by a single bond.1528... 

Only two halogenated bis(2-pyrazolin-5-ones) have been reported (Table VI). One of these is prepared by bromination of 4,4 -methylidyne-bis(3-methyl-l-phenyl-2-pyrazolin-5-one) with bromine to give the 4-bromo analog.1682 In the second case1109 bromine is added to a diolefinic system connecting two 2-pyrazolin-5-one rings. 

The alkylation of 4-nitro-2-pyrazolin-5-ones at C-4 with diazomethane478 has already been mentioned. This hydrogen atom is also replaceable with bromine.1642 Reduction of the nitro group with stannous chloride forms the corresponding amine.478,480 Picrolonic acid condenses with itself to form a bis(2-pyrazolin-5-one) connected by a double bond at the 4,4 -position, with elimination of two moles of nitrous acid.690 Condensation also occurs in the presence of phenyl-hydrazine, but 4,4 -bis[3-methyl-l-(4-nitrophenyl)-2-pyrazolin-5-one] is formed.690... 

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. 

Although by far the majority of 2-pyrazolin-5-ones used as color couplers have no substituent at C-4, this is not a necessary condition. 4,4 -Bis(2-pyrazolin-5-ones) can be used for this purpose since the 4-substituents can be eliminated and an azomethine dye formed. Such couplers may offer certain advantages. It is claimed that they are more stable and also they make it possible to form two azomethine dyes if the two portions of the molecule are different. Weissberger, Vittum and Porter1540,1603 have patented a number of 4,4 -arylidenebis(2-pyra-zolin-5-ones) for use as color couplers. Gluck580 has suggested 4,4 -bis-(2-pyrazolin-5-ones) linked by sulfur which he prepared. 

TABLE IV. 4,4 -Bis(2-pyrazolin- 5-ones) Linked by a Double Bond ... 

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