Phenylhydrazine, reaction with carbonyl compounds

Accordingly, diazobenzene and nitrous acid are related to each other in the same way as are phenylhydrazine and hydroxylamine the latter two substances, in fact, yield the same reaction products with carbonyl compounds as the former two do with the corresponding methylene derivatives. 

The large values of og for the reaction of phenylhydrazine, hydroxylamine and i-butylamine with carbonyl compounds reflect the important role of catalysis played by the solvated proton in this mechanism. Values of 2 of unity for the dehydration of carbinolamines derived from semicarbazide and aniline indicate that such dehydrations appear to be only specific acid catalyzed, except in fairly basic solutions where the concentration of hydronium ion is low . 

A four-component domino reaction of isatin 58, phenylhydrazine, 3-aminocrotononitrile 117, and cyclic 3-diketones/amide/thioamide 118 in an aqueous medium in the presence of ( )-camphor-10-sulfonic acid on heating at 100 °C for 2-3 h afforded the spiro-fused 2-oxindoles 119 (Scheme 39) [94]. The reaction was successfully extended to 5-chloro- and 5-nitroisatins. According to the proposed mechanism, an acid-catalyzed reaction of phenylhydrazine with nitrile 117 affords the 5-amino-3-methyl-l-phenyl pyrazole 111 that adds to the carbonyl carbon of isatin giving rise to an intermediate product 120. The acid-catalyzed reaction of this intermediate (that has been isolated) with carbonyl compounds 118 affords another intermediate compound 121, which eventually furnishes the final products 119 by cyclodehydration forming tetrahydropyridine ring followed by subsequent dehydration (Scheme 40). 

We recall that hydrazine and 2,4-dinitrophenylhydrazine react with carbonyl compounds to give hydrazones. However, monosaccharides do not give simple phenylhydrazone derivatives. After the initial formation of a phenylhydrazone, further reaction occurs to give the osazone, which has two molecules of phenylhydrazine incorporated into it. 

The reaction of these aldehydes, derived from periodate oxidation, with carbonyl reagents has also been investigated. Studies 147 148 were made on oxidized laminarin, a (1 —> 3)-linked polysaccharide, in which only the terminal residues had been oxidized. The addition of phenylhydrazine acetate detached the remainder of the terminal residue as glyoxal phenyl-osazone. When the aldehydic compounds derived from the periodate oxidation of raffinose and trehalose818a were reacted with p-nitrophenylhydrazine, the authors were surprised to find that one molecule of oxidized raffinose, containing six aldehydic functions, reacts with only three molecules of the reagent, and that the four aldehydic functions of the oxidized trehalose molecule react with only two. The reactions of periodate-oxidized carbo-... 

The diphenyl derivative 388, R = R = Ph, has an absorption band at 1495 cm S which has been assigned to the carbonyl group. This assignment could be questioned. The following chemical reactions of the compound 388, R = R = Ph, may be noted (a) Raney nickel desulfurization followed by oxidation with manganese dioxide yields dibenzyl ketone,(b) hydrazine yields 3,5-diphenyl-4-hydroxypyrazole (390), (c) phenylhydrazine yields PhCH2COCPh=NNHPh," (d)... 

Most classes of VOCs found in indoor environments are sampled onto sorbents by adsorption but highly reactive VOCs like carbonyl compounds are sampled by chemical reactions with the sorbent. Thus aldehydes and ketones are sampled by their reactions with sorbent gels coated with 2,4-dinitro-phenylhydrazine to form stable hydrazones [38-40]. Similarly, formaldehyde has been sampled by its reaction with N-benzylethanolamine to give 3-benzyl-oxazolidine [41,42]. 

The phenylhydrazones required for the Fischer synthesis are prepared from carbonyl compounds and phenylhydrazine. Alternatively, they can be obtained by a Japp-Klingemann reaction from CH-acidic compounds (y diketones, y -keto esters, etc.) or from enamines by interaction with aryldia-zonium salts. More complex indoles are thus accessible by a simple route. This is demonstrated by the synthesis of 3-(indol-3-yl)propionic acid 40, the starting material of Woodward s lysergic acid synthesis [52]. 

Solution The reaction of a-hydroxyl carbonyl compounds with excess phenylhydrazine produces osazones of the general structural formula ... 

Before the age of chromatography, the characterization of unknown compounds necessitated the preparation of crystalline derivatives with definite melting points. For this purpose, hydroxylamine and phenylhydrazine are not always ideal reagents, particularly for low molecular weight carbonyl compounds. These derivatives possess rather low melting points or may even be oils at room temperature. The oximes are often very soluble and therefore difficult to purify, and mixtures of stereoisomers may also be formed. With phenylhydrazine, variations in the reaction procedure can lead to different derivatives a-diketones yield mono- and dihydrazones... 

In the case of the reaction of substituted hydrazines, such as phenylhydrazine with glucose or certain other carbohydrates, one molecule of phenylhydrazine reacts with the terminal aldehyde group to form a phenylhydrazone. A second molecule of phenylhydrazine oxidizes the penultimate carbinol grouping to a carbonyl and a third molecule of phenylhydrazine converts this second carbonyl to a phenylhydrazone. This class of di-phenylhydrazones is called an osazone, a series of compounds not discussed in the present chapter. 

When unknown compounds are identified without the aid of spectroscopy classification tests are used. Reacting the carbonyl in a ketone or aldehyde with an amine (2,4 dinitro-phenylhydrazine) to form an inline is the easiest way to detect a ketone or aldehyde (Reaction l). The iinine that forms is a highly colored solid. The color of the solid also helps to indicate structural characteristics. Ketones and aldehydes with no conjugation tend to form itnines with yellow to orange colors, while highly conjugated ketones or aldehydes form imines with red color. 

Synthesis of 4-amino-2-pyrazolin-5-ones is usually achieved by treatment of an a-amido-/3-aldehydo- or /9-ketoester with hydrazines according to the classical method for preparation of 2-pyrazolin-5-ones. Variants on this procedure consist of using an a-amidoester which has /9-substituents whose reaction is equivalent to that of a /9-carbonyl substituent. Such compounds are D-benzylpenicilloic acid a-methyl ester,1027 ethyl phenylpenaldate243 and the acetal of an a-amido-/9-formyl ester.59,243 Cornforth has isomerized 2-phenyl-4-hydrazino-methylidyneoxazolidone to 4-benzamido-2-pyrazolin-5-one. The same compound was obtained by treatment of 1-ethoxyvinyl-2-phenyl-oxazolidone with phenylhydrazine.319... 

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