Phenylhydrazones decomposition

CR(Q(262)1017>. The nucleophilic reactivity of the oxygen atom has been observed in the acetylation by acetic anhydride of 2-aryl- and 2-heteryl-A2-thiazolin-4-ones (Scheme 136). 2-Alkoxy and 2-methyl derivatives of A2-thiazolin-4-one (196) react with OPCl3 to yield thiazolylphosphoric esters (197) which have insecticidal uses (Scheme 137). An example of the electrophilic reactivity of the C-4 atom is the easy formation of oxime and phenylhydrazone derivatives. 5-Aryl-A2-thiazolin-4-one (198) gives the 1,3-dipolar cycloaddition product (199) with methyl fumarate and methyl maleate (Scheme 138). Under similar conditions, treatment of (198) with dimethyl acetylenedicarboxylate (DMAD) yields a thiophene derivative (202) when R = Ph and a pyridone derivative (203) when R = H (Scheme 139). The proposed mechanism involves the formation of a mesoionic intermediate (200) which reacts in a cycloaddition with a second molecule of DMAD, yielding (201), the decomposition of which depends on the R substituent. 

Derivatives of Formaldehyde and Acetaldehyde.—According to Tafel and Pfeffermann,1 the phenylhydrazones of aldehydes are readily converted into amines by reduction in sulphuric-acid solution at a lead cathode. Thus ethylidene phenyl-hydrazine yields about 60% of the theoretical percentage of pure ethylamine salt. The decomposition of glyoxime is more complicated. Besides ammonia and glyoxal and a small quantity of an acid (glyoxylic acid ) there is formed as the principal product the crystalline sulphate of a base, C2H802N2, the nature of which could not be determined with certainty. Ethylenediamine is not formed. Nor was a diamine obtained from methylglyoxime. 

More attention has been devoted, particularly in recent years, to the direct GC separation of hydrazones of carbonyl compounds. Phenylhydrazones of aldehydes can be separated successfully in a column packed with SE-30 on Chromosorb W at temperatures ranging from 120 to 190°C [50]. Korolczuk et al. [51] considered this problem in more detail. They described the separation of phenylhydrazones of 27 aldehydes and ketones using different temperature programmes and studied the influence of the initial temperature on the retention of the derivatives. The analysis time is less than 15 min for carbonyl compounds with up to 11 carbon atoms with programming at 10°C/min in the range 150—280°C. Some derivatives provide two peaks which can be ascribed to their syn—anti isomerism, although even the decomposition of the derivatives cannot be eliminated as a cause, particularly with the use of a metallic column. 

Both N-N and N-C bond fission occurs on irradiation of the hydrazone derivatives (191). The photodegradation of the phenylhydrazone and the hydrazone of benzil have also been described. a-Ketoiminyl radicals are formed on irradiation of oximino ketones at low temperature. A study of the photochemical decomposition of sulfamic esters and their use as initiators of cross-linking of a melamine resin have been described. The bispyridinyl radical (192) is formed by one electron reduction of the corresponding pyridinium salts. The irradiation of this biradical at 77 K results in C-N bond fission with the formation of benzene-1,3-diyl. The predominant products from the irradiation (X,> 340 nm) of (193) in methanol were identified as A -hydroxy-2-pyridone and (194) from the fission of the C-O bond. Other products were 2-pyridone, (195) and (196) that arise from O-N bond fission. The reaction is to some extent substituent dependent and a detailed analysis of the reaction systems has identified an intramolecular exciplex as the key intermediate in the C-O bond heterolysis. 

In a series of papers, Suvorov et al. investigated heterogeneous catalysis of the cyclization of isolated aldehyde and ketone phenylhydrazones. y-Alumina was typically employed as catalyst in the vapor phase reaction at atmospheric pressure and at temperatures around 300 °C. A maximum yield of 60% was obtained from acetaldehyde phenylhydrazone as a result of thermal decomposition of the hydrazone [7] and the formation of benzene and aniline as by-products [8]. Kinetic studies indicated that the rate-determining step was desorption of product from the surface [9]. 

The effect of substituent groups was also studied. In a series of N-substituted hydrazones, PhNRN CMeEt, cyclization proceeded with increasing difficulty in the series R = H, Me, Et, Ph this was ascribed to the effect of increasing steric hindrance [12]. From acetaldehyde phenylhydrazones with methoxy substituents on the aromatic ring, yields were poor, which was attributed to decomposition of the substrate to non-volatile products on the alumina catalyst surface [13]. In contrast, with an acidic ion-exchange resin as catalyst, higher yields were obtained with the 4-methoxy derivative than with the 4-nitro this was interpreted as the effect of methoxy in facilitating adsorption on the resin [14]. 

An interesting intermediate, possibly deriving from Weygand s Scheme B, was isolated by Haas and Seeliger from the reaction of u-glucose with phenylhydrazine in acetic acid or hydrochloric acid. This product is 3-(D-fflrol)fno-tetrahydroxybutyl)cinoline (30), produced, not by the hydrolytic decomposition of the osazone, but by the cyclization of the intermediate glycosulose 2-(phenylhydrazone) (28) or the aldimine 2-(phen-ylhydrazone) (29). 

Tropinone is a low melting tertiary base which readily forms a methio-dide. The decomposition of this methiodide in alkali, in contrast to that of tropine and tropidine, does not give the expected des-base. With potassium hydroxide resinification of the primary product occurs (129) however, with silver oxide (128) or sodium bicarbonate (129) a product thought to be A -dihydrobenzaldehyde (oxime and phenylhydrazone (117)) was isolated in good yield. (This sensitivity towards alkali is a general characteristic of -aminocarbonyl compounds.) Silver oxide oxidizes this aldehyde to a dihydrobenzoic acid, while at elevated temperatures benzoic acid is formed. 

Two reactions used in steroid chemistry were modified by Bennett for histochemical use. Frozen sections of either unfixed or formalin-fixed tissue were used, with no differences reported in their reactivity (see, however, Section V.2) the sections were 80 to 100 microns in thickness. In the first method, sections were treated with phenylhydrazine hydrochloride (1 %) in acetate buffer, pH 6 to 6.5, overnight. The formation of yellow phenylhydrazones indicated the presence of carbonyl groups. The pH of the solution was kept low enough to prevent extensive accumulation of the decomposition products of phenylhydrazine, which are yellow and soluble in lipid. In order to avoid reaction with ascorbic acid the sections were first oxidized briefly with iodine or indophenol. Since dehydro-ascorbic acid, which is formed by the oxidation of ascorbate, also forms phenylhydrazones, it is doubtful that this procedure had any value. However, since ascorbic acid and its oxidation product are soluble in most aqueous mixtures, they probably would not remain in sections as ordinarily treated. 

The formation of well-crystallized derivatives of semicarbazine has proved extremely useful in the investigation of terpene compounds which often yield liquid oximes, and phenylhydrazones that only crystallize with difficulty and readily undergo decomposition. As a rule the aldehyde or ketone combines with semi-... 

Few simple derivatives of acylsilanes have been described, although a phenylhydrazone has been reported (1) and tosylhydrazones of several ketones have also been prepared (24). Attempts to prepare oximes led to decomposition, almost certainly the result of the sensitivity of the ketones to basic media. 

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