Phenylhydrazine, 269 Table

In order to characterize them and more readily separate them from interfering accompanying substances carbonyl compounds (aldehydes, ketones) can be converted to hydrazones at the start. The reagent mainly employed is 2,4-dinitro-phenylhydrazine in acidic solution [70], This yields osazones with aldoses and ketoses. Some examples are listed in Table 15. 

The use of substituted hydrazines, phenylhydrazine, and 2,4-dinitrophenylhydra-zine (68T4285 74JOC843) can give both 5- and 3-acetylenylpyrazole (Table VT). In this case, the direction of cyclization depends both on the hydrazine structure and the experimental conditions. 

An enol is usually characterised by treatment with ketonic reagents or with phenylhydrazine (compare Section IV,114 and Table IV,114A), or by hydrolysis with acid, followed by the identification of the ketone. 

A host of other pharmaceutical substances, namely cetrimide, hydralazine hydrochloride, phenylhydrazine hydrochloride may be assayed by titration with potassium iodate as mentioned in Table 13.3. 

A mixture of 10 gm of the respective thiourea, suspended in alcohol, and a slight excess of phenylhydrazine is refluxed for 6 hr and then poured into water. Examples of some of the products are shown in Table III. 

Table 8 Some Complexes with Hydrazine, N2H4 and Phenylhydrazine,...

These values of carbonyl oxygen are not determined by the present authors but are taken rank-wise from Blom s determination by hydroxylamine method (4). These values are considered to be the maximum estimate for carbonyl oxygen and are about double the estimate obtainable by phenylhydrazine method (Table II). The latter method is suspect... 

Other reagents that have been used to reduce support-bound aromatic nitro compounds include phenylhydrazine at high temperatures (Entry 5, Table 10.12), sodium borohydride in the presence of copper(II) acetylacetonate [100], chromium(II) chloride [196], Mn(0)/TMSCl/CrCl2 [197], lithium aluminum hydride (Entry 3, Table... 

The Fischer indole synthesis is commonly recognized as one of the most powerful and versatile tools for construction of indoles, as reflected by the amount of recent publications in which it has been used successfully. The usual approach involves initial preparation of a phenylhydrazone 323 from a suitable phenylhydrazine and an enolizable carbonyl compound, followed by an acid-induced cyclization to the target indole 324, featuring a [3,3]-sigmatropic rearrangement as the key step (Scheme 38). Some selected new examples of indoles prepared using standard Fischer conditions are collected in Table 2. 

N-a-Halo benzylidene-N -phenylhydrazines (CXXXV) (as variants of 2-halo amines) react with carbon disulfide in alkali to give 3,5-diaryl-/I4-1,3,4-thiadiazoline-2-thiones (CXXXVI) (55,126 (method C, Table 18). 

The overall reaction stoichiometry and products from the combination of 02 and phenylhydrazine (PhNHNH2) in Me2SO are represented by (Table 7-3)... 

For systematic variation of the aldehydes, ethyl acetoacetate and phenylhydrazine were used as constant building blocks (Table 6.3). 4-Trifluoromethylbenzaldehyde and phenylhydrazine were used in the variation of the P-ketoester (Table 6.4), while 4-tri-fluoromethylbenzaldehyde and ethyl acetoacetate were applied in the arylhydrazine variation (Table 6.5). All compounds were analyzed by ES-MS and HPLC (1 = 214 nm). 

Table 6.3. Variation of the aldehyde in the pyrazolone synthesis by using ethyl acetoacetate and phenylhydrazine as constant building blocks...

Table 1. Fischer indole synthesis from 1-phenyl-2-butanone and phenylhydrazine using soluble and solid acids.

Table 14.4. Diagonal (F) and interaction (/) force constants (mdyn/A), for Cu(II) bis(phenylhydrazine)-l,10-phenanthroline complex.

Several workers have described Fischer indolization without the use of acidic catalysts, the epitome of green chemistry. These thermal syntheses are shown in Table 2 [66-68]. The first practical account of noncatalytic Fischer indole synthesis appears to be that of Fitzpatrick and Riser (entries 1-3) [66]. Matsumoto and colleagues have effected indolizations with p-toluenesulfonic acid in the absence of solvent at 250 C to afford indoles 1-4 from the corresponding ketones and phenylhydrazine hydrochlorides (Scheme 5) [69]. In some cases, ttichloroacetic acid was employed. 

Now, it is worth noting (Table 9.4, 3a) that when the carbonyl group (C=0) in the aldehyde or ketone is unhindered, a second equivalent of carbonyl compound can be added to the hydrazone with the formation of an azine. The aryl-substituted hydrazines, for example, phenylhydrazine (C6H5NHNH2) and in particular 2,4-dinitrophenylhydrazine ( 2,4-DNPH ) (Table 9.4,3b) frequently form crystalline hydrazones. For many years (in a largely pre-spectroscopic era), it had been accepted that if the melting points of two derivatives (e.g., 2,4-DNP and oxime) of an unknown ketone or aldehyde corresponded to values found in published tables or lists of those previously reported, then the ketone or aldehyde had been identified. Generally, the method was successful but clearly dependent on ready access to the appropriate tables or lists. 

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