Proton phenylhydrazine

When arylhydrazones of aldehydes or ketones are treated with a catalyst, elimination of ammonia takes place and an indole is formed, in the Fischer indole synthesis.515 Zinc chloride is the catalyst most frequently employed, but dozens of others, including other metal halides, proton and Lewis acids, and certain transition-metals have also been used. Arylhydrazones are easily prepared by the treatment of aldehydes or ketones with phenylhydrazine (6-2) or by aliphatic diazonium coupling (2-7). However, it is not necessary to isolate the arylhy-drazone. The aldehyde or ketone can be treated with a mixture of phenylhydrazine and the catalyst this is now common practice. In order to obtain an indole, the aldehyde or ketone must be of the form RCOCH2R (R = alkyl, aryl, or hydrogen). 

Since neither the 2V-methyl nor the 2V-benzyl derivative of D-mannose phenylhydrazone showed a color change or the presence of paramagnetic species following treatment with base, it was concluded that the colored radical anion from D-mannose phenylhydrazone must arise following the abstraction of the acidic imino proton by base. Thus, this must be a first reaction step before fission of the phenylhydrazine moiety can occur. 

The reaction of the isotrithionium iodide (259) with aniline or phenylhydrazine to form the protonated anils or hydrazones (261) may actually involve the protonation of intermediate anils or hydra-zones (260) the isotrithione itself, moreover, cannot be condensed with these bases. 

In these last steps, two nucleophilic addition reactions take place to yield imine products. The mechanism has been worked out in greater detail in Section 19.8, but the essential steps are additions of phenylhydrazine, first to the imine, then to the ketone. Proton transfers are followed by eliminations, first of ammonia, then of H2O. 

The pKa of the methylene protons of 7 is close to that of cyanacetic ester. Thus, it was interesting to compare the reactions of these two species. We found that 7 can be acylated by various carboxylic acid halides, leading to compound 11. According to IR and NMR data 11 exists mostly as the enol-form, due to the influence of the carboranyl substituent, which strongly stabilizes conjugated double bonds.13 Compound 11 is a useful synthon for the preparation of heterocyclic compounds. It can be methylated, chlorinated and acylated twice ( compound 13). Compound 13 gives an adduct with phenylhydrazine (scheme 6). 

The experimental data allow the following interpretation of the mechanism. By the action of hydrogen sulfide, the sugar formazan (I) is reduced to a sugar hydrazidine derivative (II), which becomes protonized (III) in the course of a slow SnI process, the hydrazidine ion splits off phenylhydrazine, whereafter the arising carbonium ion (IV) unites in a rapid... 

On the basis above results the catalytic reduction of nitrogeous substances such as hydrazine, phenylhydrazine and azide was given in the following scheme 2. In which, the catalyst first formed an adduct with the nitrogeneous substancnes, followed by its series conversion into products and the regeneration of catalyst in the presence of external electron and proton sources. 

Phenylhydrazine was used for images enhanced by the NOE at natural abundance. As in the case of aniline, proton exchange leads to nearly complete collapse of the N-H couplings for both the NH and NH2 groups. The two groups are different, however, in that the process is more rapid for the NH2 than for the NH group and so leads to a narrower N line (16 Hz at 20 °C) compared with the NH2 value of 80 Hz in the single-resonance experiment. The NOE values are nearly equal at a value of about —2.9, and the T values for N were measured as 8.40 0.1 s (for NH) and 3.91 0.01 s (for NH2). 

The well-known approach to functionalized phosphorus ylides based on the three-component reactions of triphenylphosphine (TPP), dialkyl acet-ylenedicarboxylates (DAAD) and various EH-nucleophiles (E = N, O, S, C) stabilizing by protonation a reactive intermediate generated from the reaction of TPP and DAAD followed by addition of a conjugated base to the vinyltriphenylphosphonium salt formed, has continued to find application. When 2-bromoacetamide was used as a nucleophile in this reaction, a-amido phosphorus ylides (52) were formed, even despite the high reactivity of P(III) atom of phosphines towards alkyl halides and a-halocarbonyl compounds. Ethyl phenylcarbamate reacted in a similar way ((52), Y = OEt). The other series of stable a-amido phosphorus ylides (53) was produced from the above reaction with l-benzylidene-2-phenylhydrazines. The reaction of TPP,... 

TEMPO is red in color and has a UV absorption around 470 nm. This radical is reduced by phenylhydrazine to the colorless hydroxylamine [50], The PVTEMPO-Z)-PSt diblock copolymer showed an absorption with a value at 467 nm based on the TEMPO radical. It was found that the red color of the copolymer solution in benzene faded out as phenylhydrazine was added to the solution. Figure 1-2-1 shows the variation in the UV absorption of the copolymer with the addition of the phenylhydrazine. The absorbance based on TEMPO decreased with an increase in the molar ratio of the phenylhydrazine to the VTEMPO imit (PH/TEMPO). The absorbance plotted at 500 nm versus the PH/TEMPO ratio is shown in Figure l-2-2a. The absorbance continued to decrease up to 0.8 and was almost constant above it. The absorbance did not reach zero even at 1.0 due to the long foot of the large absorption peak observed at 240-390 nm. The formation of the hydroxylamine was also confirmed by the H NMR measurement of the copolymer in CDCI3 in the presence of phenylhydrazine. Signals based on the tetramethyl protons of the hydroxylamine derivative of TEMPO were observed at 1.18 and 1.26 ppm. 

Proton transfer between salicylic acid and tetra-alkylhydrazines has been studied in DMSO. The rates are remarkably low, and give a Bronsted coefficient of —1.16. Proton exchange in liquid phenylhydrazine occurs much more readily at the NHj than at the NH group. A transition state of type (3) is suggested. ... 

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