Acid Conversions of Hydrazoarenes

Banthorpe, D. V.; Cooper, Anthony; Ingold, C. K.

doi:10.1038/216232a0

Cited by 18 publications

(19 citation statements)

References 3 publications

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“…Eqn (3), structure e, of a di-C-protonated quinonoidal ring-linked intermediate in super acid as proposed by Banthorpe, Cooper, Hughes and Ingold, Scheme 2 [2,3]. The cation radical mechanism presented herein can account for Olah's experimental results, e.g.…”

Section: Benzidine Formationmentioning

confidence: 59%

“…Banthorpe, Hughes, Cooper and Ingold postulated the polar transition state theory (PTS) which suggested that the intermediate involved in disproportionation has a quinonoid structure [2,3]. This structure also provides a rationale for the rearranged products, Scheme 2.…”

Section: Previous Theoriesmentioning

confidence: 96%

“…Consequently, both the concerted rearrangements, Table 1, benzidines, 4-methoxy-p-semidine formation, Eqns (2), (3) and o,o'-biaryl-linked products, and non-concerted rearrangements, Table 2, diphenyline, o-semidine, Eqns (5), (6) and perhaps 4-chloro-psemidine, may proceed via cation radical structures involving radical C -C bond formations and homolytic N -N bond cleavages. This is contrary to the current view of the Polar Transition State theory which postulates heterolytic bond formations and cleavages, Schemes 1, 3 and 4.…”

Section: Introductionmentioning

confidence: 97%

“…Substitution in both para positions shifts the reaction predominantly towards disproportionation. With regard to the disproportionation reaction, the stoichiometry is shown in Eqn (2).…”

Section: Introduction 11 Rearrangements and Disproportionationmentioning

confidence: 99%

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The Acid-Catalysed Benzidine Rearrangements May Proceed via Cation Radicals Formed by Electron Transfer to a Proton from a Hydrazyl Nitrogen

Mamantov

2013

Progress in Reaction Kinetics and Mechanism

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The acid-catalysed benzidine rearrangements are proposed to proceed via cation radical intermediates which arise by rapid electron transfer from a neutral nitrogen of the hydrazyl moiety to a proton. Consequently, both the concerted rearrangements, Table 1, benzidines, 4-methoxy-p-semidine formation, Eqns (2), (3) and o,o'-biaryl-linked products, and non-concerted rearrangements, Table 2, diphenyline, o-semidine, Eqns (5), (6) and perhaps 4-chloro-psemidine, may proceed via cation radical structures involving radical C -C bond formations and homolytic N -N bond cleavages. This is contrary to the current view of the Polar Transition State theory which postulates heterolytic bond formations and cleavages, Schemes 1, 3 and 4. Mono-substituted and 4,4'-disubstituted hydrazobenzenes are proposed to undergo oxidation of the most basic nitrogen as inferred from the estimated pK a s as determined by the SPARC program. This can explain why of the two possible o-semidine rearrangement products, 2,N' and N,2'-linked, the observed major o-semidine has the substituent para to the amino group, e.g. Eqn (5). However, if one of the para substituents is a halogen, it is the nitrogen para to the halogen which undergoes SET and oxidation. In these second-order acid reactions, this can be explained by protonation of the most basic nitrogen followed by SET from the hydrazyl nitrogen para to the halogen. In the case of 4,4'-disubstitution, the hydrazobenzene may not lose its substituents readily and undergoes a rapid one-electron reduction and consequent disproportionation reaction as shown in Eqn (8). Thus the kinetics, first-order in hydrazoarene and the same kinetic order in acid for both disproportionation and rearrangement, are explained.

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Section: Benzidine Formationmentioning

confidence: 59%

Section: Previous Theoriesmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 97%

“…Substitution in both para positions shifts the reaction predominantly towards disproportionation. With regard to the disproportionation reaction, the stoichiometry is shown in Eqn (2).…”

Section: Introduction 11 Rearrangements and Disproportionationmentioning

confidence: 99%

See 2 more Smart Citations

The Acid-Catalysed Benzidine Rearrangements May Proceed via Cation Radicals Formed by Electron Transfer to a Proton from a Hydrazyl Nitrogen

Mamantov

2013

Progress in Reaction Kinetics and Mechanism

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“…It was found that a 1:2 ratio of components gave the corresponding 4-amino-2-methyl-3-(2'-methylindol-3'-yl)methylquinolines 3a-e in place of the expected 2-methyl-3-(2'-methylindol-3'-yl)methyl-4-phenylhydrazinoquinolines. In all probability the 4-phenylhydrazinoquinolines formed as a result of the reaction, similarly to hydrazo compounds [3,4], undergo disproportionation in accordance with a [5,5]-sigmatropic shift mechanism to give para-quinoid intermediates which decompose to the corresponding 4-aminoquinolines and aniline. EXPERIMENTAL 1 H NMR spectra were taken on a Varian Mercury-300 spectrometer (300 MHz) using DMSO and with TMS internal standard.…”

mentioning

confidence: 96%

Synthesis of 4-Hydroxy- and 4-Amino-2-Methyl-3-(2-Methylindol-3-Yl)methylquinolines and Their 6- and 8-Substituted Derivatives

Avetisyan

Aleksanyan

Pivazyan

2005

Chem Heterocycl Compd

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Keywords: 4-hydroxy(amino)-2-methyl-3-(2-methylindol-3-yl)methylquinolines, 4-hydroxy(chloro)-2-methyl-3-(3-oxobutyl)quinolines, 4-hydroxy-2-methyl-3-(3-oxobutyl)quinolines thiosemicarbazones.We have previously developed a convenient method for the synthesis of differently structured 3-(3-oxobutyl)quinolines [1, 2] as suitable starting materials for conversion to different novel heterocyclic systems. In continuing these investigations of the synthesis of quinolines also containing an indole ring we have studied the reaction of the corresponding 4-hydroxy-2-methyl-3-(3-oxobutyl)quinolines with phenylhydrazine hydrochloride.Optimum conditions for the reaction have been developed. It was found that the reaction indicated can be brought about by heating equimolar mixtures of the starting components in alcoholic solution in the presence of H 2 SO 4 for 7-8 h. Evidently the reaction takes place with the formation of an intermediate phenylhydrazone and a subsequent Fischer type rearrangement to give high yields of the corresponding indolylquinolines 1a-e. N OH CH 2 CH 2 Me R Me N OH CH 2 Me R N H Me C N Me N C NH 2 S N OH CH 2 CH 2 Me O R 1a-e C H 2a-e 1, 2 a R = H, b R = 6-Me, c R = 8-Me, d R = 6-OMe, e R = 8-OMe

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