Mechanism of the benzidine rearrangement. Kinetic isotope effects and transition states. Evidence for concerted rearrangement

Mechanism for the reaction of 2‐naphthol with N‐methyl‐N‐phenyl‐hydrazine suggested by the density functional theory investigations

“…The imaginary frequency of 299.37 icm À1 is mainly associated with the coupling of the formation of C1AC6 bond and the rupture of N1AN2 bond, which further manifests Shine's ' 'concerted' ' rearrangement mechanism as stated in the Introduction section. [32,43] In the sequential process, the diimino compound is stabilized via two water-assisted proton migrations to offer the final product. The transition state 3_TS3 is a six-membered ring structure.…”

“…[29][30][31] The mechanism and kinetics of rearrangement of hydrazo compounds were intensively studied in the mid 1900s. [32][33][34][35][36][37][38][39][40][41][42][43] In 1960, Shine and Trisler examined the influence of solvent on the rearrangement of 2,2 0 -hydrazonaphthalene and reported two rearrangement products 2,2 0 -diamino-l,1 0 -binaphthyl and carbazole, first proposing a ' 'concerted' ' rearrangement idea that carbon-carbon bond making occurs while the nitrogen-nitrogen bond is breaking. [32] Later, Shine's group investigated the detailed mechanism of the benzidine rearrangement and further explained the concerted rearrangement by three major theories involving the rate-determining ring protonation, the polar transition-state theory, and the p-complex theory.…”

“…[32] Later, Shine's group investigated the detailed mechanism of the benzidine rearrangement and further explained the concerted rearrangement by three major theories involving the rate-determining ring protonation, the polar transition-state theory, and the p-complex theory. [43] The reaction of naphthol with hydrazine has long been of great interest in synthetic organic chemistry. [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] Experimentally, 2-naphthol and hydrazine hydrate are usually used for the synthesis of 2,2 0 -diamino-l,l'-binaphthyl, which is an important starting material often used in a variety of asymmetric syntheses.…”

Rearrangements of Hydrazo, Azoxy and Azo Compounds: Kinetic, Product and Isotope Studies

“…In all cases labelled azobenzenes were prepared first, recrystallized with appropriate amounts of unlabelled azobenzenes if necessary 10 and then reduced to hydrazobenzenes with zinc and NH 4 Cl in aqueous SCHEME 1 acetone 11 , so only the azobenzene syntheses are described below. In most cases the azobenzene was prepared from the appropriately labelled aniline by oxidizing it with MnO 2 12 .…”

“…[4-14 C]azobenzene was prepared from available [1-14 C]-4-nitroaniline by removing the amino group by diazotization, diluting the resulting quite radioactive [4-14 C]nitrobenzene with ordinary nitrobenzene and reducing this with zinc dust and NaOH 10 . [4, 4 -13 C 2 ]azobenzene was prepared from [2-13 C]acetone by treating it with sodium nitromalonaldehyde to make [1-13 C]-4-nitrophenol 14 , converting this to 5-(4-nitro[1-13 C]phenoxy)-1-phenyl-1H-tetrazole with 5-chloro-1-phenyl-1H-tetrazole and hydrogenating, producing a mixture of labelled aniline and labelled phenylhydroxylamine which could be directly converted to the labelled azobenzene 10 …”