2852-70-2Relevant academic research and scientific papers
Mechanism of the Gibbs reaction. Part 4. Indophenol formation via N- chlorobenzoquinone imine radical anions. The aza-S(RN)2 chain reaction mechanism. Chain initiation with 1,4-benzoquinones and cyanide ion
Pallagi, Istvan,Toro, Andras,Horvath, Gyula
, p. 6530 - 6540 (1999)
The mechanism of the Gibbs reaction, a colorimetric phenol assay that applies N-chlorobenzoquinone imines 1 in an aqueous basic medium, was investigated. It is concluded that N-chloroimine radical anion 7 generated in a single electron transfer (SET) from the anion of phenol 4 to N-chloroimine 1 can produce indophenol dye 3 in three distinct routes. For more reactive reagent-substrate pairs, a route is proposed that involves a fast combination of the radical pair in the solvent cage and, consequently, the total rate of which exhibits a pH-independent second-order kinetics, as does the preceding SET itself. For less reactive reagents, a route is proposed in which the N- chloroimine radical anion 7 escapes from the solvent cage to initiate a chain reaction, evidenced by its characteristic kinetics. It has been found in the kinetic experiments that during propagation the chlorine of the chain carrier N-chloroimine radical anion 7 is substituted by the anion of 4 in a bimolecular rate-determining step. Therefore, the mechanism of the chain reaction is termed S(RN)2. In the case when the anion of 4 is less active, a competitive reaction along a third route can proceed in which the N-haloimine radical anion 7 yields benzoquinone imine 6 by the elimination of halogenide and the abstraction of an H-atom from the medium. Compound 6 is also known to give indophenol 3 with a second-order but pH-dependent rate that is considerably faster than the rate in the first route. On the basis of the different kinetic characteristics outlined above a clear distinction can be made among these three pathways. In this paper, evidence is also presented for the initiating SET. Furthermore, it is of high importance that the N- haloimine radical anion 7 can also be generated from reagent 1 using external electron donors and, independently of its origin, it can be spin trapped with 2,2,6,6-tetramethylpiperidine-N-oxyl.
GIBBS REACTION. PART 1. REDUCTION OF BENZOQUINONE N-CHLOROIMINES TO BENZOQUINONE IMINES
Pallagi, Istvan,Dvortsak, Peter
, p. 105 - 110 (1986)
The behaviour of benzoquinone N-chloroimines under neutral, acidic, and basic conditions has been studied.Although these compounds are stable under neutral conditions they are hydrolysed in acidic solution to the corresponding benzoquinone derivatives.In the presence of base and alcohols, they are reduced to benzoquinone imines.Kinetic investigation of the reaction suggested an ionic mechanism, in which cleavage of the Cα-H bond of the alcohol is the rate-determining step.
