Hydrogen Abstraction Reactions of Diphenylpicrylhydrazyl

Brook, A. G.; Anderson, R. J.; Patot, J. Tissot Van

doi:10.1139/v58-020

Cited by 18 publications

(4 citation statements)

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“…I t cannot occur exclusively, because this would require t h a t 2 moles D P P H woulcl react with 2 moles cliphenylamine instead of the 1.2 moles diphenylamine observed experimentally. Reaction [3] involving the disproportionation of amino radicals probabl! occurs to some Can.…”

Section: Results a N D Discussionmentioning

confidence: 99%

The Reaction of 2,2-Diphenyl-1-Picrylhydrazyl With Secondary Amines

Hazell¹,

Russell²

1958

Can. J. Chem.

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The reaction of D P P H (2,2-diphenyl-1-picrylhydrazyl) with N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, diphenylamine, and methylaniline has been studied and has been shown to be primarily a hydrogen abstraction process. Two moles D P P H react with 1-1.15 moles seconclary arnine to give 1.7-1.8 moles 2,2-diphenyl-1-picrylhydrazine ancl further -. .. . . products.The reaction between D P P H and iV-phenyl-1-naphthylalnine is first orcler with respect to each reactant. The reaction of DPPH with the other amines is retarded by the major product 2,2-diphenyl-1-picrylhydrazine and the Itinetics of the over-all reaction are comples. However second-order rate co~lstants and activation energies have been obtained sing initial rates of reaction. Possible reaction mechanisms are discussed.This study of the reaction between 2,2-diphenyl-1-picrylhydrazyl (DPPH) and secondary amines forms part of a general investigation of the rates of hydrogen abstraction processes in solution using D P P H as the acceptor molecule. In spite of its existence as a stable free radical D P P H readily abstracts hydrogen atoms from mercaptans (1) and hydroaromatic compounds such as 1,4-diliydronaphthalene (2). A similar reactivity towards many secondary amines (3, 4), phenols, and hydrogen halides is observed. Rate studies on these reactions should give information concerning the influence of structure on the ease of hydrogen abstraction from the various donors.As the acceptor molecule, DPPH has the advantage that it is a colored free radical which does not dimerize and its concentration can be estimated by its absorption in the visible region. However, it complexes with amines (3) and possibly with aromatic liydrocarbons (2) and such complexing may affect the kinetics of reaction. I t may also be involved in steric effects which are not observed with small radicals.In the present work the reactions between DPPH and certain secondary amines have been investigated with regard to stoichiometry and kinetics. I t was hoped that the single hydrogen atom attached to nitrogen would be abstracted in the primary reaction. The secondary amines used were N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, diphenj~lamine, and methylaniline. A few kinetic experiments were performed with di-n-propylamine. iVaterials 2,2-Diphenyl-1-picrylhydrazine and D P P H were prepared by the method of Goldschmidt and Iienn (5). The hydrazyl crystals were heated to 75' in vaczro for G hours to break down a DPPH-chloroform complex.Di-n-propylamine was distilled in a 20-plate column. Methylaniline was distilled under reduced pressure to give one sample. A second sample was obtained by conversion to the nitrosamine, followed by reduction with tin and hydrochloric acid and distillation. Diphenylamine was recrystallized from petroleum ether. The phenylnaphthylamines were recrystallized from ethanol. The amines were stored in the dark.'Manuscript

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Section: Results a N D Discussionmentioning

confidence: 99%

The Reaction of 2,2-Diphenyl-1-Picrylhydrazyl With Secondary Amines

Hazell¹,

Russell²

1958

Can. J. Chem.

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“…The literature reports and the results of this laboratory point to a series of complex reactions. Brook, Anderson, and Tissot Van Patot (4) have stated that there are many simul-order kinetics-i.e., rate of disappearance of hydrazyl = k2 [hydrazyl] [amine]. Despite the complexity of the reaction, it is felt that one can consider as a good first approximation the primary reaction shown above as the only reaction.…”

Section: Methodsmentioning

confidence: 99%

“…Chemical combination can cause a very marked change in these lines. Valence, coordination, electronegativity, electrical conductivity, crystal structure may all have some kind of effect on emission spectra, especially those involving transitions from the valence or conduction band (1,2,4,(9)(10)(11).…”

Section: Literature Citedmentioning

confidence: 99%

“…Diphenylpicrylhydrazyl, a stable free radical, has generated a great deal of interest among chemists within the last ten years. The many reactions of this compound and the kinetics of these reactions have been considered (3)(4)(5)(6)(7)11). The intense color of this compound and the degree and variation of its reaction rates suggest its value as an analytical reagent.…”

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confidence: 99%

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