Partial Rate Factors For Phenylation Research Articles

Aroyl peroxides. Part 7. The effects of additives on the thermolysis of aroyl peroxides in arenes and the elimination of possible complications in the measurement of partial rate factors for phenylation

Competitive homolytic arylation of arenes has been carried out under conditions in which biaryl formation is maximised. Improved yields of biaryl were obtained with o-chloroanil, nitro- and nitroso-compounds, and transition metal salts; nitrosobenzene, pentafluoronitrosobenzene, copper(II) benzoate, and iron(III) benzoate caused nearly theoretical yields of biaryl and aroic acid. Partial rate factors, measured under such conditions, are free from uncertainties arising from the selective removal of σ-complexes by side-processes such as dimerisation. The possibility that arenes form complexes with aryl radicals or their precursors as a necessary part of the selection process between substrate molecules was not confirmed in studies of the application of the additivity principle and of the multiplication rule, and of variation in the relative concentration of the two competing arenes. The absence of any discrepancies indicates that the measured partial rate factors are not influenced by such putative complex formation. The mechanism of action of these catalysts has been investigated.

Phenylazo p-Tolyl Sulfone as a Source of Phenyl Radical

Abstract Mechanism of the decomposition of phenylazo p-tolyl sulfone(I) was investigated. Orientations and partial rate factors of substituted biphenyls produced by the decomposition of I in benzene-substituted benzene mixtures were used as the criteria for judging the nature of the decomposition. When CaO- or MgO-suspension was present, autocatalytic heterolysis of I was suppressed to some extent, but for complete suppression 20–40 w/v % CaO or MgO was necessary. Pyridine and quinoline were found to be effective for suppression of the autocatalysis. When sufficient amount of pyridine, quinoline, MgO or CaO were present, orientations and partial rate factors for phenylation of substituted benzene were similar to those obtained by phenyl radical produced by benzoyl peroxide on N-nitrosoacetanilide. The rate of decomposition of I was determined in PhC2H5, PhOCH3, PhCl, PhNO2, pyridine and DMF in the presence of pyridine. An isokinetic relationship was found to hold for activation parameters for the decomposition in these solvents, and the isokinetic temperature was 88.6°C. Values of activation enthalpy and entropy were rather large; ΔH\eweq=39.6 kcal/mol and ΔS\eweq=34.4 e.u./mol in DMF.

Aromatic Arylation with Aryl Radicals. I. A Novel Method for Generating Aryl Free Radical

Abstract Benzenediazonium tetrafluoroborate in DMSO decomposed instantaneously with evolution of nitrogen upon addition of a DMSO solution of sodium nitrite. Orientations and partial rate factors for phenylation of substituted benzenes indicated that not phenyl cation but phenyl radical was produced as an intermediate. Hammett’s plots of partial rate factors of meta and para positions yielded good straight lines with ρm=0.46 and ρp=1.67. Plausible mechanisms were discussed. From m-dinitrobenzene 2,6- and 2,4-dinitrobiphenyl were produced in 47 and 23% yields, respectively, and the synthetic value of this method was pointed out.

Cationic Arylation. III. Comparison of Phenylation of Naphthalene with Phenyl Cation and Phenyl Radical

Abstract Naphthalene was phenylated with phenyl cation (from PhN2BF4) or phenyl radical (from PhN2BF4+NaNO2) in dimethyl sulfoxide. Partial rate factors for phenyl radical were somewhat larger than those reported with the phenyl radical generated from N-nitrosoacetanilide. Partial rate factors for phenylation with phenyl cation were smaller than those for free radical phenylation and those for common electrophilic substitution reactions. These small partial rate factors for phenyl cation were not compatible with the reaction scheme involving an ordinary σ-complex, and a mechanism involving a spiro cation appeared to be plausible.

Phenylation with Phenyl Radical Generated from Phenylazotriphenylmethane

Abstract Phenylazotriphenylmethane was decomposed in substituted benzenes, and orientations and partial rate factors for phenylation were determined.