A Kinetic Determination of the Dissociation Energy of the C—O Bond in Anisole

Abstract

. Can. J. Chem. 53,3330(1975). The rate of dissociation of anisole into phenoxy and methyl radicals has been measured using a toluene scavenging technique. The rate was measured by the production of methane over the range of temperature 72@-795 K and was shown to be first order in anisole concentration and homogeneous. The rate constant, expressed in the Arrhenius form, was log k (s-') = 13.7 + 0.3 -58000 + 2000 2.3RTThe dissociation energy, D298(C6H50-CH3), therefore equals 57 + 2 kcal/mol, giving AHf(C6H,0) = 5 kcal/mol. The stabilization energy of the phenoxy radical is discussed.

Pathways and Kinetics of Anisole Pyrolysis Studied by NMR and Selective 13C Labeling. Heterolytic Carbon Monoxide Generation

“…The effect of toluene was discussed in terms of the radical mechanism in the previous works. 6,9 All of our main products, benzene, phenol, and methane except for carbon monoxide were also reported in Ref. 9, whereas only phenol and methane were identified in Ref.…”

“…The E a value obtained from the wide temperature range is in reasonable agreement with those reported in the narrower temperature range. 6,7,9 As seen in Figure 8, however, one paper 8 reports a considerably smaller E a value. 25 Thus the anisole pyrolysis reaction discussed here is essentially the same as that so far studied.…”

“…1,69,12 Methane was found in most of the papers. 1,6,7,9,11,12 In several papers, 1,7,911 benzene was found as the ring product, always accompanied by phenol and carbon monoxide. All of the information on the product distribution implies the phenyl ring retention and is not contradictory to the bimolecular proton-transfer step (eq 2) followed by the unimolecular proton-transfer step (eq 1).…”

“…The 13 C, 2 H, and 1 H NMR spectroscopic study on the toluene-d 5 system clearly indicates that the minor product, bibenzyl is generated not from anisole but from the highconcentration supercritical solvation shell itself, 21 contrary to the phenoxy-radical mechanism. 6,9 Furthermore, when benzene-d 6 or toluene-d 5 is added to anisole to change the molecular environment no propagation products of methyl and hydrogen radicals assumed in the literature are detected. In other words, no 1 H-methylsubstituted derivatives of the deuterated solvents are detected.…”

“…9, whereas only phenol and methane were identified in Ref. 6. We reinvestigated the effect of toluene in the anisole (0.0011.0 M) and toluene (1.0 M) mixtures.…”