On the Reactivity of Alkoxy Radicals. Interaction Between 1‐Phenylethoxy Radical and Ethylbenzene in the Absence of Oxygen

Abstract

Alkoxy Radicals / Kinetics / Photochemistry / Radicals / Reactivity of Radicals The hydrogen abstraction from ethylbenzene by 1 -phenylethoxy radicals generated by the photodecomposition of 1 -phenylethyl terf-butyl-peroxide was investigated in acetonitrile as solvent. The rate constant ratios of Habstraction to p-scission were 14 in the case of ethylbenzene, 26 for the peroxide and 0.02 for acetonitrile at 293 K. The activation energy difference of the above two steps was 16.93~0.2 kJ mol-' for ethylbenzene. The quantum yield of the photodecomposition of the peroxide obtained is 0.8. Product accumulation curves received by gas chromatography were simulated using the suggested mechanism with the rate constants compiled both from our experiments and literature data. (HROOBu) was synthesized according to Kornblum and de la Mare (141. Its refraction index was n g = 1.4802 in agreement with literature data (nkb = 1.4806). The purity according to GC analysis was 99.5%. I-Phenylethyl-tert-Bu-peroxideAcefonitrile (AN) HPLC grade quality was used having very low absorbance in the range 2300 -3200 8,.Ethylbenzene: (RH,) has been purified as described previously [19].Nitrogen was freed of oxygen contamination by a column of 40 mm diameter and 300mm length filled with R3-11 (BASF) catalyst and followed by a gas purifier containing pyrogallol solution (50 g KOH in 100 ml water + 5 g pyrogallol) and dried over CaCI,.Reaction vessel: Thermostated quartz vessel was used (15 ml, 30mm diameter) with solutions of 14.7 ml. In each experiment 0.25 ml "zero" sample was taken after freeing the solution from oxygen by N, bubbled for 20 min. Illumination has been commenced afterwards. During illumination 0.1 ml samples were taken with syringe for analysis.Illumination: A 125 W high pressure Mercury lamp (HgLiIH125) served as light source with filter solution (lengths 20 mm, diameter 25 mm, filled with 240 g/1 NiS04.6H,0 +45 g/l CoSO,.7 H,O) as described by Kasha [20]. Transmission was in the range 2300-3200 8,.

Catalytic Performance of Ceria Nanorods in Liquid-Phase Oxidations of Hydrocarbons with tert-Butyl Hydroperoxide

“…Possibly, the CeNR material acts as an initiator in the homolysis of t -BuOOH into free alkoxy ( t -BuO • ) and alkylperoxy radicals ( t -BuO 2 • ) via the net redox reaction represented in Equation 1: Ce 4+ is a relatively strong one-electron oxidant, and the resulting Ce 3+ species may be re-oxidized by t -BuOOH [ 16 ]. The t -BuO • radical can abstract a proton from the substrate to give the corresponding radical (PhEt • ), Equation 2 [ 17 ], which reacts with t -BuO 2 • radicals to give PhEtOOT (Equation 3). It has been reported for the liquid-phase oxidation of arylbenzene compounds in homogeneous phase, in the presence of cerium ammonium nitrate/KBrO 3 that radicals of the substrates may reduce Ce 4+ into Ce 3+ species, forming intermediate carbocations, which are subsequently oxidized [ 18 ].…”

“…The PhEtOOT product may be transformed into acetophenone (PhEt=O) plus t -BuOH via radical intermediates [ 14 , 17 ] (Equation 7). This hypothesis is supported by the fact that when CeNR is filtered from the reaction mixture after 24 h, at 70 °C (at this point PhEtOOT is the only product), and the obtained solution is left to react in the absence of CeNR until 48 h, at the same temperature, the formation of acetophenone is observed.…”

Kinetic modeling of the peroxide cross-linking of polymer/monomer blends: From a theoretical model framework to its application for a complex polymer/monomer dispersion system

“…Other constants essentially control the rates of peroxide, cross-linking, cross-link degradation and specific polymer chemistry. Using these considerations, a total of 10 rate constants (with k d,i,j,k,l,m,n and k ib,i,j,k , which could not have been obtained from literature [27][28][29][30][31][32]) for all potential substituents had to be determined, that is k iha,i,j,k,l,m,n , k iar,i,j,k,l,m,n,o , k it1,i,j,k,l,m,n , k it2,i,j,k,l,m,n , k ha,i,j,k,l,m,n , k ar,i,j,k,l,m,n,o , k t1,i,j,k,l,m,n , k t2,i,j,k,l,m,n , k b,i,j,k , and k e,i,j,k,l,m,n . The rate constants and the associated activation energies and pre-exponential factors were determined utilizing molecular modeling [22,23,33].…”

“…Information about how the peroxide type affects the reactive bond is available from either experimental data or quantum chemistry calculations [27][28][29] and this effect on the rate constant had to be readily incorporated for various peroxides. The rate constants k ib,i,j,k were considered likewise [30][31][32], since these represent b-cleavage of oxy radical. Other constants essentially control the rates of peroxide, cross-linking, cross-link degradation and specific polymer chemistry.…”