Addition of Benzoyl Radicals to Butyl Acrylate:  Absolute Rate Constants by Time-Resolved EPR

Abstract

The addition rate constants of five differently substituted benzoyl radicals to butyl acrylate were determined by continuous-wave time-resolved EPR (TR-EPR at X-band (9 GHz) and at W-band (95 GHz)) spectroscopy. Remarkably, the reactivity of the benzoyl radicals, is divided into two domains: One is established at low (<1.25 M) concentrations of butyl acrylate with rate constants in the range of 10 6 mol -1 s -1 . At alkene concentrations above ca. 1.25 M, the addition reaction slows down by ∼1 order of magnitude. This decrease of the reactivity coincides with a dramatic increase of the macroscopic viscosity in the reaction medium.

Simple One-Pot Syntheses of Water-Soluble Bis(acyl)phosphane Oxide Photoinitiators and Their Application in Surfactant-Free Emulsion Polymerization

“…It consists of two signals: The central signal at g = 2.0005(1) and two lines (emission/absorption (E/A)) spaced by 34.9(1) mT centered at g = 2.0040(2). In analogy to well‐described BAPOs, the central signal can be assigned to the mesitoyl whereas the E/A doublet, with the characteristically large isotropic hyperfine coupling constant of 34.9 mT clearly shows the presence of a phosphanoyl radical. The E/A character of the doublet indicates that the chemically induced electron polarization (CIDEP) effect observed in the spectrum is dominated by the radical pair mechanism .…”

“…In analogy to well‐described BAPOs, the central signal can be assigned to the mesitoyl whereas the E/A doublet, with the characteristically large isotropic hyperfine coupling constant of 34.9 mT clearly shows the presence of a phosphanoyl radical. The E/A character of the doublet indicates that the chemically induced electron polarization (CIDEP) effect observed in the spectrum is dominated by the radical pair mechanism . The hyperfine coupling A P of 34.9 mT is the largest value reported so far for an acyl‐phosphonyl radical .…”

Chemically Induced Dynamic Nuclear Polarization during the Thermolysis of Alkoxyamines: A New Approach to Detect the Occurrence of H-Transfer Reactions

“…[11][12][13][14]. Previously, Chemically Induced Dynamic Electron Polarization (CIDEP) [15,16] and CIDNP and its modification (CIDNP with fast switching of magnetic field) have been used in NMP research to measure the rate constants of coupling between acrylate-type radicals and the persistent nitroxide [17,18]. In those experiments, the carbon centered radicals under investigation were generated by the photolysis of ketone precursors in the presence of persistent nitroxides.…”

“…The intensity of polarization is determined by CIDNP enhancement factor, nuclear relaxation time and decay rate constant. The expected time of CIDNP maximum obtained from expressions (13)(14)(15)) is equal to:…”

Phosphorous‐Functionalized Bis(acyl)phosphane Oxides for Surface Modification

“…[3] Starting from simple peroxides or a-hydroxy ketones, functionalized oxime esters, [4] organo phosphorus, [1] or, more recently, germanium compounds [5,6] have been developed as highly sophisticated photoinitiators with specific properties. [9][10][11][12][13][14][15][16] Irradiation with even a weak light source in the visible range leads to the formation of a phosphinoyl and an acyl radical through a Norrish type I cleavage reaction [Eq. [9][10][11][12][13][14][15][16] Irradiation with even a weak light source in the visible range leads to the formation of a phosphinoyl and an acyl radical through a Norrish type I cleavage reaction [Eq.…”