The Kinetics of Z/E Isomerization of Methyl Oleate Catalyzed by Photogenerated Thiyl Radicals

Abstract

The reaction of beta-mercaptoethanol with methyl oleate in tertbutyl alcohol was investigated under photochemical conditions. The time-dependent Z/E isomerization of the unsaturated moiety as well as the thiol-adduct formation were analyzed on the basis of radical generation rates and established rate constants. This provides precise room-temperature rate constants for the reversible thiyl radical addition to both Z and E isomers. The rate constants for HOCH2CH2S* addition to the Z and E forms were found to be 1.6 x 10(5) and 2.9 x 10(5) M(-1) S(-1), respectively. For the beta-elimination of the thiyl radical from the alkyl radical adduct, the rate constants were 1.7 x 10(7) and 1.6 x 10(8) S(-1), the faster associated with the formation of the E isomer. DFT-BB1K calculations on 2-butene assign this large preference of fragmentation for the E isomer to a lower activation barrier for the formation of the E transition state from the equilibrium radical adduct structure.

Photoinduced thiol–ene crosslinking of globalide/ε‐caprolactone copolymers: Curing performance and resulting thermoset properties

“…This Raman spectrum gives more details about the chemical configuration of the double bonds of the copolymer structure, indicating a clear predominance of trans ‐unsaturations over cis ‐unsaturations. From a kinetic perspective, this is advantageous because the formation of product is favored over the isomerization to cis ‐isomer 35, 36. The isomerization occurring in the system should therefore be negligible when compared with the formation of the final addition product directly from the trans ‐isomer.…”

“…In this study, we apply a different approach and investigate if thiol–ene coupling with the use of photopolymerization could be used with unsaturated copolymers derived from macrolactones to provide films with efficient curing and high conversions (Scheme ). We are building on previous research investigating the reactivity of 1,2‐disubstituted alkenes based on whether they are located in the cis or trans form, and it has been determined that this has no significant effect in the overall reaction rate, and thus a wider array of components from renewable resources are viable for this type of chemistry 34–36. Additionally, with a series of globalide‐ and caprolactone‐containing copolymers, differing in their disubstituted ene density due to varying amounts of caprolactone, it is of interest to determine the relationship between functional density and the resulting conversion.…”

Initiation of Radical Chain Reactions of Thiol Compounds and Alkenes without any Added Initiator: Thiol‐Catalyzed cis/trans Isomerization of Methyl Oleate

“…Thiyl radical-catalyzed isomerization of mono-unsaturated fatty acid methyl esters. [2][3][4] Chem. Eur.…”

An ESR Approach to the Estimation of the Rate Constants of the Addition and Fragmentation Processes Involved in the RAFT Polymerization of Styrene

“…Thus, the large decrease of entropy computed in the gas-phase in a bimolecular process on going from the reagents to the transition state is usually substantially overestimated. Indeed, a similar discrepancy between theory and experiment has been observed in computing the addition/ fragmentation rate constants involving a thiyl radical and an alkene C=C bond [32]. The harmonic-oscillator approximation employed to compute the vibrational contributions to enthalpy and entropy causes one to slightly underestimate the addition rate.…”