Untersuchungen zur Thermolyse und zur Sauerstoff‐Stabilität der 4π + 2π‐Diels‐Alder Addukte des Styrols

The 4π + 2π‐Diels‐Alder cycloadduct 1 involved in the spontaneous polymerization of styrene was investigated under conditions, where bimolecular reactions with styrene leading to a consumption of 1 can be neglected. For this reason 1 was (a) submitted to thermolysis in an inert solvent (toluene) at different temperatures (90, 100 and 110°C) and (b) oxidized with an excess of oxygen in styrene at room temperature. The reactions were followed spectrometrically at the wavelength λ = 325 nm and analyzed in terms of a first order reaction. The results show strong evidence for the involvement of two diastereomers ( 1a and 1b ) of different reactivity. This is in qualitative and quantitative agreement with the two isomers' concept, which had been deduced previously from kinetic analysis of the formation of 1 during the thermal polymerization of styrene. Rate constants and activation energies as well as possible reaction pathways are given.