Peroxy Radical Activated Addition of tert-Butylcatechol to 2,6-Di-tert-butyl-7-Substituted Quinone Methide Polymerization Retarders

Abstract

Peroxy radicals formed by the autoxidation of styrene react with 4-tert-butylcatechol (TBC) to give a tert-butylsemiquinone radical. When the TBC radical is generated in the presence of a 2,6-di-tert-butyl-7-substituted quinone methide (QM), the result is o-TBC addition at the 7-position of the QM. The effects of TBC/QM addition are observed during styrene polymerization retarder testing under aerobic conditions for 2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)acetonitrile (QM-CN), 2,6-di-tertbutyl-4-(methoxymethylene)cyclohexa-2,5-dienone (QM-OMe), and 4-benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone (QM-Ph). Increasing the concentrations of QM-Ph and TBC during aerobic batch styrene polymerization allowed for silica gel chromatography isolation of 5-(tert-butyl)-3-((3,5-di-tert-butyl-4-hydroxyphenyl)(phenyl)methyl)benzene-1,2-diol, a novel compound. Radicals generated by the autoxidation of cumene and by homolysis of dicumylperoxide also activate TBC/QM addition. TBC/QM interaction causes a reduction in the performance of QMs as styrene polymerization retarders under aerobic conditions. Under anaerobic test conditions, a better simulation of industrial styrene purification, the TBC/QM interaction leads to only minimal reduction in retarder performance.

Radicals and Polymers

“…The inhibition mechanism of 70 accord ing to Scheme 17 has been confirmed ex perimentally with styrene as a monomer by Motyakov and coworkers [102] and later by Neilson and Morisson. [103] Recently, the radicophilic reactivity of QMs has been used for mild hydroalkylation of ole fins, [104] or for novel access to spiro [4.5] deca6,9dien8ones. [105] The next task after identification of the outstanding inhibitor activity [106] of 67-70 was the development of their economi cally viable, upscalable synthesis.…”

Synthesis of Quinone Methide Substituted Neonicotinoid Derivatives via 1,6-Conjugate Addition of N-Benzyl Nitro Ketene Aminals with para-Quinone Methides Accompanying Oxidation

“…NBNKAs belong to heterocyclic ketene aminals (HKAs) − which are widely used to construct molecular diverse heterocyclic compounds − such as spirooxindoles, , quinolones, pyridines, pyrroles, and others. However, the structural features of p -QMs result from the assembly of carbonyl and olefin moieties, and they have been widely used in a variety of addition reactions as universal Michael receptors, and are also chemically defined as neutral and zwitterionic resonance entities. , These structural features also allow for natural product synthesis as well as for the production of bioactive molecules. − There have been comprehensive reports produced about para -quinone methide reactions such as [3 + 2] addition, − [4 + 2] cycloaddition, [1 + 4] addition, and others. − Since Fan and Jørgensen reported on the 1,6-addition reaction of methylene quinone compounds, − many catalytic systems such as transition-metal catalysts (Figure ), − BF 3 ·Et 2 O (Figure ), , N -heterocyclic carbene catalysts (Figure ), , K 2 CO 3 (Figure ), , phosphoric acids (Figure ), , and other catalysts were reportedly used in the 1,6-addition reaction. ,…”