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Keywords:

  • formylation;
  • oxygenation;
  • polyethylene glycol;
  • radical reactions;
  • supercritical fluids

Abstract

The thermal oxidative degradation of polyethylene glycol (PEG) is known to occur in an oxygen atmosphere at elevated temperatures. In this study, PEG radicals assumed to result from thermal oxidative degradation are successfully applied, in combination with compressed CO2, to initiate a range of free-radical reactions, such as selective formylation of primary and secondary aliphatic alcohols, oxidation of benzylic alcohols, benzylic C[DOUBLE BOND]C bond cleavage, and benzylic sp3 C[BOND]H oxidation, demonstrating enormous synthetic potential in a cost-efficient, practically useful, and environmentally friendly manner; not requiring any catalyst or additional free-radical initiator. We find that both PEG and molecular oxygen are prerequisites in order to perform these reactions smoothly. Given that dense CO2 is immune to free-radical chemistry; it is an ideal solvent for such reactions. As a result, compressed CO2 allows reactions initiated by PEG radicals to be tuned by subtly adjusting reaction parameters such as the CO2 pressure, thereby enhancing the product selectivity. By attaining a high selectivity towards the desired products this methodology is practical for organic syntheses.