Bio-based crotonic acid from polyhydroxybutyrate: synthesis and photocatalyzed hydroacylation

Abstract

A novel thermolytic distillation process was developed to depolymerize polyhydroxybutyrate (PHB) for the selective production of crotonic acid. The conditions adopted (170 °C, 150 mbar) were applied to pure PHB and PHB-enriched bacteria containing 60 and 30% of PHB, giving a recovery of crotonic acid of 92, 78 and 58%, respectively. The high efficiency of the developed process poses the basis for a drop-in production of bio-based crotonic acid, whose versatility as a platform chemical has been investigated through a photochemical approach. The photocatalytic addition (promoted by tetrabutylammonium decatungstate – TBADT) of aliphatic and aromatic aldehydes to crotonic acid took place under solar-simulated light irradiation. TBADT triggered the in situ formation of valuable acyl radicals from the corresponding aldehydes, thus inducing the desired hydroacylation via radical conjugate addition. Notably, the functionalization took place in a satisfactory yield quite independently of the adopted sample of crotonic acid (whether commercial or bio-based).