One-pot synthesis of phenylacetaldehyde from styrene via metal oxide catalysed oxidation in presence of cumene hydroperoxide

Phenylacetaldehyde (PhA) is an aromatic aldehyde which has a hyacinth-like floral, sweet and green-leafy odour. PhA is used as a perfumery chemical and a rate-controlling additive in cosmeceutical and polymer industries, respectively. The conventional process of PhA manufacturing in industries involve hazardous and costly feedstock and often lead to generation of substantial amount of waste. Moreover, usage of stoichiometric reagents often makes the processes economically impractical. This article illustrates the possibility of production of PhA from low-cost feedstock styrene through a single-step, one-pot method wherein various metal oxides have been utilized as catalysts for styrene oxidation under the influence of cumene hydroperoxide (CHP). Ag₂O is found to be the highest PhA-yielding catalyst and a promising candidate for scaling up for its considerably good reusability up to 6 consecutive uses. A maximum of ~45% PhA selectivity has been observed at ~60% styrene conversion. Interestingly, this process does not require any alkaline/acid wash and hence does not produce any organic/inorganic liquid effluent stream. Furthermore, all the major byproducts found, that is styrene oxide, benzaldehyde and acetophenone, are themselves considered as valorized styrene derivatives. Overall, the metal oxide catalysed styrene oxidation has potential to take over the conventional industrial process(es) for sustainable selective production of PhA Along with a plausible mechanism of styrene oxidation over Ag₂O, a conceptualized reaction–separation framework has been reported for intensified production of PhA from CHP-based styrene oxidation.