Thermoregulated poly(ethylene glycol) biphasic system with Pd nanoparticle catalysts for selective hydrogenation of cinnamaldehyde

Poly(ethylene glycol) (PEG)-stabilized Pd nanoparticles were prepared by simple hydrogen reduction of PdNa₂Cl₄·xH₂O in the presence of PEG₄₀₀₀ (PEG with an average molecular mass of 4000 g/mol). These were shown to be efficient and recyclable catalysts for the selective hydrogenation of cinnamaldehyde in a thermoregulated PEG biphasic system, which allows for an efficient homogeneous catalytic reaction, easy biphasic separation and catalyst reuse. Under optimized reaction conditions, the conversion of cinnamaldehyde and the selectivity of hydrocinnamaldehyde (HCAL) were 99% and 98%, respectively. The PEG₄₀₀₀-stabilized Pd nanoparticle catalyst could be easily separated from the product by phase separation and reused eight times without evident loss of activity and selectivity.