The direct oxidation of propylene to give propylene oxide is still one of the holy grails of the bulk chemicals industry.  The predominant process for making propylene oxide is via the oxidation of ethylbenzene to give ethylbenzene hydroperoxide, which oxidises propylene and generates styrene as a co-product.  More recently direct oxidation with hydrogen peroxide over a titanium silicalite (TS-1) has been investigated but the reaction only works well in the presence of methanol as co-solvent, which unfortunately is responsible for many of the by-products formed (methyl formate, acetone, acrolein, acrylic acid and propylene oxide ring-opening products).  Now a report from Beckman et al reveals that much improved selectivity can be realised if carbon dioxide is used as solvent, selectivities up to 94% are possible at moderate conversion levels (6-10%), with the only detectable by-product being propane. The conditions used have the added advantage of generating hydrogen peroxide in situ by passing hydrogen and oxygen over a Pd/TS-1 catalyst. (Angew. Chem. Int. Ed. , 2003, 42(10), 1140-1142).