Catalysis of Organic..

450Propylene Oxidation to POTable 1. Control experimentsRun Reaction condition H 2 O 2 /H 2 O Base(mmoles)Productsdetected1 21°C for 24 h 0.36 ml Pyridine (1.48) None2 40°C for 48 h 0.36 ml None None3 40°C for 12 h None Pyridine N-oxide (1.43) NoneSome consideration was given to appropriate bases for this oxidation system.Pyridine and sodium bicarbonate had been shown to be useful earlier 8 and wereincluded. Additional bases considered were a proton sponge (1,8-Bis(dimethylamino)naphthalene) and, as stated above, pyridine N-oxide. Because ofthe low solubilities in CXL systems of NaHCO 3 and the proton-sponge, pyridine wasselected for these exploratory studies.Propylene oxidation was carried out in the absence of catalysts, but in thepresence of the base pyridine, at 40-70°C for 3, 6, and 12 hr time periods. Theresults are summarized in Table 2. The control experiments were designed toinclude H 2 O 2 and a proper base because earlier studies 4, 8 had shown that both arerequired for the oxidation of other olefins, specifically cyclohexene. Water is onlyslightly soluble in supercritical carbon dioxide, and propylene is miscible withCO 2 . 10 However, the addition of propylene in the system will not enhance thesolubility of water or H 2 O 2 . At 40°C, the yield of propylene oxide was about 7%with pyridine in 6 hrs. The PO yield was decreased and trace amounts of propyleneglycol and unknown products were produced at 60 and 70°C. As expected, the POyield was increased by longer reaction times. When the amount of propylene wasdecreased by about half, the PO yield was also reduced by roughly the same fraction.From these results, we concluded that a single phase reaction has been achieved andthat the single phase reaction does enhance the yield of PO as well as the selectivityof this CXL system. This and related systems are subject to on-going studies.Table 2. Propylene oxidation at various temperaturesRxn. time(Hrs)Rxn. Temp.(°C)Solvent H 2 O 2(mmoles)Pyridine(mmoles)3 40 CO 2 /AN 10.41 1.49 < 36 40 CO 2 /AN 10.41 1.49 7.076 60 CO 2 /AN 10.41 1.49 1.666 80 CO 2 /AN 10.41 1.49 1.7312 40 CO 2 /AN 10.41 1.49 10.7Yield of PO(%)