15,144 research outputs found
Mechanistic investigations of bipyrimidine-promoted palladium-catalyzed allylic acetoxylation of olefins
Several pyridine-like ligands were found to improve Pd(OAc)2-catalyzed allylic oxidation of allylbenzene to cinnamyl acetate by p-benzoquinone in acetic acid. The best ligand examined, bipyrimidine, was used to identify the catalyst precursor for this system, (bipyrimidine)Pd(OAc)2, which was fully characterized. Mechanistic studies suggest the reaction takes place through disproportionation of (bipyrimidine)Pd(OAc)2 to form a bipyrimidine-bridged dimer, which reacts with olefin to form a Pd^II-olefin adduct, followed by allylic CâH activation to produce (η^3-allyl)Pd^II species. The (η^3-allyl)Pd^II intermediate undergoes a reversible acetate attack to generate a Pd^0-(allyl acetate) adduct, which subsequently reacts with p-benzoquinone to release allyl acetate and regenerate (bipyrimidine)Pd(OAc)2. No KIE is observed for the competition experiment between allylbenzene-d0 and allylbenzene-d5 (CD2=CDCD2C6H5), suggesting that allylic CâH activation is not rate-determining. Catalytic allylic acetoxylations of other terminal olefins as well as cyclohexene were also effected by (bipyrimidine)Pd(OAc)2
Net profitability of airline alliances, an empirical study
This study examines the net return for airlines before and after joining an
alliance. The research database was compiled from ICAOData, and comprised 15
international airlines as subjects and their net financial results for a period of 11 years as
primary research variables. Two variables, the averages of five and three years net
performance before joining an alliance, were tested against another variable, the average
net performance five years after joining the alliance. Results show a deterioration of net
profits after joining an alliance, although this trend was only significant when comparing
performance over the short-term. However, the performance of American airlines
accounted for most of this trend, which may have being partly affected by the consequences
of September 11 2001
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