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Asymmetric epoxidation of alpha-olefins having neighboring sugar chiral templates and alternating copolymerization with dicarboxylic anhydrides.

Sugar-substituted epoxides 5-8 were synthesized by asymmetric epoxidation (in CH(2)Cl(2)/water) of alpha-olefins having neighboring sugars (1-4) by use of an achiral oxidant (MCPBA), in which the sugar moiety acted as a chiral template. The diastereoselectivities depend on the methylene spacer between vinyl group and carbohydrate derivatives. The methylene spacer between sugar and vinyl groups influenced the diastereoselectvity. In the case of epoxidation of 4 at 27 degrees C for 24 h, the diastereoselectivity was the highest (99/1). Copolymerizations of 5-8 with succinic anhydride were attained at 100 degrees C for 72 h to give poly(ethylene succinate) having pendant carbohydrate [poly(SAn-alt-5), M(n) = 1.4 x 10(3); poly(SAn-alt-6), M(n) = 2.2 x10(3); poly(SAn-alt-7), M(n) = 2.9 x 10(3); poly(SAn-alt-8), M(n) = 1.8 x 10(3)]. The methylene spacer between sugar and epoxide has an effect on the reactivity of epoxide in copolymerization as well as the diastereoselectivity. Alternating copolymerization of 7 and glutaric anhydride gave a polyester of M(n) 4.2 x10(3).

Anhydrides↗
PubMed2004

Secondary organic aerosol formation from the ozonolysis of cycloalkenes and related compounds.

The secondary organic aerosol (SOA) yields from the laboratory chamber ozonolysis of a series of cycloalkenes and related compounds are reported. The aim of this work is to investigate the effect of the structure of the hydrocarbon parent molecule on SOA formation for a homologous set of compounds. Aspects of the compound structures that are varied include the number of carbon atoms present in the cycloalkene ring (C5 to C8), the presence and location of methyl groups, and the presence of an exocyclic or endocyclic double bond. The specific compounds considered here are cyclopentene, cyclohexene, cycloheptene, cyclooctene, 1-methyl-1-cyclopentene, 1-methyl-1-cyclohexene, 1-methyl-1-cycloheptene, 3-methyl-1-cyclohexene, and methylenecyclohexane. The SOA yield is found to be a function of the number of carbons present in the cycloalkene ring, with an increasing number resulting in increased yield. The yield is enhanced by the presence of a methyl group located at a double-bonded site but reduced by the presence of a methyl group at a non-double-bonded site. The presence of an exocyclic double bond also leads to a reduced yield relative to that of the equivalent methylated cycloalkene. On the basis of these observations, the SOA yield for terpinolene relative to the other cyclic alkenes is qualitatively predicted, and this prediction compares well to measurements of the SOA yield from the ozonolysis of terpinolene. This work shows that relative SOA yields from ozonolysis of cyclic alkenes can be qualitatively predicted from properties of the parent hydrocarbons.

Aerosols↗
PubMed2005

Measurements of secondary organic aerosol from oxidation of cycloalkenes, terpenes, and m-xylene using an Aerodyne aerosol mass spectrometer.

The Aerodyne aerosol mass spectrometer (AMS) was used to characterize physical and chemical properties of secondary organic aerosol (SOA) formed during ozonolysis of cycloalkenes and biogenic hydrocarbons and photo-oxidation of m-xylene. Comparison of mass and volume distributions from the AMS and differential mobility analyzers yielded estimates of "effective" density of the SOA in the range of 0.64-1.45 g/cm3, depending on the particular system. Increased contribution of the fragment at m/z 44, C02+ ion fragment of oxygenated organics, and higher "delta" values, based on ion series analysis of the mass spectra, in nucleation experiments of cycloalkenes suggest greater contribution of more oxygenated molecules to the SOA as compared to those formed under seeded experiments. Dominant negative "delta" values of SOA formed during ozonolysis of biogenics indicates the presence of terpene derivative structures or cyclic or unsaturated oxygenated compounds in the SOA. Evidence of acid-catalyzed heterogeneous chemistry, characterized by greater contribution of higher molecular weight fragments to the SOA and corresponding changes in "delta" patterns, is observed in the ozonolysis of alpha-pinene. Mass spectra of SOA formed during photooxidation of m-xylene exhibit features consistent with the presence of furandione compounds and nitro organics. This study demonstrates that mixtures of SOA compounds produced from similar precursors result in broadly similar AMS mass spectra. Thus, fragmentation patterns observed for biogenic versus anthropogenic SOA may be useful in determining the sources of ambient SOA.

Aerosols↗
PubMed1976

Letter: Isosteganacin.

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Antineoplastic Agents, Phytogenic↗