Temperature‐dependent kinetics for the ozonolysis of selected chlorinated alkenes in the gas phase

The ozonolysis of olefinic species is an important tropospheric process impacting on climate and human health. However, few studies have investigated these reactions as a function of temperature and even less information is available upon the effects of alkene heteroatomic substitution on the Arrhenius parameters. The electron‐withdrawing capacity of substituents about the olefinic bond strongly influences the rate of alkene ozonolysis. To understand better the effect of these substitutions, the temperature‐dependence of a series of ozone–chloroalkene reactions is investigated. Experiments were conducted in the EXTreme RAnge (EXTRA) chamber, over the range of 292–409 K and 760 Torr. The experimentally determined rate coefficients were fitted using an Arrhenius‐type analysis to yield the following activation energies: 30.80 ± 0.79, 23.18 ± 0.59, 65.2 ± 2.8, 116.9 ± 5.6, 29.5 ± 1.8, and 18.67 ± 0.96 kJ mol^?1 and preexponential A‐factors 1.22^+0.39_?0.29×10^?15, 9.3^+6.7_?5.4×10^?16, 1.6^+2.5_?1.0×10^?10, 6⁺²²_?3.9×10^?4, 1.7^+1.6_?0.8×10^?14, and 4.2^+1.9_?1.3×10^?15 cm³ molecule^?1 s^?1 for cis‐1,2‐dichloroethene, trans‐1,2‐dichloroethene, trichloroethene, tetrachloroethene, 2‐chloropropene, and 3‐chloro‐1‐butene, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 120–129, 2011     

[1,2]-Wittig Rearrangement of Acetals III [1]. New 1,2-Alkoxyalcohols, 1,2-Alkoxyaminesand 1,2-Dialkoxy Compounds as Chiral Ligands for Organomagnesium and Organolithium Compounds and forLithium Aluminum Hydride

Summary.  Eight O-substituted 1,2-diols and one O,N-substituted 1,2-aminoalcohol derived from 2-alkoxyoctahydro-7,8,8-trimethyl-4,7-methanobenzofurans via a [1,2]-Witting rearrangement and subsequent substitution were synthesized and tested as additives for the enantioselective addition of butyllithium and butylmagnesium chloride to benzaldehyde and for the reduction of acetophenone with lithium aluminum hydride. The selectivity of the reactions was determined by GC of the obtained 1-phenyl-1-pentanol and 1-phenylethanol on a chiral phase. Best results with regard to selectivity (52% ee and 94% ee, resp.) were achieved in the formation of 1-phenyl-1-pentanol by addition of the substituted 1,2-aminoalcohol to the organometallic reagent and in the reduction of acetophenone using an α-alkoxyalcohol (62%ee). Received March 10, 2000. Accepted March 23, 2000     

Synthesis of Regiospecific Chlorine-37 Labeled Trichlorodibenzofuran

2,3,4-Trichlorodibenzofuran was synthesized by converting 3-aminodibenzofuran to 3-amino-2,4-dichlorodibenzofuran using chlorine-saturated carbon tetrachloride, followed by diazotization of the amino group and displacement of the nitrogen by treatment with cuprous chloride. This method was used for the regiospecific synthesis of 2,3(³⁷Cl),4-trichlorodibenzofuran. NOE experiments were conducted to determine the final product.     

Multifunctional,Defect‐Engineered Metal–Organic Frameworks with Ruthenium Centers: Sorption and Catalytic Properties

A mixed‐linker solid‐solution approach was employed to modify the metal sites and introduce structural defects into the mixed‐valence Ru^II/III structural analogue of the well‐known MOF family [M₃^II,II(btc)₂] (M=Cu, Mo, Cr, Ni, Zn; btc=benzene‐1,3,5‐tricarboxylate), with partly missing carboxylate ligators at the Ru₂ paddle‐wheels. Incorporation of pyridine‐3,5‐dicarboxylate (pydc), which is the same size as btc but carries lower charge, as a second, defective linker has led to the mixed‐linker isoreticular derivatives of Ru‐MOF, which display characteristics unlike those of the defect‐free framework. Along with the creation of additional coordinatively unsaturated sites, the incorporation of pydc induces the partial reduction of ruthenium. Accordingly, the modified Ru sites are responsible for the activity of the “defective” variants in the dissociative chemisorption of CO₂, the enhanced performance in CO sorption, the formation of hydride species, and the catalytic hydrogenation of olefins.     

Radiation-induced changes in physical properties of bulk polyethylene. I. Effect of crystallization conditions

Melt crystallized polyethylenes with different crystallization histories were irradiated with γ-rays and examined for various properties. These include solubility (gel content), melting and recrystallization behavior, load extension behavior, and creep properties. Even for the same dose, very significant differences were observed for the different sample types. Although such differences have been reported previously, the present work reveals that these differences can be unusually large and that they are displayed by a range of different tests with a consistent correlation between them. The underlying trend is that in poorly crystallized samples the radiation is much more effective in forming networks than in samples of highly developed crystallinity. This finding may merely indicate that cross-linking is more abundant in the amorphous region than in the crystallites; nevertheless, analogy with single crystals suggests that in addition details of the fold surface morphology and the nature of the lamellar contact may also have a part to play. Among other properties, the elasticity of cross-linked melt was analyzed and found to be consistent with simple rubber elasticity theory, leading to an estimate of both the number of effective cross-links and of intrinsic entanglements acting as cross-links. The most conspicuous effects were observed in the creep behavior where different sample types irradiated to the same dose could behave as viscous liquids and true rubbers according to crystallization history. The relevance of such findings for the technological irradiation of polyethylene should be self-evident, particularly as the doses involved were those commonly employed in industrial applications.