The liquid phase hydrogenation of maleic anhydride and intermediates was investigated using copper-based and noble metal catalysts. The experiments were performed in a stirred tank slurry reactor in discontinuous as well as continuous operation. Copper chromites and noble metal catalysts were found to be suitable for the hydrogenation of maleic anhydride. However, the hydrogenation of succinic anhydride proceeded with high selectivity to γ-butyrolactone and 1,4-butanediol on copper zinc catalysts, whereas other copper catalysts revealed no activity in the formation of 1,4-butanediol. Selective sorption interactions of succinic anhydride with the zinc surface were assumed to be responsible for this effect. Starting from γ-butyrolactone all copper catalysts were active in the formation of 1,4-butanediol while noble metal catalysts showed no or little activity. Kinetic models have been proposed for the hydrogenation of maleic anhydride and intermediates on the basis of experimental data obtained in a continuously operated stirred tank slurry reactor.

The liquid phase hydrogenation of maleic anhydride was investigated in a packed bubble column reactor using different copper-based catalysts. A copper-zinc catalyst was found to be active in the formation of 1,4-butanediol, whereas on zinc-free copper catalysts, mainly succinic anhydride and γ-butyrolactone were formed. At suitable reaction conditions, maleic anhydride hydrogenation over a copper-zinc catalyst gave valuable products with high yield and selectivity whereas succinic anhydride was absent in the reactor outlet. Based on a three-phase reactor model and a kinetic model of the reaction mechanism, the influence of reaction conditions on reactor performance was determined. It was observed that the use of large particles and a high axial dispersion of liquid phase is a necessary condition for the feasibility of a "one-step-hydrogenation" of highly concentrated maleic anhydride feed solutions because of a significant decrease of succinic anhydride formation rate.

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Three structurally related crown compounds and cryptands have been synthesized that differ by the number and linkage of coronand units and anthracene moieties. The interaction of the fluorescent dyes with sonicated dimyristoylphosphatidylcholine (DMPC) vesicles is characterized by the relative quantum yields, uptake kinetics, binding curves, lifetimes, fluorescence titrations with water- and lipid-soluble quenching agents, fluorescence anisotropy, and equilibrium cooling curves. The most lipophilic compound II, which displays a similar quantum yield as the parent fluorophore 9,10-dimethylanthracene, shows a nearly equal distribution between solid and fluid lipid and is located at the bilayer surface. The least lipophilic compound IV is excluded from the hydrocarbon phase. The anthracenophane cryptand III preferentially partitions into solid-phase lecithins with the highest affinity for the phases L epsilon and L beta. The binding constant to DMPC amounts to (5.4 +/- 1.3) X 10(2) M-1 at 0 degrees C. From fluorescence quenching titrations it is concluded that the average position of the anthracenoyl dye III discontinuously shifts during the gel to liquid crystalline transition from the glycerol backbone to the choline head group. Electron microscopy and NMR experiments revealed that the anthracenophane induces in the liquid crystalline phase the fusion of small unilamellar DMPC vesicles to unilamellar medium-sized vesicles and macrovesicles, which subsequently fuse at the transition temperature to large multilamellar coacervates. Due to its large change of fluorescence intensity, the anthracenophane cryptand is a very sensitive probe for the detection of the pretransition of symmetrically substituted and of the subtransition of asymmetrically substituted phosphatidylcholines.(ABSTRACT TRUNCATED AT 250 WORDS)

The thermodynamics and kinetics of the subtransition L epsilon----P beta of sonicated unilamellar vesicles of 1-myristoyl-2-stearoylphosphatidylcholine (1M-2S-PC) and of 1-stearoyl-2-myristoylphosphatidylcholine (1S-2M-PC) were studied by equilibrium cooling curves and temperature-jump relaxation spectrometry with an anthracenophane cryptand as a mobile fluorescent probe. The unilamellar vesicles exhibit the midpoint temperature TsII of the subtransition about 10 degrees C below the respective main transition. The kinetics of the subtransition in the time range between 10(-4) and 10(3) s is characterized by a cooperative relaxation process in the range of milliseconds and a further noncooperative process in the range of seconds. The slow process is assigned to the rearrangement of lattice defects. The fast process is evaluated in terms of a cyclic reaction scheme that consists of two pathways for the biomolecular association of probe and vesicle coupled with the conformational change of the lipid matrix during the subtransition. The analysis reveals that the fast process comprises the nucleation and growth of cluster. The cooperative lattice transformation of the subtransition follows a first-order rate law. The rate constants at TsII are 70 s-1 for 1S-2M-PC and 170 s-1 for 1M-2S-PC. Since the plots of the relaxation time vs. the degree of transition are in accordance with the predictions of the linear Ising model, it is concluded that clusters are propagated anisotropically in a linear fashion; e.g., fluidlike P beta conformations grow along the ripple.