Catalysis and high pressure – a useful liaison?!

The influence of high pressure (1–10 kbar) in solution on transition metal and in particular on palladium catalyzed reactions is examined both under the aspect of reactivity as well as selectivity. Although the field of research described here is rather young, some general conclusion on the scope and limitation of high pressure for catalysis can be drawn. This revised version was published online in June 2006 with corrections to the Cover Date.     

维生素B6的合成工艺改进

＂噁唑法＂是目前工业上合成维生素B6的通用方法,本文对其关键步骤—芳构化进行改进,以2-正丙基-4,7-二氢-1,3-二氧七环、4-甲基-5-乙氧基噁唑为原料,经Diels-Alder、芳构化和水解三步反应制得维生素B6,总收率达81.6%。该工艺操作简单、能耗低,缩短了生产周期,适于工业化应用。     

Alder ene functionalization of polyisobutene oligomer and styrene-butadiene-styrene triblock copolymer

The Alder ene functionalization reaction of double bonds containing macromolecules such as polyisobutene oligomer (PIB) and a styrene-butadiene-styrene triblock copolymer (SBS) samples with maleic anhydride (MAH) or diethyl maleate (DEM) as enophiles is described. The analysis of the products by means of different techniques assesses the addition of the polar molecules to the reactive vinylidene units of the polymer with functional degrees (FD) depending on the type of enophile and polymer reactivity. The role of the reaction conditions and the use as Lewis acids as catalysts are discussed in terms of their influence on the addition reaction extent and on the polymer molecular weight.     

Self-healing semi-IPN materials from epoxy resin by solvent-free furan–maleimide Diels–Alder polymerization

Novel self-healing Diels–Alder (DA) polymer and the corresponding semi-interpenetrated polymer networks (semi-IPNs) were synthesized and characterized. Initially, a furan-functionalized resin (FFR) was synthesized through the ring-opening reaction of a conventional epoxy resin [diglycidyl ether bisphenol A (DGEBA)] with furfuryl alcohol as a bio-based compound. Subsequently, semi-IPNs with different compositions were obtained through the blending of DGEBA, FFR, 4,4′-diaminodiphenylmethane, and 1,1′-(methylenedi-1,4-phenylene) bismaleimide in the molten state by following a predetermined time–temperature program. Fourier transform infrared and nuclear magnetic resonance analyses confirmed the successful synthesis of the materials. Thermoreversibility via retro-DA (rDA) reaction was evidenced by differential scanning calorimetry (DSC) and sol–gel transition tests. Repeated DSC cycle was successfully performed thrice on the DA polyadduct which corroborated repeatability of the DA/rDA association/dissociation. Self-healing and mechanical properties were preliminarily evaluated by scanning electronic microscopy and flexural testing analyses, respectively. The self-healing efficiencies were around 80 and 95% for semi-IPN and DA polyadduct, respectively, based on flexural strength. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48015.     

Speculations on the molecular structure of eumelanin

Eumelanin is the polymeric black pigment commonly found in hair and skin. Its chemical intractability, to all but vigorous oxidizing agents, has hindered satisfactory understanding of its molecular structure. It is well‐established that the immediate precursor to polymerization, indole‐5,6‐quinone (IQ), is biosynthesized from the amino acid tyrosine. Current views are that the polymer consists of single bond connections between random indole and degraded indole units. In this paper, an alternative chemical scheme for the polymerization of IQ is proposed based upon the original suggestion by Horner in 1949 that a Diels‐Alder (D–A) reaction might be involved. The proposed basic chemical scheme for eumelanin formation is that D–A addition occurs specifically between the 2‐ and 3‐positions of one IQ molecule and the 7‐ and 4‐ positions respectively of a second IQ molecule, that the ensuing diketo bridge is oxidized to carboxyl groups and that, by decarboxylation and aromatization, a fused indole dimer is produced. It is envisaged that, by further D–A addition of more IQ molecules, oligomers of greater molecular mass are produced. Calculations based on published bond lengths and angles for the indole nucleus show that oligomeric units containing a total of up to 11 fused indoles could be packed into a flat circular disc of 20 Å diameter. The discs of the extensively conjugated polymer are envisaged to be stacked above each other by π–π interaction and with a spacing of 3.4 Å to produce cylindrical units, the mass density of which is calculated to be 1.54 gm cm^?3; approximating with actual physical measurements. The size and shape of the predicted cylinders are in concordance with those observed in atomic force microscope investigations of eumelanin proto‐particles. The model is also in agreement with published experimental data that 2/3rds of the carbon dioxide liberated during eumelanin formation derives from positions 5‐ and 6‐ of the IQ molecule.     

乙烯催化二聚制丁烯－1技术进展

乙烯催化二聚制丁－１技术是当今聚烯烃工业中具有重要意义的工业过程。介绍了４种竞争发展的新工艺及催化剂研究的进展，并对各新工艺的经济性进行了评价。     

Reactions of free chlorine with substituted anilines in aqueous solution and on granular activated carbon

Aqueous HOCl reacted with substituted anilines to form chlorinated derivatives. Some debromination and bromination products were also detected from two brominated anilines. When granular activated carbon was present, many additional products were formed. These compounds fall into several different groups: (1) N-acylation products, (2) N-carbomethoxylation products, (3) N=N dimerization products and (4) deamination and hydroxylation products.