Studies on high chemical reactivity of nano-NaH

A comparison between the initial reaction rates of nanometric and commercial NaH has been studied in four test reactions: 1) hydrogenolysis of chlorobenzene; 2) selective reduction of cinnamaldehyde to cinnamyl alcohol; 3) metallation of dimethyl sulfoxide; and 4) catalytic hydrogenation of olefins. The experimental results indicate that when NaH is used as a chemical reagent in the first three reactions, the initial reaction rates of nano-NaH is 230, 120 and 110 times higher than those of the commercial ones respectively, and it is in agreement with the difference in specific surface areas between these two forms of NaH. When NaH is used as a catalyst component together with Cp₂TiCl₂ in the fourth reaction, catalyst with nano-NaH gives extremely high activity in the hydrogenation of olefins, while the one with commercial NaH gives no activity at all even if a large amount of the commercial NaH is used to make the total surface area equivalent to that of nano-NaH. Thus, it is evident that although large specific surface area is important for nano-NaH to be used as a catalyst component, high surface energy with surface defects seems to be more important. The large specific surface and the activated surface of nano-NaH with high surface energy should be the main factors for their extremely high chemical reactivity, while whether the former or the latter one plays a leading role depends on the type of reactions involved. __________ Translated from Chinese Journal of Applied Chemistry, 2007, 24(1): 21–24 [译自: 应用化学]     

Ethane hydrogenolysis on silica-supported tantalum hydride. Quantum-chemical study

The structures of the (H₄Si₂O₅)O₂Ta(R, RR"R, RR) clusters (R, R", R = H, Me, Et, Pr; R = CH₂), which model the basic structural units of the catalytic cycle of ethane hydrogenolysis on silica-supported tantalum hydride, were studied by the density functional theory (B3LYP) and the perturbation theory (MP2). The possible structure of active sites was proposed based on comparison of experimental results with calculated data. Ethane hydrogenolysis and metathesis proceed by a mechanism involving the formation of ethylene -complexes and carbenium derivatives of tantalum as intermediates.     

Synthesis of a novel graft copolymer with hyperbranched poly(glycerol) as core and “Y”‐shaped polystyrene‐b‐poly(ethylene oxide)2 as side chains

The graft copolymers composed of “Y”‐shaped polystyrene‐b‐poly(ethylene oxide)₂ (PS‐b‐PEO₂) as side chains and hyperbranched poly(glycerol) (HPG) as core were synthesized by a combination of “click” chemistry and atom transfer radical polymerization (ATRP) via “graft from” and “graft onto” strategies. Firstly, macroinitiators HPG‐Br were obtained by esterification of hydroxyl groups on HPG with bromoisobutyryl bromide, and then by “graft from” strategy, graft copolymers HPG‐g‐(PS‐Br) were synthesized by ATRP of St and further HPG‐g‐(PS‐N₃) were prepared by azidation with NaN₃. Then, the precursors (Bz‐PEO)₂‐alkyne with a single alkyne group at the junction point and an inert benzyl group at each end was synthesized by sequentially ring‐opening polymerization (ROP) of EO using 3‐[(1‐ethoxyethyl)‐ethoxyethyl]‐1,2‐propanediol (EEPD) and diphenylmethylpotassium (DPMK) as coinitiator, termination of living polymeric species by benzyl bromide, recovery of protected hydroxyl groups by HCl and modification by propargyl bromide. Finally, the “click” chemistry was conducted between HPG‐g‐(PS‐N₃) and (Bz‐PEO)₂‐alkyne in the presence of N,N,N′,N″,N”‐pentamethyl diethylenetriamine (PMDETA)/CuBr system by “graft onto” strategy, and the graft copolymers were characterized by SEC, ¹H NMR and FTIR in details. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A Useful,Reliable and Safer Protocol for Hydrogenation and the Hydrogenolysis of O‐Benzyl Groups: The In Situ Preparation of an Active Pd0/C Catalyst with Well‐Defined Properties

A simple, highly reproducible protocol for the hydrogenation of alkenes and alkynes and for the hydrogenolysis of O‐benzyl ethers has been developed. The method features the in situ preparation of an active Pd⁰/C catalyst from Pd(OAc)₂ and charcoal, in methanol. The mild reaction conditions (25 °C) and low catalyst loading required (0.025 mol %), as well as the absence of contamination of the product by palladium residues (<4 ppb), make this a sustainable, useful process for organic chemists. Alternatively, the protocol can be carried out under microwave activation, to shorten the reaction times, with cyclohexene as the hydrogen source.     

Minor amounts of glycerol improve the properties of polyisobutylene‐based polyurethane and its nanocomposites

The synthesis of primary hydroxyl‐telechelic polyisobutylene, HOCH₂‐PIB‐CH₂OH, often yields product the number average terminal functionality ( $f_{n,{\mathrm{CH}}_2\mathrm{OH}}$) of which is less than theoretical 2.0, typically $f_{n,{\mathrm{CH}}_2\mathrm{OH}}$ = 1.75–1.95. Polyurethane (PU) prepared with such low‐cost imperfect PIB‐diols, unsurprisingly, exhibit poor overall properties. Herein we report that mechanical, rheological, and thermal properties of polyisobutylene‐based polyurethane (PIB‐PU) and PIB‐PU reinforced with organically modified montmorillonite (OmMMT) prepared with PIB‐diol of $f_{n,{\mathrm{CH}}_2\mathrm{OH}}$ = 1.85 are significantly enhanced by glycerol. Specifically, we document that calculated minor amounts of glycerol substantially improves tensile strength, ultimate elongation, elastic modulus, toughness, rubbery plateau, flow temperature, creep, permanent set, rate of recovery after loading, and thermal properties of PIB‐PU and OmMMT‐reinforced PIB‐PU prepared with PIB‐diol of $f_{n,{\mathrm{CH}}_2\mathrm{OH}}$ = 1.85. The observations are summarized and discussed in terms of chemistry, micromorphology, and viscoelasticity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 929–935     

Glycerol acetylation considering competing dimerization

Glycerol acetylation is a very interesting reaction for studies of consecutive kinetics. In this short communication, we present a pseudo-homogeneous model for the synthesis of triacetyl glycerol from the reaction of glycerol and acetic acid over strongly acidic Amberlyst-15 and Amberlyst-70 catalysts, considering a dimerization of diacetyl glycerol (DAG) into diglycerol tetraacetate as a parallel reaction and compare the results with a model without side reactions. The best fits were obtained for apparent zeroth-order dimerization and first-order consecutive reactions in the presence of acetic acid in excess and with removal of water. An adaptation was made for DAG. The proposed model shows that the formation of DAG is faster than the consumption of glycerol, which could be an explanation for the occurrence of DAG dimerization instead of other parallel reactions in acetylation.     

碱助剂促进Ni基催化剂氢解山梨醇制备二元醇

采用逐步湿浸渍的方法制备了一系列含有不同载体和碱促进剂的Ni基催化剂用于生物质基平台化合物山梨醇的氢解反应. 通过反应对载体和碱促进剂进行了筛选和组分含量的优化,碱性促进剂的引入不仅增强了催化剂的碱性,而且通过Ni²⁺和碱促进剂的强相互作用提高了Ni在催化剂上的分散性;10%Ni/10%La₂O₃/ZrO₂表现出了非常高的氢解活性和较好的二元醇(乙二醇和1,2丙二醇)选择性,金属Ni和碱促进剂La₂O₃之间的协同作用机理对于山梨醇选择性氢解制备二元醇影响显著. 在优化的反应条件下,山梨醇达到100%的转化并且有超过48%的二元醇产率. 研究中对催化剂进行了XRD、BET、H₂-TPR和CO₂-TPD表征,用于分析催化剂结构性能. 通过对山梨醇氢解以及中间产物动力学曲线的研究,得出多元醇氢解活性与所含羟基数正相关,产物的最终分布是氢解动力学平衡的最终结果.