A density functional theory study on lewis acid‐catalyzed transesterification of β‐oxodithioesters

The detailed mechanisms of the Lewis acid‐catalyzed transesterification of β‐oxodithioesters at a solvent‐free condition were studied using density functional theory. Five possible reaction pathways, including one noncatalyzed (channel 1) and four Lewis acid‐catalyzed channels (SnCl₂‐catalyzed channels 2 and 3 and SnCl₂·2H₂O‐catalyzed channels 4 and 5), were investigated. Our calculated results indicate that the energy barriers of the catalyzed channels are significantly lower than that of channel 1. Channel 5, which has an energy barrier of 33.70 kcal/mol as calculated at the B3LYP/[6‐31G(d, p)+LANL2DZ] level, is the most energy‐favorable channel. Moreover, one water molecule of SnCl₂·2H₂O participated in the transesterification in channel 5. Thus, we report a novel function of the SnCl₂·2H₂O catalyst, which is quite different from the function of the conventional nonhydrated Lewis acid SnCl₂. To understand the function of these two Lewis acid catalysts better, the global reactivity indexes and natural bond orbital charge were analyzed. This work helps in understanding the function of the Lewis acid in transesterification, and it can provide valuable insight for the rational design of new Lewis acid catalysts. © 2014 Wiley Periodicals, Inc.     

NMR Analysis of Hydroxyl-Terminated Polybutadiene End Groups and Reactivity Differences with Monoisocyanates

Nuclear magnetic resonance (NMR) spectroscopy was employed to investigate both the end group microstructure of R-45HTLO hydroxyl-terminated polybutadiene (HTPB) and reactivity rate differences among the different types of end groups. There is some conflict in the literature about the exact nature of the end groups and which resonance frequencies represent the three main types of methylene-hydroxyl end groups (cis, trans, or vinyl) and other possible branch point end groups (geraniol). NMR spectral analysis of small molecule model compounds supports the cis, trans, and vinyl end groups model. A model reaction scheme is proposed that produces branch points without the requirement of any “geraniol” structures. The reaction, with and without catalyst, of the various HTPB end groups with three different monoisocyanates (2-fluorophenyl isocyanate, phenyl isocyanate, and tert-butyl isocyanate) monitored by NMR spectroscopy, revealed different reactivity rates that are correlated with the assigned structures. In both the catalyzed and uncatalyzed reactions, the vinyl end groups reacted slower than the cis or trans end groups. As expected, the bulky isocyanates were the slowest to react, while the isocyanate group with electron withdrawing groups reacted the fastest. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2665–2671     

Kinetics of the Oxidation of Tartrazine with Peroxydisulfate in the Presence and Absence of Catalysts

 The food dye tartrazine is oxidized with peroxydisulfate in the absence and in the presence of Ag(I) and Fe(III) catalysts. In the absence of these metal ions, the reaction shows second-order kinetics, first-order in each of the reacting species. With the Ag(I) ion in the medium the reaction proceeds considerably faster, but still follows second-order kinetics. The reaction rate depends on the concentration of Ag(I) and S₂O₈ ²⁻, but is independent of the concentration of the substrate. When Fe(III) acts as the catalyst, a marked enhancement in the reaction rate is observed, and the reaction proceeds through two parallel pathways, the catalyzed and the noncatalyzed. The catalyzed path follows third order kinetics, being first-order in substrate, oxidant, and catalyst concentration. Mechanisms of the noncatalyzed as well as the Ag(I) and Fe(III) catalyzed reaction systems are proposed.     

Synthesis of poly(glycolic acid) in ionic liquids

The synthesis of poly(glycolic acid) (PGA) by polyesterification of glycolic acid was studied using ionic liquids, mainly 1,3‐dialkylimidazolium salts, as reaction media. The ¹H NMR spectra of PGA oligomers were assigned and end‐group signals were used to follow the reaction. Low PGA yields were obtained by the direct polyesterification of glycolic acid at 200–240 °C, because of monomer evaporation during the reaction. On the other hand, PGAs of DP _n up to 45 were obtained by the postpolycondensation of a preformed oligomer in 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIm⁺Tf₂N^?). The precipitation of PGA in reaction medium at long reaction times limited the achievable molar mass. Rate constants were determined for catalyzed and noncatalyzed reactions, assuming a second‐order reaction mechanism. The efficiency of esterification catalysts such as Zn(OAc)₂ was low in these media, as only about twofold increases in reaction rate were observed. This was assigned to the preferential interaction of Zn²⁺ with ionic liquid anion instead of the polymer carboxylic acid end‐groups. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3025–3035, 2006     

Kinetics of the Oxidation of Tartrazine with Peroxydisulfate in the Presence and Absence of Catalysts

Summary.  The food dye tartrazine is oxidized with peroxydisulfate in the absence and in the presence of Ag(I) and Fe(III) catalysts. In the absence of these metal ions, the reaction shows second-order kinetics, first-order in each of the reacting species. With the Ag(I) ion in the medium the reaction proceeds considerably faster, but still follows second-order kinetics. The reaction rate depends on the concentration of Ag(I) and S₂O₈ ²⁻, but is independent of the concentration of the substrate. When Fe(III) acts as the catalyst, a marked enhancement in the reaction rate is observed, and the reaction proceeds through two parallel pathways, the catalyzed and the noncatalyzed. The catalyzed path follows third order kinetics, being first-order in substrate, oxidant, and catalyst concentration. Mechanisms of the noncatalyzed as well as the Ag(I) and Fe(III) catalyzed reaction systems are proposed. Received June 28, 1999. Accepted (revised) September 27, 1999     

Facile Synthesis of Polyhydroxylated Polybutadiene Derived from Hydroxyl-Terminated Polybutadiene via Thiol-Ene Click Reaction

Polyhydroxylated polybutadiene (PHPB) was synthesized via a thiol-ene click reaction between hydroxyl-terminated polybutadiene (HTPB) and 2-mercaptoethanol (ME) with 2,2’-azoisobutyronitrile (AIBN) as initiator. Effects of AIBN content, reaction time and temperature on the click reaction were investigated by determining hydroxyl value of the PHPB. The PHPB was characterized by FT-IR, ¹H-NMR, ¹³C-NMR and GPC. Relative reactivity of three types of C?C double bonds (1,2-vinyl, 1,4-cis and 1,4-trans units) in the HTPB reacting with the ME was discussed. The results showed that the optimal reaction conditions were that the AIBN content, reaction time and temperature were 2.0 wt%, 180 min and 70°C, respectively. Under these conditions, the hydroxyl value of the PHPB was 3.12 mmol·g^?1 when the HTPB/ME mass ratio was 10:2. All three types of C?C double bonds in the HTPB could react with the ME and the reactivity order was: 1,2-vinyl unit > 1,4-cis unit > 1,4-trans unit.     

Regioselective Radical Aminofluorination of Styrenes

The copper‐catalyzed radical aminofluorination of styrenes with N‐fluorobenzenesulfonimide (NFSI) is realized with high regioselectivity, thus affording aminofluorination products with regioselectivities opposite that of the palladium‐catalyzed and noncatalyzed processes. Preliminary mechanistic studies suggested the reaction went through a radical pathway and was supported by DFT calculations. In these reactions, NFSI is utilized as both a radical nitrogen source and radical fluorine source, thus rendering it an attractive reagent.     

Thermal and pH responsive high molecular weight poly(urethane‐amine) with high urethane content

Aliphatic poly(urethane‐amine) (PUA) was synthesized from copolymerization of CO₂ and 2‐methylaziridine (MAZ) using Y(CCl₃COO)₃‐ZnEt₂‐glycerine coordination catalyst, the urethane content of PUA was over 80%, and its yield could reach 90%. PUA with molecular weight as high as 31.0 kg/mol was obtained when the copolymerization reaction was carried out in N,N‐dimethylacetamide (DMAc), mainly due to the good solubility of PUA in DMAc. PUA exhibited reversible thermo‐responsive property in deionized water, and the lower critical solution temperature (LCST) was highly sensitive to its urethane content and molecular weight, which was observed in a broad window from 37 to 90 °C. Furthermore, the phase transition behavior could also be controlled by change of pH value. When the pH value of the PUA aqueous solution changed from 9.2 to 13, the LCST value of the solution decreased from 48.4 °C to 30 °C. Therefore, the PUA showed thermo‐ and pH‐ dual responsive performance in water. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Theoretical study on the Diels–Alder reaction of cyclopentadiene with methacrolein catalyzed by diethylimidazolium cation

The theoretical studies of how room temperature ionic liquids control desired reactions are very scarce in contrast with their increasing applications in many fields as recyclable solvents, catalysts, and reaction mediums. The present work considers the Diels–Alder (D‐A) reaction of cyclopentadiene with methacrolein in the presence of diethylimidazolium salts as the first prototype of our systemic studies about important organic synthesis reactions catalyzed by room temperature ionic liquids. We show the mechanism details of the D‐A reactions with and without the dialkylimidazolium cation and rationalize the experimental findings based on the results from the quantum chemistry calculations at the AM1, HF/6‐31G(d), and B3PW91/6‐31G(d,p) levels of theory, respectively. It is found that the diethylimidazolium cation acts as a Lewis acid center to catalyze the D‐A reaction, which decreases the barrier and increases the asynchronicity of the D‐A reaction, but does not change the potential energy surface profile of the reaction compared to the noncatalyzed process. The present results rationalize the early experimental findings well and provide the first prototype for theoretically understanding the D‐A reaction in the presence of dialkylimidazolium salts. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Enhanced reactivity and enantioselectivity in catalytic glyoxylate-ene reactions using chiral bis(oxazoline)–copper complex in an ionic liquid

An optimal hydrophobic ionic liquid was discovered as a solvent for highly enantioselective glyoxylate-ene reactions catalyzed by a chiral bis(oxazoline)–copper complex. The reactivity and stereoselectivity were highly dependent upon the property of the ionic liquids; reactions between olefins and ethyl glyoxylate in [Bmim]SbF₆ at ambient temperature provided remarkably enhanced reactivity and stereoselectivity, which greatly exceed those of the corresponding reactions in dichloromethane. Furthermore, the metal–ligand complex was readily recycled up to eight times while exhibiting no significant decrease in reaction efficiency.     

Pd-Enriched-Core/Pt-Enriched-Shell High-Entropy Alloy with Face-Centred Cubic Structure for C1 and C2 Alcohol Oxidation

High-entropy alloy nanoparticles (HEA NPs) have aroused great interest globally with their unique electrochemical, catalytic, and mechanical properties, as well as diverse activity and multielement tunability for multi-step reactions. Herein, a facile low-temperature synthesis method at atmospheric pressure is employed to synthesize Pd-enriched-HEA-core and Pt-enriched-HEA-shell NPs with a single phase of face-centred cubic structure. Interestingly, the lattice of both Pd-enriched-HEA-core and Pt-enriched-HEA-shell enlarge during the formation process of HEA, with tensile strains included in the core and shell of HEA. The as-obtained PdAgSn/PtBi HEA NPs show excellent electrocatalytic activity and durability for methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). The specific (mass) activity of PdAgSn/PtBi HEA NPs for MOR is 4.7 mA cm⁻² (2874 mA mg_(Pd+Pt)⁻¹), about 1.7 (5.9) and 1.5 (4.8) times higher than that of commercial Pd/C and Pt/C catalysts, respectively. Additional to high-entropy effect, Pt sites and Pd sites on the interface of the HEA act synergistically to facilitate the multi-step process towards EOR. This study offers a promising way to find a feasible route for scalable HEA manufacturing with promising applications.     

Ethyl Acrylate‐Hydroxyethyl Acrylate and Hydroxyethyl Acrylate‐Methacrylic Acid: Reactivity Ratio Estimation from Cross‐linked Polymer Using High Resolution Magic Angle Spinning Spectroscopy

Solution free radical copolymerizations of hydroxyethyl acrylate/methacrylic acid (HEA/MAA) and ethyl acrylate/hydroxyethyl acrylate (EA/HEA) have been conducted in m‐xylene (60 wt% solvent level) over the temperature range of 70–130°C using tert‐butyl peroxybenzoate as initiator. High resolution magic angle spinning spectroscopy (HR–MAS) and 2D–NMR have been utilized to characterize the copolymer gel for copolymer composition. The reactivity ratio values have been determined from low conversion copolymer composition data using the computer software package RREVM, which is based on the error in variables model (EVM) method. Also, Arrhenius‐type reactivity ratio expressions have been developed that describe how reactivity ratios vary with temperature.     

Systematic Comparison of HEA and HEMA as Initiators in Enzymatic Ring‐Opening Polymerizations

Two initiators containing a cleavable ester bond were compared in the lipase‐catalyzed ROP of CL and PDL. The results show that transesterification reactions are present at high rates throughout the enzymatic ROP and start at low conversion. HEA and HEMA displayed similar reaction efficiencies as initiators (acyl acceptors) in the enzymatic ROP. However, transacylation reactions on the HEA‐initiated polyesters were found to be 15 times faster. While in both cases the amount of HEA‐ and HEMA‐initiated polymers could be maximized by short reaction times, a well‐defined (meth)acrylation by this approach was not possible. Our results show that transesterification reactions have to be considered when performing an enzyme‐catalyzed ROP.

     

HTPB／TDI,HDI聚合反应动力学研究

对端羟基聚丁二烯／甲苯二异氰酸酯，端羟基聚丁二烯／己二异氰酸酯甲苯溶液体系进行了反应动力学研究，用基团分析方法计算了相应体系的活化能，并对无催化剂和有催化剂的体系作了比较。结果表明，二丁基二月桂酸象对上述体系有强的催化作用，使体系的活化能降低，反应速度加快。对于对端差基聚丁二烯／甲苯二异氰酸酯体系，无催化剂时前后期反应活化能分别为２９．１ｋＪ／ｍｏｌ、３７．４ｋＪ／ｍｏｌ，有催化剂时前后期反应活化     

Probing the steric limits of rhodium catalyzed hydrophosphinylation. P-H addition vs. dimerization/oligomerization/polymerization

The reactivity of secondary phosphine oxides containing bulky organic fragments in hydrophosphinylation reactions has been investigated using several rhodium based catalysts. Upon heating in a focused microwave reactor, HP(O)(2-C₆H₄Me)₂ adds to prototypical terminal alkynes affording a complex mixture containing 1,2 and 1,1-addition products. Addition of a second ortho-substituent (HP(O)Mes₂) completely suppresses the hydrophosphinylation reaction for alkyl and aryl substituted alkynes. Variations in the temperature, catalyst loading, solvent, and microwave power were unable to induce an addition reaction in the case of HP(O)Mes₂. While this secondary phosphine oxide did not participate in the hydrophosphinylation reaction, it promoted the polymerization of phenylacetylene. HP(O)R₂ substrates are not commonly thought of as innocent ligands for rhodium complexes in reactions involving alkynes due to facile hydrophosphinylation. While this is certainly true for diphenylphosphine oxide, the chemistry presented herein suggests that HP(O)Mes₂ and related bulky secondary phosphine oxides have great potential as valuable ligands for rhodium catalyzed transformations involving alkynes due to their lack of reactivity towards the addition reaction.     

Chiral Ditopic Cyclophosphazane (CycloP) Ligands: Synthesis,Coordination Chemistry,and Application in Asymmetric Catalysis

A series of dichlorocyclophosphazanes [{ClP(μ‐NR)}₂] containing chiral and achiral R groups was obtained from simple commercially available amines and PCl₃. Their condensation reactions with axially chiral biaryl diols yielded ansa‐bridged chiral cyclophosphazane (CycloP) ligands. This highly modular methodology allows extensive elaboration of the ligand set, in which the chirality can be introduced at the diol bridge and/or the amido R group. This provides the possibility to observe match and mismatch effects in catalysis. A series of twenty CycloP ligands was synthesized and characterized by multinuclear NMR spectroscopy, HRMS, elemental analysis, and in selected cases, single‐crystal X‐ray diffraction. These studies show that all of the ditopic CycloP ligands are C₂ symmetric, rendering their metal coordination sites symmetry equivalent. Two well‐established enantioselective reactions were explored by using late‐transition metal CycloP complexes as catalysts; the gold‐catalyzed hydroamination of γ‐allenyl sulfonamides and the asymmetric nickel‐catalyzed three‐component coupling of a diene and an aldehyde. The steric demands of the CycloP ligands have a subtle influence on the reactivity and selectivity observed in both reactions. Good enantiomeric ratios (e.r.) as high as 89:11 in the gold‐catalyzed reaction and 92:8 in the nickel‐catalyzed bis‐homoallylation reaction were observed.     

Cross-coupling of alkenyl,aryl or allylic selenides and grignard reagents catalyzed by nickel-phosphine complexes

Alkenyl, aryl or allylic selenides smoothly couple with Grignard reagents in the presence of Ni(II)-phosphine complexes as catalysts to afford the corresponding unsaturated compounds in good yields. The reactivity order of coupling reaction with BuMgBr catalyzed by NiCl₂ [Ph₂PCH₂CH₂CH₂PPh₂] was found to be PhSeMe « PhCl > PhSMe by the competitive reactions.     

Synthesis and characterization of poly(vinyl ferrocene) grafted hydroxyl-terminated poly(butadiene): A propellant binder with a built-in burn-rate catalyst

The graft copolymer hydroxyl-terminated polybutadiene-g-polyvinyl ferrocene (HTPB-g-PVF) was synthesized free radically from HTPB and vinyl ferrocene (VF) in benzene, using azobisisobutyronitrile as the radical initiator at 75°. The graft copolymer was analysed for its structural and thermal characteristics. The chemically bound ferrocene in HTPB-g-PVF, catalysis the oxygen up-take and oxidative degradation reactions of HTPB, and the mechanisms of the catalysis are discussed. The most probable grafting sites on HTPB and the mechanism of grafting also are discussed. The extent of the grafting, which was a function of VF concentration, was low. The graft copolymer also was tried as a propellant-binder-cum-burn-rate (BR) catalyst in a composite solid propellant, using toluene diisocyanate and trimethylol propane as curatives with dibutyl tin dilaurate as the curing catalyst, and the BRs of the propellants were evaluated at 3.9 MPa. The BRs increased with the extent of VF grafting but not proportionally. The BRs also were compared with those of reference HTPB propellants containing VF, Fe₂O₃, copper chromite, and so forth as BR catalysts. Chemically linked ferrocene in the binder augmented the propellant BR, probably because of the presence of catalytically active sites in the binder for its degradation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4090–4099, 1999     

Synthesis of (2-chlorophenyl)(phenyl)methanones and 2-(2-chlorophenyl)-1-phenylethanones by Friedel-Crafts acylation of 2-chlorobenzoic acids and 2-(2-chlorophenyl)acetic acids using microwave heating

Several 2-(2-chlorophenyl)-1-phenylethanones and (2-chlorophenyl)(phenyl)methanones were prepared by the Friedel-Crafts acylation reaction of 2-(2-chlorophenyl) acetic acids and 2-chlorocarboxylic acids, respectively, in the presence of cyanuric chloride, pyridine, and AlCl₃ or FeCl₃ using microwave heating. The yields of the ketones were significantly higher than those obtained using conventional heating. In addition, similar reactions carried out with the less inexpensive and less toxic FeCl₃ gave titled ketones in comparable yields. Interestingly, the FeCl₃ catalyzed reactions gave pure ketones (no chromatographic purification required), whereas the AlCl₃ catalyzed reaction gave impure product that required chromatographic purification.     

Study of the Transient Reactive Pd(IV) Intermediate in the Pd(OAc)2‐Catalyzed Oxidative Coupling Reaction System by Electrospray Ionization Tandem Mass Spectrometry

Pd‐catalyzed oxidative coupling reaction was of great importance in the aromatic C? H activation and the formation of new C? O and C? C bonds. Sanford has pioneered practical, directed C? H activation reactions employing Pd(OAc)₂ as catalyst since 2004. However, until now, the speculated reactive Pd(IV) transient intermediates in these reactions have not been isolated or directly detected from reaction solution. Electrospray ionization tandem mass spectrometry (ESI‐MS/MS) was used to intercept and characterize the reactive Pd(IV) transient intermediates in the solutions of Pd(OAc)₂‐catalyzed oxidative coupling reactions. In this study, the Pd(IV) transient intermediates were detected from the solution of Pd(OAc)₂‐catalyzed oxidative coupling reactions by ESI‐MS and the MS/MS of the intercepted Pd(IV) transient intermediate in reaction system was the same with the synthesized authentic Pd(IV) complex. Our ESI‐MS(/MS) studies confirmed the presence of Pd(IV) reaction transient intermediates. Most interestingly, the MS/MS of Pd(IV) transient intermediates showed the reductive elimination reactivity to Pd(II) complexes with new C? O bond formation into product in gas phase, which was consistent with the proposed reactivity of the Pd(IV) transient intermediates in solution.