The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Bingfeng Shi - One of the best experts on this subject based on the ideXlab platform.
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catalyst controlled amino versus oxy acetoxylation of urea tethered alkenes efficient synthesis of cyclic Ureas and isoUreas
ChemInform, 2015Co-Authors: Weihao Rao, Xuesong Yin, Bingfeng ShiAbstract:The regioselectivity of the acetoxycyclization of N-allylUreas to furnish either imidazoles or oxazoles is controlled by choice of the transition-metal catalyst.
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catalyst controlled amino versus oxy acetoxylation of urea tethered alkenes efficient synthesis of cyclic Ureas and isoUreas
Organic Letters, 2015Co-Authors: Weihao Rao, Xuesong Yin, Bingfeng ShiAbstract:A catalyst-controlled vicinal amino- versus oxy-acetoxylation of alkenes with PhI(OAc)2 as the oxidant is described. The divergent synthesis of cyclic Ureas and isoUreas was achieved in good yields under mild conditions employing ambident urea nucleophiles. Both terminal and internal alkenes are compatible with this reaction protocol.
José Miguel Martín-martínez - One of the best experts on this subject based on the ideXlab platform.
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Structural characterization of polyurethane Ureas and waterborne polyurethane urea dispersions made with mixtures of polyester polyol and polycarbonate diol
Progress in Organic Coatings, 2017Co-Authors: Mónica Fuensanta, José Antonio Jofre-reche, Francisco Rodríguez-llansola, Víctor Costa, José Ignacio Iglesias, José Miguel Martín-martínezAbstract:Abstract Waterborne polyurethane urea dispersions (WPUUs) intended for coatings and adhesives were synthesized with mixtures of polyester polyol (PE) and polycarbonate diol (PCD) for combining the advantages of the polyurethane Ureas made with pure polyols. WPUUs made with mixtures of polyols had higher mean particle size and lower viscosity than the ones made with one polyol only. Two types of hard segments totally separated (i.e. −(IPDI-DMPA/TEA-IPDI)- and −(IPDI-HZ-IPDI)-) and two types of soft segments (i.e. −(IPDI-PCD-IPDI)- and −(IPDI-PE-IPDI)-) were produced in polyurethane Ureas made with PE + PCD mixtures. The segmented structure and phase separation of the polyurethane Ureas made with PE + PCD mixtures differed depending on their PCD content, affecting the thermal, rheological and crystallinity properties. The adhesion of chlorinated vulcanized styrene-butadiene rubber/WPUU/roughened leather joints made with WPUUs prepared with PE + PCD mixtures was very similar to the ones made with PCD and PE only. After ageing in water at 70 °C for 1-2 days, the adhesive strength of joints made with WPUUs containing more than 50 wt% PCD is excellent. The properties of the polyurethane Ureas made with mixtures of polyols containing 50 wt% or more PCD were determined by lower degree of phase separation and interactions between hard and soft domains via carbonate groups.
Weihao Rao - One of the best experts on this subject based on the ideXlab platform.
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catalyst controlled amino versus oxy acetoxylation of urea tethered alkenes efficient synthesis of cyclic Ureas and isoUreas
ChemInform, 2015Co-Authors: Weihao Rao, Xuesong Yin, Bingfeng ShiAbstract:The regioselectivity of the acetoxycyclization of N-allylUreas to furnish either imidazoles or oxazoles is controlled by choice of the transition-metal catalyst.
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catalyst controlled amino versus oxy acetoxylation of urea tethered alkenes efficient synthesis of cyclic Ureas and isoUreas
Organic Letters, 2015Co-Authors: Weihao Rao, Xuesong Yin, Bingfeng ShiAbstract:A catalyst-controlled vicinal amino- versus oxy-acetoxylation of alkenes with PhI(OAc)2 as the oxidant is described. The divergent synthesis of cyclic Ureas and isoUreas was achieved in good yields under mild conditions employing ambident urea nucleophiles. Both terminal and internal alkenes are compatible with this reaction protocol.
Kang Ni - One of the best experts on this subject based on the ideXlab platform.
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ammonia volatilization after application of urea to winter wheat over 3 years affected by novel Urease and nitrification inhibitors
Agriculture Ecosystems & Environment, 2014Co-Authors: Kang Ni, Andreas Pacholski, Henning KageAbstract:Ammonia emission from urea application negatively affects both environmental quality and human health, and so it is desirable to minimize nitrogen loss by ammonia volatilization and to improve nitrogen use efficiency. This field study aimed to assess the effects of recently introduced Urease (N-(2-nitrophenyl) phosphoric triamide, 2-NPT) and nitrification inhibitors (mixture of dicyandiamide and 1H-1,2,4-triazol) on NH3 emissions following urea application as compared to calcium ammonium nitrate (CAN) in Northern Germany. The measurements were carried out in winter wheat (Triticum aestivum) in the years 2011–2013 covering in total 12 urea application dates. Urea was applied as unamended granulated urea, or combined with Urease or nitrification inhibitor or with both inhibitors. Fertilizers were applied in multi-plot field trials with four replications and ammonia losses were measured simultaneously by a combination of a calibrated dynamic chamber and passive samplers. Application date strongly affected relative NH3 loss (% of applied N) due to seasonal variation of soil moisture, temperature, and rainfall. Initial soil moisture showed a strong effect on NH3 emission. Averaged over the three vegetation periods, relative NH3 losses from unamended urea amounted to 8%, with mean emissions of 5%, 4%, and 17% for split N applications in March, April, and early June, respectively. Compared with treatment without Urease inhibitor, the Urease inhibitor addition reduced emissions by 26–83%, resulting in emissions similar to that from CAN. Analyzing the total data set, no significant effect of the nitrification inhibitor on NH3 emission was observed while at specific applications significantly higher as well as lower emissions compared to unamended urea were detected. The results highlight that NH3 emissions after field application of urea are highly variable under north German climate conditions and simple emission factors should be reevaluated. Urease inhibitor and appropriate application timing are effective measures to reduce NH3 emission from field applied urea.
Stanisław Głab - One of the best experts on this subject based on the ideXlab platform.
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Urea sensors based on glass pH electrodes with physically immobilized Urease
Analytica Chimica Acta, 1992Co-Authors: Robert Koncki, Piotr Leszcyński, Adam Hulanicki, Stanisław GłabAbstract:Abstract Different gels were used as a matrix for physical enzyme immobilization on the sensing surface o glass pH electrodes. The recommended technique of immobilization is based on enzyme entrapment within a gel prepared in situ on the glass electrode surface. Poly(vinyl chloride), cellulose trinitrate and especially cellulose triacetate are the best matrix materials of Urease immobilization. The effect of buffer pH and buffer capacity and the effect of the stirring rate were investigated and the optimum measurement conditions are discussed.
