以醇为循环剂尿素法合成碳酸二苯酯过程探讨

碳酸二苯酯是合成聚碳酸酯的重要原料,具有广泛的用途和应用前景。本文综述了不同醇类的尿素醇解反应以及不同碳酸二烷酯与苯酚的酯交换反应,结合以醇为循环剂由尿素法合成碳酸二苯酯的研究现状,对该过程进行分析探讨。分析表明,长碳链脂肪醇是适合该反应的循环剂,并展望了其今后的发展方向。     

尿素醇解法合成碳酸二甲酯的研究进展

综述了尿素醇解法合成碳酸二甲酯的工艺研究中有关反应的热力学及相应的催化剂研究进展,归纳了工艺研究中所采用的实验装置的主要类型。分析了该工艺研究目前存在的主要问题,提出了设计融熔尿素醇解工艺和采用氨基钠作为催化剂的构想。     

改性羟基磷灰石催化尿素醇解合成碳酸丙烯酯

<正>碳酸丙烯酯(PC)是性能优良的有机溶剂和有机合成原料。PC的合成方法包括环氧丙烷环加成法、光气法和尿素醇解法,其中以尿素和1,2-丙二醇为原料的尿素醇解法,因环境友好、反应条件温和、操作安全,还能有效避免环氧丙烷环加成法对石油的依赖和光气法的剧毒,被认为是PC合成的绿色工艺。     

三级胺及酰胺硝解研究进展

综述了三级叔胺及酰胺硝解的近期研究进展，重点是已作为或有可能成为高能量密度化合物硝胺的合成。讨论了三级胺及酰胺的硝解历程，汇集了常用的硝化及硝解系统。详细阐述了烷基叔胺、叔酰胺、烷基酰基叔胺。特别是多环笼形叔胺和叔酰胺的硝解反应及硝解条件。     

四丁基二锡氧烷催化合成碳酸二酯类化合物的新方法

 以四丁基二锡氧烷为催化剂，通过尿素的醇解反应，合成了四种\r\n高沸点碳酸二酯化合物．研究结果表明，尿素的第一步醇解反应较易进\r\n行，产物收率大于60％；第二步从氨基甲酸酯醇解变为碳酸二酯的反应\r\n较难进行．尿素醇解反应与所用的醇有密切的关系，其中尿素与苯甲醇\r\n醇解为碳酸二酯的反应最易进行，正己醇次之，而正辛醇反应最难进行\r\n．提高反应温度到195℃，以官能团为NCS的四丁基二锡氧烷代替官能团\r\n为Cl的四丁基二锡氧烷为催化剂时，适当提高醇的配比，尿素与正辛醇\r\n醇解为碳酸二酯的产物收率有较大的提高．提出了尿素醇解反应的可能\r\n机理．     

尿素催化醇解合成长碳链脂肪族碳酸二酯

氧化锌;尿素催化醇解合成长碳链脂肪族碳酸二酯     

生物质转化合成新能源化学品乙酰丙酸酯

生物质是唯一可替代化石资源获取液态燃料和化学品的可再生资源,近年来由生物质转化合成乙酰丙酸酯引起了研究者们越来越广泛的关注。乙酰丙酸酯是一类重要的化学中间体和新能源化学品,具有高的反应特性和广泛的工业应用价值。目前开发的从生物质资源出发转化合成乙酰丙酸酯的潜在合成途径可概括为4种:直接酸催化醇解法、经乙酰丙酸酯化、经5-氯甲基糠醛醇解和经糠醇醇解。本文分别介绍了这4种转化合成途径的化学反应过程及最新研究进展,从反应合成工艺、催化体系、经济可行性等方面评述了各自的特点与发展趋势,并分析了目前工业规模转化生物质合成乙酰丙酸酯仍面临的一些科学难点。最后,对今后该领域的研究前景进行了展望。     

生物基甘油氢解合成1,3-丙二醇催化剂的研究进展

1,3-丙二醇（1,3-PDO）作为聚酯单体原料有广阔的市场空间,在化妆品和医药等领域也被广泛应用.由生物基甘油选择氢解一步法合成1,3-PDO工艺被认为是一条绿色环保和高经济性的技术路线.我们在这里主要介绍了甘油氢解制备1,3-PDO催化剂的研究进展,对催化剂类型、催化剂的合成方法和工艺条件进行了归类总结;分析了多种催化剂体系的甘油氢解反应机理,指出了该反应工业化过程中存在的一些问题,并展望了今后的研究发展方向.     

PRELIMINARY EXAMINATION OF THE CONCURRENT SYNTHESIS OF METHANOL IN SLURRY PHASE

本文报道了ｌ升浆液搅拌釜内一体化甲醇合成反应过程中涉及的甲醇连续羰基化、甲酸甲酯氢解和低温甲醇合成反应的初步考察结果。     

基于响应面法的螺旋藻多肽制备工艺的研究

应用响应面分析法优化木瓜蛋白酶酶解制备螺旋藻多肽的工艺条件。根据中心组合试验设计的原理,在单因素试验的基础上,以多肽得率为响应值,利用响应面法对影响螺旋藻蛋白酶解反应的各种影响因素如温度、pH、酶解时间和加酶量进行了系统研究,得到最佳工艺条件为:反应温度55℃、pH值7、酶底比1.6%、酶解2 h,制得多肽含量得率可达20.61%,与模型预测的肽含量21.25%较接近。     

Synthesis and characterization of photolabile o-nitrobenzyl derivatives of urea

We present here the synthesis and characterization of four photolabile derivatives of urea in which alpha-substituted 2-nitrobenzyl groups are covalently attached to the urea nitrogen. These derivatives photolyze readily in aqueous solution to release free urea. The alpha-substituents of the 2-nitrobenzyl group strongly influence the rate of the photolysis reaction measured with transient absorption spectroscopy. Rates of photolysis at pH 7.5 and room temperature (approximately 22 degrees C) for N-(2-nitrobenzyl)urea, N-(alpha-methyl-2-nitrobenzyl)urea, N-(alpha-carboxymethyl-2-nitrobenzyl)urea, and N-(alpha-carboxy-2-nitrobenzyl)urea are, respectively, 1.7 x 10(4), 8.5 x 10(4), 4.0 x 10(4), and 1.1 x 10(5) s(-)(1). The quantum yields determined by measurement of free urea following irradiation by a single laser pulse at 308 nm were 0.81 for N-(2-nitrobenzyl)urea, 0.64 for N-(alpha-methyl-2-nitrobenzyl)urea, and 0.56 for N-(alpha-carboxy-2-nitrobenzyl)urea. The caged N-(alpha-carboxy-2-nitrobenzyl)urea is not a substrate of the enzyme urease, while the photolytically released urea is. Also, neither this caged urea nor its photolytic side products inhibit hydrolysis of free urea by urease. Thus, the alpha-carboxy-2-nitrobenzyl derivative of urea is suitable for mechanistic investigations of the enzyme urease.     

Liquid chromatographic determination of urea in water-soluble urea-formaldehyde fertilizer products and in aqueous urea solutions: collaborative study

Water soluble urea-formaldehyde (UF) fertilizers, manufactured by complex reaction of urea and formaldehyde, typically contain varying amounts of unreacted urea. A liquid chromatography method for the analysis of urea in these products, and in aqueous urea solutions, was collaboratively studied. An amine chromatography column was used to separate the unreacted urea from numerous UF reaction products present in these liquid fertilizers. Unreacted urea was determined by using external urea standards with UV detection at 195 nm. The standards and test samples were prepared in the mobile phase of 85% (v/v) acetonitrile in water. Ten laboratories analyzed 5 different UF-based commercial products containing unreacted urea in the range of 6 to 17% by weight, and 5 different concentrations of urea in water equivalent to commercial products of that nature. The aqueous urea solutions contained 2-20% urea (w/w). The range of s(R) values for the 5 UF-based commercial fertilizers was 0.49-1.02 and the %RSD(R) was 1.94-6.14. The s(R) range for the 5 urea solutions was 0.10 to 0.79 and the %RSD(R) range was 2.54 to 4.88. The average recovery of urea from the aqueous urea solutions was 96-103%. Therefore, this method is capable of monitoring urea nitrogen manufacturers' label claims and total nitrogen claims in those cases where urea is the sole source of plant food nitrogen. Based on the collaborative study data, the authors recommend this method be approved for AOAC Official First Action status.     

The dissolution of microcrystalline cellulose in sodium hydroxide-urea aqueous solutions

It has been reported that cellulose is better dissolved in NaOH-water when a certain amount of urea is added. In order to understand the mechanisms of this dissolution and the interactions between the components, the binary phase diagram of urea/water, the ternary urea/NaOH/water phase diagram and the influence of the addition of microcrystalline cellulose in urea/NaOH/water solutions were studied by DSC. Urea/water solutions have a simple eutectic behaviour with a eutectic compound formed by pure urea and ice (one urea per eight water moles), melting at −12.5 °C. In the urea/NaOH/water solutions, urea and NaOH do not interact, each forming their own eutectic mixtures, (NaOH + 5H₂O, 4H₂O) and (urea, 8H₂O), as found in their binary mixtures. When the amount of water is too low to form the two eutectic mixtures, NaOH is attracting water at the expense of urea. In the presence of microcrystalline cellulose, the interactions between cellulose and NaOH/water are exactly the same as without urea, and urea is not interacting with cellulose. A tentative explanation of the role of urea is to bind water, making cellulose-NaOH links more stable. Member of the European Polysaccharide Network of Excellence (EPNOE),     

Evaporation of urea at atmospheric pressure

Aqueous urea solution is widely used as reducing agent in the selective catalytic reduction of NO(x) (SCR). Because reports of urea vapor at atmospheric pressure are rare, gaseous urea is usually neglected in computational models used for designing SCR systems. In this study, urea evaporation was investigated under flow reactor conditions, and a Fourier transform infrared (FTIR) spectrum of gaseous urea was recorded at atmospheric pressure for the first time. The spectrum was compared to literature data under vacuum conditions and with theoretical spectra of monomolecular and dimeric urea in the gas phase calculated with the density functional theory (DFT) method. Comparison of the spectra indicates that urea vapor is in the monomolecular form at atmospheric pressure. The measured vapor pressure of urea agrees with the thermodynamic data obtained under vacuum reported in the literature. Our results indicate that considering gaseous urea will improve the computational modeling of urea SCR systems.     

How does the urea dynamics differ from water dynamics inside the reverse micelle?

In this study, the urea dynamics inside AOT reverse micelle (RM) has been monitored without intervention of water using time-resolved fluorescence techniques from the picosecond to nanosecond time regime. It has been observed that urea dynamics inside the reverse micelle is severely retarded compared to water RM due to the formation of highly networked urea cluster inside the RM. Time-resolved fluorescence anisotropy study also confirms the existence of a confined environment around the dye at higher concentrations of urea inside the reverse micelle. The dynamics of urea-water mixtures inside AOT reverse micelle has also been monitored with increasing urea concentration to get insight about the effect of urea on the overall solvation dynamics feature. It has been observed that with the increase in urea concentration, the overall dynamics becomes slower, and it infers the presence of few water or urea molecules, those strongly associated with surrounding urea and (or) water by hydrogen bonds.     

Does Urea Preferentially Interact with Amide Moieties or Nonpolar Sidechains? A Question Answered Through a Judicious Selection of Model Systems

The transfer model suggests that urea unfolds proteins mainly by increasing the solubility of the amide backbone, probably through urea-induced increase in hydrogen bonding. Other studies suggest that urea addition increases the magnitude of solvent-solute van der Waals interactions, which increases the solubility of nonpolar sidechains. More recent analyses hypothesize that urea has a similar effect in increasing the solubility of backbone and sidechain groups. In this work, we compare the effects of urea addition on the solvation of amides and alkyl groups. At first, we study the effects of urea addition upon solvent hydrogen bonding acidity and basicity through the perturbation in the fluorescence spectrum of probes 1-AN and 1-DMAN. Our results demonstrate that the solvent's hydrogen bonding properties are minimally affected by urea addition. Subsequently, we show that urea addition does not perturb the intra-molecular hydrogen bonding in salicylic acid significantly. Finally, we investigate how urea preferentially interacts with amide and alkyl groups moieties in water by comparing the effects of urea addition upon the solubility of acetaminophen and 4-tertbutylphenol. We show that urea affects amide and t-butyl solubility (lowers the transfer free energy of both amide (backbone) and alkyl (sidechain) groups) in a similar fashion. In other words, preferential interaction of urea with both moieties contributes to protein denaturation.     

Rapid dissolution of cellulose in LiOH/urea and NaOH/urea aqueous solutions

Rapid dissolution of cellulose in LiOH/urea and NaOH/urea aqueous solutions was studied systematically. The dissolution behavior and solubility of cellulose were evaluated by using (13)C NMR, optical microscopy, wide-angle X-ray diffraction (WAXD), FT-IR spectroscopy, DSC, and viscometry. The experiment results revealed that cellulose having viscosity-average molecular weight ((overline) M eta) of 11.4 x 104 and 37.2 x 104 could be dissolved, respectively, in 7% NaOH/12% urea and 4.2% LiOH/12% urea aqueous solutions pre-cooled to -10 degrees C within 2 min, whereas all of them could not be dissolved in KOH/urea aqueous solution. The dissolution power of the solvent systems was in the order of LiOH/urea > NaOH/urea > KOH/urea aqueous solution. The results from DSC and (13)C NMR indicated that LiOH/urea and NaOH/urea aqueous solutions as non-derivatizing solvents broke the intra- and inter-molecular hydrogen bonding of cellulose and prevented the approach toward each other of the cellulose molecules, leading to the good dispersion of cellulose to form an actual solution.     

Cocondensation of urea with methylolphenols in acidic conditions

The reactions of urea with methylolphenols under acidic conditions were investigated using 2- and 4-hydroxybenzyl alcohol and crude 2,4,6-trimethylophenol as model compounds. The reaction products were analyzed with ¹³C-NMR spectroscopy and GPC. From the reaction of urea with 4-hydroxybenzyl alcohol, the formations of 4-hydroxybenzylurea, N,N′-bis (4-hydroxybenzyl) urea, and tris(4-hydroxybenzyl) urea were confirmed and the formations of N,N-bis(4-hydroxybenzyl) urea and tetrakis (4-hydroxybenzyl) urea were suggested. From the reaction of urea and 2-hydroxybenzyl alcohol, 2-hydroxybenzylurea and N,N′-bis(2-hydroxybenzyl) urea were identified. Further, the alternative copolymer of urea and phenol could be synthesized by the reaction of urea with 2,4,6-trimethylophenol. It was also found that the cocondensation between p-methylol group and urea prevails against the self-condensation of the methylolphenol even at the low pH below 3.0, and that p-methylol group has the stronger reactivity to urea than o-methylol group. © 1992 John Wiley & Sons, Inc.     

Aqueous urea solutions: structure, energetics, and urea aggregation

Urea is ubiquitously used as a protein denaturant. To study the structure and energetics of aqueous urea solutions, we have carried out molecular dynamics simulations for a wide range of urea concentrations and temperatures. The hydrogen bonds between urea and water were found to be significantly weaker than those between water molecules, which drives urea self-aggregation due to the hydrophobic effect. From the reduction of the water exposed urea surface area, urea was found to exhibit an aggregation degree of ca. 20% at concentrations commonly used for protein denaturation. Structurally, three distinct urea pair conformations were identified and their populations were analyzed by translational and orientational pair distribution functions. Furthermore, urea was found to strengthen water structure in terms of hydrogen bond energies and population of solvation shells. Our findings are consistent with a direct interaction between urea and the protein as the main driving force for protein denaturation. As an additional, more indirect effect, urea was found to enhance water structure, which would suggest a weakening of the hydrophobic effect.     

Effect of urea on self-organization of sodium N-(11-acrylamidoundecanoyl)-l-valinate in water

In this paper, the hypotheses proposed for the action of urea on the perturbation of molecular assemblies have been tested through studies of the effects of urea on the aggregation properties of a chiral surfactant, sodium N-(11-acrylamidoundecanoyl)-L-valinate in water. Surface tension, fluorescence, and circular dichroism were used to characterize the solution behavior of the amphiphile in the presence of urea. Surface tension measurement indicated decrease of critical aggregation concentration (cac) with the addition of urea in the low concentration range. Fluorescence probe studies using pyrene and 1-anilinonaphthalene indicated solubilization of urea molecules near the aggregate-water interface. Fluorescence anisotropy measurements using 1,6-diphenylhexatriene as probe molecule suggested increase of packing of the hydrocarbon chains of the amphiphiles upon addition of low concentration of urea. Dynamic light scattering measurements showed an increase of the hydrodynamic radius (R(h)) in the presence of increased concentration of urea. At higher concentrations of urea, the R(h) value decreased. Circular dichroism spectra showed the presence of chiral aggregates even in the presence of high concentration of urea.