尿素中亚甲基二脲含量测定--萘二磺酸二钠盐分光光度法的研究和应用

尿素溶液中加入甲醛，可用于大颗粒尿素的生产，同时可提高成品颗粒强度，降低粉尘，这是目前尿素企业生产控制的一种措施，甲醛在尿素成品中转化为亚甲基二脲。本文研究了用萘二磺酸二钠盐分光光度法测定尿素中亚甲基二脲含量的测试条件，并通过精密度、回收率以及对检测样品的各实验室比对试验，表明了该方法是准确、可行的。本方法已作为新的方法标准列入尿素国家标准之中。     

大颗粒尿素中亚甲基二脲分析方法的探讨

采用斯纳姆变色酸比色分析法测定大颗粒尿素中甲醛量折算为亚甲基二脲的含量。实验证明，其测定值低于真实值0.05%～0.07%，给工艺计算甲醛消耗物料平衡带来相对误差-7.3%～-15.0%。实验用蒸馏比色分析法能准确测定大颗粒尿素中亚甲基二脲的含量，可以对工艺计算甲醛物料消耗起到科学的评价作用。     

对二甲氨基苯甲醛法测定缓释包膜尿素中氮含量的方法

用对二甲氨基苯甲醛分光光度法分别测定了缓释包膜尿素、25℃恒温浸提液中的尿素态氮含量。开展了入射光波长、显色剂溶液配制、显色时间、溶液酸性条件、显色剂溶液用量等几个方面的研究。给出了最佳分析试验条件及测定缓释包膜尿素样品时去除干扰的方法。方法精密度高、回收率好。在计算氮养分含量时,应增加缩二脲态氮和亚甲基二脲态氮的含量,作为总氮的一部分。采用计算法测定缓释包膜尿素及25℃恒温浸提液中的总氮含量,比蒸馏后滴定法及凯氏定氮法更加简单、快速。     

六甲基二硅脲的合成与应用

介绍了以三甲基氯硅烷、氨及尿素为原料合成六甲基二硅脲的方法,以及六甲基二硅脲在药物合成中的应用。     

尿素改性热塑性酚醛树脂的合成及应用

先用尿素、甲醛合成二羟甲脲，然后在酸性介质下把二羟甲脲滴加在苯酚中反应合成尿素改性的热塑性酚醛树脂。研究了反应浑浊点和二羟甲脲的滴加速度，同时研究了二羟甲脲与苯酚的尿酚比与物料的出料温度、产品产率及树脂理化性能指标的关系。结果表明：（1）二羟甲脲滴加速度的合适范围是0．012－0．029mol/mol.min；（2）本树脂的出料温度为125℃以下；（3）产品收率，游离酚，软化点随尿比的增长而递增，凝胶速度变化不大。另介绍了这种树脂在酚醛模塑料中的应用。     

对二甲氨基苯甲醛比色法测定溶液中的尿素

运用分光光度法对对二甲氨基苯甲醛和尿素在酸性条件下生成的黄棕色化合物进行测定,确定测定的最佳波长后,通过单因素实验确定了影响测定的主要因素,并以尿素用量、对二甲氯基苯甲醛用量、反应温度和浓硫酸用量等为考察因素设计正交实验以优化测定条件.结果表明：尿素的最佳测定波长为426 nm;最佳测定条件为：200 mg·L-1尿素溶液用量14 mL、对二甲氨基苯甲醛用量10 mL、反应温度30℃、浓硫酸用量0.4 mL.尿素浓度在100～800 mg·L-1范围内与吸光度呈现良好的线性关系,线性回归方程为A=0.0006c＋0.0168,相关系数R=0.9996.该方法操作方便、快速、准确度高、重现性好,能够用于溶液中尿素浓度的测定.     

对二甲氨基苯甲醛法测定常量尿素

通过正确选择波长、显色条件,使对二甲氨基苯甲醛比色法能准确测定溶液中的常量尿素含量。该方法比硫酸加热消化后的甲醛滴定法,操作简便快捷,检出限低,线性范围宽、精密度好、标样回收率在９８％以上,是测定溶液中常量尿素的良好方法。     

六甲基二硅脲的合成与应用

介绍了以三甲基氯硅烷、氨及尿素为原料合成六甲基二硅脲的方法，以及六甲基二硅脲在药合物成中的应用．     

对二甲氨基苯甲醛比色法测定尿素水解系统中的微量尿素

通过正确选择波长和显色条件,用二对甲氨基甲醛比色法准确测定尿素水解系统中的微量尿素,方法检出限为０．７μｇ／ｍｌ,线性范围为０～５０μｇ／ｍｌ,测定２μｇ／ｍｌ尿素样品的变异系数为４．５％。此法检出限较低,线性范围宽,精密度好,操作简便。     

新型脲醛预缩液的产品性能及市场展望

脲醛预缩液（UFC）是由高浓度甲醛与尿素在一定条件下反应生成的一种多组份、低分子量的混合物液体。UFC的主要化学成分经测定为二羟甲脲、三羟甲脲和在脲醛树脂合成条件下根本不可能生成的四羟甲脲等的混合物。由于合成条件的不同，其中的各组分的相对含量也是不确定的，为区别因甲醛、尿素含量不同而产生的不同型号脲醛预缩液，分别在UFC代码的后面加缀－60、－62、－85等不同的百分含量，以区别不同型号。表1列出了几种已知型号的脲醛预缩液所含的甲醛、尿素的重量百分比。     

Kinetics and mechanism of urea-formaldehyde reaction

The various initial reactions in the urea-formaldehyde reaction have been isolated and the course of the reaction investigated using a quantitative thin-layer chromatographic technique developed for the purpose. The rate constants for the formation of monomethylol urea pass through a minimum in the pH range 4.5–8, thereby proving catalysis by H⁺ and OH^?. Whereas the reaction under alkaline conditions leads to methylol formation, acidic conditions favour formation of methylene bridges. It was found that the higher homologues were formed through the methylolation of methylene urea followed by its condensation with free urea and not by the reaction of methylene urea with methylol urea.     

Synthesis–structure–performance relationship of cocondensed phenol–urea–formaldehyde resins by MALDI‐ToF and 13C NMR

Matrix assisted laser desorption ionization time of flight (MALDI‐ToF) mass spectrometry has consistently confirmed on a number of PUF resins that phenol–urea cocondensates exist in phenol–urea–formaldehyde (PUF) resins. A noticeable proportion of methylene‐linked phenol to urea cocondensates were detected in all the PUF resins tried, alongside methylene bridges connecting phenol to phenol and urea to urea. The PUF, PF, and UF oligomers formed were identified. Variations of the PUF preparation procedure did always yield a certain proportion of the mixed phenol to urea cocondensates. Their relative proportion was determined and related the synthesis procedure used. Comparison of the MALDI‐ToF results with a ¹³C NMR investigation showed that in a real PUF resin in which phenol to urea cocondensates were identified the methylene bridge NMR signal at 44 ppm, characteristic of phenol to urea unsubstituted model compound cocondensates, does not appear at all. This confirmed that this peak cannot be taken as an indication of the existence of phenol and urea condensation under actual resin preparation conditions. The peak indicating cocondensation in PUF resins in which the phenolic nuclei and urea are substituted appears instead at 54.7–55.0 ppm. Thermomechanical analysis has again confirmed that the resin gel times greatly accelerates with increasing urea molar content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

摩尔比对脲醛树脂初期产物结构影响的研究

使用高分辨＾１３Ｃ核磁共振仪研究碱性环境下摩尔比对脲醛树脂初期产物结构的影响。结果表明尿素与甲醛摩尔比对初期产物结构有很大影响，即使在摩尔比为０．８的初期产物中，仍观测到大量的三羟甲基脲或交联的羟甲基和亚甲基包括交联的亚甲基存在，而此时尚有大量的游离尿素存在。     

Analyse par résonance magnétique nucléaire des polycondensats urée–formol

The oligomer reaction products between urea and formaldehyde were preliminarily studied by 60-MHz NMR spectroscopy. This analytical method was extended to urea–formaldehyde copolymers and provided means to attempt to determine their molecular stucture. Prior to NMR analysis, dilution water was removed by freeze drying in order to avoid degradation and advancement of the resin. Lithium chloride was found to enhance polycondensate solubility in deuterated dimethylsulfoxide and to improve resolution of the spectra by reducing overlapping of the signals. It was then possible to proceed to a qualitative and quantitative analysis of urea–formaldehyde copolymer structure. Structural differences appeared between one-step synthesized resins and those involving a second urea addition; in the latter case, the percentage of unreacted urea was calculated. The shape of the unresolved broad signal assigned to the various methylene groups yielded further information on the resins. A particular shoulder on the methylene signal gives evidence for polyoxymethylene sequences occurring in polycondensates synthesized from concentrated aqueous formaldehyde solutions.     

Examination of selected synthesis parameters for typical wood adhesive‐type urea–formaldehyde resins by 13C‐NMR spectroscopy. II

A particleboard adhesive‐type urea–formaldehyde (UF) resin was made at a formaldehyde ratio of 2.10 and added with a second urea at low temperature to the typical final formaldehyde/urea ratio of 1.15. Time samples taken during heat treatments of the resin sample up to 70°C over a period of 250 min showed decreases in Type II/IIi hydroxymethyl group content, accompanied with decreases in resin sample viscosity and increases in formaldehyde emission of bonded particleboards. The results indicate that various hydroxymethyl groups of polymeric UF resin components migrate to the second urea to form Type I hydroxymethyl groups. Time samples taken during the room‐temperature storage of the resin sample over a period of 1 month behaved similarly initially, but in the later stage, some polymerization progressed, shown by increases in viscosity and methylene and methylene–ether group contents. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1243–1254, 2000     

NMR studies of urea–formaldehyde resins

A procedure used for analyzing urea–formaldehyde resins by NMR spectroscopy was developed. Using this procedure, the condensation of dimethylolurea under acidic and alkaline conditions was sudied. It was confirmed that polymerization under acidic conditions proceeds via the formation of methylene linkages and under alkaline conditions, via the formation of dimethylene ether groups. The more highly condensed water-soluble urea resins were found to contain hemiformal groups, which could be quantitatively determined. Two butylated urea–formaldehyde resins with varying degrees of butylation were also studied and were found to differ in the number of methylene and dimethylene ether groups and degree of butoxylation. Both were found to contain hemiformal groups. The resin with lower degree of butylation was also found to contain dimethyl ether linkages. None of the resins studied showed any detectable amounts of fully substituted amide groups.     

大型化肥厂尿素粉尘监测方法的分析与实践

针对国内目前尚无尿素粉尘标准监测方法（国标）可依与尿素生产过程中尿素粉尘排放必需监测的矛盾，本文作者循尿素粉尘排放的成因、轨迹及其危害，对比分析现存方法的特点，并结合我厂监测的实践，对尿素粉尘科学、经济的监测方法进行了分析。     

Comparative 13C‐NMR and matrix‐assisted laser desorption/ionization time‐of‐flight analyses of species variation and structure maintenance during melamine–urea–formaldehyde resin preparation

The preparation of an industrially used sequential formulation of a melamine–urea–formaldehyde resin was followed by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry and ¹³C‐NMR analysis. The analysis allowed us to identify and follow the appearance, increase, decrease, and disappearance of a multitude of chemical species during the preparation of both the initial urea–formaldehyde (UF) phase of the reaction and the subsequent reaction of melamine with the UF resin that formed. The analysis indicated that (1) the increase and decrease in the species that formed proceeded through a cycle of the formation and degradation of species occurring continuously through what appeared to be a series of complex equilibria, (2) even at the end of the reaction a predominant proportion of methylene ether bridges was still present, (3) some small proportion of methylene bridges already had formed in the UF reaction phase of the resin even under rather alkaline conditions, and (4) the addition of melamine to the UF prepolymer induced some noticeable rearrangement of methylene ether bridges to methylene bridges. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

固体消毒剂过氧化氢脲的合成研究

以尿素与过氧化氢为原料合成过氧化氢脲，对其合成方法进行了筛选。按美国药典（ⅩⅩⅡ）的质量标准进行全面检验，结果均达到要求。