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1.
The esterification reaction of n-butanol with acetic acid ([BuOH] : [HOAc] = 1 : 15 mol/mol; 55°C, 5% H2O) was studied in the presence of tungsten heteropoly acids of the Keggin (H3PW12O40, H4SiW12O40, H5PW11TiO40, H5PW11ZrO40, and H3PW11ThO39) and Dawson structure (-H6P2W18O62, H6P2W21O71(H2O)3, H6As2W21O69(H2O), and H21B3W39O132). The reaction orders with respect to H6P2W21O71(H2O)3, H3PW12O40, and H6P2W18O69are equal to 0.78, 1.00, and 0.97, respectively. It was found that the reaction rate depends on the acidity, as well as on the structure and composition of heteropoly acids. The H21B3W39O132heteropoly acid is most active, whereas the Keggin-structure heteropoly acids exhibit the lowest activities. Of the Keggin structure heteropoly acids, H5PW11ZrO40exhibits the highest activity because of the presence of a Lewis acid site in its structure.  相似文献   

2.
稀土杂多酸性质及催化作用的研究   总被引:3,自引:1,他引:3  
稀土硅钨酸钾盐,R.D.Peacok等早已于1971年合成过,但对其性质报导甚少,尚未见应用。我们用自制的稀土杂多酸,测定了热稳定性、红外吸收谱及X射线衍射谱;探索了在催化中的应用,发现在甲醇转化为低级烃类的反应中,稀土硅钨酸有良好的催化活性,并展现出三峰的规律性。  相似文献   

3.
杂多酸的固载化研究(II)   总被引:10,自引:1,他引:10  
研究了以多种方法化学改性的不同活性炭表面化学特性及十二硅钨酸(SiW_(12))在相应表面的吸附. 首次提出,不同原料来源和改性的活性炭对SiW_(12)的吸附有不同的等温线形式和吸附力. 活性炭表面的羰基有利于SiW_(12)的吸附,而表面的羧基则是不利的.  相似文献   

4.
烟碱-磷钼杂多酸缔合微粒体系的光谱研究及分析应用   总被引:1,自引:0,他引:1  
采用分光光度法和共振散射光谱法研究了小烟碱一磷钼杂多酸缔合微粒体系.在波长300~800nm范围内,波长愈短缔合微粒体系的吸光度值愈大,在400nm处的吸光度与烟碱浓度在0.50-50.0μg/mL范围成良好线性关系,检出限(3σ)为0.1μg/mL.据此建立了一个测定烟草中烟碱含量的分光光度法.该法灵敏、简便、快速、准确、重复性好,平均回收率为99%~103%,相对标准偏差RSD为0.9%~1.3%.共振散射光谱研究结果表明,该体系存在烟碱-磷钼杂多酸缔合微粒,该微粒在420nm处存在共振散射效应.  相似文献   

5.
固载杂多酸催化性能的研究   总被引:10,自引:0,他引:10  
在气相体系中考察了固载于活性炭 (C)上的磷钨 (PW12 )、硅钨 (SiW12 )及磷钼 (PMo12 )杂多酸对异丙醇脱水反应的催化性能 .不加水时主要生成丙烯 ;加入适量的水有助于降低丙烯而提高异丙醚的选择性 ;催化活性除与酸性有关外 ,与杂多酸的特殊结构“假液相”模型密切相关  相似文献   

6.
The reactions of phenol coupling with ketones MeCOR (R = CH3, C2H5, C3H7, and C4H9) are studied in the presence of heteropoly acids with different structures and compositions in toluene solutions ([PhOH]/[MeCOR] = (2–8)/1 mol/mol; 50–70°C) with thioglycolic acid added as a promoter. The reaction rate depends on ketone and heteropoly acid, and the yield of bisphenols is as high as 24–72%. The reaction orders are 0.68, 0.77, and 0.97 with respect to H6P2W21O71, H3PW12O40, and H4SiW12O40, respectively, and the activation energies are 25.1, 21.0, and 20.6 kcal/mol, respectively. Heteropoly acids of the Dawson structure exhibited the highest activity.  相似文献   

7.
三元杂多酸荧光猝灭测定食品中硼砂的研究   总被引:3,自引:0,他引:3  
研究发现,硼钼杂多酸能与罗丹明B形成缔合物,导致罗丹明B的荧光发生静态猝灭,以此建立了荧光猝灭测定痕量硼砂的新方法.在选定的实验条件下,当λex/λem=540/582 nm,硼砂浓度在2.4~108μg/L范围内时,荧光猝灭强度与硼砂含量呈良好线性关系(r=0.9982),检出限为1.42μg/L,加标回收率在91.3%~101%之间,相对标准偏差(RSD)<3.76%.该方法用于食品中痕量硼砂的测定,结果满意.  相似文献   

8.
苯氧乙酸;酸离解常数;键电荷密度;量子化学计算;苯氧乙酸类化合物的酸离解常数测定及其量子化学计算  相似文献   

9.
 Upon aging, perborate in glacial acetic acid generates peracetic acid and thus oxidizes S-phenylmercaptoacetic acid rapidly. Perborate dissolved in ethylene glycol, however, does not show the aging effect, and the corresponding oxidation proceeds smoothly. The oxidation is of second order and not acid catalyzed. Boric acid and borate do not influence the oxidation. In the smooth oxidation, is the reactive species. The oxidation of some para-substituted S-phenylmercaptoacetic acids conforms to the Exner relationship, indicating operation of a common mechanism. Also, the oxidation obeys the Hammett equation with a negative reaction constant. However, the oxidation of p-nitro-S-phenylmercaptoacetic acid follows a different kinetic pathway.  相似文献   

10.
Summary.  Upon aging, perborate in glacial acetic acid generates peracetic acid and thus oxidizes S-phenylmercaptoacetic acid rapidly. Perborate dissolved in ethylene glycol, however, does not show the aging effect, and the corresponding oxidation proceeds smoothly. The oxidation is of second order and not acid catalyzed. Boric acid and borate do not influence the oxidation. In the smooth oxidation, is the reactive species. The oxidation of some para-substituted S-phenylmercaptoacetic acids conforms to the Exner relationship, indicating operation of a common mechanism. Also, the oxidation obeys the Hammett equation with a negative reaction constant. However, the oxidation of p-nitro-S-phenylmercaptoacetic acid follows a different kinetic pathway. Received March 15, 2000. Accepted (revised) May 3, 2000  相似文献   

11.
Selective formation of pharmaceutical intermediates like diphenylmethane, dimethyl- diphenylmethane, benzyl toluene and benzoic acid by liquid phase, toluene benzylation with benzyl chloride as a benzylating agent, was systematically studied over plane clay (K-10, montmorillonite), plane H-Beta, plane MFI structured titanosilicate (TS-1) and heteropoly acids [HPA, namely dodeca-tungstophosphoric acid [H3PO4.12WO3.xH2O] (TPA), dodeca-molybdo phosphoric acid ammonium salt hydrate [H12Mo12N3O40P aq] (DMAA), sodium tungstate hydrated purified [Na12WO4.2H2O] (STH)] supported on clay, H-beta and TS-1. The 20%TPA/Clay, 30%TPA/H-Beta and 30%TPA/TS-l, were observed to be the best catalyst samples over plane clay, plane H-Beta and plane TS-1. The catalyst samples are compared with respect to benzyl chloride conversion and selectivities for diphenylmethane, dimethyl-diphenylmethane, benzyl toluene and benzoic acid. The reaction follows the pseudo-first order rate power law model. The apparent rate constants are calculated and compared with the reported ones.  相似文献   

12.
13.
磷钨酸催化合成丙烯酸丁酯   总被引:5,自引:0,他引:5  
用磷钨酸为催化剂 ,由丙烯酸和丁醇直接酯化合成了丙烯酸丁酯。研究了醇 /酸比、酯化时间、催化剂用量、带水剂用量对酯化率的影响 ;选择了最佳反应条件 ,重复反应酯化率达到 95 %以上。  相似文献   

14.
醋酸胶片的片基材料醋酸纤维素酯水解产生的"醋酸综合症"是影像部门保存醋酸胶片过程中遇到的最大技术难题之一,目前还没有较好的治理方法,其在降解过程中释放出的醋酸严重影响胶片的耐久性,关于其物理性能变化及相关性的研究较少.本文通过模拟密闭环境中醋酸浓度的累积实验,系统地分析了醋酸在胶片降解过程中对胶片物理性能的影响.实验结果表明,醋酸环境会加速胶片的降解,且随着醋酸浓度的增加,胶片扭曲变形程度增加,胶片的降解程度(酸度)增加;抗张强度减弱,但耐折度增加;含湿量和胶片乳剂层面的亲水性增加,同时胶片的热稳定性变差.  相似文献   

15.
A facile access to trimethylsilyl acetic acid is described. The method involves the preparation of the corresponding trimethylsilyl ester in fairly good yield (70%).  相似文献   

16.
杂多酸催化剂及其在精细化学品合成中的应用   总被引:25,自引:1,他引:25  
详细介绍了环境友好的杂多化合物的结构、性能、制备、表征及其在精细化学品合成中的应用最新进展,并对负载型杂多酸和新颖的混合型杂多酸及其盐催化剂的合成及应用进行综述.认为杂多化合物的深入研究具有十分重要的理论价值和现实意义.杂多酸及盐作为绿色催化剂在精细化学品合成中具有广阔的应用前景.  相似文献   

17.
18.
碱性染料—铌钼杂多酸缔合物体系的比较研究   总被引:1,自引:0,他引:1  
  相似文献   

19.
Dynamic protonation equilibria in water of one 4‐methylimidazole molecule as well as for pairs and groups consisting of 4‐methylimidazole, acetic acid and bridging water molecules are studied using Q‐HOP molecular dynamics simulation. We find a qualitatively different protonation behavior of 4‐methylimidazole compared to that of acetic acid. On one hand, deprotonated, neutral 4‐methylimidazole cannot as easily attract a freely diffusing extra proton from solution. Once the proton is bound, however, it remains tightly bound on a time scale of tens of nanoseconds. In a linear chain composed of acetic acid, a separating water molecule and 4‐methylimidazole, an excess proton is equally shared between 4‐methylimidazole and water. When a water molecule is linearly placed between two acetic acid molecules, the excess proton is always found on the central water. On the other hand, an excess proton in a 4‐methylimidazole‐water‐4‐methylimidazole chain is always localized on one of the two 4‐methylimidazoles. These findings are of interest to the discussion of proton transfer along chains of amino acids and water molecules in biomolecules.  相似文献   

20.
Kinetics and Catalysis - Changes in the values of specific conductance χ of the solutions of high-vanadium Mо?V?Р heteropoly acids (HPA-х) in redox processes are...  相似文献   

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