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xuqinyao8239铁杆木虫 (著名写手)
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40金币求翻译一段话
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In monitoring a reaction it is important to know the reaction “kinetics.”When developing a process, “kinetics” refers to the rate of formation of the product and the amount of time needed to reach the desired process endpoint. The goals of knowing reaction kinetics are to complete processing efficiently and to limit degradation from overreaction. Periodic in-process monitoring generates the relevant kinetic data. Changing a parameter can have more than one effect on a process. For instance, pH is a critical factor in Schotten-Baumann reactions .Acid chlorides are readily hydrolyzed under strongly acidic or strongly basic conditions, so neutral conditions would minimize hydrolysis. Most primary and secondary amines exhibit pKas of 10–11.5, so that maximal reactivity would be found at high pH and poor reactivity would be expected under neutral conditions, where the amines would be predominantly protonated. Schotten-Baumann reactions are conducted under weakly basic conditions, pH 8–10, by balancing the hydrolysis of the acid chloride with the decreased reactivity of the amine. In many cases it is wise to examine changes to a process instead of rejecting such conditions on a theoretical bias. While optimizing a process the chemist usually learns its tolerance limits, the ranges of process parameters at which a process will operate successfully. Knowing these ranges is very helpful for guiding scale-up operations under suboptimal conditions, such as overcharging or undercharging components and exposing the reaction to temperatures above the optimal ranges. |
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syh9288
捐助贵宾 (著名写手)
海军上将
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2楼2010-01-11 15:19:53
syh9288
捐助贵宾 (著名写手)
海军上将
- 翻译EPI: 6
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- 金币: 1608.6
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| 例如，在Schotten-Baumann反应中，PH值是一个重要的因素。酸性的氯化物在强碱和强酸性条件下很易水解，因此中心条件能降低这种水解。大部分的一级和二级胺的PKa值在10-11.5这个范围，这使得高PH值下的反应活性很高和中性条件的反应性能很低，在这种条件下胺类物质主要以质子化的形式存在。Schotten-Baumann反应在弱碱性条件下进行，PH值在8-10之间，这种PH值环境的获得主要是通过酸性氯化物的水解与胺类降低的反应性之间的平衡来实现的（也就是说氯化物与胺之间形成了一个缓冲体系）。在很多情况下，与在理论的基础上排出某些条件相比较，监测反应的变化情况是更合理明智。 |
3楼2010-01-11 15:37:26
syh9288
捐助贵宾 (著名写手)
海军上将
- 翻译EPI: 6
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- 金币: 1608.6
- 散金: 543
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- 在线: 482小时
- 虫号: 735351
- 注册: 2009-03-30
- 性别: GG
- 专业: 有机合成
4楼2010-01-11 15:49:23