四氢呋喃脱水(共6页)

1、精选优质文档-倾情为你奉上关于钠+二苯甲酮的除水问题【最近一直在做除水，有些资料和经验分享一下】 小木虫(金币+1):奖励一下，鼓励发有价值的话题 秋天白云(金币+2):谢谢分享！ 2010-10-11 22:39:27一：二苯甲酮的物理性质 英文名：Benzophenone, diphenyl ketone. 化学名称：苯甲酮 别名：二苯酮， 苯甲酰基苯 分子量：182.21 外观：白色片状结晶，微有玫瑰香味 熔点：47-49/2k/Pa. 沸点：170. 相对密度?：1.095-1.099 溶解性：不溶于水，能溶于乙醇，醚和氯仿。 二：钠+二苯甲酮的除水原理 说法一：二苯甲酮做为指示剂在合

2、成实验中用途广泛，可以用来做为处理甲苯、苯、THF、乙 腈等的指示剂；加入后若出现了漂亮的蓝色，就可以蒸馏使用了，最好保存在钠中， 但为何生成蓝色，有很多说法，莫宗一世，不尽相同。现从一本国外的讲反应的机理 书上摘录其原因：译成中文的大概意思是：由酮生成的自由基阴离子叫作羰基自由 基，二苯甲酮做指示剂是二苯甲酮中的氧原子夺取了钠中的电子，生成了暗蓝色羰基自由基；该自由基在立体上、电性方面是稳定的，主要用来指示无氧条件！用途 广。加入二苯甲酮后，溶液越蓝，说明溶液中的氧越少，间接说明水分很少。但 是否变蓝，与加入的二苯甲酮和处理的溶剂的量有关，THF（300ml)含水多，要回流 约 6 小时以上

3、，当然与处理的溶剂量有关，越多则时间越长，甲苯、苯等含水少的回 流时间少，这样时间会缩短。 说法二：二苯甲酮和金属钠反应生成一个显蓝色的中间体 1,如果溶剂中有水,继续反应生成无色 的化合物 2.如果没水了就停留在中间体 1 的蓝色状态.黄色不大好解释，可能是有机物 碱性条件下少量被破坏产生的杂质显色，另外，如果二苯甲酮长时间（数天）在金属 钠环境中回流也会被破坏而导致不能显蓝色。二苯甲酮的作用相当于酸碱滴定分析过 程的指示剂，少量存在与蒸馏残液中，与残液一起做一般废液或废渣处理，不需要特 殊的处理方式。变蓝色是因为二苯甲酮在钠表面被还原为自由基，其对水和氧气都敏 感，没有水自然就显蓝色了。但

4、是反应过程中钠表面被 NaOH 覆盖或二苯甲酮消耗过 多，无法继续生成自由基就不能变蓝了。三：钠+二苯甲酮的除水步骤1：检验有无过氧化物 方法一：为此取少量试剂（乙醚，四氢呋喃）与等体积的 2%碘化钾溶液，加入几滴 稀盐酸一起振摇，若能使淀粉溶液呈紫色或蓝色，即证明有过氧化物存在。 方法二：用淀粉碘化钾试纸检验过氧化物是否存在。除去过氧化物可在分液漏斗中加 入试剂和相当于试剂体积 1/5 新配制的硫酸亚铁溶液，剧烈摇动后分去水溶液。 2：欲除水 先加入普通干燥剂如：碳酸钾、硫酸钠、氢氧化钠等预处理一下，或者用 4A 分子筛 【要高温干燥数个小时】，欲除水数天；3：连接装置 将处理待溶剂加到烧瓶

5、中【根据所需量要多放大约 100 毫升】，连接装置，搅拌，通 入氮气； 4：加金属钠操作方法一：取金属钠，用小刀切去被氧化的表面，然后切成薄片，用剪刀剪成细丝 放入小烧杯，用镊子加到烧瓶里，注意要少量多次，【在氮气保护下是很安全的，氢 气不会爆炸的，放心做就是】； 操作方法二：用干净的试剂瓶或其他东西压成薄片，再用剪子剪；如果有实验条件可 以做成钠沙，钠珠； 5：关于加钠问题500ml 溶剂加上指甲大小的两块钠就够了，凭感觉，多点少点也无所谓；如果没有氢 气产生了。通一会氮气后可以加氮气球。 6：加二苯甲酮加金属钠回流一段时间（4 个小时）后再加二苯甲酮效果更好，二苯甲酮 500 毫升溶 剂加

6、一勺左右就够了，它是指示剂不需要太多。 7：蒸出溶剂 液体变蓝后，就可以回收了。【因为钠表面覆盖了碱，如果不变蓝建议再加点钠回流 后加二苯甲酮，就能变蓝。】如果实在不变蓝，可能是回流时间太短，瓶内有氧气！ 蒸馏到最后，要留一部分，防止过氧化物高温爆炸。 8：剩余钠的处理 用表面皿或烧杯倒入乙醇，用镊子把剩余的钠加到乙醇中处理，要少量多次！直到 钠消失。四：两个例子：1：乙醚(CH3CH2OCH2CH3)普通乙醚中常含有一定量的水、乙醇及少量过氧化物等杂质。制备无水乙醚，首先要 检验有无过氧化物。为此取少量乙醚与等体积的 2%碘化钾溶液，加入几滴稀盐酸一 起振摇，若能使淀粉溶液呈紫色或蓝色，即证

7、明有过氧化物存在。除去过氧化物可在 分液漏斗中加入普通乙醚和相当于乙醚体积 1/5 新配制的硫酸亚铁溶液，剧烈摇动后 分去水溶液。再用浓硫酸及金属钠作干燥剂，所得无水乙醚可用于 Grignard 反应。 在 250mL 圆底烧瓶中，放置 100mL 除去过氧化物的普通乙醚和几粒沸石，装上回流 冷凝管。冷凝管上端通过一带有侧槽的软木塞，插入盛有 10mL 浓硫酸的滴液漏斗。 通入冷凝水，将浓硫酸慢慢滴入乙醚中。由于脱水发热，乙醚会自行沸腾。加完后摇 动反应瓶。 待乙醚停止沸腾后，折下回流冷凝管，改成蒸馏装置回收乙醚。在收集乙醚的接引管 支管上连一氯化钙干燥管，用与干燥管连接的橡皮管把乙醚蒸气导入

8、水槽。在蒸馏瓶 中补加沸石后，用事先准备好的热水浴加热蒸馏，蒸馏速度不宜太快，以免乙醚蒸气 来不及冷凝而逸散室内。收集约 70mL 乙醚，待蒸馏速度显著变慢时，可停止蒸馏。 瓶内所剩残液，倒入指定的回收瓶中，切不可将水加入残液中(飞溅)。 将收集的乙醚倒入干燥的锥形瓶中，将钠块迅速切成极薄的钠片加入，然后用带有氯 化钙干燥管的软木塞塞住，或在木塞中插入末端拉成毛细管的玻璃管，这样可防止潮 气侵入，并可使产生的气体逸出，放置 24 小时以上，使乙醚中残留的少量水和乙醇转 化成氢氧化钠和乙醇钠。如不再有气泡逸出，同时钠的表面较好，则可储存备用。如 放置后，金属钠表面已全部发生作用，则须重新加入少量

9、钠片直至无气泡发生。这种 无水乙醚可符合一般无水要求。 另外也可用无水氯化钙浸泡几天后，用金属钠干燥以除去少量的水和乙醇。 纯乙醚 b.p. 34.51，nD20 1.3526，d420 0.71378。2：四氢呋喃(C4H8O )四氢呋喃系具乙醚气味的无色透明液体，市售的四氢呋喃常含有少量水分及过氧化物。 如要制得无水四氢呋喃可与氢化铝锂在隔绝潮气下和氮气气氛下回流(通常 1000 mL 约 需 24g 氢化铝锂)除去其中的水和过氧化物，然后在常压下蒸馏，收集 67的馏分。 精制后的四氢呋喃应加入钠丝并在氮气氛中保存，如需较久放置，应加 0.025% 4-甲基-2,6-二叔丁基苯酚作抗氧剂。

10、处理四氢呋喃时，应先用小量进行试验，以确定只有少量水和过氧化物，作用不致过于猛烈时，方可进行。 四氢呋喃中的过氧化物可用酸化的碘化钾溶液来试验，如有过氧化物存在，则会立即出现游离碘的颜色，这时可加入 0.3%的氯化亚铜，加热回流 30min，蒸馏，以除去过氧化物(也可以加硫酸亚铁处理，或让其通过活性氧化铝来除去过氧化物)。 纯四氢呋喃 b.p. 67，nD20 1.4050，d420 0.8892。Benzophenone Ketyl Study I. Introduction A. Background The benzophenone/sodium still is a widely us

11、ed method to produce water oxygen and peroxide free solvents for organic synthesis.12 Most organic labs routinely use this method to dry their solvents that are used in moisture sensitive reactions. The most popular solvent for these reactions is tetrahydrofuran. However despite widespread use there

12、 is no information available in the literature on how dry or oxygen free the solvent really is from this method. At Mallinckrodt Baker RD we have developed a process to produce Ultra dry THF less than 10 ppm water and peroxides a study was initiated to compare our new material with material produced

13、 from the benzophenone/sodium still. B. Benzophenone/Sodium Still A literature search on the benzophenone/sodium still found only one reference to date on the subject.1 The reference was from Chemical and Engineering News in 1978.1 The procedure in the article describes adding 5 grams of sodium and

14、30 grams of benzophenone to 3 liters of tetrahydrofuran.1 The mixture is then refluxed under inert gas until the blue color of the benzophenone ketyl forms. The author of the article states that once the blue color forms distillation of the solvent will yield very pure dry oxygen and hydroperoxide f

15、ree ether.1 However the author provides no data on the purity or water level of the solvent produced from this method. We decided to carry out a study on the benzophenone/sodium still to obtain these answers. II. Results and Discussion A. Benzophenone/Ketyl THF Still Purity Study We set up a THF sti

16、ll following the exact procedure as in Chemical and Engineering News reference.1 Analysis of the THF produced from the still gave 10.1 ppm of water with no dissolved oxygen or hydroperoxides. The GC analysis of the tetrahydrofuran from the still found that it contained 150 ppm of benzene as an impur

17、ity. A study was initiated to determine the source of the benzene. We tested both the tetrahydrofuran and benzophenone starting material and found no benzene present. This indicated that the source of the benzene was from the chemical breakdown of the benzophenone in the still. A GC/MS analysis of t

18、he THF sodium/benzophenone mixture was carried out to help determine the possible mechanism of benzene formation. The GC/MS analysis showed compounds such as 1 2 3 and 4. These compounds are formed by some type of free radical reaction with phenyl radicals. The probable mechanism is the carbonyl phe

19、nyl group bond breaks forming phenyl radicals and benzaldehyde. The benzaldehyde 5 then either undergoes reduction to benzyl alcohol 6 or further reaction with the phenyl free radicals. We carried out a test to determine if the benzaldehyde is reduced in the sodium/benzophenone still. Benzaldehyde 5

20、 was added to THF in the presence of sodium the mixture was then refluxed. We found that benzaldehyde 5 was reduced to the benzyl alcohol 6. Additional further GC/MS analysis was carried out to look for the benzaldehyde 5 and benzyl alcohol 6. Unfortunately neither benzyl alcohol nor benzaldehyde wa

21、s detected. One possible explanation is the benzaldehyde and benzyl alcohol rapidly undergo further reactions in the sodium/benzophenone still to prevent their detection. For example the reaction of benzaldehyde with phenyl radicals could have resulted in the formation of compounds 1 and 2. Another

22、possible pathway would be rapid polymerization of these compounds. B. Effect of Water on the Benzophenone Ketyl The next study was to determine what effect water had on the decomposition of the benzophenone ketyl. The benzophenone ketyl was produced in THF at a concentration of 630 ppm. The loss of

23、blue color would indicate decomposition of the ketyl. Titration of the ketyl with water showed that a full 100 mol of water was required to quench the blue color. This indicates that water reacts in a simple one to one mole ratio with the ketyl. Therefore the blue color of the ketyl does not necessa

24、ry indicate super dry conditions. For example in the typical procedure the ketyl is produced at a concentration of 6311 ppm in THF. When a small amount of water is added to a sample of this mixture to increase the water concentration the solution will still remain blue since until all of the ketyl d

25、ecomposed. Thus it would be possible to have a concentration of 100 ppm water in the solvent and if the ketyl was not used up it would still have the blue ketyl color. C. Effect of Oxygen on Benzophenone Ketyl The final study was to determine how sensitive the ketyl was to oxygen. An experiment was

26、carried out where the ketyl was titrated with oxygen. We found that the color was quenched with 8 mole of oxygen. This data shows that the benzophenone ketyl reacts catalytically with oxygen and not on a one to one mole ratio as water does. Thus the benzophenone ketyl is much more sensitive to oxyge

27、n than to water. II. Conclusion Drying and purification of THF and other solvents is a widely used practice in many labs. Solvent produced from the sodium/benzophenone still is believed to be of the highest quality. Despite the fact there was no real data on the actual quality of the solvent. This belief has been passed down from lab worker to lab worker as the method of choice for producing anhydrous solvents for organometallic synthesis. Our studies have shown that while the THF produced from the still is f