制药工程专业英语第6单元逐句详解.docx

此文档收集于网络，仅供学习与交流，如有侵权请联系网站删除PART 2 BIOCHEMICAL PHARMACEUTICALS生化制药Unit 6 Isolation of Caffeine from Tea从茶叶中分离咖啡因In this experiment, Caffeine will be isolated from tea leaves. 在这个实验中，咖啡因会从茶叶中分离出来。The major problem of the isolation is that caffeine does not occur alone in tea leaves, but is accompanied by other natural substances from which it must be separated. 分离过程中的主要问题就是，茶叶中不仅仅只有咖啡因，还伴随着需要被分离除去的其他天然物质。The major component of tea leaves is cellulose，which is the major structural material of all plant cells. 茶叶中的主要成分是所有植物细胞中的主要结构材料纤维素。Cellulose is a polymer of glucose. 纤维素是葡萄糖的聚合物。Since cellulose is virtually insoluble in water, it presents no problems in the isolation procedure. 然而纤维素实际上是不溶于水的，所以在隔离的程序上不用考虑去除纤维素。Caffeine, on the other hand, is water soluble and is one of the major substances extracted into the solution called tea”. 另一方面，咖啡因是水溶性的，也是萃取到溶液（也就是茶）里的主要物质之一。Caffeine comprises as much as 5 percent by weight of the leaf material in tea plants. 咖啡因包含了茶树叶片材料总重的5%之多。Tannins also dissolve in the hot water used to extract tea leaves. 丹宁（鞣酸）也溶解于用于萃取茶叶的热水中。The term tannin does not refer to a single homogeneous compound, or even to substances which have similar chemical structure. 丹宁一词不是指单个均一的化合物，也不是具有相似化学结构的物质。It refers to a class of compounds which have certain properties in common. 它是指某些具有共同属性的化合物的种类。Tannins are phenolic compounds having molecular weights between 500 and 3000. 丹宁是一类分子质量在500到3000的含酚的化合物。They are widely used to tan” leather. 它们被广泛用于鞣革。They precipitate alkaloids and proteins from aqueous solutions. 它们从水溶液中沉淀出生物碱和蛋白质Tannins are usually divided into two classes: those which can be hydrolyzed and those which cannot. 丹宁通常被分为两类：可水解和不可水解。Tannins of the first type which are found in tea generally yield glucose and gallic acid when they are hydrolyzed. 在茶中，第一类丹宁水解后通常产生葡萄糖和五倍子酸。These tannins are esters of gallic acid and glucose. 这些丹宁是五倍子酸和葡萄糖的酯类。They represent structures in which some of the hydroxyl groups in glucose have been esterified by digalloyl groups. 它们代表着葡萄糖中的一些羟基被酯化为鞣酰基的结构。The non-hydrolyzable tannins found in tea are condensation polymers of catechin. 茶中的不可水解的丹宁是儿茶酚的缩合聚合物。These polymers are not uniform in structure, but catechin molecules are usually linked together at ring positions 4 and 8.这些聚合物在结构上是不一致的，但儿茶酚分子通常在环的4号和8号位是相连的。When tannins are extracted into hot water, the hydrolyzable ones are partially hydrolyzed, meaning that free gallic acid is also found in tea. 当丹宁被萃取到热水中，可水解的部分水解掉了，意味着茶中还有多余的五倍子酸。The tannins, by virtue of their phenolic groups, and gallic acid by virtue of its carboxyl groups, are both acidic. 由于丹宁中含有酚，五倍子酸中含有羧基，所以它们都是酸性的。If calcium carbonate, a base, is added to tea water, the calcium salts of these acids are formed. 如果茶水中加入碳酸钙，这些酸的钙盐就会形成。Caffeine can be extracted from the basic tea solution with chloroform, but the calcium salts of gallic acid and the tannins are not chloroform soluble and remain behind in the aqueous solution.咖啡因可以被茶的氯仿溶液萃取，但五倍子酸和丹宁的钙盐是不溶于氯仿的，所以它们会留在水溶液中。The brown color of a tea solution is due to flavonoid pigments and chlorophylls, as well as their respective oxidation products. 茶水呈现出褐色是由于黄酮类色素和叶绿素，以及它们各自的氧化物。Although chlorophylls are somewhat chloroform soluble, most of the other substances in tea are not. 虽然叶绿素是微溶于氯仿的，但茶叶中的其他大多数物质不是如此。Thus, the chloroform extraction of the basic tea solution removes nearly pure caffeine. 因此，碱性茶水的氯仿提取去除了几乎无杂质的咖啡因。The chloroform is easily removed by distillation (by 61C) to leave the crude caffeine. 氯仿在61蒸馏中易被去除，从而分离出咖啡因的粗产物。The caffeine may be purified by recrystallization or by sublimation. 咖啡因可以通过结晶或升华来纯化。In a second part of this experiment, Caffeine will be converted to a derivative. 本次实验的第二个部分，咖啡因会被转化为衍生物。A derivative of a compound is a second compound, of known melting point, formed from the original compound by a simple chemical reaction. 一个化合物的衍生物是一个已知熔点的第二化合物，是由原来的化合物通过简单化学反应生成的。In trying to make a positive identification of an organic compound, it is often customary to convert it into a derivative. 为了试图鉴定原始化合物，我们通常习惯将它转化成衍生物。If the first compound, Caffeine in this case, and its derivative both have melting points which match those reported in the chemical literature (e. g., a handbook), it is assumed that there is no coincidence and that the identity of the first compound, Caffeine, has been definitely established.如果第一化合物（在这也就是指咖啡因）以及它的衍生物的熔点都与化学文献上所记载的相匹配，那么就可以推测第一化合物就是咖啡因无疑。Caffeine is a base and will react with an acid to give a salt. 咖啡因是碱，可以和酸反应生成盐。Using salicylic acid, a derivative salt of Caffeine, Caffeine salicylate, will be made in order to establish the identity of the Caffeine isolated from tea leaves. 和水杨酸反应就能生成咖啡因的一种衍生物盐，叫做水杨酸咖啡因。它可以用来鉴定茶叶中分离出的咖啡因。Special Instructions 特别注意Be careful when handling chloroform. 要小心处理氯仿。It is a toxic solvent, and you should not breathe it excessively or spill it on yourself. 它是一种有毒溶剂，应防止过度吸入以及洒在身上。When discarding spent tea leaves, do not put them in the sink because they will clog the drain. 丢弃茶叶时，不应将它们扔在水槽，因为它们会堵塞排水管。Dispose of them in a waste container.应该将它们扔入垃圾桶。Procedure 程序Place 25g of dry tea leaves, 25g of calcium carbonate powder, and 250ml of water in a 500ml three neck round bottom flask equipped with a condenser for reflux. 将25克干燥茶叶、25克碳酸钙粉末和250毫升水混入一个装有回流冷凝管的500毫升三口圆底烧瓶。Stopper the unused openings in the flask and heat the mixture under reflux for about 20 minutes. 将烧瓶中未使用的开口塞住，加热混合物，回流20分钟。Use a Bunsen burner to heat. 用本生灯加热。While the solution is still hot, filter it by gravity through a fluted filter using a fast filter paper such as E&D No. 617 or S&S No. 595. 用快速过滤纸如E&D No. 617 或 S&S No. 595，通过凹槽过滤器，趁热过滤。You may need to change the filter paper if it clogs.如果堵住了就需要换一种滤纸。Cool the filtrate (filtered liquid) to room temperature and, using a separatory funnel, extract it twice with 25ml portions of chloroform. 待滤液降至室温，用25毫升氯仿在分液漏斗中萃取两次。Combine the two portions of chloroform in a 100ml round bottom flask.将两次萃取的了氯仿倒入100毫升圆底烧瓶中混合。Assemble an apparatus for simple distillation and remove the chloroform by distillation. 搭建一个简易的蒸馏装置，并通过蒸馏将氯仿去除。Use a steam bath to heat. 用蒸汽浴来加热。The residue in the distillation flask contains the caffeine and is purified as described below (crystallization). 蒸馏烧瓶中的残留物包括咖啡因，将以如下描述进行纯化（结晶）。Save the chloroform that was distilled. You will use some of it in the next step. 将蒸馏出的氯仿保留下来，用于下面的步骤。The remainder should be placed in a collection container.残余物应倒入回收容器。Crystallization (Purification) 结晶（纯化）Dissolve the residue obtained from the chloroform extraction of the tea solution in about 10ml of the chloroform that you saved from the distillation. 将从茶溶液的氯仿萃取液中获得的残留物溶解于10毫升蒸馏所得的氯仿。It may be necessary to heat the mixture on a steam bath. 用蒸汽浴加热混合物。Transfer the solution to a 50ml beaker. 将溶液转移到50毫升烧杯中。Rinse the flask with an additional 5ml of chloroform and combine this in the beaker. 再用5毫升氯仿冲洗烧瓶，倒入烧杯。Evaporate the now light-green solution to dryness by heating it on a steam bath in the hood.在通风厨中，用蒸汽浴加热浅绿色溶液，溶液蒸发，直至干燥。The residue obtained on evaporation of the chloroform is next crystallized by the mixed solvent method. 氯仿蒸发后获得的残留物接下来就会用混合溶剂的方法结晶。Dissolve it in a small quantity (about 2 to 4ml) of hot benzene and add just enough high boiling (60C to 90C) petroleum ether (or ligroin) to turn the solution faintly cloudy. 将它溶解于少量热苯中（大约2至4毫升），加入足够高沸点的石油醚（60至90摄氏度），使溶液变得轻微浑浊。Alternatively, acetone may be used for simple crystallization without a second solvent. 作为选择，丙酮可用于简单结晶，而不用其他的溶剂。Cool the solution and collect the crystalline product by vacuum filtration using a Hirsch funnel. 冷却溶液，用赫尔希漏斗真空过滤，收集结晶产物。Crystallize the product the same way a second time if necessary, and allow the product to dry by allowing it to stand in the suction funnel for a while. 如有必要的话用同样的方式再结晶一次，并通过让产物在吸入漏斗上短暂停留的方式干燥产物。Weigh the product. 称重。Calculate the weighty percentage yield based on tea and determine the melting point. 计算基于茶叶的重量百分比收率，判断熔点。If desired, the product may be further purified by sublimation as described in the next experiment.如果和推想的相符，产物将通过下面描述的实验进一步升华纯化。The Derivative 衍生Dissolve 0.20g of Caffeine and 0.15g of salicylic acid in 15ml of benzene in a small beaker by warming the mixture on a steam bath. 在小烧杯中，将0.20克咖啡因和0.15克水杨酸溶解于15毫升苯，用蒸汽浴缓慢加热混合物。Add about 5ml of high boiling (60C to 90C) petroleum ether and allow the mixture to cool and crystallize. 加入大约5毫升高沸点石油醚（60至90摄氏度），让混合物降温、结晶。It may be necessary to cool the beaker in an ice water bath or to add a small amount of extra petroleum ether to induce crystallization. 用冰水浴冷却烧杯或者再加入少量石油醚来进一步结晶是十分必要的。Collect the crystalline product by vacuum filtration using a Hirsch funnel. 用赫尔希漏斗真空过滤，收集结晶产物。Dry the product by allowing it to stand in the air, and determine its melting point. 让产物在空气中晾干，判断熔点。Check the value against that in the literature. 与文献值进行检查比对。Submit the sample to the instructor in a labeled vial.将样品放入贴标签的小瓶中，交给老师。Selected from Pavia Donald L. Introduction to Organic Laboratory Techniques: a ContemporaryApproach W. B. Saunders Company, 1976.Exercises1. Answer the following questions:(1)Can you list several plants that contain caffeine?(2) What kind of method can be used to isolate caffeine from tea?(3) How does man use caffeine in the daily life?2. Competing the following paragraph. Choose Not More Than Three Words from the passage for each answer. The active ingredient that makes tea and coffee valuable to man is _caffeine_ .Caffeine is an _tannin_ , a class o