阿司匹林的制备和止痛药的薄层层析 外文原文
阿司匹林的合成、表征及含量测定
阿司匹林的合成、表征及含量测定一.摘要1. 中文摘要医药上阿司匹林(aspirin)即乙酰水杨酸(acetylsalicylic acid),又称水杨酸乙酸脂(salicylic acid acetate.), 是一种非常普遍的治疗感冒的药物, 有解热止痛的作用,同时还可软化血管.阿司匹林的历史最早追溯于18世纪。
首先发现柳树皮的提取物是一种强效的止痛退热及抗炎消肿药，不久就分离、鉴定了其中的有效成分为水杨酸，随后用化学方法大规模生产，供医用。
但后来发现它的酸性强，严重刺激口腔，食道及胃壁黏膜，故试图改进。
先制成水杨酸钠试用，发现虽然改善了它的酸性和刺激性，但却具有令人不愉快的甜味，大多数患者不愿意服用。
18世纪末，合成了乙酰水杨酸，既保持了水杨酸钠的药效，又降低了刺激性，口味好。
Bayer公司将它的这个新产品称作aspirin。
Aspirin的产生历史是目前使用的许多药品的典型，即开始都以植物的粗提取物或民间药物的出现，再由化学家分离出其中的活性成分，测定结构并加以改造，结果才变成比原来更好的药物。
为了对阿司匹林有更进一步的了解.我们进行了阿司匹林的合成制备实验:在浓硫酸介质中，水杨酸和乙酸酐发生乙酰化反应生成乙酰水杨酸,副产品可用饱和的碳酸氢钠溶液洗涤以及乙酸乙酯重结晶除去.同时乙酰水杨酸又具有一系列特殊结构.在红外谱图中可出现多个特征振动频率.比较产品和标准的红外谱图,同时结合产品的熔点,可对合成的产品进行鉴定.除此之外,我们还用酸碱滴定测定产品的含量,并结合紫外分光度法对产品进行含量的分析.2.关键字阿司匹林, 合成,, 鉴定, 含量测定Abstract:This medicine aspirin (aspirin) or aspirin (acetylsalicylic acid), also known as salicylic acid acetate (salicylic acid acetate.), Is a very common treatment for cold medicines, hasantipyretic analgesic effect, but can also soften the blood vessels.The earliest history of aspirin back in the 18th century.First found in willow bark extract is a potent analgesic and anti-inflammatory swelling drug fever, and soon were isolated and identified the active ingredient of which is salicylic acid, followed by large-scale production by chemical methods for the medical.Acid but found it strong, severe irritation in the mouth, esophagus and gastric mucosa, it is trying to improve.Sodium salicylate into the first trial, found that while improved its acidic and pungent, but sweet with the unpleasant, most patients do not want to takeit.18th century, the synthesis of acetylsalicylic acid, while maintaining the efficacy of sodium salicylate, but also reduce the irritation, taste good.Bayer, it's this new product called aspirin.Aspirin use the production history is typical of many drugs, which were started in the plant crude extract or the appearance of folk medicine, and then isolated by the chemist, the active ingredients, and to transform the structure determination, the results become more than justhad better drugs.In order to have a better understanding of aspirin. We were prepared the synthesis of aspirin experiment: in concentrated sulfuric acid, salicylic acid and acetic anhydride acetylation reaction of acetylsalicylic acid, can be saturatedby-productssodium bicarbonate solution, washed and recrystallized ethyl acetate to remove.At the same time acetyl salicylic acid also has a special structure. In the infrared spectra may appear more characteristic vibrational frequencies. Comparison of the infrared spectrum of products and standards, combined with the melting point of products, synthetic products can be identified.In addition, we also used the content of acid-base titration products, combined with UV spectrophotometry analysis of content of the product. Keywords:Aspirin, synthesis, and identification, determination二.前言1.阿司匹林的简介中文名称：阿司匹林 (俗名:醋柳酸、东青等 )英文名称：Aspirin化学名称：乙酰水杨酸( acetylsalicylic acid )、2-(乙酰氧基)苯甲酸、(2-ethanoylhydroxybenzoic acid );分子式为：C9H8O4;分子相对质量：180.16;结构式:熔点:135℃～138℃ ;密度: 1.35g/cm3;性质:白色针状或结晶性粉末，无臭、略有酸味。
阿司匹林的合成、表征及含量测定实验预习报告
阿司匹林的合成、表征及含量测定实验预习报告姓名,班级,学号,阿司匹林的合成、表征及含量分析.阿司匹林简介中文名称:阿斯匹林(解热镇痛药),阿司匹林(退热药)中文俗名:醋柳酸、巴米尔、力爽、塞宁、东青等英文名称:Aspirin英文别名:Acenterine、Acetard、Acetophen、Acetylsalicylic Acid、Acidum Acetylsalicylicum、Adiro、Albyl、Aluprin、Asadrine、Aspirinetas、Bayaspirina、Bi-Prin、Codral Junior、Ecotri、Ecotrin、Elsprin、Empirin、Enteretas、Novosprin、Rhonal、Salitison、Salicylic Acid Acetate等拉丁名称:Aspirin化学普通命名法:乙酰水杨酸，acetylsalicylic acid化学系统命名法:2-(乙酰氧基)苯甲酸IUPAC命名法:2-ethanoylhydroxybenzoic acid分子结构式为:C9H8O4分子相对质量:180.16<B>用途:1.解热镇痛药，用于发热、疼痛及类风湿关节炎等。
2(是应用最早，最广和最普通解热镇痛药抗风湿药。
具有解热、镇痛、抗炎、抗风温和抗血小板聚集等多方面的药理作用，发挥药效迅速，药效肯定，超剂量易于诊断和处理，很少发生过敏反应。
常用于感冒发热,头痛、神经痛关节痛、肌肉痛、风湿热、急性内湿性关节炎、类风湿性关节炎及牙痛等。
是《国家基本药物目录》列入的品种乙酰水杨酸也是其他药物的中间体。
3(乙酰水杨酸是制备杀鼠剂中间体4-羟基香豆素的原料。
4(杨酸与乙酸。
微溶于水，溶于乙醇、乙醚、氯仿，也溶于氢氧化碱溶液或碳酸溶液，同时分解。
常用的解热镇痛药。
用于解热、镇痛、抗风湿，促进痛风患者尿酸的排泄，抗血小板聚集及胆道蛔虫治疗。
5(用于制造室外及有强光照射的结构件、器械部件，如汽车车身、农机部件、电表和电灯罩、道路标记等。
阿司匹林的制备zhangxinmiao
还具有抗血小板聚集作用，延长出血时间，防止血栓形成。
了解阿司匹林的一用途
目 的
调研理解酯化反应的原理 掌握阿司匹林的制备方法
实验原理
实验室制法： 本次实验使用水杨酸与乙酸酐。因为水杨 酸是一个既具有酚羟基又具羧基的双官能团化 合物，因此它能与乙酐作用，得到乙酰水杨酸。
COOH
+
OH
(CH3CO)2O
重结晶的原理
重结晶(recrystallization)
将晶体溶于溶剂或熔融以后，又重新从溶液或熔体中结晶的 过程。又称再结晶。重结晶可以使不纯净的物质获得纯化，或使 混合在一起的盐类彼此分离。重结晶的效果与溶剂选择大有关系， 最好选择对主要化合物是可溶性的，对杂质是微溶或不溶的溶剂， 滤去杂质后，将溶液浓缩、冷却，即得纯制的物质。混合在一起 的两种盐类，如果它们在一种溶剂中的溶解度随温度的变化差别 很大，例如硝酸钾和氯化钠的混合物，硝酸钾的溶解度随温度上 升而急剧增加，而温度升高对氯化钠溶解度影响很小。则可在较 高温度下将混合物溶液蒸发、浓缩，首先析出的是氯化钠晶体， 除去氯化钠以后的母液在浓缩和冷却后，可得纯硝酸钾。重结晶 往往需要进行多次，才能获得较好的纯化效果。
阿司匹林的作用
Hale Waihona Puke 阿司匹林即乙酰水杨酸,主本品解热镇痛作用较强，能降低发 热者的体温，对正常体温几乎无影响，且只能缓解症状，不 能治疗病因。本品尚可减少炎症部位具有痛觉增敏作用的物 质—前列腺素的生成，故有明显的镇痛作用，对慢性疼痛效 果较好，对锐痛或一过性刺痛无效。 抗炎抗风湿作用也较强，急性风湿热用药后24—48小时即可 退热，关节红肿疼痛症状明显减轻。
• 2碳酸氢钠的作用
• 阿司匹林可与碳酸氢钠反应生成水溶性的钠盐，而作 为杂质的副反应物则不能与碱作用可在用碳酸氢钠溶 液进行纯化时将其分离除去
阿司匹林11
2) Residual titration
在中和后的溶液中精密加氢氧化钠滴定 液(0.1mol／L)40ml，置水浴上加热 15min并时时振摇，迅速放冷至室温， 用硫酸标准溶液(0.05mol／L)滴定， 并将滴定的结果用空白试验校正。每lml 氢氧化钠标准溶液相当于18．02mg C9H8O4。
+ NaOH
钠盐 + H2O
COONa
+NaOH
OCOCH3
+H2O
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2) Residual titration(剩余滴定 )
COONa OCOCH3 COONa OH
+NaOH
(定量过量）? ©
+ CH3COONa
2NaOH（过量）＋H2SO4 ＝Na2SO4＋2H2O
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阿司匹林
水杨酸类解热镇痛药 分子结构中具有苯环和特征官能团，均具有紫外 和红外特征吸收光谱 分子中具有游离羧基，故具有较强酸性
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Ⅱ.
Principle
1) neutralization(中和 )
酒石酸 枸橼酸 水杨酸 醋酸
COOH OCOCH3
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Aspirin一经问世就风靡世界，成为最常用 的药物之一，发现Aspirin作用的1982年诺贝 尔奖得主文尼说，全世界每年要消耗45000吨 Aspirin 。 虽然这药品已有100年的历史，但 它在今时今日仍在发挥作用。
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近年来，随着医学科学的发展， Aspirin越来越 多的新用途被逐步发现。首先是能降低心肌缺血 患者的死亡率。另外它可增加老年人的认知功能， 且痴呆症患病率也低。临床上，阿司匹林还对直 肠癌有良好的治疗效果，还可用于治疗脚癣、偏 头痛、下肢静脉曲张引起的溃疡等。 需要指出的是，口服小剂量阿司匹林会引起 上消化道出血以及过敏反应仍是一个在临床上棘 手的问题，尽管阿司匹林这个老药新用前途广阔， 但慎用仍是不可忽略的。
药品英文说明书-Aspirin Description(阿司匹林)
Aspirin Description（阿司匹林英文说明书）Generic Name: ASPIRINPronunciation: (as' pir in)Trade Name(s): Aspent, Aspicot, Aspin, Colsprin-100, Cotasprin, Ecosprin, E-prin, GR.ASA-50, Loprin-75, Loprin-DS, Lowdose Aspirin, Mazoral, Myosprin, OtaspirinWhy it is prescribed: 1. Aspirin relieves mild to moderate pain.2. It reduces fever, redness, and swelling.3. It prevents blood from clotting.4. It is used to relieve discomforts caused by numerous medical problems including headache, infections, and arthritis.When it is to be taken: 1. Aspirin is often taken without a prescription.2. Follow the instructions on the label and package.3. If your doctor prescribes aspirin for you, you will receive specific instructions for how often you should take it.4. If you are taking aspirin to treat a chronic illness such as arthritis, you must follow the schedule prescribed by your doctor carefully.5. Keep in touch with your doctor.How it should be taken: 1. Aspirin comes in the form of suppositories, capsules, and regular, coated, extended-release, chewable, and effervescent tablets.2. If regular aspirin tablets cause a bad taste or burning sensation in the throat, try taking coated tablets to avoid these problems.3. Regular, coated, and extended-release aspirin tablets and capsules should be swallowed with a full glass of water or milk or after meals, to avoid stomach upset.4. Chewable aspirin tablets may be chewed, crushed, dissolved in a liquid, or swallowed whole; a full glass of water, milk, or fruit juice should be drunk immediately after taking these tablets.5. An oral liquid form of aspirin can be prepared by dissolving effervescent tablets according to the directions on the package.6. To insert an aspirin suppository into the rectum, follow these steps: a) Remove the wrapper. b) Dip the tip of the suppository in water. c) Lie down on your left side and raise your right knee to your chest. d) Using your finger, insert the suppository into the rectum, about 1/2 to 1 inch in infants and children and 1 inch in adults. Hold it in place for a few moments. You may stand up after abut 15 minutes. e) Wash your hands thoroughly and resume your normal activities.Special Instruction: 1. Children should not take aspirin for fevers associated with flu or chickenpox because such use has been linked with a serious illness known as Reye's Syndrome.2. Adults should not take aspirin for pain for more than 10 days (five days for children) without consulting a doctor.3. Aspirin should not be taken by adults or children for high fever, fever lasting longer than threedays, or recurrent fever without a doctor's supervision.4. Do not give more than five doses to a child in a 24-hour period unless directed to do so by a doctor.5. If you miss a dose, take the missed dose as soon as you remember it and resume the prescribed schedule.Side Effects: 1. Although side effects from aspirin are not common, they can occur.2. Nausea, vomiting, stomach pain, indigestion and heartburn are common. Take aspirin after meals, with a full glass of water or milk. If these effects continue, contact your doctor.3. Ringing in the ears, bloody or black stools, wheezing, difficulty breathing, dizziness, mental confusion and drowsiness are rare. Stop taking the drug and contact your doctor.Other Precautions: 1. If you are pregnant or breast-feeding women, inform your doctor before taking aspirin.2. Do not take aspirin if you are within three months of delivery.3. Do not take aspirin if you are allergic to it or to other arthritis medications (e.g., ibuprofen).4. If you have diabetes, regular use of eight or more regular strength aspirin tablets a day may affect test results for urine sugar. Consult your doctor.5. If you are taking a drug to thin the blood (e.g., warfarin), acetazolamide, corticosteroids, medication for gout or diabetes, or methotrexate, consult your doctor before using aspirin.6. You should not take aspirin except on the advice of a doctor if you have certain medical conditions including allergies, anemia, bleeding problems, a history of ulcers, asthma, kidney or liver disease, gout, Hodgkin's disease, and a history of nasal polyps.7. If you are taking large doses of aspirin on a long-term basis, avoid drinking alcoholic beverages because alcohol can increase stomach problems.8. If you have congestive heart failure or on a sodium-restricted diet, do not take effervescent aspirin tablets because they are high in sodium content.9. Aspirin is an ingredient in many nonprescription (over-the-counter) drugs.10. To prevent an overdose of aspirin, read the labels before taking other pain relievers and cold products to be sure that they do not contain aspirin.11. If you have had oral surgery or your tonsils removed in the last seven days, do not use chewable aspirin tablets, effervescent aspirin and aspirin in crushed tablets or gargles.Storage Conditions: 1. Store aspirin suppositories in a cool place or in a refrigerator.2. Keep aspirin tablets and capsules in a tightly closed bottle in a cool and dry place.3. Do not store aspirin in the bathroom because the dampness there can cause it to lose its effectiveness.4. Throw away aspirin that smells strongly of vinegar.5. Keep this medication out of the reach of children.Read more: /TULARC/health/Drugs-Herbs-Manual/Aspirin.html#ixzz1plITxWaL。
阿司匹林提取方案
阿司匹林提取方案1. 引言阿司匹林（Aspirin）是一种常用的非处方药，广泛应用于缓解疼痛、退热和抗炎等方面。
它是白色结晶性固体，化学名为乙酰水杨酸，化学式为C9H8O4，分子量为180.16 g/mol。
本文将介绍一种从阿司匹林原料中提取和纯化阿司匹林的方案。
2. 原料准备2.1 阿司匹林片阿司匹林片是制备阿司匹林所需的原料，在药店或医疗器械销售点均可购得。
准备一定数量的阿司匹林片用于后续步骤的提取工作。
2.2 辅助试剂提取阿司匹林所需的辅助试剂包括乙酸乙酯（ethyl acetate）、乙酸脂（acetic anhydride）、硫酸（sulfuric acid）、水（water）等。
这些试剂可在化学试剂供应商等渠道购买到。
3. 阿司匹林提取方案3.1 预处理阿司匹林片将一定数量的阿司匹林片放入研钵中，使用粉碎器将其研磨成细粉末。
研磨过程应尽量避免过热，以免影响后续步骤的正常进行。
3.2 酸解反应将研磨后的阿司匹林片细粉末加入大瓶中，并加入适量的乙酸脂和硫酸，充分搅拌使其充分混合。
注意，在该步骤中应避免产生气泡，以免剧烈反应造成危险。
3.3 加热反应混合液将酸解反应混合液加热至适当温度，通常在40-60°C之间。
加热后，反应液将由黄色变为深红色，同时放出浓烟。
加热反应时间通常为30分钟到1小时。
3.4 提取阿司匹林待加热反应混合液冷却至室温后，加入适量的冷水，充分搅拌混合。
然后，加入乙酸乙酯并充分摇动。
静置一段时间后，将分离的有机相（乙酸乙酯层）转移至干净的容器中。
3.5 纯化阿司匹林将提取得到的有机相加入碱性溶液中，例如10%氢氧化钠溶液。
然后，将混合溶液进行搅拌和过滤，以除去杂质和不溶性物质。
接下来，将过滤溶液酸化至pH≈2-3，可使用稀硫酸调节pH值。
4. 实验注意事项•操作过程需要进行充分通风，避免有害气体的积聚。
•加热反应液时需小心，避免剧烈反应造成危险。
•实验器材要求干净，以免影响实验结果。
美国药典阿司匹林翻译
阿司匹林C9H8O4180.16本品为2—（乙酰氧基）苯甲酸，又名乙酰柳酸[50-78-2]. 按干燥品计算，含C9H8O4在99.5%~100.5%。
【包装及贮存】保存在密闭容器中。
美国药典对照标准品11—USP阿司匹林RS。
【鉴定】1.用热水加热数分钟，冷却，然后加入1或2滴氯化铁。
测试结果显示：会有紫红色出现。
2.红外吸收197K干燥失重在硅胶板上干燥5小时，它失去的重量不超过0.5%。
易碳化物质溶解每500mg本品加硫酸5ml。
本方法相比采用其他任何溶液要好，不会有杂色。
炽灼残渣不超过0.05%本品不溶于碳酸钠，解决方案是取500mg在10ml温的碳酸钠溶液中溶解，溶液澄清。
氯化物取药品1.5g，用75ml的水煮沸5分钟，冷却，添加足够的水到原体积，滤过。
取25ml的滤液，对比0.10ml0.020 N 盐酸(0.014%)没有更多的氯。
硫酸盐溶解本品6.0 g在37ml的丙酮中，并加3ml的水，从电势测定上讲，与0.02M高氯酸盐滴定。
通过溶解9.20 g的高氯酸盐在1000ml的水中，使用一个误差值为±0.1 mV(见pH值791）的pH酸度计，一个特定的由铅电极和一个银—氯化银玻璃大电极组成的电极系统，包含一个解决方案的四乙铵高氯酸盐在冰乙酸(1在44)(参见滴定分析541），不超过每0.02M高氯酸盐1.25ml的消耗量(0.04%)。
（注意使用后洗净，参考电极排水，达到指定的状态，用清水冲洗，再用甲醇漂洗，晾干）重金属溶解本品2 g在25ml的丙酮中，添加1ml的水，再加1.2ml 的硫代乙酰胺甘油基地和2ml的pH值3.5的醋酸盐缓冲液(参见重金属231），待5分钟，颜色比由25ml的丙酮和2ml 的标准液的颜色要浅（见重金属铅231），以相同的方式处理。
最高限制是10 µg/ g。
游离水杨酸用足量的酒精溶解本品2.5 g，使体积为25.0ml。
每两个颜色匹配的比色管内添加48ml的水和1ml现配的稀释硫酸铁铵溶液(1ml的1 N盐酸，2ml的硫酸铁铵溶液混合后，用水稀释到100ml)。
《阿司匹林的合成》文字素材2(苏教版选修6)
阿司匹林Aspirin〔历史〕本品为历史悠久的解热镇痛药。
1999年3月6日是阿司匹林正式诞生100周年的日子，也是德国拜尔〔Bayer〕公司为类作出的奉献。
早在1853年夏尔.弗雷德里克.热拉尔〔Gerhardt〕就用水杨酸与醋酐合成了乙酰水杨酸，但没能引起人们的重视；1898年德国化学家菲.霍夫曼〔Felit Hoffmann〕又进行了合成，并为他父亲治疗风湿关节炎，疗效极好；1899年由德莱塞〔Dreser〕介绍到临床，并取名为阿司匹林〔Aspirin〕。
我国于1958年开始生产。
到目前为止，已应用百年，成为医药史上三大经典药物之一，至今它仍是世界上应用最广泛的解热，镇痛和抗炎药，也是作为比较和评价其他药物的标准制剂。
〔其他名称〕乙酰水杨酸；醋柳酸；巴米尔；Acetylsali-cylic Acid)。
〔性状与稳定性〕本品为白色结晶或结晶性粉末；无臭或微带醋酸臭，味微酸，易溶于乙醇，溶于氯仿和乙醚，微溶于水，性质不稳定，在潮湿空气中可缓缓分解成水杨酸和醋酸而略带酸臭味，故贮藏时应置于密闭，枯燥处，以防分解。
〔体内过程〕本品口服后易吸收，在体内迅速分解为游离型水杨酸，并分布全身组织。
其血浆有效抗炎浓度为每毫升150—300微克，而中毒浓度在每毫升200微克以上，因此要防止蓄积中毒。
本品主要在肝脏代谢，由肾脏排泄，当与碳酸氢钠同服时，游离型药物排泄增加，血浆药物浓度降低，那么药物作用时间缩短。
〔药物作用〕本品解热镇痛作用较强，能降低发热者的体温，对正常体温几乎无影响，且只能缓解病症，不能治疗病因。
本品尚可减少炎症部位具有痛觉增敏作用的物质—前列腺素的生成，故有明显的镇痛作用，对慢性疼痛效果较好，对锐痛或一过性刺痛无效。
本品抗炎抗风湿作用也较强，急性风湿热用药后24—48小时即可退热，关节红肿疼痛病症明显减轻。
本品还具有抗血小板聚集作用，延长出血时间，防止血栓形成。
〔适应病症〕广泛用于各种原因引起的发热，头痛，以及牙痛，肌肉痛，关节痛，腰痛，月经痛，术后小伤口痛。
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Distance analyte A has travelled
A
B
Bef ore
A
B
Af ter
Analyte A is more strongly attracted to the stationary phase than analyte B. The position of the analyte spot is defined by its retention factor, Rf.
O
+ R'OH R OH
O
+
O
R OR'
HH
At 20 °C the rate of reaction in both the forward and the backward directions is slow and it takes many days to attain equilibrium. Heating increases the rate of both the forward and reverse reactions, thus achieving the equilibrium state much faster, but it does not significantly alter the position of equilibrium. The value of the equilibrium constant, K, at room temperature is typically about 10 (i.e. the reaction does not go to completion), so the yield of the desired product will not be very high.
E29-3
Other analgesics
Some acylated aromatic amines that have been used as pain-killers, include acetanilide, acetaminophen and phenacetin.
Phenacetin is now known to be carcinogenic as well as having other undesirable side-effects and was withdrawn in the late 1960s after almost a century of use. The only one of these compounds still in general use is acetaminophen (paracetamol, Panadol®). It is the analgesic of choice for people who are allergic to aspirin, although prolonged use can cause kidney damage and overdoses can cause fatal liver damage. Aspirin and acetaminophen are active ingredients in different commercial pain-killers and in “cold cures”. In addition to these there may be other active ingredients such as ibuprofen, caffeine and inert ingredients including binders such as starch or carboxymethylcellulose.
Preparation of Aspirin (Acetylsalicylic Acid) and Thin-Layer Chromatography of Analgesic Drugs
INTRODUCTION
Salicin, a β-glycoside of salicylic acid, present in the leaves and bark of willow trees (genus Salix), has been used for centuries in a variety of herbal remedies. In vivo, it is converted into salicylic acid which acts to reduce inflammation and lower the temperature of patients suffering from fever.
Rf = distance analyte has travelled / distance solvent front has travelled
Since many analytes are colourless it is necessary to treat the TLC plate so that the spots can be seen. This can be achieved in a number of ways including, as in this experiment, the use of UV light or iodine vapour. Different analytes can be distinguished by their Rf values as well as by their appearance under UV light or after treatment with other visualising reagents.
This experiment uses TLC to analyse standards of caffeine and three analgesics, acetylsalicylic acid (aspirin), acetaminophen (paracetamol) and ibuprofen. You will then attempt to identify the active ingredient(s) of a commercial tablet by comparison with these standards.
E29-1
E29-2
An alternative method for the preparation of esters is to treat the alcohol with a reactive carboxylic acid derivative, for example a carboxylic acid anhydride. These reactions are effectively irreversible. They are also rapid, particularly when catalysed by strong acids.
The following diagram illustrates the appearance of a TLC plate before and after development:
Position of solvent f ront
Distance solvent f ront has travelled Distance analyte B has travelled
O
+ HO R
acid anhydride
alcohol
ester
carboxylic acid
Thin-layer chromatography
Thin-layer chromatography (TLC) is an important technique in organic chemistry. TLC can be used to assess the course of a reaction, to assess the purity of a sample and also to identify unknown compounds by comparison with standards. TLC is used in this experiment to identify the components of analgesic (pain-killing) tablets as well as confirming the identity and purity of the aspirin synthesised.
In TLC, a thin-layer of stationary phase is applied to a carrier plate. The plates supplied are prepared commercially and consist of a thin layer of silica on an aluminium carrier plate. The developing liquid or mobile phase travels up the plate by capillary action and the compounds being analysed are carried along with it at varying speeds depending upon the strength of their attraction to the stationary phase and the polarity of the mobile phase.