应用化学专业英语 Lesson 28 翻译.doc

Lesson 28 A Experiment Ease: Synthesis of Salicylic Acid From Oil of Wintergreen (Methyl Salicylate) overview Methyl salicylate (水杨酸酯) (oil of wintergreen) and salicylic acid (水杨酸) are naturally occurring compounds with medicinal uses. You will try to prepare salicylic acid by boiling methyl salicylate with aqueous sodium hydroxide(lye碱液). You will also try to purify your product by recrystallization (再结晶) and characterize it by measuring its melting temperature. Time require:2 laboratory sessions. Background Methyl salicylate and salicylic acid are naturally occurring compounds with medicinal uses. The procedure used here to convert methyl salicylate into salicylic acid is called saponification (皂化)。It is chemically related to the process used to convert natural fats into soap. Salicylic acid and aspirin Many plants produce salicylic acid naturally. Among these, willow trees (柳树) have been recognized since antiquity as a potent (有效) source of medicine. Hippocrates (一个希腊的名医) encouraged the pregnant women of ancient Greece to chew willow leaves and drink willow tea to alleviate (减轻) labor and birth pains. Chinese, Native Americans, and others also used willow. Salicylic acid is found mainly in the willow’s leaves and bark (树皮).The pure acid possesses several useful medicinal properties. It is an antipyretic (a fever reducer), an analgesic (a pain reducer), and an anti-inflammatory (a swelling reducer). Unfortunately, pure salicylic acid and even the concoctions (混合物) derived from willow, make for an extremely unpleasant medicine. The salicylic acid molecule contains two acidic functional groups, the phenol group (PhOH) and the carboxylic acid group (-COOH). These groups make salicylic acid an irritating (刺激性的) substance that burns the sensitive linings of the mouth, throat, esophagus (食道)， and stomach. [Interestingly, salicylic acid’s ability to burn living tissue makes it useful for other applications. S’s harsh (令人生厌的) qualities is to replace the acidic hydroge