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1、 Chapter 15 Alcohols,Diols,and Thiolsl烷烃分子中的氢原子被羟基取代后的化合物，称为醇 。l烷烃分子中一个氢原子被羟基取代的，称一元醇，用 ROH表示；几个氢被取代的，称多元醇。l 羟基所连接的碳原子为一级碳原子，称为一级醇（伯醇）；Primary alcohol为二级碳原子, 称为二级醇（仲醇）；Secondary alcohol为三级碳原子, 称为三级醇（叔醇）Tertiary alcohol15.1 Sources of Alcohols工业来源 从醇能制得其他各种脂肪族化合物：烯烃、卤代烷、醚、醛、 酮、酸、脂以及其他化合物。 从卤代烷，可制得格氏试
2、剂和醛、酮又可制得复杂的醇，如此 等等。 醇不仅可用作原料，往往还可用醇作为反应时的溶剂和产物复 结晶时的溶剂。醇之所以在脂肪族化学中成为如此重要的原料，不仅仅是由 于醇能进行多种多样的反应，还由于价格便宜，有大量供应。 一些简单的醇，是有机合成的基础，借两种主要的方法得到： 通过石油裂化所得的烯烃的水合作用， 碳水化合物的发酵。 除这两种主要方法外，还有其他一些方法，但应用较少 糖水合谷物糖浆淀粉杂醇油 1醇的混合物酵母发酵CH3CH2OH 乙醇甘蔗脂肪还原裂化Ziegler-Natta 聚合，空气CH3(CH2CH2)nCH2OH 长直链的碳为偶数的醇石油RCH=CH2RCH2（OH）CH
3、3 Markovnikov加成水合裂化CH2=CH215.1.1 烯烃的水合作用四或五个碳原子的烯烃可以从石油裂化所得 的混合物中分离出来。烯烃通过直接和水加成 或硫酸加成再水解，很容易转变为醇。用这个方法只能得到按Markovnikov法则 而形成的醇。例如 可以得到异丙醇，而得不到正丙醇； 可以得到仲丁醇，而得不到正丁醇； 可以得到叔丁醇，而得不到异丁醇。 用这个方法所得到的伯醇只有乙醇。15.1.2 碳水化合物的发酵 用酵母使糖发酵，是人类所用的最古老的化学合成法 ，但对于制乙醇和其它一些醇至今仍是极为重要的。 糖的来源广泛，主要来源于甘蔗的糖浆，或各种谷 物的淀粉；英文中谷物叫grai
4、n,因此乙醇也称作“ grain alcohol”. 当淀粉作原料时，除得到乙醇外，还得到数量较少 的杂醇油（英文fusel oil,来自德文Fusel,劣等酒），它 是伯醇的混合物：大部分是异戊醇，还含有正丙醇、 异丁醇和2-甲基-1丁醇，即所谓旋光性戊醇。 15.2 Overview of Preparation of AlcoholslHydrations of AlkeneslOxymercuration- Demercuration (羟汞化) of AlkeneslHydroboration- Oxidation of AlkeneslHydrolysis of Alkyl Hal
5、ideslOrganometallic with Aldehydes and KetoneslOrganometallics with Easters lReductions of Aldehydes and KetoneslReductions of EasterslReductions of Carboxylic AcidslOpening Epoxides15.3 Hydration of AlkenesReaction type: Electrophilic Addition SummarylWhen treated with aq. acid, most commonly H2SO4
6、, alkenes form alcohols. lRegioselectivity predicted by Markovnikovs rule lReaction proceeds via protonation to give the more stable carbocation intermediate. lNot stereoselective since reactions proceeds via planar carbocation15.4 Hydroboration / Oxidation of AlkenesReaction type: Electrophilic Add
7、itionlReagents (two steps) 1.BH3 or B2H6 then 2. NaOH/ H2O2 SummarylRegioselectivity : Anti-Markovnikov, since the B is the electrophile. lStereoselectivity : Syn since the C-B and C -H bonds form simultaneously from the BH3. lThe alcohol is formed over a series of steps involving the B center , wit
8、h retention of configuration at the C. 15.5 Oxymercuration-Demercuration (羟汞 化) of AlkenesReaction type: Electrophilic Addition lOverall transformation : C=C to H-C-C-OH lTypical reagents are mercury acetate, Hg(OAc)2 in aqueous THFMechanism for Reaction of Alkenes With Hg(OAc)2 / H2oStep 1: The p e
9、lectrons act as the nucleophile with the electrophilic Hg and loss of an acetate ion as a leaving group, forming the mercurinium ion. Step 2: Water functions as a nucleophile and attacks one of the mercury substituted carbons resulting in cleavage of the C-Hg bond. Step 3: The acetate ion functions
10、as a base deprotonating the oxonium ion to give the alcohol. This completes the oxymercuration part of the reaction.Step 1Step 2Step 3Step 4:(mechanism not shown) The hydride reduces the Hg off, creating a C-H bond while breaking the C-Hg bond. This is the demercuration part of the process.Step 4lRe
11、gioselectivity predicted by Markovnikovs rule (most highly substituted alcohol) lReaction proceeds via the formation of a cyclic mercurinium ion (compare with bromination of alkenes) lThe mercurinium is opened by the attack of water to complete the oxy-mercuration lDemercuration is effected by a red
12、uction using sodium borohydride, NaBH4Summary 15.6 Synthesis of Alcohols Using Grignard ReagentsThe principals synthetic application of Grignard reagents is their reaction with certain carbonyl-containing compounds to produce alcohols.Reaction usually in Et2O followed by H3O+ work-up. 若用水，则生成的Mg(OH)
13、X为胶状物，难以处理。通 常用稀酸(HCl,H2SO4)处理Alkoxymagnesiumhalide15.6.1 The substituents on the carbonyl dictate the nature of the product alcoholAddition to methanal (formaldehyde) gives primary alcoholsAddition to other aldehydes gives secondary alcohols.Addition to ketones gives tertiary alcoholsReactions of R
14、MgX with EstersCarboxylic esters, RCO2R, react with 2 equivalents of organolithium or Grignard reagents to give tertiary alcoholsThe tertiary alcohol contains 2 identical alkyl groups与甲酸酯反应，产物为仲醇Reactions of RMgX with EpoxidesRing strain makes epoxides more reactive than simple ethersOrganolithium o
15、r Grignard reagents react with the carbonyl group, C=O, in aldehydes or ketones to give alcohols. Addition to methanal (formaldehyde) gives primary alcohols. Addition to other aldehydes gives secondary alcohols. Addition to ketones gives tertiary alcohols. The acidic work-up converts an intermediate
16、 metal alkoxide salt into the desired alcohol via a simple acid base reaction.SummaryStep 1: The nucleophilic C in the organometallic reagent adds to the electrophilic C in the polar carbonyl group, electrons from the C=O move to the electronegative O creating an intermediate metal alkoxide complex.Step 2: This is the work-up step, a simple acid/base reaction. Protonation of
