《有机合成氧化》PPT课件.ppt

第二章 氧化反应氧化反应定义和分类定义：有机分子中的碳原子失去电子或碳氧化数增加称氧化反应。分类：催化氧化和催化脱氢化学氧化电解氧化催化氧化与催化脱氢一、催化氧化 均相催化氧化-氧气通入带有催化剂的液态反应物中，均相催化一般为自由基反应。均相催化剂：乙酸钴，丁酸钴，乙酸锰催化氧化与催化脱氢非均相催化氧化-反应物蒸气与氧气接触，通过固体催化剂。反应步骤：1.反应物在催化剂表面的扩散2.吸附3.吸附后产生氧化反应，放热 4.脱附5.扩散催化氧化与催化脱氢非均相催化剂：V2O5、钼的氧化物、银、钯等金属。实例：催化氧化与催化脱氢影响催化氧化的因素：1.结构：2.位阻效应使伯醇 比仲醇易氧化3.环上多元醇催化氧化往往发生在竖直键上的羟基。催化氧化与催化脱氢介质的影响一般指PH的影响，伯醇在中性介质中氧化为醛，在碱性介质中氧化为酸催化剂的影响催化氧化与催化脱氢二、催化脱氢催化脱氢-有机物在催化剂的作用下，受热分解脱去一分子的氢。实例：苯乙烯的制备：化学氧化反应化学氧化-即用化学氧化剂使有机物氧化，氧化剂的用量按氧化计量计算。氧化剂的种类：通用氧化剂：氧化能力强，选择性差，例如：KMnO4 K2Cr2O7。专用氧化剂：氧化能力弱，选择性强，例如：Hg(Ac)2、CrO3、SeO2、Pb(Ac)4H2O2一、过氧化物1、过氧化氢它是一种弱酸性的温和氧化剂。市售为30%的H2O2。作为高能燃料有90%，有机过氧化物制备常用过氧化氢。过氧化物作为氧化剂，主要氧化双键，生成环氧化物和二元醇。酸性介质中的历程碱性介质中历程2、有机过氧酸 通式：RCOOOH氧化能力最强的为CF3COOOH。过氧酸的氧化作用，主要用于烯烃的环氧化，邻二羟基化，羰基的酯化和胺、硫醚的氧化。A、氧化烯烃二种条件下的产物：有质子介质中，通常在无机酸作用下与过氧酸反应得到反式二醇氧化烯烃无质子介质中得到环氧烷B、羰基酯化Baeyer-Villiger反应反应式：历程：烷基重排中与亲核性大小有关亲核性越大重排也就越容易发生。烷基中：叔丁基仲丁基丙基芳基：对甲氧基苯苯硝基苯总体为：叔烷基仲烷基苯环己基伯烷基C、胺和硫醚的氧化C、胺和硫醚的氧化硫醚氧化为亚砜和砜二、锰化合物1、高锰酸钾用于芳环或杂环的侧链氧化，最终产物为苯甲酸或杂环取代甲酸，氧化反应中电子云密度大的易氧化。用于烯烃的氧化可得到相应的酮或酸，环烯氧化可得到1,6-二氧化物二、锰化合物2、活性二氧化锰活性二氧化锰适应于氧化烯丙醇，苄醇 制备-不饱和醛、酮。二、锰化合物三、铬酸及其衍生物1、铬酸 H2Cr04 是一种通用氧化剂，主要用于芳烃的侧链氧化，醇的氧化。酸性介质中：侧链氧化为酸中性介质中：可使侧链保留碳数氧化弱酸性介质：不是将侧链氧化而是氧化得到醌。三、铬酸及其衍生物2、铬酸衍生物铬酸衍生物是一类具有选择性氧化特点，不同的衍生物具有不同的选择性A、醋铬混合酐CrO2(OAc)2制备：铬酐分批加到醋酐中主要用于芳醛的制备。三、铬酸及其衍生物B、铬酰氯CrO2Cl2CrO3+2HCl CrO2Cl2+H2O三、铬酸及其衍生物B、铬酰氯CrO2Cl2C、铬酸叔丁酯制备：三氧化铬加叔丁醇用于烯丙基的氧化得不饱和醛、酮D、铬酐吡啶复合物优点：选择性强，温和氧化剂，对酸敏感的基团不影响，选择氧化烯丙位亚甲基。四、硝酸硝酸是一类强氧化剂，稀硝酸氧化能力更强，与KMnO4有同样的作用。五、含卤氧化剂常用的含卤氧化剂：NaOCl、HIO4、FeCl3、NBS、NBA、NCA1、NaOCl氧化能力强，选择性差、与HNO3氧化能力差不多。2、高碘酸氧化1,2-二醇，-氨基醇，-羟基酮并定量反应操作简单，可用于定量分析。刚性的环状二醇，反式异构体不反应，因为历程中形成环酯过渡态。3.三氯化铁是一类弱氧化剂，对多元酚、芳胺的氧化，产物为醌。4、N-溴代丁二酰亚胺类是一类选择性较强的氧化剂，并且选择性与溶剂的关。在含水丙酮中选择性强，但叔丁醇溶剂中，氧化能力强，选择性差，主要是与Br+离子产生的量有关例如：六、二氧化硒二氧化硒是一种有毒的白色固体，于340熔化，可在常温下升华，可用于多种有机物的氧化。用途：醛、酮 1,2-二羰基化合物1,4-二酮 2,3-不饱和1,4-二酮烯 烯丙醇七、四乙酸铅四乙酸铅是一种晶体固体，mp175180，迂水和醇会迅速反应。忌用溶剂：水、醇、常用溶剂：冰醋酸、苯、氯仿、二氯甲烷、三氯乙烯、硝基苯、乙腈八、二甲亚砜二甲亚砜是一种非质子性溶剂，与许多溶剂可混溶，主要用于氧化的是：活性卤化物、羰基化合物、生物碱、糖 类。1.1 Oxidation with chronium(VI)Chromium trioxide in acetone:Jones OxidationAcetone as a cosolventChromium trioxideDilute sulfuric acidExampleChromium trioxide-pyridine:Sarret oxidationUseful for the general oxidation of primary and secondary alcohols.Alkene,ketals and sulfide are oxidized much slower than alcohols.Drawback:Isolation of product from the pyridine solution is very difficult.Collins oxidationA modification of Sarret oxidation:the chromium trioxide pyridine complex is first removed from the pyridine solution and added to dichloromethane.Advantages:facilitate isolation;improved yields of primary alcohol to aldehydes.Pyridinium Chlorochromate(PCC)Superior for the conversion of primary alcohols to aldehyde but less efficient than the Collins regent for the oxidation of allylic alcohols.Preparation:Addition of pyridine to the solution of chromium trioxide in the aqueous HCl results pyridium chlorochromate(PCC).Pyridinium dichromate(PDC)Superior to the oxidation of allylic alcohols.Neutral regent pyridinium dichromate1.2 Dimethyl sulfoxide oxidationProblems:Alcohols bearing sensitive functional groups require neutral oxidizing conditions;and PCC or PDC give poor yields to some oxidation reactions(hindered alcohols).DMSO with mild base leads to removal of appropriate hydrogen and expulsion of DMS generates ketones and aldehydes from alcohols.Modification of DMSO oxidation:Swern oxidationSwern found that DMSO can be activated for the oxidation of alcohols by addition of trifluoroacetic anhydride.The reaction is usually done in dichloromethane at temperatures below-30.Swern oxidationSwern also found that oxalyl chloride activates DMSO for the oxidation of alcohols and the resulting regent is superior to the DMSO-trifluoroacitic anhidride regent.Moffatt OxidationMoffatt functionalized the DMSO with DCC in the present of an acids and a mild and efficient oxidizing regent for alcohols is formed.ExampleOther examplesExample 1.3 Other metal oxidantsTetropropylammonium perruthenate-Ley oxidation:a very mild oxidizing agent that is compatible with many sensitive functional groups.Oppenauer oxidationOppenauer used aluminum alkoxide to oxidize the alcohol to ketone.The character of this reaction is the reversibility.Side reaction:migration of a non-conjugated double bond into conjugation;and an acid catalyzed aldol condensation.ExampleCyclopentadienyl zirconium regent is an effective catalyst to the Oppenauer oxidation.Oxidation with manganese dioxideManganese dioxide is capable of oxidizing alcohols to ketones or aldehydes,especially for allylic and benzylic alcohols.The reaction proceeds via a radical intermediate.Examples ExampleOxidation with silverSilver carbonate:Saturated primary and secondary alcohols can be converted to aldehydes or ketones.Polar solvent inhibit the reaction;hindered alcohols show a reduced activity.Fetizons RegentFetizon found that reaction of primary alcohol give excellent yields of the corresponding aldehyde when silver carvonate is condensed on Celite.Silver(I)oxideSelective oxidation of aldehydes to carboxylic acids.ExampleSilver(II)oxideSilver(II)oxide can convert aldehyde or alcohols to carboxylic acids.The isomerization of conjugated double bond is avoided.1.4 Other oxidation regentsDess-Martin periodinane oxidationMild oxidizing regent for converting alcohols or aldehydes to ketones under neutral condition.ExampleOxidation with oxammonium saltThis regent is compatible for the mild oxidation of many alcohols,including alipharic primary and secondary as well as allylic and benzylic alcohol.One group disconnectionsExample ExampleExampleExample1.Epoxides from halohydrinsHalohydrins can be synthesized by the reaction of alkenes and hypohalous.Subsequent treatment of with a base such as sodium hydride generates the alkoxide,which is anti-to the adjacent bromine.2.Peroxides induced epoxidationsHydrogen peroxideAlkyl hydroperoxidesOrganic peroxyacidsHydrogen peroxideSolvent:Water or water miscible solventsMetal catalysts:V2O5,WO3,MoO3HThe hydroxyl moiety can be faster than the oxidation of alkene moiety.