{"id":1185,"date":"2018-11-28T16:47:51","date_gmt":"2018-11-28T16:47:51","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/?post_type=chapter&p=1185"},"modified":"2019-01-08T14:58:47","modified_gmt":"2019-01-08T14:58:47","slug":"19-7-oxidation-of-alkenes","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/chapter\/19-7-oxidation-of-alkenes\/","title":{"raw":"19.7. Oxidation of alkenes","rendered":"19.7. Oxidation of alkenes"},"content":{"raw":"

Dihydroxylation of alkenes<\/h2>\r\n
Alkenes are oxidized to cis<\/em>-1,2-diols by osmium tetroxide (OsO4<\/sub>)<\/strong>.\u00a0 The stereospecificity is due to the formation of a cyclic osmate ester intermediate.\u00a0 Osmium tetroxide can be used directly, but it is normally used in catalytic amounts, and is regenerated by N-methylmorpholine-N-oxide.\"image218.png\"\r\n
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Examples<\/h3>\r\n
\r\n\r\nQuestions:\r\n\r\n1. Give the major product.\r\n\r\n\"Problem\r\n\r\n2. What is the product in the dihydroxylation of (Z)-3-hexene?\r\n\r\n\"Problem\r\n\r\n3. What is the product in the dihydroxylation of (E)-3-hexene?\r\n\r\n\"Problem\r\n\r\n4. Draw the intermediate of this reaction.\r\n\r\n\"Problem\r\n\r\n5. Fill in the missing reactants, reagents, and product.\r\n\r\n\"Problem\r\n\r\n<\/div>\r\n
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Solutions<\/h3>\r\n[reveal-answer q=\"18923\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"18923\"]\r\n\r\n1. A syn-1,2-ethanediol is formed. There is no stereocenter in this particular reaction. The OH groups are on the same side.\r\n\r\n\"Answer\r\n\r\n2. Meso-3,4-hexanediol is formed. There are 2 stereocenters in this reaction.\r\n\r\n\"Answer\r\n\r\n3. A racemic mixture of 3,4-hexanediol is formed. There are 2 stereocenters in both products.\r\n\r\n\"Answer\r\n\r\n4. A cyclic osmic ester is formed.\r\n\r\n\"Answer\r\n\r\n5. The Diels-Alder cycloaddition<\/a> reaction\u00a0is needed in the first box to form the cyclohexene. The second box needs a reagent to reduce the intermediate cyclic ester (not shown). The third box has the product: 1,2-cyclohexanediol.\r\n\r\n\"Answer[\/hidden-answer]\r\n\r\n<\/div>\r\n
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Epoxidation of alkenes<\/h2>\r\nAlkenes can be oxidized to epoxides using a 'peroxyacid<\/strong>' such as m<\/em>-chloroperoxybenzoic acid (MCPBA). Notice the presence of a third oxygen in the peroxyacid functional group.\r\n\r\n\"image228.png\"\r\n\r\nThe mechanism was covered earlier in section 10.7<\/a>.\u00a0 The \u03c0 electrons in the alkene double bond attacking the 'outer' oxygen of the peroxyacid and cleaving the reactive O-O peroxide bond.\r\n\r\n\"image230.png\"\r\n\r\nUncatalyzed epoxidation of an asymmetric alkene generally results in two diastereomeric epoxide products, with the epoxide adding either from above or below the plane of the alkene.\r\n\r\n\"image232.png\"\r\n\r\nEpoxides are very useful intermediates in organic synthesis, as we learnt in section 9.6<\/a>.\r\n
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\r\n\r\nA reaction of immense industrial importance is the formation of oxacyclopropane itself (most often called ethylene oxide) by oxidation of ethene with oxygen over a silver oxide catalyst at $$300^\\text{o}$$:\r\n\r\n\"\"\r\n\r\nOxacyclopropane (ethylene oxide) is used for many purposes, but probably the most important reaction is ring opening with water to give 1,2-ethanediol (ethylene glycol, bp $$197^\\text{o}$$). This diol, mixed with water, is employed widely in automotive cooling systems to provide both a higher boiling and lower freezing coolant than water alone:\r\n\r\n\"\"\r\n
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\r\n\r\nExternal links<\/strong>\r\n\r\nCarey 5th Ed Online, <\/em>Epoxidation of Alkenes<\/a>\r\n\r\n<\/div>\r\n<\/section><\/div>\r\n
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Exercises<\/h3>\r\n
\r\n\r\n1. Predict the product of the reaction of cis-2-hexene with MCPBA (meta-chloroperoxybenzoic acid)\r\n\r\na) in acetone solvent.\r\n\r\n\"1_a.png\"\r\n\r\nb) in an aqueous medium with acid or base catalyst present.\r\n\r\n\"1_b.png\"\r\n\r\n2. Predict the product of the reaction of trans-2-pentene with magnesium monoperoxyphthalate (MMPP) in a chloroform solvent.\r\n\r\n\"2.png\"\r\n\r\n3. Predict the product of the reaction of trans-3-hexene with MCPBA in ether solvent.\r\n\r\n\"3.png\"\r\n\r\n4. Predict the reaction of propene with MCPBA.\r\n\r\na) in acetone solvent\r\n\r\n\"4a.png\"\r\n\r\nb) after aqueous work-up.\r\n\r\n\"4b.png\"\r\n\r\n5. Predict the reaction of cis-2-butene in chloroform solvent.\r\n\r\n\"5\r\n\r\n<\/div>\r\n
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Answers<\/h3>\r\n[reveal-answer q=\"935928\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"935928\"]\r\n\r\n1. \u00a0\u00a0\u00a0\u00a0a) Cis-2-methyl-3-propyloxacyclopropane\r\n\r\n\"1_a_ans.png\"\r\n\r\nb) Racemic (2R,3R)-2,3-hexanediol and (2S,3S)-2,3-hexanediol\r\n\r\n\"1_b_ans.png\"<\/a>\r\n\r\n2.\u00a0\u00a0\u00a0\u00a0 Trans-3-ethyl-2-methyloxacyclopropane.\r\n\r\n\"2_ans.png\"\r\n\r\n3.\u00a0\u00a0\u00a0\u00a0 Trans-3,4-diethyloxacyclopropane.\r\n\r\n\"3_ans.png\"\r\n\r\n4.\u00a0\u00a0\u00a0 a) 1-ethyl-oxacyclopropane\r\n\r\n\"4a_ans.png\"\r\n\r\nb) Racemic (2S)-1,2-propandiol and (2R)-1,2-propanediol\r\n\r\n\"4b_ans.png\"\r\n\r\n5. Cis-2,3-dimethyloxacyclopropane\r\n\r\n\"5_ans_4.png\"[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
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Contributors<\/h3>\r\n