{"id":1289,"date":"2018-11-28T16:59:36","date_gmt":"2018-11-28T16:59:36","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/?post_type=chapter&p=1289"},"modified":"2019-01-08T07:26:18","modified_gmt":"2019-01-08T07:26:18","slug":"20-2-addition-of-hydride-reducing-agents","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry2\/chapter\/20-2-addition-of-hydride-reducing-agents\/","title":{"raw":"20.2. Addition of hydride reducing agents","rendered":"20.2. Addition of hydride reducing agents"},"content":{"raw":"
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Nucleophilic Addition of H\u2013 and R\u2013\u2014A Review<\/span><\/h2>\r\n<\/div>\r\n<\/header>
Addition of a hydride anion (H:-<\/sup>) to an aldehyde or ketone gives an alkoxide anion, which on protonation yields the corresponding alcohol. This reaction was covered previously in section 19.3<\/a>.\u00a0 Aldehydes produce 1\u00ba-alcohols and ketones produce 2\u00ba-alcohols.\u00a0 In metal hydride reductions, the resulting alkoxide salts are insoluble and need to be protonated (with care) before the alcohol product can be isolated. In the sodium borohydride reduction the ethanol solvent system achieves this hydrolysis automatically. In the lithium aluminum hydride reduction water is usually added in a second step. The lithium, sodium, boron and aluminum end up as soluble inorganic salts at the end of either reaction.\u00a0 Note! LiAlH4<\/sub> and NaBH4<\/sub> are both capable of reducing aldehydes and ketones to the corresponding alcohol.\r\n
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Mechanism<\/h3>\r\nThis mechanism is for a LiAlH4<\/sub> reduction.\u00a0 The mechanism for a NaBH4<\/sub> reduction is the same except ethanol is the proton source used in the second step.\r\n\r\n1) Nucleophilic attack by the hydride anion\r\n\r\n\"Fix1.jpg\"\r\n\r\n2) The alkoxide is protonated\r\n\r\n\"Fix2.jpg\"\r\n\r\n<\/div>\r\n<\/div>\r\n
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Contributors<\/h3>\r\n