CHEM 3331 1nd Edition Lecture 24Outline of Last Lecture I. Organometallic compoundsII. Grignard reagentsIII. Addition to C=O bondsIV. Addition of H-V. thiolsOutline of Current Lecture I. OxidationII. Biological oxidationIII. Formation of sulfonate estersIV. Reduction of alcoholsV. Reaction of alcohols with HXCurrent LectureI. OxidationThere are plenty of reactions with alcohols, dehydrogenation yields alkenes, Sn2 reaction yields RX, reduction yields RH, oxidation yields a C=O bond.Oxidation in organic chemistry is the loss of hydrogen or the addition of an electronegative element (O,N, X). Reduction is the addition of hydrogen or the loss of and electronegative element.When an alkane is oxidized (adding O) it results in an alcohol, when oxidized again it yields a diolwhich is unstable and loses H2O forming an aldehyde, oxidized one last time it yields a carboxylic acid. Oxidation of secondary alcohols: oxidizing agents= Na2Cr2O7 or KMnO4.When an alcohol reacts with Na2Cr2O7 in H2SO4 it results in a ketone with 80-90% yield.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.The acid and oxidizing agent react together forming 2 moles of HO-Cr=(O)2-OH. When this reacts with the alcohol it loses water and the two compounds bond together forming a chromate ester. Since it is in an aqueous solution water acts as a base on the chromate ester and yields H3O+, R2C=O, and Cr-O,=O,-OH.Oxidation of primary alcohols: the alcohol reacts with the previous mixture of H2SO4 and Na2Cr2O7 to create an aldehyde which reacts with water in aqueous solution creating a diol. This diol reacts with remaining Cr2O7 to yield carboxylic acid. To stop this reaction at aldehyde we must not do the reaction in water. We do this by using PCC. Tertiary alcohols cannot be oxidized without breaking a C-C bond.The Swern oxidation: II. Biological OxidationIn nature there isn’t a surplus of Na2Cr2O7 to be used to oxidize alcohols. Alcohols are nucleophiles. Carbon is electrpphilic but OH- is a bad leaving group so alcohols act as a nucleophile. R-CH2-OH +HBr RCH2Br +H2O (-H2O) RCH2BrIII. Formation of Sulfonate estersThe sulfonate ester is named by its R group. Tosylate is the most common one used.IV. Reduction of alcoholsReduction of an alcohol is done through the use of sulfonate esters. Cyclopentanol reacts with TosCl to yield 1-TosO-cyclopentane which we react with LiAlH4 to achieve cyclopentane. We can also reduce cyclopentane using H2SO4 and high temperature to yield cyclopentene which reacts with H2/Pt to yield cyclopentane. This way is much more cost effective since most of the components are cheap or reusable. Whereas TosO is thrown away as waste and not reused. V. Reaction with HXR-OH +HX R-O(+)-H2 + X(-) (Sn1/Sn2) R-X + H2O(R)3COH +HBr (R)3CBr (Sn1)CH3(CH2)3OH +HBr CH3(CH2)3Br (Sn2)(R)3COH +HCl (R)3CCl with 98% yield. HCl works well with tertiary substrates but becomes slower with secondary and almost doesn’t react with primary. To speed up the reaction we use a mixture of HCl and ZnCl2. CH3(CH2)3OH + HCl/ZnCl2 CH3(CH2)3O-H,-ZnCl2 +Cl(-) CH3(CH2)3Cl + HOZnCl2Secondary reactions move faster but reactions with primary substrates still move slowly. Problems with Sn11) produce cation (rearrangement)2) competes with E13) HCl vs. ZnCl24) works poorly with alkyl
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