© 2011 Pearson Education, Inc. 1 Organic Chemistry 6 th Edition Paula Yurkanis Bruice Chapter 20 More About Oxidation–Reduction Reactions

© 2011 Pearson Education, Inc. 2 Oxidation is always coupled with reduction. Loss of electrons is oxidation. Gain of electrons is reduction. The oxidation state of a carbon atom equals the total number of its C—O, C—N, and C—X bonds.

© 2011 Pearson Education, Inc. 3 Reduction at carbon increases the number of C—H bonds or decreases the number of C—O, C—N, or C—X bonds. Oxidation at carbon decreases the number of C—H bonds or increases the number of C—O, C—N, or C—X bonds.

© 2011 Pearson Education, Inc. 4 Hydrogen, sodium borohydride, and hydrazine are the reducing agents:

© 2011 Pearson Education, Inc. 5 Bromine and chromic acid are the oxidizing agents:

© 2011 Pearson Education, Inc. 6 H 2 as a Reducing Agent H 2, Pd on charcoalNa or Li metal in liq NH 3 NaBH 4 or LiAlH 4

© 2011 Pearson Education, Inc. 7 Reduction by Catalytic Hydrogenation Addition of two hydrogen atoms:

© 2011 Pearson Education, Inc. 8 Only the alkene substituted to benzene is reduced: Reduction of carbon–nitrogen double and triple bonds:

© 2011 Pearson Education, Inc. 9 Reduction of Ketones and Aldehydes

© 2011 Pearson Education, Inc. 10 Rosenmund Reduction

© 2011 Pearson Education, Inc. 11

© 2011 Pearson Education, Inc. 12 Dissolving-Metal Reduction Addition of an electron, a proton, an electron, and a proton:

© 2011 Pearson Education, Inc. 13 Reduction by Addition of a Hydride Ion and a Proton

© 2011 Pearson Education, Inc. 14 Aldehydes, ketones, and acyl halides can be reduced to alcohols by sodium borohydrides:

© 2011 Pearson Education, Inc. 15 LiAlH 4 is a stronger reducing agent than NaBH 4 LiAlH 4 is used to reduce compounds that are unreactive toward NaBH 4

© 2011 Pearson Education, Inc. 16 DIBALH allows the addition of one equivalent of hydride to an ester: Replacing some of the hydrogens of LiAlH 4 with –OR groups decreases the reactivity of the metal hydride:

© 2011 Pearson Education, Inc. 17 Formation of Amines by Reduction

© 2011 Pearson Education, Inc. 18 NaBH 4 can be used to selectively reduce an aldehyde or a keto group in a compound: Alkenes and alkynes do not possess a partial positive charge:

© 2011 Pearson Education, Inc. 19 Sodium borohydride can be used as a chemoselective reducing agent:

© 2011 Pearson Education, Inc. 20 Oxidation of Alcohols

© 2011 Pearson Education, Inc. 21 Oxidation of a Primary Alcohol

© 2011 Pearson Education, Inc. 22 Mechanism of Alcohol Oxidation by the Swern Oxidation

© 2011 Pearson Education, Inc. 23 Oxidation of Aldehydes and Ketones

© 2011 Pearson Education, Inc. 24 The Tollens reagent oxidizes only aldehydes:

© 2011 Pearson Education, Inc. 25 Both aldehydes and ketones can be oxidized by peroxyacid: the Baeyer–Villiger oxidation

© 2011 Pearson Education, Inc. 26

© 2011 Pearson Education, Inc. 27 Mechanism of the Baeyer–Villiger Oxidation

© 2011 Pearson Education, Inc. 28 Predicting Baeyer–Villiger reaction products:

© 2011 Pearson Education, Inc. 29 Controlling Stereochemistry in Synthesis An enantioselective reaction forms more of one enantiomer than of another:

© 2011 Pearson Education, Inc. 30

© 2011 Pearson Education, Inc. 31 Hydroxylation of Alkenes

© 2011 Pearson Education, Inc. 32 Mechanism for cis-Glycol Formation Higher yields of the diol are obtained with osmium tetroxide than with permaganate

© 2011 Pearson Education, Inc. 33 Oxidative Cleavage of 1,2-Diols

© 2011 Pearson Education, Inc. 34 Summary of Alkene Hydroxylation Reactions

© 2011 Pearson Education, Inc. 35 Permaganate Cleavage of Alkenes

© 2011 Pearson Education, Inc. 36 Examples of permaganate-mediated alkene cleavage reactions:

© 2011 Pearson Education, Inc. 37 Oxidative Cleavage of Alkenes by Ozonolysis Examples:

© 2011 Pearson Education, Inc. 38 Structure of Ozone

© 2011 Pearson Education, Inc. 39 The alkene and ozone undergo a concerted six-electron cycloaddition Mechanism of ozonide formation: The molozonide is unstable because it has two O—O bonds, but the ozonide is stable

© 2011 Pearson Education, Inc. 40 Ozonides can be cleaved to carbonyl compounds:

© 2011 Pearson Education, Inc. Ozonolysis Mechanism 41

© 2011 Pearson Education, Inc. 42 Examples of the Oxidative Cleavage of Alkenes by Ozonolysis

© 2011 Pearson Education, Inc. 43 The benzene ring is not oxidized under mild ozonolysis conditions:

© 2011 Pearson Education, Inc. 44 Oxidative Cleavage of Alkynes The same reagents that oxidize alkenes also oxidize alkynes:

© 2011 Pearson Education, Inc. 45 Designing a Synthesis by Functional Group Interconversion Conversion of an aldehyde to other functional groups:

© 2011 Pearson Education, Inc. 46 Conversion of a Ketone into an Ester or an Alcohol