Organic Chemistry 4 th Edition Paula Yurkanis Bruice
Organic Chemistry 4 th Edition Paula Yurkanis Bruice Chapter 20 More About Oxidation–Reduction Reactions Irene Lee Case Western Reserve University Cleveland, OH © 2004, Prentice Hall
• 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
Hydrogen, sodium borohydride, and hydrazine are the reducing agents
Bromine and chromic acid are the oxidizing agents
H 2 as a Reducing Agent
Reduction by Catalytic Hydrogenation
Dissolving-Metal Reduction
Reduction by Addition of a Hydride Ion and a Proton
Li. Al. H 4 is a stronger reducing agent than Na. BH 4 Li. Al. H 4 is used to reduce compounds that are nonreactive toward Na. BH 4
DIBAL allows the addition of one equivalent of hydride to an ester Replacing some of hydrogens of Li. Al. H 4 with OR groups decreases the reactivity of the metal hydride
Formation of Amines by Reduction
Na. BH 4 can be used to selectively reduce an aldehyde or a keto group in a compound
Oxidation of Alcohols
Oxidation of a Primary Alcohol
Mechanism of Alcohol Oxidation by Chromic Acid
The oxidation of a primary alcohol can be stopped at the aldehyde if pyridinium chlorochromate (PCC) is used as the oxidizing agent
The Swern Oxidation
Mechanism of the Swern Oxidation
Oxidation of Aldehydes and Ketones
The Tollens Reagent Oxidizes Only Aldehydes
Both aldehydes and ketones can be oxidized by peroxyacid: The Baeyer–Villiger oxidation
Mechanism of the Baeyer–Villiger Oxidation
Therefore, the product of the Baeyer–Villiger oxidation of cyclohexyl methyl ketone will be cyclohexyl acetate, because a secondary alkyl group is more likely to migrate than a methyl group
Oxidation of Alkenes with Peroxyacids
Mechanism of Epoxidation of an Alkene
The addition of oxygen to an alkene is a stereospecific reaction
Hydroxylation of Alkenes
Mechanism for cis-Glycol Formation
Higher yields of the diol are obtained with osmium tetroxide
Oxidative Cleavage of 1, 2 -Diols
Oxidative Cleavage of Alkenes by Ozonolysis
The alkene and ozone undergo a concerted cycloaddition Mechanism of ozonide formation The molozonide is unstable because it has two O–O bonds Ozonide is stable
Ozonides can be cleaved to carbonyl compounds
Examples of the Oxidative Cleavage of Alkenes by Ozonolysis
A peroxyacid, Os. O 4, and (cold basic) KMn. O 4 break only the p bond of the alkene Ozone and acidic KMn. O 4 break both the p bond and the s bond
Table 20. 1 Summary of the Methods Used to Oxidize an Alkene
Oxidative Cleavage of Alkynes
Conversion of an Aldehyde into Other Functional Groups
Conversion of a Ketone into an Ester or an Alcohol
Biological Oxidation–Reduction Reactions
NAD+ oxidizes ethanol by accepting a hydride ion
NADH reduces a carbonyl compound by donating a hydride ion
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