Oxidation of 2 Alcohols 。2° alcohol becomes a ketone. OH NazCr2O/H,SO R-CH-R' R -R ·Oxidizing agent is secondary alcohol ketone Na2Cr207/H2S04: Example H ·Active reagent NazCr2O7 OH H,S04 probably is H2CrO4. cyclohexanol cyclohexanone (90%) ·Color change is orange to greenish- blue. Chapter 11 6
Chapter 11 6 Oxidation of 2° Alcohols • 2° alcohol becomes a ketone. • Oxidizing agent is Na2Cr2O7 /H2SO4 . • Active reagent probably is H2CrO4 . • Color change is orange to greenishblue
Oxidation Mechanism Formation of the chromate ester R一CO一H H-O-Cr-OH R OH H 0 alcohol chromic acid chromate ester Elimination of the chromate ester and oxidation of the carbinol carbon R R R OH R-C ' H2O:H .0. H.O 0 Cr(VI) Cr(IV) Copyright2010 Pearson Prentice Hall,Inc. Chapter 11 7
Chapter 11 7 Oxidation Mechanism
Oxidation of 1 Alcohols to Carboxylic Acids CH,OH C一OH NaCr2O7 H2SO4 cyclohexyl methanol cyclohexanecarboxylic acid (92%) Chromic acid reagent oxidizes primary alcohols to carboxylic acids. The oxidizing agent is too strong to stop at the aldehyde. Chapter 11 8
Chapter 11 8 Oxidation of 1° Alcohols to Carboxylic Acids • Chromic acid reagent oxidizes primary alcohols to carboxylic acids. • The oxidizing agent is too strong to stop at the aldehyde
Pyridinium Chlorochromate (PCC) Pyridinium chlorochromate (PCC). CrO,C1 CrO3'pyridine·HCI or pyH+CrOCI- Copyright010Pearson Prne Hall Inc PCC is a complex of chromium trioxide, pyridine,and HCI. Oxidizes primary alcohols to aldehydes. Oxidizes secondary alcohols to ketones. Chapter 11 9
Chapter 11 9 Pyridinium Chlorochromate (PCC) • PCC is a complex of chromium trioxide, pyridine, and HCl. • Oxidizes primary alcohols to aldehydes. • Oxidizes secondary alcohols to ketones
Pyridinium Chlorochromate (PCC) OH CrO3'pyridine-HCI(PCC) R一C一H R- 一H CH2Cl2 H primary alcohol aldehyde Example 0 PCC CH3(CH2)s-CH2OH CH2C12 CH3(CH2)5-C一H 1-heptanol heptanal(78%) Copyright2010 Pearson Prentice Hall,Inc. Chapter 11 10
Chapter 11 10 Pyridinium Chlorochromate (PCC)