2444-100711

2444-100711 - QUIZ 4 Avg. 17.5 / 25 Stnd. Dev. 6.3 Tape for...

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Unformatted text preview: QUIZ 4 Avg. 17.5 / 25 Stnd. Dev. 6.3 Tape for Mondays lecture: http: //mediasite .dl. uconn . edu/Mediasite /Viewer/ ?peid=763f7f1dcf7c4f47847418db9 171a3451d Ch2444F11 87254 Exam 2: Wed., Oct. 12. 7:30-9:30 A-M A-120 N-Z A-203 Oxidation of Alcohols with Chromium (VI): PCC & PDC 2 The reaction of chromium trioxide ( 5 ) with pyridine, in aqueous HCl generates a specific compound known as pyridinium chlorochromate (PCC, 31 ) that is isolated and purified. The CrO 3 forms HCrO 4 ( 6 ) in dilute aqueous acid, which reacts with HCl to form HCrClO 3 . Pyridine then reacts as a base with this acidic proton to form PCC. If the reaction conditions are modified to increase the amount of pyridine in the water solution. and the HCl is omitted, the reaction generates pyridinium dichromate (PDC, 32 ), presumably by reaction of an excess of pyridine with H 2 Cr 2 O 7 . In dilute solution, CrO 3 is in equilibrium with H 2 Cr 2 O 7 , and pyridine reacts with both acidic hydrogen atoms to produce PDC. N H N H 2-2 31 32 CrO 3 Cl Cr 2 O 7 Oxidation of Alcohols with Chromium (VI): PCC & PDC 3 Both PCC and PDC are less reactive than chromium trioxide in the Jones reagent, but they are very effective for converting primary alcohols to the aldehyde, in good yield and under mild conditions. Secondary alcohols are readily converted to ketones by both reagents. Dichloromethane is typically used as the solvent with both reagents. An example is the reaction of 2-cyclopentylethanol ( 33 ) and PCC in dichloromethane gave 1- cyclopentylethanal, 34 in 72% yield. The reaction of 4-propylcyclohexanol ( 35 ) and PDC, gives 4-propylcyclohexanone ( 36 ) in 97% isolated yield. PCC , CH 2 Cl 2 PDC , CH 2 Cl 2 33 35 OH CHO 72% OH O 36 34 Oxidation of Alcohols with Chromium (VI): PCC & PDC 3 Both PCC and PDC are less reactive than chromium trioxide in the Jones reagent, but they are very effective for converting primary alcohols to the aldehyde, in good yield and under mild conditions. Secondary alcohols are readily converted to ketones by both reagents. Dichloromethane is typically used as the solvent with both reagents. An example is the reaction of 2-cyclopentylethanol ( 33 ) and PCC in dichloromethane gave 1- cyclopentylethanal, 34 in 72% yield....
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2444-100711 - QUIZ 4 Avg. 17.5 / 25 Stnd. Dev. 6.3 Tape for...

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