Ch_322b_22.04

Ch_322b_22.04 - Chemical Methodologies Oxidation Methods...

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Chemical Methodologies Oxidation Methods Bromine water (Br 2 /H 2 O) is a mild oxidant that selectively oxidizes aldehydes to carboxylic acids called aldonic acids . CHO Br 2 H 2 O COOH aldose aldonic acid Nitric acid is a strong oxidant that produces dicarboxylic acids called aldaric acids . CHO CH 2 OH aldose HNO 3 COOH COOH aldaric acid Periodic acid oxidatively cleaves 1,2-diols, etc. R-CH-CH-R' OH OH HIO 4 RCH + R'CH O = O
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Osazone Formation The reaction of aldoses with the reagent phenylhydrazine (discovered by Emil Fischer) identifies diastereomers that differ in configuration at C2. Stereoisomers with multiple stereocenters that differ in configuration at only one center are called epimer s. CHO OH H * CHO HO H * 3 eq. C 6 H 5 NHNH 2 3 eq. C 6 H 5 NHNH 2 HC=NNHC 6 H 5 C=NNHC 6 H 5 Aldoses that are epimeric at C-2 yield the same osazone. Osazone formation proceeds stepwise: H C=O H-C-OH C 6 H 5 NHNH 2 H C=N-NHC 6 H 5 H-C-OH phenylhydrazone C 6 H 5 NHNH 2 H C=N-NHC 6 H 5 C=O + C 6 H 5 NH 2 + NH 3 C 6 H 5 NHNH 2 H C=N-NHC 6 H 5 C=N-NHC 6 H 5 osazone
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This note was uploaded on 10/20/2009 for the course CHEM 322BL at USC.

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Ch_322b_22.04 - Chemical Methodologies Oxidation Methods...

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