Oxidation States of Carbon Oxidation and Reduction in Biology

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Oxidation States of Carbon Oxidation and Reduction in Biology

Oxidation States of Carbon • Addition of H (or “H-”) Reduction 2 • Loss of O2 or O H R H H carboxylic aldehyde alcohol alkane acid (or ketone) • Loss of H 2 Oxidation • Addition of O2 or O + Neither oxidation nor reduction: Addition or loss of H , H2O, or HX Oxidation and Reduction in Biology • Addition of H (or “H-”) Reduction 2 • Loss of O2 or O + h, in plants H OH carbon dioxide e.gg,g., glucose H O 4 C-O bonds per C HO 1 C-O bond per C 0 C-H bond per C HO OH 1 C-H bond per C H OH H H +O+ O2, in animals • Loss of H 2 Oxidation • Addition of O2 or O + Neither oxidation nor reduction: Addition or loss of H , H2O, or HX Biological Oxidation Gone Wrong component of glue alcohol 2 NAD+ dehydrogenase 2 NADH gamma-hydroxybutyrate (GHB, an intoxicant/ date rape drug) Dr. Kevin Carpenter, biochemical geneticist (specialist in pediatric metabolic disorders), Children’s Hospital at Westmead (Sydney), Australia. Behind him: The Agilent GC/MS New York Times, Nov. 8, 2007 used to analyze the Aqua Dots. “Sleuthing for Danger in Toy Beads” Hydrides as Reducing Agents Lithium aluminum hydride (LiAlH4) is a strong reducing agent. It will reduce any C=O containing functional group to an alcohol. + 2. H3O 1. LiAlH4 (or just H2O) carboxylic acid primary alcohol andthd then ano ther equivalent adds, unavoidably. One Reduced by LiAlH : equivalent of 4 H- adds, aldehyde ketone carboxylic ester acyl halide amide acid Hydrides as Reducing Agents Sodium borohydride (NaBH4) is a mild reducing agent. It is only capable of reducing aldehydes and ketones to alcohols. NaBH4 EtOH aldehyde primary alhllcohol NaBH4 EtOH Reduced by NaBH4: ketone secondary alcohol aldehyde ketone Hindered Reducing Agents Stop At Aldehyde H Al Al (Chapter 21) O H O R OR' “DIBAL-H” R H ester alde hy de O R OH O carboxylic acid Li H Al O O O O R Cl (Chapter 21) LiAlH(OtBu)3 R H acyl halide aldehyde Strong Organic Oxidizers Chromate (LiAlH4) is a strong oxidizing agent; it oxidizes primary alcohols all the way to carboxylic acids, and secondary alcohols to ketones. Na2Cr2O7 unavoidably H2SO4 aldehyde carboxylic acid primary alcohol Na2Cr2O7 Cannot be oxidized further. H2SO4 ketone secondary alcohol Mild Organic Oxidizers Swern oxidation is a mild oxidation process; it oxidizes primary alcohols just to aldehydes (and not all the way to carboxylic acids). It also oxidizes secondary alcohols to ketones. 1. DMSO , -60 °C O O oxalyl chloride aldehyde primary alcohol Cl Cl 2. Et3N Wade describes PCC as Swern another mild oxidizing agent that achieves the same goal. oxidation The reagen ts an d was te ketone products from Swern oxidation secondary alcohol are much less toxic; no one uses PCC any more. Mild Organic Oxidizers Ag2O is a mild oxidizing agent; it interacts specifically with the C=O double bond (and not with alcohols), and oxidizes aldehydes to carboxylic acids. Na2Cr2O7 H2SO4 O O R H R OH aldehyde carboxylic acid 1Ag1. Ag2ONHO, NH3 + 2. H3O Biological Cofactors as Redox Agents Cofactor: A small-molecule “helper” that is required by an enzyme to catalyze a reaction. Many vitamins are cofactors. NADH reduces by acting as an H- donor enzyme NADH NAD+ (derived from niacin, vitamin B3) NAD+ oxidizes by acting as an H- acceptor.

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