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Organic Chemistry
Table of Contents
Unit 17 Overview: Alcohols and Phenols
17.1 Naming Alcohols and Phenols
17.2 Properties of Alcohols and Phenols
17.3 Preparation of Alcohols: A Review
17.4 Alcohols from Carbonyl Compounds: Reduction
17.5 Alcohols from Carbonyl Compounds: Grignard Reaction
17.6 Reactions of Alcohols
17.7 Oxidation of Alcohols
17.8 Protection of Alcohols
17.9 Phenols and Their Uses
17.10 Reactions of Phenols
17.11 Spectroscopy of Alcohols and Phenols

Alcohol oxidation is a crucial process in organic chemistry, transforming primary, secondary, and tertiary alcohols into different products. Primary alcohols can become aldehydes or carboxylic acids, while secondary alcohols form ketones. Tertiary alcohols, however, resist oxidation.

The mechanism involves hydride transfer and oxygen addition, creating carbonyl groups. Various oxidizing agents like chromic acid, PCC, and Swern oxidation are used. In biology, coenzymes NAD+ and NADP+ play key roles in alcohol oxidation, essential for metabolic processes.

Oxidation Products of Alcohols

Oxidation products of alcohol types

  • Primary alcohols ($RCH_2OH$) undergo two-stage oxidation process
    • Mild oxidation converts primary alcohols to aldehydes ($RCHO$) with chromium(VI) oxide or pyridinium chlorochromate (PCC)
    • Strong oxidation further oxidizes aldehydes to carboxylic acids ($RCOOH$) using potassium permanganate or chromic acid
  • Secondary alcohols ($R_2CHOH$) oxidize to ketones ($R_2C=O$)
    • Oxidation stops at ketone stage due to lack of α-hydrogens on carbonyl carbon
    • Typical oxidizing agents include chromic acid, PCC, or Swern oxidation (DMSO, oxalyl chloride, triethylamine)
  • Tertiary alcohols ($R_3COH$) generally resistant to oxidation
    • Lack of hydrogen atoms on hydroxyl-bearing carbon prevents hydride transfer
    • May undergo elimination (dehydration) or substitution reactions instead of oxidation

Mechanism of alcohol oxidation

  • Involves removal of hydride ($H^-$) from carbon bearing hydroxyl group
    • Hydride ion transferred to oxidizing agent, reducing it
    • Oxygen atom from oxidizing agent simultaneously transferred to carbon, forming carbonyl group (aldehyde or ketone)
  • Common oxidizing agents and their mechanisms:
    1. Chromic acid ($H_2CrO_4$): Strong oxidant prepared from sodium dichromate ($Na_2Cr_2O_7$) and sulfuric acid ($H_2SO_4$); oxidizes primary alcohols to carboxylic acids via aldehyde intermediate
    2. Pyridinium chlorochromate (PCC): Milder oxidant; selectively oxidizes primary alcohols to aldehydes without over-oxidation to carboxylic acids
    3. Swern oxidation: Uses DMSO activated by oxalyl chloride and triethylamine; oxidizes primary alcohols to aldehydes and secondary alcohols to ketones
    4. Dess-Martin periodinane (DMP): Hypervalent iodine compound; mild and selective oxidant for converting primary alcohols to aldehydes and secondary alcohols to ketones

Biological oxidation of alcohols

  • Coenzymes NAD+ (nicotinamide adenine dinucleotide) and NADP+ (phosphorylated form) are essential electron acceptors in biological oxidation reactions
    • Reduced to NADH and NADPH, respectively, during alcohol oxidation
  • Alcohol dehydrogenases (ADH) catalyze oxidation of alcohols using NAD+/NADP+ coenzymes
    1. Hydride ($H^-$) transferred from alcohol to NAD+/NADP+, forming NADH/NADPH
    2. Primary alcohols oxidized to aldehydes; secondary alcohols to ketones
  • Aldehyde dehydrogenases (ALDH) further oxidize aldehydes to carboxylic acids using NAD+ coenzyme
  • Reduced coenzymes (NADH, NADPH) important in metabolic pathways
    • NADH oxidized in electron transport chain to generate ATP (cellular energy currency)
    • NADPH used in biosynthetic reactions (fatty acid synthesis, steroid hormone production)

Redox reactions in alcohol oxidation

  • Oxidation of alcohols involves electron transfer from the alcohol to the oxidizing agent
  • Oxidizing agents (e.g., chromic acid, PCC) accept electrons, becoming reduced in the process
  • Alcohols are oxidized to carbonyl compounds (aldehydes or ketones) through loss of electrons
  • The overall process is a redox reaction, with the alcohol acting as the reducing agent and the oxidizing agent as the electron acceptor

Key Terms to Review (36)

Hydride shift: A hydride shift is a rearrangement process where a hydrogen atom with its pair of electrons moves from one carbon to an adjacent carbocation center, stabilizing the molecule during electrophilic additions. This mechanism is key in understanding how carbocations can rearrange to form more stable intermediates in reactions involving alkenes.
Carboxylic acids, RCO2H: Carboxylic acids are organic compounds characterized by the presence of a carboxyl group (-COOH), where "R" represents an alkyl or aryl group attached to the carbon atom of the carboxyl group. They are known for being acidic due to the ability of the hydroxyl (OH) part of the carboxyl group to release a proton (H+).
Dess–Martin periodinane: Dess–Martin periodinane is a chemical reagent used in organic chemistry for the oxidation of primary and secondary alcohols to aldehydes and ketones, respectively, without overoxidizing to carboxylic acids. It is favored for its mildness and selectivity in these transformations.
Ketones: Ketones are organic compounds characterized by a carbonyl group (C=O) bonded to two other carbon atoms within the molecule. They are formed by the oxidation of secondary alcohols.
Alcohols: Alcohols are organic compounds containing a hydroxyl (-OH) functional group attached to a saturated carbon atom. They are widely used in various chemical reactions and have diverse applications in industry, medicine, and everyday life.
Carboxylic Acids: Carboxylic acids are a class of organic compounds containing a carboxyl functional group (-COOH) attached to an alkyl or aryl group. They are characterized by their acidic properties and play a crucial role in various chemical reactions and biological processes.
Carbonyl Compounds: Carbonyl compounds are a class of organic compounds that contain a carbon-oxygen double bond (C=O), known as the carbonyl group. This functional group is found in a variety of important molecules, including aldehydes, ketones, carboxylic acids, esters, and amides, which are all integral to many organic chemistry topics and reactions.
Ketones: Ketones are a class of organic compounds containing a carbonyl group (C=O) bonded to two alkyl or aryl groups. They are characterized by the presence of a carbonyl carbon flanked by two carbon atoms. Ketones are important in various organic chemistry topics, including chirality, oxidation reactions, mass spectrometry, infrared spectroscopy, and NMR spectroscopy.
Aldehydes: Aldehydes are a class of organic compounds characterized by the presence of a carbonyl group (C=O) with a hydrogen atom attached to the carbon. They are important intermediates in many chemical reactions and have a wide range of applications in various industries, from pharmaceuticals to fragrances.
Hydride: A hydride is a compound in which hydrogen is bonded to a more electropositive element, such as a metal or a metalloid. Hydrides play a crucial role in various organic chemistry reactions, including the hydration of alkenes, the oxidation of alcohols, the nucleophilic addition of hydrides and Grignard reagents, and the chemistry of esters.
Oxidation: Oxidation is a fundamental chemical process in which a substance loses electrons, resulting in an increase in its oxidation state. This term is central to understanding various reactions and transformations in organic chemistry, from the hydration of alkenes to the oxidation of alcohols and aldehydes.
Potassium Permanganate: Potassium permanganate is a strong oxidizing agent with the chemical formula KMnO4. It is a dark purple crystalline solid that is widely used in various chemical reactions and processes due to its powerful oxidizing properties.
PCC: PCC, or Pyridinium Chlorochromate, is a versatile oxidizing agent used in organic chemistry for the selective oxidation of alcohols to aldehydes and ketones. This powerful reagent is widely employed in various reactions across multiple topics, including the hydration of alkynes, the oxidation of alcohols, and the preparation and oxidation of aldehydes and ketones.
Oxidizing Agents: Oxidizing agents, also known as oxidants, are substances that have the ability to oxidize other substances by removing electrons from them. They play a crucial role in various organic chemistry reactions, including the oxidative cleavage of alkynes, the oxidation of aromatic compounds, the oxidation of alcohols, the preparation of aldehydes and ketones, and the preparation of carboxylic acids.
Tertiary Alcohols: Tertiary alcohols are a class of organic compounds where the hydroxyl (-OH) group is attached to a carbon atom that is connected to three other carbon atoms. This unique structural feature gives tertiary alcohols distinct properties and reactivity patterns compared to primary and secondary alcohols.
Secondary Alcohols: Secondary alcohols are organic compounds in which the hydroxyl group (-OH) is attached to a carbon atom that is bonded to two other carbon atoms. This structural feature distinguishes secondary alcohols from primary alcohols, where the hydroxyl group is attached to a terminal carbon, and tertiary alcohols, where the hydroxyl group is attached to a carbon with three other carbon substituents.
Primary Alcohols: Primary alcohols are organic compounds with the hydroxyl (-OH) functional group attached to the first (primary) carbon atom of an alkyl chain. These alcohols are important intermediates in various organic reactions, including the preparation of alkyl halides, the oxidation of alcohols, and the synthesis of carboxylic acids.
Swern Oxidation: The Swern oxidation is a chemical reaction used to convert primary and secondary alcohols into aldehydes and ketones, respectively. It is a mild and selective method for the oxidation of alcohols without over-oxidation to carboxylic acids.
Chromic Acid: Chromic acid, also known as chromium(VI) oxide, is a strong oxidizing agent commonly used in organic chemistry. It is a bright orange-red crystalline compound with the chemical formula CrO3, which can be used to oxidize various organic compounds.
Electron Transfer: Electron transfer is the fundamental process in which an electron moves from one atom or molecule to another, resulting in the oxidation of one species and the reduction of another. This process is central to many chemical reactions, including those involved in organic chemistry and the oxidation of alcohols.
Sodium Dichromate: Sodium dichromate, also known as sodium bichromate, is an inorganic compound with the chemical formula Na2Cr2O7. It is a powerful oxidizing agent that has various applications in organic chemistry, particularly in the oxidation of alcohols, the preparation of aldehydes and ketones, and the preparation of carboxylic acids.
Aldehyde Dehydrogenases: Aldehyde dehydrogenases are a group of enzymes that catalyze the oxidation of aldehydes to carboxylic acids, playing a crucial role in the metabolism of alcohols and other organic compounds. These enzymes are essential in the detoxification of acetaldehyde, an intermediate in the breakdown of ethanol.
Alcohol Dehydrogenases: Alcohol dehydrogenases (ADHs) are a group of enzymes that catalyze the oxidation of alcohols to aldehydes or ketones, playing a crucial role in the metabolism of alcohols in both plants and animals. These enzymes are particularly relevant in the context of the oxidation of alcohols and biological reductions.
NAD+: NAD+ (Nicotinamide Adenine Dinucleotide) is an essential coenzyme involved in numerous metabolic processes within the body. It plays a crucial role in the oxidation of organic compounds, serving as an electron acceptor in various redox reactions.
NADH: NADH, or nicotinamide adenine dinucleotide, is a coenzyme that plays a crucial role in numerous metabolic processes within the body. It is the reduced form of NAD+, an important electron carrier that is involved in oxidation-reduction reactions throughout the cell's energy-producing pathways.
Redox Reactions: Redox reactions, or reduction-oxidation reactions, are a class of chemical reactions where the oxidation state of atoms is changed. They involve the transfer of electrons between chemical species, with one substance losing electrons (being oxidized) and another gaining electrons (being reduced).
Chromium(VI) oxide: Chromium(VI) oxide, also known as chromium trioxide, is a highly oxidizing chemical compound consisting of chromium and oxygen. It is an important industrial chemical with a wide range of applications, particularly in the context of the oxidation of alcohols.
Pyridinium Chlorochromate: Pyridinium chlorochromate (PCC) is an oxidizing agent commonly used in organic chemistry for the selective oxidation of alcohols to aldehydes and ketones. It is a versatile reagent that plays a key role in the preparation and oxidation of carbonyl compounds.
DMP: DMP, or Dimethyl Phosphate, is a chemical compound that plays a crucial role in the oxidation of alcohols, a key topic covered in section 17.7 of the organic chemistry curriculum. DMP is a versatile reagent used in various organic reactions and is particularly important in the context of alcohol oxidation.
NADPH: NADPH, or Nicotinamide Adenine Dinucleotide Phosphate, is a coenzyme that plays a crucial role in various metabolic processes, including the oxidation of alcohols, the biosynthesis of steroids, and the biosynthesis of fatty acids. It serves as a reducing agent, providing the necessary electrons for these important chemical reactions within the cell.
Triethylamine: Triethylamine is a colorless, flammable liquid with a distinctive fishy odor. It is a tertiary amine, meaning it has three ethyl groups attached to a central nitrogen atom. Triethylamine is a commonly used organic compound in various chemical reactions and processes, particularly in the context of oxidation of alcohols, protection of alcohols, and the chemistry of amides.
Oxalyl Chloride: Oxalyl chloride is a highly reactive organic compound with the chemical formula (COCl)2. It is commonly used as a reagent in organic synthesis, particularly in the oxidation of alcohols to aldehydes or ketones.
Dess-Martin periodinane: The Dess-Martin periodinane is a mild, selective, and efficient oxidizing agent used to convert primary and secondary alcohols into aldehydes and ketones, respectively, in organic synthesis. It is a versatile reagent that can be used in a variety of oxidation reactions.
NADP+: NADP+ (Nicotinamide Adenine Dinucleotide Phosphate) is an important coenzyme involved in various metabolic processes, particularly in the context of the oxidation of alcohols. It serves as an electron acceptor and plays a crucial role in redox reactions, facilitating the transfer of hydrogen atoms and electrons during chemical transformations.
Jones Oxidation: The Jones oxidation is a chemical reaction used to selectively oxidize primary and secondary alcohols to their corresponding aldehydes and ketones, respectively. It is a powerful tool in organic chemistry for the controlled conversion of alcohols to carbonyl compounds.
DMSO: DMSO, or dimethyl sulfoxide, is a highly polar organic solvent known for its ability to dissolve both polar and nonpolar compounds. Its unique properties make it a valuable reagent in various chemical reactions, particularly in nucleophilic substitution processes, where it enhances the solubility of reactants and facilitates the formation of intermediates.