Alcohols Phenols Thiols and Ethers Dr Michael P

Alcohols, Phenols, Thiols, and Ethers Dr. Michael P. Gillespie

Introduction • The characteristic functional group of alcohols and phenols is the hydroxyl group (-OH). • Alcohols have the general structure R-OH, in which R is any alkyl group. • Phenols have the general structure R-OH, in which R is an aryl group. • They are substituted water molecules in which one of the hydrogen atoms has been replaced by either an alkyl group or an aryl group.

Introduction • Ethers have two alkyl or aryl groups attached to the oxygen atom. • Thiols contain the sulfhydryl group (-SH). • Many important biological molecules, including carbohydrates, lipids, and proteins, contain hydroxyl and/or thiol groups.

Alcohols: Structure & Properties • Alcohols are characterized by the hydroxyl group (-OH). • They have the general formula R-OH. • The hydroxyl group is polar; therefore, alcohols are polar and form hydrogen bonds. This gives them higher boiling points. • Smaller alcohols are very water soluble.

Alcohols

Medically Important Alcohols • Methanol is a toxic alcohol that is used as a solvent. • Ethanol is the alcohol consumed in beer, wine, and distilled liquors. • Isopropanol is used as a disinfectant. • Ethylene glycol is used as antifreeze. • Glycerol is used in cosmetics and pharmaceuticals.

Classification of Alcohols • Alcohols can be classified as primary, secondary, or tertiary depending upon the number of alkyl groups attached to the carbinol carbon (the carbon bearing the hydroxyl group).

Preparation of Alcohols • Alcohols can be prepared by the hydration of alkenes or the reduction of aldehydes and ketones.

Dehydration of Alcohols • Dehydration of alcohols produces alkenes.

Dehydration of Alcohols

Oxidation Reactions • Primary alcohols undergo oxidation reactions to produce aldehydes. • Secondary alcohols undergo oxidation reactions to produce ketones. • Tertiary alcohols do not undergo oxidation.

Oxidation of Alcohols

Oxidation & Reduction in Living Systems • In organic and biological systems, oxidation involves the gain or loss of hydrogen. • Reduction involves the loss of oxygen or gain of hydrogen. • Nicotinamide adenine dinucleotide, NAD+, is a coenzyme involved in many biological oxidation and reduction reactions.

Phenols • Phenols are compounds in which the hydroxyl group is attached to a benzene ring. • The have the general formula Ar-OH. • Many phenols are important as antiseptics and disinfectants.

Phenol

Ethers • Ethers are characterized by the R-O-R functional group. • They are generally non-reactive, but are extremely flammable. • Diethyl ether was the first general antiseptic used in medicine. It has been replaced by Penthrane and Enthrane, which are less flammable.

Ether

Thiols • Thiols are characterized by the sulfhydryl group (-SH). • The amino acid cycteine is a thiol that is extremely important for maintaining the correct shapes of proteins. • Coenzyme A is a thiol that serves as a carrier of acetyl groups in biochemical reactions.

Thiols