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Reactions Involving Alcohols Review: dehydration dehydration (elimination) The removal of water from an alcohol to produce an alkene. For reaction that yield multiple possible products, the major product is predicted using Saytzeff’s Rule A simplified mechanism for dehydration follows: 1. Protonation of alcohol 3. The Resulting carbocation loses a hydrogen to the catalyst ion from an adjacent carbon to form an alkene while the catalyst is regenerated. 2. Loss of water resulting in carbocation formation You are not responsible for this mechanism Alcohol Reactions Dehydration Dehydration Synthesis (elimination) Under slightly different conditions, a dehydration reaction can occur between two alcohol molecules to produce an ether. dehydration synthesis occurs at lower temperatures than normal dehydration and results in the formation of a new functional group. Alcohol Reactions, cont. Oxidation – Oxidation reactions occur when a molecule gains an oxygen, loses a hydrogen or loses electrons. Under the right conditions, alcohols can by oxidized by removing two hydrogen atoms from the same molecule, one from a hydroxyl group and the second from the carbon of the hydroxyl group, resulting in the formation of a double bond between the carbon and remaining oxygen atoms. Alcohol oxidations will occur in the presence of an oxidizing (O) agent: •K2Cr2O7 and KMnO4 are common oxidizing agents 1 Alcohol Reactions, cont. Primary Primary alcohol oxidation •A primary alcohol can undergo a two step reaction: –In the first reaction, the alcohol loses two hydrogen atoms to form a carbonyl group on a terminal carbon by an oxidizing agent (O), creating an aldehyde. –In the second reaction, the newly formed aldehyde can undergo further oxidation when the remaining hydrogen one the carbonyl carbon is substituted with a hydroxyl forming a carboxyl group, creating a carboxylic acid. Alcohol Reactions, cont. Secondary Secondary alcohol oxidation •A secondary alcohol can only undergo one oxidation –the alcohol loses two hydrogen atoms to form a carbonyl group on an intermediate carbon, creating a ketone. – What about a tertiary alcohol? Reactions with Phenols Phenol behaves as a weak acid in water And can react with bases to form salt. 2