The Appel Reaction is a chemical transformation involving the conversion of alcohols into alkyl halides through the use of triphenylphosphine (Ph3P) and a halogenating agent, commonly carbon tetrachloride (CCl4). The process typically involves the nucleophilic substitution of the hydroxyl group in the alcohol with a halide ion, resulting in the formation of an alkyl halide. This reaction is particularly useful for the preparation of alkyl halides from various types of alcohols and is widely employed in organic synthesis. The Appel Reaction is named after the chemist Werner E. Appel, who developed this method in the 1970s.