ArndtEistert

The Arndt-Eistert synthesis is a method in organic chemistry used to lengthen a carbon chain by one methylene group (CH2). It is particularly useful for converting a carboxylic acid into its next higher homologue, meaning a carboxylic acid with one additional carbon atom. The process typically involves three main steps. First, the carboxylic acid is converted into its acid chloride, usually by reaction with thionyl chloride or oxalyl chloride. Second, the acid chloride is reacted with diazomethane (CH2N2) to form a diazoketone. This step is often considered the most hazardous due to the toxicity and explosive nature of diazomethane. Finally, the diazoketone is treated with a silver catalyst (such as silver oxide or silver benzoate) in the presence of water or an alcohol. This causes a Wolff rearrangement, followed by hydrolysis (if water is used) or esterification (if an alcohol is used), yielding the desired carboxylic acid or ester, respectively, with the lengthened carbon chain. The Arndt-Eistert synthesis is a valuable tool for synthesizing a variety of organic compounds, particularly in cases where direct chain elongation is difficult.