The reaction between acetic acid CH3COOH and thionyl chloride SOCl2 to form acetyl chloride CH3COCl is an acid-chloride formation reaction. The mechanism of this reaction can be described in the following steps:1. Nucleophilic attack: The oxygen atom of the carbonyl group C=O in acetic acid acts as a nucleophile and attacks the electrophilic sulfur atom in thionyl chloride SOCl2 . This forms a tetrahedral intermediate with a positive charge on the oxygen atom.2. Rearrangement: One of the chloride ions Cl- from thionyl chloride acts as a leaving group, and the sulfur-oxygen bond breaks, releasing a molecule of sulfur dioxide SO2 and forming a positively charged intermediate with a chlorine atom attached to the carbonyl carbon.3. Deprotonation: The positively charged oxygen atom abstracts a proton from the adjacent -OH group, which in turn forms a bond with the chloride ion Cl- that was released earlier. This leads to the formation of acetyl chloride CH3COCl and a molecule of hydrogen chloride HCl .Overall, the reaction can be summarized as:CH3COOH + SOCl2 CH3COCl + SO2 + HClThis reaction is commonly used to convert carboxylic acids into their corresponding acid chlorides, which are important intermediates in organic synthesis.