A Fischer Esterification reaction is an acid-catalyzed nucleophilic acyl substitution reaction of a carboxylic acid with an alcohol. Benzococaine, a local anesthetic, is prepared by direct Fischer Esterification of p-aminobenzoic acid with ethanol, with the use of sulfuric acid as a catalyst. The carbonyl oxygen is protonated by sulfuric acid, and this activates the carboxylic acid. After protonation, the carbonyl oxygen holds a positive charge, which causes the oxygen atom to take up an electron pair from the double bond. This creates a positive charge on the carbonyl carbon, which then becomes a subject of nucleophile attack by the alcohol group of ethanol, yielding a tetrahedral intermediate. Hydrogen sulfate, the conjugate base of sulfuric
