The optimum ratio of p-aminobenzoic acid to ethanol in the preparation of benzocaine with maximum yield depends on the specific reaction conditions and the desired purity of the final product. However, a general guideline for the esterification reaction between p-aminobenzoic acid and ethanol to form benzocaine is to use a stoichiometric ratio of 1:1.In this reaction, one mole of p-aminobenzoic acid reacts with one mole of ethanol to produce one mole of benzocaine and one mole of water as a byproduct. To ensure maximum yield, it is crucial to maintain a stoichiometric balance between the reactants.However, it is common practice in synthetic chemistry to use an excess of one of the reactants, usually the cheaper or more readily available one, to drive the reaction to completion. In this case, you might use a slight excess of ethanol to ensure that all of the p-aminobenzoic acid is converted to benzocaine. A typical excess might be 10-20%, but this can be adjusted based on the specific reaction conditions and desired product purity.It is also important to consider other factors, such as the reaction temperature, catalyst if used , and reaction time, to optimize the yield of benzocaine.