Preparation of p-Toluenesulfonic Acid

p-Toluenesulfonic acid was prepared by the reaction-crystallization method.It was formed when toluene and sulfuric acid were refluxed at (110°C).At the end of the reaction the mixture was cooled to (80°C)and water was added.The monohydrate p-toluenesulfonic acid was crystallized while the o and m-isomers remained in the solution Then,the reagents were added again and the reaction was recycled.This process does not discharge waste acid or toluene,and the yield and purity of the product reaches 90% and 98%,respectively.