P-TOLUENESULFONIC ACID SEC-BUTYL ESTER Benzenesulfonic acid, 4-Methyl-, 1-Methylpropyl ester sec-Butyl-p-toluenesulfonate butan-2-yl 4-methylbenzenesulfonate sec-Butyl 4-methylbenzenesulfonate Isobutyl p-benzenesulfonate (topirastat) Sec-Butyl 4-Methylbenzenesulfonate (>80%, with an impurity of pTSA)