toluene-4-sulfonic acid ketal dissolved in cyclohexanone containing p-toluenesulfonic acid and some water, 1 h at 140°C, then addn. of further amt. of water; extn. with ether, organic layer washed with a 10 percent NaHCO3 soln. and dried over K2CO3, evapn. of ether and cyclohexanone, chromy. on SiO2 ( elution with benzene ), elem. anal.;