toluene-4-sulfonic acid in acetic acid 1) 37 deg C, 6h; 2) room temp., overnight;

1: 67 percent / trifluoroacetic acid / benzene / 1) 30 min.(addition); 2) 52 h, room temp. 2: 97 percent / 4-toluenesulfonic acid / acetic acid / 1) 37 deg C, 6h; 2) room temp., overnight View Scheme