sulfuric acid T=25°C; 1 h;

PPA T=125°C; 2 h; other conditions: conc. H2SO4, 25 deg C, 1h; 70percent H2SO4, 100 deg C, 2h; CF3COOH, reflux, 2h; P2O5, xylene , reflux, 2h or 0.5h; SOCl2- benzene, reflux, 0.5h; 70percent HClO4/ AcOH, reflux, 1h; Product distribution;

PPA T=125°C; 2 h; other conditions: conc. H2SO4, 25 deg C, 1h; 70percent H2SO4, 100 deg C, 2h; CF3COOH, reflux, 2h; P2O5, xylene , reflux, 2h or 0.5h; SOCl2- benzene, reflux, 0.5h; 70percent HClO4/ AcOH, reflux, 1h; Product distribution;