The sodium and potassium salts of H2PO4 were clearly more effective
than the HPO4 2– counterparts. Another distinct feature
of Table 3 was the catalytic activity of NH4H2PO4 supported on
silica gel. Only 2.5 mmol of ammonium dihydrogen phosphate
in supported form was enough to be efficient. 88% of conversion
was obtained with 21 mg of NH4H2PO4/SiO2 after 4 h
(entry 7), but a lower conversion (79%) was attained with the
higher amount of 42 mg in the same time. The study of the
catalytic efficiency of supported NH4H2PO4 on different solid
materials is under investigation.