Protonation of carbonate in aqueous tetraalkylammonium salts at 25 degrees C.

Protonation constants of carbonate were determined in tetramethylammonium chloride (Me(4)NCl(aq) 0.1</=I/molkg(-1)</=4) and tetraethylammonium iodide (Et(4)NI(aq) 0.1</=I/molkg(-1)</=1) by potentiometric ([H(+)]-glass electrode) measurements. Dependence of protonation constants on ionic strength was taken into account by modified specific ion interaction theory (SIT) and by Pitzer models. Literature data on the protonation of carbonate in NaCl(aq) (0.1</=I/molkg(-1)</=6) were also critically analysed. Both protonation constants of carbonate follow the trend Et(4)NI>Me(4)NCl>NaCl. An ion pair formation model designed to take into account the different protonation behaviours of carbonate in different supporting electrolytes was also evaluated.