Dimer neutral ion pairs and associative ions in saturated vapor of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid

In the temperature range of 388-506 K in saturated vapor over 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMImTfO) ionic liquid along with the monomer neutral ionic pairs (NIP) C(+)A(-), where C+ is EMIm(+) (cation) and A(-) is TfO- (anion), the dimers (C(+)A(-))(2) were registered with a fraction of 0.5% for the first time. The corresponding associative ions C(2)A(+) and C(3)A(2)(+) formed as a result of attachment of the cation C+ to the monomer and dimer NIPs were also found. The evaporation enthalpies Delta H-v degrees(298.15 K) = 128 +/- 5 kJ mol(-1) (monomer) and Delta H-v degrees(298.15 K) = 161 +/- 9 kJ mol(-1) (dimer) were determined. The enthalpy of formation of the monomer and dimer NIP of EMImTfO at 298.15 K in the state of ideal gas were derived from the evaporation enthalpies:-1033 +/- 50 kJ mol(-1) and -2160 +/- 50 kJ mol(-1), respectively. The desorption enthalpies Delta H-des degrees(T) of the C+, C(2)A(+), and C(3)A(2)(+) cations were found to be 164 +/- 5 kJ mol(-1) (435 K), 159 +/- 7 kJ mol(-1) (435 K), and 152 +/- 21 kJ mol(-1)(457 K), respectively. The equilibrium constants of the heterophase ion-molecular reactions were measured and the formation enthalpies of associative ions were calculated: Delta H-f degrees(C(2)A(+), 298.15 K) =-493 +/- 50 kJ morl and Delta H-f degrees(C(3)A(2)(+), 298.15 K) =-1631 +/- 50 kJ mol(-1).