The heat capacity and parameters of fusion of 1-bromobutane (BuBr) were measured in the temperature range (5 to 370) K using adiabatic calorimetry. The thermodynamic functions for the compound in the crystal and liquid states were calculated from these data. On the basis of the experimental spectroscopic data and the results of quantum-chemical calculations, the ideal-gas properties for BuBr were calculated by methods of statistical thermodynamics. The obtained entropy S(m)degrees(g; 298.15 K) = 366.9 J.K(-1).mol(-1) is in excellent agreement with the value 367.0 +/- 1.2 J.K(-1).mol(-1) obtained from the experimental data. The ideal-gas thermodynamic properties were also calculated for isomeric bromobutanes and 1-butyl-3-methylimdiazolium bromide ionic liquids that allowed us to find the changes of thermodynamic properties in the reactions of synthesis of 1-butyl-3-methylimidazolium bromide isomers. The literature data on the enthalpies of formation for isomeric bromobutanes were collected, and the recommended values were developed. It was demonstrated that the synthesis of ionic liquids from bromoalkanes and 1-methylimidazole in the gas phase, unlike the liquid-phase reaction, is not a thermodynamically favorable process. It possesses more positive enthalpy changes and more negative entropy changes compared to the synthesis in the liquid phase.