We present a kinetic and thermodynamic analysis of the phase transitions in stoichiometric Tl2Ba2CuO6 samples prepared under a pressure of 100 bar. We have found a first-order transformation which maintains the orthorhombic structure from high pressure to 1 bar. The as-prepared tetragonal structure in an inert gas converts to orthorhombic symmetry when annealed in an oxygen flux. The activation energies have been deduced from a dynamic analysis of weight losses during the phase changes. The enthalpy and entropy for the formation of oxygen vacancies have been determined.