Calorimetric, thermal expansion, dielectric and optical measurements reveal an interesting sequence of phase transitions from a quasi-ordered phase at room temperature up to an isotropic liquid phase above 438K. In the first phase transition there is an interchange between high and low refraction indexes. The second is an order-disorder phase transition. In the third, an important configurational change occurs which finally leads the crystal to an isotropic liquid phase. This sequence is interpreted within the scope of a phenomenological approach.