Thermal behavior of Sterculia striata oil

The thermal behavior of Sterculia striata oil, which is rich in fatty acids containing a cyclopropenyl ring in their chain, mainly malvalic acid (7-(2-octylcycloprop-1-en-1-yl) heptanoic acid) and sterculic acid (8-(2-octylcycloprop-1-en-1-yl) octanoic acid), is evaluated. Thermogravimetric analysis (TGA) has shown that weight loss occurs from 280 °C. Differential scanning calorimetric (DSC) analysis indicates two exothermic events: one related to the ring opening in cyclopropenoids fatty acids chains and another to the pyrolitic decomposition of the oil, mainly the cracking of the ester groups. 1H NMR analysis revealed that the opening process of the cyclopropenyl ring starts at 150 °C, probably via either a di-radical or a vinylcarbene intermediates. This process leads to the formation of a six members ring with a double bond in a terminal chain. After 280 °C, the pyrolysis starts to decompose the ester groups into carboxylic acids. FT-IR analysis corroborated the results found by the other techniques.