Determination Of Thermodynamic Properties And Geometry Structureoptimization Of Dehydroabietic Acid

Dehyroabietic acid is a very important fine chemical raw materials and it has a prosperous future in the field of medicine,pesticide,surfactant and fine organic synthesis and so on.Dehyroabietic acid have wide range application in many area,but it is hard to separate from disproportionated rosin.Therefore,the study of basal technical data and the geometry of the dehyroabietic acid is very insistent and necessity.On the basis of a lot of experiments, many basal technical data for dehyroabietic acid is obtain by experiment.The geometry of the dehyroabietic acid is study by the quantum chemistry methods.This paper covers the contents as follows:High purity dehydroabietic acid was prepared from disproportionated rosin by means of fractional acidification.Quantitative and qualitative analyses of the product by the IR and UV,the purity of the dehydroabietic acid is 99.99%determinated by means of GC.To get the chemical thermodynamic data,firstly,the melting point of the dehyroabietic acid were determinated to be 171.6℃,171.39℃by the digital melting point instructor and DSC.The melting enthalpy of dehyroabietic acid was determinated to beâ–³_mH=-19.74kJ/mol by the DSC techniques.Second,the standard combustion enthalpy was measured to beâ–³_cH⁰_m=-11234.85kJ/mol by means of Oxygen Bomb Calorimeter.The standard formation enthalpy was calculated to beâ–³_fH⁰_m=-636.38kJ/mol.The non-isothermal decomposition kinetics of dehydroabietic acid in Ar was investigated by TG-DTG techniques with various heating rates of 5℃/min,15℃/min and 20℃/min.The non-isothermal kinetics parameters were analyzed by means of Achar-Brindley-Sharp and Satava-Setak respectively,and the thermal decomposition mechanism of dehydroabietic acid was also studied with the Satava-Sestak method.The results show that the thermal decomposition mechanism of dehydroabietic acid was controlled by random nuclear producing and growing process,the apparent activation energy and pre-exponential factor are E=106.92kJ/mol and lnA=20.45s^-1,respectively,the reaction order is n=2/3,and the kinetic equation can be expressed as,G(α)= 3(1-α)^2/3.The optimization of geometrical structure of abietic acid was carried out by three semi-emperical molecular orbital methods of MINDO/3,MNDO,PM3.It is showned that the PM3 methods is better than the MINDO/3 and the MNDO methods for geometrical structure of rosin acids.Therefore,the geometrical structure of dehydroabietic acid is optium by PM3 methods.The optimization of geometrical structure of dehydroabietic acid as fellows:the A ring of geometrical structure of dehydroabietic acid is chair conformation;the B ring of geometrical structure of dehydroabietic acid is half-chair confomation;the C ring of geometrical structure of dehydroabietic acid is plane conformation.The benzene C8-C14 of dehyroabietic acid is in the same plane.Otherwise,the C7,C10,C15 is also in the same plane with the benzene group of dehyroabietic acid.