| Oxidation was an important factor affecting the quality of rosin.Studying oxidation process of solid abietic acid and rosin,their oxidation characteristics and oxidation reaction law would lay a theoretical foundation for improving the antioxidant abilities of rosin.In this paper,the oxidation process and peroxide concentration of solid abietic acid and rosin were studied.The main experiments and results drawn were as follows.?1?The analysis methods of the oxidation process and peroxide concentration in initial oxidation reaction of abietic acid and rosin was established.Abietic acid and rosin produced peroxide in their early oxidation.In order to measure their peroxide concentration quantificationally,the modified iodimetry method of determining the peroxide concentration of oil and fat by the national standard GB/T5538-2005 "Animal and vegetable fats and oils-Determination of peroxide value" was improved.The modified iodimetry method was to change the solvent to ethanol,so that the abietic acid and rosin could be better dissolved.The samples of glacial acetic acid and KI were placed in the dark for 5 h,so that the peroxide of abietic acid and rosin could be completely decomposed.The modified iodimetry method applied to measure the peroxide concentration of abietic acid and rosin had the characteristics of high precision and good stability.?2?The quantitative analysis of peroxide concentration of abietic acid and rosin during thermal oxidation.The peroxide of abietic acid and rosin was titrated by the modified iodimetry method.The peroxide concentration increased with oxidation temperature,oxygen pressure and time increasing at 30?60 ?range.Moreover,in a 0.5 Mpa oxygen atmosphere,the added peroxide concentration in abietic acid oxidation process was 264.0 mmol·kg-1 at 60 ? for 8 hours.The change of peroxide concentration of rosin was silimilar to that of abietic.But when it was oxidized in oxygen,peroxide concentration of rosin was different from that of abietic acid at 50 ?.The peroxide concentration of rosin increased first and then decreased with the increased of time.The added peroxide concentration formed in rosin oxidation process was 120.1 mmol kg-1 at 50 ? for 6 hours.?3?The thermal oxidation reaction and reaction kinetics of abietic acid and rosin.The behaviors of conjugated double bond of abietic acid and rosin were determined by ultraviolet spectrophotometry?UV?.The results showed that the thermal oxidation of solid state abietic followed a pseudo-first-order reaction,the equation as ln?ct/cO?=-kt+ b,where k and b were constant parameters related with temperature.In oxygen,when the reaction temperature were:30,40,50 and 60 °C,respectively,the apparent rate constants of oxidation reaction of abietic acid were:0.01237 h-1,0.03486 h-1,0.05221 h-1 and 0.07710 h-1,respectively.In air,when the reaction temperature were:30,40,50 and 60 ?,respectively,the apparent rate constants of oxidation reaction of abietic acid were:0.001477h-1?0.004052 h-1?0.007499 h-1 and 0.01090 h-1,respectively.The apparent activation energies of abietic acid in oxygen and air were 49.76 kJ/mol and 55.79 kJ/mol,respectively.At the same oxidation temperature and oxidation time,with the increase of oxidation temperature and oxidation time,the reaction proportion of rosin increased,but the rate of rise decreased with time.?4?The oxidation reaction characteristics and reaction kinetics of abietic acid and rosin which was under the ultraviolet light.The oxidation of abietic acid and rosin was induced by 254 nm and 365 nm ultraviolet irradiation.The quantitative analysis of peroxide concentration and conjugated double bond was studied by modified iodimetry method and ultraviolet spectrophotometry.The peroxide concentration of abietic acid and rosin increased with the increased of oxidation time.When the reaction time was 8 h,the added peroxide concentration of abietic acid were 97.80 mmol·Kg-1 and 73.10 mmol·Kg-1 under 254 and 365 nm UV irradiation,respectively.The added peroxide concentration of rosin were 60.85 mmol·Kg-1 and 51.92 mmol Kg-1 under the same UV irradiation and reaction time.The photo-oxidation of abietic acid and rosin fitted pseudo-first-order kinetics under 254 and 365 nm UV irradiation.Under 254 and 365 nm UV irradiation,the rate constants of abietic acid were 0.03533 h-1 and 0.02306 h-1,the rate constants of rosin were 0.01749 h-1 and 0.01228 h-1,respectively.At the same oxidation temperature,the order of reaction conditions that reaction of abietic acid and rosin from easy to difficult was:254 nm ultraviolet radiation>365 nm ultraviolet radiation>in air. |
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