NO_(2)和SO_(3)氧化聚苯硫醚的密度泛函理论计算

DFT calculation on oxidation of polyphenylene sulfide by NO_(2) and SO_(3)

通过密度泛函理论(Density Functional Theory,DFT)中的B3LYP-D3/6-31G(d,p)方法研究二氧化氮(NO_(2))、三氧化硫(SO_(3))氧化聚苯硫醚(Polyphenylene Sulfide,PPS)生成亚砜与砜结构的过渡态,并使用内禀反应坐标(Intrinsic Reaction Coordinate,IRC)确认其连接的反应物和产物,考察了PPS被氧化的反应路径,指出反应中分子几何结构与原子电荷的改变,揭示了NO_(2),SO_(3)氧化PPS滤料的微观机理。在此基础上,进一步计算不同温度下PPS氧化过程中的自由能垒,通过反应速率常数与半衰期定量比较NO_(2),SO_(3)氧化PPS的能力。结果表明,在180~220℃范围内,SO_(3)氧化PPS生成亚砜的反应速率常数是NO_(2)的107倍;SO_(3)氧化亚砜结构生成砜结构的反应速率常数是NO_(2)的104倍,即SO_(3)对于PPS分子链上S原子的氧化能力远强于NO_(2);在实际环境中NO_(2)除了直接氧化PPS外,还可能存在能垒更低的反应路径。

Through the B3 LYP-D3/6-31 G(d,p)method of density functional theory(DFT)and using intrinsic reaction coordinate(IRC)to confirm its connected reactants and products,the reaction paths of polyphenylene sulfide(PPS)oxidation were explored by looking for the transition state of sulfoxide and sulfone structure from PPS oxidized by NO_(2) and SO_(3).The change of the geometric structure and charge of the middle molecule revealed the microscopic mechanism of NO_(2) and SO_(3) oxidation PPS filter material.It showed that part of the electrons were attracted by the benzene ring and O atom when oxidizing S atom,which weakened the bond orders of the C-S bond and made it easier to break.It also increased the aromaticity of the benzene ring,making it easier to undergo substitution reactions and be attacked by free radicals.On this basis,the free energy barriers during the PPS oxidation process at different temperatures were further calculated.The ability of NO_(2) and SO_(3) to oxidize PPS was quantitatively compared by the reaction rate constant.Finally,the difficulty of the reactions were compared by calculating the half-life.The calculation results showed that the oxidation ability of SO_(3) to the S atom in the PPS molecular chain was stronger than that of NO_(2);in the actual environment,NO_(2) may not directly oxidize PPS,there were additional reaction paths;the half-life of sulfoxide formation was less than 2.5 h and the half-life of sulfone formation was less than 20 days when sulfur trioxide was less than 5 mol/L,therefore SO_(3) had a strong oxidizing effect on PPS,and the concentration of SO_(3) need to be strictly controlled in the environment using PPS.