【作者】 徐亚飞；

【导师】 薛荣书；

【作者基本信息】 重庆大学 ， 物理化学， 2008， 硕士

【摘要】 偏二甲肼(Unsymmetrical dimethylhydrazine, UDMH)是导弹、卫星和飞船发射试验以及运载火箭的主体燃料,其在水中的最高浓度不得超过500mg/m3,长征系列火箭就是以UDMH为主体燃料的。近年来随着我国载人航天事业的蓬勃发展,UDMH使用量不断增加,由此产生的水体污染不能忽视。目前,我国已经开始关注UDMH污水对环境以及参试人员身体健康的影响。因此对UDMH降解机理的研究具有非常重要的意义。随着计算方法和计算机技术的飞速发展,计算化学在化学研究中已经占有越来越重要的地位。其中,密度泛函方法由于计算量适中、计算精度较高,已成为计算化学领域中最重要的理论方法之一。本文用量子化学计算的方法研究偏二甲肼与?OH在气态室温下发生降解反应生成中间产物二甲基二氮烯、四甲基四氮烯、偏腙、亚硝基二甲胺、甲醛等的反应机理;及二甲基二氮烯和甲醛继续降解反应的机理。采用密度泛函理论的B3LYP方法、6-31+G(d)基组全参数优化了各反应体系中的反应物、中间体、过渡态及产物的几何构型,通过振动分析和内禀反应坐标(IRC)技术确定各反应可能的中间体和过渡态;在频率计算的基础上,得到了各个反应途径的能量曲线。研究的主要结果如下:1.偏二甲肼在一定的条件下可以降解生成二甲基二氮烯,该反应的势垒较高,反应速率较慢。生成的二甲基二氮烯继续降解的反应主要是它自身的单分子反应:顺反异构反应、异构化为甲醛一甲基腙的反应、分解生成N2与CH3的反应。这些反应的势垒都比较低,是易于进行的反应。故正如实验测得的二甲基二氮烯是偏二甲肼降解过程中的中间产物,而不是最终产物。2.生成的中间体1,1-二甲基二氮烯发生耦合生成四甲基四氮烯;同二甲基二氮烯一样,作为对称性的氮烯化合物,四甲基四氮烯也存在着顺反异构反应,且该反应的活化能不高,是个易于进行的反应。3.中间体1,1-二甲基二氮烯除了可以发生耦合生成四甲基四氮烯外,1,1-二甲基二氮烯不含甲基的氮原子还可以利用它的孤对电子吸引另一个1,1-二甲基二氮烯的甲基,生成中间体(CH3)2NNCH3,再脱去一个H原子,生成偏腙。从计算得到的相对能量看,这是个相当容易进行的反应。4.先用UHF方法、6-31+G(d)基组,研究了H2O2+?OH→H2O+ ?OOH的反应机理,并结合实验结果,证实了反应体系中存在着?OOH自由基,并参与反应。接下来采用密度泛函理论的B3LYP方法和6-31+G(d)基组研究了中间体(CH3)2NN?H与?OOH生成亚硝基二甲胺的反应机理。从计算得到的相对能量看,采用从中间体(CH3)2NN(H)OOH上脱去一个H2O分子的反应途径,是一个易于进行的反应。5.用密度泛函理论的B3LYP方法、6-31+G(d)基组研究了生成甲醇及甲醛的反应机理,之后又用同样的方法和基组研究了甲醛与?OH继续降解生成小分子的反应。计算得到甲醛与?OH反应有三条途径:(1)发生抽氢反应,生成CHO和H2O,这是最容易进行的反应途径;(2)HCOH + ?OH→HCOOH + H ,这是次易进行的反应;(3)HCOH + ?OH→COOH + H2 ,这是反应机理最复杂也最难进行的反应。结果表明,采用?OH作为氧化剂,可彻底的消除甲醛带来的二次污染。本文利用量子化学计算的方法研究偏二甲肼的降解机理尚属首次,这对进一步改善偏二甲肼污水治理的方法和实验条件将有一定的帮助。更多还原

【Abstract】 Unsynnetrical dimethylhydrazine(UDMH), the principal component of liquid rocket propellant, is known as a primary eco-toxicant with the maximum permissible concentration in ambient warer as low as 500mg/m3. It is the“long march”series rocketes that employed the UDMH as their main fuel. Recently the spaceflight projectes of our country developes flourishly, and abundant UDMH were used. Sequently, a lot of water area was polluted. It is very bad for environment and participant. So it is very important to research the mechanism of the detoxification of UDMH.Along with the rapid development of computational methods and computer technology, computational chemistry has become more and more important in modern chemistry. Due to its moderate computational consume and high precision, density functional theory (DFT) has become one of the most important methods in computational chemistry.We employed quantum chemistry to research the mechanism of the reaction of the UDMH and ?OH in the gas phase at the room temperature to dimethyldiazene, TMT, dimethylhydrazone(FDMH), N-nitrosodimethylamine(NDMA), formaldehyde; and the monomolecular reaction of dimethyldiazene, the reaction of formaldehyde and ?OH to micromolecule.All the reactants, middle complexes and transition state structures are fully optimized by using the analytical gradients at B3LYP theory with 6-31+G(d) basis set. All transition states are characterized by one imaginary frequency on the PES. Intrinsic reaction coordinate (IRC) is proceeded to confirm transition states connecting the designated local minima. On the basis of the vibrational calculation, we get the energy curve of all of the reaction.The following are the main results:1. The results show that UDMH and ?OH react can produce dimethyldiazene. The potential barrier is high, and the reaction rate is low. The dimethyldiazene is instable, they can invert to other products or decompose to other products, including the trans-cis isomerization reaction, the automerization reaction to FMMH, the decomposition reaction to N2 and ?CH3. All the potential barrier are low. So dimethyldiazene is not the final product, but the intermediate product in the process of the UDMH decomposition, just like the experiment results. 2. The 1,1- dimethyldiazene, which appeared in the Chapter 3, can couple to the TMT. And TMT is also one of the symmetric azo, there is trans-cis imomerization reaction, which has a low potential barrier.3. The N atom of 1,1- dimethyldiazene can employ the lone pair electrons pull the ?CH3 of another 1,1- dimethyldiazene to intermediate (CH3)2NNCH3, then a H atom drop from it . FDMH is produced. From the relative energy, we known this reaction is very easy.4. In chapter 6, we first use UHF/6-31+G(d) to research the mechanism of the reaction of H2O2+?OH→H2O+?OOH. With the results of the others’experiment, we confirm that there are ?OOH in the reaction system, and take part in the reaction. Then, we use the B3LYP/6-31+G (d) to research the mechanism of the reaction of UDMH and ?OOH to NDMA. This reaction path is drop a H2O molecular form the intermediate (CH3)2NN(H)OOH. From the relative energy, it is a easy reaction.5. In chapter 7, we first use the B3LYP/6-31+ G (d) to research the mechanism of the reaction to methanol and formaldehyde. Then research the mechanism of the reaction of formaldehyde and ?OH. There are three paths: (1) the hydrogen abstraction to CHO and H2O, this is the most easiest path; (2) HCOH + ?OH→HCOOH + H, this is the easier path; (3) HCOH + ?OH→COOH + H2, this is the most complicated and most difficult path. The results show that when ?OH as oxidant formaldehyde will not bring secondary pollution.This is the first time of using the calculation chemistry to research to mechanism of the detoxification of UDMH. It will be helpful for improving the practical technology.更多还原