Theoretical Study On The Degradation Mechanism Of 1, 1-Dimethylhydrazine And Hydroxyl Radical

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.