1,3,5-三乙氧基-2,4,6-三硝基苯的连续化制备反应机理的理论研究

doi:10.6023/A24110355

摘要/Abstract

三氨基三硝基苯(TATB)具有出色的安定性, 机械感度极低, 作为重要组分应用于核武器的高聚物黏结炸药(PBX). 然而, 目前工业制备TATB的主要方法存在效率低、杂质残留等问题. 基于以间苯三酚为原料的TATB的新合成路线, 我们发明了一种连续化高效制备TATB前体三乙氧基三硝基苯(TETNB)的方法. 鉴于该反应的重要性, 在M062X/6-31+G**水平上对其反应机理进行了深入的理论研究, 阐明了原甲酸三乙酯作为烷基化试剂进行烷基化反应的详细反应机理, 反应的关键中间体是二乙氧基碳正离子, 关键反应过程是双分子亲核取代(S_N2)和芳香亲核取代(S_NAr). 研究发现, 和反应物相比, 醚化产物在热力学上是稍微不利的, 达到平衡时产物所占比例较小. 因此, 实验中要不断移除副产物乙醇和甲酸乙酯, 拉动平衡向产物方向移动.

关键词: 三氨基三硝基苯(TATB)合成, 含能材料, 醚化反应机理, 原甲酸三乙酯, 理论研究

1,3,5-Triamino-2,4,6-trinitrobenzene (TATB) has excellent stability and very low mechanical sensitivity and is used as an important component in polymer binder explosive (PBX) for nuclear weapons. However, at present, the methods of industrial preparation of TATB have problems such as low efficiency and residual impurities. Based on a new method to synthesize TATB from phloroglucinol, we developed a continuous and efficient method for preparing 1,3,5-triethoxy-2,4,6- trinitrobenzene (TETNB), the key intermediate to synthesize TATB. In view of the importance of this reaction, in-depth theoretical research on the reaction mechanism has been conducted with the Gaussian 16 software at the M062X/6-31+G** level. The reaction mechanism and the thermodynamic equilibrium of the etherification process were clarified. Under the catalysis of protic acid, triethyl orthoformate eliminates one ethanol molecule to form a diethoxy-carbocation intermediate. Since the lone pair electrons of the adjacent oxygen atoms can partially fill the empty p orbital of the carbocation, the diethoxy-carbocation intermediate is relatively stable. Subsequently, there are two reaction modes for diethoxy-carbocation. In the first mode, trinitrophloroglucinol (TNPG) anion acts as a nucleophile to attack the diethoxy-carbocation intermediate in S_N2 fashion, grabbing an ethyl carbocation and achieving the alkylation. In this mode, the diethoxy-carbocation intermediate directly provides an alkyl carbocation. In the second mode, addition reaction occurs between the TNPG negative ions and the diethoxy-carbocation intermediate to produce new orthoformate, which can be regarded as transesterification. Then, the ethanol molecule conducts an aromatic nucleophilic substitution (S_NAr) to replace the diethyl orthoformate on the aromatic ring and complete the alkylation. In comparison, diethyl orthoformate is a relatively better leaving group. In addition, this etherification reaction has a remarkable feature: the thermodynamic stability of the product is slightly worse than that of the reactants. Therefore the yield is lower when chemical equilibrium is reached. This requires continuous removal of the by-products of the system in the experiment to pull the chemical balance toward the direction of the product.

Key words: 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) synthesis, energetic material, etherification mechanism, triethyl orthoformate, theoretical research

引用此文

马玲玲, 凌琳, 吴亚明, 李玉学, 吕龙. 1,3,5-三乙氧基-2,4,6-三硝基苯的连续化制备反应机理的理论研究[J]. 化学学报, 2025, 83(4): 360-368.

Lingling Ma, Lin Ling, Yaming Wu, Yuxue Li, Long Lu. Theoretical Study on the Mechanism of Continuous Preparation of 1,3,5-Triethory-2,4,6-Trinitrobenzene[J]. Acta Chimica Sinica, 2025, 83(4): 360-368.

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图/表 13

图1. (A)均三氯苯法合成TATB; (B)间苯三酚法合成TATB

Figure 1. (A) Synthesis of TATB by homotrichlorobenzene; (B) Synthesis of TATB by phloroglucinol

图2. 可能的反应机理

Figure 2. Proposed reaction mechanisms

图3. Path-1初始分解机理:原甲酸三乙酯的质子解; 键长单位: ?. 计算在M062X/6-31+G**水平上进行

Figure 3. Path-1: The initial decomposition mechanism, the protonolysis of triethyl orthoformate. Selected bond lengths are in angstroms (?), calculated at the M062X/6-31+G** level

图4. 二乙氧基碳正离子中间体的结构. (1)轨道共轭作用示意图和NBO电荷分布; (2)和共轭相关的几个主要分子轨道

Figure 4. The structure of the diethoxy carbocation intermediate. (1) The diagram of the orbital conjugation and the NBO charge distribution; (2) and the conjugation related molecular orbitals

图5. (1) Path-4: 亲核加成机理; (2) Path-3: 协同反应机理; (3) Path-2: SN2亲核取代机理; 键长单位: ?. 计算在M062X/6-31+G**水平上进行

Figure 5. (1) Path-4: nucleophilic addition; (2) Path-3: the concerted mechanism; (3) Path-2: the SN2 nucleophilic substitution mechanism. Selected bond lengths are in angstroms (?), calculated at the M062X/6-31+G** level

图6. 乙醇对INT2进行芳香亲核取代, 乙氧基转移到TNPG中, 完成“烷基化”过程. 键长单位: ?. 计算在M062X/6-31+G**水平上进行

Figure 6. After an aromatic nucleophilic substitution, an ethoxy is transferred to the TNPG and the first “alkylation” process is completed. Selected bond lengths are in angstroms (?), calculated at the M062X/6-31+G** level

图7. Path-6: 乙醇对酚羟基的芳香亲核取代. 键长单位: ?. 计算在M062X/6-31+G**水平上进行

Figure 7. Path-6: The nucleophilic aromatic substitution of phenolic hydroxyl group by ethanol. Selected bond lengths are in angstroms (?), calculated at the M062X/6-31+G** level

图8. Path-7: 催化的乙醇对酚羟基的芳香亲核取代. 键长单位: ?. 计算在M062X/6-31+G**水平上进行

Figure 8. Path-7: The catalyzed nucleophilic aromatic substitution of phenolic hydroxyl group by ethanol. Selected bond lengths are in angstroms (?), calculated at the M062X/6-31+G** level

图9. Path-8: 乙醇对硝基的芳香亲核取代. 键长单位: ?. 计算在M062X/6-31+G**水平上进行

Figure 9. Path-8: The nucleophilic aromatic substitution of nitro group by ethanol. Selected bond lengths are in angstroms (?), calculated at the M062X/6-31+G** level

图10. 第一步醚化机理的最优路径. 键长单位: ?. 计算在M062X/6-31+G**水平上进行

Figure 10. The optimal path of the first step of etherification. Selected bond lengths are in angstroms (?), calculated at the M062X/6-31+G** level

图11. 第二步醚化机理的最优路径. 键长单位: ?. 计算在M062X/6-31+G**水平上进行

Figure 11. The optimal path of the second step of the etherification. Selected bond lengths are in angstroms (?), calculated at the M062X/6-31+G** level

图12. 第三步醚化机理的最优路径. 键长单位: ?. 计算在M062X/6-31+G**水平上进行

Figure 12. The optimal path of the third step of the etherification. Selected bond lengths are in angstroms (?), calculated at the M062X/6-31+G** level

图13. 醚化反应的整体热力学分析和改变化学平衡提高产率的策略

Figure 13. The overall thermodynamics of the etherification reaction and the strategy to drive chemical equilibrium to increase the yield

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