Radiation-induced C—C bond cleavage in 1,2-diarylethanes as model compounds of coal. Part 2.—Pulse and steady-state radiolysis of 1,2-di(pyren-1-yl)ethane in tetrahydrofuran, dimethoxyethane and toluene in the presence of sodium dihydridobis(2-methoxyethoxy)aluminate
Radiation-induced C—C bond cleavage in 1,2-diarylethanes as model compounds of coal. Part 2.—Pulse and steady-state radiolysis of 1,2-di(pyren-1-yl)ethane in tetrahydrofuran, dimethoxyethane and toluene in the presence of sodium dihydridobis(2-methoxyethoxy)aluminate
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作为煤模型化合物的 1,2-二芳基乙烷中辐射诱导的 C—C 键断裂，第 2 部分：四氢呋喃、二甲氧基乙烷和甲苯中 1,2-二（芘-1-基）乙烷的脉冲和稳态辐射分解。在二氢双(2-甲氧基乙氧基)铝酸钠存在下
DOI：
10.1039/ft9938900891
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
U. Richter
中科院分区：
文献类型：
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作者：
S. Solar;N. Getoff;M. Haenel;U. Richter
以1,2-二（芘-1-基）乙烷（1,2- dpe）为模型，研究了含NaAlH2(OCH2CH2OCH3)2[NaAlH2(OR)2]的溶液在辐射分解过程中乙醇键的C-C键裂解。在NaAlH2(OR)2和NaAlH2(OR)2不存在的情况下，对1,2- dpe、1-甲基芘（1- mp）和芘(P)在THF、二甲醚和甲苯中的溶液进行脉冲辐射分解，研究了瞬态物种。在非极性溶剂甲苯的存在下，1,2- dpe、1- mp和P等稳定且长寿命的阴离子/钠离子自由基对也能生成。醚溶剂（四氢呋喃或二甲醚）和甲苯溶液的反应机理有很大不同。在乙醚溶剂（SH）中，NaAlH2(OR)2对溶剂自由基SH˙+和电离产生的溶剂阳离子SH（H+）起清除作用。这产生了稳定的钠离子/电子对（Na+, e-s），将芳香底物还原为其自由基阴离子/钠离子对。在甲苯溶液的辐射分解过程中产生的主要物质是溶剂和底物的电子激发分子，被激发的三重态分子在电子转移过程中被NaAlH2(OR)2优先还原为自由基阴离子。1,2- dpe溶液在含NaAlH2(or)2的THF、二甲醚或甲苯中的稳态辐射（60Co γ射线）导致乙醇键的C-C键断裂。这是由于（1,2- dpe˙-,Na+）在两次连续还原中形成的不稳定离子（1,2- dpe2 -, 2Na+）。紫外可见光谱和产物分析表明，辐射诱导的1,2- dpe， 1- mp和P的还原需要THF和二甲醚的剂量低于甲苯的剂量。然而，（1,2- dpe˙-,Na+）与THF和二甲醚反应形成底物-溶剂加成产物限制了C-C键的裂解（THF为16%，二甲醚为32%）。甲苯对这些副反应的惰性使得1,2- dpe在这种溶剂中（尽管需要更高的剂量）的辐射诱导裂解过程比在THF和DME中更有效，水解后的产率高达52% 1- mp。NaAlH2(OR)2 -甲苯体系中多环芳烃的辐射诱导还原对于用紫外-可见光谱和EPR光谱研究这些芳烃的自由基阴离子非常有用，因为基本上没有形成其他干扰物质。
1,2-Di(pyren-1-yl)ethane (1,2-DPE) has been used as a model for coal to study the C—C bond cleavage of the ethano linkage in the radiolysis of solutions containing NaAlH2(OCH2CH2OCH3)2[NaAlH2(OR)2]. Transient species were investigated by pulse radiolysis of solutions of 1,2-DPE, 1-methylpyrene (1-MP) and pyrene (P) in THF, DME and toluene in the absence and the presence of NaAlH2(OR)2. In the presence of the latter stabilized and long-lived radical anion/sodium cation pairs of 1,2-DPE, 1-MP and P were generated even in the non-polar solvent toluene. The reaction mechanisms differ substantially for the ether solvents (THF or DME) and solutions in toluene. In the case of the ether solvents (SH) NaAlH2(OR)2 acts as a scavenger for solvent radical cations SH˙+ and solvent cations SH(H+) generated through ionization. This produces stabilized sodium cation/electron pairs (Na+, e–s) which reduce the aromatic substrates to their radical anion/sodium cation pairs. The prevailing species generated in the radiolysis of solutions in toluene are electronically excited molecules of the solvent and the substrate from which the excited triplet molecules are preferentially reduced to radical anions by NaAlH2(OR)2 in an electron-transfer process. Steady-state radiolysis (60Co γ-rays) of solutions of 1,2-DPE in THF, DME or toluene containing NaAlH2(OR)2 resulted in the C—C bond cleavage of the ethano linkage. This is attributed to the unstable dianion (1,2-DPE2–, 2Na+) formed in two successive reductions via(1,2-DPE˙–, Na+). UV–VIS spectroscopy and product analysis showed that the radiation-induced reduction of 1,2-DPE, 1-MP and P requires lower doses in THF and DME than in toluene. However, reactions of (1,2-DPE˙–, Na+) with THF and DME to form substrate–solvent addition products limit C—C bond cleavage (16% in THF and 32% in DME). The inertness of toluene towards such side reactions makes the radiation-induced cleavage process of 1,2-DPE in this solvent (despite of the higher dose required) much more efficient than in THF and DME, yielding after hydrolysis up to 52% 1-MP. Radiation-induced reduction of polycyclic arenes in the NaAlH2(OR)2–toluene system is very useful for investigating the radical anions of these arenes by UV–VIS and EPR spectroscopy, since essentially no other interfering species are formed.