Reaction of phenyl radical with propylene as a possible source of indene and other polycyclic aromatic hydrocarbons: an ab initio/RRKM-ME study.
Reaction of phenyl radical with propylene as a possible source of indene and other polycyclic aromatic hydrocarbons: an ab initio/RRKM-ME study.
复制标题
DOI：
10.1021/jp212338g
复制
发表时间：
2012-04
期刊：
影响因子：
--
通讯作者：
V. Kislov;A. Mebel;J. Aguilera-Iparraguirre;W. Green
中科院分区：
文献类型：
--
作者：
V. Kislov;A. Mebel;J. Aguilera-Iparraguirre;W. Green
采用从头计算G3（MP2，CC）//B3 LYP/6- 311 G ** 方法研究了苯基自由基与丙烯反应的势能面和反应机理，并通过RRKM-ME方法计算了不同温度和压力下的反应速率常数和产物支化比.该反应可以通过直接夺氢产生苯和三个C（3）H（5）自由基[1-丙烯基（CH（3）CHCH）、2-丙烯基（CH（3）CCH（2））和烯丙基（CH（2）CHCH（2））]或通过将苯基加成到丙烯的CH或CH（2）单元上，然后在C（9）H（11）PES上重排，在H或CH（3）损失后产生九种不同的产物来进行。在1000-2000 K温度范围内，H提取通道在动力学上是优选的，占总产物产率的55-75%，其中烯丙基是主要产物（约45%）。苯基加成通道的相对贡献在1000 K时约为35%，在2000 K时降至15%，主要产物为苯乙烯+ CH（3）和3-苯基丙烯+ H。C（6）H（5）+ C（3）H（6）加成络合物的碰撞稳定性仅在1000-1200 K的温度下才有意义，这取决于压力，在300-700 K的低温下最大，达到总产物产率的90%。在T > 1200 K时，碰撞稳定化变得可以忽略不计，而解离产物苯乙烯+甲基和3-苯基丙烯+ H占总产物产率的45%。在所有研究条件下，发现双环芳族物质（包括茚满C（9）H（10））的产生可忽略不计，表明苯基加成到丙烯上不能成为C（9）H（11）PES上多环芳烃（PAH）的来源。或者，PAH分子茚C（9）H（8）的形成可以通过在C（6）H（5）+ C（3）H（6）加成反应的主要产物3-苯基丙烯活化后的次级反应来完成，通过小基团如H、OH、CH（3）、结果表明，在典型的燃烧温度下，77-90%的3-苯基丙烯抽氢生成的C（9）H（9）自由基通过低势垒闭合环戊烯环，然后失去一个氢原子生成茚。这导致在1000-2000 K温度范围内茚的产率相对于初始C（6）H（5）+ C（3）H（6）反应物为7.0-14.5%。
Ab initio G3(MP2,CC)//B3LYP/6-311G** calculations have been performed to investigate the potential energy surface (PES) and mechanism of the reaction of phenyl radical with propylene followed by kinetic RRKM-ME calculations of rate constants and product branching ratios at various temperatures and pressures. The reaction can proceed either by direct hydrogen abstraction producing benzene and three C(3)H(5) radicals [1-propenyl (CH(3)CHCH), 2-propenyl (CH(3)CCH(2)), and allyl (CH(2)CHCH(2))] or by addition of phenyl to the CH or CH(2) units of propylene followed by rearrangements on the C(9)H(11) PES producing nine different products after H or CH(3) losses. The H abstraction channels are found to be kinetically preferable at temperatures relevant to combustion and to contribute 55-75% to the total product yield in the 1000-2000 K temperature range, with the allyl radical being the major product (~45%). The relative contributions of phenyl addition channels are calculated to be ~35% at 1000 K, decreasing to ~15% at 2000 K, with styrene + CH(3) and 3-phenylpropene + H being the major products. Collisional stabilization of C(6)H(5) + C(3)H(6) addition complexes is computed to be significant only at temperatures up to 1000-1200 K, depending on the pressure, and maximizes at low temperatures of 300-700 K reaching up to 90% of the total product yield. At T > 1200 K collisional stabilization becomes negligible, whereas the dissociation products, styrene plus methyl and 3-phenylpropene + H, account for up to 45% of the total product yield. The production of bicyclic aromatic species including indane C(9)H(10) is found to be negligible at all studied conditions indicating that the phenyl addition to propylene cannot be a source of polycyclic aromatic hydrocarbons (PAH) on the C(9)H(11) PES. Alternatively, the formation of a PAH molecule, indene C(9)H(8), can be accomplished through secondary reactions after activation of a major product of the C(6)H(5) + C(3)H(6) addition reaction, 3-phenylpropene, by direct hydrogen abstraction by small radicals, such as H, OH, CH(3), etc. It is shown that at typical combustion temperatures 77-90% of C(9)H(9) radicals formed by H-abstraction from 3-phenylpropene undergo a closure of a cyclopentene ring via low barriers and then lose a hydrogen atom producing indene. This results in 7.0-14.5% yield of indene relative to the initial C(6)H(5) + C(3)H(6) reactants within the 1000-2000 K temperature range.