• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>RSC Advances >On the mechanism of retro-Diels–Alder reaction of partially saturated 2-pyrones to produce biorenewable chemicals
【24h】

On the mechanism of retro-Diels–Alder reaction of partially saturated 2-pyrones to produce biorenewable chemicals

机译：关于部分饱和2-乳酮类生产生物愈性化学品的替代二氧化物反应的机理

获取原文
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Partially saturated 2-pyrone molecules undergo ring-opening and decarboxylation via retro-Diels–Alder (rDA) reaction. Density functional theory (DFT) simulations were utilized to calculate the intrinsic activation barrier and reaction energies of the steps involved in rDA reaction of biomass-derived 5,6-dihydro-4-hydroxy-6-methylpyran-2-one (5DHHMP), 4-hydroxy-3,6-dimethyl-pyran-2-one (4HDMP) and 4-hydroxy-6-(2-oxo-propyl)-3,6-dihydro-pyran-2-one (4HOPP). The rDA reaction of the three molecules in water proceeds in two steps via the formation of a zwitterionic intermediate. The calculated activation barrier ( E _(a) = 61 kJ mol ~(?1) ) for the rDA reaction of 5DHHMP in water compares well with the experimentally measured value. In the absence of hydrogen bonding interactions such as in the solvent n -hexane and gas-phase, the rDA reaction is concerted and activation barriers of the three molecules were estimated to be relatively higher. Substituents at C _(6) , C _(4) and C _(3) position in partially saturated 2-pyrones showed a clear effect on the reactivity of the molecules which was correlated back to the resultant normal electron demand frontier molecular orbital (FMO) gap of the product diene and dienophile. The electronic and geometric (steric) effects of the substituents were separated by including several other structurally similar molecules having variations in the position, type and number of substituents. In general, the electronic effect of the substituents follow a linear trend, where FMO gap for normal electron demand serves as a good descriptor of the reactivity. The geometric effect was represented on a linear scale to quantify the steric hindrance offered by the methyl substituents. Molecules having no hydroxyl substituent at C _(4) such as 6-methyl-3,6-dihydro-2 H -pyran-2-one (4HMTHP) and 4,6,6-trimethyl-3,6-dihydro-2 H -pyran-2-one (DTMP) showed a concerted route for rDA reaction in water without the formation of the intermediate. The rates of rDA reaction of the molecules were observed to be accelerated in water as compared to n -hexane. In solvents, the reactivity of the molecule doesn't correlate to the FMO gap of the products, likely due to the differential stabilization of the reactant and transition state. In general, polar solvents (water, DMSO, ethanol and methanol) were calculated to show lesser activation energy despite of a greater FMO gap as compared to non-polar solvents ( n -hexane). In a solvent, the rDA reaction of the molecules follows a Br?nsted–Evans–Polanyi (BEP) relationship. In presence of a Br?nsted acid catalyst the rDA reaction of 5DHHMP proceeds via the formation of an oxocarbenium ion which further helps in facilitating the reaction with a significantly reduced activation barrier ( E _(a) = 15 kJ mol ~(?1) ).
机译：部分饱和的2-吡喃酮分子通过Ricro-Diels-Alder（RDA）反应进行开环和脱羧。利用密度功能理论（DFT）模拟来计算生物质衍生的5,6-二氢-4-羟基-6-甲基吡喃-2-一（5dhhmp）的RDA反应中所涉及的步骤的内在活化屏障和反应能量， 4-羟基-3,6-二甲基吡喃-2-一（4HDMP）和4-羟基-6-（2-氧代丙基）-3,6-二氢-Pyran-2-one（4Hopp）。通过形成两步中间体，在水中进行三个分子的RDA反应。计算的活化屏障（E _（a）= 61 kJ mol〜（α1））用于水中的5dhmp在水中的RDA反应与实验测量值良好。在没有氢键相互作用的情况下，例如在溶剂N-己烷和气相中，RDA反应是齐节的，并且估计三种分子的活化屏障相对较高。在部分饱和的2-吡喃酮中的C _（6），C _（4）和C _（3）的取代基对与所得正常电子需求前部分子轨道相关的分子的反应性显示出明显的影响。 FMO）二烯和腙的间隙。通过在所述位置，类型和数量的含有变化的若干其他结构上类似的分子，分离取代基的电子和几何（空间）效应。通常，取代基的电子效果遵循线性趋势，其中用于正常电子需求的FMO间隙用作反应性的良好描述符。几何效果在线性刻度表示以量化甲基取代基提供的空间障碍。在C _（4）下没有羟基取代基，例如6-甲基-3,6-二氢-2H-吡喃-2-一（4HMTHP）和4,6,6-三甲基-3,6-二氢-2 H-Pyran-2-One（DTMP）显示了在没有形成中间体的水中的RDA反应的一致途径。与N-己烷相比，观察分子的RDA反应的RDA反应的速率在水中加速。在溶剂中，分子的反应性与产品的FMO间隙不相关，这可能是由于反应物和过渡状态的差异稳定。通常，计算极性溶剂（水，DMSO，乙醇和甲醇）以显示与非极性溶剂（N-己烷）相比的FMO间隙尽管更大的FMO间隙。在溶剂中，分子的RDA反应遵循BR？nsted-evans-polanyi（bep）的关系。在Brα的存在下，5DhMP的RDA反应通过形成氧化羰烯Ion，进一步有助于促进与显着减少的活化屏障（E _（a）= 15kJ mol〜（α1）的反应进行促进反应）。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号