Department of Chemistry and Catalysis Research Center, Technische Universität München, 85747 Garching, Germany.
J Am Chem Soc. 2012 Dec 26;134(51):20768-75. doi: 10.1021/ja309915e. Epub 2012 Dec 12.
A novel Ni/SiO(2)-catalyzed route for selective cleavage of ether bonds of (lignin-derived) aromatic ethers and hydrogenation of the oxygen-containing intermediates at 120 °C in presence of 6 bar H(2) in the aqueous phase is reported. The C-O bonds of α-O-4 and β-O-4 linkages are cleaved by hydrogenolysis on Ni, while the C-O bond of the 4-O-5 linkage is cleaved via parallel hydrogenolysis and hydrolysis. The difference is attributed to the fact that the C(aliphatic)-OH fragments generated from hydrolysis of α-O-4 and β-O-4 linkages can undergo further hydrogenolysis, while phenol (produced by hydrolysis of the 4-O-5 linkage) is hydrogenated to produce cyclohexanol under conditions investigated. The apparent activation energies, E(a)(α-O-4) < E(a)(β-O-4) < E(a)(4-O-5), vary proportionally with the bond dissociation energies. In the conversion of β-O-4 and 4-O-5 ether bonds, C-O bond cleavage is the rate-determining step, with the reactants competing with hydrogen for active sites, leading to a maximum reaction rate as a function of the H(2) pressure. For the very fast C-O bond cleavage of the α-O-4 linkage, increasing the H(2) pressure increases the rate-determining product desorption under the conditions tested.
一种新型的 Ni/SiO(2)催化途径可在 120°C 下、存在 6 巴氢气的水相中选择性断裂（木质素衍生的）芳基醚的醚键，并对含氧中间体进行加氢。α-O-4 和 β-O-4 键合的 C-O 键通过氢化作用在 Ni 上断裂，而 4-O-5 键合的 C-O 键通过平行的氢化作用和水解作用断裂。这种差异归因于这样一个事实，即从 α-O-4 和 β-O-4 键合的水解生成的 C(脂肪族)-OH 片段可以进一步经历氢化作用，而苯酚（由 4-O-5 键合的水解产生）在研究条件下被氢化生成环己醇。表观活化能 E(a)(α-O-4) < E(a)(β-O-4) < E(a)(4-O-5) 与键离解能成比例变化。在β-O-4 和 4-O-5 醚键的转化中，C-O 键断裂是速率决定步骤，反应物与氢竞争活性位，导致反应速率达到最大值，这是氢气压力的函数。对于 α-O-4 键非常快速的 C-O 键断裂，在测试条件下增加氢气压力会增加速率决定产物的解吸。
