4920-95-0Relevant articles and documents
Palladium-Catalyzed Cross-Dehydrogenative Coupling of o-Xylene: Evidence of a New Rate-Limiting Step in the Search for Industrially Relevant Conditions
álvarez-Casao, Yolanda,van Slagmaat, Christian A. M. R.,Verzijl, Gerard K. M.,Lefort, Laurent,Alsters, Paul L.,Fernández-Ibá?ez, M. ángeles
, p. 2620 - 2626 (2018)
An efficient cross-dehydrogenative coupling of o-xylene under neat conditions, which brings important industrial benefits towards the synthesis of a monomer used in polyimide resins, is reported. The catalyst based on the combination of Pd/N ligand/carboxylate=1:1:2 does not require a Cu cocatalyst and proceeds at 11 bar of O2 pressure. Evaluation of the deuterium kinetic isotope effect (KIE) provides evidence for three different rate-determining steps, which depend on the reaction conditions (medium, temperature). Under the reported neat conditions, the dissociation of a carboxylate-bridged dimer to generate a more reactive monometallic Pd species is proposed to be the rate-limiting step.
Single-site metal-organic framework catalysts for the oxidative coupling of arenes: Via C-H/C-H activation
Van Velthoven, Niels,Waitschat, Steve,Chavan, Sachin M.,Liu, Pei,Smolders, Simon,Vercammen, Jannick,Bueken, Bart,Bals, Sara,Lillerud, Karl Petter,Stock, Norbert,De Vos, Dirk E.
, p. 3616 - 3622 (2019)
C-H activation reactions are generally associated with relatively low turnover numbers (TONs) and high catalyst concentrations due to a combination of low catalyst stability and activity, highlighting the need for recyclable heterogeneous catalysts with stable single-atom active sites. In this work, several palladium loaded metal-organic frameworks (MOFs) were tested as single-site catalysts for the oxidative coupling of arenes (e.g. o-xylene) via C-H/C-H activation. Isolation of the palladium active sites on the MOF supports reduced Pd(0) aggregate formation and thus catalyst deactivation, resulting in higher turnover numbers (TONs) compared to the homogeneous benchmark reaction. Notably, a threefold higher TON could be achieved for palladium loaded MOF-808 due to increased catalyst stability and the heterogeneous catalyst could efficiently be reused, resulting in a cumulative TON of 1218 after three runs. Additionally, the palladium single-atom active sites on MOF-808 were successfully identified by Fourier transform infrared (FTIR) and extended X-ray absorption fine structure (EXAFS) spectroscopy.
A method for preparing four methyl biphenyl
-
Paragraph 0039; 0042; 0043, (2017/01/12)
The invention provides a preparation method of tetramethyl biphenyl, which comprises the following steps: mixing o-xylene, oxidizer, additive and metal catalyst, and reacting to obtain the tetramethyl biphenyl, wherein the additive is organic acid and/or organic acid anhydride, and the oxidizer is inorganic oxidizer and/or organic oxidizer containing metal cation. Compared with the prior art of synthesizing tetramethyl biphenyl from halogenated o-xylene, the invention uses the o-xylene for direct coupling to obtain the tetramethyl biphenyl. The raw material o-xylene is cheap and accessible, and the preparation of the halogenated o-xylene is not needed, so the invention lowers the production cost, is simple to operate and has the advantages of mild reaction conditions and low facility request; and under the action of the catalyst, the o-xylene is directly coupled to prepare the tetramethyl biphenyl, and all the carbon atom frameworks of the o-xylene enter the product, so the invention also has the advantage of high economical efficiency of atoms.
