Alkyl-substituted benzoquinones serve as versatile building blocks for a variety of biologically active compounds. In this work, we present an approach for the environmentally benign synthesis of alkyl-p-benzoquinones, in particular trimethyl-p-benzoquinone (TMBQ, vitamin E precursor), which employs aqueous hydrogen peroxide as oxidant and a divanadium-substituted γ-Keggin polyoxotungstate, [γ-PW₁₀O₃₈V₂(μ-O)(μ–OH)]^4– (V₂-POM), immobilized on nitrogen-doped carbon nanotubes (N-CNTs) as heterogeneous catalyst. A series of supported catalysts V₂-POM/N-CNTs containing 5–25 wt % of V₂-POM and 0–4.8 atom % of N has been prepared and characterized by elemental analysis, N₂ adsorption, SEM, TEM, XPS, and FTIR techniques. The catalytic performance of V₂-POM/N-CNTs was assessed in the selective oxidation of 2,3,6-trimethylphenol (TMP) with H₂O₂ under mild reaction conditions (60 °C, MeCN). The presence of nitrogen in the support ensures strong adsorption and molecular dispersion of V₂-POM on the carbon surface, leading to highly active and selective heterogeneous catalysts, which do not suffer from metal leaching and can be used repeatedly without loss of the catalytic performance. By application of the optimal catalyst V₂-POM/N-CNTs enclosing 15 wt % of V₂-POM and 1.8 atom % of N, TMBQ could be obtained with 99% yield and 80% oxidant utilization efficiency. The catalyst demonstrated the truly heterogeneous nature of the catalysis and high turnover frequencies (500 h^–1) and space–time yield (450 g L^–1 h^–1). FTIR and XPS techniques confirmed the stability of V₂-POM and N-CNT support under the turnover conditions.

中文翻译：

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基于钒取代的多金属氧酸盐和N掺杂的碳纳米管的高效催化剂，用于烷基酚的选择性氧化

烷基取代的苯醌是多种生物活性化合物的通用构建基块。在这项工作中，我们提出了一种环境友好的烷基对苯醌，特别是三甲基对苯醌（TMBQ，维生素E前体）的合成方法，该方法使用过氧化氢水溶液作为氧化剂，并用二氮取代的γ-Keggin polyoxotungstate，[γ-PW ₁₀ ö ₃₈ V ₂（μ-O）（μ-OH）] ^4- （V ₂ -POM），固定在氮掺杂的碳纳米管（N-CNT）的作为非均相催化剂。一系列载体催化剂情况√ ₂含第V 5-25重量％-POM / N-CNT的₂-POM和0-4.8原子％的N已制备并通过元素分析，N ₂吸附，SEM，TEM，XPS和FTIR技术进行了表征。在温和的反应条件（60°C，MeCN）下，用H ₂ O ₂选择性氧化2,3,6-三甲基苯酚（TMP），评估了V ₂ -POM / N-CNTs的催化性能。载体中氮的存在确保了V ₂ -POM在碳表面上的强烈吸附和分子分散，从而导致高活性和选择性的多相催化剂，这些催化剂不会遭受金属的浸出，可以重复使用而不会损失催化性能。通过应用最佳催化剂V ₂ -POM / N-CNT，其中包含15 wt％的V可以以99％的收率和80％的氧化剂利用效率获得_2- POM和1.8原子％的N，TMBQ。该催化剂表现出了真正的多相催化性质，并且具有高周转频率（500 h ^–1）和时空产率（450 g L ^–1 h ^–1）。FTIR和XPS技术证实了在周转条件下V ₂ -POM和N-CNT载体的稳定性。