Hydrogen-Independent Reductive Transformation of Carbohydrate Biomass into γ-Valerolactone and Pyrrolidone Derivatives with Supported Gold Catalysts
Hydrogen-Independent Reductive Transformation of Carbohydrate Biomass into γ-Valerolactone and Pyrrolidone Derivatives with Supported Gold Catalysts
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DOI：
10.1002/anie.201100102
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Fan, Kang-Nian
中科院分区：
文献类型：
--
作者：
Du, Xian-Long;He, Lin;Fan, Kang-Nian
生物质及其衍生物为液体燃料和有价值的化学品的可持续生产提供了化石燃料资源的可再生替代品。[1]有效利用这些可持续资源的挑战是开发具有成本效益的加工方法，将高度功能化的碳水化合物转化为增值化学品。[2]从木质纤维材料中提取的碳水化合物构成陆地生物质的最大部分，目前正在制定各种有效利用其作为商业化学原料的战略，目的是补充并最终取代化石燃料。戊内酯(GVL)已被认为是最有前景的可再生分子之一：它可以转化为各种中间体化学品，从这些中间体中可以生产各种生物燃料以及商品和精细化学品。通过乙酰丙酸(LA，4-氧基戊酸)的催化氢化，[5]可从木质纤维生物质中通过简单而可靠的水解过程获得。[1C，6]分子氢通常用于LA的催化氢化(方案1)；[4，5]然而，对于生物质生产GVL，最小的氢耗将是首选的，[4d]，特别是在低成本氢气不容易获得的情况下。从经济和工程的角度来看，迫切需要开发新的高效方法，以甲酸(FA，通过生物质的酸解形成等摩尔量的FA)作为原位氢源。[7]这种方法可以消除对外部氢源的需求，因此在利用可再生生物质生产GVL方面具有巨大的工业潜力，特别是如果可以使用高效和可重复使用的催化剂的话。虽然在催化转移加氢反应中使用FA作为氢供体是一种非常成熟的还原羰基官能团的方法，[9]用FA有效地还原LA被证明是非常困难的，许多报道的步骤需要大量使用FA或添加外部氢来提高催化剂的活性。[7，10]迄今为止报道的最成功的催化体系是RuCl3/PPh3络合物[8a]，它能够高产率(高达95%)将LA和FA的1：1整齐混合物转化为GVL。然而，除了均相催化用于开发可持续催化过程的固有局限性外，该体系还需要严格的无水和添加大量碱来改善还原动力学并将失活降至最低。鉴于生物质水解产物的高水分和极高的酸度，这些特点可能在能源消耗和加工成本方面存在严重缺陷，以及额外的处理问题。因此，成功地开发出一种优秀的可重复使用的固体催化剂，仅用生物质水解得到的FA进行无碱LA还原，将代表着这一重要转化的重大进展。支持的金纳米颗粒(NPs)最近已成为一系列有机转化的通用催化剂，包括一些涉及氢的反应。[11]尽管许多注意力都集中在几个用于绿色和原子高效有机合成的经典化学反应上，但负载金在生物质转化，特别是高附加值精细化学品的可持续合成方面的潜力仍然很大程度上仍未被发掘。[13…]
Biomass and its derivatives provide renewable alternatives to fossil-fuel resources for the sustainable production of liquid fuels and valuable chemicals.[1] The challenge for the effective utilization of these sustainable resources is to develop costefficient processing methods for the transformation of highly functionalized carbohydrates into value-added chemicals.[2] Carbohydrates derived from lignocellulosic materials comprise the largest fraction of terrestrial biomass, and various strategies for their efficient use as a commercial chemical feedstock are currently being established with the aim to supplement and ultimately replace fossil fuels.[3] In this respect, g-valerolactone (GVL) has been identified as one of the most promising renewable molecules: it can be converted into a variety of intermediate chemicals, from which a diverse range of biofuels as well as commodity and fine chemicals can be generated.[4] GVL can be obtained in high yield (> 99%) by the catalytic hydrogenation of levulinic acid (LA, 4-oxopentanoic acid),[5] which is accessible from lignocellulosic biomass by a simple and robust hydrolysis process.[1c, 6] Molecular hydrogen has generally been used for the catalytic hydrogenation of LA (Scheme 1);[4, 5] however, minimization of H2 consumption would be preferable for the production of GVL from biomass,[4d] especially when low-cost hydrogen is not readily available. From both economic and engineering points of view, the development of new efficient methods for GVL production with formic acid (FA, formed in an equimolar amount with LA by the acidic hydrolysis of biomass) as an in situ source of hydrogen is much needed.[7] This procedure can eliminate the need for an external source of hydrogen and thus has great industrial potential for the production of GVL from renewable biomass,[8] especially if an efficient and reusable catalyst can be employed. Although the use of FA as a hydrogen donor in catalytic transfer hydrogenation reactions is a wellestablished method for the reduction of carbonyl functionalities,[9] effective LA reduction with FA has proven to be very difficult, and many reported procedures require the use of FA in large excess or the addition of external hydrogen to enhance the activity of the catalyst.[7, 10] The most successful catalyst system reported to date is a RuCl3/PPh3 complex [8a] that enables the conversion of a 1: 1 neat mixture of LA and FA into GVL in high yield (up to 95%). However, besides the inherent limitation of homogeneous catalysis for the development of a sustainable catalytic process, this system requires the strict absence of water and the addition of copious amounts of a base to improve the reduction kinetics and minimize deactivation. Given the high water content and the extremely high acidity of the products of biomass hydrolysis, these features may present serious drawbacks in terms of energy consumption and processing cost as well as additional handling problems. Hence, the successful development of an excellent reusable solid catalyst for base-free LA reduction solely with FA derived from biomass hydrolysis would represent a significant advance for this important transformation.Supported gold nanoparticles (NPs) have recently emerged as versatile catalysts for a broad array of organic transformations, including a number of reactions involving hydrogen.[11] Whereas much attention has been focused on several classical chemical reactions for green and atomefficient organic synthesis,[12] the potential offered by supported gold for catalytic biomass transformation, especially toward the sustainable synthesis of high-value-added fine chemicals, remains largely unexplored.[13 …