Lignocellulosic Micro- and Nanomaterials as Copper Frames for the Evaluation of the Copper(I)-Catalyzed Azide-Alkyne Cycloaddition

Received Feb 22, 2017; Accepted Jun 15, 2017

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1. Introduction

The “Huisgen click” reaction refers to an azide-alkyne 1,3-dipolar cycloaddition. This reaction has many useful applications for drug discovery [1], polymer synthesis [2], and material science [3], among other biological applications [4, 5]. However, this reaction often requires high temperatures, has a low reaction rate, and typically produces a mixture of 1,5-substituted and 1,4-substituted triazoles [6].

Copper (Cu) based catalyst for the “Huisgen click” reaction has received significant attention during the last decade due to its versatile reactivity and much lower cost compared with noble metals, such as Pd and Rh. The rate of this copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is increased by a factor of 10⁷ relative to the purely thermal process [6]. Most CuAAC procedures involve in situ reducing agents to reduce Cu(II) salts in the generation of Cu(I) catalysts [7]. This reaction is quite insensitive to its environment and is also unaffected by most functional groups, so it may be performed in an aqueous or organic solution. However, it is most commonly performed in a water/alcohol mixture [6, 8, 9], though, without somehow immobilizing the copper on a homogeneous support, this CuAAC reaction is still very limited due to the low recoverability of copper from the product [10].

In general catalytic metal particles have been immobilized on solid supports that include the following: silica, alumina, zirconia, ceria, zeolites, glass fibers, and synthetic polymers [11–14]. The concept of sustainable chemistry is opening incredible opportunities for supporting materials coming from renewable natural polymers. Cellulose-based materials were studied as a support material for metal catalysts some years ago [15]. In recent years, the utilization of cellulose nanomaterials, such as cellulose nanofibers and cellulose nanocrystals, has demonstrated excellent performance to be used as scaffold...