Key Takeaways & Executive Findings
- •• FeOOH/Fe3O4/MOF polygonal mesopores microflower catalyst synthesized via room-temperature templating from MIL-88B(Fe) exhibits high catalytic activity for NMST oxidation to NMSBA using oxygen as a clean oxidant. • The continuous-flow microreactor system significantly accelerates reaction rate, shortens reaction time, and enhances selectivity compared to traditional batch reactors. • The sustainable protocol uses an inexpensive and environmentally friendly NaOH/methanol mixture, enabling gram-scale preparation of carboxylic acid and benzyl alcohol derivatives with high chemoselectivities. • The approach offers a green alternative to conventional strong oxidants, reducing environmental pollution and holding potential for industrial applications.
Abstract
The development of efficient systems for the catalytic oxidation of 2-nitro-4-methylsulfonyltoluene (NMST) to 2-nitro-4-methylsulfonyl benzoic acid (NMSBA) with atmospheric air or molecular oxygen in alkaline medium presents a significant challenge for the chemical industry. Here, we report the synthesis of FeOOH/Fe3O4/metaleorganic framework (MOF) polygonal mesopores microflower templated from a MIL-88B(Fe) at room temperature, which exposes polygonal mesopores with atomistic edge steps and lattice defects. The obtained FeOOH/Fe3O4/MOF catalyst was adsorbed onto glass beads and then introduced into the microchannel reactor. In the alkaline environment, oxygen was used as oxidant to catalyze the oxidation of NMST to NMSBA, showing impressive performance. This sustainable system utilizes oxygen as a clean oxidant in an inexpensive and environmentally friendly NaOH/methanol mixture. The position and type of substituent critically affect the products. Additionally, this sustainable protocol enabled gram-scale preparation of carboxylic acid and benzyl alcohol derivatives with high chemoselectivities. Finally, the reactions can be conducted in a pressure reactor, which can conserve oxygen and prevent solvent loss. Moreover, compared with the traditional batch reactor, the self-built microchannel reactor can accelerate the reaction rate, shorten the reaction time, and enhance the selectivity of catalytic oxidation reactions. This approach contributes to environmental protection and holds potential for industrial applications.
1. Introduction
With the expansion of the global corn planting area, the market demand for herbicides in corn fields has increased rapidly. Mesotrione, also known as 2-(4-mesyl-2-nitrobenzoyl)-1,3-cyclohexanedione (NTBC), is recognized as a broad-spectrum, high-efficiency, low-toxicity, and environmentally friendly herbicide for corn fields, developed through the modification of sulcotrione [1]. Notably, NTBC has demonstrated outstanding biological activity, approximately 10 times higher than sulcotrione [2]. 2-Nitro-4-methylsulfonyl benzoic acid (NMSBA) serves as a crucial intermediate in the synthesis of dyes, medicines, and pesticides, particularly NTBC [3]. Conventionally, NMSBA is derived from the oxidation of 2-nitro-4-methylsulfonyltoluene (NMST) [4]. However, due to the presence of two potent electron-withdrawing substituents (NO2 and SO2CH3) on the benzene ring of NMST, the methyl on the aromatic ring is rather difficult to oxidize NMST to NMSBA except by strong oxidants. Previous studies reported that concentrated nitric acid and concentrated sulfuric acid were used as oxidants for the reaction [5]. This method will produce a large amount of NOx or sulfide and has the characteristics of a violent reaction and many by-products [6]. Notably, nitric acid and sulfuric acid not only corrode equipment but also pollute the environment [7]. Therefore, it is urgent to develop a green technology to replace the strong oxidation technology for the transformation of NMST to NMSBA under a mild environment.
Traditionally, various oxidants such as H2O2 [8], potassium permanganate [9], sodium hypochlorite [10], or organic peroxides [11] are necessary for effective conversion. However, these oxidants are relatively costly and generate significant waste. Compared with those oxidants, the oxidation of NMST to NMSBA with oxygen as the oxidant is a promising and green process and provides environmental protection, with the only byproduct of H2O. Nonetheless, the reported activity of the catalyst in this process remains relatively low, underscoring the critical importance of developing an efficient catalyst system [5,12]. Metal–organic frameworks (MOFs) are a new type of hybrid inorganic–organic microporous crystalline material composed of metal ions and organic ligands. Due to its unique characteristics and functions, it has been widely used in many fields such as catalytic o
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Jianzhi Wang, Xugen Li, Cheng Zhang, Yuan Pu, Jiawu Liu, Jie Liu, Yanping Liu, Xiao Lin, Faquan Yu (2024). Polygonal mesopores microflower catalysts for the catalytic oxidation of 2-nitro-4-methylsulfonyltoluene to 2-nitro-4-methylsulfonylbenzoic acid in a continuous-flow microreactor. Chinese Journal of Chemical Engineering. https://doi.org/10.1016/j_cjche_1448
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Frequently Asked Questions
What is the main contribution of this paper?
The paper presents a novel FeOOH/Fe3O4/MOF polygonal mesopores microflower catalyst for the efficient catalytic oxidation of 2-nitro-4-methylsulfonyltoluene to 2-nitro-4-methylsulfonylbenzoic acid using oxygen as a clean oxidant in a continuous-flow microreactor, offering a green and sustainable alternative to traditional strong oxidants.
How does the continuous-flow microreactor improve the reaction compared to batch reactors?
The self-built microchannel reactor accelerates the reaction rate, shortens the reaction time, and enhances the selectivity of catalytic oxidation reactions compared to traditional batch reactors, as demonstrated in the study.
What is the significance of using oxygen as an oxidant?
Using oxygen as an oxidant is environmentally friendly because it produces only water as a byproduct, avoiding the hazardous waste and corrosion issues associated with strong oxidants like nitric acid and sulfuric acid.
What are the key features of the FeOOH/Fe3O4/MOF catalyst?
The catalyst is synthesized at room temperature via templating from MIL-88B(Fe) and features polygonal mesopores with atomistic edge steps and lattice defects, which contribute to its high catalytic activity.
What are the potential industrial applications of this work?
The sustainable protocol enables gram-scale preparation of carboxylic acid and benzyl alcohol derivatives with high chemoselectivities, and the use of a pressure reactor conserves oxygen and prevents solvent loss, making it promising for industrial applications in the synthesis of herbicides and pharmaceuticals.
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