Overview of the Synthesis Method of 2-Phenylimidazole

2-phenylimidazole compounds are of great research value in the fields of polymer materials, organic synthesis, proton exchange materials and organic luminescent materials, which promote the continuous exploration and research of their synthesis methods.2-PZ has also developed many preparation methods and systems in the past research work. According to recent literature reports, the synthesis method of 2-PZ can be summarized into four categories: Debs method, 2-phenylimidazoline dehydrogenation method, alkylation method and other categories.

Debus method

The famous Debus Radziszewski reaction is well over a century old. In 1858, Heinrich first dehydrated glyoxal, formaldehyde and ammonia in acetic acid solvent to produce imidazole. Since then, methods to synthesize imidazole compounds such as heterocyclic imidazole or aromatic substitution with α-dicompounds, aldehydes and ammonia have been developed and studied.

Debus The method is the direct condensation of glyoxaldehyde, benzaldehyde and ammonia to obtain 2-benzimidazole. This method, only one one step reaction, has the advantages of short process route, mild reaction conditions, wide raw material source and low production cost, and has become the preferred route of 2-phenylimidazole manufacturers at home and abroad. However, there are some deficiencies in this process route, such as low product yield, by-product generation, troublesome subsequent separation and purification, and short supply of high-quality products. In recent years, with the need of industrial production and the improvement of science and technology, many scholars are attracted to improve the synthesis route.(2-phenylimidazole is synthesized by Debus)

Introducing catalyst

Many scholars have improved the process by introducing catalysts in the reaction system. Song Yanmin et al. used benzyl acyl, aromatic aldehyde derivatives and ammonium acetate as raw materials to synthesize 2-phenylimidazole derivatives under the catalytic action of ethanol solvent and silica tungstic acid. This reaction was performed at 78 C for 1 h, in up to 82% yield.(The following below shows the synthesis of 2-phenylimidazole compounds by Debus method).

Commonly used catalysts include: Lewis acid, molecular iodine, silica tungstic acid, Sanshui indium trichloride, silica gel, zeolite, FeCl3, magnetic nanomaterials, ionic liquid and PEG-400. To some extent, the use of these catalysts makes up for the deficiencies of slow reaction rate, low reaction yield and long reaction time, but it also brings about the problems such as complicated post-processing, increased reaction cost, catalyst loss and inactivation, and environmental pollution.

Improve the synthetic device

In the patent, Zeng Zhouhua et al. discloses a gas-liquid-liquid phase synthesis device, which integrates pure NH3 into a mixing solution of benzaldehyde and glyoxal, controls the temperature within the range of 50 C to 80 C, and performs the reaction under micropressure for 12 h to synthesize 2-PZ. This method increases the contact area of the gas-liquid phase, improves the chemical reaction speed, and avoids the difficulty of the subsequent separation process caused by the addition of the phase transfer catalyst.

Select a new ammonia source

Ammonia is the source of N atoms on the imidazole ring. In theory, ammonium salt and amine compounds can provide N atoms as ammonia source. The traditional Debus method for imidazole using ammonia or NH 3 as ammonia source. In recent years, ammonium salts such as ammonium acetate have been gradually introduced into the imidazole compound production process. However, there are very few literature reports and studies on the preparation of 2-phenylimidazole.

Introducing the microwave radiation technology

Microwave radiation technology was first designed in 1990 by Chen et al., the device could be used for esterification, hydrolysis and cyclization reactions. The development of microwave continuous reactor is the innovation and development of organic synthesis technology. Microwave radiation is also widely used in the synthesis of imidazole compounds. Zheng et al. Using intermittent microwave irradiation technology, and KI as a catalyst to catalyze the aromatic aldehyde and phthalylenediamine reaction, the reaction only takes 7~10 min, and synthesized benzimidazole with good yield, providing a new method for the synthesis of benzimidazole.

The introduction of microwave radiation technology is beneficial to improve the reaction rate, reduce side reactions and make easy product purification. However, the conditions of this method are demanding and require high temperature and high pressure. Therefore, it is still in the experimental stage, and it is difficult to truly realize industrialization.

2-phenylimidazoline dehydrogenation method

2-phenylimidazoline dehydrogenation method requires two steps: the first step is 2-phenylimidazoline; the second step is 2-phenylimidazoline dehydrogenation.

2-phenylimidazoline is synthesis in the next article.

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