Green synthesis of benzonitrile using ionic liquid with multiple roles as the recycling agent

Preparation of benzonitrile from benzaldehyde and hydroxylamine hydrochloride is one of the most advantageous approaches. Nevertheless, it suffers from various constraints such as longer reaction time, corrosion and recovery of hydrochloric acid, the use of metal salt catalysts and their separation. For these reasons, a novel green benzonitrile synthetic route was proposed with ionic liquid as the recycling agent in this study. The results indicated that hydroxylamine 1-sulfobutyl pyridine hydrosulfate salt ((NH₂OH)₂·[HSO₃-b-Py]·HSO₄) was an expert alternative to hydroxylamine hydrochloride. Meanwhile, the ionic liquid [HSO₃-b-Py]·HSO₄ exhibited the multiple roles of co-solvent, catalysis and phase separation, thus the use of metal salt catalyst was eliminated, and no additional catalyst was needed. Hence, the separation process was greatly simplified. When the molar ratio of benzaldehyde to (NH₂OH)₂·[HSO₃-b-Py]·HSO₄ was 1 : 1.5, the volume ratio of paraxylene to [HSO₃-b-Py]·HSO₄ was 2 : 1, the benzaldehyde conversion and benzonitrile yield were both 100% at 120 °C in 2 h. Even better, the ionic liquid could be recovered easily by phase separation, and recycled directly after reaction. Additionally, this novel route is applicable to the green synthesis of a variety of aromatic, heteroaromatic and aliphatic nitriles with excellent yields.