Abstract
In the field of organic syntheses, the development of environmentally friendly methods based on the concept of green chemistry has been always required. In response to this requirement, we reported solvent- and catalyst-free syntheses of imines using the pressure reduction technique as a key technology. We found that this reaction proceeded very rapidly in the initial stage, but its rate decreased with the passage of time. It was also found that the reaction of benzaldehyde with aniline had a specificity that the phase transition occurred. In this method, the desired imines could be obtained in good to excellent yields, but target compounds had to be given by purifications using organic solvents. Therefore, we tried to develop the perfect synthetic method of imine derivatives without organic or inorganic solvents. We selected two methods and took them into this investigation. One was exactly mixing (1:1, substance ratio) aldehydes and amines and the other was employing lower pressure (>0.1 mmHg, previous method: 1.0 mmHg) at the pressure reducing technique. When this improved synthetic method was performed, it was revealed that pure target imines were obtained in excellent yields without any purification.
Highlights
From the viewpoint of green chemistry, it was considered that using organic solvents in organic syntheses aimed at formation convenient compounds was not environmentally friendly, in recent years
We found that target imines were obtained in excellent yields when aldehydes and amines were mixed without a solvent and a catalyst
P-Tolualdehyde reacted with o-toluidine for 1.5 h without any solvent followed by the vacuum operation (3.0 h) to give the corresponding imine (Compound 1) in 99% yield
Summary
From the viewpoint of green chemistry, it was considered that using organic solvents in organic syntheses aimed at formation convenient compounds was not environmentally friendly, in recent years. The method attracting attention was to use water instead of an organic solvent [1] [2] [3] [4]. In our previous reaction system, it was found that target imines could be obtained in good yields by removing water under reduced pressure conditions. We found that this reaction proceeded rapidly in the initial stage, but its rate decreased with the passage of time This reaction system gave target products in good yields, the purification of the target product was required, such as the column chromatography using hexane/ether combination or the recrystallization using dichloromethane/hexane combination. It was found that pure target imines were obtained in excellent yields without any purification using organic solvents, when we tried improved reaction methods (Scheme). We will report the details of the improved reaction method
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
