High value-added application of turpentine as a potential renewable source for the synthesis of heterocyclic Schiff base derivatives of cis-1,8-p-menthane-diamine serving as botanical herbicides

Abstract

Cis-1,8-p-menthane-diamine and its heterocyclic Schiff base derivatives (C1-C8) were designed and synthesized with turpentine as the raw material. These compounds were identified by FT-IR, ESI+-MS, 1H NMR and 13C NMR, then determined for their pre-emergence herbicidal activities against ryegrass. As results, both cis-1,8-p-menthane-diamine and its heterocyclic Schiff base derivatives had good herbicidal activities, and all of the heterocyclic Schiff base derivatives displayed much higher herbicidal activities than cis-1,8-p-menthane-diamine. Some compounds showed comparable herbicidal activities to diuron. Compound C3 had 51.0% higher herbicidal activities against ryegrass shoot growth than diuron. In addition, introduction of a bromine atom (an electron-withdrawing group) into the heterocyclic Schiff base derivatives containing furan ring (compound C1) was beneficial for the whole herbicidal activity. However, the herbicidal activity hadn't been improved when a methyl group (an electron-donating group) was introduced into compound C1. It was also observed that type of the heteroatom of the five-membered heterocyclic Schiff base and position of substitute on pyridine Schiff base had a significant influence on the activity of the core structure.