Fabrication Of β-Cyclodextrin Polymer Via Cross-linking Reaction As Oxidative Catalyst For Synthesis Of Benzaldehyde

Benzaldehyde production is attractive in industry, as benzaldehyde is the second largest perfume in the world. With more cares about food quality, consumers prefer for natural benzaldehyde, which leads to the increasing demand for natural benzaldehyde representing a strong market of interest. The natural benzaldehyde is mainly from alkaline hydrolysis of natural cinnamon oil or cinnamaldehyde, which is rich in Guangdong and Guangxi Provinces. Our team has developed a clean process to produce benzaldehyde under mild conditions catalyzed byβ-cyclodextrin (β-CD), but the yield of benzaldehyde was only 42%.β-CD has a limited solubility in water and high-cost recycling, which limit its industry application. Therefore we modifiedβ-CD into insolubleβ-cyclodextrin polymer (β-CDP) to solve the problem, and devote to develop a new environmentally-friendly way from cinnamaldehyde to benzaldehyde under much milder conditions. Moreover, the mechanism has been investigated by various characteristic methods and experiments.In this paper, insolubleβ-CDP was prepared from P-CD crosslinked with epichlorohydrin (EPI) at first and their solubility could be well controlled by optimizing the processes. The polymers were characterized by FTIR, TG and XRD. The results demonstrated that the polymerization between EPI andβ-CD indeed occurred. In addition, theβ-CDP also has better chemical stability and thermal stability thanβ-CD.Then,β-CDP was adopted as catalyst in the oxidations of cinnamaldehyde to benzaldehyde with sodium hypochlorite as oxidant. Theβ-CDP showed excellent activity for the oxidation under mild conditions. The influencing factors have been investigated, and 63.27% yield of benzaldehyde was obtained under the optimum conditions (60℃,15min, NaClO 1mL). Moreover, a plausible mechanism has been researched by intermittent sampling and GC-MS.At the same time, the amplification experiment was successfully conducted in the labmax automatic lab reactor. The oxidation of cinnamaldehyde catalyzed byβ-CDP was verified by in situ FTIR spectra. The yield of benzaldehyde was 67%, indicating thatβ-CDP is available for producing natural benzaldehyde at ambient atmosphere.At last,β-CDP were prepared byβ-CD using 2,4-diisocyanatotoluene (TDI) as crosslinking agent in DMSO/PDMS emulsion system. It was demonstrated thatβ-CDP not only retained the cavity structure ofβ-CD but also combined with the thermostability, chemical stability and mechanical strength of polymer, especially the mechanical strength is better than the polymer synthesized by EPI. Theβ-CDP also presented catalytic activity for aqueous oxidation of cinnamaldehyde under mild reaction conditions. These results demonstrate that the polymer can be used as a new material in organic liquid reaction.In all, two kinds of insolubleβ-CDP were synthesized by different crosslinkers, and they can catalyze natural benzaldehyde from natural cinnamaldehyde under mild conditions, using green solvent. These widen the application scope ofβ-CDP and develop a clean, efficient and environmentally-friendly process for the conversion of cinnamaldehyde to natural benzaldehyde, which offered theoretical and technical foundation for industrial production.