The role of cyclodextrins in the acceleration of the reaction rate in a biphasic hydroformylations

The role of cyclodextrins in accelerating the reaction rate in biphasic hydroformylation: Cyclodextrins facilitate the transport of the substrate 1-octene from the organic bulk phase to the liquid–liquid interface and simultaneously remove the product nonanal from the interfacial region. [Display omitted] •Water based biphasic hydroformylation assisted by cyclodextrins.•Examined for the first time using an in-situ image-based boroscopic technology.•RAME-β cyclodextrins increased the aLL by 84 %•Kinetic study showed that RAME-β cyclodextrins reduce the rate limiting effect of the nonanal concentration.•Increasing RAME-β cyclodextrins concentration decrease dependency of the reaction rates on the conversion progress. Water based biphasic hydroformylation assisted by cyclodextrins is known for enhanced reaction rates in comparison to the non-assisted biphasic hydroformylation. In this paper, the liquid–liquid interface of the hydroformylation of 1–octene, enhanced by randomly methylated-β cyclodextrins (RAME-β cyclodextrins), was examined for the first time using an in-situ image-based boroscopic technology. This technique enables the observation of the liquid–liquid interfacial area (aLL) during the reaction and under reaction conditions, facilitating an explicit analysis of the droplet population. In this study defined mixtures of the reaction components with RAME-β cyclodextrins increased the aLL by 84 %. A kinetic study showed that RAME-β cyclodextrins reduce the rate limiting effect of the nonanal concentration in the two phasic water/octene system on the interphase. The kinetic expression shows consequently higher reaction rates for this three-phase conversion, leading to a 387 % increase in aldehyde yield. When comparing four different amounts of RAME-β cyclodextrins (nCD:nRh(acac)(CO)2 = 0 / 12:1 / 24:1 / 50:1), we observed a decreasing dependency of the reaction rates on the conversion progress and therefore on the nonanal formation for higher cyclodextrin concentrations. A recovery test of the aqueous phase involving nonanal and 1-octene reveals a drastically increased concentration of 1029 % 1-octene (coctene = 1.08 10-3 mg mg−1) and 13676 % nonanal (cnonanal = 14.41 10–3 mg mg−1) after the addition of 0.002 mol RAME–β cyclodextrins. These findings affirm that RAME-β cyclodextrins primarily remove nonanal from the interfacial region while facilitating an increased availability of 1-octene for the surface bound reaction.