Benzyltributylammonium chloride is an organic salt compound, usually used in catalytic reactions and surfactants. It can play a catalytic role in some organic synthesis reactions, and can be used as a cleaning agent, lubricant and emulsifier. In addition, the compound is widely used in certain industrial fields, such as in the plastic, rubber and textile manufacturing processes.

One-Pot Synthesis of 5-(Chloromethyl)furfural using Benzyltributylammonium chloride

5-(Chloromethyl)furfural (CMF), a bio-renewable chemical building block, has been produced in good isolated yields from biomass-derived carbohydrates within a closed aqueous HCl-1,2-dichloroethane biphasic reactor in the presence of benzyltributylammonium chloride (BTBAC) as a phase transfer catalyst (PTC). Initially, a slightly modified literature process of CMF preparation was adopted. Glucose was chosen as the model substrate for process optimization. In a typical reaction, glucose was suspended in aq. HCl (35%)-DCE biphasic reaction mixture taken in a sealed round-bottomed glass pressure reactor fitted with a magnetic stirring rod and Teflon screw top. Benzyltributylammonium chloride (10 wt% of glucose) was added as a phase transfer catalyst. The reactor was sealed and magnetically stirred in a pre-heated (90 °C) for 3 h. The control reactions were carried out using the same reaction conditions except no BTBAC was added. The BTBAC catalyst was recovered from the silica gel column by eluting with 20% methanol in chloroform where 96% of benzyltributylammonium chloride was successfully recovered.[1]

The optimized reaction was applied to various carbohydrates for the production of CMF. Control reactions were conducted for each substrate and compared with reaction using BTBAC as PTC. In the presence of 10wt% of BTBAC, glucose provided CMF in 64% isolated yield whereas the control reaction provided only 47% CMF under identical conditions. Fructose provided 62% yield of CMF in the presence of Benzyltributylammonium chloride whereas the control reaction provided CMF in 53% isolated yield. The 1H and 13C NMR spectra of recovered Benzyltributylammonium chloride shows some (ca. 10%) impurity due to acid-induced decompostion of BTBAC. Use of the recovered BTBAC without further purfication provided CMF in 55% yield from glucose. Use of BTBAC afforded CMF in roughly 10% higher yields from all the carbohydrates studied. LA was also isolated in marginally higher yields in reactions using Benzyltributylammonium chloride compared to the control reactions. Humic matter formed in noticeably lower quantities in reactions using BTBAC.

Hydrochloric acid-catalyzed coproduction assisted by a phase transfer catalyst

The renewable and carbon-neutral character of biomass makes it an environment-friendly alternative to the exhaustible fossilized carbon sources for the production of liquid transportation fuels and chemicals. The idea is to sequester the furanic molecules into the organic phase as soon as they form and slow down their decomposition in aqueous acid. Benzyltributylammonium chloride (BTBAC) is a known phase transfer catalyst (PTC) for various organic synthetic applications. In a recent report, we had shown that CMF could be prepared from various carbohydrates in concentrated hydrochloric acid-1,2-dichloroethane (DCE) biphasic reaction using BTBAC as a PTC. The reaction was optimized on reaction temperature, duration, loading of Benzyltributylammonium chloride, and concentration of HCl. The optimized reaction condition was then applied for the one-pot coproduction of furfural and CMF from a mixture of pentose and hexose sugars such as glucose and xylose. The azeotropic concentration of HCl was used to allow straightforward recovery of the aqueous acid by distillation while minimizing the decomposition of BTBAC.[2]

Selective dissolution of the furanics in hot petroleum ether (60–80 °C) left behind BTBAC in excellent mass balance (>95%). The use of recovered BTBAC for the preparation of furfural or for the coproduction of CMF and furfural did not show any noticeable change in isolated yields up to three consecutive cycles.  The use of Benzyltributylammonium chloride afforded significantly higher yields of furfural starting from xylose when compared to the control reaction. The insoluble humic matter formed in noticeably lower quantities in reactions using Benzyltributylammonium chloride. CMF and furfural were coproduced from a physical mixture of xylose and hexose carbohydrates. The yields of CMF and furfural were higher when using BTBAC as PTC. The azeotropic concentration of HCl allowed conducting the reaction under the refluxing condition without evaporative loss of the HCl gas. No chemical decomposition of BTBAC was observed, and it was recovered in near-quantitative yield after the reaction Benzyltributylammonium chloride was conveniently separated from the product mixture by chromatography or trituration with petroleum ether.

References

[1]Bandibairahanhalli Onkarappa, S., & Dutta, S. (2019). Phase Transfer Catalyst Assisted One - Pot Synthesis of 5 - (Chloromethyl)furfural from Biomass - Derived Carbohydrates in a Biphasic Batch Reactor. ChemistrySelect, 4(25), 7502 - 7506. https://doi.org/10.1002/slct.201901347

[2]Bhat, Navya Subray et al. “Hydrochloric acid-catalyzed coproduction of furfural and 5-(chloromethyl)furfural assisted by a phase transfer catalyst.” Carbohydrate research vol. 496 (2020): 108105. doi:10.1016/j.carres.2020.108105