Quaternary Alkyl Ammonium Salt-Catalyzed Transformation of Glycidol to Glycidyl Esters by Transesterification of Methyl Esters

Abstract

Catalytic transformation of glycidol while maintaining its epoxide moiety intact is challenging because the terminal epoxide that interacts with the hydroxyl group via a hydrogen bond is labile for the ring-opening reaction. We found that a quaternary alkyl ammonium salt catalyzes the selective transformation of glycidol to glycidyl esters by transesterification of methyl esters. The developed method can be applied to the synthesis of multiglycidyl esters, which are valuable epoxy resin monomers. Mechanistic studies revealed the formation of a binding complex of glycidol and quaternary alkyl ammonium salt in a nonpolar solvent and the generation of the alkoxide anion as a catalyst through the ring-opening reaction of the epoxide. Computational studies of the reaction mechanism indicated that the alkoxide anion derived from glycidol tends to abstract the proton of another glycidol rather than work as a nucleophile, initiating the catalytic transesterification. Payne rearrangement of the deprotonated glycidol, which produces a destabilized base that promotes nonselective reactions, is energetically unfavorable due to the double hydrogen bond between the anion and diol. The minimal interaction between the quaternary alkyl ammonium cation and the epoxide moiety inhibited the random ring-opening pathway leading to polymerization.

DNP NMR spectroscopy enabled direct characterization of polystyrene-supported catalyst species for synthesis of glycidyl esters by transesterification

“…The higher activity of alkylammoniums with longchain alkyl groups (2-Cl, 3-Cl and 4-Cl) compared to 1-Cl parallels what is observed in homogeneous catalysis. 6 The catalytic activity of 4-Cl was slightly lower than that of 2-Cl, 3-Cl, owing to the absence of the smaller Me group(s). 8 Yet, it should be noted that 1-Cl showed lower activity in spite of the presence of three Me groups bound to nitrogen.…”

“…Considering that the substituents of the ammonium fragment plays an important role in the transesterification with molecular catalysts, 6,8 we first optimized the N-substituents of ammonium salts for transesterification of methyl ester with GD. Thus, 1-Cl, 2-Cl, 3-Cl, and 4-Cl were prepared by reactions of Merrifield resin with four types of alkyl amines, NMe 3 , NMe 2 n Oct, NMe n Oct 2 , and N n Oct 3 , respectively (Scheme 1).…”

Integrated and Metal Free Synthesis of Dimethyl Carbonate and Glycidol from Glycerol Derived 1,3-Dichloro-2-propanol via CO2 Capture

“…In this case, considering previous reports regarding the compositions of various deep eutectic solvents (DES), the chloride anion containing ionic liquids such as choline chloride and a hydroxyl group comprised of molecules such as glycerol, ethylene glycol, etc., performed as a HBD and HBA, respectively to form a DES [30]. Sato et al also showed that a similar hydrogen bonding interaction between the -OH group of glycidol and the Cl − anion of the quaternary alkylammonium salt was established and resulted in the formation of a binding complex [31]. Therefore, the hydrogen bonding interaction possibly does not allow the precipitation of [DBUH][Cl] salt in 2-Me-THF.…”

Amide/Iminium Zwitterionic Catalysts for (Trans)esterification: Application in Biodiesel Synthesis

“…These results suggest that the Brønsted basicity, structurally rigidity, and cation/anion distance in 5d might be the determining factors of catalytic performance. It was also found that other catalysts including Brønsted bases (NaOMe, tBuOK), Lewis bases (Et 3 N, DMAP, PPY, PPh 3 ), and ammonium salts [tetra-n-butylammonium iodide (TBAI), tri-n-dodecylmethylammonium chloride, 56 and tetramethylammonium methyl carbonate 57 ] were much less effective in promoting the reaction under the same conditions. The reaction was also found to be applicable to other fatty acid esters 6b−f.…”

“…Interestingly, lactone 11j was obtained quantitatively through the intramolecular transesterification of hydroxyl ester 10h (entry 10). However, the transesterification of methyl benzoate and glycidol, 56 which is a useful but challenging reaction, was sluggish when catalyst 5d was used. It appears that the reaction scope of 5d is complementary to that of tri-n-dodecylmethylammonium chloride.…”