Zwitterionic Hydrobromic Acid Carriers for the Synthesis of 2‐Bromopropionic Acid from Lactide

Abstract

A convenient and highly efficient way of synthesizing 2-bromopropionic acid (2-BrPA) from lactide is presented. The procedure uses ionic liquids obtained from the addition of HBr to ammonium-based zwitterions as the solvent and bromination agent. The buffered HBr acidity, high polarity, and charge stabilizing character of the ionic liquid (IL) enable the synthesis of 2-BrPA with excellent selectivity. The best results are obtained with an imidazolium-based IL, that is, 1-(4-butanesulfonic acid)-3-methylimidazolium bromide ([MIMBS]Br). The HBr loading and water content of the IL are crucial parameters for the bromination reaction. The formed 2-BrPA product can be selectively isolated by extraction from the IL, and the unconverted substrate remains in the [MIMBS]Br IL for the next run. Successful recycling of the IL over four cycles is demonstrated.

Acrylic Acid Synthesis from Lactide in a Continuous Liquid-Phase Process

“…We recommend that in an industrial process HBr should be trapped in water to form an aqueous HBr solution. The latter can be used to form 2-BrPA from lactide or LA as shown previously . This step would close the HBr cycle in the process.…”

“…Our group reported the highly selective conversion of lactide to AA with hydrobromic acid as the catalyst. In detail, 2-bromopropionic acid (2-BrPA) is applied as acidic bromide source in [PBu 4 ]Br as the reaction matrix without additional solvent. − 2-BrPA can be effectively synthesized using a zwitterionic-based molten salt serving as water-free HBr carrier and acidity buffer. When the zwitterionic-based molten salt is loaded with HBr, the formed ionic liquid has been shown to act as a selective and efficient brominating agent and reaction matrix (solvent, proton source, and buffer) for the bromination of LA to 2-BrPA.…”

“…Especially, imidazole-based ILs showed exceptional selectivity in the synthesis of 2-BrPA from lactide. The best results were obtained with [MIMBS]Br and [EIMBS]Br reaching 60% yield to 2-BrPA and 100% selectivity …”

Highly Selective Synthesis of Acrylic Acid from Lactide in the Liquid Phase

“…For this purpose, we prepared 2-BrPAi ndependently according to ar ecently published protocol and added it in a molar concentrationo f5 %t ot he reaction mixture. [36] Note that 2-BrPAi sc onvertedd uring the reactiont oA Aa nd liberates water-free HBr,w hich acts as the acidic catalyst. In our conversion and selectivity calculations, we account for the added 2-BrPAa saf eedstock molecule.…”

“…We chose tetrabutylphos-phonium bromide ([PBu 4 ]Br) as bromides ource and stabilizer for the reaction, which has am elting point of 100 8C. [36] Note that 2-BrPAi sc onvertedd uring the reactiont oA Aa nd liberates water-free HBr,w hich acts as the acidic catalyst. [34,35] Owing to the liquid nature of all components under the reaction conditions, we performed our experimentsw ithout any additional solvent.…”