An Efficient and Environmentally Benign Method for the Preparation of Diglycerol Dicarbonate

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Abstract
Glycerol is the main byproduct produced in the oleochemical and biodiesel industries. Surplus crude glycerol devalues commercially available refined glycerol and is perceived as waste. Currently, crude glycerol is mainly used as a low-value, low-energy fuel as well as a feed additive for ruminants. The valorisation of crude glycerol through novel, sustainable processes that generate valuable chemicals is crucial, as this approach creates new revenue streams from this industrial byproduct for both the biodiesel and oleochemical industries. Along this line, glycerol can be converted into diglycerol, which can subsequently be employed to prepare diglycerol dicarbonate. Diglycerol dicarbonate is a potential monomer for the synthesis of biobased Non- Isocyanate Polyurethanes (bio-NIPUs), biomaterials, and surfactants. In this contribution, for the first time, diglycerol dicarbonate was synthesised under microwave irradiation in the absence of a catalyst or solvent. Initially, the reaction was carried out under conventional heating conditions, yielding 56% of the product in 36 hours. Around 88% yield of diglycerol dicarbonate was achieved in 35 minutes when the transesterification of diglycerol with dimethyl carbonate was performed under microwave irradiation. Furthermore, fifteen readily available green catalysts were tested for the carbonyl transfer reaction. The results revealed that the use of catalysts reduced reaction time from 35 to 20 minutes, with 82-95% product yield. The resulting diglycerol dicarbonate product was characterized using 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy, Infrared (IR) spectroscopy, and melting point measurements. The method described here is environmentally benign as it is performed at a reduced reaction time using green catalysts, resulting in a more sustainable process.

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