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    Review of 'The neighbouring effect of isosorbide and its epimers in their reactions with dimethyl carbonate'

    The neighbouring effect of isosorbide and its epimers in their reactions with dimethyl carbonateCrossref
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    The neighbouring effect of isosorbide and its epimers in their reactions with dimethyl carbonate

    ABSTRACT – The reactions of isosorbide and its epimers, isomannide and isoidide, with dimethyl carbonate have been herein investigated as easy access to bio-based products by a free-halogen chemistry approach. Isosorbide and its epimers show a different reactivity in bimolecular nucleophilic substitution with DMC. Carboxymethylation reaction was carried out in the presence of DMC and a weak base resulting in the high-yielding synthesis of dicarboxymethyl derivatives. Isomannide was the most reactive anydro sugars due to the less sterically hindered exo position of the OH groups. On the other hand, methylation of isosorbide and its epimers, conducted in the presence of a strong base and DMC, showed the higher reactivity of the endo hydroxyl group, isoidide being the most reactive epimer. This result has been ascribed to the neighbouring effect due to the combination of the oxygen in β-position and the intramolecular hydrogen bond within the anhydro sugar structure. Methylation reactions were also conducted in autoclave at high temperature with the amphoteric catalyst hydrotalcite using DMC as reagent and solvent. In this case, the reactivity of the epimers resulted quite different with isosorbide being the most reactive reagent possibly as a result of the structure of hydrotalcite comprising of both acidic and basic sites. The neighbouring effect was observed with good evidence in these methylation reactions.

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      Review text

      The authors studied the reactions of isosorbide, isomannide and isoidide, with dimethyl carbonate under various conditions. As a whole, this manuscript is well written. The manuscript would benefit from improved a consideration of the following points. First, in the experiment concerning Carboxymethylation reaction of isosorbide and its epimers, the temperature was maintained at 90 °C with a reflux. However, the reaction temperature must be lower than the set temperature due to the production of MeOH. It is recommended that authors determine the temperature of the reactants directly. Furthermore, if authors add some curves along with the change of time, the paper would most certainly be more informative. Secondly, for all reactions, the authors used excessively high DMC, is this really needed?! Removal of DMC consumes energy. It would be appreciated if authors could provide the effect of the molar ratio of DMC: isosorbide and its epimers.


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