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 dimethyl carbonate (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 anhydro sugar 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 neighboring 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 differently with isosorbide being the most reactive reagent possibly as a result of the structure of hydrotalcite comprising of both acidic and basic sites. The neighboring effect was observed with good evidence in these methylation reactions.

Effect of Catalyst on the Molecular Structure and Thermal Properties of Isosorbide Polycarbonates

“…The relative contents of terminal groups, including the terminal hydroxyl group (−OH, including exo–OH and endo–OH; peaks in 1 H NMR at δ4.40 and 3.60 ppm, respectively) and the terminal phenoxy group (PhO–, peak in 1 H NMR at δ7.40 ppm), were calculated by peak integration. , The peak integration of 3 signals at δ4.90 ppm in a repeating unit is normalized to be 1.…”

“…prepared isosorbide dimethyl derivatives from isosorbide and dimethyl carbonate (DMC), and they reported that using the larger ionic radius metal (K + ) as the catalyst makes it easier for the exo–OH to attack the DMC carbonyl carbon. In the case of the smaller ionic radius metal (Na + ), endo–OH was found to react easier with DMC . Tundo et al also observed the high reactivity of exo–OH with the K + or Cs + catalysts in the DMC and ISB reactive systems, whereas the endo–OH became more reactive under the catalytic condition of the Na + compound .…”

The future of isosorbide as a fundamental constituent for polycarbonates and polyurethanes

“…It behaves like a versatile reactive, not only in the carbonylation reaction, but also in the methylation to give dimethyl isosorbide (DMI). The preference by one or other pathway depends on factors such as the catalyst basicity strength and nucleophile character and the reaction conditions (time and temperature) (16,17).…”

“…Catalysts containing larger ionic radius metal (K + or Cs + ) easily promoted the exo-OH attack to carbonyl groups of DMC. On the other hand, the catalysts composed of smaller ionic species (Na + ) preferentially promoted the reaction between the endo-OH of the isosorbide and the DMC (6,16,22).…”

“…Polycarbonates (PC) constitute a principal family of polymers of daily use in many fields due to their properties as mechanical strength, good transparency, and excellent thermal stability (16). Accordingly, polycarbonate diols are an important PC sub-class, precursors of polyurethanes, which find broad applications in the manufacture of adhesives but also in coatings such as paints, varnishes, and lacquers among others (30).…”