Catalytic Conversion of a Chitin-Derived Sugar Alcohol to an Amide-Containing Isosorbide Analog

Chitin
is an attractive feedstock for the production of organonitrogen
compounds. The hydrolysis of chitin produces N-acetylglucosamine,
and subsequent hydrogenation gives a sugar alcohol, 2-acetamide-2-deoxysorbitol
(ADS). However, the transformation of these compounds to useful chemicals
has remained a challenge due to the complicated reactivity of the
N-containing molecules. Here, we report the catalytic conversion of
ADS to 2-acetamide-2-deoxyisosorbide (ADI), which is a potential platform
chemical for the production of organonitrogen compounds such as polymers.
This study shows that ADS hardly undergoes the dehydration condensation
to ADI under the reaction conditions used for a widely studied dehydration
reaction of a similar sugar alcohol, sorbitol. Instead, a large amount
of a super strong acid, CF3SO3H, under vacuum
conditions is required to produce ADI from ADS. Density functional
theory calculations indicate that acetamide groups in the substrate
trap acid protons, and therefore, a large amount of strong acid is
necessary to compensate for this neutralization effect. Moreover,
the decrease in pressure facilitates water removal and inhibits deacetylation
side reactions.