sc9b03359_si_001.pdf (4.93 MB)
Acid-Catalyzed Reactions of Isopropenyl Esters and Renewable Diols: A 100% Carbon Efficient Transesterification/Acetalization Tandem Sequence, from Batch to Continuous Flow
journal contribution
posted on 2019-11-08, 17:03 authored by Davide Rigo, Giulia Fiorani, Alvise Perosa, Maurizio SelvaA new
acid-catalyzed tandem sequence was investigated for the upgrading
of renewable 1,2-diols such as propylene glycol (PG) and ethylene
glycol (EG), with isopropenyl esters. For example, at 50 °C and
in the presence of Amberlyst-15, the reaction of PG with nontoxic
isopropenyl acetate allowed an initial irreversible monotransesterification
of the diol, releasing acetone which then promoted acetalization on
a second molecule of the glycol. The overall protocol was 100% carbon
efficient, affording water as the sole byproduct. The reaction scope
was extended to higher homologues of enol esters as isopropenyl-octanoate
and phenylbutyrate. Additionally, the tandem sequence was successfully
transferred in the continuous-flow (CF) mode where the catalyst (Amberlyst-15)
could be used virtually indefinitely without loss of performance,
and the solvent (THF or CPME) was quantitatively recovered and reused.
Under CF conditions, the reaction of PG with isopropenyl acetate could
be run at 30 °C and atmospheric pressure with a (nonoptimized)
productivity up to 9.7 mmol gcat–1 h–1, 3 times higher than that achieved in the batch mode.
When ethylene glycol was used, a lower tandem selectivity was observed
due to predominance of transesterification products, mono- and diesters,
over the acetal compound.