A macroporous dual-functional acid–base covalent
organic
polymer catalyst poly(St-VBC)-NH
2
-SO
3
H was prepared
using high internal phase emulsion polymerization using vinylbenzyl
chloride (VBC), styrene (St), and divinylbenzene (DVB) as substrates
toluene as a porogenic solvent, and subsequent modification with ethylenediamine
and 1,3-propane sultone. The role of various amounts of toluene as
the porogenic solvent as well as the amount of 1,3-propane sultone
(different ratio of acid/base sites) on the structure of the prepared
materials have been carefully investigated. The prepared materials
were characterized by Fourier transform infrared (FT-IR), CHNS elemental
analysis, energy-dispersive X-ray (EDX), elemental mapping, field
emission scanning electron microscopy (FE-SEM), and thermalgravimetric
analysis (TGA). The catalytic activity of the poly(St-VBC)-NH
2
-SO
3
H series with different acid/base densities
was assessed for one-pot cascade C–C bond-forming reactions
involving deacetylation–Henry reactions. The poly(St-VBC)-NH
2
-SO
3
H(20) sample bearing 1.82 mmol/g of N (base
site) and 1.16 mmol/g (acid site) showed the best catalytic activity.
The catalyst demonstrated superior activity compared to the homogeneous
catalysts, poly(St-DVB)-SO
3
H+EDA, poly(St-VBC)-NH
2
+chlorosulfonic acid, and poly(St-DVB)-SO
3
H+poly(St-VBC)-NH
2
as the catalyst system. The optimized catalyst showed excellent
catalytic performance with 100% substrate conversion and 100% yield
of the final product in the one-pot production of β-nitrostyrene
from benzaldehyde dimethyl acetal under cascade reactions comprising
acid-catalyzed deacetalization and base-catalyzed Henry reactions.
It was shown that these catalysts were reusable for up to four consecutive
runs with a very slight loss of activity. The excellent performance
of the catalyst was attributed to the excellent chemical and physical
properties of the developed support since it provides an elegant route
for preparing site-isolated acid–base dual heterogenized functional
groups and preventing their deactivation via chemical neutralization.