Cascades with carbon dioxide: Making substances out of CO2
Making substances Out of CO2

Date:
September 8, 2020
Source:
Wiley
Summary:
Carbon dioxide is not just an undesirable greenhouse gas, it is
also an interesting source of raw materials that are valuable and
can be recycled sustainably. Researchers have now introduced a
novel catalytic process for converting carbon dioxide into valuable
chemical intermediates in the form of cyclic carbonates.



FULL STORY ========================================================================== Carbon dioxide (CO2) is not just an undesirable greenhouse gas, it
is also an interesting source of raw materials that are valuable and
can be recycled sustainably. In the journal Angewandte Chemie, Spanish researchers have now introduced a novel catalytic process for converting
CO2 into valuable chemical intermediates in the form of cyclic carbonates.


========================================================================== Getting CO2 to react is unfortunately not easy. Currently, most
research is focused on the conversion of CO2 into methanol, which can
be used as an alternative fuel as well as a feedstock for the chemical industry. Innovative catalytic processes could allow CO2 to be converted
into valuable chemical compounds without taking a detour through methanol, perhaps for the production of biodegradable plastics or pharmaceutical intermediates.

One highly promising approach is the conversion of CO2 into organic
carbonates, which are compounds that contain a building block derived
from carbonic acid, comprising carbon atom attached to three oxygen
atoms. Researchers working with Arjan W. Kleij at the Barcelona Institute
of Science and Technology (Barcelona), the Institute of Chemical Research
of Catalonia (Tarragona), and the Catalan Institute of Research and
Advanced Studies (Barcelona), have developed a conceptually new process
to produce carbonates in the form of six- membered rings, starting from
CO2 and basic, easily accessible building blocks.

These cyclic carbonates have great potential for the creation of new
CO2-based polycarbonates.

The starting materials are compounds with a carbon-carbon double bond
and an alcohol group (-OH) on a neighboring carbon atom (homoallylic
alcohols). In the first step of the reaction, the double bond is converted
into an epoxide, a three-membered ring with one oxygen and two carbon
atoms. The epoxide is able to react with CO2 in the presence of a specific catalyst. The product is a cyclic carbonate in the form of a five-membered
ring with three carbon and two oxygen atoms. The carbon atom at the "tip"
of the five-membered ring is attached to an additional oxygen atom. In
the next step, an organic catalyst (N-heterocyclic base) activates the OH
group and causes the five-membered ring to rearrange into a six-membered
ring. The oxygen atom from the OH group is integrated into the new ring,
while one of the oxygen atoms from the original five-membered ring forms
a new OH group. However, the reverse reaction also takes place because the original five-membered ring is significantly more energetically favorable,
and only a vanishingly small amount of the six- membered ring is present
at equilibrium. The trick is to trap the six-membered ring. The new
OH group binds to a reagent (acylation) because its different position
makes it considerably more reactive than the original OH group.

This newly developed process gives access to a broad palette of novel,
six- membered carbonate rings in excellent yields, with high selectivity
and under mild reaction conditions. This widens the repertoire of
CO2-based heterocycles and polymers, which are difficult to produce by conventional methods.


========================================================================== Story Source: Materials provided by Wiley. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Chang Qiao, Alba Villar‐Yanez, Josefine Sprachmann, Bart
Limburg,
Carles Bo, Arjan W. Kleij. Organocatalytic Trapping of Elusive
Carbon Dioxide Based Heterocycles by a Kinetically Controlled
Cascade Process.

Angewandte Chemie International Edition, 2020; DOI: 10.1002/
anie.202007350 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200908122455.htm

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