Blog de cursos y estudiantes de Químicas del Departamento de Ciencias Quimico-Biológicas en la Universidad de las Américas Puebla.
Tuesday, May 05, 2015
Novel catalyst used to make styrene in one step
(Phys.org)—Styrene is an important industrial chemical. It is the
precursor to polystyrene which is used in various every day plastic products,
like disposable cups, packaging, and insulation. Over 18.5m tons of styrene is
produced industrially around the world. Typically, styrene synthesis begins
with benzene and ethylene, and involves a multi-step process under harsh
reaction conditions and often leads to unwanted by-products.
In research that aims to streamline and optimize
styrene synthesis Benjamin A. Vaughan, Michael S. Webster-Gardiner, Thomas R.
Cundari, and T. Brent Gunnoe from the Department of Chemistry at the University
of Virginia and the Center for Advanced Modeling in the Department of Chemistry
at the University of North Texas have devised a single-step synthesis of
styrene using a novel rhodium catalyst. Their work appears in Science.
The production of styrene,
or vinyl arenes in general, involves benzene alkylation. This is typically done
under harsh conditions involving high temperatures and either a Friedel-Crafts
or zeolite catalyst. This process typically involves poly-alkylated
bi-products. Additionally, the alkyl substituent will then need to be oxidized
to form the vinyl group, which is usually accomplished with a metal oxide at
high temperatures. The products are the target vinyl arene and hydrogen gas, as
well as any bi-products from poly-alkylation. Products from poly-alkylation are
converted to ethylbenzene in a trans-alkylation step, which follows the
Prior research from this group, found that this synthetic process can be
streamlined using a platinum catalyst for the alkylation of benzene, and the alkyl group will
subsequently undergo beta-hydride elimination, forming free styrene. However,
this process degrades the platinum catalyst, likely because the platinum ion
further reduces to platinum metal during the beta-elimination phase of the
To make this one-step
process industrially feasible, they need to find an optimal catalyst. Ideally,
this catalyst would directly vinylate the benzene ring rather than initial
alkylation followed by oxidation of the alkyl group. Additionally this catalyst
would not lead to multiple side reactions and have a high turnover number even
in harsh oxidative conditions and in the presence of highly reactive metal
hydrides. Furthermore, industrially favorable mechanisms would involve
recovering and recycling the oxidant using air or oxygen.
For this paper, Vaughan et al. designed a catalyst with rhodium rather
than platinum in hopes that the less favorable reduction of Rh(I) to elemental
rhodium compared to the reduction of Pt(II) would maintain the integrity of the