CHEMSUSCHEM
COMMUNICATIONS
DOI: 10.1002/cssc.201402396
Vitamin B1-Catalyzed Acetoin Formation from
Acetaldehyde: A Key Step for Upgrading Bioethanol to
Bulk C Chemicals
Ting Lu, Xiukai Li, Liuqun Gu, and Yugen Zhang*
4
[
a]
The production of bulk chemicals and fuels from renewable bi-
obased feedstocks is of significant importance for the sustaina-
bility of human society. The production of ethanol from bio-
mass has dramatically increased and bioethanol also holds
considerable potential as a versatile building block for the
chemical industry. Herein, we report a highly selective process
also industrial processes available for the production of C
4
[6]
[7]
chemicals, such as butadiene or 1-butanol. However, these
processes still suffer from poor selectivity and/or efficiency,
[4]
which eliminates a significant part of their economic value. It
is highly desirable to develop a highly selective, green, and ef-
ficient process for the conversion of ethanol to C bulk chemi-
4
for the conversion of ethanol to C bulk chemicals, such as 2,3-
cals.
4
butanediol and butene, via a vitamin B1 (thiamine)-derived N-
heterocyclic carbene (NHC)-catalyzed acetoin condensation as
the key step to assemble two C acetaldehydes into a C prod-
A major challenge for the conversion of ethanol to C chemi-
4
cals is the selectivity in the condensation or coupling of C to
2
[8a]
C4 (Scheme 1). The Guerbet reaction allows facile CÀC bond
2
4
uct. The environmentally benign and cheap natural catalyst vi-
tamin B1 demonstrates high selectivity (99%), high efficiency
(97% yield), and high tolerance toward ethanol and water im-
purities in the acetoin reaction. The results enable a novel and
efficient process for ethanol upgrading.
The development of sustainable processes for the production
of biobased commodity chemicals is one of the significant sci-
[
1]
entific challenges of today. Utilizing renewable biobased
chemicals as starting point for further transformations/prod-
ucts is highly desirable. This strategy not only offers benefits
from an environment point of view—biobased chemical trans-
formations are closely related to carbon-neutral cycles and bio-
2 4
Scheme 1. Possible C to C reactions for ethanol upgrading processes.
[2]
degradable materials—but also important economic benefits.
formation from alcohols, which is described as “borrowed hy-
drogen” chemistry. However, ethanol is a specifically difficult
The amount of ethanol produced from biomass has dramati-
cally increased recently (reaching 105 billion liters in 2011), and
hence ethanol has become one of the more prominent sources
[8]
substrate for these borrowed-hydrogen processes. Very re-
cently, Wass et al. reported a ruthenium-catalyzed system for
the conversion of ethanol to n-butanol, in which the selectivity
could be improved to 94%. However, this system still suffered
[
3]
of biofuel. In addition, bioethanol holds considerable poten-
tial as a versatile building block for chemical industries. Bio-
ethanol is considered as one of the most profitable chemicals
from renewable resources as compared to the fossil resour-
[9]
from low conversion (20%). The base-catalyzed aldol reaction
of aldehydes is another well-studied protocol for CÀC bond
[
4,5]
[10a]
ces.
Therefore, the utilization of bioethanol for the produc-
formation,
However, from the reactive acetaldehyde (oxi-
tion of value-added chemicals is more economically viable and
dized from ethanol), the selectivity for the aldol product 3-hy-
droxybutanal is always low, and is accompanied by undesired
could also help to reduce CO emissions. A number of impor-
2
[10b]
tant processes for the conversion of ethanol to bulk chemicals
oligomeric and polymeric products.
N-heterocyclic carbene
[
4]
have been established. However, most of the successfully ac-
(NHC)-catalyzed acyloin condensation usually provides a milder
[11]
cessible products from bioethanol are still C chemicals or re-
option for the CÀC bond formation of two aldehydes. How-
ever, the condensation of acetaldehyde to acetoin is rarely ex-
plored, probably due to low selectivity and poor tolerance to
2
lated products (on a million-ton scale), such as ethylene, acet-
[
4]
aldehyde, acetic acid, ethylacetate, and hydrogen. There are
[12]
polar protic compounds.
Although Breslow disclosed the mechanism of thiazolyli-
[a] Dr. T. Lu, Dr. X. Li, Dr. L. Gu, Dr. Y. Zhang
[11]
Institute of Bioengineering and Nanotechnology
dene-catalyzed benzoin condensation as early as 1958, the
successful preparation of acyloins with thiazolylidene or triazo-
lylidene catalysts was mostly limited to aromatic aldehydes or
3
1 Biopolis Way, The Nanos
Singapore 138669 (Singapore)
E-mail: ygzhang@ibn.a-star.edu.sg
[12b,13]
aldehydes with alkyl chain longer than a methyl group.
A
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201402396.
thiazole-based, enzyme-catalyzed acetoin reaction was also re-
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2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2014, 7, 2423 – 2426 2423