Environmental Engineering Reference
In-Depth Information
very relevant to platform molecules considering the various functionalities
present. As a whole, the syngas and broader thermal treatment platform are useful
in obtaining a wide range of chemical products, fuel and energy from almost any
carbonaceous biomass; it is the fact that any biomass can be used to generate
syngas that makes this route to platform molecules so appealing to the bio-based
economy.
4.8.2
5-(Chloromethyl)furfural: Chemical-Catalytic Treatment
The preparation of 5-CMF was first described in 1901 [164], its bromo analogue
having been characterised as early as 1899 [165]. Remarkably, these halomethyl-
furfurals were assigned correct structures even before the structure of 5-HMF had
been confirmed, based on a comparison with the known 5-(bromomethyl)-2-
furoic acid [166]. These early efforts involved the treatment of fructose, sucrose
or cellulose with a saturated solution of the hydrogen halide in an organic solvent,
giving yields in the range 12-30%. The first high-yielding preparation of CMF
was published in a 1977 patent and involved the use of a biphasic aqueous acid/
organic solvent reactor, by which a 77% yield of CMF from fructose was obtained
[167]. This result was followed up in a 1981 paper by Szmant and Chundury, who
performed a detailed optimisation study and found that CMF could be produced
from fructose in up to 95% yield, although glucose and starch gave much lower
yields [168]. Notable research groups of the twentieth century that involved CMF
in their research include those of Henry J.H. Fenton [164, 165], Emil Fischer
[169], Norman Haworth [170], and Donald Cram [171].
In 2008, Mascal and Nikitin reported the production of CMF from either
glucose, sucrose or cellulose in 71-76% yield, alongside 14-18% yield of a
mixture of HMF, levulinic acid and 2-(2-hydroxyacetyl)furan [172]. This was
significant in that it described the first synthesis of CMF in good yield from
practical biomass feedstocks (glucose, cellulose). This was followed up by a study
involving raw biomass, which reported similar findings [173]. In 2009, an
optimised procedure was published whereby either glucose, sucrose, cellulose or
corn stover was heated in a biphasic aqueous hydrochloric acid/organic solvent
reactor at 80-100°C for 3 hr to give CMF in 80-90% isolated yield, depending on
the feedstock, alongside 5-8% levulinic acid [174]. The method has recently been
adapted to a continuous flow reactor, and to processing under microwave
irradiation [175, 19]. CMF has therefore been established as a viable alternative to
the highly popular platform chemical HMF, which is presently derived in good
yield only from fructose and has serious issues associated with its isolation [176].
The derivative chemistry of CMF is essentially identical to that of HMF, the
only differences being that CMF is more reactive towards nucleophilic substitu-
tion at the methylene carbon and that it is more lipophilic than HMF.
CMF has basically two derivative manifolds: furanic and levulinic. Under mild
conditions, CMF reacts with nucleophiles to give halide substitution products
