Chemistry Reference
In-Depth Information
Fig. 13.2
Schematization of two-steps synthesis of ILs
appear to be most frequently used in literature, as those adapted from (Ranke et al.
2007a
). In this way, the cation head groups were abbreviated as stated above, and
the alkyl chains attached to the head group are given as numbers corresponding to
the number of carbon in the alkyl residues, with the exception of pyridinium cation
which abbreviation was made by noting the position of attachment and a symbol
for the attached group (e.g. Py4-3Me-4Me BF4 for 1-butyl-3,4-dimethylpyridinium
tetrafluoroborate) (Ranke et al.
2007a
; Pham et al.
2010
).
ILs are usually obtained in a two step synthesis, which involves the preparation
of cation in the first step and anion exchange in the second step (Fig.
13.2
) (Zhang
et al.
2009
; Scammells et al.
2005
). Synthesis method obviously may suffer small
variations depending on the type of ILs (Zhang et al.
2009
; Carrera et al.
2010
; Ohno
and Fukumoto
2007
; Pernak et al.
2011
; Zhao et al.
2007
; Scammells et al.
2005
;
Harjani et al.
2009
; Papaiconomou et al.
2007
, 2010). Commonly the cations are
prepared essentially by protonation with a free acid, or by quaternization of an amine
or an phosphine. This involves the alkylation of an organic substrate (e.g., pyridine,
imidazole, trialckylamine, etc.)—reaction of a Lewis-basic nucleophile heteroatom
with an alkyl halide, the mixture being stirred and heated (Fig.
13.2
) (Zhang et al.
2009
; Pernak et al.
2011
; Zhao et al.
2007
; Scammells et al.
2005
; Harjani et al.
2009
; Papaiconomou et al.
2007
,
2010
). In the second step, the precursor obtained
in the first step is used for anion metathesis with Lewis acids or metal salts of the
desired anions finally obtaining a mixture which contain the desired IL (Fig.
13.2
)
(Zhang et al.
2009
; Pernak et al.
2011
; Zhao et al.
2007
; Scammells et al.
2005
;
Harjani et al.
2009
; Papaiconomou et al.
2007
,
2010
). The resulting mixtures can
form either a biphasic system or a homogeneous phase with water, which depends
on the IL solubility in water (Zhang et al.
2009
; Scammells et al.
2005
). From these
mixtures the IL must be separated very carefully because the impurities may have a
drastic effect on the physicochemical properties (Zhang et al.
2009
; Scammells et al.
2005
).
From the desire to obtain ILs in just one reactor and also to avoid separation and
purification processes of the intermediate chemical compounds, the researchers have
been able to realize one-pot synthesis of a part of ILs (Zhang et al.
2009
; Allen et al.
2006
).
