Chemistry Reference
In-Depth Information
Fig. 13.1
Examples of the cationic and anionic structures that may be found in the ionic liquids'
constitution
quinolinium (Quin), pyrrolidinium (Pyr), piperidinium (Pip), morpholinium (Mor),
quaternary ammonium (N), quaternary phosphonium (P), guanidinium (G), sulfo-
nium, and other cations (Fig.
13.1
) (Zhang et al.
2009
; Pham et al.
2010
; Frade and
Afonso
2010
; Carrera et al.
2010
; Zhao et al.
2007
). This cations can be found in com-
bination with different anions such as: Cl
−
,Br
−
,I
−
, AlCl
4
,NO
3
, HSO
4
,PF
6
,BF
4
,
[CF
3
COO]
−
, [CF
3
SO
3
]
−
or [TfO]
−
, [N(CF
3
SO
2
)
2
]
−
or [NTf
2
]
−
, [ N(C
2
F
5
SO
2
)
2
]
−
or [Pf
2
N]
−
, [N(CN)
2
]
−
, [OctSO
4
]
−
, and others (Fig.
13.1
), see Wei and Ivaska
(
2008
); Frade and Afonso (
2010
); Petkovic et al. (
2011
).
By incorporating carboxylic acids, glucose, non-nutritive sweeteners as acesulfa-
mate [Ace]
−
and saccharinate [Sac]
−
, amino acids (AA) scientists are trying to obtain
biocompatible ILs (Petkovic et al.
2011
; Imperato et al.
2007
) Because amino acids
have in their molecule both a carboxylic residue and an amino group, they can be used
either as anions or cations (e.g. from glycine [Gly]
−
as anion or from proline [Pro]
+
as cation) so obtaining amino acid ionic liquids (AAILs) (Fig.
13.1
) (Fukumoto et al.
2005
; Ohno and Fukumoto
2007
; Gao et al.
2010
; Rahman et al.
2010
; Mohajeri and
Ashrafi
2011
;Muetal.
2012
). Also by trying to reduced the number of additional
chemicals required per application, the combination [cation][anion] of ILs, wich can
include two active chemicals as a single moiety has become very attractive, so was
made the design of herbicidal ionic liquids—HILs, with herbicidal anions such as
2,4-D (2,4-dichlorophenoxyacetic acid) or MCPA (4-chloro-2-methylphenoxyacetic
acid) (Pernak et al.
2011
; Praczyk et al.
2012
).
Another classification of ILs can be done according to generation they belong to:
first generation of ILs
, researchers focused mainly on their special physicochemical
properties (density, viscosity, conductivity, solubility, and high thermal and chemical
stability);
second generation of ILs,
researchers explore the potential to tune some of
physicochemical properties, allowing the formation of TSIL, more environmentally
friendly (greener);
third generation of ILs,
researchers involve active pharmaceutical
ingredients (API), which are being used to produce ILs with biological activity
(Ferraz et al.
2011
; Hough et al.
2007
).
The acronyms used in the literature for ILs are slightly differing from one au-
thor to another. For ILs mentioned in this article we have used abbreviations that
