Chemistry Reference
In-Depth Information
NHR
NHR
NH
2
R
F
F
F
2
, 250-400 °C
NH
2
NH
2
,
i
-PrOH
NHR
NHR
R
F
F
R
RMgBr or RLi
R
R
Fig. 20 Scheme illustrating fluorination on the nanotubes allowing further functionalization
as it requires the use of highly reactive species. In general, addition reactions
to carbon-carbon double bonds cause a transformation of sp
2
-hybridized into
sp
3
-hybridized carbon atoms. Such changes are associated with the modification
of the predominantly trigonal-planar local bonding geometry into a tetrahedral
geometry. As previously explained, this process is energetically more favorable
in the cap region where the curvature is more emphasized; it is also probable that
reactions preferably occur in the proximity of structural defects sites.
Addition reactions on CNTs can be performed at different steps of functiona-
lization and do not necessarily require previous oxidation, making CNT derivative
properties easier to tune.
Fluorination
The addition of fluorine to CNTs can be achieved by applying high temperatures
(between 250 and 400
C) and using hydrofluoric acid as catalyst. The method was
firstly reported by Mickelson et al. with best yields allowing the insertion of one
fluorine atom every two carbon atoms [
77
].
Fluorination is of great interest since it facilitates further functionalization on the
tubes by nucleophilic substitutions [
78
]. Taking advantage of the weakness of the
C-F bond, organolithium and Grignard reagents are typically employed to afford
alkyl-modified nanotubes [
79
].
Fluorinated nanotubes were reported to have moderate solubility in alcoholic
solvents, which is by the way significantly improved in the alkylated tubes. One
advantage of this method is that pristine nanotubes could be effectively recovered
by using anhydrous hydrazine in isopropanol [
80
] (Fig.
20
).
