Chemistry Reference
In-Depth Information
M
n
+
R
RM(X)
cyclohexane
sonication
R
M
n+
R
O
2
washings
R
Fig. 26 Nucleophilic alkylation-reoxidation functionalization of CNTs
affords CNT-derivatives with a similar yield of functionalization but with an optimal
reaction time of 5 min, whereas thermal treatments take days.
Reductive alkylation of CNTs also yields sidewall functionalized tubes. In these
reactions, CNTs are treated with lithium, sodium, or potassium in liquid ammonia,
followed by the addition of alkyl/aryl iodides or alkyl/aryl sulfides [
110
,
111
]. The
debundling observed in liquid ammonia is associated with the fast electron transfer
process from the metal to the nanotubes: charged carbon nanotube intermediates are
exfoliated due to electrostatic repulsion. Addition of the alkyl halide leads to the
formation of a radical anion that dissociates to yield halide and the alkyl radical,
which can then react with the CNT sidewalls. Some authors have shown that
reductive alkylation is dependent on the tube diameter and shows some selectivity
of metallic toward semiconducting tubes [
112
]. Similar arguments have been made
for diazonium reactions and the reaction could be used as a potential way for the
separation of metallic vs semiconducting nanotubes.
Nucleophilic and Electrophilic Additions
The nucleophilic addition of carbenes to CNTs was reported by Hirsch and
co-workers [
85
]. The same group has also described nucleophilic additions using
organolithium and organomagnesium compounds, producing highly functionalized
alkyl nanotube derivatives, or with amine-based nucleophiles leading to
amino-functionalized CNTs which exhibit enhanced solubility in many solvents
[
113
-
115
] (Fig.
26
).
Non-conventional techniques such as microwave irradiation or ball milling have
been used for the electrophilic addition of alkyl halides [
116
]. Other electrophilic
reactions have also been reported upon mechanochemical reactions in the presence
of a Lewis acid and CHCl
3
[
117
].
