Chemistry Reference
In-Depth Information
F
a
O
Cl
O
O
O
O
O
Cl
F
O
O
O
OH
O
K
2
CO
3
,
N
N
+
EtOH, 90°C
F
Hex
Hex
S
b
S
O
O
O
O
O
O
O
O
SH
ν
THF, r.t.
h
+
N
N
c
N
N
O
N
O
O
O
Hex
N
O
O
Hex
O
O
N
3
CuI, DBU
DMF, 65°C
+
Fig. 23 Functionalization of CNTs from well-defined precursors: (a) via S
N
2 reaction; (b) via
thiol addition; (c) via click chemistry
with conventional heating. Moreover, the solvent-free conditions pave the way to
green protocols and large-scale functionalization [
97
].
Microwave irradiation has also been successfully applied for the function-
alization of CNTs by using the Bingel reaction and it was found that, by changing
the output power,
the amount of covalently linked substituents could be
controlled [
66
].
In general, [4
2] or Diels-Alder cycloadditions to CNTs have been less used
because of the low stability of the final products. The first example in this direction
was reported by Langa and co-workers, who performed a MW-assisted Diels-Alder
cycloaddition by reaction of ester-functionalized SWCNTs with
o
-quinodimethane,
generated in situ from 4,5-benzo-1,2-oxathin-2-oxide [
98
].
Finally, a novel cycloaddition approach using zwitterions has been reported.
The reaction involves the initial formation of a positively charged five-membered ring
resulting from attack of highly nucleophilic species in the presence of an electrophile. It
was first described by the addition of 4-dimethylaminopyridine (DMAP) to dimethyl
acetylenedicarboxylate (DMAD). In the final step the addition of a second nucleophile
replaced DMAP with an alkoxy group to yield the functionalized CNTs [
99
]
.
Following this zwitterionic approach, cobalt porphyrin-functionalized CNTs
have been prepared, showing, when mixed with Nafion, excellent catalytic
performances for oxygen reduction in acidic media at room temperature. Further
derivatives obtainable through this synthetic protocol are reported in Fig.
23
.
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