Carbon nanotubes cycloaddition reactions

Figure 15.16 Some modification methods that are useful for fullerenes also can be used with carbon nanotubes. The reaction of an N-glycine compound with an aldehyde derivative can result in cycloaddition products, which create pyrrolidine modifications on the nanotube surface.

The covalent methods previously discussed for fullerene modification using cycloaddition reactions also can be applied to carbon nanotubes. This strategy results in chemically linking molecules to the graphene rings on the outer surface of the cylinder, resulting in stable... 

The demonstration that the 1,3-dipolar cycloaddition process with azomethine ylides works with nanotubes implies that similar reactions developed for use with fullerenes also may be successful with carbon nanotubes. In particular, the cyclopropanation reactions discussed previously for the modification of Cg0, likely will work for derivatization of SWNTs and MWNTs (Zakharian et al., 2005). 

In the section discussing Diels-Alder cycloadditions, it was shown how this reaction can be exploited as a way to link polymeric chains to the nanotube sidewalls. Attachment of polymers to carbon nanotubes is an important possibility for the chemistry of nanotubes as even low degrees of derivatization considerably enhance their solubility. 

Accordingly, many reactions can be performed on the sidewalls of the CNTs, such as halogenation, hydrogenation, radical, electrophilic and nucleophilic additions, and so on [25, 37, 39, 42-44]. Exhaustively explored examples are the nitrene cycloaddition, the 1,3-dipolar cycloaddition reaction (with azomethinylides), radical additions using diazonium salts or radical addition of aromatic/phenyl primary amines. The aryl diazonium reduction can be performed by electrochemical means by forming a phenyl radical (by the extrusion of N2) that couples to a double bond [44]. Similarly, electrochemical oxidation of aromatic or aliphatic primary amines yields an amine radical that can be added to the double bond on the carbon surface. The direct covalent attachment of functional moieties to the sidewalls strongly enhances the solubility of the nanotubes in solvents and can also be tailored for different... 

This is mainly due to their laborious purification procedures and their required chemical modification for solubilization. Only recently, Prato et al. reported the electrochemistry of carbon nanotubes functionalized using the 1,3-dipolar cycloaddition reaction.120 The cyclic voltammogram obtained is shown in Fig. 8.9. 

In general, on chemical modification carbon nanotubes exhibit much less toxicity or nontoxicity to living cell lines that have been investigated so far.117,118 For instance, Dumortier et al. conducted an in vitro cell uptake study of the functionalized SWNTs with B and T lymphocytes and macrophages.117 Two types of functionalized SWNTs were used, one prepared via 1,3-dipolar cycloaddition reaction and the other obtained through oxidation/amidation treatment. Both types of the functionalized nanotubes were rapidly taken up by lymphocytes and macrophages without affecting the overall... 

Suitable reactions for side-wall functionalization are mainly those that attack the TT-system of the nanotube. Primarily, these are transformations like the addition or cycloaddition known from the chemistry of double bonds. These transformations shall be discussed in the following. The direct attack to the n-system of the tube has yet another interesting aspect Unlike the functionalization of the ends it enables a control over the electronic structure of the entire tube. A suitable modification thus allows for the construction of complex electronic systems based on carbon nanotubes. At first, however, the more simple side-wall functionalizations wiU be discussed. 

The reaction with azomethine yUdes is a typical [3+2]-cycloaddition. It leads to the products shown in Figure 3.74b. The reaction is particularly suitable to couple biologically active moieties to carbon nanotubes, which is of great relevance, for example, for the preparation of nanotube-peptide composites. The reaction is normally performed on a nano tube suspension in DMF that is treated with an N-substituted glycine and paraformaldehyde or with an aldehyde carrying a further residue to be coupled. The azomethine ylide is then formed in situ it constitutes the actual reagent. The method is appUcable to single- and multiwalled nanotubes. 

Another interesting example of the use of o-QDM as diene was reported by Delgado et al. [69]. The first DA cycloaddition of o-QDM 58 to ester-functionalized single-wall carbon nanotubes (SWNT) 61 was performed in accordance with to Scheme 11.18. The authors showed that such DA reactions could be performed very efficiently in o-dichlorobenzene (o-DCB) under the action of microwave irradiation at 150 W for 45 min (Scheme 11.18). Conventional heating in o-DCB under reflux required 72 h and resulted in less conversion. 

Two different approaches were also adopted to bind phthalocyanines to carbon nanotubes using 1,3-dipolar cycloaddition reaction [133] or amidation of carboxylic residues [134] with the same goal to achieve efficient charge separation mimicking the PSn. 

Criado et al. (2013) have investigated the functionalization of single wall carbon nanotubes (SWCNT) by cycloaddition reaction with arynes under microwave... 

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