Photochemical studies of single-walled carbon nanotube ozonides and alpha-azoxy ketones
Engel, Paul S.
Doctor of Philosophy
This thesis contributes to two disparate problems in chemistry: studying properties of carbon nanotube ozonides and products of their decomposition and determining behavior of alpha-azoxy radicals. This work demonstrates that interaction of ozone with single-walled carbon nanotubes (SWNT) results in formation of 1,2,3-trioxolanes (SWNTO3). Their formation rate was found to be on the order of subseconds at room temperature for diluted SWNT---1% aqueous SDS suspensions. SWNTO3 decayed to SWNT epoxides (SWNTO) with release of molecular oxygen. Gas evolution measurements performed on dry ozonated SWNT showed oxygen release to follow a simple exponential rise with rates approximately 1.5 - 2 min-1 at r. t. The lifetime of SWNTO3, with a dissociation activation energy of approximately 0.7 eV, depends on temperature and SWNT type. At room temperature, it is less than two minutes for small-diameter SWNTs suspended in water. Ozonides exhibited extreme quenching of SWNT fluorescence and substantial bleaching of NIR absorption. The maximum number of 1,2,3-trioxolanes forming on the surface of SWNT at any given time was found to be less than 4% of the theoretical value, indicating a saturation point. Reaction of ozonated nanotubes with excess ozone is limited by the SWNTO3 decomposition rate. Thinner tubes exhibited faster ozonide decay rates resulting in greater oxidation levels over time in excess of ozone. Ozonation with small quantities of ozone did not result in a D-band increase in the Raman spectra, both for solid and liquid state experiments, though substantial decrease of the G band was observed. IR absorbance kinetics of SWNT films revealed exponential intensity drift over time with rates close to those in fluorescence and NIR absorbance techniques. Ozonated SWNTs were found to abstract electrons from amines and thiols, thus resulting in covalent attachment of nucleophiles to the sidewall. The azoxy functional group greatly stabilizes an attached carbon-centered radical, but the chemistry of such alpha-azoxy radicals is unclear. This work reports that generation of alpha-azoxy radicals by irradiation of alpha-azoxy ketones PhCO-C(Me)2-N=N(O)-R causes ketone rearrangement to azoester compounds PhCOO-C(Me)2-N=N-R. This study proposes a mechanism for this rearrangement.
Organic chemistry; Physical chemistry