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An attempt was made to determine if NO reacted with the parent compound, diphenylamine. A solution of 3 xlQ-3 mol Ph2NH in 15cm3 cyclohexane was

degassed for 1 hour. After this time, NO was bubbled through the solution for 2 hours. A sample was taken for EPR analysis and showed no signals. A sample was also analysed by GC-MS. The chromatogram revealed only solvent and starting material. A further sample was taken and no spectra were observed by EPR analysis. When the solvent was decanted off, crystals remained in the reaction vessel. More crystals were obtained on evaporation of the solvent. Analysis of these crystals by NMR and GC-MS revealed them to be starting material. It can be said therefore that Ph^NH does not react directly with NO to generate a nitroso compound.

As an alternative, the reaction of NO2 with diphenylamine was investigated. A

solution of 3 xlO'^ mol Ph2NH was prepared but not degassed. Concentrated HCl

was dripped onto solid NaN0 2 , liberating NO2. This was bubbled directly through the Ph2NH solution. After about 20 minutes, the solution turned from colourless to a greeny/yellow, an indication that a nitroso compound had formed. A sample was sent for EPR analysis, and this, as expected, showed no spectrum. Analysis of the

solution by NMR showed only cyclohexane was present.

When the solution was decanted off, crystals were observed in the flask. These, along with the mother liquor, were analysed by GC-MS. The chromatogram of the solution showed little sign of starting material, and what appeared to be many minor

products. The only major product was identified as 2-nitro-N-nitroso-N-

phenylbenzenamine

(15),

NO.

N—N=0

Ph

15

Scheme 3.0 shows a possible mechanism for this reaction if nitration was followed by abstraction of a proton to generate the aminyl radical.

N O - / HNO2 •NO + OH* N — N

=0

The chromatogram of the flask crystals revealed some starting material, the above

nitroso compound and other high molecular weight products, such as 4-nitro-N- phenylbenzenamine, 2-nitro-N-(2-nitrophenyl)-benzeneamine, and 2-nitro-N-(4-

nitrophenyl)-benzenamine. The third analysis, the crystals from the evaporated solution, revealed a similar set of products. Thus it can be seen that NO2 reacts with PH2NH to give direct nitrosation, and even some nitration products. This supports the work of Alm^^9 who found that NO was inert toward Ph2NH and its derivatives, whereas NO2 gave degradation products and in some cases, liberated NO2.

3 .2 .6 .G a lv ino x y l.

A second radical source which was investigated was 2,6-di-fgrf -butyl-a-(3,5- di-fer?-butyl-4-oxo-2,5-cyclohexadiene-l-ylidene)-p-tolyloxy, hereafter referred to as "galvinoxyl", 16. This is a stable, long-lived free radical which can act as a scavenger for other transient free radicals

A solution of galvinoxyl in tert -butylbenzene was submitted for EPR spectroscopy. A signal was obtained which became less resolved as the temperature was raised. Nitric oxide was bubbled through the solution for ~5mins. No immediate change was

observed in the EPR trace. This could mean that galvinoxyl does not rapidly scavenge NO, or that there was excess galvinoxyl in the solution. The EPR analysis was repeated after four days. The signal had decreased in intensity by a factor of -50, possibly due to the gradual combination of NO with the galvinoxyl. It is not clear at which site nitric oxide attacks the galvinoxyl. It could be at the oxyl radical centre or at the =CH-, breaking the double bond, or at a double bond in the phenyl ring. Infra-red analysis was carried out on the reacted sample, giving a peak at 1675 cm 'E If the

nitric oxide was bound to the radical centre to give 0-N =0, then this would give a peak between 1680 and 1650 cm"E However, the peak would be masked by the presence of the caibonyl group which also appears in this region.

3.2.7. Conclusions.

From the experimental data obtained, it was observed that the reaction between R«, (where R* = Ph2N»), and NO was a very rapid process, being completed in some cases where the NO concentration was high, in less than 30 seconds. The EPR spectroscopy experiments revealed the presence of the diphenylaminyl radical and this was very persistent; it reacted with NO to form a coloured nitroso compound, N-

nitrosodiphenylamine. This compound was easily detected by UV/vis spectroscopy.

By com parison with authentic N-nitrosodiphenylam ine, the molar extinction coefficient, e, was evaluated and thus the concentration of product was calculated. This type of experiment could form the basis of an effective diagnostic test for the presence and concentration of NO.

An attempt was also made to generate a different type of stable radical from the bispentamethylcyclopentadiene?:dirrier, but this was unsuccessful.

3.3. Experimental.

UV/vis spectra were obtained on a Philips PU8730 scanning spectrometer

operating between 200 and 900nm, and a Shimadzu UV2101PC spectrophotometer

operating at 415 and 390nm. Spectra were plotted directly from a HP440LC laser

printer. Samples were analysed in 3cm^ quartz cuvettes. All solutions were degassed by bubbling N2 through for at least 15 minutes.

3.3.1. Preparations.