Iodoanilines, protonated

Ionized aniline possesses an isomeric stable species, the 4- (or 3-) dehydroanilinium distonic ions (m/z 93). It is thus expected that their identification could afford some additional pieces of information related to the localization of the initial site of protonation. The distonic ions can readily be prepared by protonation of iodoanilines followed by collisional deiodination. Such a protonation-deiodination sequence is also readily performed in the quadrupole-time of flight instrument and the CID spectra of all the m/z 93 ions are collected in Table 5. As a reference for aniline radical cations, AZ-methylaniline was used and was observed to intensively expel a methyl radical after protonation and excitation (high cone voltage). 

In Ai-protonated 4-haloanilines, the C—X bond energies rapidly decrease in going from X = F to X = I. With a bonding energy of just around 224 kJ mol-1, cleavage of a C—I bond in (V-protonated iodoanilines readily takes place upon collisional activation giving the distonic isomers b, c or d. 

FIGURE 34. CoIIisional activation spectra of protonated 4-iodoaniline I-ANI-H 1 in (a) a low kinetic energy regime (Ar, ca 20-30 eV) and (b) a high kinetic energy regime (oxygen, 8 keV)... 

Similar results were obtained with protonated 3-iodoaniline 3 and 2-iodoaniline 4 (Scheme 5). Deiodination is again the most intense process upon collisional activation with argon in the Qcell. The CA spectra of the so-produced ions (m/z 93) (Figure 36) are similar but not superimposable on the spectrum of the distonic ions b, suggesting that isomeric species such as c and d are formed in the protonation-deiodination reaction sequence (Scheme 5). The most striking features of the CA spectra are again the increased... 

FIGURE 35. Collisional activation spectra (nitrogen collision gas) of the m/z 93 ions produced by electron ionization of aniline (a), and collisional deiodination of protonated 2-, 3- and 4-iodoaniline cations within the quadrupole collision cell (argon collision gas, Figures b-d). CS refers to charge stripping... 

NR spectrum together with a significant peak at m/z 17 for reionized ammonia. The protonation-deiodination sequence to the 4-iodoaniline and 3-iodoaniline has been applied using the LSIMS ion source. The high-energy CA spectra (Figure 36) of the protonated para-iodoaniline (4-I-ANI-H+) and meta-iodoaniline (3-I-ANI-H+) forms obtained in these conditions are indeed completely different from the spectra shown in Figure 35, and feature very intense peaks at m/z 76, 74 and 50. These peaks, associated with the dehydroanilinium structure b-d in the Cl experiments, are expected for such a distonic ion structure. 

Ionized aniline may exist in a conventional-ion form as well as in isomeric distonic forms, and gas-phase MS experiments performed by Chyall and Kenttamaa134,135 have also been used to form and to study the intrinsic reactivity of these high-energy isomers. Via collision-induced dissociation (CID) of protonated 2-, 3- and 4-iodoanilines in a dual-cell Fourier transform ion cyclotron resonance spectrometer, the 2-, 3- and 4-dehydroanilinium ions were formed as the result of loss of an iodine atom (Scheme 41). Ion/molecule reactions and energy-resolved CID experiments demonstrated that these three ions as well as ionized aniline behave distinctively. The reactivity of three distonic ions... 

The NMR spectra of 6-CiO-a-CD in the absence and presence of /7-iodoaniline (ATc=2800 M" ) or /7-iodophenol ( c=2300 M" ) showed that the protons of the guests shifted downfield with some broadening and the signals of 6-CiO-a-CD also shifted with some sharpening. These results indicate that the guest molecules added were included in the CD cavity and that the cinnamoyl group was exposed to water. 

The effect of amine substituents in protodehalogenations has been examined qualitatively Iodine is replaced by a proton more easily in -iodo-i, iV-dimethylaniline than in iodoaniline. On the other hand, NH2 is more efficient than NMeg in halogen displacement of the corresponding 2,4,6-triiodoanilines, as a result of the greater steric inhibition of resonance of the bulky dimethylamino group by the ortho iodines. More recentiy, the kinetics of deiodination of p-iodoaniline (reaction 41) in aqueous acid media was shown to be... 

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