The mass spectra of some N-methylpyridinium, quinoliniurn, isoquinolinium and phenanthridinium salts (R+X-)* are analyzed (X-= Ior Clod-). For X-= I-, thermal decomposition gives rise mainly to the superimposed spectra of CHJ and the free base. Hence, iodide salts cannot be determined specifically by their mass spectra. When an a-methyl group is present, e.g. 2methylpyridinium methiodide, elimination of HI becomes an important thermal process. For X-= C10,-, the same pattern is observed, but in addition a generally important peak at [R + 151 is present. This peak is due to the oxidation, mainly a to the nitrogen of the organic moiety by the C10,-ion, giving rise to the corresponding amide. In some cases, chlorination of the organic moiety has been observed as well as double oxidation. The thermal processes for the perchlorate salts are characteristic and are useful in the elucidation of the quaternary structure.
I N T R O D U C T I O NIN THE course of the synthesis of 10,l 1-15bH-dihydrotribenzo[a,c,h]quinolizine~ (I), 1 ,Zdipheny1-1,2,3,4-tetrahydroisoquinoline (11) was oxidized by mercury (11) acetate to 1,2-diphenyl-3,4-dihydroisoquinolinium perchlorate (111) and 1,2-diphenylisoquinolinium perchlorate (IV). However, the low resolution mass spectra of (111) and (IV), exhibited several anomalous features, and were not readily interpretable in terms of structures I11 and IV. While the n.m.r. spectrum was in accordance with structure IV, the high resolution mass spectrum suggested an amide as the oxidation product of IV. (Scheme 1).Although the behaviour of quaternary ammonium salts in a mass spectrometer is well known since the work of Hesse and co-worker~,~-~ no references are found in the literature concerning the behaviour of N-aromatic salts. Thus we synthesised a number of N-aromatic iodides (Va -+ XVIIIa) and perchlorates (Vb -+ XVIIb) in order to investigate their behaviour in a mass spectrometer. (Structure 1).In order to differentiate between electron-impact fragmentation and thermal degradation processes, 70 and 12 eV spectra of the different salts were obtained, the major or unexpected fragments being checked for precursor ions by metastable scanning using the defocusing technique6*' (see Table 3). This, combined with high resolution results, permitted the proposal of a fragmentation scheme for the different salts, thermally and by electron-impact to be made.* The salt will be represented by R+X-or RX, R+ being the organic moiety, with its associated mass and Xthe inorganic anion. 351 R. SALSMANS and G. VAN BINST (1) SCHEME 1 Ri J J R 3 , + / R2 w&R, I m-\ CHI CH3 x-CH3 Ri (V) R, = R, = R, = -H (a)(b) (XII) R, = -H (a)(b) (XIII) R, = -CH, (a)(b) (XIV) R, = -C,H, (a)(b) (XV) Rl = -H (a)(b) (XVI) R l = -C,H, (a)(b) (VI) R, = -CH,, R, = R, = -H (a)(b) (VII) R, = R, = -CHI, R, = -H (a)(b) (VIII) R, = -C2H5, R, = R, = -H (a) 0x1 R, = R, = -H, R, = -CH, (a) (X) R, = -C6H5, R, = R, = -H (a)(b) (XI) R, = Rz = -H, R, = -C2H5 (a)(b) (a) x-= 1-(b) X-= (210, STRUCTURE 1 (XVII) R1 = -H (a)(b) (XVIII) R1 = -CH, (a)
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