Chemistry of ZSubstituted Adamantanes. 111.' Mass Spectra of 1- and 2-Adamantanethiol, 2-Adamantanol, and ZAdamantanamine

Transcription

1 Chemistry of ZSubstituted Adamantanes. 111.' Mass Spectra of 1- and 2-Adamantanethiol, 2-Adamantanol, and ZAdamantanamine Department of Chemistry. The University of Calgary, Calgary 44, Alberta Received November The mass spectra of 1- and 2-adamantanethiol(1 and 2a), 2-adamantanol (Zc), and 2-adamantanamine (2d) have been studied. The isomeric thiols give almost identical spectra and loss of the sulfhydryl radical produces the most abundant ion, while the molecular ion peaks have 9 and 21% relative intensity for 1 and 2a, respectively. Elimination of H2S is an insignificant process. In the fragmentation of 2c and d, loss of H,O and NH, as a single group occurs (metastable peaks), giving M-H,O and M-NH, ions, both at mle 134; this produces the base peak for 2c and the second most intense (93%) peak for 2d. Further fragmentation of these ions results in very similar peak patterns for 2c and d. The amine shows a very intense molecular ion peak (79%) and an M-l base peak ion. The mass spectra of 2c and dare very different from those of I-adamantanol and I-adamantanamine. Les spectres de masse des adamantanethiols-1 et -2 (1 et 2a), de I'adamantanol-2 (2c), et de I'adamentanamine-2 ont ete etudies. Les thiols isomeres donnent des spectres pratiquement idcntiques et la perte du radical sulfhydrile conduit a I'ion le plus abondant alors que I'intensite relative des pics dues aux ions moleculaires de 1 et 2a est respectivement de 9 et 21%. L'tlimination de H2S est un processus insignifiant. Dans la fragmentation de 2c et d, la perte des seuls groupes H,O et NH, se produit (pics metastables), pour donner les ions M-H20 et M-NH,, tout deux situes a m/e = 134; ceci conduit au pic de base pour 2c et au deuxieme pic le plus important (93%) pour 2d. La fragmentation ulterieure de ces ions conduit a des systemes tres semblables pour 2c et d. L'amine prtsente un ion moleculaire tris intense (79%) et un pic de base a M-1. Les spectres de masse de 2c et d sont trbs differents de ceux de l'adamantanol-1 et de l'adamantamine-1. Canadian Journal of Chemistry, 49, 3210 (1971) Introduction or prepared by published procedures (I-adamantanol (2), 2-adamantan01 (3), I-adamantanethiol (4), 2-adaman- Some time ago DoleJgek et Ql. (1) reported the tanethiol (5), and 2-methylthioadamantane (5)), and mass spectra of a variety of I-substituted adaman- carefully purified. tane compounds, and suggested a number of The mass spectra, some of which are shown in Figs. 1 fragmentation reactions to account for the oband 2, were recorded with a Varian Atlas CH-5 spectrometer, with a nominal ionizing energy of 70 or 12 ev, a served data. there has been very much source temperature of 250, and by use of a direct probe interest in the chemistry of adamantanes in the (20-25"). The relative intensities of the peaks are given as last few years, no mass spectral study has been percentages of the most intense peak (base peak) in a reported to our knowledge for 2-substituted spectrum. Peaks with a relative intensity lower than 2% were not reproduced, unless they had a special signifiadamantanes. Such a study was started by us be- cance. cause of its intrinsic interest, as well as for the purpose of identification and, if possible, of Results and Discussion analysis of isomer mixtures by low-resolution 1- and 2-Adam~ntQnefhiol mass spectroscopy. The molecular ion peaks (nzle 168) in the mass As will be seen from the results, such an analy- Spectra (70 ev) of the thiols 1 (~ig. la) and 2a sis would be well feasible in some cases, but would (Fig. lb) are of medium to high relative intensity be much harder in another instance. (8.5 and 21%, respectively) and the. base peak in both spectra is found at mle 135. A metastable Experimental peak for the transformation M + (M-SH) is present at rille (calcd ) in the spectra (at 70 The compounds investigated were obtained from comand 12 ev). mercial sources (I-adanlantanamine, 2-adanlantanamine) Elimination of hydrogen sulfide is a process of 'For Part I1 of this series, see ref. 5. very minor significance, especially in the tertiary 2Present address: school of Natural Sciences, univer- thiol 1 where peak m/e 134 has a relative intensity sity of Zambia, P.O. Box 2379, Lusaka, Zambia. of only 0.5% (70 ev). Although it has been

2 as GREIDANUS: 2-SUBSTITUTED ADAMANTANES. I11 FIG. 1. Mass spectra (70 ev) of (a) 1-adamantanethiol and (6) Zadamantanethiol. established (6) that loss of H2S is an important fragmentation of the molecular ion of secondary thiols (especially at low electron energies), we observed on lowering the ionizing energy to 12 ev only negligible changes in the relative intensities of the mle 134 peaks in either of the thiols. At this low ionizing energy the molecular ion gave rise to the base peak (mle 168) and peak M-33 had a relative intensity of 89%. No metastable peak corresponding to the loss of hydrogen sulfide from the molecular ion could be found in the spectrum of 2a. The finding that loss of H,S from the molecular ion of 1 does not play any role in the fragmentation is not surprising as a favorable spatial relationship for a 1,3- or 1,4-elimination is not present in the molecule. The M-H2S ion (mle 134) is a likely precursor (eq. 1) for the formation of fragment + C9H,, the metastable peak for this transformation (mle 105.7) is present in the spectrum of 2a. Loss of the neutral fragment C,H; from the molecular ion of various I-substituted adamantanes gives rise to the most abundant ion in the spectra of I-adamantanol (3a) and I-adamantanaminz (36). These fragmentations have been formulated by DolejSek et al. (I) as the formation of protonated phenol (5a) and aniline (5b), respectively (eq. 2). In the spectrum of I-adamantanethiol(1) only a weak peak is present at mle 111 (2.4% relative intensity) and the fragmentation M -t M-57 plays therefore no significant role in this compdund. This behavior was unexpected as sulfur is known (7) to participate readily in the type of new bond formation that would lead to 4 (X = SH). The approximately ten times higher intensity of the peaks at mle 134 and 119, and the double intensity of the molecular ion peak in the spectrum of 2a are the main differences between the spectra of 1 and 2a. Except for some minor variations in relative intensities the rest of the spectra are virtually the same even when the many metastable peaks are compared. It is clear that I-adamantanethiol(1) belongs in

3 3212 CANADIAN JOURNAL OF CHEMISTRY. VOL. 49, 1971 ZI loo Q, C.- C m/ e FIG. 2. Mass spectra (70 ev) of (a) 2-adamantanol and (b) 2-adamantanamine. the same group as I-nitro, I-bromo-, and 1- volving C1,H1,+ and its derived ions are listed in alkyladamantane (I). All lose their substituent Table 1. Those for the transformations numbered readily, forming C,,H,,+ which upon further 6 and 10 were not reported by DolejSek et al. (1) fragmentation produces many even-electron ions. for any of their 1-substituted adamantanes which Metastable peaks for the transformations in- showed the same fragmentation behavior. These

4 GREIDANUS: 2-SUBSTITUTED ADAMANTANES TABLE 1. Metastable ion peaks (mle) for transformations A+ -t B+ + C involving CloH15+ and smaller fragments in the spectra of 1 and 2a Transformation no. A(m/e) B(m/e) c mje* 1 CloH15(135) CEHI 1(107) C2H C1oH15(135) C7Hd93) C3H CloHld135) C6H9(81) C4Hs CioH15(135) C,H7(79) C4Ha C1oH15(135) C5H7(67) C5Ha CsH11(107) C7H7(91) CH CEHII(~O~) CsH7(79) C2H C7Hd93) C7H7(91) Hz C6H7(79) C6H5(77) Hz 75.O 10 CsH7(67) C3H441) CzHz 25.1 *Calculated values; observed values differed at the most 0.2 m/e units from these. authors suggested that a metastable peak at mle these systems while H20 elimination takes place probably arose from fragmentation of an ion At the present time 1,2-hydride shifts in adamanmle 121 (eq. 3). However in their spectra, as in tyl carbonium ions of high energy, such as occur [3] C9Hl?+ (121) + C5H7+ (67) + in electron-impact fragmentation reactions, can- C4H6 not be discounted. ours, the peak mle 121 has very low relative intensity (<0.5%). It is much more likely that one or both of the fragmentations nzle mle 55 and m/e m/e 39 (for which metastable ion peaks at mle 37.4 and 37.1, respectively, are calculated) give rise to this metastable peak. It should be noted here that the mass spectrum of 2-methylthioadamantane (2b) also has its base peak at mle 135 and is at mle < 135 almost identical with that of 1 and 2a. It shows metastable ion peaks corresponding to the transformations numbered I, 2, and 4-9 in Table 1, and to the loss of CH,S' from the molecular ion at mle (calculated for M(m/e 182) + M-CH,S(nz/e 135) : mle 100.1). A peak at m/e 134 (relative intensity 3.5%) indicates that elimination of CH,SH occurs as well, analogous to the loss of H2S from 2a. The compounds 1, 2a and 2b give rise to an abundant even-electron ion C,,H,,+ which may or may not be the same in all three cases, but which appears to give identical fragmentations. Apparent intramolecular 1,2-hydride shifts in adamantanes have very recently been shown to be intermolecular processes (8) in solution. At this time it is not known whether the energetically unfavorable twisted transition state for such an intramolecular 1,2-hydride shift (8) can occur in an adamantyl cation in a state of high energy under conditions which exclude an intermolecular process. Very recently reported results (9) of the study of electron-impact fragmentation of vari- ous deuterated bicyclic alcohols indicate that very rapid hydride and C-C bond shifts occur in 2-Adamantanol and 2-adaman fanumine The striking similarity of the mass spectra (Fig. 2) of 2-adamantanol (2c) and 2-adamantanamine (2d) is apparent at first glance. The amine gives a much more abundant molecular ion and shows a large number of peaks of considerable relative intensity (nine peaks with more than 40% relative intensity). The base peak for 2c and the second most intense peak in the spectrum of 2d (both at mle 134) represent loss of H20 and NH, from the molecular ions 6 and 7, respectively (Scheme 1). The presence of a metastable peak at mle ~ 1 0 ~ 1 4 ~ m/e 152 (6.5%) m/e 134 m/e 151 (79%) From 2c: 100% From Zd: 93%

5 3214 CANADIAN JOURNAL OF CHEMISTRY. VOL. 49, 1971 (calcd ) for the transformation 6 (m/e 152) -+ [C,,H,,]?, and at n?/e (calcd ) for the transformation 7 (mle 151) -+ [C,,H,,]~ indicates that 18 and 17 mass units, respectively, are lost as a single group. These metastable peaks occur also in spectra run at low ionizing energy (12 ev). The loss of NH, appears to be one of the major fragmentation processes of 2-adamantanamine and the M-17 peak is in fact the second strongest peak (relative intensity 57%) in its 12 ev mass spectrum. The facility with which this fragmentation occurs is surprising as loss of NH, from primary amines is an uncommon reaction (10). A 1,3-elimination, for which the spatial relationship is favorable, would give rise to the molecular ion (8) of 2,4-dehydroadamantane (tetracyclo-[ ' ]decane (11)). The source of the hydrogen atoms in the dehydration of cyclohexanols as a result of electron impact has been thoroughly investigated (12, 13). The main course for which good evidence is available in the case of cyclohexanol is a 1,4- elimination involving cis-oriented groups (13). An example has been reported (14) where 1,4- elimination was impossible (as it is in 2-adamantanol). In this case a diaxial 1,3-elimination occurred exclusively. In cyclohexanol it has been demonstrated that the hydroxyl-bearing carbon atom does not supply also the hydrogen for the dehydration (12). This finding has been corroborated recently (9) in the case of several bicyclic alcohols, where evidence for rapid 1,3-hydride shifts and/or C-G bond shifts was obtained. The adamantane skeleton would permit analogous 1,3-hydride shifts but these would result in identical cations. Stabilization may occur ultimately by loss of a hydrogen atom. We tentatively interpret the formation of radical ion 8 from either 6 or 7 as resulting from this process. In the mass spectrum (Fig. 2) of 2c M-l and M-2 peaks occur with a relative intensity slightly lower than that of the molecular ion peak. Loss of a hydrogen atom from the molecular ion (7) of 2-adamantanamine gives rise to the most abundant species C!,H,,N+ Qm/e 150) in its 70 ev spectrum (Fig. 2a) and to a strong meta- stable peak at ni/e for the transformation M -+ M-1 (calcd. m/e 149.0). It is the fragmentation of 7 and of Cl0H,,Nf with retention of nitrogen in the fragment ions which probably gives rise to the main differences between the spectra of 2c and d. It is surprising that these differences are still so minor (in view of the fact that C,,H,,N+ (mle 150) causes the base peak) except for the very intense (75%) peak at nz/e 30, + representing the fragment CH2=NH2, a frequently occurring abundant species in the spectra of many primary amines. No metastable peak could be found for a fragmentation involving this ion. The metastable peaks assigned to transformations of CloHl,? (m/e 134) and its smaller fragments as they occur in the spectra of 2c (Fig. 2a) and d (Fig. 2b) are listed in Table 2. Apart from the peak at m/e 30 and the very intense M and M-1 peaks in the spectrum of 2d, the most characteristic difference between Figs. 2a and b is the presence of a peak at m/e 108 (relative intensity 20%) in the spectrum of the amine. This ion may be di- rectly derived from the molecular ion CsoH,,N+ (7) or from ion C,,H,,N+ by elimination of C,H," (eq. 4) and C3H6 (eq. 5), respectively. If the first fragmentation [4] would give rise to a metastable peak one would expect it at m/e The mass spectrum of 2d shows indeed a metastable peak at m/e 77.2, but this has been tentatively assigned to transformation number 10 in Table 2, as it occurs also in the spectrum of 2c. Cleavage of the carbon-carbon bond adjacent to the nitrogen after electron impact is the preferred reaction of amines and elimination of a hydrogen atom does not normally result in an abundant species (15). The fact that the M-l ion gives rise to the base peak in the case of the amine and that PJH, elimination occurs to such an extent must be considered as additional evidence that the adamantane skeleton resists fragmeniation (16). It was one of the original goals of this investigation to see whether it would be possible to distinguish easily between 1- and 2-substituted adamantane isomers by means of low-resolution mass spectroscopy. Our 70 ev spectra of 1-

6 GREIDANUS: 2-SUBSTITUTED ADAMANTANES TABLE 2. Metastable ion peaks (mle) for transformations A+ + B+ f C involving C,,H,,? and smaller fragments in the 70 ev spectra of 2c and d -- - Transformation mle no. A(mle) B(m/e) C 2c 2d Calculated 1 C1oHi4(134) CloHi3(133) H ' CloHi4(134) C9H11(119) CH; CloH;,(134) CsHio(106) C2H C1oHid134) C~Hg(105) C2H5' CloHi,(134) C7H,(92) C3H C9H11(119) C7Hd91) C2H C,H9(93) C7H7(91) Hz C7Hi(92) C7H,(91) H' C,H,(91) C5H5(65) C2H C6H7(79) c6h6(78) H' * 77.0 *See text regarding this assignment. adamantanol and 1-adamantanamine agree close- The financial support of this work by the National ly with those reported by ~ ~ l et al. ~ (1) j and ~ ~ Research k Council of Canada is gratefully acknowledged. with one exception we agree with their findings 1. Z. DOLEJSEK, S. HALA, V. HANGS, and S. LANDA. and tentative interpretations which need not be Coll. Czech. Chem. Commun. 31, 435 (1966). discussed again. It was reported (1) that in the 2. H. W. GELUK and J. L. M. A. SCHLATMANN. Tetraspectrum of 1-adamantanamine a metastable hedron, 24, 5361 (1968). peak was present at m/e 21.5, corresponding to 3. H. W. GELUK and J. L. M. A. SCHLATMANN. Tetratransformation [6]. In our work this peak was not hedron, 24, 5369 (1968). [6] CIOHl7N+ (mle 151) + C3H,N+ (mle 57) f C7H10 observed, but instead thcrc was a metastable peak at n~/e 22.4 which was assigned to transformation [7]. For fragmentation [7] a metastable peak is expected to occur at iv/e It was also found in the 12 ev spectrum and at that ionizing energy the peak mle 58 (relative intensity 8%) is the third strongest in the spectrum after those at n~le 151 (base peak) and 94. It is characteristic for the 1- substituted adamantane compounds of group 11 as defined by DolejSek ef a/. (1)) to which 1- adamantanol and I-adamantanamine belong, that they retain their substituent in the main fragmentation of the molecular ion, with the formation of an M-57 ion (after loss of C,H,"), which gives rise to the base peak. This behavior is so different from that of the secondary alcohol (2c) with the base peak at m/e 134, and 2-adamantanamine (24 with base peak at mle 150, that no confusion between the identity of the isomers seems possible. This situation contrasts sharply with that of the two isomeric thiols, which were found to give almost identical spectra. 4. J. R. GEIGY A-G. Belg. Pat (1963); Chem. Abstr. 60, 9167c (1964). 5. J. W. GREIDANUS. Can. J. Chem. 48, 3593 (1970). 6. A. M. DUFFIELD, W. CARPENTER, and C. DJERASSI. Chem. Commun. 109 (1967). 7. K. BIEMANN. Mass spectrometry. McGraw-Hill Book Co., Inc., New York, N.Y., pp P. v. R. SCHLEYER. L. K. M. LAM. D. J. RABER. J. L. FRY, M. A. MCKERVEY, J. R. ALFORD, B. D. CUDDY, V. G. KEIZER, H. W. GELUK, and J. L. M. A. SCHLATMANN. J. Am. Chem. Soc. 92, 5246 (1970). 9. H. KWART and T. A. BLAZER. J. Org. Chem. 35, 2726 (1970). 10. H. BUDZIKIEWICZ, C. DJERASSI, and Y. H. WILLIAMS. Mass spectrometry of organic compounds. Holden- Day, Inc., San Francisco, California, p. 299; F. W. MCLAFFERTY. Interpretation of mass spectra. W. A. Benjamin, Inc., New York, N.Y., pp. 132 and A. C. UDDING, J. STRATING, and H. WY~BERG. Chen~. Commun. 657 (1966). 12. C. G. MACDONALD, J. S. SHANNON, and G. SUGOWDZ. Tetrahedron Lett. 807 (1963); H. BUD- ZIKIEWICZ, Z. PELAH, and C. DJERASSI. Monatsh. 95, 158 (1964). 13. R. S. WARD and D. H. WILLIAMS. J. Org. Chern. 34, 3373 (1969). 14. J. KARLINER, H. BUDZIKIEWICZ, and C. DJERASSI. 9. Org. Chem. 31, 710 (1966). 15. R. S. GOHLKE and F. W. MCLAFFERTY. Anal. Chem. 34, 1281 (1962). 16. R. C. FORT, JR., and P. v. R. SCHLEYER. Chem. Rev. 64, 277 (1964).