1. Unusual fragmentation of N-Perfluoroacylaryl(cycloalkyl)amines Kirill Tretyakov, Nino Todua, Anzor Mikaia National Institute of Standards and Technology, Gaithersburg, Maryland Novelty. Novelty. Competing processes of dissociation of N-trifluoroacetyl- and N-methyl-N-trifluoroacetyl derivatives of arylamines are determined. Chemical structure – fragmentation direction dependences are identified, and their use for structure elucidation is revealed. I-III IV-XIIIXIV-XV XVI XVII Introduction. Determination of aromatic amines is becoming more critical due to the exposure of general population to these chemicals through pharmaceuticals, pesticides, dyes and more. Mass spectrometry and chromatography methods are the most efficient in amine structure elucidate when examining their chemical modification products by blocking amino functions with alkyl, trialkylsilyl and acyl groups [1]. We have earlier [2] demonstrated the effectiveness of perfluoroacylation for differentiation of region-isomers of hydroxy- and mercaptoanilines, and benzenediamines by GC-MS method. Perpetuating these studies we report a study of aromatic amines as their mixed derivatives. This choice is induced by the ability of N-alkyl-N-acyl- amino acids [3,4]] revealing characteristic ions under EI conditions. A study has been performed for the following compounds: regioisomeric benzenediamines ( I-III ), substituted diphenylamines ( IV-XIII ), phenylnaphthylamines ( XIV-XV ), N,N´-diphenyl- paraphenylenediamine ( XVI ) and N-phenyl-2- iodobenzamide( XVII ) as a representative for arylbenzamides. Molecular ions of N-trifluoroacetyl-N,N-diarylamines easily undergo “oxygen rearrangement” resulting formation of characteristic for these molecules N-Aryltrifluoronitrilium cations; “Oxygen rearrangement” for N-methyl-N-trifluoroacetyl-N- arylamines gives rise to N-Methyltrifluoronitrilium cations; the latter is typical also for the spectra of meta- and para- aryldiamine derivatives; “Ortho” position of two N-methyl-N-trifluoroacetylamino substituents leads to both - hydrogen and oxygen rearrangements, the latter resulting the loss of a carbonyl oxygen leaving jointly with trifluoroacetyl group. However, formation of N-Methyltrifluoronitrilium cations is diminished. I-XVII, Materials: Chemicals – (a) arylamines I-XVII, (b) reagents: iodomethane, iodomethane-D 3, trifluoroacetic anhydride (TFAA) and chlorodifluoroacetic anhydride (ClDFAA), (c) solvents: acetonitrile (AcN), N,N-dimethylformamide (DMF) and chloroform were commercially available Methylation: 100 µL of the stock solution (2 mg/mL) of an amine in AcN was diluted with DMF and 2-5 mg NaOH and15-30 µL Iodomethane or Iodomethane-D 3 were added. The reaction products were separated with chloroform/water liquid–liquid extraction after the mixture was stirred for 1 h at a room temperature. Acylation: 1 mg sample was dissolved in 100 µL AcN and 35 μl TFAA or ClDFAA added. Reaction was accomplished in one hour at a room temperature. Solvent and reagent were evaporated, derivatives re-dissolved in AcN and analyzed. Instrumentation and measurements: EI mass spectra were measured on GC/MS systems with quadrupole analyzers (ionization energy 70 eV; MS source temperature 230 o C). ESI experiments were performed on an instrument with quad analyzers. Scheme 1. Formation of arylnitrilium cations. Nitrilium cations. IV Nitrilium cations. Diphenylamine and its isomers, such as benzyl- and tolyl-pyridines and aminobiphenyls, exhibit similar behavior under EI conditions and close GC retention index values [5]. Major peaks in their spectra correspond to molecular ions and products of loss one and two hydrogen atoms from M +·. Introduction of trifluoroacetyl group to N-atom of tolylphenylamine ( IV ) initiates carbonyl oxygen attack to.ipso.-positions followed by N-C (aryl) bond dissociations. Peaks of resulting N-phenyl- (m/z 172) (ion a 1 ) and N-tolyl-trifluoromethylnitrilium cations (m/z 186) (ion a 2 ) are present in the spectrum (Fig 1a). The preference of an “.ipso.-attack” in oxygen rearrangement processes has been earlier demonstrated experimentally and by quantum chemistry [6,7] calculations. IVXIVXIVVIIXVIXVII Figure 1. EI mass spectra (70eV) of the a – IV -TFA, b – XIV -TFA, c – XIV -ClorodiFA, d – VII -TFA, e – XVI -TFA, f – XVII -TFA REFERENCES [1] Zaikin V., Halket J. A Handbook of Derivatives for Mass Spectrometry, IMPublications, Chichester, 2009, P. 517; [2] K.V. Tretyakov, et al. Rapid Commun. Mass Spectrom. 2010, V. 24, P. 2529; [3] N.G. Todua et al. Manuscript; [4] R.A.W. Johnstone, et al. Chem. Commun. 1967, P. 826; [5] NIST/NIH/EPA Mass Spectral Library 2014; [6] N.G. Todua, et al. Rapid Commun. Mass Spectrom. 2011, V. 25, P. 750; [7] K.K. Irikura, et al. Rapid Commun. Mass Spectrom. 2014, V. 28, P. 829; [9] E.R.Talaty, et al. Rapid Commun. Mass Spectrom. 2011, V. 25, P. 1119. Figure 3. ESI mass spectra (collision energy 22 eV) of the XIIIXVI a – XIII -TFA, b – XVI -diTFA “Ortho” – effect. IV “Ortho” – effect. 1,2-Location of trifluoroacetylamino fuctions in the aromatic ring ( I –diMe-diTFA, V –Me-diTFA) initiates new processes due to the interaction of these functional groups and formation of type a ions is diminished (Fig. 2 a, d). At the same time type a ions are well represented in the spectra of their meta- and para-isomers (Fig. 2 c, f). Characteristic ions for ortho-isomers are result of simple bond cleavages along with hydrogen rearrangements and oxygen rearrangements. Schemes 3a,b depict major fragmentation pathways for the ortho-isomers leading ions of to primary dissociation of M+., such as [M-CF 3 ] +, [M- COCF 3 ] +, [M-N(CH 3 )COCF 3 ] +. However, major peaks are result of rearrangement processes: (a) carbonyl oxygen migration to a neighboring trifluoroacetylamino group and elimination of trifluoroacetyloxy radical leads to a base peak at m/z 277 in the spectrum of diaryl-diamino derivative (Scheme 3b, Fig. 2 a, b); (b) N-methyl hydrogen migration resulting loss of trifluoroacetaldehyde from [M-COCF 3 ] + ion gives rise to a base peak at m/z 133 in the spectrum of diaminobenzene derivative (Scheme 3a, Fig. 2 d, e). Scheme 3. Fragmentation of ortho-isomers of a – phenylene- and b – diazyl-diamines. VVVIII Figure 2. EI mass spectra (70eV) of the a – V -diTFA-CH 3, b – V -diTFA-CD 3, c – VI -diTFA-CH 3, d – I -diTFA-diCH 3, e – I -diTFA-diCD 3, II f – II -diTFA-diCH 3 Heavier than phenyl aromatic substituents greater attract the carbonyl oxygen and aryloxy-radical is eliminated as observed for tolyl- (IV–TFA), anisyl (IX–TFA), meta- (VII–TFA) and para-trifluorocaetoxyaryl- (VIII–di- TFA), and naphthyl (XIV, XV–TFA) derivatives. Therefore in the spectrum of N-phenyl-N-napthyl-N-TFA-amine (XIV–TFA) presented in Fig 1b. peak intensities of naphthylnitrilium ions are insignificant (m/z 222) compared to phenylnitrilium cations (m/z 172). The same is true for chlorodifluoroacetyl derivatives (Fig. 1c). An effect of additional substituents at aryl group can be demonstrated by the analysis of a spectrum of meta-N-trifluorocaetoxyphenyl-N- trifluoroacetyl-benzamine (VII–di-TFA) and para-N-trifluoroacetoxy- phenyl-N-trifluoroacetyltolylamine (X–di-TFA). A spectrum of VII–di-TFA depicted in Fig. 1d shows a change of type a ions ratio: peak of an ion [M-OC 6 H 5 ] + (m/z 284) becomes greater than peak of [M- OC 6 H 4 OC(O)CF 3 ] + (m/z 172). This phenomena can be explained by strengthening effect of trifluoroacetoxy substituent of a bond between an aromatic ring and N atom. N,N’-Bis(trifluoroacyl)-N,N´-Diphenylbenzene-1,4-diamine (XVI–di-TFA) contains two N-trifluoroacylphenyl moieties capable producing N- phenynitrilium cations, and the spectrum (Fig. 1e) exhibits a base peak at m/z 172 of an ion a 1; formation of the other nitrilium cation due to elimination of phenoxy radical (m/z 359; 5%) is less favorable (Fig. 1e). Two molecules under study(V, VI) contain both - primary and secondary amino groups. The derivatization products of primary amines contain methyl, aryl and trifluoroacetyl substituents. As a result the formation of methylnitrilium cations (ion b) along with type a ions becomes possible, both being results of oxygen migration (Scheme 2). A spectrum of VI– diTFA-CH 3 presented in Fig. 2c exhibits two type a ions at m/z 172 and 297, and methylnitrilium cations [CF 3 -C≡N-CH 3 ] + (ion b) at m/z 110; mass value of their chlorodifluoro- analogs is 126/128. Mechanism of formation of ion b is similar to the one suggested for the ion a. Peaks of these ions are of maximum intensity in the spectra of N-trifluoroacetyl-N- phenyl-N-(N´-methyl-N´-trifluoroacetylaminophenyl)amine (IX–Me-di- TFA,) (Fig. 2c) and meta- and para- (Fig. 2d) isomers of N,N´-dimethyl- N,N´-difluoroacetylphenylenediamines (II–di-TFA-di-Me; III–di-TFA-di- Me). The presence of a carbonyl group attached to aryl C-atom in arylamides as expected leads to the formation of benzoyl cations, and M +· of N-aryll- N-trifluoroacetylbenzamides do not show arylnitrilium ions of essential intensity (Fig. 1f). a b I I R= NH 2 (o-) II II R= NH 2 (m-) III III R= NH 2 (p-) IV IV R= H, R 1 = CH 3 (p-) V V R= H, R 1 = NH 2 (o-) VI VI R= H, R 1 = NH 2 (p-) VII VII R= H, R 1 = OH (m-) VIII VIII R= H, R 1 = OH (p-) IX IX R= H, R 1 = OCH 3 (m-) X X R= CH 3 (p-), R 1 = OH (p-) XI XI R= R 1 = H XII XII R= R 1 = CH 3 (m-, m-) XIII XIII R= R 1 = CH 3 (p-, p-) XIV XIV R= H XV XV R= Cl (m-) XVI XVII a b ESI data. ESI data. TFA derivatives of the amines can undergo “oxygen rearrangement” and form nitrilium cations under soft ionization as well (Scheme 4). However, competing reactions of simple cleavages and elimination of hydrofluoride molecules from [M+H] + and fragment ions are becoming more favorable than in EI conditions as seen in the ESI spectra depicted in Fig. 3. It should be noted that the formation of arylnitrilium cations under ESI conditions has been reported earlier for protonated N-phenylamide of acetylglycine [9]. Scheme 4. Fragmentation of N,N´-di(trifluoroacetyl)-N,N´-diphenyl- paraphenylenediamine under ESI conditions. OVERVIEWRESULTS AND DISCUSSION Scheme 2. Formation of ions type a and b in the spectra of mixed derivatives. Relative Intensity, % m/z a b c d e f b b b b b b a a EXPERIMENTAL CONCLUSIONS m/z a b c d e f a a a a a a a a a a Relative Intensity, %