Electron ionization mass spectral fragmentation study of sulfation derivatives of polychlorinated biphenyls

Background  

Polychlorinated biphenyls are persistent organic pollutants that can be metabolized via hydroxylated PCBs to PCB sulfate metabolites. The sensitive and selective analysis of PCB sulfate monoesters by gas chromatography-mass spectrometry (GC-MS) requires their derivatization, for example, as PCB 2,2,2-trichloroethyl (TCE) sulfate monoesters. To aid in the identification of unknown PCB sulfate metabolites isolated from biological samples, the electron impact MS fragmentation pathways of selected PCB TCE sulfate diesters were analyzed and compared to the fragmentation pathways of the corresponding methoxylated PCBs.     

Distribution coefficients of 2,2-dimethyl-4-hydroxymethyl-1,3-dioxolane between aqueous and hydrocarbon liquid phases

Gas-liquid chromatography was used to study the distribution of 2,2-dimethyl-4-hydroxymethyl-1,3-dioxolane between aqueous and organic liquid phases for seven binary solvents water-hydrocarbon (n-heptane, n-octane, n-decane, benzene, toluene, p-xylene). The distribution coefficients at low solute contents were measured in the temperature range 283–313 K. In all the systems, the ratio between the solute concentrations in the organic and aqueous phases is substantially smaller than unity and grows with increasing temperature. The ratios between the limiting activity coefficients of 2,2-dimethyl-4-hydroxymethyl-1,3-dioxolane in the hydrocarbon and aqueous phases were estimated.     

Synthesis of 1,3-dioxolane derivatives

Chloral cyanomethylhemiacetal is converted to 2-trichloromethyl-4-imino-1,3-dioxolane under the influence of hydrogen chloride or pyridine. Acetone cyanohydrin reacts with chloral to give 2-trichloromethyl-4-imino-5,5-dimethyl-1,3-dioxolane, the hydrochloride of which in water gives 2-trichloromethyl-4-oxo-5,5-dimethyl-1,3-dioxolane.     

The mass spectral fragmentation of 2-aryl-N,N′-dimethyl-1,3-imidazolidines and 2-aryl-1-3-dioxolanes

2-Aryl-N,N'-dimethyl-1,3-imidazolidines and 2-aryl-1,3-dioxolanes were subjected to 70 eV spectral analysis. Fragmentation pathways for both series of compounds are suggested. Aryl vs. benzylic hydrogen fragmentations were subjected to Hammett σ⁺  ρ plots. Incipient charge on the benzyl carbonium ion was stabilized by electron donating groups in both series of compounds. Dioxolanes were more sensitive to substituent effects (ρ = −0.639) than the imidazolidines (ρ = −0.251) implying that the positive charge on the fragmenting ion is more localized at the benzylic position of the imidazolidines than of the dioxolanes.     

Electron impact mass spectra of 2-hydrazono-1,3-thiazolidin-4-one derivatives

Mass fragmentation of 2-hydrazono-1,3-thiazolidin-4-ones is dominated by two processes, namely cleavage of the hydrazone fragment with accompanying proton transfer from the latter to the thiazolidine ring, and cleavage of a hydrazone imide residue.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1117–1119, August, 1990.     

Electron impact fragmentation of 2-arylhydrazonopropandioic acid derivatives

Examination of the mass spectra of eleven 2-arylhydrazonopropandioic acid derivatives reveals that a radical ion which is tentatively formulated as a 1H-diazirine species is produced in each case (except for the diphenyl este) by more than one process. Formation of what is formally the aryl amine radical ion occurs by a novel hydrogen rearrangement. Simple cleavage of the bonds β to either the aromatic ring or the C?N moiety also produces abundant ions. The diphenyl ester behaves anomalously yielding the phenol ion instead of the amine. The proposed mechanisms were confirmed by metastable studies, deuterium labelling and exact mass measurements.     

Electron ionization mass spectral fragmentation of deoxynivalenol and related tricothecenes

Careful analysis of the electron impact (EI) mass spectral data obtained for the trimethylsilyl (TMS) ethers of known trichothecene mycotoxins of the deoxynivalenol group permitted the construction of a database useful for the identification of these mycotoxins directly from a gas chromatography/mass spectrometry (GC/MS) run. Structures of the ions at m/z 103, 117, 147 and 191 were elucidated by high-resolution mass spectrometry (HRMS) and a fragmentation scheme was suggested. The relative abundances of these ions in the mass spectra of the trichothecenes allowed a fast structural diagnosis during analysis of biological matrices. A new mycotoxin of this group, 3-acetylnivalenol, was tentatively identified by using MS data interpretation only.     

Electron impact induced fragmentation of some 1,2,4-triazole derivatives

The mass spectra of eight 1,2,4-triazole derivaties have been recorded and found tao reveal extensive hydrogen and skeletal migrations. The structures of the fragments have been confirmed by deuterium labelling and exact mass measurement. The compounds revealed striking differences in their spectra depending on the nature of the substituents.     

Electron impact induced fragmentations of some 2,2-disubstituted 1,3-oxathiolanes

The electron impact induced fragmentations of nine 2,2-disubstituted 1,3-oxathiolanes have been studied by means of exact mass measurement and metastable ion analysis. The ring cleavage almost always takes place so that the C(2)? S and C(5)? O bonds are broken, leading to the most stable products. The nature of the substituents determines the primary fragmentations of molecular ions. Ring cleavage is important only if both substituents are alkyl groups or if the carbon attaching to the ring has an alkyl character. The loss of the substituent becomes the most favourable process if it is attached to the ring through the electron-deficient carbon atom.     

Electron impact induced fragmentations of some 2,2-disubstituted 1,3-dithiolanes

Electron impact induced fragmentations of the title compounds were studied by exact mass measurement and metastable ion analysis. Sulphur atoms within the ring effectively stabilize the positive charge. In most cases the loss of the larger substituent, and not the other, methyl group, gives rise to the base peak in the spectrum. Examination of competing metastable transitions shows that generally this is also the lowest activation energy primary process. In general primary ring cleavage reactions are not important unless there is a heteroatom in the substituent that can assist this cleavage.     

Electron impact mass spectral fragmentation of 2a,4-disubstituted 2-chloro/2,2-dichloro-2,2a,3,4-tetrahydro-1H-azeto[2,1-d][1,5]benzothia zepin-1-ones

The mass spectrometric behaviour of nine 2a,4-disubstituted 2-chloro/2,2-dichloro-2,2a,3,4-tetrahydro-1H-azeto[2,1-d][1,5]b enzothiazepin-1-ones has been studied with the aid of mass-analysed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate a neutral chlorine atom, or a chloroketene, or neutral propene, or styrene or substituted styrene molecule, plus Cl and/or H (or Cl) atom(s), to yield [M-Cl]+ ions, 2,3-dihydro-1,5-benzothiazepine derivative ions, 4,5-dihydro-5H-1,5-benzothiazepin-4-one ions which can further lose CO to give 1,4-benzothiazine ions. Both molecular ions and [M-Cl]+ ions show a tendency to eliminate an ethyl or benzyl/substituted benzyl radical to produce 2,2a-dihydro-1H-azeto[2,1-c][1,4]benzothiazin-1-one ions. The [M-Cl]+ ions could undergo rearrangement to yield 2,2a-dihydro-1H-azeto[2,1-d][1,5]benzothiazepin-1-one ions, 2,2a,3,4-tetrahydro-1H-azeto[1,2-a]quinoline ions or 1,1a,2,3-tetrahydro-azirino[2,1-d][1,5]benzothiazepine ions by loss of an ethane or a benzene/substituted benzene, a SH radical or a CO molecule. The molecular ions could also undergo rearrangement reactions to form other small fragment ions.     

Electron impact mass spectrometry of praziquantel derivatives

The electron impact mass spectra of a series of compounds related to the anthelmintic substance praziquantel are described in sufficient detail to permit their assay in biological samples by selected ion monitoring.     

Synthesis, molecular structure and spectral properties of quaternary ammonium derivatives of 1,1-dimethyl-1,3-propylenediamine

1,1-Dimethyl-3-oxo-1,4-diazepan-1-ium chloride (1) and 1,1-dimethyl-1-carboxymethyl-3-aminopropyl ammonium hydrochloride (2) have been obtained by the reactions of 1,1-dimethyl-1,3-propylenediamine with ethyl chloroacetate and chloroacetic acid, respectively. The products have been characterized by FTIR, Raman and NMR spectroscopy. B3LYP calculations have also been carried out. The screening constants for (13)C- and (1)H- atoms have been calculated by the GIAO/B3LYP/6-31G(d,p) approach and analyzed. The FTIR and NMR spectra of the investigated compounds 1 and 2 are in excellent agreement with the structures optimized by Density Functional Theory (DFT) calculations.     

N-(2-Thenyl)derivatives of aminoalkyltriethoxysilanes,-silatranes and 2,2-dimethyl-1,3-dioxa-6-aza-silacyclooctane

The reactions of aminoalkylethoxysilanes and 2,2-dimethyl-1,3-dioxa-6-aza-2-silacyclooctane with 2-(chlormethyl)thiophene and its 5-chloroderivative lead to the correspondingN-(2-thenyl) derivatives. TheN-methyl-N-(2-thenyl)aminomethyltriethoxysilane and 5-chlorothyenyl derivative formed are converted by triethanolamine into silatranes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 384–386, February, 1995.     

Electron impact fragmentation of some tetramethyl derivatives of thiathrene and phenoxathiin

Mass spectra of thiathrene and three tetramethylthiathrenes (II), (III) and (IV) are reported and discussed. The principal mode of fragmentation of these compounds consists of the loss of sulphur to give the corresponding dibenzothiophene ion. The general pattern of electronolytic decomposition among the tetramethylthianthrenes is, however, much more complex. The mass spectrum of 2,3,7,8-tetramethylphenoxathiin (VI) is also reported and compared with the spectrum of the corresponding thianthrene derivatives.     

Electron ionization mass spectral fragmentation of derivatized 4,5- and 5,6-epoxysterols

The electron ionization (EI) mass spectral fragmentation of derivatized 4,5- and 5,6-epoxysterols was investigated. Interesting fragmentation processes involving a transannular cleavage of the epoxide ring after transfer of the trimethylsilyl group are significant in the case of 4,5-epoxysterol trimethylsilyl ethers (affording abundant fragment ions at m/z 403 and 404). Different pathways, which have been substantiated by deuterium labelling, are proposed in order to explain the formation of these ions. In contrast, this transfer is not significant in the case of 5,6-epoxysterol trimethylsilyl ethers. The EI mass spectra of these latter compounds appear to be very complex and to differ slightly according to the stereochemistry of the epoxy group. Acetate and trifluoroacetate derivatives of 4,5-epoxysterols display interesting EI mass spectra dominated by a fragment ion at m/z 332 resulting from cleavage of the steroid ring A.     

Electron impact mass spectral study of halogenated N-acetyl- and N-propionylcytisines

(-)-Cytisine and its derivatives, characterised by high affinity to neuronal nicotinic acetylcholine receptors with specificity for the α4β2 subtype, have been shown to be important probes in central nervous system (CNS) research. Electron impact mass spectral (EI-MS) fragmentations of halogenated derivatives of N-acetylcytisine and N-propionylcytisine have been investigated. Detailed fragmentation pathways have been identified for all significant ions including a few characteristic fragment ions. The principal mass spectral fragmentation routes of iodine and bromine compounds have been determined on the basis of low (EI), high resolution (HRD) and B(2)/E linked scan mass spectra as well as linked scans at constant B/E.     

Mass spectral fragmentation patterns of 2-methyl-, 2,3-methyl-, 2,3-dimethyl-, 2-aryl- and 3-phenylindole derivatives

The electron impact mass spectrometric fragmentation pathways for several 2-methyl-, 3-methyl-, 2,3-dimethyl-, 2-aryl- and 3-phenylindole derivatives were investigated. An interesting relationship between the substitution pattern in the framework of the indole derivatives and the fragmentation patterns was observed.