Electric dipole moments in polar solvents. II. Tetraisoamylammonium nitrate ion pairs in chlorobenzene. Effect of mutual polarization of the ions

The dielectric constant and conductivity of dilute solutions of tetraisoamylammonium nitrate in chlorobenzene are measured between –34.6° and 99.0°C to give association constants for the formation of ion pairs (K _A) and triple ions, and electric dipole moments. The quantityK _A as a function of temperature is reproduced by the Denison-Ramsey-Fuoss treatment for unolarized ion pairs [Eq. (2)] with a distance of closest approach of 4.90 Å. The dielectric data are reproduced by Onsager's equation with an inherent (gas-phase) dipole moment of the ion pairs of 14.2±0.3 D. Other methods of calculation lead to consistent dipole moments, confirming that the mutual polarization of the ions is important. The energetics of ionic association is considered on the basis that the ion pair may be treated as a polarizable dipole in a spherical cavity.     

Tandem mass spectrometry of peptides. Relationship between translational energy loss and fragment ion mass

Incident ion energy E₁ and collision gas pressure have been adjusted so as to obtain a satisfactory tandem mass spectrum of the m/z 1882 ion formed from valme-gramicidin A (relative molecular mass 1881). Translational energy losses ΔE have been determined (at E_i = 14.8 keV) from the precise positions of a large number of fragment ion peaks in the spectrum. The variation in ΔE for different fragment ions is great and the magnitudes of ΔE are large (being commonly of the order of 10² eV). It is shown how very large energy losses ΔE can arise, if the parent ion decomposes to a small fragment ion which itself collides and decomposes further. Implications of the dependence of ΔE upon fragment ion mass for the scan laws of four-sector instruments are discussed briefly.     

Mechanism of Azo Coupling Reactions XXXIII. pH-dependence and micromixing effects on the product distribution of couplings with 6-amino-4-hydroxy-2-naphthalenesulfonic acid. Evidence for N-coupling of a naphthylamine derivative

Azo coupling of 6-amino-4-hydroxy-2-naphthalenesulfonic acid (1) with 3-trifluoromethyl- and 4-nitrobenzenediazonium ion in relative highly concentrated aqueous alkaline solutions gave ratios of aminoazo to hydroxyazo compounds which are much higher than expected on the basis of the acid-base pre-equilibria of 1 . These product ratios are disguised by effects of micromixing. In dilute solution (≤10^?2 mol/l) product ratios and kinetics both correspond to the theory of acid-base pre-equilibria. A bisazo dye 10 was formed as a by-product in couplings with 3-trifluoromethylbenzediazonium ion, as expected for reactions with micromixing effects. In the reaction with benzenediazonium ions, the products of azo coupling of diazotized 1 with 1 (compound 8 ) and of the monoazo compound 8 with benzenediazonium ion (compound 9 ) were found. It is likely that diazotized 1 is formed by N-coupling of 1 with benzenediazonium ion, tautomeric rearrangement and protonation of the triazene to diazotized 1 and aniline. This seems to be the first case of N-coupling of a naphthylamine which was assumed to be capable of C-coupling only.     

Reaction of inorganic cyanates with halides. II. Reactions of chlorohydrins

The reaction of ethylene and trimethylene chlorohydrins with cyanate ion in anhydrous dimethylformamide (DMF) forms 2-oxazolidinone and tetrahydro-2H-1, 3-oxazin-2-one, respectively. These are the major products over a wide concentration range, and at initial chlorohydrin concentration of 1 M and lower, the yields are high enough to make the reaction useful for synthesis of oxazine and oxazolidine derivatives. The corresponding reaction with tetramethylene chlorohydrin gave tetrahydrofuran as the major product with the by-products being polymeric. Pentamethylene and hexamethylene chlorohydrins yield linear polyurethanes when allowed to react with cyanate in DMF. Examination of the relative rates of reaction of these chlorohydrins indicate that the mechanism by which urethanes are formed (both cyclic and polymeric) is an S_N2 displacement of chloride by cyanate ion to give an isocyanate intermediate which then reacts with an alcohol group to form urethane.     

Dediazoniation of Arenediazonium Ions in Homogeneous Solutions. Part XVI. Kinetics and mechanisms of dediazoniation of p-chlorobenzenediazonium tetrafluoroborate in weakly alkaline aqueous solutions under nitrogen gas

The kinetics of reactions of p-chlorobenzenediazonium ions in aqueous buffer solutions (pH 9.0–10.6) under N₂ (< 5 ppb of O₂) have been measured between 20 and 50°C. The formation of trans-diazotate is first-order with respect to the concentration of hydroxyl ions and to the equilibrium concentration of diazonium ions, if the diazonium ion?cis-diazotate equilibrium is considered as a fast prior equilibrium. This indicates that the p-chlorobenzenediazonium ion, in contrast to all previous investigations with the p-nitrobenzenediazonium ion and benzenediazonium ions carrying similar substituents with a ?M effect, rearranges from the cis- to the trans-configuration as diazohydroxide and not as diazotate. The formation of trans-diazotate is catalyzed by carbonate and inhibited by hydrogen carbonate ions; mechanisms of these catalyses are discussed, and the solvent isotope effect K_H2O/K_D2O measured by an ¹H-NMR. technique reported. The kinetics of the dediazoniations can be analyzed as a mixture of two reactions, a relatively fast first reaction, reaction A, which is responsible for about 5% of the total reaction, and a second reaction F. Both are first-order with respect to diazonium ion; reaction A is also first-order in hydroxyl ions. There are some indications that reaction A corresponds to the hydrolysis of the diazonium ion to give eventually amine and nitrite ions. Reaction F shows a complex dependence on hydroxyl ions; it is related to the homolytic dediazoniation.     

Mass spectral fragmentation patterns of heterocycles. IV . Tetracyclic phenothiazines. IX. Electron impact promoted mass spectral fragmentation of pyrrolo[3,2,1-kl]phenothiazine

The mass spectral fragmentation patterns of pyrrolo[3, 2, 1-kl]phenothiazine ( 1 ) and its 1, 10-dideuterioderi-vative [2] are reported. The site of deuterium substitution in 2 was established by examination of its ¹³C nuclear magnetic resonance spectrum. The heteroaromatic stability of 1 to electron impact is exemplified by the occurrence of the molecular ion as the base peak and the formation of a reasonably intense M²⁺ ion. An intense M-1 ion is also observed. The more abundant fragment ions appear to result from sulfur ionization. Fragment ions arising from ionization of the nitrogen constitute only a small fraction of the total ion current. Proposed fragmentation pathways of 1 are supported by the detection of appropriate metastable ions, exact mass measurements, and electron impact spectrum of 2 .     

Reaktionen von Glutaminsäuredimethylester im Massenspektrometer. 21. Mitteilung über das massenspektrometrische Verhalten von Stickstoffverbindungen

The mass spectral fragmentation of dimethyl glutamate ( 1 ) and its deuterated derivatives 1a , 1b and 1c has been investigated. By loss of a methoxycarbonyl group from the molecular ion an ion of m/e 116 is generated. The latter splits off methanol (m*), the resulting fragment of m/e 84 giving raise to the base peak of the spectrum. Only part of the hydrogen transferred to the leaving group originates from thc amino group, as was suggested earlier [2] [3]. Basing on experiments with deuterated compounds we propose an additional mechanism for the reaction, i.e. hydrogen transfer from C(3) to methoxyl. The fragment generated by both processes is most likely to be a pyrrolinonium ion. Thermal side reactions in the mass spectrometer (formation of pyroglutamic acid ester) followed by fragmentation may lead to the same ion. – The mechanisms discussed are supported by the mass spectral fragmentation of N-acetyl-glutamic acid diesters 3 , 3a , 3b and 3d and of the N, N-dimethyl derivatives 4 and 4a . – The fragmentation reactions investigated are similar to some of 1,3-trimethylenediamine derivatives [7]. This means that there are parallels in the mass spectral fragmentation of difunctional compounds irrespective of the nature of the functional groups.     

Vinyl polymerization. 432. Initiation mechanism of uncatalyzed polymerization in the presence of copper(II) ion

The initiation mechanisms of the uncatalyzed polymerization of methyl acrylate and methyl methacrylate by the system of starch, α-amylase or water-soluble nylon 3/copper(II) ion/H₂O were investigated by spin trapping techniques. Using 2,4-dimethyl-3-nitrosobenzene sulfonate d₈ and 5,5-dimethyl-1-pyrroline-N-oxide as the water-soluble spin trapping agents, the simultaneous generation of both monomer and hydroxyl radicals has been observed, and the propriety of the initiation mechanism proposed previously was confirmed. Thus, the initiation of polymerization in the presence of copper(II) ion was concluded to take place through a hydrogen atom transfer from the complexed water to the β-carbon of the complexed monomer.     

High‐throughput approaches towards the definitive identification of pharmaceutical drug metabolites. 2. An example of how unexpected dissociation behaviour could preclude correct assignment of sites of metabolism

S‐oxidation is a common metabolic route for sulfur‐containing compounds. Whilst investigating the dissociation of a series of chemically synthesised model S‐oxide metabolites, two unexpected losses of 62 m/z units were observed in the collision‐induced dissociation (CID) product ion spectrum of protonated 3‐dimethylaminomethyl‐4‐(4‐methanesulfinyl‐3‐methylphenoxy)benzenesulfonamide. A single loss was initially assigned using the low‐resolution product ion spectrum, acquired by electrospray ionisation quadrupole ion trap mass spectrometry (ESI‐QIT‐MS), as methanethial, S‐oxide via a charge‐remote, four‐centred rearrangement. This assignment was consistent with well‐documented hydrogen rearrangements in the literature. Further, the loss was not observed for the parent compound. Thus, it was inferred that the site of metabolism was involved in the dissociation and the attractive nature of the four‐centred rearrangement meant that the loss of methanethial, S‐oxide was a logical assignment. However, deuterium‐labelling experiments and accurate mass measurements, performed using electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FT‐ICR‐MS), showed that the nominal loss of 62 m/z units occurs via two distinct dissociation pathways. Neither of these losses was of methanethial, S‐oxide as initially hypothesised from the low‐resolution product ion spectrum of the protonated molecule. Mechanisms consistent with the experimental findings are postulated. An MS³ spectrum of the fully exchanged, deuterated species supported the proposed mechanisms by suggesting that 3‐dimethylaminomethyl‐4‐(4‐methanesulfinyl‐3‐methylphenoxy)benzenesulfonamide has multiple sites of protonation in the gas phase. The planar structures of the posited product ions are likely to provide the driving force for the rearrangements. The relevance of the observations with regards to pharmaceutical drug metabolite identification is discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

The n.m.r. of paramagnetic complexes of vanadyl acetylacetonate with organic phosphites and hydroperoxides

The vanadium IV ion in vanadyl acetylacetonate (V^IV) forms labile paramagnetic complexes with organic phosphites in the first coordination sphere. The enthalpy of complex formation between V^IV and triphenyl phosphite was 2.6 kcal mol^?1. Complex formation enthalpies ΔH and the activation energies E of ligand (hydroperoxide) escape from the metal ion sphere were determined from the temperature dependence of paramagnetic broadening of the n.m.r. lines of hydroperoxides in the presence of vanadyl acetylacetonate. At low temperatures the phosphite sharply weakens the bond between the metal ion and hydroperoxide in the second coordination sphere (ΔH decreases fivefold). Taken in excess, phosphite displaces the hydroperoxide molecules from the coordination sphere of the V^IV ion and thus blocks it. The observed n.m.r. characteristics of the paramagnetic complexes explain, on the model level, the kinetic regularities of the reaction of hydroperoxides with phosphite catalysed by transient metal ions.     

Struktur und Mechanismus bei Fragmentierungsreaktionen 1. Teil. Die stereoisomeren 10-Chlor-decahydro-isochinoline. Fragmentierungsreaktionen, 23. Mitteilung

cis-10-Chloro-N-methyl-decahydro-isoquinoline ( 5 ) and its trans-isomer 6 undergo heterolytic fragmentation in 80% ethanol by different mechanisms. As predictable on stereo-chemical grounds the cis-isomer 5 reacts by the accelerated synchronous mechanism, the trans-isomer 6 , however, by the two-step carbonium ion mechanism. Synchronous fragmentation therefore dominates over the two-step process even when the latter would lead to a relatively stable tertiary carbonium ion. In both cases the more highly substituted and thermochemically more stable olefinic fragment 8 is formed.     

Cationic polymerization of cyclic dienes. X. Cationic polymerization of 1-vinylcyclohexene and 3-methyl-1,3-pentadiene

1-Vinylcyclohexene (VCH), which has one of the double bonds in the ring and the other outside the ring, was synthesized and polymerized by cationic catalysts. The reactivity of VCH was very large in the polymerizations catalyzed by boron trifluoride etherate (BF₃OEt₂) and stannic chloride–trichloroacetic acid complex. Similar to other cyclic dienes, the polymerization of VCH was a nonstationary reaction having a very fast initiation step. The polymerization proceeded by either a 1,2- or a 1,4-propagation mode in which vinyl group was always involved. Particularly when BF₃OEt₂ was used as a catalyst, an intramolecular proton or an intramolecular hydride ion transfer reaction took place, resulting in the formation of methyl groups in the polymer. The degree of polymerization of polymer formed was about 10. This indicates the preponderance of monomer transfer reaction. To investigate the reason for the high reactivity of cyclic dienes, cationic copolymerizations of VCH and 3-methyl-cis/trans-1,3-pentadiene (cis/trans-MPD) was carried out. The relative reactivity of monomers decreased in the order VCH > trans-MPD > cis-MPD. On the other hand, the resonance stabilization of monomers decreased in the order VCH > trans-MPD > cis-MPD. Therefore, it could be considered that the monomer reactivity is mainly determined by the stability of carbonium ion intermediate. The relative stability of carbonium ion must be VCH > trans-MPD > cis-MPD. Thus the influence of the conformation of ion on its stability was clearly demonstrated.     

Mass Spectral fragmentation patterns of heterocycles. V . Electron impact promoted mass spectral fragmentation of indolo[1,7-ab][1]benzazepine and Some of its Derivatives

The fragmentation patterns of 1,2,6,7-tetrahydroindolo[1,7-ab][l]benzazepin-1-one ( 1 ), 6,7-dihydroindolo-[1,7-ab][l]benzazepine ( 2 ) and indolo[1,7-ab][1]benzazepine ( 3 ) on electron impact have been examined. Loss of carbon monoxide to form the base peak at m/e 207 and loss of CHO radical to give m/e 206 consititute the major fragmentation pathways for 1. The moleclar ions ( M ⁺) are abundant for each of the compounds; observed as the second most intense peak for 1 (85% relative intensity) and the base peaks for 2 and 3 . The spectrum of 2 is characterized by intense M-1 and M-2 ions and by the presence of a M-15 ion (m/e 204) of moderate intensity (11.4%). In all other respects the spectra of 2 and 3 are strikingly similar. The M-15 ion from 2 , assigned the heteroaromatic pyrroloacridinium structure, is also formed in the spectrum of 1. A second heteroaromatic ion at m/e 191, common to the spectra of 1 , 2 and 3 , is believed to have the pyrrolocarbazol-ium structure. Metastable ion transitions and exact mass measurements support most of the proposed fragmentation pathways and structural assignments.     

Beckmann Fragmentation and Rearrangement. Part VII. Fragmentation and cyclization of α-methylthio-ketoximes. Fragmentation reactions no. 27

α-Methylthio-propiophenone anti-oxime p-toluenesulfonate (tosylate) ( 12b ) fragments quantitatively in 80% ethanol yielding benzonitrile and a methylidenesulfonium ion 15 . The syn-isomer, however, undergoes a Beckmann rearrangement. The fragmentation of α-methylthio-isobutyropher one anti-oxime tosylate ( 13b ) is accompanied by cyclization to the 1, 2-thiazetin-1-ium ion 27 , which is hydrolyzed via the sulfimine 29 to the keto sulfide 20 and the keto sulfoxide 30 . A comparison of the rates of the α-alkylthio anti-ketoxime tosylates 12b and 13b and of the homomorphous oxime tosylates 16b and 17b shows that fragmentation and cyclization are strongly assisted by the sulfur atom. Whereas both the anti- and syn-isomers of α-amino ketoxime derivatives fragment quantitatively, only the anti-isomers of α-alkylthio ketoxime derivatives undergo facile fragmentation.     

Electron impact and chemical ionization mass spectra of bis(methoxycarbonyl) [2.2](2,5)pyridinophanes. Formation of quinolizinium ions under electron impact

For four isomeric bis(methoxycarbonyl)[2.2](2,5)pyridinophanes differing only in the mutual orientation of the two nicotinic ester units, electron impact mass spectra were measured. The fragmentations observed distinguish surprisingly well between the isomers, depending on the transannular substitution pattern. Of special interest is that for one isomer the otherwise unimportant ion at m/z 298 is found as base peak. This ion is formed by expulsion of HCN from the molecular ion, transannular cycloaddition and aromatization to a stable quinolizinium ion. Fragmentation pathways of the isomers are compared, and chemical ionization and negative ion chemical ionization mass spectra are discussed.     

Kinetics and mechanism of the reactions of the superoxide ion in solutions. I. Absorption spectra and interaction with solvents and cations

Absorption spectra of the superoxide ion have been studied in dimethylformamide (DMF) and acetonitrile (AN). It was found that the superoxide ion existed in equilibrium with an ion pair in AN (K_eq = 20M^?1, Bu₄N⁺ is the cation) and as “free” (solvated) ion in DMF. The addition of DMF caused the destruction of an ion pair in AN. The addition of the proton donors HX (water or ethanol) to the \documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document} solutions in DMF and AN caused the formation of new ion pairs (Bu₄N⁺\documentclass{article}\pagestyle{empty}\begin{document}${\rm O}_{\rm 2}^{\overline {\rm .} }$\end{document})₂HX. The equilibrium constants of these ion pairs were determined in DMF and AN.     

Polymerization of monolayers. V. Tacticity of the insertion poly(methyl methacrylate)

Insertion poly(methyl methacrylate) (PMMA) formed within a monolayer of monomer adsorbed on montmorillonite was studied by means of NMR spectroscopy and shown to be composed of short stereosequences with a predominant isotactic component. The stereospecificity of the insertion PMMA can be understood in terms of the organization of the monomer adsorbed on the surface of the mineral. The monolayer of monomer is assumed to be composed of monads and isotactic diads due to dipole-ion interactions between the molecules of methyl methacrylate and exchangeable cations. Results of experiments relating factors such as temperature, density of ion population of the surface, and the nature of ions are discussed. It is shown that the populations of isotactic and syndiotactic triads P_i and P_s determined experimentally in the insertion PMMA are in a reasonable agreement with values calculated from the model. It is shown, furthermore, that P_i increases with increase in the density of the ion population, in agreement with the equations derived from the model.     

Beckmann Fragmentation and Rearrangement. Part VI thian-3-one oximes. Fragmentation reactions no. 26

In 70% aqueous dioxane thian-3-one anti-oxime p-toluenesulfonate (tosylate) ( 8b ) undergoes concerted fragmentation to the methylidenesulfonium ion 14 , part of which recyclizes to 1,3-thiazepin-4-one ( 11 ). With the syn-isomer 8b rearrangement to 1,4-thiazepin-3-one ( 10 ) and fragmentation to 14 occur in the ratio 4:1. Analysis of the rate data in 80% ethanol shows that anti fragmentation is 142 times as fast as syn fragmentation, but only 26 times as fast as rearrangement of the ‘homomorphous’ thian-4-one oxime tosylate ( 18b ). A comparison of the rates of cyclohexanone oxime tosylate 20 , thian-3- and -4-one oxime tosylates reveals the rate retarding influence of sulfur. – The configurations assigned to the stereoisomeric thian-3-one oximes ( 8a ) in the literature have to be reversed in the light of present results.     

Anionic polymerization with alkaline-earth counterion. II. Polymerization of styrene initiated by dicarbanionic oligostyrylbarium in THF

The propagation kinetics of anionic polymerization of styrene initiated by dicarbanionic oligostyrylbarium (PS⁼Ba⁺⁺) in THF are described. The apparent propagation rate constant k_p increases drastically with the degree of polymerization (DP) of living chains and tends at 20°C, for the highest molecular weight (DP ? 5000), to the value determined for monocarbanionic polystyrylbarium(PS^?)₂Ba⁺⁺. At given DP, the propagation step follows usual first-order kinetics with respect to monomer, and k_p is inversely proportional to carbanion concentration; as observed for (PS^?)₂Ba⁺⁺. Similar behavior is observed in the temperature range from ?60 to +20°C. The activation energy of the propagation is 4–5 kcal/mole (16.7–21 kJ/mole). It is shown that k_p may be considered as directly proportional to the dissociation constant K_d of ion pairs (～S^?Ba^++?S～ is considered as an ion pair ～(SBa)⁺S^?～). The striking variation of k_p with the DP living chains is interpreted in terms of cyclic living chains, in which both carbanionic ends are bound to the same cation. Values of the intramolecular dissociation constant K_d of ion pairs included in such a model are computed as a function of DP, and their variation is found to fit rather well with experimental data.     

Kinetics of polyesterification. I. Dibasic acid and glycol systems

Polyesterification of diacid and diol in the absence of foreign acid is carried out under constant reaction temperatures from 140 to 180°C (rather than under constant oil bath temperature as is usually done) and molar ratios r of diol to diacid from 1 to 3.55. The experimental data obtained cannot fit conventional rate equations as they appear in the literature. Based on ion pair formation and considering additional proton transfer from acid to alcohol, we propose a reaction mechanism and rate equations. The rate equation is found to fit our experimental data very well except for r = 1. At r = 1, the kinetic plot shows two straight lines rather than one as predicted. This is attributed to unremoved water due to the higher molecular weight (and therefore higher viscosity) at r = 1 which causes a reverse reaction and slower apparent reaction rate.