The products of the thermal degradation at 95 °C over 10 months of ω‐saturated and non‐saturated poly(methyl methacrylate) (pMMA) model compounds were identified with high accuracy via quadrupole ion trap and quadrupole ion trap‐time of flight (Q‐ToF) mass spectrometry. Analysis of the samples taken via these techniques indicated that degradation of vinyl terminated pMMA proceeds via the incorporation of oxygen via the formation of ethylene oxide type end groups, which subsequently rearrange under the expulsion of formaldehyde and 2‐oxo‐propionic acid methyl ester. The corresponding saturated model compounds were demonstrated to be stable over the same time period. The present findings highlight for the first time that poly(methyl methacrylate) degradation does not necessarily and exclusively proceed via radical intermediates.
Pd‐catalyzed oxidative coupling reaction was of great importance in the aromatic C? H activation and the formation of new C? O and C? C bonds. Sanford has pioneered practical, directed C? H activation reactions employing Pd(OAc)2 as catalyst since 2004. However, until now, the speculated reactive Pd(IV) transient intermediates in these reactions have not been isolated or directly detected from reaction solution. Electrospray ionization tandem mass spectrometry (ESI‐MS/MS) was used to intercept and characterize the reactive Pd(IV) transient intermediates in the solutions of Pd(OAc)2‐catalyzed oxidative coupling reactions. In this study, the Pd(IV) transient intermediates were detected from the solution of Pd(OAc)2‐catalyzed oxidative coupling reactions by ESI‐MS and the MS/MS of the intercepted Pd(IV) transient intermediate in reaction system was the same with the synthesized authentic Pd(IV) complex. Our ESI‐MS(/MS) studies confirmed the presence of Pd(IV) reaction transient intermediates. Most interestingly, the MS/MS of Pd(IV) transient intermediates showed the reductive elimination reactivity to Pd(II) complexes with new C? O bond formation into product in gas phase, which was consistent with the proposed reactivity of the Pd(IV) transient intermediates in solution. 相似文献
Open access mass spectrometry now provides the opportunity to move this spectroscopic method to the beginning of the analytical chain, a place formerly the exclusive province of NMR and TLC. To date this transition has been occurring in industrial settings but there has been less change in the academic environment. This paper provides one blueprint for setting up such a facility, primarily in support of organic synthesis but also for the use of biological scientists. The open access format used at UCI utilizes four instruments: an ESI-TOFMS system used in the flow injection mode, two GC/MS systems (one in EI and one in CI) and a MALDI-TOFMS system. The first three instruments have autosamplers and open access software whereas the MALDI system has a fully automated plate handling interface. This level of automation allows access to the instruments by a user community of more than 100 users, day or night. The decisions made in setting up these instruments were based on a 'keep it simple' philosophy, given the fact that the primary type of data of interest is the molecular mass of the analyte and that data are required for a very wide range of structures. 相似文献
Inorganic polymers in aqueous solutions are being proposed as essential components in new theories concerning nonclassical nucleation and growth of nanominerals relevant to environmental nanogeosciences. The study of those complex natural processes requires multi‐technique analytical approaches able to characterize the solutions and their constituents (solutes, oligomers, polymers, clusters and nanominerals) from atomic to micrometric scales. A novel analytical approach involving an electrospray ionization source (ESI) coupled to time‐of‐flight mass spectrometry (TOF/MS) was developed to identify inorganic polymers in aqueous solution. To this end, the presence of initial Al oligomers and their polymerization processes was studied during a nanomineral aqueous synthesis (hydrobasaluminte, Al4SO4(OH)10·12‐36H2O). Ensuring the feasibility and robustness of the methodology as well as the stability of the polymers under study (avoiding undesirable fragmentation), a meticulous study of the ESI‐TOF MS working conditions was performed. Precision of the methodology was evaluated obtaining relative standard deviations below 3.3%. For the first time in the study of inorganic polymers in the earth sciences, the mass accuracy error (ppm) has been reported and the use of significant decimal figures of the m/z signal has been taken into account. Complementary to this, a four‐step polymer assignment methodology and a database with the Al? and Al‐SO42? polymers assigned were created. Several polymers have been assigned for the first time, including Al (SO4)+·H2O, Al2O(SO4)2+·H2O, Al5O4(OH)52+·2H2O, and Al3O5(OH)2?·4H2O, among others. The results obtained in the present study help create a foundation to include mass spectrometry as a routine analytical technique to study mineral formation in aqueous solution. 相似文献
In this paper we describe the application of electrospray time-of-flight mass spectrometry (ESI-TOFMS) to structural elucidation of the fragment ions formed from a range of natural and synthetic allelochemical derivatives. The extensive mass spectrometric characterisation of ten non-glucosylated benzoxazinone derivatives using this method is described here for the first time. The analytes include six naturally occurring 1,4-benzoxazin-3(4H)-one derivatives, including the hydroxamic acids DIMBOA [2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one] and DIBOA [2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one], lactams HBOA [2-hydroxy-2H-1,4-benzoxazin-3(4H)-one] and HMBOA [2-hydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one], benzoxazolinones BOA [benzoxazolin-2(3H)-one] and MBOA [6-methoxy-benzoxazolin-2(3H)-one] and four synthetic variations, 2'H-DIBOA [4-hydroxy-2H-1,4-benzoxazin-3(4H)-one], 2'OMe-DIBOA [2-methoxy-4-hydroxy-2H-1,4-benzoxazin-3(4H)-one], 2'H-HBOA [2H-1,4-benzoxazin-3(4H)-one] and 2'OMe-HBOA [2-methoxy-2H-1,4-benzoxazin-3(4H)-one]. Assignments of the mass spectral fragments were aided by elemental composition calculation results, comparison of structural analogues and background literature, and acquired knowledge regarding feasible structures for the compounds. The influence of substituents on the chemical reactivity of the compounds with respect to the observed MS behaviour over varying nozzle potentials is addressed and, through comparison of the structural analogues, generic fragmentation patterns have also been identified. 相似文献
