Filtern
Dokumenttyp
- Zeitschriftenartikel (4) (entfernen)
Sprache
- Englisch (4)
Referierte Publikation
- ja (4)
Schlagworte
- Gasfluorierung (2)
- IR (2)
- XPS (2)
- -COOH und NF2-Gruppen (1)
- AFM (1)
- Dissociative electron attachment (1)
- Green chemistry (1)
- Low-energy electrons (1)
- NF2-Gruppe (1)
- Polyamid-6 (1)
Organisationseinheit der BAM
One of the major challenges in chemical synthesis is to trigger and control a specific reaction route leading to a specific final product, while side products are avoided. Methodologies based on resonant processes at the molecular level, for example, photochemistry, offer the possibility of inducing selective reactions. Electrons at energies below the molecular ionization potential (<10 eV) are known to dissociate molecules via resonant processes with higher cross sections and specificity than photons. Here we show that even subexcitation electrons with energies as low as 1 eV produce ethylene and acetylene from dimethyl sulfide in competing reactions. However, the production of ethylene can specifically be targeted by controlling the energy of electrons (∼3 to 4 eV). Finally, pure ethylene is selectively desorbed by heating the substrate from 90 to 105 K. Beyond the synthesis of these versatile hydrocarbons for various industrial applications from a biogenic sulfur compound, our findings demonstrate the feasibility of electron-induced selective chemistry applicable on the nanoscale.
Efficient formation of difluoramino (NF2) groups within the polymer matrix upon exposure of polyamides (PA6 and PA12) to elemental fluorine is reported. The reaction was assessed on bulk and thin-film samples by means of RA-FTIR (reflection–absorption FTIR), XPS (X-ray photoelectron spectroscopy), and NMR (nuclear magnetic resonance) techniques. Direct fluorination causes cleavage of the amide C–N bond and concomitant formation of the NF2 chain-end functionalities as evident from an exceptionally large shift (+5 eV) of the N 1s binding energy and an increase of the v(CO) frequency by about 80 cm-1. The structural model is supported by the 19F NMR spectra of volatile reaction products that clearly reveal the presence of the NF2 group.
Bulk samples and thin films of polyamides (PA6 and PA12) were exposed to fluorine (1 - 10 vol.-% F2 in N2) and analysed with photoelectron (XPS) and infrared spectroscopy. Fluorination affects both, the amide and the hydrocarbon parts of the polymers. However, only the carbon atom next to the carbonyl is readily fluorinated. Chemical modification of the amide group is apparent in a large binding energy shift (+5 eV) of the N1s level and the appearance of a CO band at 1734 cm-1. It is concluded that the amide C-N bond is cleaved in the fluorination process and that COOH and NF2 end groups are formed. This conclusion is corroborated by the appearance of ester oxygen in the XPS and by the 19F NMR spectra of the volatile products that show fluorine signals chemically shifted about 200 ppm towards lower field as compared with the CHF environment.
Thin polyamide-6 films were exposed to fluorine gas and analysed with photoelectron and infrared spectroscopies. Fluorine cleaves the amide CN bond resulting in the formation of the COOH and NF2 terminal groups. This is evident from large shifts in the N1s binding energy (+5 eV) and C=O stretching frequency (~80 cm-1), appearance of ester oxygen in the XPS spectra, as well as by the 19F nmr spectra of volatile products consistent with a terminal NF2 group.