Reaction with atomic xenon

Dlchlorophenol in aqueous solution was illuminated with filtered xenon light (A >295 nm) at various time intervals. The first-order conversion rate constant was 5.73 x lO Vsec. The loss of chlorine atoms seemed to be the major early process during the reaction (Svenson and Kaj, 1989). 

To overcome problems associated with the removal of iodobenzene and its derivatives formed upon fluorination of arylalkenes and arylalkynes with (difluoroiodo)arenes, polymer-supported (difluoroiodo)arenes were proposed.139 With these agents, the separation procedures are reduced to filtration of the iodinated polymer. For this purpose popcorn polystyrene is io-dinated and then transformed into the difluoroiodide by treatment with xenon difluoride in the presence of hydrogen fluoride in dichloromelhane at 25 C. The amount of active fluorine bonded to iodine atoms on the polymer support is estimated by iodometric titration. The reactions with phenyl-substituted alkenes result in rearranged gew-difluorides. The procedure provides the same fluorination products as with (difluoroiodo)benzenc (see Section 4.13.) but in much higher yields, e.g. PhCF2CH2Ph (96%), PhCF2CH(Me)Ph (95%). PhCH2CF2H (86%), and l,l-difluoro-2-phenylcyclopentanc (91 %). 

Alkanes do not usually react with xenon difluoride at room temperature, while thermally initiated fluorinations of organic molecules have received much less attention than liquid-phase reactions. Zajc and Zupan16 have shown that several hydrocarbons react with xenon difluoride when heated to 95-120 °C. Reproducible results can be observed only when a teflon jacket is used in the stainless reactor with appropriate preconditioning. Cyclohexane is converted to fluorocyclohexane, while the reaction with -hexane gives three monofluoro-substituted products. Fluorination of adamantane results in the formation of four products, from whose distribution it is evident that the difference in the reactivity between the secondary and the tertiary carbon atom is much larger than the difference between the reactivities of the primary and secondary carbon atoms of hexane. Liquid-phase functionalization of a tertiary carbon atom is observed in reactions in carbon disulfide, where 1-fluoroadamantane is formed17. 

Replacements of one or two chlorine atoms and hydrogen by fluorine were observed in various organosilicon compounds in reactions with xenon difluoride99,135, while aryl-silicon bond cleavage was observed in the presence of potassium fluoride136,137 (Scheme 57). 

To observe the intermediate structures one must collect the intensity data rapidly. We designed and made a diffractometer, R-AXIS lies, for rapid collection [7] of data, which has been marketed in a revised form by Rigaku Company as R-AXIS RAPID since 1998. The two-step crystalline-state reaction was first found in the inversion of a chiral alkyl group bonded to the cobalt atom in a cobaloxime complex when the crystal on the diffractometer was irradiated with a xenon lamp [8]. Figure 5-2 shows the two-step structural change of the complex, ((R)-l-methoxy-carbonylethyl) [(S)-l-phenylethylamine] cobaloxime. After exposure for 2h, the structure (Figure 5-2b) showed the disordered structure of the chiral (R)-... 

As for XeF the X-ray component for irradiated Xe/CH2Br2 was negligibly small. The xenon dimer fluorescence was typically complete within 100 ns and its intensity was proportional to the xenon pressure. The exciplex fluorescence formed by the reaction of excited xenon atoms with CH2Br2 was also observed within the first hundred nanoseconds, however its intensity was strongest at low xenon pressures. The ionic recombination formed exciplex fluorescence again had the slowest rate of production, being observed for many hundreds of nanoseconds. Its intensity was also dependent on total xenon gas pressure being comparable to the excited-state formed fluorescence at low... 

The Group 18 elements are called the noble gases because of their low reactivity. Like a noble man (as opposed to a nobleman) who does not interfere with others, these elements rarely involve themselves in reactions with other atoms. These gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). 

Radical-cations may also be involved in the formation of phenyl esters from aromatic carboxylic acids and benzene in the presence of xenon difluoride, and can apparently be detected by e.s.r. spectroscopy during the reaction of iViV-dimethylaniline with perfluoropiperidine. The last reagent gives a low yield of o- and p-fluorophenol in the ratio 3.5 1 in its reaction with sodium phenoxide, and the predominance of ortho substitution is ascribed to a cage mechanism of the type shown in (3). However, towards 2,4,6-tri-t-butylphenoxyl radicals the piperidine acts as a source of fluorine atoms to give the dienone (4). ... 

It was found that the 2-cyanoethyl (2-ce) group bonded to the cobalt atom is isomerized to the 1-ce group on exposure to visible light only in the solid state as shown in Scheme 5.1 [1]. The reachon is not observed in solutions probably because the comphcated coupling reactions between the produced alkyl radicals would occur. Since the crystals are usuahy decomposed as the reaction proceeded, the reaction rate is estimated from the change of the IR spectra due to the C-N triple bond. Several KBr discs of a cobaloxime complex were irradiated with a xenon lamp under the same conditions and the IR spectra were measured one by one at a constant interval. The spectra due to the stretching vibration mode of the cyano... 

The reaction of F atoms with excess xenon was studied in the same discharge-flow apparatus used for the F + CO reaction, eind XeF2 was identified as a product (4). The rate determining step was assumed to be... 

Flamm, D. L. Ibbotson, D. E. Mucha, J. A. Dormelly, V. M., "Xenon Difluoride and Fluorine Atom Reactions with Silicon Their Significance for Plasma Etching," Solid State Technol. 1983,26,117. 

---