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Multi-fluorinated

For toluene fluorination, the impact of micro-reactor processing on the ratio of ortho-, meta- and para-isomers for monofluorinated toluene could be deduced and explained by a change in the type of reaction mechanism. The ortho-, meta- and para-isomer ratio was 5 1 3 for fluorination in a falling film micro reactor and a micro bubble column at a temperature of-16 °C [164,167]. This ratio is in accordance with an electrophilic substitution pathway. In contrast, radical mechanisms are strongly favored for conventional laboratory-scale processing, resulting in much more meta-substitution accompanied by imcontroUed multi-fluorination, addition and polymerization reactions. [Pg.72]

GL 1] [R 4] [P 2] Selectivities of up to 36% at 33% conversion were achieved using acetonitrile as solvent (1.0 fluorine-to-toluene equivalent) [13]. When including multi-fluorinated toluenes and chain-fluorinated toluenes, in addition to the mono-fluorinated toluenes, in the selectivity balance, the value increases to 49%. The remainder is lost in other side reactions such as additions or polymerizations. [Pg.600]

C) when approximately 12.4% nonafluoro-3-hydroxynonanoate was present in the polymer. The repeating units found in these PH As included trifluoro-3-hydroxybutyrate, heptafluoro-3-hydroxyoctanoate, and nonafluoro-3-hydroxy-nonanoate. The thermal properties and the PHA composition changed with growth time, which indicated that the multi-fluorinated 3HA units were not distributed in the PHA randomly but chains, or chain segments, existed with relatively high multi-fluorinate 3HA units. [Pg.72]

Fluorinatedphenyl)pyridines were prepared by coupling 2-halopyridines with multi-fluorinated phenylboronate. Pd(0) and AgO were the coupling agents necessary for optimal yield <03TL1503>. [Pg.314]

The Halex reaction for the synthesis of multi-fluorinated isoquinoUne was investigated in detail by Matthews et al., and they attempted chlorine-flnorine exchange reactions of several multi-chlorinated isoquinolines [36], When 3,5,6,7, 8-pentachloroisoquinoUne was treated with an excess of cesium fluoride in deuter-ated dimethyl sulfoxide (DMSO-de) at 100 °C, 3,5,7,8-tetrachloro-6-fluoroiso-quinoUne and 3,5,6,7-tetrachloro-8-flnoroisoquinoline were formed in a 7 3 ratio after 20 min (Scheme 11). The observation of the predominant substitution at the 6-position was consistent with the fact that the 6-position of heptafluoroisoquino-Une was the second most reactive to nucleophiles after the 1-position (vide supra, Schane 5) [17]. Similar reaction conditions were also employed in the reaction of heptachloroisoquinoline, where the 1-position was found to be more reactive than other positions (Scheme 12). [Pg.187]

J. Dykstrra, A. P. Huber, and B. H. Thompson, "Multi-Ton Production of Fluorine for Manufacture of Uranium Hexaduoride," paper presented... [Pg.133]

For this reason, industrial fluorinations of aromatics are performed by other routes, mostly via the Schiemann or Halex reaction [54, 55]. As these processes are multi-step syntheses, they suffer from low total selectivity and waste production and demand high technical expenditure, i.e. a need for several pieces of apparatus. [Pg.597]

The fact that LEIS provides quantitative information on the outer layer composition of multi-component materials makes this technique an extremely powerful tool for the characterization of catalysts. Figure 4.19 shows the LEIS spectrum of an alumina-supported copper catalyst, taken with an incident beam of 3 keV 4He+ ions. Peaks due to Cu, A1 and O and a fluorine impurity are readily recognized. The high intensity between about 40 and 250 eV is due to secondary (sputtered) ions. The fact that this peak starts at about 40 eV indicates that the sample has charged positively. Of course, the energy scale needs to be corrected for this charge shift before kinematic factors Ef/E-, are determined. [Pg.121]

Because the number of orbitals available for boron is higher than electrons (three electrons, four orbitals) boron is an electron-pair acceptor, a Lewis acid and it is prone to form multi-centre bonds. Boron is inert under normal conditions except for attack by fluorine. [Pg.484]

Trisubstituted carbon-centred radicals chemically appear planar as depicted in the TT-type structure 1. However, spectroscopic studies have shown that planarity holds only for methyl, which has a very shallow well for inversion with a planar energy minimum, and for delocalized radical centres like allyl or benzyl. Ethyl, isopropyl, tert-butyl and all the like have double minima for inversion but the barrier is only about 300-500 cal, so that inversion is very fast even at low temperatures. Moreover, carbon-centred radicals with electronegative substituents like alkoxyl or fluorine reinforce the non-planarity, the effect being accumulative for multi-substitutions. This is ascribed to no bonds between n electrons on the heteroatom and the bond to another substituent. The degree of bending is also increased by ring strain like in cyclopropyl and oxiranyl radicals, whereas the disubstituted carbon-centred species like vinyl or acyl are bent a radicals [21]. [Pg.6]

From a chemical point of view, the half-life of fluorine-18 allows multi-step synthetic approaches that can be extended over hours. Fluorine-18 has therefore, in spite of its somewhat limited chemical repertoire, been effectively used for the labelling of numerous both relatively simple and complex bioactive chemical structures [3,5-9], including high-molecular-weight macromolecules such as peptides, proteins [10-13] and oligonucleotides [14-18]. General considerations on radiochemistry involving short-lived positron emitters will be discussed in Section 2.3. [Pg.6]

Finally, fluorine-18 can be reliably and routinely produced at the multi-Curie level [19] on widely implemented biomedical cyclotrons of relatively low-energy proton beam (e.g. 18MeV). This fact, combined with its favourable half-life. [Pg.6]

Noteworthy is a recent multi-step method for the production of molecular [ F]F2 of considerable higher specific radioactivity (100-925 Ci/mmol or 3.7-34 TBq/ mmol) starting from aqueous [" Fjfluoride produced with the 0(p,n) F reaction [38], The dried and activated [ F]fluoride is reacted with methyl iodide to yield methyl [ F]fluoiide (CHsf FjF) which is isolated by gas chromatography. The latter is then subjected to an electrical discharge (20-30 kV, 280 pA, 10 s) in the presence of small amounts of carrier fluorine (150 nmol) resulting in about 30% conversion of the original [ F]fluoride into molecular [ F]F2. [Pg.11]

Aliphatic and aromatic nucleophilic substitutions with p Fjfluoride are usually performed either on an immediate precursor of the target molecule (direct labelling using a one-step process) or on an indirect precursor followed by one or more chemical steps leading to the target radiotracer. The first approach, if highly desirable, is in fact rarely practicable. The reaction conditions are often not compatible with the structure or with the various chemical functions borne by the radiopharmaceutical. It is therefore common that the radiosynthesis comprises at least two chemical steps first the introduction of fluorine-18 followed by what is often a (multi)deprotection step. It is not unusual either that fluorine-18 is first incorporated into a much simpler and chemically more robust molecule which is then coupled to a more sensitive entity under milder conditions, possibly still followed by a final deprotection step. Suchlike multi-step procedures are possible thanks to the favourable half-life of fluorine-18. However, the more complicated the process, the more chance of side reactions and complicated final purifications (see also Section 2.3), which may seriously hamper the automation of the process. [Pg.28]

Multi-step synthesis of a radiopharmaceutical involving an aliphatic nucleophilic fluorination... [Pg.32]

Single- or multi-step preparation of [ F]fluoroaryl-type molecular building blocks and some applications A large number of no-carrier-added fluorine-18-labelled aromatic key-intermediates have been synthesised, opening the way to the preparation of more complicated radiopharmaceuticals via multi-step approaches. Scheme 42 non-exhaustively lists a number of para-substituted [ F]fluorobenzene compounds indicating some of their possible chemical interconnections. It also shows some of the precursors for labelling (P1-P7) that have been used for their preparation. [Pg.36]

In the following, those ion beam analysis techniques that allow for fluorine detection will be presented. By far, the most important technique in this respect is nuclear reaction analysis (NRA). Although it can be rather complex to perform, it is the most often applied technique for fluorine trace element studies, due to a number of convenient and prolific resonant nuclear reactions which make it very sensitive to fluorine in most host matrices. NRA is often combined with particle-induced X-ray emission (PIXE) which allows for simultaneous determination of the sample bulk composition and concentrations of heavier trace elements. By focusing and deflecting the ion beam in a microprobe, the mentioned techniques can be used for two- or even three-dimensional multi-elemental imaging. [Pg.217]

The evaluation of D by fitting an error function, which is based upon an undisturbed diffusion model in a single component system, will not lead to a proper description of the fluorine uptake in a natural multi-component system. [Pg.238]


See other pages where Multi-fluorinated is mentioned: [Pg.597]    [Pg.608]    [Pg.71]    [Pg.170]    [Pg.70]    [Pg.597]    [Pg.608]    [Pg.71]    [Pg.170]    [Pg.70]    [Pg.353]    [Pg.58]    [Pg.60]    [Pg.393]    [Pg.395]    [Pg.526]    [Pg.12]    [Pg.327]    [Pg.32]    [Pg.291]    [Pg.291]    [Pg.353]    [Pg.103]    [Pg.531]    [Pg.1]    [Pg.94]    [Pg.202]    [Pg.332]    [Pg.333]    [Pg.409]    [Pg.190]    [Pg.246]    [Pg.297]    [Pg.71]   
See also in sourсe #XX -- [ Pg.3 , Pg.70 ]




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