Fluorine nucleophilic

As fluorinated polymers, poly[(N-3-n-perfluorooctyl propionyl-ethylenimine)-f7-(N-propionylethylenimine)] can be used (6). Alternatively a water-soluble B block can be synthesized first, and a fluorinated nucleophilic compound then used to terminate the living ends to provide the fluorine containing A block (6). The preparation of the polymers has been described in detail (6). 

Whilst Sn2 displacement is a viable strategy for aliphatic fluorination, nucleophilic fluorination of aromatic systems is much more challenging. The traditional approach to aromatic fluorination is the Balz-Schiemann reaction, which is the thermal decomposition of aiyl diazonium tetra-fluoroborate salts, which are potentially explosive reagents. This decomposition also gives the toxic, fuming gas BF3 as a by-product and this should be removed in a basic aqueous scrubber. Modern alternatives should seek to provide safer and cleaner aromatic fluorination protocols. 

One of the most important application of fluorine nucleophilic substitution in diazines was found in reactive dyes industry. In a reactive dye a chromophore contains a substituent that is activated and allowed to directly react to the surface of the substrate. Reactive dyes have good fasmess properties owing to the bonding that occurs during dyeing. Reactive dyes are most commonly used in dyeing of cellulose like cotton or flax, but also wool is dyeable with reactive dyes. 

The order of alkyl halide reactivity in nucleophilic substitutions is the same as their order m eliminations Iodine has the weakest bond to carbon and iodide is the best leaving group Alkyl iodides are several times more reactive than alkyl bromides and from 50 to 100 times more reactive than alkyl chlorides Fluorine has the strongest bond to car bon and fluonde is the poorest leaving group Alkyl fluorides are rarely used as sub states m nucleophilic substitution because they are several thousand times less reactive than alkyl chlorides... 

The most common types of aryl halides m nucleophilic aromatic substitutions are those that bear o ox p nitro substituents Among other classes of reactive aryl halides a few merit special consideration One class includes highly fluormated aromatic compounds such as hexafluorobenzene which undergoes substitution of one of its fluorines on reac tion with nucleophiles such as sodium methoxide... 

Nucleophilic Reactions. The strong electronegativity of fluorine results in the facile reaction of perfluoroepoxides with nucleophiles. These reactions comprise the majority of the reported reactions of this class of compounds. Nucleophilic attack on the epoxide ring takes place at the more highly substituted carbon atom to give ring-opened products. Fluorinated alkoxides are intermediates in these reactions and are in equiUbrium with fluoride ion and a perfluorocarbonyl compound. The process is illustrated by the reaction of methanol and HFPO to form methyl 2,3,3,3-tetrafluoro-2-methoxypropanoate (eq. 4). 

Nucleophilic Displacement Reactions. The presence of activating groups, eg, o,p mX.1.0 groups, makes aromatic fluorine reactive in nucleophilic displacement reactions. This has been demonstrated by deterrnination of the relative fluorine—chlorine displacement ratios from the reaction of halonitroben2enes with sodium methoxide in methanol (137) F is displaced 200—300 times more readily than Cl. 

Fluoropyridine is readily hydroly2ed to 2-pyridone in 60% yield by reflux in 6 Ai hydrochloric acid (383). It is quite reactive with nucleophiles. For example, the halogen mobiUty ratio from the comparative methoxydehalogenation of 2-fluoropyridine and 2-chloropyridine was 85.5/1 at 99.5°C (384). This labihty of fluorine has been utili2ed to prepare fluorine-free 0-2-pyridyl oximes of 3-oxo steroids from 2-fluoropyridine for possible use as antifertihty agents (385). 

Difluoropyridines. 2,4-Difluoropyridine can be prepared (26% yield) from 2,4-dichloropyridine and potassium fluoride in sulfolane and ethylene glycol initiator (403). The 4-fluorine is preferentially replaced by oxygen nucleophiles to give 2-fluoro-4-hydroxypyridine derivatives for herbicidal apphcations (404). 

In the general preparation of quinolones by forming the nitrogen aryl bond a in the ring closure, typical precursors are prepared as shown in Figure 2. The ring closure involves nucleophilic displacement of a halogen, usually a chlorine or fluorine (76) eg, (29) and (30) lead to (31) [86483-54-7] and (32) [123942-15-4] respectively. 

Direct iodination or fluorination leads to ill-defined products and fragmentation, respectively. Sandmeyer chemistry and nucleophilic substitution of... 

N-fluorine displacement, 7, 272 1-Azetine, 2-alkoxy-nucleophilic reactions, 7, 271 1-Azetine, 2-aryl-mass spectrometry, 7, 268 nucleophilic reactions, 7, 271 1-Azetine, 2-chIoro-nucleophilic reactions, 7, 271... 

The formation of ethyl cyano(pentafluorophenyl)acetate illustrates the intermolecular nucleophilic displacement of fluoride ion from an aromatic ring by a stabilized carbanion. The reaction proceeds readily as a result of the activation imparted by the electron-withdrawing fluorine atoms. The selective hydrolysis of a cyano ester to a nitrile has been described. (Pentafluorophenyl)acetonitrile has also been prepared by cyanide displacement on (pentafluorophenyl)methyl halides. However, this direct displacement is always aecompanied by an undesirable side reaetion to yield 15-20% of 2,3-bis(pentafluoro-phenyl)propionitrile. 

Nucleophilic Substitution iii Polyfluoro-dtomatic Compounds Kobnna L, S Fluorine Chem Rev 7, I-H4 189... 

Intramolecular Nucleophilic Displacement of Fluorine Hudlicky, M Isr J Chem 17, 80-91 68... 

Kinetics of Nucleophilic Substitution Reactions of Polyfluoroaromatic Compounds Rodionov, P P, Furin, G G J Fluorine Chem 47. 361 34 105 ... 

Nucleophilic Substitution in Aromatic Compounds with Fluorinated Substituents (Russ ) Boiko, V N hv Sib Old Akad NaukSSSR 126-136 53 a c S... 

Fluonde Ion as Nucleophile and a Leaving Group in Aromatic Nucleophilic Substitution Reactions Vlasov V M J Fluorine Chem 6i. 193-216 77... 

Fluorine and sulfur (in the form of a methylthio group) are added to nucleophilic olefins with Markovnikov regwselectivity and anti stereoselectivity by di-methyl(niethylthio)sulfoninni fluoroborate and triethylamine tris(hydrogen fluoride) [777] (equation 21)... 

Fluorine and selenium, in the form of a phenylselenenyl group, add to nucleophilic olefins with Markovnikov regioselectivity and anti stereoselectivity on reaction with several reagents that may form phenylselenenyl fluoride in situ [792, 193, 194] (equation 30)... 

Addition of fluorine and carbon to nucleophilic olefins is little studied, a rare example being the photochemical addition of benzotrifluonde to electron-rich cyclic olefins [202] (equation 40)... 

The simplest method for obtaining selective fluonnation is to conduct reactions under conditions that invigorate the electrophilicity of fluorine In practice this method entails the creation of anionic or strongly nucleophilic reactive centers on substrate molecules while suppressing or reducing the tendency toward radical attack Numerous examples of seleetive fluorine attack on carbanionic, amido and carboxylato species are documented Especially abundant is alpha fluonnation of nitroalkanes in polar solvents [42 43, 44, 45 46] (equations 10-14)... 

The fluoroxy reagents react readily with activated aromatic systems (Table 1) to give moderate yields of fluoroaromatic compounds. The fluorine atom shows a preference for ortho orientation because of complexation between the fluoroxy reagent and the ring substituent [75, 22] Nucleophilic attack by the substrate on... 

The fluoraza reagents consist of two types of compounds one in which a fluorine atom is bound to the nitrogen atom of an amide or, more often, a sulfonamide and one in which a fluorine atom is bound to the nitrogen atom of a tertiary amine such as pyridine, quinuclidine, or triethylenediamine 1,4-diaza-bicyclo[2 2.2]octane. The positive charge on the nitrogen is counterbalanced by a non-nucleophilic anion such as triflate or tetrafluoroborate. 

Xenon difluoride [4, 5, 7, 8,10] is a white crystalline material obtained through the combination of fluorine and xenon m the presence of light The reagent is commercially available and possesses a relatively long shelf-life when stored cold (freezer) Xenon difluoride is very effective for small-scale fluormation of alkenes and activated nucleophilic substrates. The reactions are usually conducted between 0 °C and room temperature in chloroform or methylene chloride solutions Hydrogen fluoride catalysis is sometimes helpful Xenon difluoride reacts in a manner that usually involves some complexation between the substrate and reagent followed by the formation of radical and radical cation intermediates... 

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