G.P. Gambaretto

Liquid-phase fluorination of aromatic compounds by elemental fluorine

Abstract The fluorination of aromatic compounds (benzene, toluene, phenol and benzoic acid) by elemental fluorine diluted with nitrogen has been investigated in various solvents (Freon 11, chloroform, methanol, trifluoroacetic acid, 2,2,2-trifluoroethanol, water) in order to define the influence of the experimental conditions on the reaction. Experiments have been carried out by varying the temperature, the substrate concentration in solution, the molar ratio of fluorine to substrate, and the concentration of fluorine in the fluorine/nitrogen mixture. In all cases, the effects on the yield of fluorinated products were studied. Monofluorinated compounds were mainly found in the reaction mixture, the isomers formed being in accord with the mechanism for electrophilic substitution. The highest yield of monofluorinated products was obtained with polar solvents and the following order was found: CFCl 3 3 3 OH 3 CH 2 OH 3 COOH. Interesting results were also found using particular additives (for instance, KOH or C 4 F 9 SO 3 Na in methanol) or water as the solvent. A direct relationship was observed between the yield of monofluorinated compounds and the molar ratio of fluorine to substrate, which has to be less than one in order to obtain high yields. In contrast, low selectivity, expressed as the yield ratio of ortho to para (or meta ) isomers, was found.

Electrochemical production of partially fluorinated organic compounds: N-methylmorpholine fluorination

Abstract The usual electrochemical fluorination of organic compounds in anhydrous HF produces completely fluorinated materials. In order to obtain partially fluorinated compounds, electrofluorination has been conducted under various conditions, including the use of solvents. None of the solvents lead to satisfactory results. Experiments have also been carried out with high concentrations of N-methylmorpholine in anhydrous HF and they have provided information about the selectivity and the mechanism of the reaction. Various partially fluorinated derivatives of N-methylmorpholine have been identified, and some of them separated from the reaction mixture.

Diblock semifluorinated n-alkanes purification by gel phase formation in organic solvents: C8F17C1837 in alcohols

Abstract The formation of a gel-like phase observed with some diblock semifluorinated n-alkanes dissolved in organic solvents was investigated as a purification method for these compounds. Experiments were carried out with F(CF 2 ) 8 (CH 2 ) 18 H by using absolute ethanol or methanol as solvent. Starting from samples with different initial degrees of purity, and using a very strict methodology, the amount of solvent giving the highest yield of purification was determined. The different solubilizing power of the solvents used did not greatly influenced the purification process. Different cooling rates were also investigated, but only small influences on the treatment effectiveness were observed.

Preparation of 4-fluorophenol and 4-fluorobenzoic acid by the Baeyer-Villiger reaction

Abstract The possibility of preparing 4-fluorophenol or 4-fluorobenzoic acid via the Baeyer-Villiger reaction starting from unsymmetrical fluoroaryl ketones is discussed. Several unsymmetrical 4-fluorobenzophenones having different substituents in the fluorine-free aryl group were prepared and converted to esters by treatment with peracetic acid. The electrophilicity of the substituents influenced the molecular structure of the ester formed as a result of a carbon-to-oxygen migration, and hence 4-fluorophenol or 4-fluorobenzoic acid formation. Electron-withdrawing substituents favoured the formation of 4-fluorophenol in good yield, while electron-donating substituents formed4-fluorobenzoic acid preferentially.

Polyfluorinated olefins from reaction of perfluoroalkyl iodides with allyl chloride

Abstract During experiments on addition of perfluoroalkyl iodides to allyl chloride an unexpected reaction has been observed leading to polyfluorinated olefins R F -CH 2 -CH=CH 2 in addition to the expected adduct R F -CH 2 -CHI-CH 2 Cl. Preliminary experimental results show that the relative amounts of these two products depend particularly on the molar ratio of reagents and on temperature. A mechanism for the formation of the polyfluorinated olefin is suggested.

Determination of the solubility of fluorine in various solvents

Abstract Fluorine solubility is an important parameter in fluorination reactions, both from the viewpoint of controlling reaction exothermicity and of carrying out reactions homogeneously. Several solvents have been studied in order to define their solubilization ability towards fluorine; some (such as CFCl3 or CFCl2CF2Cl) were virtually inert, whilst others (such as CF3COOH or CF3CH2OH) were capable of forming hypofluorites with fluorine. Particular additives (such as pentachlorophenol, 2,4-dinitrophenol or 3,5-dichloropyridine) were used in order to favour the formation of hypofluorites or complexes able to increase the amount of dissolved fluorine.

Fluorination of Hydrogen-containing with elemental fluorine

Abstract The hydrohalo-olefins cis and trans CHC1=CHC1, CHC1=CC12, CHC1=CH-CH2C1 and CH2=CC1-CH2C1 have been fluorinated with elemental fluorine to give good yields of hydrohalofluoroalkanes. The best operational conditions for F2 addition to the double bond rather than hydrogen and/or chlorine atom substitution, dimerization and oligomerization of radical intermediates have been studied. Preliminary studies on the reaction of Freon 12 and Freon 22 towards elemental fluorine have also been carried out.

p-Fluorobenzaldehyde and p-fluorobenzoic acid by oxidation of p-fluorobenzyl derivatives

Abstract Experiments on the oxidation reactions of p -fluorobenzyl alcohol and chloride were carried out. Several oxidizing agents (manganese dioxide, 30% hydrogen peroxide and hypochlorite solutions at different concentrations) were used, and a mixture of p -fluorobenzaldehyde and p -fluorobenzoic acid in different proportions was obtained. In the case of p -fluorobenzyl chloride, some p -fluorobenzyl alcohol was also found in the reaction mixture. The experimental conditions required to obtain an increase in the yield of the aldehyde or acid were also studied.

On the mechanism of electrofluorination of organic compounds

Abstract After a short review of the current mechanisms, the Authors describe the electrofluorination process of organic compounds in anhydrous HF. Several electrofluorination experiments carried out for some years with a particular attention to their industrial applications are reconsidered in view of the fluorination mechanism. These experiments carried out either with organic acids (butirric, isobutirric, benzensulfonic and toluensulfonic), either with tertiary amines (tripropylamine, tributylamine, N-ethylpiperidine and N-methylmorpholine), bring new support to the mechanism suggesting an initial anodic oxidation of the organic molecule adsorbed on the anode thus forming a radical-cation, which originates the corresponding cation whose stabilisation is effected by addition of a fluoride anion.