Trifluoride reactions

The aluminium ion, charge -I- 3. ionic radius 0.045 nm, found in aluminium trifluoride, undergoes a similar reaction when a soluble aluminium salt is placed in water at room temperature. Initially the aluminium ion is surrounded by six water molecules and the complex ion has the predicted octahedral symmetry (see Table 2.5 ) ... 

In each case the configuration around the boron changes from trigonal planar to tetrahedral on adduct formation. Because of this ability to form additional compounds, boron trifluoride is an important catalyst and is used in many organic reactions, notably polymerisation, esterification, and Friedel-Crafts acylation and alkylations. 

Other catalysts which may be used in the Friedel - Crafts alkylation reaction include ferric chloride, antimony pentachloride, zirconium tetrachloride, boron trifluoride, zinc chloride and hydrogen fluoride but these are generally not so effective in academic laboratories. The alkylating agents include alkyl halides, alcohols and olefines. 

The controlled thermal decomposition of dry aromatic diazonium fluoborates to yield an aromatic fluoride, boron trifluoride and nitrogen is known as the Schiemann reaction. Most diazonium fluoborates have definite decomposition temperatures and the rates of decomposition, with few exceptions, are easily controlled. Another procedure for preparing the diazonium fluoborate is to diazotise in the presence of the fluoborate ion. Fluoboric acid may be the only acid present, thus acting as acid and source of fluoborate ion. The insoluble fluoborate separates as it is formed side reactions, such as phenol formation and coupling, are held at a minimum temperature control is not usually critical and the temperature may rise to about 20° without ill effect efficient stirring is, however, necessary since a continuously thickening precipitate is formed as the reaction proceeds. The modified procedure is illustrated by the preparation of -fluoroanisole ... 

A mixture of an acid anhydride and a ketone is saturated with boron trifluoride this is followed by treatment with aqueous sodium acetate. The quantity of boron trifluoride absorbed usually amounts to 100 mol per cent, (based on total mola of ketone and anhydride). Catalytic amounts of the reagent do not give satisfactory results. This is in line with the observation that the p diketone is produced in the reaction mixture as the boron difluoride complex, some of which have been isolated. A reasonable mechanism of the reaction postulates the conversion of the anhydride into a carbonium ion, such as (I) the ketone into an enol type of complex, such as (II) followed by condensation of (I) and (II) to yield the boron difluoride complex of the p diketone (III) ... 

Boron trifluoride method. Fit a 1 litre three-necked flask with a gas inlet tube, a gas outlet leading to an alkali trap (compare Fig. 11,8, laori for the unabsorbed boron trifluoride), and stopper the third neck. Place 68 g. (73 ml.) of pure, anhydrous acetone (1) and 255 g. (236 ml.) of A.R. acetic anhydride in the flask and cool in a freezing mixture of ice and salt. Connect the gas inlet tube through an empty wash bottle to a cylinder of commercial boron trifluoride (2), and bubble the gas through the reaction mixture at such a rate that 250 g. is absorb in about 5 hours (2 bubbles per second). Pour the reaction mixture into a solution... 

Concerning my research during my Dow years, as I discuss iu Chapter 4, my search for cationic carbon intermediates started back in Hungary, while 1 was studying Friedel-Crafts-type reactions with acyl and subsequently alkyl fluorides catalyzed by boron trifluoride. In the course of these studies I observed (and, in some cases, isolated) intermediate complexes of either donor-acceptor or ionic nature. 

When mixed with Lewis acids, dinitrogen pentoxide yields crystalline white solids, which were identified as the corresponding nitronium salts by their infra-red spectra. The reaction with boron trifluoride can be formulated in the following way... 

When the 2-hydroxy group of a monosaccharide reacts with (diethylamino)sulfur trifluoride (DAST), quantitative and stereoselective rearrangements are observed (K.C Nico-laou, 1986). This reaction may simultaneously introduce fluorine to C-1 and a new oxygen, sulfur, or nitrogen residue to C-2 with inversion of configuration. 

From these results it appears that the 5-position of thiazole is two to three more reactive than the 4-position, that methylation in the 2-position enhances the rate of nitration by a factor of 15 in the 5-position and of 8 in the 4-position, that this last factor is 10 and 14 for 2-Et and 2-t-Bu groups, respectively. Asato (374) and Dou (375) arrived at the same figure for the orientation of the nitration of 2-methyl and 2-propylthiazole Asato used nitronium fluoroborate and the dinitrogen tetroxide-boron trifluoride complex at room temperature, and Dou used sulfonitric acid at 70°C (Table T54). About the same proportion of 4-and 5-isomers was obtained in the nitration of 2-methoxythiazole by Friedmann (376). Recently, Katritzky et al. (377) presented the first kinetic studies of electrophilic substitution in thiazoles the nitration of thiazoles and thiazolones (Table 1-55). The reaction was followed spec-trophotometrically and performed at different acidities by varying the... 

Ammonia. Ammonia (qv) reacts with excess fluorine ia the vapor phase to produce N2, NF, N2F2, HF, and NH F. This reaction is difficult to control ia the vapor phase because of the iatense heat of reaction, and ia some cases only N2 and HF are produced. Nitrogen trifluoride was obtained ia 6% yields ia a gas-phase reaction over copper (42). Yields of ca 60% are achieved by the reaction of fluorine and ammonia ia a molten ammonium acid fluoride solution (43,44). 

Aluminum trifluoride trihydrate [15098-87-0], AIF. -3H20, appears to exist in a soluble metastable a-form as well as a less soluble P-form (3). The a-form can be obtained only when the heat of the reaction between alumina and hydrofluoric acid is controlled and the temperature of the reaction is kept below 25°C. Upon warming the a-form changes into a irreversible P-form which is insoluble in water and is much more stable. The P-form is commercially available. 

High Purity Aluminum Trifluoride. High purity anhydrous aluminum triduoride that is free from oxide impurities can be prepared by reaction of gaseous anhydrous HF and AlCl at 100°C, gradually raising the temperature to 400°C. It can also be prepared by the action of elemental fluorine on metal/metal oxide and subsequent sublimation (12) or the decomposition of ammonium duoroaluminate at 700°C. 

Arsenic pentafluoride can be prepared by reaction of fluorine and arsenic trifluoride or arsenic from the reaction of NF O and As (16) from the reaction of Ca(FS02)2 and H AsO (17) or by reaction of alkaH metal or alkaline-earth metal fluorides or fluorosulfonates with H AsO or H2ASO2F (18). 

Boron trifluoride [7637-07-2] (trifluoroborane), BF, was first reported in 1809 by Gay-Lussac and Thenard (1) who prepared it by the reaction of boric acid and fluorspar at duU red heat. It is a colorless gas when dry, but fumes in the presence of moisture yielding a dense white smoke of irritating, pungent odor. It is widely used as an acid catalyst (2) for many types of organic reactions, especially for the production of polymer and petroleum (qv) products. The gas was first produced commercially in 1936 by the Harshaw Chemical Co. (see also Boron COMPOUNDS). 

Chemical Properties. In addition to the reactions Hsted in Table 3, boron trifluoride reacts with alkali or alkaline-earth metal oxides, as well as other inorganic alkaline materials, at 450°C to yield the trimer trifluoroboroxine [13703-95-2] (BOF), MBF, and MF (29) where M is a univalent metal ion. The trimer is stable below — 135°C but disproportionates to B2O2 and BF at higher temperatures (30). 

Manufacture. Boron trifluoride is prepared by the reaction of a boron-containing material and a fluorine-containing substance in the presence of an acid. The traditional method used borax, fluorspar, and sulfuric acid. 

Numerous other reactions are available for the preparation of small quantities of boron trifluoride, some of which are of high purity (55). 

Boron trifluoride catalyst may be recovered by distillation, chemical reactions, or a combination of these methods. Ammonia or amines are frequently added to the spent catalyst to form stable coordination compounds that can be separated from the reaction products. Subsequent treatment with sulfuric acid releases boron trifluoride. An organic compound may be added that forms an adduct more stable than that formed by the desired product and boron trifluoride. In another procedure, a fluoride is added to the reaction products to precipitate the boron trifluoride which is then released by heating. Selective solvents may also be employed in recovery procedures (see Catalysts,regeneration). 

Boron trifluoride is used for the preparation of boranes (see Boron compounds). Diborane is obtained from reaction with alkafl metal hydrides organoboranes are obtained with a suitable Grignard reagent. 

Cobalt trifluoride is readily prepared by reaction of fluorine (qv) and C0CI2 at 250°C or C0F2 at 150—180°C. Direct fluorination of C0F2 leads to quantitative yields of 99.9% pure CoF (4). 

The halogen fluorides are binary compounds of bromine, chlorine, and iodine with fluorine. Of the eight known compounds, only bromine trifluoride, chlorine trifluoride, and iodine pentafluoride have been of commercial importance. Properties and appHcations have been reviewed (1 7) as have the reactions with organic compounds (8). Reviews covering the methods of preparation, properties, and analytical chemistry of the halogen fluorides are also available (9). 

The halogen fluorides are best prepared by the reaction of fluorine with the corresponding halogen. These compounds are powerful oxidising agents chlorine trifluoride approaches the reactivity of fluorine. In descending order of reactivity the halogen fluorides are chlorine pentafluoride [13637-63-3] 1 5 chlorine trifluoride [7790-91-2] 3 bromine pentafluoride [7789-30-2], BrF iodine heptafluoride [16921 -96-3], chlorine... 

Liquid Halogen Fluorides as Reaction Media. Bromine trifluoride and iodine pentafluoride are highly dimerized and behave as ionizing... 

The use of CIF and BrF as ionizing solvents has been studied (102,103). At 100°C and elevated pressures, significant yields of KCIF [19195-69-8] CsClF [15321-04-7], RbClF [15321-10-5], I-CBrF [32312-224], RbBrF [32312-224], and CsBrF [26222-924]obtained. Chlorine trifluoride showed no reaction with lithium fluoride or sodium fluoride. 

Bromine Trifluoride. Bromine trifluoride is produced commercially by the reaction of fluorine with bromine ia a continuous gas-phase process where the ratio of fluorine to bromine is maintained close to 3 1. It is also produced ia a Hquid-phase batch reaction where fluorine is added to Hquid bromine at a temperature below the boiling poiat of bromine trifluoride. 

Chlorine Trifluoride. Chlorine trifluoride is produced commercially by the continuous gas-phase reaction of fluorine and chlorine ia a nickel reactor at ca 290°C. The ratio of fluorine to chlorine is maintained slightly in excess of 3 1 to promote conversion of the chlorine monofluoride to chlorine trifluoride. Sufficient time ia the reactor must be provided to maintain high conversions to chlorine trifluoride. Temperature control is also critical because the equiHbrium shift of chlorine trifluoride to chlorine monofluoride and fluorine is significant at elevated temperatures. 

K [14881-07-3], Rb [72151 -96-3], and Cs [72138-72-8]), are prepared by reaction of elemental fluorine, chlorine trifluoride, or xenon difluoride and a mixture of nickel fluoride and alkaH metal fluorides or other metal haHdes (16,17). If the fluorination is carried out using mixed fluorides, a lower temperature can be used, yields are quantitative, and the final products are of high purity. Bis(tetrafluoroammonium) hexafluoronickelate [6310540-8], (NE 2N iF6> prepared from Cs2NiF3 and NE SbE by a metathesis in anhydrous HE, is also known (18). 

The existence of diamagnetic salts of AgF was first reported in 1957 (26), butHttle was known about their properties. In 1988 (27) it was claimed that AgF3 was prepared by a reaction of Ag metal and O2F2 iu CIF. Silver trifluoride [91899-63-7], AgF, has since been prepared (28) from anhydrous HF solutions of AgF 4 salts by addition of BF, PF, or AsF. ... 

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