Anilines fluoroborate

Treatment of aniline 1 with nitric acid in the presence of tetrafluoroboric acid leads to a relatively stable benzenediazonium tetrafluoroborate 2 by the usual diazotization mechanism. There are several variants for the experimental procedure. Subsequent thermal decomposition generates an aryl cation species 4, which reacts with fluoroborate anion to yield fluorobenzene 3 " ... 

In the context of this section it is important that Ruchardt and Tan (1970 a) found that (solid) benzenediazonium fluoroborate gave benzyne adducts with potassium acetate in the presence of aryne trapping agents such as tetracyclone or anthracene. This is, however, not the case if water is present (Cadogan, 1971). As a consequence of these observations, Cadogan et al. (1971) simplified the formation of arynes from diazonium ions by converting aniline or its substitution products into arynes in a... 

Photolysis (2537 A) in methyl cyanide solution of the compound 243, R = Me, = Ph, gives iV-methylthiobenzamide. This reaction has been interpreted in terms of the homolysis of the valence tautomer 244, which has been detected spectroscopically ( % 2260 cm N=C=0). The l,3,4-thiadiazol-2-ones have dipole moments (243, R = R = Ph,/U = 7.75 D 243, R = Me, R = Ph, /U = 7.7 D) consistent with their meso-ionic formulation. They react with triethyloxonium tetra-fluoroborate, yielding the salts 245. The compound 243, R = Me, R = Ph, and aniline gives the semicarbazide 246. ... 

Finally, it has also been reported that the reaction of anilines with ethylimino-(ethylthio) acetate fluoroborate and treatment of the resulting product with formaldehyde is an interesting and general procedure for the synthesis of 4-(alkylamino)-5(2//)-oxazolones. 

SYNTHESIS A solution of 76.6 g 2,5-dimethoxyaniline in 210 mL H20 containing 205 mL fluoroboric acid was cooled to 0 °C. with an external ice bath. There was then added, slowly, a solution of 35 g sodium nitrite in 70 mL H20. After an additional 0.5 h stirring, the precipitated solids were removed by filtration, washed first w ith cold H20, then with MeOH and finally Et20. Air drying yielded about 100 g of the fluoroborate salt of the aniline as dark purple-brown solids. This salt was pyrolyzed with the cautious application of a flame, with the needed attention paid to both an explosion risk, and the evolution of the very corrosive boron trifluoride. The liquid that accumulated in the receiver was distilled at about 120 °C at 20 mm/ Hg, and was subsequently washed with dilute NaOH to remove dissolved boron trifluoride. The product, 2,5-dimethoxyfluorobenzene, was a fluid, straw-colored oil that weighed 7.0 g. 

Fluoroboric acid supported on silica (HBF4-silica) has recently been found to be a highly efficient catalyst in the protection of various functional groups. Structurally diverse alcohols, phenols, thiophenols, and anilines can be acylated under solvent-free conditions at room temperature.669 Even acid-sensitive tertiary alcohols (1-alkylcyclo-hexanols) and sterically hindered compounds, such as endo-borneol, give the acylated products in high yields. A triflic acid-silica catalyst also shows high activity in the (9-acetylation with Ac20 of alcohols and phenols.359... 

Dissolve 46.5 g (45.5 ml, 0.5 ml) of aniline in a mixture of 126 ml of concentrated hydrochloric acid and 126 ml of water contained in a 1-litre beaker. Cool to 0-5 °C in a bath of ice and salt, and add a solution of 36.5 g (0.53 mol) of sodium nitrite in 75 ml of water in small portions stir vigorously with a thermometer and maintain the temperature below 10 °C, but preferably at about 5 °C by the addition of a little crushed ice if necessary. The diazotisation is complete when a drop of the solution diluted with 3-4 drops of water gives an immediate blue coloration with potassium iodide-starch paper the test should be performed 3-4 minutes after the last addition of the nitrite solution. Prepare a solution of 76 g (0.69 mol) of sodium fluoroborate (1) in 150 ml of water, cool and add the chilled solution slowly to the diazonium salt solution the latter must be kept well stirred and the temperature controlled so that it is below 10 °C. Allow to stand for 10 minutes with frequent stirring. Filter the precipitated benzenediazonium fluoroborate with suction on a Buchner funnel, drain well and wash the yellow solid with about 30 ml of ice-water, 15 ml of methanol and 30-40 ml of ether suck the solid as free as possible from liquid after each washing (2). Spread the salt upon absorbent filter paper and allow to dry overnight, if possible in a current of air. The yield of benzenediazonium fluoroborate is 60—65 g the pure salt melts with decomposition at 119-120 °C. 

Fluoruarenes from Anilines via the One-Pot, Thermal Balz-Schiemann Reaction Using Nitrosonium Tetra-fluoroborate General Procedure ... 

These same workers accomplished the synthesis of the radioactive XX as follows. Sodium nitrite (38.2 mg, 0.553 mmole) in 0.17 ml of water was added dropwise to a solution of 34.4 mg of ( H)-m-nitro-aniline and 30.9 mg of carrier m-nitroaniline in 0.5 ml of 50 % fluoroboric acid and 0.25 ml of water. The reaction mixture was stirred magnetically during the addition and for an additional 1 hr. After the product precipitated as a cream solid, it was filtered and washed successively with ice cold 25 % fluoroboric acid, anhydrous ethanol and anhydrous ether. The product could be recrystallized as white needles from acetone-ether if the temperature did not exceed 50°C. The yield was 39.3 mg specific activity was 7.72 x 10 dpm//imole. The product can be stored at — 20°C in 0.01 M hydrochloric acid at a concentration of 2x10 M. 

Halogen exchange with a fluoride anion is one of the two main techniques to introduce a fluorine atom on an aromatic nucleus, which is a useful complement of diazotization of anilines in hydrogen fluoride or thermal decomposition of arenediazonium fluoroborates (Schiemann reaction). It is used on an industrial scale to produce, for example, 2,6-difluorobenzonitrile (the precursor of the insecticide Diflubenzuron) or 2,4-difluoroaniline (the precursor of Diflufenican or other herbicides). 

Completely different monomers were called for. Before long, three of today s workhorses had been identified pyrrole, aniline and thiophene. In Japan, Yamamoto [38] and in Germany, Kossmehl [39] synthesized polythiophene doped with pentafluoroarsenate. At the same time, the possibilities of electrochemical polymerization were recognized. At the IBM Lab in San Jose, Diaz used oxidative electrochemical polymerization to prepare polypyrrole [40] and polyaniline. [41] Electrochemical synthesis forms the polymer in its doped state, with the counter-ion (usually an anion) incorporated from the electrolyte. This mechanism permits the selection of a wider range of anions, including those which are not amenable to vapor-phase processes, such as perchlorate and tetra-fluoroborate. Electrochemical doping also overcomes an issue associated with dopants... 

Treatment of 156 with silver acetate and aniline resulted in isolation of the sulfenamide derivative (189) in 90% yield (Kamiya et al., 1975). Reaction of 189 with silver fluoroborate yielded the 3-anilinocepham... 

The novel concept of elaboration of unactivated olefins by nucleophiles has been reported. Nucleophilic attack is initiated by reaction of the olefin with dimethyl(tnethylthio)sulphonium fluoroborate (4) and, in conjunction with nitrogen nucleophiles, a high degree of regiocontrol is observed in an azasul-phenylation reaction (Scheme 7), the products of which not only permit an overall olefin amination, but also an oxazoline synthesis, a m-hydroxyamination, and an aziridine synthesis. The analogous selenium reagent, dimethyl(phenyl-seleno)sulphonium fluoroborate, p-phenylselenates a variety of anilines in moderate yield. ... 

Arylazo tosylates that are obtained fi om aniline derivatives via diazonium fluoroborates in a two-step procedure can be used as alternative starting materials. They react with a broad range of functionalized Grignard reagents under mild conditions. Subsequent allylation of the addition products with allyl iodide, followed by the reductive cleavage of the intermediate hydrazine derivatives, ftimishes polyfunctionalized... 

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