Fluoroboric acid, sodium salt preparation

Fluoroboric acid, sodium salt, preparation of, 54, 30 Fluoroboric acid-acetic anhydride, 54, 99... 

Carboxylic acids can be prepared in moderate-to-high yields by treatment of diazonium fluoroborates with carbon monoxide and palladium acetate or copper(II) chloride. The mixed anhydride ArCOOCOMe is an intermediate that can be isolated. Other mixed anhydrides can be prepared by the use of other salts instead of sodium acetate." An arylpalladium compound is probably an intermediate." ... 

B. Preparation of Cyclopropyldiphenylsulfonium Fluoroborate. A suspension of 118.7 g. (0.339 mole) of 3-chloropropyldiphenylsulfonium fluoroborate (Note 2) in 500 ml. of dry tetrahydrofuran (Note 12) is placed in a 2-1., one-necked flask equipped with a magnetic stirring bar and nitrogen inlet tube under nitrogen. Then 5-g. portions of 55% sodium hydride-mineral oil dispersion (15.2 g., 0.350 mole) are added in 30-minute intervals. The resulting mixture is stirred (Note 13) at room temperature for 24 hours. An aqueous solution of 25 ml. of 48% fluoroboric acid (Note 14), 15 g. of sodium fluoroborate (Notes 7, 15), and 400 ml. of water is added to the well-stirred reaction to destroy residual hydride and swamp out chloride ion (Note 16). After 5 minutes 300 ml. of methylene chloride is added, and the top methylene chloride layer is removed from the lower aqueous layer (Note 17). The methylene chloride solution is then extracted with 100 ml. of water. This water layer is combined with the first aqueous layer, and the combined water layers are extracted with an additional 100 ml. of methylene chloride. The methylene chloride portions are combined, dried over anhydrous sodium sulfate, and evaporated at reduced pressure until precipitation occurs. Addition of 1 1. of ether completes the precipitation of the salt. 

In general the required diazonium fluoroborate is obtained as a precipitate when a concentrated solution of sodium fluoroborate is added to a solution of a diazonium salt. In an alternative procedure (e.g. the preparation of p-fluoroanisole, cognate preparation in Expt 6.77), the amine is diazotised in solution in aqueous fluoroboric acid. The diazonium fluoroborates are less sensitive to shock and heat than most diazonium salts and may be prepared and handled in the dry state with relative safety. Most diazonium fluoroborates have definite decomposition temperatures and the rates of decomposition, with few exceptions, are easily controlled. Diazonium fluoroborates containing the nitro group, however, usually decompose suddenly and with violence on heating in such cases the fluoroborate should be mixed with 3-4 times its weight of dry sand and heated cautiously until decomposition commences. 

The diazonium salt (70) is prepared from the amine with sodium nitrite in fluoroboric acid. Photolysis of the resulting solution gives the 3-fluoro derivative (71) (77JMC386). 

The diazotization of aminopyrazines has been described in earlier sections. Section V.IH records the preparation of 2-fluoropyrazine from 2-aminopyrazine in fluoroboric acid containing copper powder with sodium nitrite (882, 884) and Section V.ll the preparation of iodopyrazines from some aminopyrazines via isodiazotate salts (30) (887). These salts were assigned the isodiazotate structure, on the basis of their inability to couple with 0-naphthol in alkaline solution (887) and they were characterized by hydrolysis in cold 40% aqueous sulfuric acid to the hydroxypyrazine (887). Section V.I K describes the conversion of aminopyrazines to bromopyrazines (798, 800, 807, 890-892) for example, 2-amino-3-methoxy-carbonylpyrazine with hydrobromic acid, bromine, and sodium nitrite in water gave 2-bromo-3-methoxycarbonylpyrazine (798, 890). The diazotization of aminopyrazines to hydroxypyrazines has been described in Section VI. 1C, to alkoxy-pyrazines in Section V1.3C, and to oxopyrazines in Section V1.9A(5). 2-Amino-pyrazine with isopentyl nitrite in benzene gave 2-phenylpyrazine (45%) and some 2-isopentoxypyrazine and 2,2 -dipyrazinyl amino isomers (1211). 

Reduction of the 1,3-dithiolium cation with hexacarbonylvanadate anion yields the colourless dimer (46), which can be oxidized to tetrathiafulvalene with manganese dioxide. Reduction of 2-methylthio-l,3-dithiolium salts with sodium borohydride and treatment of the resulting 2-methylthio-l,3-dithiole with fluoroboric acid provides a convenient small-scale preparation of 1,3-dithiolium fluoroborate. The method has been extended to the preparation of l-selena-3-thiolium and 1,3-diselenolium fluoroborates. For large-scale preparation of the 1,3-dithiolium cation, the route involving peroxy-acid oxidation of l,3-dithiole-2-thione and isolation of the hexafluorophosphate is recommended. This method fails with selenium-containing compounds. ... 

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. 

Cognate preparations, p-Fluorotoluene. Diazotise 53.5 g (0.5 mol) of p-toluidine in a mixture of 126 ml of concentrated hydrochloric acid and 126 ml of water contained in a 1-litre beaker following the procedure given in Expt 6.71. Add a chilled solution of 76 g (0.69 mol) of sodium fluoroborate in 150 ml of water slowly and with good stirring to the cold diazonium salt... 

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