Benzenediazonium fluoborate

The diazonium salt that should be used in this experiment is benzenediazonium fluoborate (C6H5N2BF4, M = 191.9). The great majority of diazonium salts are notoriously unstable solids and ean deeompose with explosive violence. The fluoborates are by far the safest to use and are not known to explode however, reasonable caution should be used in preparing the compound. Since even benzenediazonium fluoborate will decompose slowly, it should not be prepared too far in advance, and it must be stored in a refrigerator. A simple high-yield procedure for its preparation has been given by Dunker, Starkey, and Jenkins. Recrystallization of the product from 5 percent fluoboric acid yields white needlelike crystals, which can be dried by vacuum pumping at 1 Torr for several hours, t... 

Benzenediazonium fluoborate (75 mg), stored in a refrigerator 0.2 M hydrochloric acid (400 tnU) crushed ice. 

Also obtained (poor yield) by diazotization of 2-aminobenzophenone, followed by hydrolysis of the diazonium salt formed [7,56], (6%) [57] or by thermal decomposition of 2-benzoyl-benzenediazonium fluoborate in dilute sulfuric acid between 25° and 50° (37%) [17] n these conditions, the fluorenone was the major compound formed [7],... 

Preparationbydiazotizationof2-amino-3 -nitrobenzo-phenone followed by thermal decomposition of the 2-(3 -nitrobenzoyl)benzenediazonium fluoborate formed with 0.05 M sulfuric acid at 45° or 65° (67%) [17]. 

S) Attack on a polarized double bond in the Markovnikov sense is taken as evidence for a heterolytic reaction. If an addition follows the direction normally taken in the Meerwein-Koelsch reaction, a nonpolar reaction is indicated. Thus, for example, when benzenediazonium fluoborate is decomposed in ethyl crotonate, the product, after hydrolysis, is methylatropic acid. 

Both diazonium salts and iodonium salts can be effectively used as arylating agents. The aryl group is transferred either heterolyt-ically or homolytically, depending on the choice of salt and reaction conditions. In acid solution diazonium salts decompose relatively cleanly to give products consistent with a polar mechanism. In basic solution the product is a complex mixture resulting from free radical intermediates (6). When either benzenediazonium chloride or fluoborate is decomposed in acidic methanol, the major product, formed in 93% yield, is anisole, and less than 1% biphenyl is isolated. In the same solvent with an acetate buffer, the product contains 85-90% benzene, 4.5% biphenyl, 0.6% azobenzene, some anisole, and 80-90 mole % formaldehyde per mole of diazonium salt decomposed (7). 

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