Tetraphenylphosphonium bromide

Polymer-supported tetraphenylphosphonium bromide is a recyclable catalyst for halogen-exchange reactions. The reaction of 1 equivalent of chloro-2,4-dinitrobenzene with 1 5 equivalents of spray-dned potassium fluoride and 0.1 equivalent of this catalyst in acetonitnle at 80 C for 12 h gives 2,4-dinitro-fluorobenzene m 98% yield An 11% yield is obtained without the catalyst [3 /]. 

Tetrasubstituted phosphonium halides are just as effective as their ammonium counterparts. A combination of tetraphenylphosphonium bromide and either 18-crown-6 or polyethylene glycol dimethyl ether with spray-dried potassium fluoride converts 4-chlorobenzaldehyde to 4-fluorobenzaldehyde in 74% yield [67] In addition, the halogen of a primary alkyl chloride or bromide is easily displaced by fluorine in aqueous saturated potassium fluoride and a catalytic amount of hexadecyltributylphosphonium bromide [68] (Table 7 Procedure 4, p 194)... 

The use of phthaloyl dichlonde as a scavenger for potassium nitrite and/or potassium oxide [108, 109, III] significantly increases yields of aryl fluorides, m fluoronitrobenzene is obtained in 70% yield with sulfolane as a solvent at 200 °C after 72 h Addition of tetraphenylphosphonium bromide as a phase-transfer catalyst to the phthaloyl dichlonde scavenger system further increases the yield of m-fluoronitrobenzene to 89% under less forcing conditions 150-180 C, 5 h) [if 2] This optimized technique can be applied to give m-fluorobenzonitnle from in-m-trobenzonitnle in 86% yield [/i2]... 

Finally, quatemization of aromatic phosphines (example 21, Table XI) is exemplified for tetraphenylphosphonium bromide. 

A catalytic amount of tetraphenylphosphonium bromide is required for the preparation of 3,4-difluorobenzoyl fluoride (11) from 3,4-dichlorobenzoyl chloride (9) with potassium fluoride.32 While 11 is formed only in 23% yield, the partially fluorine substituted intermediate 10 can be treated again with potassi um fluoride and tetraphenylphosphonium bromide at 230 °C for 10 h. In this way besides the chlorine atom of the acid chloride in 9 both the aromatic chlorine atoms are also displaced.32... 

Much better yields have been obtained by using phthaloyl chloride to trap the eliminated nitrite ion and tetraphenylphosphonium bromide as a catalyst in the fluoride substitution reactions.140 The less easily accessible 3-fluorobenzonitrile derivatives have been prepared this way. Table 6 illustrates some of the nitro derivatives which have been transformed into fluoro analogs in good yield.140... 

A warm (60°C) solution of sodium perrhenate (1.5 g, 5.5 mmol) in demineralized water (60 mL) in a 250-mL conical flask is added to a warm (60°C) solution of tetraphenylphosphonium bromide (2.8 g, 6.7 mmol) in demineralized water (60 mL) contained in a 250-mL conical flask. The mixture is then stirred for 30 min at room temperature. The white precipitate which forms is collected by filtration on a No. 3 sintered-glass filter tube, washed with distilled water (4 x 20 mL) and absolute ethanol (4 x 30 mL), and then dried in vacuo for 5 h at 56°C (boiling acetone) (yield 2.80 g, 87%). 

Similarly, a detailed study of the reaction of tetraphenylphosphonium bromide with vinyl- and isopropenyllithium gave evidence of the intermediacy of tetraphenyl-vinylphosphorane derivatives 24a 38). 

Tetraphenylphosphonium bromide is obtained in 45% yields from the reaction between 100 g. pulverized aluminum trichloride, 105 g. powdered triphenylphosphine, 60 g. pure bromobenzene, and 70 g. potassium bromide using the method outlined by Chatt and Mann.9... 

Methyllithium shows greatly enhanced reactivity in THF over ether. Thus methyllithium and tetraphenylphosphonium bromide react very slowly in ether (4 months, Nj) to give a mixture of several phosphorus-containing compounds," but when the reaction is carried out in THF-ether (4 1) the following reaction can be realized "... 

There are various methods for the synthesis of cyclopropyltriphenylphosphonium bromides, the precursor of choice for the preparation of cyclopropylidenetriphenylphosphoranes. Interestingly, attempts to generate the former salt from cyclopropane derivatives, e.g. 1-bromocy-clopropane, have been unrewarding. One exception is the reaction of cyclopropyllithium with tetraphenylphosphonium bromide followed by elimination of benzene from the initial adduct. The intermediate phosphorane 5 was converted into phosphonium salt 13 by reaction with hydrogen bromide. 

A comparison of the kinetic data for alkaline hydrolysis and alkoxide-promoted decomposition of the salts (135), their n-propyl analogues, and tetraphenylphosphonium bromide indicates that hexacovalent intermediates, e.g. (136), are involved... 

Vinyllithium reacts with tetraphenylphosphonium bromide in ether solution to give styrene and triphenylphosphine 4... 

A series of papers describes the synthesis (and some reactions) of highly sterically hindered phosphinic acids based on the dibenzophosphole system, e.g., (36) and (37). These papers describe an improved synthesis of 5-phenyldibenzo-phosphole from tetraphenylphosphonium bromide, as well as that of 5-hydroxy-... 

Clark, J.H. Macquarrie, D.J. The s3mthesis of organofluorine compounds using potassium fluoride-tetraphenylphosphonium bromide systems. Tetrahedron Lett. 1987, 25(1), 111-114. 

Quaternary onium salts. Quaternary ammonium salts include trioctymethylammo-nium chloride (Starks catalyst), Aliquat 336, tricaprylmethylammonium chloride, tetrabutylammo-nium hydrogen sulfate (Brandstrom s catalyst), and benzyltrimethylam-monium chloride (Mqkosza s catalyst) quaternary ammonium salts can also be generated in situ from trialkylamines, etc. Other quaternary onium salts include tetrabutylphospho-nium bromide, tetraphenylphosphonium bromide, triphenylbenzylphosphonium chloride, tetraphenylarsonium chloride, and triphenylsulfonium chloride, etc. Special quaternary salts are 4-aminopyridinium salts, bis-(quaternary ammonium) [R3N -(CH2) -NR3" R3N -(CH2) -0-(CH2) -NRj ] salts, 4,4 -dialkylbipyridinium salts, cluster quaternary ammonium [e.g., P(C6H4S03"NR4)3] salts, crown-quaternary salts [e.g. (18-crown-6)-(CH2)9PBuj Br ], and chiral V-(4-trifluoromethyl)benzylcinchonium bromide, etc. 

Tetraphenylphosphonium bromide s. under KF Antimony pentachloride s. under BrF ... 

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