Phosphonium salts fluoroborates

A publication discussing the uses of reactive arsonium ylides for the stereospecific preparation of epoxides draws attention to the fact that arsonium salts are less readily prepared than phosphonium salts because of the poorer nucleophilicity of arsenic compared to phosphorus, and suggests methods for obtaining them. Primary salts were made from alkyl triflates, while a-branched salts were prepared from alkyldiphenylarsines, obtained from iodo compounds as, for example, in equation 23. Reaction of alkyl halides with arsines to form arsonium salts is also promoted by the presence of silver tetra-fluoroborate . 

An intramolecular Wittig reaction of the phosphonium salt PhsP—CH2-CH2CH20C0Ph Br yields the dihydrofuran (15). Compound (16) is formed from styrene and acetone in the presence of lead dioxide by a free-radical mechanism. The A -dihydrofuran (17) is produced by the action of silver fluoroborate on the allenic alcohol HOCH2CH=C=CMeBu another compound of this type, namely (18), is the product of the reaction of the sulphurane H2C=SMe2 with salicylideneacetone. ... 

Tri-p-tolylphosphine refluxed several hrs. with 10%-excess monodiloromethyl ether in benzene, and the resulting dhloride treated with Na-fluoroborate soln. in water (methoxymethyl)tris-(p-tolyl)phosphonium fluoroborate (Y 91%) added to nitryl fluoroborate and sulfolane, heated 6 hrs. at 110, pyridine hydrochloride added, and stirred 2 hrs. at 115° tris-(3-nitro-4-methylphenyl)phosphine (Y 51%). - Phosphonium salt formation protects the phosphorus from oxidation. F. e. s. G. P. Schiemenz and K. Rohlk, B. 104, 1219 (1971). 

The only data that permit such an analysis on organic salts are viscosity coefficients for tetrapropylammonium, phosphonium, and arsonium tetra-fluoroborates. The hardsphere theory would suggest that the arsonium salt has the greatest viscosity because of its large size and mass. At 1 atm the measured arsonium viscosity is lowest however, if the salts are compared at the same volume and temperature, the predicted order is observed as shown in Fig. 4. 

---