General Description

Sodium tetraphenylborate (Ph4BNa) undergoes rhodium-catalyzed addition reactions with N-phenylsulfonyl aldimines to afford R(Ph)CHNHSO2Ph.

Purification Methods

Dissolve the borate in dry MeOH and add dry Et2O. Collect the solid and dry it in a vacuum at 80o/2mm for 4hours. It can also be extracted (Soxhlet) using CHCl3, and it crystallises from CHCl3 as snow-white needles. It is freely soluble in H2O, Me2CO but insoluble in pet ether and Et2O. An aqueous solution has pH  5 and can be stored for days at 25 or lower, and for 5 days at 45o without deterioration. Its solubility in polar solvents increases with decrease in temperature [Wittig & Raff Justus Liebigs Ann Chem 573 204 1950]. The salt can also be recrystallised from acetone/hexane or CHCl3, or from Et2O/cyclohexane (3:2) by warming the solution to precipitate the compound. Dry it in a vacuum at 80o. It dissolves in Me2CO at 50-60o to give a clear solution. After standing at this temperature for 10minutes the mixture is filtered rapidly through a pre-heated Büchner funnel, cooled and the crystals are collected and dried in a vacuum desiccator at room temperature for 3days [Abraham et al. J Chem Soc, Faraday Trans 1 80 489 1984]. If the product gives a turbid aqueous solution, the turbidity can be removed by treating with freshly prepared alumina gel and filtering. [Beilstein 16 IV 1624.]