Ligands for Aqueous-Organic Biphasic Catalysis

The solubility of these phosphine ligands in water can be extraordinarily high. The sodium salt of the fnT-sulfonated triphenylphosphine (tppts) has a solubility in water of 1.1 kg 1 [20], Apart from high solubility, these sulfonated phosphines are widely used for several reasons including  

2 Very poor solubility in nonpolar organic solvents. 

3 They are usually stable under catalytic conditions. 

4 Many can be prepared qnite easily from cnrrently available phosphines by derivatization of a phenyl ring with the snlfonate gronp. 

A wide range of polar, hydrophilic functional groups may be used to induce solubility in water, and these include sulfonates, alcohols, nitriles, amines. 

With this last point in mind, the synthesis of mono-, bis- and tra-sulfonated triphenylphosphine will be described, but the same methodology can be applied to the preparation of other sulfonated arylphosphines. In general, these phosphines are made by direct sulfonation using fuming sulfuric acid (oleum) [21], The extent of sulfonation is determined by the SO3 strength, as well as factors such as the temperature and time of the reaction. The monosulfonated phosphine (tppms) is prepared using oleum of 20% SO3 strength, with typically 30% SO3 used 

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