1131322-83-2Relevant academic research and scientific papers
Cationic boranes for the complexation of fluoride ions in water below the 4 ppm maximum contaminant level
Kim, Youngmin,Gabbai, Francois P.
experimental part, p. 3363 - 3369 (2009/07/30)
In search of a molecular receptor that could bind fluoride ions in waterbelow the maximum contaminant level of 4 ppm set by the Environmental P rotection Agency (EPA), we have investigated the water stability and fluoride binding properties of a series of phosphonium boranes of general formula [p-(Mes 2 B)C 2 H 2 (PPh 2 R)] + with R ) Me ([1] + ), Et ([2] + ), n-Pr ([3] + ), and Ph ([4] + ). These phosphonium boranes are water stable and react reversibly with water to form the corresponding zwitterionic hydroxide complexes of general formula p-(Mes 2 (HO)B)C 6 H 4 (PPh 2 R). They also react with fluoride ions to form the corresponding zwitterionic fluoride complexes of general formula p-(Mes 2 (F)B) 6 H 4 (PPh 2 R). Spectrophotometric acid-base titrations carried out in H 2 O/MeOH (9:1 vol.) afford pK R+ values of 7.3(±0.07) for [1] + , 6.92(±0.1) for [2] + , 6.59(±0.08) for [3] + , and 6.08(±0.09)for [4] + , thereby indicating that the Lewis acidity of the cationic boranes increases in following order: [1] + + -1 for [1] + , 2500(±200) M -1 for [2] + , 4000(±300) M -1 for [3] + , and 10 500(±1000) M -1 for [4] + ) increase in the same order. These results show that the Lewis acidity of the cationic boranes increases with their hydrophobicity. The resulting Lewis acidity increase is substantial and exceeds 1 order of magnitude on going from [1] + to [4] + . In turn, [4] + is sufficiently fluorophilic to bind fluoride ions below the EPA contaminantlevel in pure water. These results indicate that phosphonium boranes re lated to [4] + could be used as molecular recognition units in chemosensors for drinking water analysis.
