Magnesium tetraphenylborate

Enantioselective Diels-Alder catalyst. The chiral bis(oxazoline) 1, prepared from (S)-phenylglycine, in combination with Mgl2 or magnesium tetraphenylborate (2) serves as a highly enantioselective catalyst for the Diels-Alder reaction of cyclopentadiene with 3-acryloyloxazolidine-2-one (equation I). 

Polarography has also been applied to the determination of potassium in seawater [535]. The sample (1 ml) is heated to 70 °C and treated with 0.1 M sodium tetraphenylborate (1 ml). The precipitated potassium tetraphenylborate is filtered off, washed with 1% acetic acid, and dissolved in 5 ml acetone. This solution is treated with 3 ml 0.1 M thallium nitrate and 1.25 ml 2M sodium hydroxide, and the precipitate of thallium tetraphenylborate is filtered off. The filtrate is made up to 25 ml, and after de-aeration with nitrogen, unconsumed thallium is determined polarographically. There is no interference from 60 mg sodium, 0.2 mg calcium or magnesium, 20 pg barium, or 2.5 pg strontium. Standard eviations at concentrations of 375, 750, and 1125 pg potassium per ml were 26.4, 26.9, and 30.5, respectively. Results agreed with those obtained by flame photometry. 

The solubility of the precipitate is lowest between pH 4 and 6. Its solubility product is around 2.3-10 (at 20 °C). If a minor excess of the precipitating agent (Le., sodium tetraphenylborate) is available in solution, the solubility of the precipitate is negligible. Co-precipitation of calcium and magnesium ions may lead to serious errors when they are first precipitated. This interference is minimized, however, as carbonates which, in contrast to potassium tetraphenylborate, are soluble in acetic acid. Potassium tetraphenylborate is crystalline and starts to decompose when heated above 100 °C. Other cations which form stable precipitates with tetraphenylborate under the conditions applied are rubidium, cesium, ammonium, mercury, thallium(/) and silver (see Section 11.2.3.6). In natural seawaters, however, the concentrations of these constituents are so low as to be negligible. 

Cs ijHs BC0 2NaNa06, Bis- (N,N -ethylene-bis (salicylideneiminato)cobalt-(II))-bis-tetrahydrofuran-sodium(l) tetraphenylborate, 40B, 671 CesHy2Cl2MgN12O1af Magnesium hexa-antipyrine perchlorate, 32B, 324 CeeHesBrN1oNaO11, Sodium (phe(4)-val(6))antamanide bromide ethanol solvate, 40B, 671... 

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