Potassium tetraphenylborate

Discussion. Potassium may be precipitated with excess of sodium tetraphenyl-borate solution as potassium tetraphenylborate. The excess of reagent is determined by titration with mercury(II) nitrate solution. The indicator consists of a mixture of iron(III) nitrate and dilute sodium thiocyanate solution. The end-point is revealed by the decolorisation of the iron(III)-thiocyanate complex due to the formation of the colourless mercury(II) thiocyanate. The reaction between mercury( II) nitrate and sodium tetraphenylborate under the experimental conditions used is not quite stoichiometric hence it is necessary to determine the volume in mL of Hg(N03)2 solution equivalent to 1 mL of a NaB(C6H5)4 solution. Halides must be absent. 

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. 

Potassium tetraphenylborate [3244-41-5] M 358.3. Ppted from a soln of KCl acidified with dilute HCl, then crystallised twice from acetone, washed thoroughly with water and dried at 110° [Findeis and de Vries AC 28 1899 7956]. 

Potassium. Quality standards for bottled wines now require a high degree of clarity. Even slight precipitates of potassium acid tartrate are considered detrimental. Whether wines are stabilized by cold treatment, long aging, or ion exchange, determination of their potassium content may be necessary. Precipitation as the acid tartrate (6) is widely used. However, precipitation as potassium tetraphenylborate is used in Europe (4, 22). Flame photometry and atomic absorption spectrophotometry are... 

Disodium hexabromotungstate(lV) Dipotassium pentacyanonitrosyIferrate(2 ) TrichloroseIenium(II) tetrachloroferrate(III) Tetrafluorobromate(III) ion Potassium tetraphenylborate(l-)... 

NMR titration experiments showed that the presence of an alkali metal cation greatly enhances halide-binding constants. [21] For example, the 13/CF association constant in CDCl3 DMSO-t/6 (85 15) was increased from 80 M 1 to 2.5 x 104 M 1 by the presence of one molar equivalent of potassium tetraphenylborate. Additional NMR titration experiments showed that receptor 13 binds KC1 better than NaCl. X-ray analysis of the 13 KC1 complex uncovered two independent but structurally similar complexes in the unit cell. One of the stmctures is shown in Figure 2. The salt is clearly a contact ion-pair whose K-Cl distance of 2.989 A is slightly shorter than that observed in solid KC1. We also obtained the X-ray structures of receptor 13 complexed with LiCl, LiBr, NaCl, NaBr, Nal, KC1, KBr, and KI. [22,23] As expected, the larger anions do not fit perfectly inside the macrocyclic cavity, and so salt affinities are decreased. 

Most polymer membrane ISEs are prepared by dissolving an ionophore in a polyvinylchloride (PVC) membrane. A large variety of plasticisers are used to increase the dielectric constant of the PVC and improve its hydrophilicity. Some membranes have complexes of the ions to be sensed to increase membrane conductivity, such as potassium tetraphenylborate in K -selective membranes. There is an extensive literature on the arcane arts of polymer membranes for electrodes with dissolved ionophores and a good review of this is given by Professor Ronald Armstrong in Section 3.7 of Gabor Harsanyi s book. Polymer films in sensor applications [14]. 

Potassium tetraphenylborate, normally dried at 105 to 120°C, is stable up to 265°C, according to the thermolysis curve of Wendlandt. At 715 to 825°C the metaborate KBO2 is formed. 

The water-soluble material was filtered through a 1.4- xm frit. An aliquot of the solution was treated with excess sodium tetraphenylborate. The potassium tetraphenylborate that precipitated was collected and dried. This analysis indicates that 18.7 meq of potassium ion was formed in the reaction. 

Dilituric acid (5-nitrobarbituric acid) forms a sparingly soluble compound with potassium ions. The decrease in absorbance of the reagent gives a measure of the K content in the solution. Potassium ions can be precipitated by tetraphenylborate. The excess reagent forms an ion-pair with the cationic Cu(I)-neocuproine complex, and this ion-pair is extractable into methyl acetate. The absorbance of the extract is measured at 456 nm [83]. An indirect method involving the reaction of potassium tetraphenylborate with mercury(II) ehloranilate is very sensitive [84]. 

Addition of potassium tetraphenylborate to the DMSO solution of receptor 26 gave no changes in the electrochemical behavior, probably due to the fact that the crown ether moieties in 26 are situated rather far from the electro-active U02-center. However, an indirect procedure for the determination of complexation constants, based on competition between thallium TT and ions gave a value of 1.0 X 10 M for K+ [ref 33]. 

Quantitative determination of the potassium content of a water sample can be effected by way of flame emission, atomic absorption or precipitation as potassium tetraphenylborate (see Section 3.3.3). 

The mixtures were stirred until the liquid phase had a constant composition. The chloride ion content was determined argentlmetrically, potassium was determined as potassium tetraphenylborate, phosphorus was determined by differential colorimetry on an FEK-56 apparatus, and sodium was determined by difference. 

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. 

Potassium ( K) (I = 3j2). The quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) and double frequency sweep (DFS)/QCPMG pulse sequences were applied to acquire solid-state NMR spectra of organometallic complexes. The results show there are significant quadrupolar interactions, which depend on temperature, in the polymeric main group metallocenes cyclopenta-dienyl potassium and pentamethylcyclopentadienyl potassium. Sodium and potassium tetraphenylborates were examined by solid-state Na and NMR spectroscopy as mentioned in 2.1.5 Sodium. ... 

The transfer of potassium from oil to water, where the potassium salt (potassium tetraphenylborate) is dissolved in the organic phase with an equimolar concentration of the ionophore. Recent work using micro liquid-liquid interfaces supported at the tip of micropipettes has shown this process to occur by TID mechanism (transfer by interfacial dissociation). 

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