Removal by Complexation

Ligand exchange with an excess (4-5 equiv.) of an isonitrile substituted at its distal end with a potassium carboxylate functionality provides derivatives that can 

Of course, the term simple filtration is a most attractive one in this respect. This can indeed be achieved using the technique of nanofiltration [21], specifically employing a commercially available polyimide membrane, STAR-MEM 228 [22]. Not only does the method appear very simple, the filtrate can contain only 9 ppm of ruthenium, while the retained solution contains the unaffected 

Perhaps unexpectedly, reagents that are very successful in solution with other metathesis reactions, such as tris(hydroxymethyl)phosphine (THMP) 3 and 

2-mercaptonicotinic acid 9, are not quite as successful in examples of ROMP product purification. Instead, when a ROMP process leads to relatively insoluble, monolithic materials, simply washing these with solutions of ethyl vinyl ether in tetrahydrofuran, with or without the addition of dimethyl sulfoxide, followed by a final methanol wash, can often result in the essentially complete removal of the ruthenium complexes ( 0.1 ppm) [29]. Presumably, this is related to the aforementioned method involving Fisher carbene complex formation [19]. 

An exceptionally simple method for separating many metathesis products from the catalyst is to extract the former into supercritical carbon dioxide [30]. Presumably, this is only effective in examples of relatively nonpolar products, which of course many are. The procedure can be run as a semi-continuous process, although the availability of suitable equipment will likely be a problem in many laboratories. 

---

Chloryl fluoride is slightly less volatile than CIF3O2, and, therefore, most of it can be removed from CIF3O2 by fractional condensation in a —112°C trap. The remaining FClOg, however, has to be removed by complexing with BFg ... 

Methylamino-5-(l-methylalIylamino)-l,3,4-thiadiazoIe is an oxidation product of methallibure, a veterinary oestrus regulator. Separation can be achieved by chromatography on alkylated polydextran gel and elution with mixed organic solvents. Metal salts can be removed by complexation with diphenylthiocarbazone (70JPS835). 

If the sample to be analyzed contains organic acids, the metal ion fixed at the ion-exchange group can be removed by complexation, which increases the frequency of ion exchanger regeneration. 

In another experiment involving an initial tetramine mixture similar to that used in experiment 2 of Table IV, virtually all the iso-HMTT was removed by complexation with sodium iodide in pentane. Fractional vacuum distillation of the remaining tetramine mixture separated n-HMTT from the cyclic TMTT isomers. Gas-chromatographic analysis showed that the polyamine recovered this way was more than 99% n-HMTT. 

In another example, a sample of TMCHD (ca. 5 mmoles, containing 86% trans-TMCHD with the cis isomer as the major contaminant) was contacted for 2 days with 4.3 mmoles of MgCL> 6H20 in 2.3 ml of saturated hydrocarbon diluent. After removing solids by filtration, the amine content of the filtrate was 96.2% trans-TMCHD, showing that the cis isomer had been removed by complexation. 

Nickel forms a red chelate with dimethylglyoxime (DMG), which is quite suitable for gravimetric analysis. Precipitation of the chelate is complete in an acetic acid-acetate buffer or in an ammoniacal solution. Acetate buffer is generally used when Zn, Fe, or Mn is present in the alloy. The sample given to you is a nichrome alloy that has Ni (approximately 60%), Cr, and Fe as the major constituents. Interference from Cr and Fe is removed by complexation with tartrate or citrate ions. Precipitation is then carried out in an ammoniacal solution. The Ni content is calculated from the weight of the precipitate (see Table 10.2 for the formula). 

Fluorescence Spectroscopy. - A method for the spectrofluorimetric determination of six organophosphorus pesticides has been established. The fluorescence of the solutions was measured at excitation wavelength, 380 nm and emission wavelength, 488 nm. The optimum pH for measurement is 9.3 - 9.6 and transition metal ions interfere but can be removed by complexation. Detection limits varied between 10and 10 g/ml, depending on the substance. There are... 

CyD applications are by no means restricted to the pharmaceutical industry. Several examples, mainly prospective ones, are scattered throughout this book. CyDs are used to remove unpleasant tastes, odors, or other undesirable components in the food industry, in agrochemistry, cosmetics, dying, cleaning, and in many other areas. To name just a few examples of numerous CyDs applications grapefruit juice loses its unpleasant taste when its bitter component naringine is removed by complexation with yS-CyD [61] similarly, removal of phenylalanine and tyrosine... 

Pyrophosphates such as Na2H2P207 can be used to counteract the blackening of raw potato or apple juice. This is a deterioration which arises from the oxidation of diphenolic compounds in the presence of heavy metal ions. The latter are removed by complexing with the pyrophosphate anions. 

Rover fuel is in the form of graphite rods having dispersed UCj or UO and some NbC and ZrC. The rods are burned, resulting in an ash of U , NbiOj, small amounts of carbon, and minor impurities. The ash is transferred batch-vme into the dissolver vessel. It is dissolved with 8 M HNOs, dilution water, and 22 M HF, all borated at 3.85 g B/S. Excess fluoride is removed by complexing with 2.2 M A1 03)3. 

By their very nature, all of the metathesis catalysts should be amenable to removal by complexation with additional ligands added after completion of the metathesis step. An especially simple and straightforward procedure is to use the triol 3 (Figure 13.1) to convert the catalyst into water-soluble derivatives. The one drawback is that this method is somewhat wasteful, as a large excess is required - up to 86 equiv. of triol 3 for the removal of Grubb s first-generation catalyst, and at least 10 mol equiv. for others [15]. An aqueous wash or filtration through silica gel suffices to reduce ruthenium levels to at least below 200 ppm, and often even lower. 

Okura (296) recommended the following procedure to 50 ml of the hot sample in a platinum dish add 4 drops concentrated H SO, 1 ml 10% ammonium molybdate solution, and 20 mg NaF, in that order cool and measure the color. On the other hand, Tarutani (308) stated that F" ion interferes with the silicomolybdic method and must be removed by complexing with boric acid or The difference... 

Interference due >0 chioride ions is removed by complexing with HgS04 ... 

---