Partial precipitation

Production of A1 metal involves two stages (a) the extraction, purification and dehydration of bauxite, and (b) the electrolysis of AI2O3 dissolved in molten cryolite Na3AlF6. Bauxite is now almost universally treated by the Bayer process this involves dissolution in aqueous NaOH, separation from insoluble impurities (red muds), partial precipitation of the trihydrate... 

C and weighed. The precipitate is almost insoluble in hot water, but dissolves readily in ammonia and cyanide solutions. Gold is reduced to the metal by the reagent, and platinum (if present in appreciable quantity) is partially precipitated either as a greenish complex compound or as the metal, upon boiling the solution. The precipitation of palladium is not complete in the presence of nitrates. 

It was found29,111 114 122 124 126 127 131 136 137 174 that, if an equimolar mixture of sodium metaperiodate and potassium chloride was used, partial precipitation of potassium metaperiodate occurred, and the resulting, low, constant concentration of periodate ion evoked less overoxidation. ... 

Coprecipitation upon partial precipitation of the natural calcium and magnesium with sodium hydroxide. 

If the analyte metal ion forms a stable EDTA complex rapidly, and an end point can be readily detected, a direct titration procedure may be employed. More than thirty metal ions may be so determined. Where the analyte is partially precipitated under the reaction conditions thereby leading to a slow reaction, or where a suitable indicator cannot be found, back titration procedures are used. A measured excess of EDTA is added and the unreacted EDTA titrated with a standard magnesium or calcium solution. Provided the analyte complex is stronger than the Ca-EDTA or Mg-EDTA complex a satisfactory end point may be obtained with eriochrome black T as indicator. An alternative procedure, where end points are difficult to observe, is to use a displacement reaction. In this case, a measured excess of EDTA is added as its zinc or magnesium complex. Provided the analyte complex is the stronger, the analyte will displace the zinc or magnesium. 

Fig. 4 Cyclic voltammograms for 0.2 mmol dm-3 pentaoxa[13]ferroceneophane (in the presence of 0.1 mol dm-3 Bu"NPF6 in CH2C12) in the absence of NaCICX, (a) and in the presence of 1 mmol dm-3 NaC104 (partially precipitated) in the course of stirring a solution for (b) 5 min and (c) 1 h. Scan rate 40 mV s-1.

The experimental procedure was essentially the same for all substances mentioned, namely, the method used in the case of nitrobenzene. Some complication arises, however, due to the fact that the solids do not disperse as easily in the fermentation mixture. Although the materials were always added in alcoholic solution to the yeast preparation, partial precipitation was unavoidable. With 21.4 g. of nitrosobenzene a yield of 4 g. of aniline was obtained addition of the same quantity of phenylhydroxylamine gave 7.5 g. of aniline. In both cases azobenzene appeared as a by-product and could be isolated in the pure state. Its formation can be readily explained by a condensation of the intermediary nitrosobenzene with the end product aniline. 

Warming a solution of nickel chloride and sodium hydroxide at moderate concentrations may partially precipitate a basic salt of indefinite composition. The average composition of this salt is NiCF 3Ni(OH)2. Salt composition may vary depending on reaction conditions. 

The flask was filled with (4S,55)-2-(5-methyl-2-phenyl4,5-dihydro-oxazol4-yl)-l,3-diphenyl-propan-2-ol (337 mg) and 15 mL of dry and degassed pentane. The solution was cooled to —78 °C using a dry ice/acetone bath. Under these conditions the alcohol partially precipitated. 

Nickel salts in aqueous solution are partially precipitated as basic salts on the addition of aqueous ammonia. The precipitate so formed, however, dissolves in excess of ammonia, yielding a blue liquid containing complex ammino-salts. In the dry state the salts rapidly absorb ammonia gas, with formation of ammino-compounds. 

A pentane (450 mL) solution of 5.6-dimethylenebicyclo[2.2.1]heptan-2-one was degassed at 20 "C with dry N2 for 30 min. After cooling to — 30 C, the stirred solution was irradiated (253.7 nm, Hanau TNN 15/32) in a quartz vessel for 24 h. The slightly yellow solution contained starting material ( 28%), 2,3-dimethylenebicyclo[2.1.1]hexane (26%) and polymers (46%, partially precipitated at — 30 C). The solution was concentrated by distillation. The residue was combined with four other residues obtained under the same conditions. Distillation afforded the crude diene yield 490-500mg (36% based on reacted ketone) bp 80 C/2 Torr. The diene was purified by preparative GC (FFAP 10% or SE 30 10% on WAW Chromosorb, 60/80 mesh). 

The Penniman process is probably the most widely used production method for yellow iron oxide pigments [3.26], [3.27], This method considerably reduces the quantity of neutral salts formed as byproducts. The raw materials are iron(II) sulfate, sodium hydroxide solution, and scrap iron. If the sulfate contains appreciable quantities of salt impurities, these must be removed by partial precipitation. The iron must be free of alloying components. The process usually consists of two stages (Fig. 23, Route B). 

Five grams of copper sulfate 5-hydrate are dissolved in 20ml of water and 3.5g of dipropylenetriamine are added with stirring. Acetone is added to the blue liquid until the product has been completely precipitated as an oil the supernatant liquid should be almost colorless. The oil is repeatedly triturated with small portions of acetone in a mortar until it forms a solid it is brought onto the filter with the same solvent and washed with a little ether. While the deep blue product is still moist, it is rapidly transferred to a vacuum desiccator and pumped dry. The material is extremely deliquescent. Losses in the preparation are only mechanical. The complex sulfate gives no precipitate with solutions of iodide, dithionate, ferricyanide, or persulfate ions. In concentrated aqueous medium, however, the addition of solid sodium fluoroborate causes partial precipitation of the relatively insoluble complex fluoroborate. 

The product of oxidation of a mixture of MPP and DPP homopolymer crystallized on heating. No clear glass transition was observed on the first heating, but on reheating, the transition occurred at 172°C. The NMR spectrum shows some randomization but resembles that of a mixture of homopolymers much more closely than that of a random copolymer (Figure 6). The product dissolves readily in m-xylene, but partially precipitates on standing overnight on a steam bath. 

The second flowsheet was therefore implemented in 24 stages (Figure 3.13) (177). This time, the An(III) + Ln(III) product solution contained only 0.66% Sr and 1.31% Mo. However, the large amounts of oxalic acid (up to 0.4 M) introduced in the feed and scrubbing solutions to avoid Zr extraction led to partial precipitation of An(III) and Ln(III) oxalates in the low acidity conditions of the stripping section. 

The poly amine hydrogenation of [60]fullerene to produce C3v C6QH18 involves addition of [60]fullerene to a standard round bottomed flask containing diethylenetriamine (DETA) with 10-50 mg of [60]fullerene utilized per every milliliter of DETA. The solution is boiled under N2 in the dark for 2-20 h. Upon cooling, the bright orange product partially precipitates from solution. Further precipitation is... 

Ammonia solution, sodium hydroxide Partial precipitation of white magnesium hydroxide Ammonium carbonate White precipitate of magnesium carbonate, only in the absence... 

These authors used titanium taddolate as a chiral catalyst, under heterogeneous conditions, giving partial precipitation of an inactive meso dimer. Titanium... 

Fig.7 TEM histograms of Au particles of (a) PEI21 and (b) PEI21GLU (without filtration, partial precipitation occurred after 1 week after reduction) mean diameter of PEI2i and PEI21GLU is 6.3 and 1.4 nm, respectively, at a ratio of [Auln]/[polymer] of 5. The black bar in the TEM pictures corresponds to 50 nm...

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