Filtration of precipitates

Isolated yield after evaporation of the solvent (entry 1) or filtration of precipitated amino nitrile 3 (entries 2-9). 

Poster and Baker [91] modified Eq. 8 to include the scavenging of submicron particles that are present in the filtrate of precipitation samples ... 

To carry out this transformation, a mixture of appropriate solvents or no solvent is used [25], The final complexes are isolated by filtration of precipitate from reaction mixture, cooled or partially evaporated under low pressure. 

While evaporation is used for the concentration and removal of solvents, usually the reaction by-products are not volatile. Similarly, filtration of precipitated or crystallized solids is not likely to be applicable to all the members of a library, and furthermore the automation of these processes is not straightforward an interesting example of general precipitation of library members from an organic medium due to the presence of a basic ionizable group has been recently reported by Perrier and Labelle (87). Extraction procedures possess the desired separation properties and have been used for the purification of several solution-phase libraries we will cover this subject in more depth in this section. An excellent review (88) has recently been published in which the interested reader will find a description of available strategies for separation and purification of single compounds and arrays. 

Pukall Cells.— For the filtration of precipitates, like calcium sulphate, barium sulphate, of strongly acid liquids, etc., Pukall s... 

Secondly, under what conditions will the dispersion flocculate or coagulate The answer to this is of vital importance in the many practical situations in which colloids must either be avoided or eliminated (e.g. in the filtration of precipitates or in water purification). 

Sulphate concentrations may also be determined accurately by potentiometric back-titration of excess Ba + with a mercury electrode following the precipitation of BaS04 Mucci, 1991). The seawater sample is freed from most seasalt cations with an ion-exchange-column. Then the eluate is reacted with an excess of barium, and after filtration of precipitated BaS04, the solution is titrated potentiometrically with an EGTA solution (see also Section 11.2) to the endpoint. The method applies over a wide range of salinities and sulphate concentrations in 1 mL or less of seawater and marine pore water samples, however, it is somewhat less precise (c.v. of about 0.6 %) than the simple gravimetric procedure described. 

The industrial process [23, 212, 213] of ethoxylation and propoxylation is usually a semi-batch process. The starter alcohol and KOH are mixed and water is removed by distillation. In a second step, monomers are fed into the reactor, where the feed rate is chosen so as to be able to remove the heat of polymerization and to keep the latent heat of polymerization of unreacted monomers in a safe state. By this process, homopolymers and random copolymers are accessible. Block copolymers are produced by successive feeds of the respective monomers. Catalyst is removed by addition of acids and subsequent crystallization and filtration of precipitated salts. An optional fourth step is the removal of volatile compounds by distillation. 

V(DMS0)eI[a04]3 [T147] Addition of DMSO to aqueous V(C104)3, partial evaporation of solvent followed by filtration of precipitate formed. Compound recrystallized from DMSC). 

Place a mixture of 53 g. of A.R. lactic acid (85-88 per cent, acid), 75 g. (85-5 ml.) of commercial anhydrous isopropyl alcohol, 300 ml. of benzene and 20 g. of Zeo-Karb 225/H (1) in a 700 ml. bolt-head flask, equipped with an automatic water separator (e.g., a large modified Dean and Stark apparatus with a stopcock at the lower end, see Fig. Ill, 126, 1) carrying an efficient reflux condenser at its upper end, and a mercury-sealed stirrer (alternatively, the hquid-sealed stirrer shown in Fig. 11,7,11, c. may be used). Reflux the mixture, with stirring, on a steam bath for 5 hours or until water no longer collects in appreciable amount in the water separator run off the water from time to time. Filter off the resin at the pump and wash it with two 25 ml. portions of benzene. Shake the combined filtrate and washings with about 5 g. of precipit-ated calcium... 

Benzylatnine. Warm an alcoholic suspension of 118-5 g. of finely-powdered benzyl phthalimide with 25 g. of 100 per cent, hydrazine hydrate (CAUTION corrosive liquid) a white, gelatinous precipitate is produced rapidly. Decompose the latter (when its formation appears complete) by heating with excess of hydrochloric acid on a steam bath. Collect the phthalyl hydrazide which separates by suction filtration, and wash it with a little water. Concentrate the filtrate by distillation to remove alcohol, cool, filter from the small amount of precipitated phthalyl hydrazide, render alkaline with excess of sodium hydroxide solution, and extract the liberated benzylamine with ether. Dry the ethereal solution with potassium hydroxide pellets, remove the solvent (compare Fig. //, 13, 4) on a water bath and finally distil the residue. Collect the benzylamine at 185-187° the 3ueld is 50 g. 

Place 45 g. (43 ml.) of benzal chloride (Section IV,22), 250 ml. of water and 75 g. of precipitated calcium carbonate (1) in a 500 ml. round-bottomed flask fltted with a reflux condenser, and heat the mixture for 4 hours in an oil bath maintained at 130°. It is advantageous to pass a current of carbon dioxide through the apparatus. Filter off the calcium salts, and distil the filtrate in steam (Fig. II, 40, 1) until no more oil passes over (2). Separate the benzaldehyde from the steam distillate by two extractions with small volumes of ether, distil off most of the ether on a water bath, and transfer the residual benzaldehyde to a wide-mouthed bottle or flask. Add excess of a concentrated solution of sodium bisulphite in portions with stirring or shaking stopper the vessel and shake vigorously until the odour of benzaldehyde can no longer be detected. Filter the paste of the benzaldehyde bisulphite compound at the pump... 

Medium 10-15 Filtration of crystalline precipitates. Removal of floaters from distilled water. 

Fine 4-5.5 Filtration of fine precipitates. As a mercury valve. In extraction apparatus. 

Particulate interferents can be separated from dissolved analytes by filtration, using a filter whose pore size retains the interferent. This separation technique is important in the analysis of many natural waters, for which the presence of suspended solids may interfere in the analysis. Filtration also can be used to isolate analytes present as solid particulates from dissolved ions in the sample matrix. For example, this is a necessary step in gravimetry, in which the analyte is isolated as a precipitate. A more detailed description of the types of available filters is found in the discussion of precipitation gravimetry and particulate gravimetry in Chapter 8. 

A sample containing 60 mg of Mg + will generate approximately 600 mg, or 0.6 g, of MgNH4P04 6H2O. This is a substantial amount of precipitate to work with during the filtration step. Large quantities of precipitate may be difficult to filter and difficult to adequately rinse free of impurities. 

The most common catalysts are sodium hydroxide and calcium hydroxide, generally used at a modest excess over the nominal stoichiometric amount to avoid formaldehyde-only addition reactions. Calcium hydroxide is cheaper than NaOH, but the latter yields a more facile reaction and separation of the product does not require initial precipitation and filtration of the metal formate (57). 

Salts of alkyl hydrogen sulfates that are free of sulfuhc acid can be prepared from crude hydrogen sulfates containing ROSO H and sulfuhc acid in a two-step reaction. Eirst, the crude product reacts in aqueous solution with the hydroxide or carbonate of a metal whose sulfate is insoluble in water. After filtration of the insoluble metal sulfate, the necessary amount of a water-soluble metal sulfate is added to the filtrate, which precipitates the insoluble metal sulfate, leaving the desired salt of the alkyl hydrogen sulfate in solution. 

Enzymes. Invertase (P-fmctofuranosidase) is commercially produced from S. cerevisiae or S. uvarum. The enzyme, a glycoproteia, is not excreted but transported to the cell wall. It is, therefore, isolated by subjecting the cells to autolysis followed by filtration and precipitation with either ethanol or isopropanol. The commercial product is available dry or ia the form of a solutioa containing 50% glycerol as a stabilizer. The maia uses are ia sucrose hydrolysis ia high-test molasses and ia the productioa of cream-ceatered candies. 

Drainage from active mining areas is considerably less than from inactive mines because of the disposal methods currently employed. Prior to discharge, Hquid effluents are limed and settled to precipitate metals as hydroxides. Elocculants are used to reduce the total suspended soHds and, in some instances, filtration of thickener overflow is practiced. 

Cesium isotopes can be recovered from fission products by digestion in nitric acid, and after filtration of waste the radioactive cesium phosphotungstate is precipitated using phosphotungstic acid. This technique can be used to prepare radioactive cesium metal or compounds. Various processes for removal of Cs isotopes from radioactive waste have been developed including solvent extraction using macrocycHc polyethers (62) or crown ethers (63) and coprecipitation with sodium tetraphenylboron (64). 

When cake washing is involved, it is usually convenient to weigh the wet cake and then repulp it in a known quantity of distilled water or in water at the same pH as the filtrate, if precipitation of... 

Amlnoacrldlne (6) 4 (37 g 0 2 mol) glycerol (150 g) formic acid (9 2 g, 0 2 mol) and cone HCI (17 ml) were healed to 155 C maintained at this temp (or 30 min and heated to 175 C (or 30 mm The product was treated with scdium acetate (10 g) in water (400 mL) After filtration of N N diphenylproflavine the filtrate was treated with NaOH solution and boiled to precipitate the crude product After recrystallization from alcohol there was obtained 6 23 g (59%), mp216°C... 

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