Separation by Solubility

Ammonium sulfate, (NH4)2S04, is the most commonly used compound for salting out of proteins because it is very soluble (706 g/L) and has four ionic charges per molecule. Precipitations are generally performed slowly with cold solutions to minimize protein denaturation due to the heat 

CHAPTERS Protein Isolation and Determination of Amino Acid Sequence 

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As shown in Figure 6, proteins of the gluten complex can be separated by solubility differences into saline-soluble albumins and globulins, 70% ethanol-soluble glladlns, acetic acid-soluble glutenln, and an insoluble protein residue. 

Figure 6. Types of proteins in wheat flour as separated by solubility...

The main evidence for the associative mechanism consists in double-labeling experiments conducted by Farnham and Sogah [33, 34]. At -90 °C in THF a mixture of PMMA with a dimethyltolylsilyl ketene acetal end group and PBMA with a dimethylphenylsilyl ketene acetal end group was treated with a small amount of BMA and TASF catalyst (Scheme 20). After 5 min the polymerization was quenched and the polymers separated by solubility. NMR showed a small PBMA block on the PMMA polymer but the end group was only tolyldimethylsilyl. 

The separation methods described in Section IV for pairs of optically active diastereoisomers have also been applied to mixtures of diaste-reoisomeric pairs of enantiomers. By one or other of the following methods, it was possible to separate diastereoisomeric pairs of enantiomers completely or, at least, to obtain enriched fractions. In chromatography under achiral conditions, enantiomers are eluted at identical rates. Therefore, the.pairs of enantiomers (RR )l(SS ) and (RS )I(SR ) can be separated chromatographically in the same way as a pair of optically active diastereoisomers (RS1) and (SS ). By application of the methods based on solubility differences for many examples, fractions containing the less soluble pair of enantiomers could be separated from fractions containing the more soluble pair of enantiomers. However, with respect to the separation.by solubility differences, the situation with two diastereoisomeric pairs of enantiomers is more complicated than that of a pair of... 

Pyrolysis of biomass is known to produce a complex mixture of phenolic compounds, which are derived primarily from the lignin fraction of the biomass (1-4) Elder and Soltes (5, 6) have investigated a phenolic fraction obtained from pyrolysis oils made in an updraft gasifier by TECH AIR as a source of phenolic adhesives a phenolics fraction was separated by solubility differences of oil fractions based on solubility of acids in aqueous bicarbonate solutions and... 

The steam distillation residue contains heavy oils and asphaltenes. These were separated by solubility differentiation. Both of these materials were sufficiently soluble in CCl, to permit examination by both IR and NMR. Principal featuris of the IR and NMR spectra are shown in Table VI. The possibility of colloidal dispersion of the asphaltenes instead of true solubility may have caused some loss of fine structure for the aromatic absorption regions. 

Separation by Solubility. Fractionation (qv) of a polymer has traditionally been based on solubility using precipitation, fractional dissolution (extraction), coacervate extraction, thin-layer chromatography, counter current distribution, and turbidimetry (5). 

The amino-acid sequence of 72 chymotryptic peptides isolated from P C], [ H]-labelled carboxymethyl-j8-D-galactosidase of E. coli has been determined. A variety of techniques were used in isolation procedures including separation by solubility, size, and chromatography. These peptides contain approximately 500 amino-acids. Peptides from this study and those reported earlier account together for the sequence of about 600 of the 1021 residues in the subunit. 

The primary goal of solvent dewaxing is to make the pour and cloud point requirements. This is accomplished by paraffin separation by solubility of non-paraffins in cold solvent, fractional crystallization, and filtering the solid paraffins from the slurry. This may be done in ketone units which use MEK, MEK/MIBK, MEK/Toluene solvents or in propane units which use liquefied propane as the solvent. Secondary effects include viscosity increase, density increase, sulfur increase, and reduction in VI. 

When used, it is always ahead of extraction. The primary goal is to remove asphaltenes, which could be a possible byproduct and to make the viscosity specification that is required. This is accomplished by asphaltenes separation by solubility of non-asphaltenes in a solvent and precipitation of asphaltenes using e.g. propane as a solvent. Secondary effects include Conradson Carbon reduced, metals reduced, saturates increased, viscosity index increased, and color improved. 

KCl —NaCl —MgS04) and in many brines. Separated by fractional crystallization, soluble water and lower alcohols. Used in fertilizer production and to produce other potassium salts. 

The nitration of phthalic anhydride with a mixture of concentrated sulphuric and nitric acids yields a mixture of 3-nitro- and 4 nitro phthalic acids these are readily separated by taking advantage of the greater solubility of the 4 nitro acid in water. Treatment of 3 nitrophtlialic acid with acetic anhydride gives 3 nitrophthahe anhydride. 

Separations based upon differences in the physical properties of the components. When procedures (1) or (2) are unsatisfactory for the separation of a mixture of organic compounds, purely physical methods may be employed. Thus a mixture of volatile liquids may be fractionally distilled (compare Sections 11,15 and 11,17) the degree of separation may be determined by the range of boiling points and/or the refractive indices and densities of the different fractions that are collected. A mixture of non-volatile sohds may frequently be separated by making use of the differences in solubilities in inert solvents the separation is usually controlled by m.p. determinations. Sometimes one of the components of the mixture is volatile and can be separated by sublimation (see Section 11,45). 

These methods are now obsolete in comparison with spectroscopic methods. Werbel has shown that the structures of these isomers are easily determined by NMR (125) (see also Table VI-5). Furthermore. 2-imino-4-thiazoline derivatives are characterized by their stretching C=N vibration at 1580 cm , absent in their 2-aminothiazole isomers, and by the stretching NH vibration that appears in the range of 3250 to 3310 cm for the former and between 3250 to 3340 cm" for the latter (131). Ultraviolet spectroscopy also differentiates these isomers (200). They can be separated by boiling in ethanol the thiazoline isomer is usually far less soluble in this solvent (131),... 

The metals are impregnated together or separately from soluble species, eg, Na2PdCl4 and HAuCl or acetates (159), and are fixed by drying or precipitation prior to reduction. In some instances sodium or potassium acetate is added as a promoter (160). The reaction of acetic acid, ethylene, and oxygen over these catalysts at ca 180°C and 618—791 kPa (75—100 psig) results in the formation of vinyl acetate with 92—94% selectivity the only other... 

Sodium iodide [7681-82-5] Nal, mol wt 149.92, mp 662°C, 84.66% I, forms colorless cubic crystals, which are soluble in water, ethanol, methanol, and acetone. It is used in photography, for the production of organic chemicals, and as an expectorant in cough medicines. Nal is separated by addition of sodium hydroxide or sodium carbonate to an acidic iodide solution (see also Expectorants, antitussives, and related agents). 

Diketones. y-Diketones contain two carbonyl groups separated by two carbon atoms. With the exception of 2,5-hexanedione which is a high boiling Hquid, 1,4-diketones ate low melting white soHds with only faint odors. Lower members are soluble in organic solvents and water. Properties of representative 1,4-diketones are shown in Table 14. 

The lanthanides form many compounds with organic ligands. Some of these compounds ate water-soluble, others oil-soluble. Water-soluble compounds have been used extensively for rare-earth separation by ion exchange (qv), for example, complexes form with citric acid, ethylenediaminetetraacetic acid (EDTA), and hydroxyethylethylenediaminetriacetic acid (HEEDTA) (see Chelating agents). The complex formation is pH-dependent. Oil-soluble compounds ate used extensively in the industrial separation of rate earths by tiquid—tiquid extraction. The preferred extractants ate catboxyhc acids, otganophosphoms acids and esters, and tetraaLkylammonium salts. 

The principle of solvent extraction in refining is as follows when a dilute aqueous metal solution is contacted with a suitable extractant, often an amine or oxime, dissolved in a water-immiscible organic solvent, the metal ion is complexed by the extractant and becomes preferentially soluble in the organic phase. The organic and aqueous phases are then separated. By adding another aqueous component, the metal ions can be stripped back into the aqueous phase and hence recovered. Upon the identification of suitable extractants, and using a multistage process, solvent extraction can be used to extract individual metals from a mixture. 

Chemical Properties The formation of salts with acids is the most characteristic reaction of amines. Since the amines are soluble in organic solvents and the salts are usually not soluble, acidic products can be conveniendy separated by the reaction with an amine, the unshared electron pair on the amine nitrogen acting as proton acceptor. Amines are good nucleophiles reactions of amines at the nitrogen atom have as a first step the formation of a bond with the unshared electron pair of nitrogen, eg, reactions with acid anhydrides, haUdes, and esters, with carbon dioxide or carbon disulfide, and with isocyanic or isothiocyanic acid derivatives. 

In the case of low temperature tar, the aqueous Hquor that accompanies the cmde tar contains between 1 and 1.5% by weight of soluble tar acids, eg, phenol, cresols, and dihydroxybenzenes. Both for the sake of economics and effluent purification, it is necessary to recover these, usually by the Lurgi Phenosolvan process based on the selective extraction of the tar acids with butyl or isobutyl acetate. The recovered phenols are separated by fractional distillation into monohydroxybenzenes, mainly phenol and cresols, and dihydroxybenzenes, mainly (9-dihydroxybenzene (catechol), methyl (9-dihydtoxybenzene, (methyl catechol), and y -dihydroxybenzene (resorcinol). The monohydric phenol fraction is added to the cmde tar acids extracted from the tar for further refining, whereas the dihydric phenol fraction is incorporated in wood-preservation creosote or sold to adhesive manufacturers. Naphthalene Oils. Naphthalene is the principal component of coke-oven tats and the only component that can be concentrated to a reasonably high content on primary distillation. Naphthalene oils from coke-oven tars distilled in a modem pipe stiU generally contain 60—65% of naphthalene. They are further upgraded by a number of methods. 

Suspension Polymerization. At very low levels of stabilizer, eg, 0.1 wt %, the polymer does not form a creamy dispersion that stays indefinitely suspended in the aqueous phase but forms small beads that setde and may be easily separated by filtration (qv) (69). This suspension or pearl polymerization process has been used to prepare polymers for adhesive and coating appHcations and for conversion to poly(vinyl alcohol). Products in bead form are available from several commercial suppHers of PVAc resins. Suspension polymerizations are carried out with monomer-soluble initiators predominantly, with low levels of stabilizers. Suspension copolymerization processes for the production of vinyl acetate—ethylene bead products have been described and the properties of the copolymers determined (70). Continuous tubular polymerization of vinyl acetate in suspension (71,72) yields stable dispersions of beads with narrow particle size distributions at high yields. 

In the initial formation of the cupric xanthates, soluble xanthate complexes form prior to the precipitation of the cuprous xanthate with the concurrent formation of the dixanthogen (51). The dixanthogen can be separated by virtue of its solubiUty in ether. Older samples of alkah metal xanthates contain some dixanthogen, which is thought to form by the following reaction (33) ... 

Zirconium and hafnium are separated by fractional distillation of the anhydrous tetrachlorides in a continuous molten solvent salt KCl—AlCl system at atmospheric pressure (56,57). Zirconium and hafnium tetrachlorides are soluble in KCl—AlCl without compound formation and are produced simultaneously. 

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