Pseudo solvent

Tie lines of the system can be generated from the equilibrium compositions for each run and selectivities computed. The results of measurements obtained for the 5% by volume of ammonia/ethylene are represented in the binodal diagram in Fig. 3. Butene is represented as the distributed component between the solvent phase and the butadiene-rich phase. The ammonia-solvent gas mixture was considered to behave as a pseudo-solvent of fixed composition. The ratio of the integrated peaks for butene(i) and butadiene(j) was used to compute the selectivity, B (beta), defined on a solvent-free basis, as ... 

The selectivity in programmed solvent LC may be varied by varying the solvents used or by the application of ternary or even more complicated gradients. However, most ternary gradients can in fact be reduced to binary ones using mixed (pseudo-) solvents. 

Solution Polymerization of Vinyl Chloride in a Pseudo-Solvent. 404... 

Kuchanov and Bort do not seem to draw any distinction in their discussion between a true solvent for both the monomer and the polymer (such as tetrahydrofuran) and a pseudo-solvent, which is essentially a nonsolvent for the polymer beyond a certain low polymer concentration and/or molecular weight. 

In discussing solution polymerizations of vinyl chloride we must recall that poly(vinyl chloride) is insoluble in its monomer as well as in many common solvents. Therefore we have to distinguish between true solution polymerizations, /.e., systems in which the monomer, the added solvent, and the polymer are truly in solution and pseudo-solution polymerizations, i,e, systems in which the monomer is in true solution but from which the polymer separates as a swollen phase. Among the true solvents are tetra-hydrofuran (THF) chlorobenzene 1,2-dichloroethane diethyl oxalate 2,4,6-trichloroheptane and many plasticizers. Examples of pseudo-solvents are methanol, aliphatic hydrocarbons, and cyclohexane [22]. 

In a pseudo-solvent such as cyclohexane, the polymerization process is similar to that of a bulk polymerization except that the rate of conversion is lower. In methanol the rate is enhanced. 

In a patent, a polymer prepared in a pseudo-solvent was treated with a plasticizer such as epoxidized linseed oil or di-2-ethylhexyl phthalate before the solvent was removed. Then, after the solvent had been evaporated under reduced pressure, a PVC paste containing up to 50% of plasticizer was readily produced [169]. 

Heat a little pseudo-saccharin chloride with excess of the anhydrous alcohol in a test-tube until hydrogen chloride is no longer evolved. Recrystallise from alcohol or other organic solvent. 

Enone formation-aromatization has been used for the synthesis of 7-hydro-xyalkavinone (716)[456]. The isotlavone 717 was prepared by the elimina-tion[457]. The unsaturated 5-keto allyl esters 718 and 719, obtained in two steps from myreene. were subjected to enone formation. The reaction can be carried out even at room temperature using dinitriles such as adiponitrile (720) or 1,6-dicyanohexane as a solvent and a weak ligand to give the pseudo-ionone isomers 721 and 722 without giving an allylated product(458]. 

Drawing pseudo-binaryjy—x phase diagrams for the mixture to be separated is the easiest way to identify the distillate product component. A pseudo-binary phase diagram is one in which the VLE data for the azeotropic constituents (components 1 and 2) are plotted on a solvent-free basis. When no solvent is present, the pseudo-binaryjy—x diagram is the tme binaryjy—x diagram (Eig. 8a). At the azeotrope, where the VLE curve crosses the 45° line,... 

Fig. 8. Pseudo-binary (solvent-free)jy-x phase diagrams for determining which component is to be the distillate where (—) is the 45° line, (a) No solvent (b) and (c) sufficient solvent to eliminate the pseudo-a2eotiope where the distillate is component 1 and component 2, respectively (51) and (d) experimental VLE data for cyclohexane—ben2ene where A, B, C, and D represent 0, 30, 50, and 90 mol % aniline, respectively (52).

For cases B and C, Robbins ( Liquid-Liquid Extraction, in Schweitzer, Handbook of Separation Techniques for Chemical Engineers, McGraw-Hill, New York, 1979, sec. 1.9) developed the concept of pseudo solute concentrations for the feed and solvent streams entering the extractor that will allow the Kremser equations to be used. 

Likewise, one knows that Y will be on the equilibrium line with X (see Fig. 15-12). One can therefore calculate a pseudo concentration of solute in the inlet extraction solvent Yf that 011 fall on the operating line [Eq. (15-12)] where=Xr [Eq. (15-20)]. 

On an XY diagram for case C the operating line will go through points Xr, Ys and Xf, with a slope of R /S similar to Fig. 15-13. When using the Kremser equation for case C, one uses the pseudo feed concentration X from Eq. (15-21) and the stripping factor from Eq. (15-22). One uses the raffinate concentration X and inlet solvent concentration Y, without modification. 

The points that we have emphasized in this brief overview of the S l and 8 2 mechanisms are kinetics and stereochemistry. These features of a reaction provide important evidence for ascertaining whether a particular nucleophilic substitution follows an ionization or a direct displacement pathway. There are limitations to the generalization that reactions exhibiting first-order kinetics react by the Sj l mechanism and those exhibiting second-order kinetics react by the 8 2 mechanism. Many nucleophilic substitutions are carried out under conditions in which the nucleophile is present in large excess. When this is the case, the concentration of the nucleophile is essentially constant during die reaction and the observed kinetics become pseudo-first-order. This is true, for example, when the solvent is the nucleophile (solvolysis). In this case, the kinetics of the reaction provide no evidence as to whether the 8 1 or 8 2 mechanism operates. 

GPC has many uses and is a powerful analysis technique for acrylate polymers. With care in selecting solvents and stationary phases, one finds that many polymers can be analyzed successfully. Opportunities always exist to use analytical GPC columns in nonstandard ways (semiprep, HDC, pseudo-ElPLC combined with GPC ) to the benefit of the analyst, but the analyst must always be keenly aware of which mode of operation is dominating when practicing such nonroutine analyses. 

First, mention should be made of the metathetical reaction, replacing an anion of a pyrylium salt by another-, when the solubility of the latter salt is lower than that of the former, the conversion is easy. In the opposite case, one has to find a solvent in which the solubilities are reversed (perchlorates are less soluble in water than chloroferrates or iodides, but in concentrated hydrochloric or hydroidic acids, respectively, the situation is reversed For preparing chlorides which are usually readily soluble salts, one can treat the less soluble chloroferrates with hydrogen sulfide or hydroxylamine. Another method is to obtain the pseudo base in an organic solvent and to treat it with an anhydrous acid. 

Reactions with uncharged species such as amines, alcohols, and water offer frequent opportunities for investigations under pseudo-first-order conditions since many of these reagents are suitable solvents. However, the reactions with amines have often been investigated in alcohols and in non-hydroxylic solvents 27-29a have been found to follow second-order kinetics. 

The rate constants (in absolute solvents unless otherwise specified) are measured at a temperature giving a convenient reaction rate and calculated for a reference temperature used for comparison. These constants have all been converted to the same units and tabulated as 10 A . Where comparisons could otherwise not be made, pseudo-unimolecular constants (Tables IX and XIII, and as footnoted in Tables X to XIV) are used. The reader is referred to the original articles for the specific limits of error and the rate equations used in the calculations. The usual limits of error were for k, 1-2% or or 2-5% and logio A, 5%, with errors up to double these figures for some of the high-temperature reactions. 

Carried out in the nucleophile as solvent. f Pseudo-unimolecular rate constant in sec i. 

Studies of halogenation of the partially reduced systems (e.g., 148) have shown that the 6- (148) or 8-nitro-2,3-dihydrothiazolo[3,2-a]pyridinium bromides were brominated in hydroxylic solvents with a regiochemistry and ease of reaction consistent with the intermediacy of a pseudo base... 

A particularly interesting system for the epoxidation of propylene to propylene oxide, working under pseudo-heterogeneous conditions, was reported by Zuwei and coworkers [61]. The catalyst, which was based on the Venturello anion combined with long-chained alkylpyridinium cations, showed unique solubility properties. I11 the presence of hydrogen peroxide the catalyst was fully soluble in the solvent, a 4 3 mixture of toluene and tributyl phosphate, but when no more oxidant was left, the tungsten catalyst precipitated and could simply be removed from the... 

---