Heterogeneous solution

The Poisson equation assumes that the solvent is completely homogeneous. However, a solvent can have a significant amount of charge separation. An example of a heterogeneous solution would be a polar solute molecule surrounded by water with NaCl in solution. The positive sodium and negative... 

Other Fe-S Clusters. Spontaneous self-assembly reactions using phosphines as terminal ligands have been reported to yield a variety of new Co-S (22) and Ni-S clusters (23). Extension to Fe-S clusters was initially effected by the following reaction in heterogeneous solution (2A). 

When a monomer such as acrylonitrile is polymerized in a poor solvent, macroradicals precipitate as they are formed. Since these are living polymers, polymerization continues as more acrylonitrile diffuses into the precipitated particles. This heterogeneous solution polymerization has been called precipitation polymerization. 

Under a nitrogen atmosphere a solution of 18.0 g (88 mmol) of (4.S ,5.5 )-2-cthyl-4,5-dihydro-4-hydroxymethyl-5-phenyIoxazole in 150 mL of dry THE is added dropwise at 20 C to a stirred heterogeneous solution of 2.53 g (105.3 mmol) of sodium hydride (oil removed by washing with 50 mL of dry benzene) at a rate to maintain a mild evolution of hydrogen. When the addition is complete, the mixture is heated at 50-60 °C for 1.5 h, cooled to r.L. and a solution of 16.2 g (114 mmol) of iodomethane in 10 mL of dry THF is added dropwise. The reaction mixture is stirred for 2 h and slowly poured into. 300 mL of ice water, then extracted with two 200-mL portions of diethyl ether. The combined extract is dried over Na2S04 and concentrated to give an oil, which is distilled in vacuo, yield 87% bp 91-93 °C/0.25 Torr [at] 4 —84.2 (r = 10.1, CHC13). 

Table 2. Slope (a) and Intercept (TASq) of the AH-7AS Plots for Supramolecular Interactions of Natural and Synthetic Hosts with a Variety of Ionic, Molecular, and Biomolecular Guests in Homogeneous and Heterogeneous Solutions...

In contrast, a heterogeneous solution of noncritical composition (e.g., v < xc, as shown by the arrow and dashed line in Fig. 7.11) shows a qualitatively different behavior as it is rises through the coexistence boundary and into the homogeneous region near and above Tc. For each increase in temperature along the dashed line in Fig. 7.11, a horizontal tie-line yields both the compositions of the A-rich and B-rich liquids (from the two ends of the tie-line), as well as the relative amounts of each phase (from the lever rule). Clearly, the critical composition xc remains near the middle of the tie-line as T increases toward Tc, whereas a noncritical composition x xc moves toward one or other terminus of the tie-line as the temperature is raised. 

Relatively stable macroradicals have also been obtained by the polymerization of vinyl chloride (15) or by the copolymerization of this monomer with vinyl acetate (32) in poor solvents—i.e., by heterogeneous solution polymerization. Appropriate solvents for this type polymeriza-... 

No product was obtained when attempts were made to copolymerize styrene and maleic anhydride in benzene at 50° C in the absence of bis-azoisobutyronitrile. Likewise, no free radicals were detectable when these solutions were examined using EPR techniques. Negative results were also noted in solutions of the alternating copolymer prepared in acetone. However, the presence of free radicals was noted when the alternating copolymer produced by heterogeneous solution polymerization in benzene was examined. This peak was observed with freshly prepared and aged copolymer samples that had been stored in an inert environment. However, no peak was observed in product that had been washed with methanol. 

Polymerization activity of proteinoid or polynucleotide-phosphorylase has been compared in ADP solution at pH 8.5 48). The results show that the activity of the neutral proteinoid is approximately 20 times lower than that of the enzyme, and the lower molecular-weight fraction of the proteinoid has negligible activity. The polymerization by polynucleotide-phosphorylase is increased approximately three times when Leuchs polylysine is supplied, polylysine and enzyme yield a heterogeneous solution 48). 

Abstract The principle of chromatographic NMR, a version of NMR diffuso-metry devised for a facilitated study of mixtures using the addition of a selectively retarding agent, is illustrated. The technical requirements for acquiring exploitable H NMR diffusometry spectra for a heterogeneous solution/solid mix are described. Applications of the technique to test mixtures for several choices of solvents/ interacting phase are reviewed. Key Words Mixtures, Porous materials, Diffusion, HRMAS, DOSY. 

The solution of ca. 0.30 mol of cyclopentadienylsodium is decanted from residual sodium sand with a U-tube into the dropping funnel (Note 12) and is added dropwlse over a 2-hr period (Note 13), A white precipitate of sodium bromide forms during the addition. The heterogeneous solution is stirred overnight at -78 C to insure complete formation of methyl 2,4-cyclopentadiene-1-acetate. 

Ethyl 2-butyrylacetate. In a 1-L, three-necked, round-bottomed flask fitted with a mechanical stirrer, dry nitrogen inlet, and thermometer is placed 19.8 g (0.150 mol) of monoethyl malonate (Note 1), 350 mL of dry tetrahydrofuran (THF, Note 2), and 5 mg of 2,2 -bipyridyl. The solution is cooled to approximately -70°C (in an isopropyl alcohol-dry ice bath) and a 1.6M solution of n-butyllithium in hexane is added from a dropping funnel while the temperature is allowed to rise to approximately — 10°C. Sufficient n-butyllithium is added (approx. 190 mL) until a pink color persists for several minutes (Note 3). The heterogeneous solution is recooled to -65°C and 7.90 mL (7.98 g, 75 mmol) of iso-butyryl chloride (Note 4) is added dropwise over 5 min. The reaction solution is stirred for another 5 min (Note 5) and then poured into a separatory funnel containing 500 mL of ether and 300 mL of cold, 1 N hydrochloric acid (Note 6). The funnel is shaken, the layers are separated, and the organic phase is washed with two 150-mL portions of saturated aqueous sodium bicarbonate, followed by 150 mL of water, and dried over anhydrous sodium sulfate. Removal of the solvents under reduced pressure leaves 11.70 g (98%) of ethyl 2-butyrylacetate (Note 7). The crude product can be distilled at 70-74°C (7 mm) (80% yield, 96% purity by GLC). 

These forms are convenient because of their simplicity, and because of their utility for ideal heterogeneous solutions. Whenever i indexes a pure condensed phase the corresponding factor on the right-hand side is unity this latter feature was stressed in Section 2.11. To be consistent with earlier discussions we will also restrict ourselves to the case P - 1 atm in Eq. (3.9.5b). A further simplification is possible through the definition (K K,)... 

Monomers, such as styrene which are good solvents for their polymers do not retard the bulk polymerization rate. However, this rate does not increase in a viscous good solvent medium that is present toward the end of the polymerization. Heterogeneous solution polymerization in nonvlscous poor solvents (1 ) and in viscous poor solvents is faster than rates observed in good solvents. 

Heterogeneous systems comprising (a) heterogeneous bulk polymerizations, (b) heterogeneous solution polymerizations, (c) suspension systems, (d) emulsion systems, (e) dispersion polymerization, (0 gas phase polymerization, and (g) interfacial polymerizations. 

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