Solids mixed solvent

When the correct solvent for recrystallisation is not known a procedure similar to that given on pp. 15-16 should be followed, but on the semi-micro scale not more than 10 mg. of the solid should be placed in the tapered-end test-tube (Fig. 29(B)) and about o i ml. of the solvent should be added from the calibrated dropping-pipette (Fig. 30(B)). If the compound dissolves readily in the cold, the solvent is unsuitable, but the solution should not be discarded. [In this case recourse should be had to the use of mixed solvents (p. 18). For example if the substance is very soluble in ethanol, water should be added from a calibrated pipette with shaking to determine whether crystallisation will now take place, indicated by a cloudiness or by the separation of solid.]... 

Figure 8 shows the light dispersion curves for PVA (broken line) and mixed solvents of benzene and bromobenzene is (solid lines). Because the negative inclination of the dispersion curve for PVA is slower then those of... 

The alkali-catalysed methanolysis of poly(2,2-bis(4-hydroxyphenyljpropane carbonate) (PC) in a mixture of methanol (MeOH) and toluene or dioxane was studied. The treatment of PC in meOH, with a catalytic amount of sodium hydroxide, yielded only 7% bisphenol A. Using a mixed solvent of MeOH and toluene completely depolymerised PC to give 96% free bisphenol A in solid form and dimethyl carbonate in solution. The eharaeteristies of the catalysis are discussed together with the pseudo-first rate kinetics of the depolymerisation. The reaetion eonditions were investigated to facilitate the reeyeling of PC plasties. 17 refs. 

Supersaturation can also be achieved by adding a liquid that is miscible with the solvent and decreases the solubility of the solute in the mixed solvent. This is called precipitation. In fine chemicals manufacture, the solid is usually dissolved in an organic solvent and water is used as the desalting agent. Precipitation also occurs when a solid product, which is insoluble in the reaction mixture, is formed by chemical reaction. For instance, a phenolic product can be purified by three possible routes ... 

Figure 3.30. (a) UV-vis absorption spectra of the HPAA product (solid line) and the HPDP substrate (dash line) in a H20/MeCN (1 1) mixed solvent, (b) Picosecond time-resolved resonance Raman (ps-TR ) spectra of HPDP obtained with a 267 nm pump and 200 nm prohe wavelengths in a HjO/MeCN (1 1) mixed solvent. Resonance Raman spectrum of an authentic sample of HPAA recorded with 200 nm excitation is displayed at the top. (Reprinted with permission from reference [49]. Copyright (2006) American Chemical Society.)... 

Bis(indolyl)nitroethanes are obtained readily in 7-10 min in high yields (70-86%) on fine TLC-grade silica gel (5-40 pm) by Michael reaction of 3-(2 -nitrovinyl) indole with indoles. The same reaction reported requires 8-14 h for completion at room temperature [77]. Several functionalized resins have been prepared from Merrifield resin via a MW-assisted procedure that utilized mixed solvent system to facilitate the swelling of resins and coupling with microwaves [78], These resins can function as solid supports or polymeric scavengers in solid phase synthesis. 

Alternatively, lipospheres might be prepared by a solvent technique. In this case, the active agent, the solid carrier, and the phospholipid are dissolved in an organic solvent such as acetone, ethyl acetate, ethanol, or dichloromethane. The solvent is then evaporated and the resulting solid mixed with warm buffer solution, and mixing is continued until a homogeneous dispersion of lipospheres is obtained. 

Add more solvent. If it s a mixed-solvent system, try adding more of the solvent the solid is NOT soluble in. Or add more of the OTHER solvent. No contradiction. The point is to change the composition. Single solvent or mixed solvent, changing the composition is one way out of this mess. 

In recent years, it has been shown (Douzou and Maurel, 1976) that some proteins can behave as polyanions or polycations, and the stability of their solid state might be endangered at lower salt concentration due to repulsive forces between protein molecules. Much more important is the problem of enzyme activity in crystals suspended in cooled mixed solvents as a consequence of cosolvent- and temperature-induced changes in salt concentration and therefore in electrostatic potentials. 

Fig. 18 Top CD spectra. Oligomer 15 (solid line) oligomer 15 in the presence of 100 equiv of (-)-a-pinene (dotted line) and 100 equiv of (+)-a-pinene (dashed line) in a mixed solvent of 40% water in acetonitrile (by volume) at 295 K. [15]=4.2 pmol. Bottom Plot of IniCn for 15 against the solvent composition. The solid line is the least-squares linear fit (correlation coefficient=0.9987), and the dotted line is the extrapolation to 100% water. Error bars are from the nonlinear fitting of the data to...

EXAFS studies on tris-maltolatoiron(III) in the solid state and in solution, and on [Fe(Ll)3] hydrate, pave the way for detailed investigation of the hydration of complexes of this type in aqueous media.Solubilities and transfer chemical potentials have been determined for tris-maltolatoiron(III) in methanol-water, and for tris-etiwlmaltolatoiron(III) in alcohol-water mixtures and in isobutanol, 1-hexanol, and 1-octanol. Solubility maxima in mixed solvents, indicating synergic solvation, is relevant to trans-membrane transport of complexes of this type. Solubilities of tris-ethylmaltolatoiron(III) and of [Fe(Ll)3] have been determined in aqueous salt solutions (alkali halides NH4 and NR4 bromides). ... 

Supercritical carbon dioxide extraction (SCDE) is an ex sitn process for the treatment of low-level solid mixed and land disposal restricted (LDR) wastes. SCDE can extract hazardons solvents from waste snbstrates to prodnce land-disposable, low-level wastes. The process employs the snpercritical finid carbon dioxide as a solvent. This finid is noncombustible, nontoxic, and environmentally safe. In its supercritical state, carbon dioxide can dissolve organic contaminants allowing the fluid to quickly penetrate and facilitate transfer out of a contaminated matrix. 

There are a great many kinds of neat non-aqueous solvents. Substances that are solid or gaseous at ambient temperatures also work as solvents, if they are liquefied at higher or lower temperatures. For mixed solvents, it is possible to vary the mixing ratio and thus the solvent properties continuously. Therefore, if both non-... 

Methanol and Water. Methanol and water mixtures have been a popular choice for workers interested in free energies of transfer of ions from water into a mixed solvent. Such mixtures exhibit a drop in dielectric constant with increasing methanol content. Hence the electrical term must be estimated in order to compare spectroscopic and thermodynamic quantities. Feakins and Voice (28) have presented new data and revised earlier data for the alkali metal chlorides. In advance of carefully determined and extrapolated emf data for fluorides, using the solid state fluoride selective electrode based on lanthanum fluoride, some data of moderate accuracy have been presented (27). On the... 

Mesoporous silica spheres were synthesized under the catalyst of ammonia in the mixed water-DMF solvent. In typical synthesis, 0.8 g (2.2 mmol) CTAB was heated slightly to allow it dissolved in the mixed solvent of 19.0 g (1.06 mol) water and 19.0 g (0.26 mol) DMF. After cooling to room temperature, 1.0 g (15 mmol) ammonia and 2.08 g (10 mmol) TEOS were added to the mixture with an electromagnetic stirrer and the stirring rate was kept about 480 rpm. After stirring for 16 to 25 h, the white solid product was Filtered on a Buchner funnel and allowed to dry in air at room temperature. The dried precipitate was immersed into highly diluted aqueous ammonia (pH 10) and kept at 100 °C for 2 days, the product was washed with distilled water and dried at room temperature in air. Then the product was calcined at 550 °C for 4h to remove the templates. 

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