Solvent mixture A

To eliminate the need to recover the product by distillation, researchers are now looking at thermomorphic solvent mixtures. A thermomorphic system is characterized by solvent pairs that reversibly change from being biphasic to monophasic as a function of temperature. Many solvent pairs exhibit varying miscibility as a function of temperature. For example, methanol/cyclohexane and n-butanol/water are immiscible at ambient temperature, but have consolute temperatures (temperatures at which they become miscible) of 125°C and 49°C, respectively (3). 

Nanocapsules of biodegradable polymers, such as PLA and PLA copolymers or poly (e-caprolactone), have been prepared by an interfacial polymer deposition mechanism [163-166], An additional component, a water-immiscible oil, is added to the drug-polymer-solvent mixture. A solution of the polymer, the drug, and a water-immiscible oil in a water-miscible solvent such as acetone is added to an external... 

Figure 3.55 Examples of solvatochromic plots in solvent mixtures, (a) The fluorescence of 4-aminophthalimide in ether/dimethylformamide shows a much steeper non-linearity than its absorption band because of the large dipole moment of the emitting state, (b) The absorption spectrum of an aminobenzene in dioxan/water displays a red shift followed by a steep blue shift at high water concentrations...

In the ozonation of indenes in dichloromethane, a decrease in temperature led to increased proportions of the more thermodynamically stable ozonide stereoisomer but had no effect on total ozonide yield. In methanol-rich solvent mixtures, a temperature decrease had the same effect on the ozonide stereoisomer ratio but markedly increased competition from solvent incorporation into ozonides (Miura et al. 1985). 

In a limited sense solutions are homogeneous liquid phases eonsisting of more than one substanee in variable ratios, when for eonvenienee one of the substanees, whieh is ealled the solvent and may itself be a mixture, is treated differently from the other substanees, whieh are ealled solutes [1], Normally, the eomponent whieh is in exeess is ealled the solvent and the minor eomponent(s) is the solute. When the sum of the mole fraetions of the solutes is small eompared to unity, the solution is ealled a dilute solution A solution of solute substanees in a solvent is treated as an ideal dilute solution when the solute aetivity eoeffieients y are elose to unity (y=l) [1, 171], Solute/solvent mixtures A+ B that obey Raoult s law over the entire eomposition range from pure A to pure B are ealled ideal solutions. Aeeording to Raoult, the ratio of the partial pressure of eomponent AljpfO to its vapour pressure as a pure liquid (p ) is equal to the mole fraetion of A xa) in the liquid mixture, i.e. xa = Pa/Pa- Many mixtures obey Raoult s law very well, partieularly when the eomponents have a similar moleeular strueture e.g. benzene and toluene). 

When l,2-bis(methoxycarbonyl)-3,4-bis(2-naphthyl)cyclobutane is irradiated in solution (cyclohexane/tetrahydrofuran and tetrahydrofuran/acetonitrile mixtures) in the presence of triethylamine, it undergoes [2 -I- 2]cycloreversion via an exciplex with triethylamine [680], Interestingly, as shown in Eq. (5-144), the mode of cycloreversion changes with the solvent polarity, reflecting the different dipolar electronic structure of the exciplex. In nonpolar solvent mixtures, a horizontal cleavage of the cyclobutane... 

A striking solvent effect was observed in the reduction of a chiral a-keto amide, C6H5-CO-CO-NR2 (NR2 = (5)-proline methyl ester), with sodium tetrahy-dridoborate, leading to mandelic acid after hydrolysis [704]. When the a-keto amide was reduced in pure tetrahydrofuran or methanol, the resulting enantiomeric excess of (5)-mandelic acid produced was 36% and 4%, respectively. However, when a tetrahydrofuran/methanol (99 1 cL/L) solvent mixture was used, the enantiomeric excess increased to 64% ( ). In other solvent mixtures, a catalytic amount of a protic solvent (CH3OH or H2O) was found to be necessary for good asymmetric induction [704]. 

The model has been further tested in terms of the behavior of solvent molecules isotherms for binary-solvent mixtures A/B adsorption energies (ch values) of the polar solvent B in such mixtures as a function of surface coverage 6b, etc. Again, good agreement of experimental data with calculated values is observed. An important requirement of the model and related experimental correlations is that the solvent molecule must be treated (thermodynamically) in the same manner as solute molecules. Thus, if. solute adsorption energies are measured for a molecule X, the behavior of X as a component (solvent) of the mobile phase should then be predictable. 

Values of K for equilibrium of solvent mixtures A/B and B/C with adsorbent surface [Eq. (I0)j... 

Wetzler and coworkers123 employed 4-aminophthalimide (63) and 4-amino-lV-methyl-phthalimide (64) as solvatochromic (and thermochromic) fluorescent probes in solvent mixtures. A bathochromic shift of the emission spectra was found in mixtures of toluene with ethanol and with acetonitrile123 when the more polar solvent was added to toluene, but raising the temperature causes a relative hypsochromic effect. Mixtures of benzene and acetonitrile were studied by Nevecna and coworkers124 for their polarity by means of the probes 46 and 47 and with respect to the correlation of this with the rate constants of the reaction of triethylamine with ethyl iodide. The fluorescence of the ammonium salt of 4-(l-naphthylsulfonate)aniline (84) in dioxane and water mixtures was studied by Hiittenhain and Balzer125. 

Plots of logA s for solvolysis versus Y are markedly scattered in many cases but consist of a number of straight lines, one for each binary solvent mixture. A parameter, is defined which is a function of the... 

One of the most important applications of the theory of PS is to biomolecules. There have been numerous studies on the effect of various solutes (which may be viewed as constituting a part of a solvent mixture) on the stability of proteins, conformational changes, aggregation processes, etc., (Arakawa and Timasheff 1985 Timasheff 1998 Shulgin and Ruckenstein 2005 Shimizu 2004). In all of these, the central quantity that is affected is the Gibbs energy of solvation of the biomolecule s. Formally, equation (8.26) or equivalently (8.28), applies to a biomolecule s in dilute solution in the solvent mixture A and B. However, in contrast to the case of simple, spherical solutes, the pair correlation functions gAS and gBS depend in this case on both the location and the relative orientation of the two species involved (figure 8.5). Therefore, we write equation (8.26) in an equivalent form as ... 

The quantification of the metabolites of CYPs 2D6, 3A4, and 2C19 reactions is carried out using a SCIEX API 3000 mass spectrometer, running in the positive ion, selected reaction monitoring (SRM) mode. The HPLC gradient system used consists of two solvent mixtures. Solvent mixture A (SMA) consists of 94.9% H20, 5% MeOH, and 0.1% formic acid and solvent mixture B consists of 94.9% MeOH, 5% H20, and 0.1% formic acid. The analytical column used is a Develosil Combi-RP5, 5 pm, 3.5x20mm (Phenomenex, Inc., Torrance, CA), with a mobile phase flow rate of 1.1 mL/min. A short run time (1 min) HPLC method is used because of the specificity of the mass spectrometer and the lack of matrix effects (this was thoroughly... 

At present the most versatile method of obtaining a fluid solution of protein at subzero temperatures seems to be that of using aqueous organic solvent mixtures. A number of such solvent systems are known with freezing points in the vicinity of — 100°C. These usually contain 60-80% of the organic component. The most useful cryosolvents are... 

Figure 1 reveals that furfural and liquid CO2 are completely miscible, that furfural has a low solvent power for the oil, and that liquid CO2 has a low solvent power for the oil. The solubility of oil in furfural is 3% as indicated by point f of Figure 1. The solubility is increased to about 16% at i, by adding about 60% of liquid CO2 the solvent mixture. A system s is assembled with about 30% oil, 20% furfural and 50% CO2 this separates into two layers, e (upper) an extract layer, and r (lower) a raffinate layer. ... 

Figure 6.22. The reciprocal of pitch vs. (a) temperature for PBLG with concentration c = 0.15 vol% in a mixture of dioxane and dichloroethylene and (b) dichloroethylene concentration for PBLG in a mixture of m-cresol and dichloroethylene. The curves, 1-6 in (a) and 1-7 in (b) correspond to 0, 20, 40, 60, 80, 100% dichloroethylene in the solvent mixture (a) and 20, 30, 40, 50, 60, 70, 80°C (b). (From Uematsu, 1984.)...

Distillation diagrams of a solvent mixture a = Engler distillation,... 

Nair and co-workers [8] have coupled of semi-continuous NF with the Heck reaction. The objective was the synthesis of trans-stilbene from styrene and iodobenzene using Pd(OAc)2(PPh3)2 as catalyst and Pjo-tolyljj as stabilizing agent. They used solvent-resistant membranes and different aqueous/solvent systems (ethyl acetate and acetone/H20 methyl tert-butyl ether and acetone/H20 tetra-hydrofuran/H20). The best conversion was obtained with the first-mentioned solvent mixture. A selectivity of 100% of trans-stilbene with a cumulative turnover number of 1200 was reported, where the rejection of the catalyst turned out to be as high as 97%. Therefore, the authors concluded that NF was a convenient technique to run catalytic reactions with catalyst recycling, since this method saves the catalyst, prevents the metal contamination of the products, and increases reactor productivity. 

The foundations for almost all quantitative discussions of solvent effects upon electron spin resonance spectra were laid down by the theory of Gendell, Freed and FraenkeF (G.F.F. theory), who assumed that changes in hyperfine splitting constants were solely due to redistribution of a radical s spin density. This redistribution was assumed to accompany the formation of complexes between the radical and the solvent molecules. In formulating a model for the complexes, Gendell et al. restricted their attention to radicals containing polar substituents and postulated that each substituent was able to form a localised complex with one solvent molecule. Thus for a radical RX dissolved in a binary solvent mixture A B, two solvates of the radical are postulated to be in equilibrium with each other according to eqn. 4.16.1... 

The use of solvatochromic compounds as polarity indicators may be extended to solvent mixtures and micellar systems. In this case, an additional difficulty is introduced in the assessment of systems that are not homogeneous from a microscopic point of view The microenvironment actaally seen by the sensor does not correspond to the bulk characteristics of the medium. In a binary solvent mixture, a solvatochromic probe may be more solvated by one of the components, thus reflecting through its spectrum a solvent composition that may be different from that of the bulk mixture. In micellar systems, the solvatochromic response of a probe reflects the nature of its microenvironment and is dependent on the relative solubility of the sensor in the aqueous or the organic pseudophases, or in the micellar interphase. 

In testing the steam distillation properties of solvent mixtures a Dean and Stark still head is very useful. 

Numerous experimental data exist in the literature on flic solubility of organic solutes, including both drugs and environmental pollutants, in various mixtures of water and cosolvents. Experimental observations are often illustrated by plotting the logarithm of solubility of the solute versus the volume fraction of cosolvent in the solvent mixture. A few examples of solubilization curves are shown in Figure 14.21.2.1, which shows three typical situations for solutes of different hydrophobicity in the mixture of water and ethanol. 

A more intricate solvent effect must be taken into account in complex formation reactions in solvent mixtures. A particularly complicated correlation is to be expected between the reaction rate and the composition of the solvent in systems where both components of the solvent mixture are capable of coordinating to the central ion. 

Flash point values quoted in the literature, in general, are for pure solvents. The presence of contaminants can have a significant effect on the flash point, particularly if the contaminant is relatively more volatile. For example, pure ethylene glycol has a flash point of 111°C. However, the flash point is reduced to 29°C when acetaldehyde at a level of only 2% is present. Similarly, when handling solvent mixtures, a small change in the composition can have a significant effect on the flash point. Thus, whenever possible, flash points should be measured when it is known or suspected that more than one component will be present. 

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