Selection of Solvent

As for all polymers, the molecular weight of a lignin sample is a characteristic of isolated lignin molecules and all methods for its determination require that the 

The solvents used for lignins are mainly tetrahydrofuran (Pla and Robert 1974a, 1984), dioxane (Pla 1980), N,N-dimethylformamide (Kim 1985), and 2-methoxyethanol (Piastre 1983, Pla et al. 1986, Dolk et al. 1986). 

The composition of the extraction liquid is very important for the magnitude of the partition coefficient of a solute. Several quantities have been studied to describe solvent properties. Snyder [20,21] grouped the relative selectivity of solvents into solvent selectivity classification groups, each group formed according to proton donating, proton accepting and dipole interaction properties. 

REGRESSION MODELS OF LN P, AND LN Pj FOR TWO CASES USED IN THE VALIDATION OF THE ROBUSTNESS ALGORITHM FOR THE PARTITION COEFFICIENT AND THE SELECTIVITY 

COMPOSITIONS OF THE EXTRACTION LIQUIDS USED FOR THE ALGORITHM VALIDATION EXPERIMENT AND FOR THE MODELLING OF THE EXTRACTION OF A NUMBER OF SULPHONAMIDES 

Solvents used here for a general liquid-liquid extraction method were selected from Snyders solvent selectivity triangle. As extraction liquids have to be composed of mixtures of three solvents which may enter into maximum interaction with the analyte, three solvents had to be selected that represent a wide variety of selective interactions. In addition, the solvents should be sufficiently polar to ensure quantitative extraction. Besides selectivity and polarity requirements, the solvents should also meet a few other criteria, mainly for practical reasons they should not be miscible with water, have low boiling points (for relatively fast evaporation procedures) and have densities sufficiently different from the density of water, for pure solvents as well as for selected binary or ternary mixtures of solvents. 

Solvents selected were similar to the solvents that Glajch et al. [35] used for Normal Phase Liquid Chromatography. Methyl tert- butyl ether (a proton acceptor) was selected instead of ethyl ether, since the former one is less volatile. The other two selected solvents were methylene chloride (dipole interactions) and chloroform (proton donor). These three solvents meet all practical requirements. The polarity P [21] of the solvents is 2.5, 3.1 and 4.1, respectively. The solvents were used in pure form no supporting solvent was used. 

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Selection of solvents. The choice of solvent will naturally depend in the first place upon the solubility relations of the substance. If this is already in solution, for example, as an extract, it is usually evaporated to dryness under reduced pressure and then dissolved in a suitable medium the solution must be dilute since crystallisation in the column must be avoided. The solvents generally employed possess boiling points between 40° and 85°. The most widely used medium is light petroleum (b.p. not above 80°) others are cycZohexane, carbon disulphide, benzene, chloroform, carbon tetrachloride, methylene chloride, ethyl acetate, ethyl alcohol, acetone, ether and acetic acid. 

The selection of solvents for quantitative work is not easy. Nitro-alkanes are sufficiently inert, but nitronium tetrafluoroborate is poorly soluble in them c. 0-3 %). Nitronium salts react rapidly with acetic anhydride, and less rapidly with acetic acid, A, A -dimethylformamide and acetonitrile, although the latter solvent can be used for nitration at low temperatures. Sulpholan was selected as the most suitable solvent ... 

Carboxylic acids are produced in water. Selection of solvents is crucial and the carbonylation of the enol triflate 480 can be carried out in aqueous DMF, and that of the aryl triflate 481 in aqueous DMSO using dppf as a ligand[328,334]. The carbonylation of the enol triflate 482 to form the a, 0. unsaturated acid 483 using dppf as a ligand in aqueous DMF has been applied in the total synthesis of multifunctionalized glycinueclepin[335]. 

The selection of solvents for a given separation depends largely on equiHbrium considerations. Other important factors include cost, ease of solvent... 

Solvent Polarity and Temperature. The dielectric constant and polarizabihty are of Htde predictive value for the selection of solvents relative to polymerization rates and behavior. In spite of the similarity of the dielectric constants of CH2CI2, CH Cl, and C2H C1 these solvents yield quite different isobutylene polymerization rates that decrease in the same order. 

Selection of Solvent When choice is possible, preference is given to liquids with high solubilities for the solute a high solubility reduces the amount of solvent to be circulated. The solvent should be relatively nonvolatile, inexpensive, noncorrosive, stable, nonviscous, nonfoaming, and preferably nonflammable. Since the exit gas normally leaves saturated with solvent, solvent loss can be costly and may present environmental contamination problems. Thus, low-cost solvents may be chosen over more expensive ones of higher solubility or lower volatility. 

Brignole, E. A., Botdni, S., and Gani, R, (1986). A strategy for the design and selection of solvents for separation processes. Fluid Phase Equilibria, 29, 125-132. 

We have already encountered the ir, a, and p quantities. The 8h term is inserted to account for the cavity effect. Equation (8-80) is a 12-parameter equation for which considerable generality is claimed, in that it is said to be applicable to chemical rates and equilibria, spectra, solubilities, partition coefficients, and even biological responses. Usually, of course, by judicious selection of solvents, it is possible to reduce the number of parameters by ensuring that some terms are negligible.An example requiring most of the parameters in Eq. (8-80) is the solvolysis/dehydrohalogenation of r-butyl chloride in 21 HBD and non-HBD solvents, for which this correlation was found ... 

Gani, R., Jimenez-Gonzalez, C., Constable, D.J.C. (2005) Method for Selection of Solvents for Promotion of Organic Reactions. Computers and Chemical Engineering, 29, 1661-1676. 

One of the most important problems of planar chromatography is that of the optimization of solvent systems for the separation of mixtures of different samples. An analyst is interested in obtaining the expected result using a minimum number of experiments. Snyder has introduced a new system for solvent classification that permits a logical selection of solvents both in term of polarity indices (F ) and selectivity parameters (Xj), proving theoretically the validity of such universal solvent systems [18,38,41,42]. 

Restricted selection of solvents (suitable for host polymer and additives and deformulation technique)... 

Selection of Solvents. The extraction yield of a low rank coal (Annesley) has been determined after digestion using a selection of solvents (Table II). The results show large variations in solvent power and, in particular, the high extraction yields obtained with hydrogen donor solvents. It is important to differentiate between the ability of a solvent to prevent polymerisation of the dissolved coal by hydrogen transfer, and its ability to retain the dissolved coal in solution. For example, Tetralin is frequently quoted as an... 

The reaction has been improved to a satisfactory process by modifying the reaction conditions. A remarkable effect of the addition of amines on the reaction was observed (49). For example, the reaction of butadiene (4 moles) and acetic acid (4 moles) in the presence of 2-(N,/V-dimethyl-amino)ethanol (4 moles) using Pd(acac)2 (3 mmoles) and PPh3 (3 mmoles) at 90°C gave complete conversion after 2 hours. The product was found to consist of 8-acetoxy-1,6-octadiene (47) (71%), 3-acetoxy-1,7-octadiene (48) (21%) and 1,3,7-octatriene (16) (8%). Various tertiary amines, such as triethylamine, )V-methylmorpholine, Af,Af,N, N -tetramethyl-1,3-bu-tanediamine, and triethylenediamine, showed the same favorable effect. Other basic salts, such as sodium and potassium acetate, accelerate the reaction, especially at high concentrations (50, 51). The selection of solvents is also important. Arakawa and Miyake found that electron-donating type solvents (e.g., THF and triethylamine) are good solvents... 

Solvents play an important role in organic synthesis. Choice of solvent is important in improving and deciding the chemical process. Selection of solvents should be such that it has minimal effect on the environment. Today chemists are interested in designing solvents which does not pose any risk to human health and the environment. The reason why solvents are of great environmental concern is that... 

Fig. 3.5. Similarities and dissimilarities between the selectivity of solvents, simultaneously taking into consideration each tetrazolium salt. Two-dimensional nonlinear selectivity map. Number of iterations, 547 maximal error, 1.42 X 1CT2. Reprinted with permission from E. Forgacs et al. [85].

Like dissolves like is the basic concept for the selection of solvents in the eluent for liquid chromatography. Controlling the solubility of analytes is the key to success. If the selected solvent or mixture of solvents does not interfere with detection, it is a good eluent. The selection of a suitable solvent for low-wavelength absorption detection and post-column derivatization detection is important to obtain highly sensitive detection. The selection of a volatile solvent is the key for preparative-scale liquid chromatography and for mass spectro-metric detection. 

Both inter- and intramolecular [5 + 2] cycloaddition modes have been utilized in the synthesis of natural products. Successful intermolecular cycloaddition depends on making an appropriate selection of solvent, supporting electrolyte, oxidation potential, and current density. This is nicely illustrated in Schemes 23 to 25. For example, in methanol the controlled potential oxidation of phenol (101) affords a high yield (87%) of (102), the adduct wherein methanol has intercepted the reactive intermediate [51]. In contrast, a constant current electrolysis conducted in acetonitrile rather than methanol, led to an 83% yield of quinone (103). 

The selection of solvents for LLPC is similar to the selection of solvents in liquid-liquid extraction systems. The solid support has little effect upon the selection of the solvent pair, except for the obvious fact that a hydrophilic support for a polar stationary phase requires a hydrophobic... 

In general, the formation of monolayers with silanization reagents requires a precise reaction scheme regarding humidity, the selection of solvents, temperature, and reaction time. Often, not enough consideration is given to these factors. As a result a number of authors concluded that the reproducibility of homogeneous silane-monolayers is insufficient, that their stability in aqueous solution is limited, or that they are prone to the formation of multilayers. 

Table 4.2 summarises a selection of solvent pairs that are sufficiently immiscible to form biphasic mixtures suitable for LLE. Klick used LLE as one step in a method to measure an epoxide degradant of a pharmaceutical [12]. In an application of SEC to environmental analysis, LLE was found to give higher extraction efficiencies than solid-phase extraction (SPE - see below) [29]. 

Recently extensive mechanistic studies of this reaction involving kinetic H NMR were conducted (08JOC1954). Thorough selection of solvents (water, MeOH, CH2CI2, DMSO), catalysts (EtaN, NaHCOs, Na2C03), and conditions allowed selective isolation of iminochromenes 159, 4-dicyanomethylenechromenes 160, as well as bis-chromenes 167 and 168, and to study their mutual conversions (Scheme 61). 

Often the enzyme stability can be improved by using a suitable water-immiscible solvent instead of a water-miscible one. Two-phase systems are obtained with the enzyme and other hydrophilic substances present in the aqueous phase while hydrophobic substrates and products mainly partition to the organic phase (Figure 9.1). Water immiscible solvents often used for enzymatic reactions are hydrocarbons, ethers and esters further details on solvents are found in the section 9.5 Selection of solvents , below. In order for the bioconversion to occur, the substrates must be transferred to the enzyme in the aqueous phase after the reaction hydrophobic... 

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