Solvents power

CH3)2N]3P0. M.p. 4°C, b.p. 232"C, dielectric constant 30 at 25 C. Can be prepared from dimethylamine and phosphorus oxychloride. Used as an aprotic solvent, similar to liquid ammonia in solvent power but easier to handle. Solvent for organolithium compounds, Grignard reagents and the metals lithium, sodium and potassium (the latter metals give blue solutions). 

Solvent power characterizes the miscibility of solute and solvent. This concept covers two types of uses dissolving a solid or reducing the viscosity of a liquid. The solvent power should be as high as possible. However, a solvent used as an extractant should also be selective, i.e., extract certain substances preferentially from the feed being treated. 

There are several criteria used to define solvent power. Chemical analysis is ideal because it can indicate the proportion of hydrocarbons known to be good solvents in particular, the aromatics. 

The aromatic extracts are black materials, composed essentially of condensed polynuclear aromatics and of heterocyclic nitrogen and/or sulfur compounds. Because of this highly aromatic structure, the extracts have good solvent power. 

The aromaUc extracts are sought mainly tor their solvent power. They are characterized particularly by componential analyses such as the separation according to hydrocarbon family by liquid phase chromatography. 

The most desirable characteristics of a solvent for recrystalhsation are (a) a high solvent power for the substance to be purified at elevated temperatures and a comparatively low solvent power at the laboratory temperature or below (6) it should dissolve the impurities readily or to only a very small extent (c) it should yield well-formed crystals of the purified compound and (d) it must be capable of easy removal from the crystals of the purified compound, i.e., possess a relatively low boiling point. It is assumed, of course, that the solvent does not react chemically with the substance to be purified. If two or more solvents appear to be equally suitable for the recrystallisation, the final selection will depend upon such factors as ease of manipulation, inflammability and cost. 

Tetrachloroethane is a good solvent for many compounds which dissolve only slightly in the common solvents it is, however, inferior in solvent power to nitrobenzene, but, on the other hand, it does not possess oxidising properties at the boiling point. 

Extraction of hemiceUulose is a complex process that alters or degrades hemiceUulose in some manner (11,138). Alkaline reagents that break hydrogen bonds are the most effective solvents but they de-estetify and initiate -elimination reactions. Polar solvents such as DMSO and dimethylformamide are more specific and are used to extract partiaUy acetylated polymers from milled wood or holoceUulose (11,139). Solvent mixtures of increasing solvent power are employed in a sequential manner (138) and advantage is taken of the different behavior of various alkaUes and alkaline complexes under different experimental conditions of extraction, concentration, and temperature (4,140). Some sequences for these elaborate extraction schemes have been summarized (138,139) and an experimenter should optimize them for the material involved and the desired end product (102). 

Examples of polar organic solvents that dissolve HPC are methanol, ethanol, propylene glycol, and chloroform. There is no tendency for HPC to precipitate as the temperature is raised. In fact, elevated temperatures improve the solvent power of organic Uquids. 

The acetates of most alcohols are also commercially available and have diverse uses. Because of their high solvent power, ethyl, isopropyl, butyl, isobutyl, amyl, and isoamyl acetates are used in ceUulose nitrate and other lacquer-type coatings (see Cellulose, esters). Butyl and hexyl acetates are exceUent solvents for polyurethane coating systems (see Coatings Urethane polymers). Ethyl, isobutyl, amyl, and isoamyl acetates are frequentiy used as components in flavoring (see Flavors and spices), and isopropyl, benzyl, octyl, geranyl, linalyl, and methyl acetates are important additives in perfumes (qv). 

Compared with ethyl acetate and isopropyl acetate, propyl acetate has slow evaporation rate and good solvent power which promote improved flow and leveling characteristics in a variety of coating formulations. 

Black, viscous residuum direc tly from the still at 410 K (390°F) or higher serves as fuel in nearby furnaces or may be cooled and blended to make commercial fuels. Diluted with 5 to 20 percent distillate, the blend is No. 6 fuel oil. With 20 to 50 percent distillate, it becomes No. 4 and No. 5 fuel oils for commercial use, as in schools and apartment houses. Distillate-residual blends also serve as diesel fuel in large stationaiy and marine engines. However, distillates with inadequate solvent power will precipitate asphaltenes and other high-molecular-... 

Since a knowledge of a solubility parameter of polymers and liquids is of value in assessing solubility and solvent power it is important that this may be easily assessed. A number of methods have been reviewed by BurrelP and of these two are of particular use. 

Lube oil extraction plants often use phenol as solvent. Phenol is used because of its solvent power with a wide range of feed stocks and its ease of recovery. Phenol preferentially dissolves aromatic-type hydrocarbons from the feed stock and improves its oxidation stability and to some extent its color. Phenol extraction can be used over the entire viscosity range of lube distillates and deasphalted oils. The phenol solvent extraction separation is primarily by molecular type or composition. In order to accomplish a separation by solvent extraction, it is necessary that two liquid phases be present. In phenol solvent extraction of lubricating oils these two phases are an oil-rich phase and a phenol-rich phase. Tne oil-rich phase or raffinate solution consists of the "treated" oil from which undesirable naphthenic and aromatic components have been removed plus some dissolved phenol. The phenol-rich phase or extract solution consists mainly of the bulk of the phenol plus the undesirable components removed from the oil feed. The oil materials remaining... 

L se-gef s, n. dissolving vessel, -geschwiadig-keit, /. rate of dissolving, -kraft, /. solvent power. 

Alcohols it has been found that determinations of salts of organic acids and especially of soaps are best carried out in solvent mixtures of glycols and alcohols or of glycols and hydrocarbons. The most common combinations of this type are ethylene glycol (dihydroxyethane) with propan-2-ol or butan-l-ol. The combinations provide admirable solvent power for both the polar and non-polar ends of the molecule. Another suitable solvent mixture is methanol and benzene. 

Supercritical fluids (SCFs) have densities similar to those of liquids and a solvent power higher than that of gases, so that compounds which are insoluble in a fluid in ambient conditions become soluble in fluids under supercritical conditions [75]. 

Solvent power (W) time (min) ratio cisitrans yield (%)... 

Dichloromethane (DC 9.10) is one of the most suitable solvent for ortho-bromination because of its easy handling, and high solvent power for NBS. 

Water forms hydrogen-bonded clusters with itself and with other proton donors or acceptors. Hydrogen bonds account for the surface tension, viscosity, liquid state at room temperature, and solvent power of water. 

The exponent a is a function of solvent power usually a > 1/2, but for an idealized random-flight polymer, a = 1/2. 

Simha [53] made the first attempts to model the transition from a dilute to a concentrated solution. He assumed that in the range from lscaling laws a theory has been developed which allows for the prediction of the influence of Mw c and the solvent power on the screening length [54,55]. This theory is founded on the presumption that above a critical concentration, c, the coils overlap and interpenetrate. Furthermore it is assumed that in a thermody-... 

The constant K is a function of the solvent power and increases with improving solvent quality. Furthermore c has been shown to be a constant for a given polymer [56]. 

The explanation for this is that with increasing solvent power intermolecular repulsion becomes decisive. Enhancement of the polymer concentration leads therefore to coil shrinkage [64], whereas in the limiting case of a 0-solvent no concentration-induced shrinkage is to be expected. Raising c further leads to a critical concentration, c, at which the coils begin to overlap and interpenetrate. 

The range of semi-dilute network solutions is characterised by (1) polymer-polymer interactions which lead to a coil shrinkage (2) each blob acts as individual unit with both hydrodynamic and excluded volume effects and (3) for blobs in the same chain all interactions are screened out (the word blob denotes the portion of chain between two entanglements points). In this concentration range the flow characteristics and therefore also the relaxation time behaviour are not solely governed by the molar mass of the sample and its concentration, but also by the thermodynamic quality of the solvent. This leads to a shift factor, hm°d, is a function of the molar mass, concentration and solvent power. 

Below a critical concentration, c, in a thermodynamically good solvent, r 0 can be standardised against the overlap parameter c [r)]. However, for c>c, and in the case of a 0-solvent for parameter c-[r ]>0.7, r 0 is a function of the Bueche parameter, cMw The critical concentration c is found to be Mw and solvent independent, as predicted by Graessley. In the case of semi-dilute polymer solutions the relaxation time and slope in the linear region of the flow are found to be strongly influenced by the nature of polymer-solvent interactions. Taking this into account, it is possible to predict the shear viscosity and the critical shear rate at which shear-induced degradation occurs as a function of Mw c and the solvent power. 

Conventional methods of polymer extraction use large quantities of solvents as in shake-flask extraction or a Soxhlet extraction apparatus. For all classical extraction methods, solvent selectivity, in general, is low, i.e. solvents with high capacity tend to have low selectivity. In reflux extractions, which are still quite popular in polymer applications, the polymer is refluxed with a hot solvent, which disperses it to provide a solvent phase containing additives. In these conditions solvents are at their atmospheric boiling point. These methods are lengthy and labour intensive. Fractional extraction is based on solvents with increasing solvent power (cf. also [81]). 

Principles and Characteristics Fractional solution procedures usually consist of consecutive extractions with solvents of increasing solvent power. These labour intensive methods benefit from a larger surface area to mass ratio. Other methods for fractionation by solubility rely on fractional precipitation through addition of a nonsolvent, lowering the temperature or solvent volatilisation (Section 3.7). 

Limited) manipulation of selectivity (variation of SF solvent power)... 

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