Useful Solvents

Changes in temperature of the sample alter the Boltzmann distribution of spins in the various energy levels in proportion to 1/T, as indicated in Eq. 2.20. For example, a reduction in temperature from 27°C (300 K) to — 60°C causes an increase in signal intensity of 40%. 

Many substances that are vapors at room temperature and atmospheric pressure may be used as NMR solvents in sealed tubes or at reduced temperature. For example, S02 has a vapor pressure of about 3 atm at room temperature and can be easily contained in sealed thin-walled, 5 mm diameter NMR sample tubes. Supercritical fluids are also used as NMR solvents in specialized sample tubes. For NMR studies of nuclei other than hydrogen and carbon, suitable solvents that do not contain the nucleus being studied are usually readily available. Frequently, the use of two or more solvents can provide valuable information on molecular structure, as indicated in Chapter 4. 

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Caution During a sininlation, solvent temperature may increase wh ile th e so In te cools. This is particii larly true of sm all solven t molecules, such as water, that can acquire high translational and rotational energies. In contrast, a macromolecule, such as a peptide, retains most of its kinetic energy in vibrational modes. This problem rem ains un solved, an d this n ote of cau tion is provided to advise you to give special care to simulations using solvent. 

It is important to appreciate clearly the function of solvents in chromatographic adsorption. Whereas in any one analysis only one adsorbent will normally be employed, several solvents may be used. Solvents have a triple role —... 

Diethylene dioxide is a very useful solvent for a variety of organic compounds its action is similar to that of ether but more pronounced. It is miscible with water in all proportions. Dioxan vapour is poisonous. 

The substance is examined in a dilute solution in a solvent. A wide choice of solvents, transparent to ultraviolet radiation, is available. The paraffin hydrocarbons are all suitable, as are the ahphatic alcohols and the chlorinated hydrocarbons, such as chloroform and carbon tetrachloride. The most useful solvents are re-hexane, cycZohexane, chloro-... 

In 1965, the Dubna workers found a longer-lived lawrencium isotope, 256Lr, with a half-life of 35 s. In 1968, Thiorso and associates at Berkeley used a few atoms of this isotope to study the oxidation behavior of lawrencium. Using solvent extraction techniques and working very rapidly, they extracted lawrencium ions from a buffered aqueous solution into an organic solvent — completing each extraction in about 30 s. 

Many substances have more than one ether linkage Two such compounds often used as solvents are the diethers 1 2 dimethoxyethane and 1 4 dioxane Diglyme also a commonly used solvent is a triether... 

Section 16 7 Dialkyl ethers are useful solvents for organic reactions but must be used cautiously due to their tendency to form explosive hydroperoxides by air oxidation in opened bottles... 

Acetic anhydride is a useful solvent in certain nitrations, acetylation of amines and organosulfur compounds for mbber processing, and in pesticides. Though acetic acid is unexceptional as a fungicide, small percentages of anhydride in acetic acid, or in cold water solutions are powerful fungicides and bactericides. There are no reports of this appHcation in commerce. It is possible that anhydride may replace formaldehyde for certain mycocidal apphcations. 

The removal of volatile organic compounds (VOC) from air is most often accompHshed by TSA. Air streams needing treatment can be found in most chemical and manufacturing plants, especially those using solvents. At concentrations from 500 to 15,000 ppm, recovery of the VOC from steam used to regenerate activated carbon adsorbent thermally is economically justified. Concentrations above 15,000 ppm ate typically in the explosive range and... 

Solutions. To dehver a spray, the formulated aerosol product should be as homogeneous as possible. That is, the active ingredients, the solvent, and the propellant should form a solution. Because the widely used halocarbon and hydrocarbon propellants do not always have the desired solubiUty characteristics for all the components in the product concentrate, special formulating techniques using solvents such as alcohols (qv), acetone (qv), and glycols (qv), are employed. 

By convention, the components C and D are assigned so that the ratio exceeds unity. The greater the selectivity, the easier is the separation of C and D using solvents A and B. Selectivity can be defined in terms of mass ratio, mole ratio, or concentration. 

Fig. 18. Diagrammatic representation of copper extraction using solvent extraction (273).

A process developed in Israel (263) uses solvent extraction using a higher alcohol or other solvating solvent. This removes phosphoric acid and some hydrochloric acid from the system driving the equiHbrium of equation 42 to the right. The same principle can be appHed in other salt—acid reactions of the form... 

There are five components to the cost of using a Grignard reagent (/) magnesium metal, (2) the haUde, (J) the solvent, (4) the substrate, and (5) disposal of the by-products. The price of magnesium in mid-1992 was 3.20/kg, having risen from 1.20/kg in 1966 to 1.36/kg in 1970 and 2.90/kg in 1979. Prices for tetrahydrofuran and diethyl ether, the two most commonly used solvents, have also increased (Table 3) in the same period. The cost of the hahde depends on its stmcture, but as a general rule the order of cost is chloride < bromide < iodide. 

Solvents. The most widely used solvent is deionized water primarily because it is cheap and readily available. Other solvents include ethanol, propjdene glycol or butylene glycol, sorbitol, and ethoxylated nonionic surfactants. There is a trend in styling products toward alcohol-free formulas. This may have consumer appeal, but limits the formulator to using water-soluble polymers, and requires additional solvents to solubilize the fragrance and higher levels of preservatives. 

Rotogravure Inks. Since there are no mbber or plastic components in contact with the solvents contained in gravure ink formulations, it is permissible to use solvents such as ketones and aromatic hydrocarbons which cannot be tolerated in flexo inks. This provides the gravure ink formulator with much greater latitude in regard to binder selection. In other respects the compositions generally are similar. 

The alcohols, proprietary denatured ethyl alcohol and isopropyl alcohol, are commonly used for E-type inks. Many E-type inks benefit from the addition of small amounts of ethyl acetate, MEK, or normal propyl acetate to the solvent blends. Aromatic hydrocarbon solvents are used for M-type inks. Polystyrene resins are used to reduce the cost of top lacquers. T-type inks are also reduced with aromatic hydrocarbons. Acryflc resins are used to achieve specific properties for V-type inks. Vehicles containing vinyl chloride and vinyl acetate copolymer resins make up the vinyl ink category. Ketones are commonly used solvents for these inks. 

Emulsives are solutions of toxicant in water-immiscible organic solvents, commonly at 15 ndash 50%, with a few percent of surface-active agent to promote emulsification, wetting, and spreading. The choice of solvent is predicated upon solvency, safety to plants and animals, volatility, flammabiUty, compatibihty, odor, and cost. The most commonly used solvents are kerosene, xylenes and related petroleum fractions, methyl isobutyl ketone, and amyl acetate. Water emulsion sprays from such emulsive concentrates are widely used in plant protection and for household insect control. 

Uses. Diacetone alcohol is a widely used solvent in the coatings industry where it finds appHcation in hot lacquers which require high boiling components, and in bmshing lacquers where its mild odor, blush resistance, and flow-out properties are desired. Diacetone alcohol is also a solvent for nitrocellulose, cellulose acetate, and epoxy resins. 

The second process to finish phthalocyanine, which is more important for P-copper phthalocyanine, involves grinding the dry or aqueous form in a ball mill or a kneader (64). Agents such as sodium chloride, which have to be removed by boiling with water after the grinding, are used. Solvents like aromatic hydrocarbons, xylene, nitrobenzene or chlorobenzene, alcohols, ketones, or esters can be used (1). In the absence of a solvent, the cmde P-phthalocyanine is converted to the a-form (57,65) and has to be treated with a solvent to regain the P-modification. The aggregate stmcture also has an impact on the dispersion behavior of a- and P-copper phthalocyanine pigments (66). 

Effect of Solvents. The most commonly used solvents in poly(amic acid) preparation are dipolar amide solvents such as DMAc and NMP. 

Reaction and Heat-Transfer Solvents. Many industrial production processes use solvents as reaction media. Ethylene and propylene are polymerized in hydrocarbon solvents, which dissolves the gaseous reactant and also removes the heat of reaction. Because the polymer is not soluble in the hydrocarbon solvent, polymer recovery is a simple physical operation. Ethylene oxide production is exothermic and the catalyst-filled reaction tubes are surrounded by hydrocarbon heat-transfer duid. 

A good example of the effect of regulations on wood stains is the issue surrounding methanol (qv). Methanol is the most widely used solvent for wood stains because of its fast-drying properties, low cost, and the solubiHty of dyes in methanol. Because methanol is Hsted by the U.S. EPA as a ha2ardous air poUutant (HAP), and because of the extremely low soHds of wood stains, it is most likely that wood stains such as NGR, body stains, and sap stains will need to be reformulated before the end of the twentieth century. 

Sulfur is insoluble in water but soluble to varying degrees in many organic solvents, such as carbon disulfide, ben2ene, warm aniline, warm carbon tetrachloride, andUquid ammonia (18). Carbon disulfide is the most commonly used solvent for sulfur. 

Polyethers are usually found in both the filtrate and the mycelial fraction, but in high yielding fermentations they are mosdy in the mycelium because of their low water-solubiUty (162). The high lipophilicity of both the free acid and the salt forms of the polyether antibiotics lends these compounds to efficient organic solvent extraction and chromatography (qv) on adsorbents such as siUca gel and alumina. Many of the production procedures utilize the separation of the mycelium followed by extraction using solvents such as methanol or acetone. A number of the polyethers can be readily crystallized, either as the free acid or as the sodium or potassium salt, after only minimal purification. 

The process (Fig. 3) is a countercurrent Hquid-Hquid extraction. The feedstock is introduced near the top of an extraction tower and the Hquid propane near the bottom, using solvent-to-oil ratios from 4 1 to 10 1. The deasphalted oil—propane solution is withdrawn overhead and the asphalt from the bottom, and each is subsequently stripped of propane. 

Separation and Purification. Separation and purification of butadiene from other components is dominated commercially by the extractive distillation process. The most commonly used solvents are acetonitrile and dimethylformarnide. Dimethylacetamide, furfural, and... 

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