Solvency

The Kauri-butanol value, used to rate solvency of hydrocarbon solvents, is defined in ASTM Method D 1133 as the volume in milliliters of the hydrocarbon solvent at 25 °C that is required to produce a defined degree of turbidity when titrated into a specified quantity of a standard clear solution of kauri resin in n-butyl alcohol. Kauri-butanol values range from approximately 20 for the weakest hydrocarbon solvents to more than 100 for stronger aromatic solvents. The test is limited to hydrocarbon solvents and is not applicable to oxygenated solvents. As Kauri resin (a natural resin) is no longer easily available, the test has not maintained its acceptance in the industry. Aniline point (or mixed aniline point), another measure of solvency of hydrocarbon solvents, is more accepted. The ani- 

The toluene dilution ratio is used for rating solvency of oxygenated solvents. This test method involves the determination of the volume ratio of toluene to active solvent required to cause precipitation in a standard solution of nitrocellulose. Toluene dilution ratios vary from approximately 6 for very strong solvents to approximately 1.5 for weak solvents. 

All these empirical test methods for arbitrary rating of solvency have the common limitation that they compare the ability of a solvent to keep in solution one solute, namely kauri resin, aniline and nitrocellulose for Kauri-butanol value, aniline point and toluene 

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A different class, in between polymer lattices and polymer solutions, is tliat of microgels, consisting of weakly crosslinked polymer networks. Just as for polymer solutions, small changes in tire solvency conditions may have large... 

In addition to low volatility, the chosen liquid should be a good all-around solvent. Since no one liquid is likely to have the required solvency characteristics, several are in use (Table 4.1). If a mass spectmm cannot be obtained in one solvent, it is useful to try one or more others before deciding that an FAB spectrum cannot be obtained. 

Physical Properties. Tetrahydrofurfuryl alcohol (2-tetrahydrofuranmethanol) [97-99-4] (20) is a colorless, high-boiling liquid with a mild, pleasant odor. It is completely miscible with water and common organic solvents. Tetrahydrofurfuryl alcohol is an excellent solvent, moderately hydrogen-bonded, essentially nontoxic, biodegradable, and has a low photochemical oxidation potential. Most appHcations make use of its high solvency. The more important physical properties of tetrahydrofurfuryl alcohol are Hsted in Table 1. 

Product Concentrate. An aerosol s product concentrate contains the active ingredient and any solvent or filler necessary. Various propellent and valve systems, which must consider the solvency and viscosity of the concentrate—propellent blend, may be used to deUver the product from the aerosol container. Systems can be formulated as solutions, emulsions, dispersions, or pastes. 

Other Fire-Resistant Hydraulic Fluids. Phosphate and more recently polyol esters are marketed as fire-resistant compounds. They are formulated with additives to control wear, oxidation, corrosion, and misting. Seal compatibdity and solvency characteristics of these fluids may be quite different from those of mineral ods. 

Other than fuel, the largest volume appHcation for hexane is in extraction of oil from seeds, eg, soybeans, cottonseed, safflower seed, peanuts, rapeseed, etc. Hexane has been found ideal for these appHcations because of its high solvency for oil, low boiling point, and low cost. Its narrow boiling range minimises losses, and its low benzene content minimises toxicity. These same properties also make hexane a desirable solvent and reaction medium in the manufacture of polyolefins, synthetic mbbers, and some pharmaceuticals. The solvent serves as catalyst carrier and, in some systems, assists in molecular weight regulation by precipitation of the polymer as it reaches a certain molecular size. However, most solution polymerization processes are fairly old it is likely that those processes will be replaced by more efficient nonsolvent processes in time. 

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. 

Typical chemical stmctures and representative sources of different classes of synthetics are given in Table 6. Properties and uses of representative synthetics foUow in Table 7. In addition to considering thek physical properties, selection is needed of appropriate paints, seals, hoses, plastics, and electrical insulation to avoid problems with the pronounced solvency and plasticizing action of many of these synthetic oils. 

The uses of decahydronaphthalene are similar to those of 1,2,3,4-tetrahydronaphthalene. Mixtures of the two are used for certain appHcations where a synergistic solvency effect is noted. 

Mineral spirits, a type of petroleum distillate popular for use in solvent-based house paints, consist mainly of aUphatic hydrocarbons with a trace of aromatics. This type of solvent finds use in oil- and alkyd-based house paints because of its good solvency with typical house paint binders and its relatively slow evaporation rate which imparts good bmshabiUty, open-time, and leveling. Other properties include lower odor, relatively lower cost, as well as safety and health hazard characteristics comparable to most other organic solvents. 

Typical cosolvents include methanol [67-56-17, ethanol [64-17-5] isopropyl alcohol [67-65-OJ, or toluene. The selection of cosolvents depends on the requirement of the formula and their interaction with other ingredients. Methanol is a common cosolvent in methylene chloride formulas since it has good solvency and is needed to swell ceUulose-type thickening agents. A typical methylene chloride formula used to strip wood is as follows (7). 

Uses. l-Methyl-2-pyrrohdinone is a dipolar aprotic solvent. It has a high dielectric constant and is a weak proton acceptor. AH of its commercial uses involve its strong and frequendy selective solvency. It has replaced other solvents of poorer stabiUty, higher vapor pressures, greater dammabiUties, and greater toxicides. 

A number of other N-substituted 2-pyrroHdinones have been offered commercially or promoted as developmental products. These materials offer different and sometimes unique solvency properties. AH are prepared by reaction of butyrolactone with suitable primary amines. Principal examples are Hsted in Table 4. 

Computerized optimization using the three-parameter description of solvent interaction can facihtate the solvent blend formulation process because numerous possibihties can be examined quickly and easily and other properties can also be considered. This approach is based on the premise that solvent blends with the same solvency and other properties have the same performance characteristics. Eor many solutes, the lowest cost-effective solvent blends have solvency that is at the border between adequate and inadequate solvency. In practice, this usually means that a solvent blend should contain the maximum amount of hydrocarbon the solute can tolerate while still remaining soluble. 

Hydrocarbon Solvents. Most hydrocarbon solvents are mixtures. Few commercial hydrocarbon solvents are single compounds. Toluene is an exception. Hydrocarbon solvents are usually purchased and suppHed on specification. The most important specification properties are distillation range, solvency as expressed by aniline cloud poiat and Kauri-Butanol (KB) value, specific gravity, and dash poiat. Composition requirements such as aromatic content and benzene concentration are also important ia many appHcations. 

Solvent Selection. A thorough knowledge of the requkements of each solvent appHcation is necessary to formulate a solvent system successfully and meet all needs at the lowest possible cost. The most important properties are solvency, evaporation rate, flash poiat, and solvent balance. In nearly every appHcation, these properties are important even though the specific requkements differ greatly from one appHcation to another. Each potential solvent has a particular set of properties, and the solvent chosen and the amount of each depend on the specific appHcation requkements. 

In terms of general solvency, solvents may be described as active solvents, latent solvents, or diluents. This differentiation is particularly popular in coatings applications, but the designations are useful for almost any solvent appHcation. Active solvents are strong solvents for the particular solute in the apphcation, and are most commonly ketones or esters. Latent solvents function as active solvents in the presence of a strong active solvent. Alcohols exhibit this effect in nitrocellulose and acryUc resin solutions. Diluents, most often hydrocarbons, are nonsolvents for the solute in the apphcation. 

The specific solvents that make up the three solvency categories depend on the solute in question. For example, an aUphatic hydrocarbon may have adequate solvency for a long oil alkyd, but would be a diluent for an acryUc or vinyl resin, which require stronger solvents such as ketones or esters. The formulator must understand the solvency requirements of the solute to know which category a particular solvent would occupy. 

Agricultural Products. Pesticides are frequendy appHed as emulsiftable concentrates. The active insecticide or herbicide is dissolved in a hydrocarbon solvent which also contains an emulsifier. Hydrocarbon solvent selection is critical for this appHcation. It can seriously impact the efficacy of the formulation. The solvent should have adequate solvency for the pesticide, promote good dispersion when diluted with water, and have a dash point high enough to minimise dammabiUty ha2ards. When used in herbicide formulas, low solvent phytotoxicity is important to avoid crop damage. Hydrocarbon solvents used in post-harvest appHcation require special testing to ensure that polycycHc aromatics are absent. 

Solution polymerization can use various solvents, primarily aUphatic and aromatic hydrocarbons. The choice of solvent is usually dictated by cost, avaHabihty, solvency, toxicity, flammabiUty, and polymer stmcture. SSBR polymerization depends on recovery and reuse of the solvent for economical operation as well as operation under the air-quaUty perrnitting of the local, state, and federal mandates involved. 

Vatty Acids andFattyAcidLsters. Sulfolane exhibits selective solvency for fatty acids and fatty acid esters which depends on the molecular weight and degree of fatty acid unsaturation (40—42). AppHcations for this process are enriching the unsaturation level in animal and vegetable fatty oHs to provide products with better properties for use in paint, synthetic resins, food products, plastics, and soaps. 

H)- and (+)-1imonenes are widely used ia the manufacture of terpene resias. Additionally, a (-)-limonene and (+)- P-pheUandrene mixture from sulfate turpentine has been used to produce terpene resias. (+)-Limoaeae from the citms iadustry coatiauaHy fiads aew uses as a solveat aot only for its solvency properties but also for its orange oil fragrance. 

Dichloroethane [107-06-2] ethylene chloride, ethylene dichloride, CH2CICH2CI, is a colorless, volatile Hquid with a pleasant odor, stable at ordinary temperatures. It is miscible with other chlorinated solvents and soluble in common organic solvents as well as having high solvency for fats, greases, and waxes. It is most commonly used in the production of vinyl chloride monomer. 

Stabili2ed 1,1,1-dichloroethane is stable to normal shipping conditions, and has been shipped in metal and lined dmms, tank tmcks, rail cars, barges, and ships. Care must be taken that the container is free from previously contained material because of the high solvency of 1,1,1-trichloroethane. Shipping containers should also be dry. 

Inhibited grades of 1,1,1-trichloroethane are used in hundreds of different industrial cleaning appHcations. 1,1,1-Trichloroethane is preferred over trichloroethylene or tetrachloroethylene because of its lower toxicity. Additional advantages of 1,1,1-trichloroethane include optimum solvency, good evaporation rate, and no fire or flash point as determined by standard test methods. Common uses include cleaning of electrical equipment, motors, electronic components and instmments, missile hardware, paint masks, photographic film, printed ckcuit boards, and various metal and certain plastic components during manufacture (see Metal surface treatments). 

The principal use of 1,1,2-trichloroethane is as a feedstock intermediate in the production of 1,1-dichloroethylene. 1,1,2-Trichloroethane is also used where its high solvency for chlorinated mbbers, etc, is needed, as a solvent for pharmaceutical preparation, and in the manufacture of electronic components. 

Tetrachloroethane [79-34-5] acetylene tetrachloride, CHCI2CHCI2, is a heavy, nonflammable Hquid with a sweetish odor. It is miscible with the chlorinated solvents and shows high solvency for a number of natural organic materials. It is also a solvent for sulfur and a number of inorganic compounds, eg, sodium sulfite. 

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