Solvents chemical constitution

Workers involved in the manufacture or use of trichloroethylene as a metal degreaser or general solvent may constitute a group at risk because of the potential for occupational exposure. Occupational exposure to trichloroethylene may also occur during its use as a chemical intermediate in the production of polyvinyl chloride (McNeill 1979). 

The influence of the chemical constitution as related to solvent and migration resistance opens up a number of options to improve pigment performance ... 

Classification by Chemical Constitution Classification of solvents according to chemical constitntion allows certain qualitative predictions. In general, a compound dissolves far more easily in a solvent possessing related functional groups than in one of a completely different nature (see table 3.11). A proper choice of solvent, based on the knowledge of its chemical reactivity, helps to avoid undesired reactions between solute and solvent. 

Some other classification schemes are provided in a work by Kolthoff (Kolthoff, 1974). It is according to the polarity and is described by the relative permittivity (dielectric constant) e, the dipole moment p (in 10 ° C.m), and the hydrogen-bond donation ability Another suggested classification (Parker, 1969) stresses the acidity and basicity (relative to water) of the solvents. A third one (Chastrette, 1979), stresses the hydrogen-bonding and electron-pair donation abilities, the polarity, and the extent of self-association. A fourth is a chemical constitution scheme (Riddick et al., 1986). The differences among these schemes are mainly semantic ones and are of no real consequence. Marcus presents these clearly (Marcus, 1998). 

Solvent-based recycling processes can separate plastics from other types of waste by selective dissolution. In particular, polymers of different chemical constitution can be separated and also blends of polymers (129). 

Dissolution measurements under the microscope give several results which will be discussed separately. The first and most evident result is the penetration velocity of the solvent into the polymer. In order to judge the influence of the solvent s chemical constitution on the polymer we have chosen a number of phthalic acid esters which differ only in their ester groups and which are well known plasticizers. The polymer was a vinyl chloride-vinyl acetate (87 13) copolymer. The following plasticizers have been tested, (the abbreviations are indicated)... 

Although chemical constitution obviously plays the major role in determining the thermodynamic quality of a solvent, the influence of steric properties on solvent quality remains an open question. In order to answer this question we have plotted our dissolution-measurement-indicator for thermodynamic quality—the gel fraction molecular weight which stands for the size of the molecule (Figure... 

For practical reasons the different solubility can be used as a basis for a classification of solvent dyes, although there is no strict differentiation. Chemical constitution is defined here as a structure which meets the corresponding solvent requirements. 

The features of chemical constitution associated with the special requirement of solvent solubility include a number of chemical groups on the chromophores. Sulfo groups are often absent, and only hydroxy or amine groups are present. There are mostly cationic and neutral and sometimes also anionic azo, 1 2 azo metal-complex, and a few anthraquinone dyes. An example is C.I. Solvent Yellow 21, 18690 [5601-29-6] (22, 1 2 Chrome alsoC.7. Acid Yellow 121). 

The properties of perfume materials are intimately related to their chemical constitution, but the mechanisms whereby chemical structure leads to odor perception involve, in crucial ways, a physical phenomenon the mutual attraction forces between molecules. These forces determine the rate of evaporation of odor materials from solutions or surfaces, they are the basis of fixation and substantivity, they explain why the odor quality of mixtures varies depending upon the solvent or base in which they are incorporated. They are also involved in the very process of odor perception, in the contact between the odorant molecule and the receptor cell. Moreover they are at the heart of distillation, extraction, solubility, and the mechanism of chromatography. In this chapter, we will briefly discuss the physical basis of some of these phenomena, showing also how the attraction forces between molecules are related to their chemical structure. 

Solvents can be classified as EPD or EPA according to their chemical constitution and reaction partners [65]. However, not all solvents come under this classification since e.g. aliphatic hydrocarbons possess neither EPD nor EPA properties. An EPD solvent preferably solvates electron-pair acceptor molecules or ions. The reverse is true for EPA solvents. In this respect, most solute/solvent interactions can be classified as generalized Lewis acid/base reactions. A dipolar solvent molecule will always have an electron-rich or basic site, and an electron-poor or acidic site. Gutmann introduced so-called donor numbers, DN, and acceptor numbers, AN, as quantitative measures of the donor and acceptor strengths [65] cf. Section 2.2.6 and Tables 2-3 and 2-4. Due to their coordinating ability, electron-pair donor and acceptor solvents are, in general, good ionizers cf. Section 2.6. 

The diversity of solvents makes classification very complex and many different ways of classifying solvents have been used. Broadly, solvents may be classified as aqueous, nonaqueous molecular, nonaqueous ionic, and atomic. The ways in which solvents are classified according to their chemical constitution and then according to their physical properties are briefly discussed below. 

Efficient asymmetric catalytic hydrogenation reactions intrinsically generate little waste excess reagents typically are not required and generally few byproducts are formed. In chemical synthesis and manufacturing, solvents often constitute the preponderance of waste that must be disposed of or recovered. This scenario... 

---