EPA solvents

An analogous empirical quantity for characterizing the electrophilic properties of EPA solvents has been derived by Gutmann and coworkers from the P NMR chemical shifts produced by the electrophilic actions of acceptor solvents A in triethylphos-phane oxide, according to Eq. (2-11) (cf. also Section 7.4) [70, 199, 207, 213],... 

Using the neutral Fe(II) complex [Fe(phen)2(CN)2], the different Lewis acidities of EPA solvents can easily be visualized by its colour change solutions of this Fe(II) complex are blue in HMPT, violet in dichloromethane, red in ethanol, and yellow in trifluoroacetic acid [204],... 

Table 2-5. Acceptor numbers (acceptivities) AN [70, 213, 339] of forty-eight organic EPA solvents, determined P-NMR spectroscopically at 25 °C.

The ionization of an ionogen can therefore be regarded as a coordinative interaction between substrate and solvent [281]. The polarization of the covalent bond to be ionized can occur via a nucleophilic attack of the EPD solvent on the electropositive end of the bond, or by an electrophilic attack of an EPA solvent on the electronegative end. Both attacks can, of course, also occur simultaneously. The following examples are illustrative. 

In EPD solvents, ionization depends on the stabilization of the eation through eoordination and, in some solvents, on solvation of the anions as well. In EPA solvents, the anion is stabilized through eoordination and, to a lesser extent, additional solvation of the cation may occur. 

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. 

A detailed discussion and comparison of all these and further solvent softness scales can be found in references [173, 238, 239]. For other Lewis acid/base parameters of EPD and EPA solvents, derived from calorimetric measurements [e.g. Gutmann s donor and acceptor numbers), see reference [65] and Section 2.2.6. 

Sections 2.2.6 and 2.6 dealt with Lewis acid/base equilibria in which principally the solvent itself is involved in the chemical reaction, either as a Lewis acid (EPA solvents) or as a Lewis base (EPD solvents). This Section includes some examples of solvent-dependent Lewis acid/base equilibria in which the solvent is not directly involved as the reaction partner, but as the surrounding and interacting medium. 

In solution, ions are produced by the heterolysis of covalent bonds in ionogens. This ionization reaction is favored by solvents due to their cooperative EPD and EPA properties (c/ Section 2.6). In the gas phase, however, ionization of neutral molecules to form free ions is rarely observed because this reaction is very endothermic. For example, in order to ionize gaseous H—Cl into H and Cl , an energy of 1393 kJ/mol (333 kcal/ mol) must be provided. This considerably exceeds the 428 kJ/mol (102 kcal/mol) needed to homolytically cleave H—Cl into hydrogen and chlorine atoms. Thus, for the creation of isolated ions in the gas phase, energy must be supplied by some means other than solvation with EPD/EPA solvents. The most widely used method is ionization by elec-... 

Likewise the different behavior of HCIO4 and (CeH5)3C0H in water and sulfuric acid cannot be explained by simple electrostatic models (25) as both solvents have nearly the same dielectric constant. Perchloric acid, which has pronounced EPA properties, is completely ionized in the EPD solvent, water, but it remains essentially unionized in the strong EPA solvent, sulfuric acid. Triphenylcarbinol, on the other hand, reacts quantitatively with the strong EPA solvent, H2SO4, but no interaction occurs with the strong EPD solvent, water. 

In Fig. 12 (curves 1 and 2) the double peaked absorption maximum, 520 and 560 m a is shown, characteristic of the positive ion-radical of dimethyl-p-phenylene diamine (MejN—Ph—NHa)t (77), which was here obtained by adsorption of the vapor under high vacuum conditions (27, 78). The same interpretation is given to the absorption maximum 850 m/a for benzidine vapor, adsorbed on silica-alumina gel (curves 3 and 4), which does not appear on silica gel. The band of the benzidine ion-radical, obtained by photoionization in the rigid EPA solvent at - 180°C is situated at 885 m/x (76). The accompanying bands 760 and 450 seem to be intimately connected with that at 850 m/a. 

Tetrahydrofurfuryl alcohol is a solvent and coupling agent for a phosphate-type insecticide used to control the gypsy moth. Esters of tetrahydrofurfuryl alcohol are used in preparations employed as insect repeUents. Tetrahydrofurfuryl alcohol is also used as a solvent—carrier for an EPA-approved paper sHmicide formulation. In this appHcation, the exceptional solvent action of tetrahydrofurfuryl alcohol prevents separation of the... 

The 1990 Clean Air Act Amendments Hst 189 hazardous air pollutants (HAPs) that the EPA must regulate to enforce maximum achievable control technology (MACT) to standards which are to be set by the year 2000. The 33/50 project calls for reduction of emissions of 17 specified solvents to predetermined levels by 1995. The SARA statute provides a mechanism by which the community can be informed of the existence, quantities, and releases of toxic chemicals, and requires that anyone releasing specific toxic chemicals above a threshold level to annually submit a toxic chemical release form to the EPA. The status of various ketones under these regulations is shown in Table 4. 

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. 

U.S. EPA, Resources Conservation Company B.E.S.T Solvent Extraction Technology Applications Analysis Report, EPA/540/AR-92/079 (1993). 

U.S. EPA, Project Summary Temoval ofPCBs from Contaminated Soil Using the CF Systems Solvent Extraction Process Treatability Study, EPA/540/SR-95/505, Cincinnati, Ohio, 1995. 

In 1966, the Los Angeles Air Pollution Control Board designated trichloroethylene as a photochemically reactive solvent that decomposes in the lower atmosphere, contributing to air pollution. In 1970 all states were requited to submit pollution control plans to EPA to meet national air quaUty standards. These plans, known as State Implementation Plans (SIPS), controlled trichloroethylene as a volatile organic compound (VOC). They were designed to have each state achieve the National Ambient Air QuaUty Standard (NAAQS) for ozone. The regulations were estabUshed to control the emission of precursors for ozone, of which trichloroethylene is one. 

Control Technique Guidelines (CTG) EPA documents designed to assist state and local pollution authorities to achieve and maintain air quality standards for certain sources (e.g., organic emissions from solvent metal cleaning known as degreasing) through reasonably available control technologies (RACT). 

AC filtration does remove some organic chemicals that can be harmful if present in quantities above the EPA Health Advisory Level (HAL). Included in this category are trihalomethanes (THM), pesticides, industrial solvents (halogenated... 

European Photochemistry Association (EPA), 264 European Solvents hidustry Group (ESIG), See European Chemical Industry Council (CEFIC), 257 EVIK , ametryn, 67 Exaxol Chemical Corporation, 227 EXCEDRIN , asphm, 67 Excel hidustries Ltd., 171 EXOLIT , ammonium phosphates, 67 Expro Chemical Products hic., 148 EXTRAZINE , cyanazm, 67 Exxon Mobil Chemical Company, 227, 228 Exxon Mobil Coal Minerals Company, 227, 228 Exxon Mobil Corporation, 228... 

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