Active solvents

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. 

Formulator s Dilemma. The regulatory discussion included a listing of solvents designated as HAP compounds. Emissions of these solvents are to be significantly reduced. For many appHcations this means that less is to be allowed. In a situation where the allowed VOC emission levels are also being reduced, the formulator would like to use the most effective solvents available. In the past, MEK and MIBK were frequently used as active solvents and aromatic hydrocarbons as diluents. These solvents have been popular because they are cost-effective. 

Reformulating to reduce HAP solvents frequently means that solvent blend costs increase. The newer blends are generally not be as effective. For example, many coatings were usually formulated using ketones as the active solvents with aromatic hydrocarbons as diluents. This combination produced the most cost-effective formulations. However, when MEK, MIBK, toluene, and xylene became HAP compounds, less-effective solvents had to be used for reformulation. Esters are the most common ketone replacements, and aUphatic diluents would replace the aromatic hydrocarbons. In this situation, more strong solvent is required compared to the ketone/aromatic formulation and costs increase. The combination of reduced VOC emissions and composition constraints in the form of HAP restrictions have compHcated the formulator s task. 

The laboratory preparation of the Udel-type polymer has been described. Bis-phenol A is mixed with chlorobenzene (solvent) and dimethyl sulphoxide (active solvent) and heated to 60°C to obtain a clear solution. Air is displaced from the system by nitrogen or argon and an aqueous solution of caustic soda added. This results in a two-phase system, one predominantly chlorobenzene the... 

Partial replacement of ethanol by methanol has nearly no effect. In the case of propanol an increase in grafting is visible. This can be attributed to the mixing of higher carbon alcohols, e.g., butanol and isobutanol, with the active solvent methanol, which increases the miscibility of the monomer in these grafting systems and, consequently, increases the penetration of monomer to the active sites on the cellulose chains. 

Lifting may also occur if a paint containing strong solvents (xylol or solvent naphtha, not to mention such active solvents as esters and ketones) is applied (not necessarily by brushing) over a paint which is not resistant to them. The older an oxidising paint film becomes, the more solvent-resistant it will be. Short-oil media and pigment-rich paints are not so prone to lifting. This type of failure is not restricted to oil-base materials it can, for example, also occur with chlorinated rubber paints. 

In general, it may be said that enantiomers have identical properties in a symmetrical environment, but their properties may differ in an unsymmetrical environment. Besides the important differences previously noted, enantiomers may react at different rates with achiral molecules if an optically active catalyst is present they may have different solubilities in an optically active solvent., they may have different indexes of refraction or absorption spectra when examined with circularly polarized light, and so on. In most cases these differences are too small to be useful and are often too small to be measured. 

Optically active oxaziridines are useful reagents for the enantioselective oxidation of olefins 37 39). The following three preparative methods to make this reagent available have been reported enantioselective oxidation of an imine by (-)-peroxycam-phoric acid 37,38), photocyclization of a nitrone which has a chiral substituent39), and photocyclization of a nitrone in an optically active solvent 39). However, an... 

Table 4 Catalysts performance of NaBr- activating solvent-based packages with lead based co-catalyst (0.25 mM Pd, 50 eq. PbO).

After quenching with DzO or Bu OD, analysis of the products from the Grignard reagents formed from PhCHXMe (X = Cl, Br, I) in the optically active solvent -(R)-2-methoxypentane leads to the conclusion that Grignard reagent formation occurs on the Mg surface within a solvent cage by a one-electron transfer mechanism.1... 

The efficiency of fluorous Stille coupling reactions [5 a] is enhanced by use of microwave irradiation (Scheme 8.2). The reaction proceeds in 79% yield after 2 min with DMF as the microwave-active solvent. 

Besides using pure and non-electro-active solvents and chemicals (see Mobile Phase in Chapter 4) for the mobile phase to reduce background current the relationship between working electrode potential and background current must be determined before you can select the optimum working electrode potential for analysis of the substance. 

Some polar monomers such as vinyl chloride, vinyl-acetate and acrylonitrile may be polymerised by this method using an active solvent such as tetrahydrofuran. 

Recently, the first example of chiral solvation of a polysilane was demonstrated dissolution of the inherently optically inactive poly(methylphenylsilyene), PMPS, and poly(hexylmethylsilylene), PHMS, in the optically active solvents (V)-2-methyl-l-propoxybutane and (V)-(2-methylbutoxymethyl)benzene induced the polymer chains to adopt PSS helical conformations as evidenced by (positive-signed) Cotton effects almost coincident with the UV a-a transition at 340 and 305 nm, respectively.332... 

Figure 2. Initial ( (/a) and final ( J/b) state potential-energy contours for the complete (two-mode) active space the abscissa refers to the inner-sphere mode and the ordinate governs the low-frequency active solvent mode. The difference in frequencies leads to a curved reaction path. Equilibrium coordinate values for the reactant ( j/A) and product ( J/b) states are labeled qA and qB, respectively. For the case of qin, qB° - qA° = Aqin°, as given by Eq. 16.

Despite the numerous modelling works on the subject (e.g. Sivaraman et al., 2001 Huang, 2005) and the great interest on the solubility of fullerenes in hydrophilic solvents, in water and in biologically active solvents for the potential application of fullerenes as drugs, none was able to predict that C60 and C70 fullerenes... 

Dimethyl isosorbide (VI) has been prepared in quantitative yield from isosorbide and dimethyl sulphate according to known procedure (1). It is a liquid possessing a low vapor pressure at room temperature and boiling point of 95°C at 0.1 mm Hg. In addition, it also possesses optical activity. It is expected to be a relatively inexpensive solvent (for an optical active solvent with 100% purity of the optical isomer) in comparison to... 

Peng YQ, Song GH (2007) Amino-functionalized ionic liquid as catalytically active solvent for microwave-assisted synthesis of 4H-pyrans. Catal Commun 8 111-114... 

To summarize, the more hydrophobic phenolic compounds are extracted better than the less hydrophobic ones, and the extraction is maximal at pH < pfCg. In general, for all the compounds distribution ratios are relatively high and comparable to those achieved with conventional active solvents like 1-octanol. This may be attributed to the ability of IL s imidazolic proton at Cj to hydrogen bonding and specific solvation of the phenolic molecule. 

Ionic liquids have very low volatilities and are easily recycled. Many of these materials can act as both a solvent and a catalyst depending on their Lewis acidities and other properties. These catalytically active solvents can eliminate the need to use additional catalysts that may be toxic or may produce large amounts of wastes. Reactions in ionic liquids are usually carried out under mild conditions, and the products are often easily removed from the solvent by phase separation or low-pressure distillation from the ionic liquid. 

Despite numerous screening studies, the literature contains little evidence that homogeneous catalyst systems based on metals other than Co, Rh, or Ru have significant activity for catalytic CO reduction. As seen for the known active catalytic systems, however, properties of solvents and additives or promoters can have enormous effects on catalytic activities. Solvents and additives can serve many roles in these catalytic systems. One important function of promoters in the Rh and Ru systems appears to be that of stabilizing metal oxidation states involved in catalytic chemistry. Other... 

---