Additives/cosolvents

For reactants (sohd or liquid), which are not sufficiently soluble in water, additional cosolvents can be used in order to obtain a homogeneous solution. Examples are alcohols, such as ethanol or 2-propanol,... 

Figure 75 shows the dependence of the normalized SET on the concentration of different additives/ cosolvents in a baseline electrolyte 1.0 M LiPEe/EC/ EMC (1 1). Apparently, the flammability decreases steadily with the concentration of TMP, TEP, and HMPN, but even in high concentrations, they fail to render the electrolytes completely nonflammable. 

The solubilizing capacity of the choline residue is so pronounced that even substrates combining two hydrophobic amino acids are homogeneously soluble in aqueous buffer without any additional cosolvent. These favorable physical properties were also used in the enzymatic formation of peptide bonds. The amino acid choline ester 38 acts as the carboxyl component in kinetically controlled peptide syntheses with the amino acid amides 39 and 40 [52] (Fig. 11). The fully protected peptides 41 and 42 were built up by means of chymotrypsin in good yields. Other proteases like papain accept choline esters as substrates also, and even butyrylcholine esterase itself is able to generate peptides from these electrophiles. 

Additives (cosolvents) w power of Smlj. Allylic ao species, and the proton souro Chiral allenic esters are o organosamarium species der... 

Additives (cosolvents) which serve as ligands have great influence on the reducing power of Smlj. Allylic and propargylic derivatives are reduced via it-allylpalladium species, and the proton source has important effects on the generation of allenes or alkynes. Chiral allenic esters are obtained when pantolactone delivers a proton to racemic organosamarium species derived from 4-phosphato-2-alkynoic esters. ... 

Anacardol, tetrahydro- Cyclogallipharaol EINECS 207-921-9 Hydrocardanol Hydroginkgol 3-Pentadecylphenol 3-n-Pentadecylphenol m-Pentadecylphenol NSC 9781 Phenol, 3-pentadecyl- Phenol, m-pentadecyl- Xetrahydroanacardol. Starting raw material for surfactants, antioxidants, anticorrosives lubricant additive cosolvent for insecticides, germicides resin modifier. Needles, mp = 53.5° bps = 230°, bpi = 190-195° very soluble in MezCO, CeHe, EtOH. Whitecouit. 

As exemplified by the case of oxfenidine, the solubilization approach by cosolvent mixtures appears unattractive for polar substances simply because they are less soluble in nonpolar solvents than in water. Electrolytes are at least partly ionized, and therefore they exhibit pH-dependent solubility in aqueous media, while the fraction of the less water-soluble nonionized species may benefit from cosolvent solubilization as shown in Fig. 37.5. Although the solubility of dexoxadrol hydrochloride (see Chapter 35) in water exceeds that of the free base by more than two orders of magnitude, still an increase can be achieved by additional cosolvent (PEG 300), although the effect is much less pronounced than with the free base. 

In aqueous solutions of surfactants at concentrations above the critical micelle concentration (CMC), the molecules self-assemble to form micelles, vesicles, or other colloidal aggregates. These may vary in size and shape depending on solution conditions. In addition to surfactant molecular structure, the effects of concentration, pH, other additives, cosolvents, temperature, and shear affect the nanostructure of the micelles. The presence of TLMs or cylindrical, rodlike, or wormlike micelles at concentrations > CMCii are generally believed to be necessary for surfactant solutions to be drag reducing [Zakin et al., 2007]. 

In addition, cosolvent machines and this classification system were also discussed at that year s Precision Cleaning Conference as a symposium titled "Cosolvent Machines Symposium " It was publi ed on page 1 of the proceedings of that event. The paper can be downloaded from http/Awvw.p2pays.org/fef/01/00863 pdf. 

Evaporation Retardants. Small molecule solvents that make up the most effective paint removers also have high vapor pressure and evaporate easily, sometimes before the remover has time to penetrate the finish. Low vapor pressure cosolvents are added to help reduce evaporation. The best approach has been to add a low melting point paraffin wax (mp = 46-57° C) to the paint remover formulation. When evaporation occurs the solvent is chilled and the wax is shocked-out forming a film on the surface of the remover that acts as a barrier to evaporation (5,6). The addition of certain esters enhances the effectiveness of the wax film. It is important not to break the wax film with excessive bmshing or scraping until the remover has penetrated and lifted the finish from the substrate. Likewise, it is important that the remover be used at warm temperatures, since at cool temperatures the wax film may not form, or if it does it will be brittle and fracture. Rapid evaporation occurs when the wax film is absent or broken. 

Some hquid defoamers are preemulsified relatives of paste defoamers. In addition to the fatty components mentioned above, kerosene [8008-20-6] or an organic cosolvent such as 2-propanol have been used to enhance stabiUty of the oil—water emulsion and the solubiUty of the defoamer s active ingredients. These cosolvents are used less frequently as concerns increase about volatile organic emissions (VOCs) from the paper machine. Additionally, the use of ultrapure mineral oil in defoamers has become commonplace. Concern about the creation of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDF) in the pulping process has led to the discovery of unchlorinated precursor molecules, especially in recycled mineral oil and other organic cosolvents used in defoamer formulations (28). In 1995 the mineral oil that is used is essentially free of dibenzodioxin and dibenzofuran. In addition, owing to both the concern about these oils and the fluctuating cost of raw materials, the trend in paper machine defoamers is toward water-based defoamers (29). 

Eatty bisamides are used primarily to kicrease sHp, reduce blocking, and reduce static ki polymeric systems. Other specialty appHcations kiclude cosolvents or coupling agents for polyamide reskis, fillers for electrical kisulation coatings, additives for asphalt to reduce cold flow, and synthetic waxes for textile treatments (68). Bisamides have been used ki all the traditional primary amide appHcations to kicrease lubricity and have become the amide of choice because of thek better efficiency. Bisamides have the highest commercial value ki the amide market. 

Humectants and low vapor pressure cosolvents are added to inhibit drying of ink in the no22les. Surfactants or cosolvents that lower surface tension are added to promote absorption of ink vehicle by the paper and to prevent bleed. For improvements in durabiUty, additional materials such as film-forming polymers have been added. Ink developments are providing ink-jet prints with improved lightfastness, waterfastness, and durabiUty. As a result, such prints are beginning to rival the quaUty of electrophotographic prints. 

Dica.rboxyIic AcidMonoesters. Enzymatic synthesis of monoesters of dicarboxyUc acids by hydrolysis of the corresponding diesters is a widely used and thoroughly studied reaction. It is catalyzed by a number of esterases. Upases, and proteases and is usually carried out in an aqueous buffer, pH 6—8 at room temperature. Organic cosolvents may be added to increase solubiUty of the substrates. The pH is maintained at a constant level by the addition of aqueous hydroxide. After one equivalent of base is consumed the monoesters are isolated by conventional means. 

Hydrolysis of esters and amides by enzymes that form acyl enzyme intermediates is similar in mechanism but different in rate-limiting steps. Whereas formation of the acyl enzyme intermediate is a rate-limiting step for amide hydrolysis, it is the deacylation step that determines the rate of ester hydrolysis. This difference allows elimination of the undesirable amidase activity that is responsible for secondary hydrolysis without affecting the rate of synthesis. Addition of an appropriate cosolvent such as acetonitrile, DMF, or dioxane can selectively eliminate undesirable amidase activity (128). 

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. 

Product recoveiy from reversed micellar solutions can often be attained by simple back extrac tion, by contacting with an aqueous solution having salt concentration and pH that disfavors protein solu-bihzation, but this is not always a reliable method. Addition of cosolvents such as ethyl acetate or alcohols can lead to a disruption of the micelles and expulsion of the protein species, but this may also lead to protein denaturation. These additives must be removed by distillation, for example, to enable reconstitution of the micellar phase. Temperature increases can similarly lead to product release as a concentrated aqueous solution. Removal of the water from the reversed micelles by molecular sieves or sihca gel has also been found to cause a precipitation of the protein from the organic phase. 

Aromatic steroids are virtually insoluble in liquid ammonia and a cosolvent must be added to solubilize them or reduction will not occur. Ether, ethylene glycol dimethyl ether, dioxane and tetrahydrofuran have been used and, of these, tetrahydrofuran is the preferred solvent. Although dioxane is often a better solvent for steroids at room temperature, it freezes at 12° and its solvent effectiveness in ammonia is diminished. Tetrahydrofuran is infinitely miscible with liquid ammonia, but the addition of lithium to a 1 1 mixture causes the separation of two liquid phases, one blue and one colorless, together with the separation of a lithium-ammonia bronze phase. Thus tetrahydrofuran and lithium depress the solubilities of each other in ammonia. A tetrahydrofuran-ammonia mixture containing much over 50 % of tetrahydrofuran does not become blue when lithium is added. In general, a 1 1 ratio of ammonia to organic solvents represents a reasonable compromise between maximum solubility of steroid and dissolution of the metal with ionization. 

In the aqueous biphasic hydroformylation reaction, the site of the reaction has been much discussed (and contested) and is dependent on reaction conditions (temperature, partial pressure of gas, stirring, use of additives) and reaction partners (type of alkene) [35, 36]. It has been suggested that the positive effects of cosolvents indicate that the bulk of the aqueous liquid phase is the reaction site. By contrast, the addition of surfactants or other surface- or micelle-active compounds accelerates the reaction, which apparently indicates that the reaction occurs at the interfacial layer. 

Remarkably, the ketones 16 and 19 lead to an/i-aldoLs when the aldol addition is mediated by the appropriate metal and/or cosolvent (see Section 1.3.4.2.1.2.). 

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