Water tolerance

Methanol is more soluble in aromatic than paraffinic hydrocarbons. Thus varying gasoline compositions can affect fuel blends. At room temperature, the solubiUty of methanol in gasoline is very limited in the presence of water. Generally, cosolvents are added to methanol—gasoline blends to enhance water tolerance. Methanol is practically insoluble in diesel fuel. 

Cellulose ester Shrinking point, °C Mp °C Water tolerance value 50% di 75% di 95% di Density, g/mL Tensile strengtl MPa ... 

The mixture is refluxed until the reaction has proceeded sufficiently. It may then be neutralised and the water formed distilled off, usually under reduced pressure to prevent heat-hardening of the resin. Because of the presence of hydroxymethyl groups the resol has a greater water-tolerance than the novolak. 

For laminating and other purposes the initial product is further heated to about 85°C with continuous stirring. After about 30 minutes, and at regular intervals thereafter, samples of the resin are taken and added to ice-cold water. Diminished water tolerance is indicated when the resin solution becomes cloudy on entering the water. Reaction is then continued until the stage is reached when addition of 3 cm of water will cause 1 cm of resin to become turbid. 

As mentioned above, insulation applied to externally located equipment can be subjected to rain and weather contamination if the outer cladding fails. Insulants with water-repellant, water-tolerant or free-draining properties offer an additional benefit in this type of application. In the structural field insulants used as cavity wall fills must be of those types specially treated and designed for this application. 

For use in lubrication oils Ca salts of isostearyl ether carboxylic acids are described as multifunctional additives to achieve a good water tolerance of the oil and good antiwear characteristics [182]. 

Interest in the aqueous medium spread quickly and many, sometimes surprising, discoveries were made [3]. Today pericyclic [4], condensation [5], oxidation [6] and reduction [7] reactions are routinely carried out in aqueous medium. The recent discovery of water-tolerant Lewis acids such as lanthanide triflates, Bi(OTf)j, Sc(OTf)j and Y(OTf)j has revolutionized organometallic chemistry [5a, 7]. 

In the case of Lewis acids, protic solvents such as water or alcohol can strongly influence their reactivity, cause it to react via an alternative path to the one desired, or even cause decomposition. Recently, rare earth metal triflates were used to develop water tolerant Lewis acids that can be used in many organic reactions. ... 

Rare Earth Metal Trifluoromethanesulfonates as Water-Tolerated Lewis Acid Catiaysts Organic Synthesis," Kobavashi. Synlett, 1994, 679... 

At an industrial scale, the esterification catalyst must fulfill several conditions that may not seem so important at lab-scale. This must be very active and selective as by-products are likely to render the process uneconomical, water-tolerant and stable at relatively high temperatures. In addition, it should be an inexpensive material that is readily available on an industrial scale. In a previous study we investigated metal oxides with strong Bronsted acid sites and high thermal stability. Based on the literature reviews and our previous experimental screening, we focus here on application of metal oxide catalysts based on Zr, Ti, and Sn. 

Pseudo-C3-symmetrical trisoxazoline copper(II) complexes prove to be excellent catalysts in the Friedel-Crafts alkylation of indoles with alkylidene malonates (Eq. 7.13). Water tolerance of chiral catalyst trisoxazoline/Cu(OTf)2 was examined, and it was found that the addition of up to 200 equivalents of water relative to the catalyst in /,vo-butyl... 

Si. rra(pentafluorophenyl)boron was found to be an efficient, air-stable, and water-tolerant Lewis-acid catalyst for the allylation reaction of allylsilanes with aldehydes.167 Sc(OTf)3-catalyzed allylations of hydrates of a-keto aldehydes, glyoxylates and activated aromatic aldehydes with allyltrimethylsilane in H2O-CH3CN were examined. a-Keto and a-ester homoallylic alcohols and aromatic homoallylic alcohols were obtained in good to excellent yields.168 Allylation reactions of carbonyl compounds such as aldehydes and reactive ketones using allyltrimethoxysilane in aqueous media proceeded smoothly in the presence of 5 mol% of a CdF2-terpyridine complex (Eq. 8.71).169... 

Mg. Li and co-worker first reported magnesium-mediated Barbier-Grignard allylation of benzaldehyde in water (Eq. 8.73).172 Recently, a study was completed in which some water-tolerant allylating agents were prepared in situ from allylmagnesium chloride and various metallic salts reacted with aldehydes in THF-FLO to afford the desired homoallylic alcohols.173... 

Recently, water-tolerating Lewis acid has been used to catalyze various Diels-Alder reactions in aqueous media. An important aspect of the Diels-Alder reaction is the use of Lewis acids for the activation of the substrates. While most Lewis acids are decomposed or deactivated in water, Bosnich reported that [Ti(Cp )2(H20)2]2+ is an air-stable, water-tolerant Diels-Alder catalyst.35 A variety of different substrates were subjected to the conditions to give high yields and selectivity (Eq. 12.6). 

Sulphur and water tolerance of perovskite-based catalysts for stationary sources... 

A variety of other transition-metal-based Lewis acids are used in organic transformations. Some of them are water tolerant and promising as sources of highly functionalized Lewis-acid catalysts. 

AGRICULTURAL CROPS Irrigation water, tolerated level AQUATIC LIFE Freshwater organisms Sensitive species, tolerated level <15,000 pg/L 1... 

In the preceding paragraphs the advantages of water in uncatalysed Diels-Alder reactions were outlined. An important question is whether these advantages can be transferred to Lewis acid catalysed reactions as well. Since the majority of Diels-Alder reactants are likely to have a negligible tendency to interact with Lewis acid catalysts in water, this issue was addressed only recently. The first step was the development of water-tolerant catalytic systems for [4 + 2]-cycloadditions, and there are now a few examples of Lewis acid catalysed Diels-Alder reactions that not only tolerate the presence of small amounts of water281-284 but even benefit from it285. An example of a Lewis acid catalysed Diels-Alder reaction carried out in water THF mixture is presented in Scheme 12286. 

In this paragraph it was demonstrated that Lewis acid catalysis can be extended to aqueous media. Although water is likely to alter the complexation step, the use of Lewis acids is not restricted to organic solvents. Most importantly, the advantageous effects of Lewis acid catalysis and water are often additive. Since the development of catalytic systems which are water-tolerant or even benefit from the presence of water is still in its infancy, these results are highly promising and open new avenues for future research. 

Methanol is not miscible with hydrocarbons and separation ensues readily in the presence of small quantities of water, particularly with reduction in temperature. On the other hand, anhydrous ethanol is completely miscible in all proportions with gasoline, although separation may be effected by water addition or by cooling. If water is already present, the water tolerance is higher for ethanol than for methanol, and can be improved by the addition of higher alcohols, such as butanol. Also benzene or acetone can be used. The wear problem is believed to be caused by formic acid attack, when methanol is used or acetic acid attack when ethanol is used. 

The addition of water causes the formation of a coagulated phase of PBT solutions in any of the solvents named above (of course, the amount of water tolerated varies with the solvent, with the PPA solvent being the most tolerant toward water) (4). In very dilute solutions, the water causes enhanced depolarized scattering, interpreted to be the result of the formation of aggregates in which the rodlike chains are in parallel arrays (10). In more concentrated solutions, a gel phase is created (11,12). In either case, the electronic absorption spectra is altered from that characteristic of the protonated chain to that characteristic of the deprotonated, dry polymer (10). In the following we will report observations on this phase transition. 

In 1991, Cottier et al. classified the acid catalysts, known to be active for the production of HMF, in five groups organic acids, inorganic acids, organic and inorganic salts, Lewis acids, and others [60]. As reported in Table 1, heterogeneous catalysts are rarely used for the production of HMF mainly due to the difficulty to design a water-tolerant solid catalyst. 

As in conventional AlCl3-promoted acylations the ketone product forms a strong complex with the chloroaluminate IL. Lanthanide triflates, in particular Sc(OTf)3, have been widely studied as water-tolerant Lewis acids in a variety of transformations, including Friedel-Crafts alkylations and... 

Micellar and pre-micellar solutions of methanol in triolein were studied with three different surfactant systems using 2-octanol as a co-surfactant. Surfactants evaluated by viscosity, conductivity, density, refractive index and particle size data along with polarizing microscopic examinations were bis(2-ethylhexyl) sodium sulfosuccinate, triethylammonium linoleate and tetradecyldimethylammonium linoleate. Data show phase equilibria regions of liquid crystalline phases as well as micellar solutions. All systems were effective for solubilizing methanol in triolein. The order of effectiveness for water tolerance is Tetradecyldimethylammonium linoleate>... 

Figure 11. Bar graph of water tolerances at 298°K for triolein/ surfactant/ methanol (6/3/1) systems where surfactant is a 4/1 molar ratio of 2-octanol to either bis(2-ethylhexyl) sodium sulfosuccinate, triethylammonium linoleate or tetradecyldimethylammonium linoleate.

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