Temperature in water

Polymers in Solution. Polyacrylamide is soluble in water at all concentrations, temperatures, and pH values. An extrapolated theta temperature in water is approximately —40° C (17). Insoluble gel fractions are sometimes obtained owing to cross-link formation between chains or to the formation of imide groups along the polymer chains (18). In very dilute solution, polyacrylamide exists as unassociated coils which can have an eUipsoidal or beanlike stmcture (19). Large aggregates of polymer chains have been observed in hydrolyzed polyacrylamides (20) and in copolymers containing a small amount of hydrophobic groups (21). 

Properties. Hydroxypropylcellulose [9004-64-2] (HPC) is a thermoplastic, nonionic cellulose ether that is soluble in water and in many organic solvents. HPC combines organic solvent solubiUty, thermoplasticity, and surface activity with the aqueous thickening and stabilising properties characteristic of other water-soluble ceUulosic polymers described herein. Like the methylceUuloses, HPC exhibits a low critical solution temperature in water. 

The protonation equilibria for nine hydroxamic acids in solutions have been studied pH-potentiometrically via a modified Irving and Rossotti technique. The dissociation constants (p/fa values) of hydroxamic acids and the thermodynamic functions (AG°, AH°, AS°, and 5) for the successive and overall protonation processes of hydroxamic acids have been derived at different temperatures in water and in three different mixtures of water and dioxane (the mole fractions of dioxane were 0.083, 0.174, and 0.33). Titrations were also carried out in water ionic strengths of (0.15, 0.20, and 0.25) mol dm NaNOg, and the resulting dissociation constants are reported. A detailed thermodynamic analysis of the effects of organic solvent (dioxane), temperature, and ionic strength on the protonation processes of hydroxamic acids is presented and discussed to determine the factors which control these processes. 

The major reasons for the beluu ior of vertical temperature in water bodies are the low thermal condnctii ity and the absorption of heat in the first few meters. As tlie surface waters begin to heat, transfer to low er layers is reduced and a stability condition develops. The prediction of thermal behavior in lakes and reser oirs is an important power plant siting consideration and also is a major factor in preienting e.xcessive thermal effects on sensitive ecosystems. Furthermore, the extent of thermal stratification influences the vertical dissolved ox)gen (DO) profiles where reduced DO often results from minimal exchiuige with aerated water. ... 

Franks, F. The Properties of Aqueous Solutions at Subzero Temperatures, in Water — a Comprehensive Treatise, (ed. Franks, F.), Vol. 7, chapter 3, New York, Plenum Press 1982... 

Chloramine-B (CAB, PhS02NClNa) and chloramine-T (CAT, p-Me-C6H4S02NClNa) have also been used for the oxidation of sulphoxides107-115. The required sulphone is produced after initial attack by the sulphoxide sulphur atom on the electrophilic chlorine-containing species, forming a chlorosulphonium intermediate as shown in equation (34). These reactions take place at room temperature, in water and aqueous polar solvents such as alcohols and dioxane, in both acidic and basic media. In alkaline solution the reaction is slow and the rate is considerably enhanced by the use of osmium tetroxide as a catalyst115. 

The first step is a slow ionization of the substrate and is the rate-determining step. The second is a rapid reaction between the intermediate carbocation and the nucleophile. The ionization is always assisted by the solvent, since the energy necessary to break the bond is largely recovered by solvation of R" " and of X. For example, the ionization of f-BuCl to f-Bu" and Cl" in the gas phase without a solvent requires ISOkcalmol" (630kJmol" ). In the absence of a solvent such a process simply would not take place, except at very high temperatures. In water, this... 

Solubility generally decreases with increase in chain size and extent of branching. The solubility of dextran can be divided into four groups — those that are readily soluble at room temperature in water, IMF, DMSO and dilute base those that have difficulty dissolving in water those that are soluble in aqueous solution only in the presence of base and, those that are soluble only under pressure, at high temperatures (> 100°C) and in the presence of base. Dextran B-512 readily dissolves in water and 6M, 2M glycine and 50% glucose aqueous solutions. 

Recently, Pal et al. found that (.S )-prolinol could facilitate the coupling reaction of terminal alkynes with 3-iodoflavone under palladium-copper catalysis in aqueous DMF to give 3-alkynyl substituted flavones of potential biological interest (Eq. 4.17). The coupling of iodobenzene with terminal alkynes at room temperature in water without any cosolvent was completed within 30 minutes, affording the desired product in good yield.36... 

Recently, Li et al. have reported an efficient 1,3-dipolar cycloaddition of azides with electron-deficient alkynes without any catalysts at room temperature in water.128 The reaction has been applied successfully to the coupling of an azido-DNA molecule with electron-deficient alkynes for the formation of [l,2,3]-triazole heterocycle (Eq. 4.66). 

Chiral dienophiles, prepared from an aldehyde and asparagine in water followed by reacting with acryloyl chloride, reacted with cyclopentadiene at room temperature in water or ethanol-water to provide cycloadducts diastereoselectively and chiral products upon separation and hydrolysis (47-64% ee for the endo isomers endo/exo 82 18) (Eq. 12.18).61... 

Fig. 8 Model of the grafting of functional copolymers with PEO for reactions carried out at two different temperatures in water a before grafting, b after grafting, c at room temperature [170]...

So, these reactions cannot lead to effective chain termination in oxidized alcohol. The decomposition of tetroxides depends on pH and apparently proceeds homolytically as well as heterolytically in an aqueous solution. The values of the rate constants (s 1) of tetroxide decomposition at room temperature in water at different pH values are given below [38,39],... 

Figure 5.14 Freeze-etch electron micrograph of glycolipid nanotubes from 24 1 nonhydroxy galactocerebrosides (21) cryofixed from room temperature in water. Bar = 250 nm. Reprinted from Ref. 64 with permission of the Biophysical Society.

The catalytic asymmetric aldol reaction has been applied to the LASC system, which uses copper bis(-dodecyl sulfate) (4b) instead of CufOTf. 1261 An example is shown in Eq. 6. In this case, a Bronsted add, such as lauric add, is necessary to obtain a good yield and enantioseledivity. This example is the first one involving Lewis acid-catalyzed asymmetric aldol reactions in water without using organic solvents. Although the yield and the selectivity are still not yet optimized, it should be noted that this appredable enantioselectivity has been attained at ambient temperature in water. 

The reaction of sodium 1,2,4-octatrienoate occurred at a relatively low temperature in water [169]. 

Sound waves provide a periodic oscillation of pressure and temperature. In water, the pressure perturbation is most important in non-aqueous solution, the temperature effect is paramount. If cu (= 2 nf, where/is the sound frequency in cps) is very much larger than t (t, relaxation time of the chemical system), then the chemical system will have no opportunity to respond to the very high frequency of the sound waves, and will remain sensibly unaffected. 

Under appropriate conditions (acid catalyzed Isomerization In dilute CH2CI2. NH4CI catalysis at room temperature In water), 9 Is the predominate product and can be Isolated as an... 

The effect of the butyl side chains on the LCST s of copolymers of NIPAAM is interesting, especially in the case of the n-butyl copolymer. One hypothesis is that the n-butyl groups associate and precipitate more readily than the less flexible t-butyl groups do. This is consistent with the observation that poly-N-n-propyl acrylamide is insoluble at room temperature in water (3). 

The observed diastereoselectivity in the asymmetric Strecker step via the crystallization-induced asymmetric transformation can be explained as shown in Figure 2. Apparently, the re face addition of CN to the intermediate imine 4 is preferred at room temperature in methanol and results in a dr 65/35. At elevated temperatures in water, the diastereomeric outcome and yield of the process are controlled by the reversible reaction of the amino nitriles 3 to the intermediate imine and by the difference in solubilities of both diastereomers under the applied conditions. . .. 

The optical absorption spectra depend on the solvent. They are red-shifted with the decreasing polarity of the solvents as in EDA, liquid NH3, where they appear at a longer wavelength than in water [49], and blue-shifted in methanol [38]. Moreover, the maximum in NH3 is red-shifted with the increase of temperature. In water, the Ag band is almost unchanged in the range 20-200 °C, while that of Ag2 is markedly shifted to the red [50]. Electron spin echo modulation analysis of Ag in ice or methanol glasses has concluded to a charge transfer character to solvent (CTTS) of the absorption band [51]. 

There is one example of annulation of a pyrimidine ring to a saturated thiophene ring. Ketone 477 is condensed with. J-ethylthiourea HBr at room temperature in water over 18 h. The product is the reduced thienopyrimidine 478 (Equation 179) <1994NN1 B5>. 

The substance is also soluble in concentrated hydrochloric acid, acetone, acetic acid, nitrobenzene, aniline, pyridine, and nitroglycerine, at room temperature. In water its solubility is only 0.08% at 25°C. 

At room temperature in water cycloaddition of (S)-a-acetylvinyl sulfoxide (35) to furanone 36 leads to the formation of the chiral adduct 37 (Scheme 10) (94SC447). 

Normally, ester hydrolysis at ambient temperatures in water at neutral pH will occur very slowly—over a period of many days—unless something is done to accelerate the reaction. Usually, reactions are accelerated by raising the temperature because molecules react more vigorously as the temperature rises. However, a better way to accelerate a reaction is to add a catalyst, that is, a molecule that accelerates the reaction without undergoing any net consumption. Frequently, the main job of the catalyst is to make a potentially reactive center more attractive for reaction, i.e., to potentiate the electrophilic or nucleophilic character of the reactive centers of the reacting species. 

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