Acetone, solvent variation

Solvent effects on relative rate constants are also usually small. When a heteroaromatic compound quaternizes at more than one site, for example, the product ratio can be insensitive to solvent variations. A constant isomer ratio is recorded for methylation (Mel) of 3-/erf-butyl-6-dimethylaminopyridazine (10), in hexane, benzene, carbon tetrachloride, acetone, and acetonitrile, but not in dimethoxyethane or tetrahydrofuran. The suggestion was made that Mel may have reacted with the last two ether solvents to give an oxonium ion. Since the identity of the quaternizing agent changes, the product ratio varies as well.13... 

A considerable amount of work has been done on the hydroformylation of alkyl acrylates. The formation of y-oxobutyrates has previously been reported (15). Iwanaga (70) studied the effect of solvent variation and found that the rate of hydroformylation was in the order alcohols > acetone > toluene. Pyridine and some of its homologs also increased the rate of reaction. At higher temperatures and pressures, lactones were formed (32, 35, 135), presumably by reduction of the Oxo ester to the hydroxy ester followed by ring closure with elimination of alcohol. 

The acid-catalyzed hydrolyses of the axial and equatorial anomers 61 and 62 were studied in aqueous HCI/acetone solvent mixtures maintained at constant temperature in a water bath. The dependence of on acid concentration and temperature was measured because the conclusions are justified mily if the anomers show similar variations in rate with changes in the catalyzing acid and temperature. 

The effect of the nature of various di-imine ligands in reactivity has been studied for reaction with hydroxide and with cyanide. In the latter investigation the effects of ligand denticity were probed by employing a series of SchiflF-base ligands with denticities between two and six. Kinetic parameters for the reaction of the [Fe(5-Br-phen)3] + cation with cyanide in aqueous solution have been reported kinetics of reactions of di-imine-iron(ii) complexes with cyanide have also been studied in ethylene carbonate- and propylene carbonate-water mixtures. Effects of solvent variation on reactivity have been dissected into initial-state and transition-state components for the reaction of [Fe(phen)3] + with hydroxide in methanol- and in acetone-water mixtures (cf. p. 294). 

Several years ago we reported(l) that the reduction potential,s E, for several iron(III) dithiocarbamates in acetone-water mixtures was markedly dependent with solvent variations at least as great as 0.3 V between E values for an iron(III) dithiocarbamate in acetone and in water. We interpreted these results by considering, in a simple way, the interaction of a polar molecule in the solvent with the iron(III) dithiocarbamate. 

Rates of aquation of [Co(NH3)5Br], and of its chromium(III) analog, have been determined in methanol-, ethanol-, isopropanol-, and r-butyl-alco-hol-water mixtures at various temperatures. The well-known compensation effect is apparent for all these cosolvents. In the aqueous methanol and aqueous ethanol series of solvent mixtures there is correlation of rate constants with solvent ionising power. A correlation of rate constants with solvent polarity was established in a much more limited investigation of aquation of a-cis-[Co(edda)(OH2)Cl], studied in water and in 20% methanol, ethanol, and acetone. The variation of rate constants, and of the activation parameters and A5, with solvent composition was claimed to indicate an mechanism. 

The excited state energies of triplet ketones are solvent polarity dependent. In the case of acetone, the variation from polar (79.4 kcal/mol) to non-polar solvents (78.9 kcal/mol) is only 0. 5 kcal/ mol. Please see Reference 23. 

A variation of this procedure is simply to precipitate the material in a microcrystalline form from solution in one solvent at room temperature, by adding a little more of the second solvent, filtering off the crystals, adding a little more of the second solvent and repeating the process. This ensures, at least in the first or last precipitation, a material which contains as little as possible of the impurities, which may also be precipitated in this way. With salts, the first solvent is commonly water, and the second solvent is alcohol or acetone. 

There will usually not be much variation observed in fluorine chemical shifts for the three most common solvents used for obtaining NMR spectra, that is CDC13, DMSO-d6, and acetone-, as can be seen in the data presented in Table 2.3 for spectra of a series of typical fluorine-containing compounds in various solvent. The variation in fluorine chemicals shifts for these three solvents is no more than 1 ppm. Thus, in reporting chemical shifts in this book, no mention of specific solvent will be made, although the vast majority of spectra will have been measured in CDC13. 

We shall discuss now the variation of the three main thermodynamic functions with solvent composition for the case of n-Bu4NBr-water-acetone system and shall extend this discussion to the n-Bu4NBr-water-THF system. Figure 4 and Table IV present the results obtained. The figure was constructed as follows first the standard enthalpy of transfer AH°t, obtained by Ahluwalia and co-workers (12) from pure water to Z2 = 0.30, was used in order to get the standard entropy of transfer function from the relation ... 

This, although correctly predicting the direction of the variation in apparent order in solvent for benzoyl chloride hydrolysis at 25°C in changing from 2.9 (2-5% water/dioxan) to 1.15 (5-15% water/acetone) does not do so unambiguously. The unified mechanism of Minato is, nevertheless, a very valuable contribution and may be preferred on the grounds that it uses the hydrated carbonium ion rather than the acylium ion, a species which although undoubtedly known, has never, to the knowledge of the present author, been detected in the media used for hydrolysis. However, there is still no evidence to decide between the mechanism of Minato and a combination of routes (a) or (6), and (d) (p. 227). 

However, dielectric constant cannot be a decisive factor in determining the variation in solvolysis rate with solvent composition. If the amount of acetone in ethanol is increased from 0 to 50%, the dielectric constant changes from about 25 to 21 and remains practically constant at this value although the rate of ethanolysis of benzoyl chloride decreases as the 1.56 second power of... 

Rutin extraction from buckwheat was optimally performed using between 50% and 60% ethanol with a 3-hr maceration (Kreft et al., 1999). Repeating the extraction two times was sufficient to extract most of the rutin. Lie et al. (2000) demonstrated the optimization of influencing factors such as extraction temperatures, extraction times, and solvent concentrations in a conventional extraction of dry powdered material of Hypericum perforatum. Applied extraction conditions caused variations to favor different components in the mixture. Higher extraction efficiency was achieved with moderately polar solvents to extract flavonoids such as rutin, isoquercitrin, and quercetin. The optimum extraction conditions for dry Hypericum perforatum leaf powder were determined as 44% to 69% ethanol in acetone with a 5.3- to 5.9-hr maceration at 55°C. 

Another important feature is the solvent. For example, in dry organic solvents like acetone, methanol, acetonitrile or methylene chloride la was not oxidized by potassium permanganate within 24 h. If a small amount of water (pH 4.1) was added to the reaction mixture, the oxidation took place. Figure 1 shows the variation of the yield of 2a and 4a as... 

The four systems were simulated at T — 298K and were consisted of one /3-carotene molecule and 900 solvent molecules in a rectangular box with linear dimensions, which correspond to the solvent densities[49]. The solvent density, the box size, the dielectric constant and the normalized E Reichardt polarity [1] are shown in table 1. Note the variation of the dielectric constants of the selected solvents. These solvents also exhibit large variations of the normalized solvent polarity, changing from 0.006 (isopentane) to 0.762 (methanol) with the intermediate values of 0.355 (acetone) and 0.460 (acetonitrile)[42], The intermolecular interactions were described by the Lennard-Jones plus... 

Alkyl, halo, and the other substituents exhibiting a modest influence on the rate of solvolysis of the tertiary chloride were examined under the standard conditions selected as 90% aqueous acetone at 25° (Brown et al., 1957a Brown et al., 1957b). The extension of the study to highly activating and deactivating substituents required the use of special procedures for the estimation of rate data under the standard conditions. It was convenient in most instances to determine the activation parameters at suitable temperatures and calculate the rate at 25°. For more extreme variations in reactivity, as with p-methoxy- and p-nitro-phenyldimethylcarbinyl chloride, both the temperature and composition of the solvent were modified (Okamoto and Brown, 1957b). These... 

Nevertheless, the demonstrated variations in solvolytic reactivity made a study of solvent effects mandatory. The solvolysis of eighteen substituted phenyldimethylcarbinyl chlorides was examined in two or more solvents (Okamoto et al., 1958). Anhydrous methanol, ethanol, and propan-2-ol were employed in addition to 90% aqueous acetone. The results presented in terms of the a—constants are summarized in Table 21. 

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