Solvation with methanol

For comparison purposes, the proton mobility. Do (for Nafion solvated with water), which is closely related to the self-diffusion coefficient of water, is also plotted. At low degrees of hydration, where only hydrated protons (e.g., H3O+) are mobile, it has a tendency to fall below the water diffusion coefficient (this effect is even more pronounced in other polymers), which may be due to the stiffening of the water structure within the regions that contain excess protons, as discussed in Section 3.1.1. . Interestingly, the proton mobility in Nafion solvated with methanol (Da(MeOH) in Figure 14a) is even lower than the methanol self-diffusion (Z ieon). This may... 

Table IV compares for a series of dienes the yields of 1,2 addition products obtained with Rh(NBD)(dppe)+ as the catalyst precursor under intercalated and homogeneous reaction conditions. The yields of terminal olefins are consistently higher for the intercalated catalyst. The deviation from solution yields are larger when the intercalated catalyst is solvated with methanol than with acetone.0 Methanol swells the interlayers to an average thickness of 12 A, whereas acetone swells the interlayers to w 15 A. Since the more constricted methanol solvated interlayers provide the higher yields of terminal olefins, spacial factors as well as polarization effects induced by the charged silicate sheets may be contributing to the deviations from solution behavior. In this reaction system polarization effects may well be more important than spacial factors in directing hydrogenation transfer because the spacial requirements of the transition states derived from or r 3 allyl intermediates should be very similar.

When the macroporous resin column was used with the same acidic eluent in 100 % methanol, the chromatographic separation was improved considerably. Now the alkali-metal ions are solvated with methanol and the resin matrix is probably coated with a thin layer of methanol, which makes the ions and the resin surface more compatible with one another. 

It may be instructive to consider some examples of solvate formation. The compound 5-methoxysulphadiazine forms 1 1 host-guest solvates with dioxane, chloroform, and tetrahydrofuran [78]. These were prepared by heating to boiling a solution of the sulfonamide in the appropriate solvent, followed by slow cooling to obtain large crystals. Spironolactone forms 1 1 solvates with methanol, ethanol, ethyl acetate, and benzene. It also forms a 2 1 spironolactone-acetonitrile solvate [79,80]. The spironolactone solvates were prepared by crystallization in a refrigerator from solutions that were nearly saturated at room temperature. 

Large concentrations of halide ions, preferably iodide, favour the formation of /ra/i5-stilbene from benzaldehyde and benzyltriphenylphosphonium halides in methanol with methoxide as base, whereas large concentrations of methoxide ions slightly favour formation of the m-isomer. These effects have been explained by the preferential solvation of P+ by halide ions, leading to greater reversibility of betaine formation. Methoxide ions, on the other hand, are preferentially solvated by methanol. 

The solvent can also affect regioselectivity. Consider O- vs C-alkylation of phenoxide ion with allyl chloride or bromide. In water, with allyl chloride the O- to C-alkylation ratio is 49 41 with phenol as a solvent it is 22 78 with methanol, dimethylformamide, and dioxane 100% O-alkylation is achieved. The selective solvation of the more electronegative O by the more protic solvents perhaps leads to some C-alkylations. 

Electrodes of the first kind have only limited application to titration in non-aqueous media a well-known example is the use of a silver electrode in the determination of sulphides and/or mercaptans in petroleum products by titration in methanol-benzene (1 1) with methanolic silver nitrate as titrant. As an indicator electrode of the second kind the antimony pH electrode (or antimony/antimony trioxide electrode) may be mentioned its standard potential value depends on proton solvation in the titration medium chosen cf., the equilibrium reaction on p. 46). 

The physical properties of the anhydrate form and two polymorphic monohydrates of niclosamide have been reported [61], The anhydrate form exhibited the highest solubility in water and the fastest intrinsic dissolution rate, while the two monohydrates exhibited significantly lower aqueous solubilities. In a subsequent study, the 1 1 solvates of niclosamide with methanol, diethyl ether, dimethyl sulfoxide, N,/V -dimethyl formamide, and tetrahydrofuran, and the 2 1 solvate with tetraethylene glycol, were studied [62], The relative stability of the different solvatomorphs was established using desolvation activation energies, solution calorimetry, and aqueous solubilities. It was found that although the nonaqueous solvates exhibited higher solubilities and dissolution rates, they were unstable in aqueous media and rapidly transformed to one of the monohydrates. 

The solvated electron is reactive in alcohols, both with solutes and solvents (Watson and Roy, 1972). With methanol, ethanol, and 1- and 2-propanols, somewhat different rates of e-solvent reactions have been measured by Freeman (1970) and by Baxendale and Wardman (1971). However, the (pseudo-first-order) rates... 

Just as interaction of the negative ion with solvent or with a catalyst can promote the ionization, the same is true of the interactions of the carbonium ion. The triaryl carbonium ions discussed so far should all be colored. Reports of colorless but conducting solutions of triarylmethyl derivatives are fairly common and may represent covalently solvated carbonium ions which are not expected to be colorless. For example, a colored solution of the ion XVI in acetic acid slowly fades when it is diluted with methanol containing enough acid to prevent the formation of any "color base. The fading is attributed to the formation of XVII.m... 

The reactions of the vinylcarbenes 7 and 15 with methanol clearly involve delocalized intermediates. However, the product distributions deviate from those of free (solvated) allyl cations. Competition of the various reaction paths outlined in Scheme 5 could be invoked to explain the results. On the other hand, the effect of charge delocalization in allylic systems may be partially offset by ion pairing. Proton transfer from alcohols to carbenes will give rise to carbocation-alkoxide ion pairs that is, the counterion will be closer to the carbene-derived carbon than to any other site. Unless the paired ions are rapidly separated by solvent molecules, collapse of the ion pair will mimic a concerted O-H insertion reaction. 

Tris-(2-methylquinolin-8-olato)iron(III) has three mer N and three mer O-donor atoms the 0.2 A range of Fe— N bond distances is attributed to small but significant steric effects of the methyl substituents. Solubilities of tris-(quinolin-8-olato)iron(III) complexes in methanol-water mixtures are consistent with the expected more favorable solvation by methanol. ... 

What happens for a nonracemic mixture of enantiomers Is it possible to calculate the values of the chiral properties of the solution from knowledge of the properties of the enantiopure compound In principle, yes, on the condition that there is no autoassociation or aggregation in solution. Then, the observed properties will be simply the weighted combination of the properties of two enantiomers. A nice example of where this normal law may be broken was discovered by Horeau in 1967 it is the nonequivalence between enantiomeric excess (ee) and optical purity (op, with op = [a]exi/[ ]max) for 2,2-methylethyl-succinic acid. In chloroform op is inferior to ee, while in methanol op = ee. This was explained by the formation of diastereomeric aggregates in chloroform, while the solvation by methanol suppresses the autoassociation. 

The salt effect is attributable to the formation of preferential solvation from the standpoint of molecular structure. In other words, when calcium chloride, which dissolves readily in methanol but very little in ethyl acetate, was added to the methanol-ethyl acetate system to saturation, calcium chloride formed with methanol the preferential solvate which may be written CaCl2 6CH30H. It was also shown from the observation of solubility that the solvated methanol molecules did not participate in the vapor-liquid equilibrium. 

Procedures. Sorbent Conditioning. To facilitate partitioning of organics in aqueous solution onto hydrophobic nonpolar sorbents, the sorbents must first be conditioned with methanol to increase their wettability. This solvation of the solid phase is necessary to provide efficient and reproducible extractions. The conditioning process was carried out according to the instructions accompanying tbe extraction columns. 

The data for acid-catalyzed ester formation in cyclohexanol are doubly interesting. The activation parameters are closely similar to those for the acid-catalyzed hydrolysis of the corresponding ethyl esters. The enthalpy of activation is considerably higher than for esterification in methanol this is probably a result of steric inhibition of solvation, as well as non-bonded compression in the transition state, as suggested by the entropies of activation, which are also significantly higher than with methanol, especially for compounds without ortho substituents which presumably have more transition state solvation to lose. 

Rate studies of the reaction between cesium and water in ethylenediamine, using the stopped-flow technique, have been extended to all alkali metals. The earlier rate constant (k — 20 NT1 sec.-1) and, in some cases, a slower second-order process (k — 7 Af"1 sec.-1) have been observed. This is consistent with optical absorption data and agrees with recent results obtained in aqueous pulsed-radiolysis systems. Preliminary studies of the reaction rate of the solvated electron in ethylenediamine with other electron acceptors have been made. The rate constant for the reaction with ethylene-diammonium ions is about 105 NCl sec.-1 Reactions with methanol and with ethanol show rates similar to those with water. In addition, however, the presence of a strongly absorbing intermediate is indicated, which warrants more detailed examination. 

Although the detailed nature of the reactions with methanol and ethanol remains unknown, it is clear from these studies that the reaction rate of solvated electrons with these alcohols is not very different from that with water. Pulse radiolysis studies (24) show minimum halftimes of 1.5 and 3 /xsec. for the disappearance of the electron peak in the pure alcohols but this does not represent reaction of the electron with the alcohol since no attempt was made to remove the counter ion or other radiolysis products. 

For reduction of resin 8, concerns about the possibility of traces of tin by-products contaminating subsequent assays led to the adoption of a different reduction procedure for library production.15 The tagged resins 8 are combined into one pool in a large peptide synthesis vessel, washed with methanol, filtered, and the resin left solvated. Separately, an aqueous solution of 0.5 M aqueous sodium hydrosulfite/0.5 M potassium carbonate is prepared and added to the resin (40ml/g of resin) and then the resin/solu-tion is bubbled with nitrogen at room temperature for 16 h. The resulting resin is washed with water, water/MeOH (1 1), MeOH, MeOH/NMP (1 1), NMP, DCM, MeOH, and ether, then filtered and dried overnight in vacuo prior to the next step. 

The tagged resins are pooled into one large batch in a 2-liter peptide vessel, washed with methanol, and then left solvated. Separately, solid Ox-one is dissolved in water (to a final concentration of 0.4 M), sonicating for 5 min to aid in solvation. The aqueous Oxone solution (10 equivalents with respect to the nitro group loading of the resin) is added to the methanol-solvated resin and stirred/bubbled for 16 h at room temperature. The resulting resin 10 was then washed with water, MeOH/water (1 1), MeOH, MeOH/NMP, NMP, DCM, and ether, then dried in vacuo overnight prior to the next step. 

Solvate the cartridge with methanol and equilibrate with acidified water (0.05% TFA). 

The above crystal solvent effect on the ethanolate and the methanolate of [Fe(2-pic)3] CI2 Sol has later been confirmed by magnetic susceptibility measurements181 . Sinn et al. 181) have also investigated the unsolvated bromide [Fe(2-pic)3] Br2 as well as its solvates with Sol = C2HsOH and CH3OH, respectively these systems all show temperature dependent spin transition with pronounced differences in the transition behaviour. Differences in the spin transition behaviour of corresponding solvates [Fe(2-pic)3] X2 Sol (X = Cl, Br) with different anions are also noticeable 181). 

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