Water-methanol mixtures acidity function

Measurements of the stabilization ratio s were performed on the GaAs photoanode in aqueous medium with 0.25 mol.dnr3 and with 4 mol.dm 3 LiCl, in three water + methanol mixtures with 18, 48 and 80 mol % methanol respectively, and in two water + acetonitrile mixtures with 13 and 42 mol % acetonitrile. The stabilization ratio s was measured as a function of the photocurrent density i and the concentration c of dissolved TMPD. The measurements were performed at a constant electrode potential V corresponding to high band bending, so that surface recombination can be neglected. All experiments were performed in acid medium as required for the solubility of TMPD and decomposition products of GaAs. 

In organic solvents the acidity functions H corresponding to hydrogen dissociation from neutral indicator acids were reported for solutions of alkali metal alkoxides in various alcohols (2), using nitroanilines (21), aminobenzenecarboxylic acids (22), or indols (23) as indicators. For addition reactions of methoxide and ethoxide ions to neutral indicator acids, acidity functions J (also denoted as Hr) based on use of nitrobenzenes (21) and a-cyanostilbenes (18) as indicators in methanol and dimethylsulfoxide-methanol and -ethanol mixtures were reported. Recently (24) the acidity function J- (denoted as Jm) was derived for methoxide ion solutions in methanol using substituted benzaldehydes as indicators. These scales involve arbitrary choice of water as the solvent for determination of the dissociation constant of the anchoring acid. 

The problem of lipophiles remained and here again we could make use of the acid functionality of the phenols. With less lipid soluble phenols such as the steroids, simple back extraction from organic solvent into strong base would have been sufficient. However, the high lipid solubility of A9-THC necessitated that extraction be carried out with Brodie s solvent (hexane and isoamyl alcohol) and that back extraction be done with Claisen s alkali, which is a mixture of KOH, methanol, and water. After acidification of the Claisen s alkali, A9-THC could be recovered by extraction. The external standard and the trimethylanilinium hydroxide were added and the extracted phenol (i.e. A9-THC) was converted to the 1-0-methyl derivative in the injector port and the determination carried out... 

Synthesis of Siloxane-Polyimide Elastoplastics. In a typical polymerization, a 5-L, three-neck, round-bottom flask equipped with an overhead mechanical stirrer, a Dean-Stark trap with condenser and a nitrogen inlet, and a thermometer was charged with 484.00 g (0.2406 mol) of D2o-DiSiAn, 41.61 g (0.431 mol) of mPD, 19.52 g (3 wt %) of 2-hydroxypyridine, and 2 L of o-dichlorobenzene. The mixture was warmed to 100 °C for 1 h to dissolve the monomers and the catalyst. The polyamic acids precipitated and then redissolved when the mixture was warmed to 150 °C for 2 h. To the oligomer solution was added 99.13 g of BPADA dissolved in 200 mL of o-dichlorobenzene. The mixture was maintained at 150 °C for an additional 2-h period to ensure incorporation of the dianhydride and then warmed to reflux. After approximately 100 mL of a solvent-water mixture had been removed, the solution was maintained at 180 °C for 40 h. The mixture was cooled to room temperature and diluted with 1 L of methylene chloride. Polymer was isolated from the solution by a slow addition of the polymer solution to 4 L of methanol. The resulting slurry was filtered, and the polymer was redissolved in 4 L of methylene chloride, extracted three times with 2 N aqueous HCl to remove catalyst, washed with water, dried with magnesium sulfate, reprecipitated into methanol as before, filtered, and dried in vacuo at 100 °C to obtain 522 g (85%) of a rubbery material with an IV of 0.50 dL/g. IR, NMR, and Si NMR spectroscopic analysis indicated the absence of amic acid functionalities that could be present if imidization is incomplete. 

An H acidity function scale has been constructed for methoxide ion in methanol and its mixtures with DMSO (10-80%, v/v) using the dissociation of 11 amides (114) as the anchors for the scale.The degradation pathways of the anti-flammatory and analgesic lomoxicam (115), which contains an amide bond, have been examined recently. In acid, cleavage of the amide bond was the main reaction path and in alkaline and neutral solution the proton shift of the enolic hydroxyl initiated the major degradation pathway. The mechanism of hydrolysis of some A-nitrobenzamides (116) in strong acid follow an -1 mechanism with O-protonation but, in more moderate acid, they exhibit a neutral water-catalysed mechanism. /V-Methyl-/V-nitroacetamide (117) shows only the neutral water-catalysed process. Nitrourea follows an, 4-1 acid-catalysed mechanism. ... 

In the former case [32], the production rate of 99% pme enantiomers from the racemic mixture of R- and S-2-phenylbutyric acid was maximized as a function of the sample size and the mobile phase composition. The calculations were based on the column performance and the equilibrium isotherms of the two components (bi-Langmuir isotherms. Chapter 3). The separation was performed on immobilized bovine serum albumin, a chiral stationary phase, using water-methanol solution as the mobile phase. The retention times decrease with increasing methanol content, but so does the separation factor. For this reason, the optimum retention factor is around 3. Calculated production rates agree well with those measured (Table 18.4). The recovery yield is lower than predicted. 

In RP-HPLC, the stationary phase is less polar than the mobile phase and is usually comprised of spherical silica particles (typically, 3-5 pm in diameter). The acidic functionalities on the silica material have been modified by deriv-atisation with alkyl (C2 to C18), phenyl, cyano and amino groups. Typical mobile phases used in RP-HPLC consist of mixtures of aqueous buffers mixed with water-miscible organic solvents, such as methanol and acetonitrile. In addition to modified silica stationary phases, other new developments in RP-HPLC are now available, e.g. porous polymeric, carbon and mixed modal phases. 

A variety of ion exchange resins with strong and weak acid, weak base, and quaternary ammonium ion functionality are available in bead form well suited for filtration from reaction mixtures and for use in continuous flow processes. They have been used for >30 years in flow systems for water deionization. Sulfonic acid resins are already used on a large scale as catalysts for the addition of methanol to isobutylene to form methyl terr-butyl ether, for the hydration of propene to isopropyl alcohol, and for a variety of smaller scale processes. Tertiary amine resins have been used as catalysts for the addition of alcohols to isocyanates to form urethanes. The quaternary ammonium ion resins could be used as reagents with any of a large number of counter ions, and as catalysts in two and three phase reaction mixtures, although the author is not aware of any commercial process of this sort at present. 

Dihexylxylaramide (2). To a 250 mL round-bottom flask equipped with a magnetic stirrer was added methanol (150 mL), and the flask then cooled to 5 C. Acetyl chloride (5 mL) was added to the cold methanol and then xylaric acid (18 g, 0.18 mol, reference 18) was added to the methanolic HCl solution. The reaction mixture was refluxed for 16 h, concentrated to a syrup, and residual water removed from the syrup by azeotropic distillation with benzene. Esterification was complete but the product (1) contained more than one ester component as both ester and 5-membered lactone functions were observed in its IR spectrum (neat, 1745 and 1795 cm, ester and lactone C=0 respectively). 

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