Acetonitrile as cosolvent

In the absence of moisture cation 25 is stable over a period of weeks, 5, however, decomposes slowly at room temperature to non-identified produets [14-16]. Both cations 5 and 25 show distinct behaviour towards nucleophilic solvents. While their Si-NMR and C-NMR resonances are not influeneed by arene solvents, the addition of the higher nucleophilic acetonitril as cosolvent leads to the formation of silylated nitrilium cations 26 and 27 (Scheme 8). They are characterized by their Si and C chemical shifts (see Figs. 6 and 7) [14, 16]. The silicon resonances are high field shifted by ca 51-56 ppm and similarely, the signals of the vinylic carbon atoms are shifted by 20 ppm to higher field in the NMR spectra of the nitrilium ions. This clearly indicates the breakdown of the intramolecular stabilization of the positively charged silicon center on the expense of intermolecular interactions between the silyl cations and acetonitril. 

In the case of a water insoluble quinonc or carboxylic acid, acetonitrile can be used as cosolvent.2... 

Some advice can be formulated for the choice of organic modifier, (i) Acetonitrile as an aprotic solvent cannot interact with residual silanols, whereas the protic methanol can. Thus, when measuring retention factors, methanol is the cosolvent of choice, as it reduces the secondary interactions between the solutes and the free silanol groups, (ii) For the study of the performance of new stationary phases one should use acetonitrile, as the effects of free silanol groups are fuUy expressed [35]. (iri) Acetonitrile with its better elution capacity can be considered as the best organic modifier for Hpophilicity measurements of highly Hpophihc compounds with adequate stationary phases [36]. 

Epoxidation of various acyclic and cyclic perfluorinated dienes is accomplished with an aqueous hypohalogenitc and acetonitrile as a cosolvent. The reactivity of a C = C bond toward this reagent is enhanced by the presence of the trifluoromethyl group. This activating effect is nicely illustrated by perfluoro(l-methylcyclohexa-l,4-diene), which reacts smoothly with sodium hypochlorite to give a diepoxide 11 in 58% yield,73 while the oxidation system failed for perfluorocyclohexadienes. Nonconjugated perfluorocyclohepta-1,4-diene (12) is oxidized to the corresponding diepoxide 13 by sodium hypobromite.74... 

HMPA as cosolvent, the nature of the electrophilic reagent and the reaction time and temperature [60] (Scheme 46). It was discovered that the major side products formed besides the expected 2-phenylselanylalkanenitrile are bis(phenyl-selanyl)acetonitrile and propionitrile. The authors have proposed that the formation of bis(phenylselanyl)acetonitrile would result from the decomposition of an ate complex, the latter being formed by selenophilic attack of the carbanion derived from phenylselanylacetonitrile on the substrate. The a-selanyl nitriles behave as a-phenylselanyl ketones when treated with bases. 

Besides ruthenium tetroxide, other ruthenium salts, such as ruthenium trichloride hydrate, may be used for oxidation of carbon-carbon double bonds. Addition of acetonitrile as a cosolvent to the carbon tetrachloride-water biphase system markedly improves the effectiveness and reliability of ruthenium-catalyzed oxidations. For example, RuCl3 H20 in conjunction with NaI04 in acetonitrile-CCl4-H20 oxidizes (Ej-S-decene to pentanoic acid in 88% yield. Ruthenium salts may also be employed for oxidations of primary alcohols to carboxylic acids, secondary alcohols to ketones, and 1,2-diols to carboxylic acids under mild conditions at room temperature, as exemplified below. However, in the absence of such readily oxidized functional groups, even aromatic rings are oxidized. 

The first protease-catalyzed reaction in ILs was the Z-aspartame synthesis (Scheme 10.7) from carbobenzoxy-L-aspartate and L-phenylalanine methyl ester catalyzed by thermolysin in [BMIM] [PF ] [ 14]. Subtilisin is a serine protease responsible for the conversion of A -acyl amino acid ester to the corresponding amino acid derivatives. Zhao et al. [90] have used subtilisin in water with 15% [EtPy][CF3COO] as cosolvent to hydrolytically convert a series of A -acyl amino acid esters often with higher enantioselectivity than with organic cosolvent like acetonitrile (Scheme 10.8, Table 10.2). They specifically achieved l-serine and L-4-chlorophenylalanine with an enantiomeric access (ee) of-90% and -35% product yield which was not possible with acetonitrile as a cosolvent [90]. Another example is hydrolysis of A-unprotected amino acid ester in the presence of a cysteine protease known as papain. Liu et al. 

Patrick and coworkers [66] developed an efficient method for synthesis of biaryls by slow addition of two equivalents of trifluoroaeetic acid to the solution of the aryltriazenes (VII) in an arene at 65-70 C. As reaction proceeds, the nitrogen is evolved from the reaction mixture and biaryls (II) are formed in fair yields. The efficacy can be judged from the selected examples presented in the Scheme 18. The yields can be further increased for 10-15% by adding a catalytic amount of iodine (5-10 mol%), 5% palladium on charcoal, palladium(II) acetate (5 mol%), or acetonitrile as a cosolvent (ca. 10-25%). 

In the majority of cases, the cosolvent mixtures for PMMA contain either or acetonitrile as one of the liquid components. A study of the mixture formed by these two liquids and a comparison with the results obtained in the other cosolvents studied before has been also reported. The total sorption of the cod (PMMA) was calculated from second virial coefficient and intrinsic viscosity data. According to these authors, acetonitrile can interact favorably with the ester group of PMMA and is imfavorable with its methylene backbone. The role of these opposing interactions and of liquid order in acetonitrile are taken into account to explain the dilute solution properties of PMMA in this cosolvent system. ... 

The azomethine ylides, generated from aziridines 1, xmderwent 1,3-dipolar cycloaddition wiffi dimethyl acetyl-enedicarboxylate in supercritical CO2 (Scheme 1) [17]. Under photolysis conditions, dihydropyrrole 2 was formed with 43% yield. It was foxmd that using small quantity of acetonitrile as a cosolvent improved the yield to 63%. The photolysis of similar aziridine (1, = Bn, = Ph) was not efficient and the thermolysis was used to generate a reac-... 

The solubility of 1-octene has been estimated to be 10 times higher in 50% ethanol than in pure water [48]. As cosolvents, ethanol, acetone, acetonitrile, and methanol significantly increased the reaction rate of 1-octene hydroformylation [49]. 

Hydrolysis of esters and amides by enzymes that form acyl enzyme intermediates is similar in mechanism but different in rate-limiting steps. Whereas formation of the acyl enzyme intermediate is a rate-limiting step for amide hydrolysis, it is the deacylation step that determines the rate of ester hydrolysis. This difference allows elimination of the undesirable amidase activity that is responsible for secondary hydrolysis without affecting the rate of synthesis. Addition of an appropriate cosolvent such as acetonitrile, DMF, or dioxane can selectively eliminate undesirable amidase activity (128). 

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