Acetonitrile, solvent

Block copolymers of vinyl acetate with methyl methacrylate, acryflc acid, acrylonitrile, and vinyl pyrrohdinone have been prepared by copolymeriza tion in viscous conditions, with solvents that are poor solvents for the vinyl acetate macroradical (123). Similarly, the copolymeriza tion of vinyl acetate with methyl methacrylate is enhanced by the solvents acetonitrile and acetone and is decreased by propanol (124). Copolymers of vinyl acetate containing cycHc functional groups in the polymer chain have been prepared by copolymeriza tion of vinyl acetate with A/,A/-diaIlylcyanamide and W,W-diaIl5lamine (125,126). 

The conductometric results of Meerwein et al. (1957 b) mentioned above demonstrate that, in contrast to other products of the coupling of nucleophiles to arenediazonium ions, the diazosulfones are characterized by a relatively weak and polarized covalent bond between the p-nitrogen and the nucleophilic atom of the nucleophile. This also becomes evident in the ambidentate solvent effects found in the thermal decomposition of methyl benzenediazosulfone by Kice and Gabrielson (1970). In apolar solvents such as benzene or diphenylmethane, they were able to isolate decomposition products arising via a mechanism involving homolytic dissociation of the N — S bond. In a polar, aprotic solvent (acetonitrile), however, the primary product was acetanilide. The latter is thought to arise via an initial hetero-lytic dissociation and reaction of the diazonium ion with the solvent (Scheme 6-11). 

The influence of the solvent on the oxidation of film under conformational relaxation control is illustrated in Fig. 47, which shows chronoamperograms obtained by steps from -2000 to 300 mV vs. SCE at room temperature (25°C) over 50 s in 0.1 M LiC104 solutions of different solvents acetonitrile, acetone, propylene carbonate, (PC), dimethyl sulfoxide (DMSO), and sulfolane. Films were reduced over 120 s in the corresponding background solution. Despite the large differences observed in the relative shape of the curves obtained in different solvents, shifts in the times for the current maxima (/max) are not important. This fact points to a low influence of the solvent on the rate at which confor-... 

A strong acceptor TCNE undergoes [2+2] rather than [4+2] cycloaddition reactions even with dienes. 1,1-Diphenylbutadiene [20] and 2,5-dimethyl-2,4-hexadiene (Scheme 5) [21] afford mainly and exclusively vinyl cyclobutane derivatives, respectively. In the reactions of 2,5-dimethyl-2,4-hexadiene (1) the observed rate constant, is greater for chloroform solvent than for a more polar solvent, acetonitrile (2) the trapping of a zwitterion intermediate by either methanol or p-toluenethiol was unsuccessful (3) radical initiators such as benzyl peroxide, or radical inhibitors like hydroquinone, have no effect on the rate (4) the entropies of activation are of... 

Figs. 1.6 and 1.7). This type of CD spectrum is observed for certain heterooligomeric peptoid sequences with as few as 33% chiral aromatic residues, in both aqueous and polar organic solvent (acetonitrile, methanol). 

Reaction conditions Catalyst wt = 0.75 g phenol H2O2 = 3 1, mole reaction time = 8 h Temp = 353 K solvent = acetonitrile PBQ = para benzoquinone CAT = Catechol HQ = hydroquinone TON = moles of phenol converted per mole of copper in the catalyst... 

OS 14] [R 17] [no protocol[ Further studies related to the desymmetrization of thiorueas showed that for the diphenylthiourea/cydohexylamine system reasonable reaction rates and conversions were achieved [42, 85], It is notable that the temperatures of up to 91°C applied slightly exceed the boiling point of the solvent acetonitrile. 

FIGURE 4.5 The influence of solvent viscosity on migration characteristics on preparative plates (a) Nonviscous solvent (acetonitrile) (b) Viscous solvent (methanol). (Adapted from Botz, L., Nyiredy, S., and Sticher, O., J. Planar Chromatogr.,3,10-14,1990. With permission.)... 

Sodium sulfate, anhydrous, ACS grade (Fisher Scientific) or equivalent Solvents acetonitrile (ACN), acetone, dichloromethane (DCM), methanol (MeOH) and water (pesticide or HPLC grade)... 

In Fig. 4.6, the titration of p-hydroxybenzoic acid in pyridine shows that the COOH and OH groups can be clearly determined. However, in acetonitrile there is half-way the titration of the COOH group an additional potential jump this can be explained by a phenomenon which was already known for acetic acid23, viz., in the inert solvent acetonitrile intermolecular hydrogen-bridge... 

Aromatic diazo compounds can be reduced in water via a radical process (Scheme 11.5).108 The reduction mechanism of arenediazo-nium salts by hydroquinone was studied in detail.109 Arenediazonium tetrafluoroborate salts undergo facile electron-transfer reactions with hydroquinone in aqueous phosphate-buffered solution containing the hydrogen donor solvent acetonitrile. Reaction rates are first order in a... 

Irradiation in polar solvents (acetonitrile, dimethylformamide, or methanol) leads to mixtures of (78) and (79) with the former predominating.<90 91) Nonpolar solvents (dioxane, benzene, or ethyl acetate) or the presence of benzophenone as sensitizer lead to a predominance of the anti isomer... 

In the aprotic solvent acetonitrile, the trianion of cyclic trimetaphosphoric acid 115 is formed via the phosphorane 112 and the pyrophosphate dianion 113 protic solvents differ by reacting via the phosphorane 114 to give the phosphates 104 or H2PO . 

Fontes tt al. [224,225 addressed the acid—base effects of the zeolites on enzymes in nonaqueous media by looking at how these materials affected the catalytic activity of cross-linked subtilisin microcrystals in supercritical fluids (C02, ethane) and in polar and nonpolar organic solvents (acetonitrile, hexane) at controlled water activity (aw). They were interested in how immobilization of subtilisin on zeolite could affected its ionization state and hence their catalytic performances. Transesterification activity of substilisin supported on NaA zeolite is improved up to 10-fold and 100-fold when performed under low aw values in supercritical-C02 and supercritical-ethane respectively. The increase is also observed when increasing the amount of zeolite due not only to a dehydrating effect but also to a cation exchange process between the surface proton of the enzyme and the sodium ions of the zeolite. The resulting basic form of the enzyme enhances the catalytic activity. In organic solvent the activity was even more enhanced than in sc-hexane, 10-fold and 20-fold for acetonitrile and hexane, respectively, probably due to a difference in the solubility of the acid byproduct. 

The checkers did not employ benzene sis a solvent. Acetonitrile was used in excess, 3 mols of acetonitrile per mol of decaborane. 

The use of more polar solvents (acetonitrile, DMF) improved the N 0 ratio in the Mitsunobu alkylation of 3-benzoyl thymine with cyclopentanol <06SL324>. N vs. O-selectivity in the alkylation of 2-pyrimidinones has been investigated and the results rationalised on the HSAB principle <06T6848>. 

The solvent acetonitrile, the supporting electrolyte, TBAHP, and the reactant thianthrene were purified by well-known procedures described in detail elsewhere /8/. The reactant t-stilbene (Fluka Gmbh) was recrystallised twice from a methanol water mixture. The optical arrangement consisted of focusing lenses, a high efficiency Bausch and Lomb monochromator and a polarising filter. The electrochemical cell was mounted on an X, Y, Z manipulator with calibrated rotation facilities (Fritz-Haber-Institut). The detection... 

The redox characteristics, using linear sweep and cyclic voltammetry, of a series of (Z)-6-arylidene-2-phenyl-2,3-dihydrothiazolo[2,3-r][l,2,4]triazol-5(6//)-ones 155 (Figure 24) have been investigated in different dry solvents (acetonitrile, 1,2-dichloroethane, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO)) at platinum and gold electrodes. It was concluded that these compounds lose one electron forming the radical cation, which loses a proton to form the radical. The radical dimerizes to yield the bis-compound which is still electroactive and undergoes further oxidation in one irreversible two-electron process to form the diradical dication on the newly formed C-C bond <2001MI3>. 

Ion-exchange chromatography techniques that provide cationic surfactant residues suitable for a conductivity analysis are also developed [47,48]. They usually employ strong cation exchange columns and a mobile-phase based on an organic solvent (acetonitrile or... 

Product 34 predominates in the polar aprotic solvent (acetonitrile), while in the polar protic solvent (methanol) products 35 are formed preferentially. The different products are caused by the relative rate of deprotonation against desilylation of the aminium radical, that is in turn governed by the action of enone anion radical in acetonitrile as opposed to that of nucleophilic attack by methanol. In an aprotic, less silophilic solvent (acetonitrile), where the enone anion radical should be a strong base, the proton transfer is favoured and leads to the formation of product 34. In aprotic solvents or when a lithium cation is present, the enone anion radical basicity is reduced by hydrogen bonding or coordination by lithium cation, and the major product is the desilylated 35 (Scheme 4). 

The experimental procedures were essentially the same as reported (Figure 1, (16, 17)). Reagents other than those described in (16. 17) were as follows. Acrylic acid(Wako Pure Chemicals) was distilled once under reduced pressure under a nitrogen stream. Solvents(acetonitrile, n-hexane, and benzene) were purified by accepted procedures. 

The determination of accurate and precise limiting conductivities and ion association constants requires care in the design and use of the conductance apparatus, and in the purification and handling of solvents and salts. For this reason attention is given initially here to experimental aspects of conductance measurements. This is followed by a tabulation of selected data, primarily in dipolar apro-tic solvents, and a brief discussion of data taken in one solvent, acetonitrile, which is intended to show the scope of interpretation possible at the present time. 

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