Acidity acetonitrile

Exp. No Acetonitrile (%) Acid Type Flow- rate (ml/min) Temperature Wavelength (nm) Response time (s)... 

In many circnmstances, photovoltages are found to be almost constant for redox conples whose formal potentials span a range exceeding the band gap of sihcon as shown for example in Table 6.5. ° A similar effect has been observed in pure acetonitrile and acetonitrile-acid mixtures in which a large number of redox couples with a large span of formal potentials exhibit a similar photovoltage. The departure from the ideal situation described by Eq. (1.96) is often attributed to Fermi level pinning... 

As mobile phase acetonitrile - acidic phosphate buffer was used. Dilute samples of urine and... 

Protonation of a polyhydride can occur at the metal, increasing the number of hydride ligands or leading to a rj -Uz ligand, which can liberate as H2. In spite of the low kinetic and thermodynamic (pXa = 25.5 in acetonitrile) acidity of [ReH4(PMe2Ph)4] +, deprotonation occurs by abase like potassium phenolate. Replacement of one phosphine by CO enhances the acidity of the complex by at least 7 orders of magnitude (pXg < 18.5). ... 

Aqueous acid acetonitrile. Acid concentration uncorrected for co-solvent. Cation not thermally stable under acidic conditions. 

Feces The amount of feeal homogenate needed for the desired level of radioactivity per injection is determined. The feeal homogenate is extracted with three volumes of an appropriate solvent (e.g., aeetonitrile, acetonitrile/ methanol, acetonitrile/acidic acid). The fecal homogenate/solvent mixture is vortexed and sonicated and centrifuged. The extraction is repeated at least one more time to recover a desirable >85% of radioactivity. The sample is combined, dried, reconstituted in an appropriate solvent (e.g., 20-40% acetonitrile in water), vortexed and centrifuged at 3000 x g for 5 min. The aliquots of the reconstituted sample are counted by LSC to determine the final recovery of radioactivity (>80% desired). 

Figure 4.6 On the bandwith of retention and separation (actors by the separation of metabolites of tricyclic anti-depressants in acetonitrile/acidic phosphate buffer. Reproduced from Kromidas [6] with permission of John Wiley Sons.

Mobile phase acid acetonitrile acid acetonitrile acetonibri]e THF ... 

Acetonitrile % Acid analyte correction factor Base analyte correction factor Acidic buffer correction Total correction factor... 

The largest errors in predicted compositions occur for the systems acetic acid-formic acid-water and acetone-acetonitrile-water where experimental uncertainties are significantly greater than those for other systems. 

However, the term saturated is often applied to compounds containing double or triple bonds which do not easily undergo addition reactions. Thus ethanoic acid is termed a saturated carboxylic acid and acetonitrile a saturated nitrile, whereas a Schiff base is considered to be unsaturated. 

The crude acetonitrile contains as impurity chiefly acetic acid, arising from the action of phosphoric acid on the acetamide. Therefore add to the nitrile about half its volume of water, and then add powdered dry potassium carbonate until the well-shaken mixture is saturated. The potassium carbonate neutralises any acetic acid present, and at the same time salts out the otherwise water-soluble nitrile as a separate upper layer. Allow to stand for 20 minutes with further occasional shaking. Now decant the mixed liquids into a separating-funnel, run off the lower carbonate layer as completely as possible, and then pour off the acetonitrile into a 25 ml, distilling-flask into which about 3-4 g. of phosphorus pentoxide have been placed immediately before. Fit a thermometer and water-condenser to the flask and distil the acetonitrile slowly, collecting the fraction of b.p. 79-82°. Yield 9 5 g. (12 ml.). 

Hydrolysis of Acetonitrile. Nitriles, like acid amides, undergo hydrolysis to give the corresponding carboxylic acid and ammonia. Consequently... 

Boil a mixture of 5 ml. (4 g.) of acetonitrile and 75 ml. of 10% aqueous sodium hydroxide solution in a 200 ml. flask under a refluxwater-condenser for 30 minutes, when hydrolysis will be complete. Detach the condenser and boil the solution in the open flask for a few minutes to drive off ull free ammonia. Then cool the solution, and add dilute sulphuric acid (i volume of concentrated acid 2 volumes of water)... 

For practice, the student should carry out both alkaUne (compare Section 111,83) and acid hydrolysis of acetonitrile, n-valeronitrile (n-butyl cyanide) and n-capronitrile (n-amyl cyanide). 

By the action of concentrated hydrochloric acid at about 40° upon aryl-acetonitriles hydrolysis is arrested at the arylacetamide stage (see Section IV, 160 for the preparation of phenylacetamide by this method) ... 

It is of interest to note that by substituting alkyl bromides for cyciohexyl bromide the corresponding a-phenyl-a-alkyl-acetonitriles are obtained, which may be hydrolysed to the a-phenylaliphatic acids thus with ethyl iodide a-phenyl-lwt3Tonitrile is produced, hydrolysed by ethanoUo potassium hydroxide to a-phenylbutyric acid. 

A similar approach is followed in a recent study of the Lewis-acid catalysis of a Michael addition in acetonitrile. See Fukuzumi, S. Okamoto, T. Yasui, K Suenobu, T. Itoh, S. Otera, J. Chem. Lett. 1997, 667. 

Interestingly, at very low concentrations of micellised Qi(DS)2, the rate of the reaction of 5.1a with 5.2 was observed to be zero-order in 5.1 a and only depending on the concentration of Cu(DS)2 and 5.2. This is akin to the turn-over and saturation kinetics exhibited by enzymes. The acceleration relative to the reaction in organic media in the absence of catalyst, also approaches enzyme-like magnitudes compared to the process in acetonitrile (Chapter 2), Cu(DS)2 micelles accelerate the Diels-Alder reaction between 5.1a and 5.2 by a factor of 1.8710 . This extremely high catalytic efficiency shows how a combination of a beneficial aqueous solvent effect, Lewis-acid catalysis and micellar catalysis can lead to tremendous accelerations. 

In contrast to the situation in the absence of catalytically active Lewis acids, micelles of Cu(DS)2 induce rate enhancements up to a factor 1.8710 compared to the uncatalysed reaction in acetonitrile. These enzyme-like accelerations result from a very efficient complexation of the dienophile to the catalytically active copper ions, both species being concentrated at the micellar surface. Moreover, the higher affinity of 5.2 for Cu(DS)2 compared to SDS and CTAB (Psj = 96 versus 61 and 68, respectively) will diminish the inhibitory effect due to spatial separation of 5.1 and 5.2 as observed for SDS and CTAB. 

As expected, the solvent has a significant effect on the endo-exo selectivity of the uncatalysed Diels-Alder reaction between 1 and 2. In contrast, the corresponding effect on the Lewis-acid catalysed reaction is small. There is no beneficial effect of water on the endo-exo selectivity of the catalysed Diels-Alder reaction. The endo-exo selectivity in water is somewhat diminished relative to that in ethanol and acetonitrile. 

The selection of solvents for quantitative work is not easy. Nitro-alkanes are sufficiently inert, but nitronium tetrafluoroborate is poorly soluble in them c. 0-3 %). Nitronium salts react rapidly with acetic anhydride, and less rapidly with acetic acid, A, A -dimethylformamide and acetonitrile, although the latter solvent can be used for nitration at low temperatures. Sulpholan was selected as the most suitable solvent ... 

This h)rpothesis has, however, been supported. The o p-ratio in chlorobenzene was found to be lower when acetic anhydride was the solvent, than when nitric acid or mixed acids were used. The ratio was still further reduced by the introduction into the solution of an even less polar solvent such as carbon tetrachloride, and was increased by the addition of a polar solvent such as acetonitrile. The orientation of substitution in toluene in which the substituent does not posses a strong dipole was found to be independent of the conditions used. The author... 

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