Acetonitrile as a solvent

From discussions with many people now worldng with ionic liquids, we know that, at least for the start of their work, the ability to buy an ionic liquid was important. In fact, a synthetic chemist searching for the ideal solvent for his or her specific application usually takes solvents that are ready for use on the shelf of the laboratory. The additional effort of synthesizing a new special solvent can rarely be justified, especially in industrial research. Of course, this is not only true for ionic liquids. Very probably, nobody would use acetonitrile as a solvent in the laboratory if they had to synthesize it before use. 

When the anodic fluorination of 2-monofluoroethyl sulfide 5 is carried out in methanol containing Et3N-3HF instead of acetonitrile as a solvent, interestingly the a-methoxylated product 7 rather than the a-flourinated product 6 is obtained exclusively (Scheme 6.10) [51]. As described above, 7 is not obtained from 5 under conventional anodic methoxylation conditions. Therefore, that this novel fluoride ion promoted anodic methoxylation is remarkable. As shown... 

These authors found that the tetrazinylhydrazone derivative 46 when reacted with pyrrolidinoenamine 47 in methanol yields the cyclopenta-fused derivative of the title ring system 48 in 94% yield. A similar transformation was carried out successfully by using morpholine-enamine in somewhat poorer yield. When the transformation was tried in acetonitrile as a solvent, a totally different reaction was observed a regular Diels-Alder reaction between the tetrazine ring and the enamine double bond (of inverse electron demand) took place to yield pyridazines. 

The mechanism which could explain the formation of these products is described in Scheme 27. In an EC mechanism, the intermediate radical cation 48a could undergo a follow-up reaction with water as a nucleophile to form radical 48b which could than dimerize through S-N or S-S bond formation or react with 48a to yield 50 and 51 as the fianl one-electron oxidation products. In an ECE mechanism, intermediate 48b is further oxidized to 48c which reacts with acetonitrile as a solvent to give 49 as the final two-electron oxidation product. The cation intermediate 48c can react with the parent molecule 48 through [2 -f 3]-cycloaddition to give the final products 50 and 51. The [2 -f 3]-... 

On one-electron rednction, aldehydes and ketones give anion-radicals. It is the carbonyl group that serves as a reservoir for the unpaired electron Ketones yield pinacols exclusively. Thus, acetophenone forms 2,3-diphenylbutan-2,3-diol as a result of electrolysis at the potential of the first one-electron transfer wave (nonaqueous acetonitrile as a solvent with tetraalkylammonium perchlorate as a supporting electrolyte) (van Tilborg and Smit 1977). In contrast, calculations have shown that the spin densities on the carbonyl group and in the para position of the benzene ring are equal (Mendkovich et al. 1991). This means that one should wait for the formation of three types of dimer products head-to-head, tail-to-tail, and head-to-tail (cf. Section 3.2.1). For the anion-radical of acetophenone, all of the three possible dimers are depicted in Scheme 5.21. 

Various alkenes react with diphenyl diselenide/(NH4)2S208, in an aqueous acetonitrile as a solvent in the presence of trifluoromethanesulfonic acid to afford the amidoseleny-lation products. It has been observed that some unsaturated nitriles in dioxane undergo intramolecular cyclization reaction to give the corresponding phenylselenolactones. 

Our resolution to this dilemma has been to work out a compact procedure based upon the fluorinating agent SbF3 catalyzed by SbCl5 using acetonitrile as a solvent (i.e., the Swarts reaction).6... 

It is assumed that at the initial stage, after benzimidazoline-2-thione has been added to compound 1, the resultant anion formed, then is deprotonated by triethylamine added to the resulting suspension. The ensuing intermediate undergoes intramolecular heterocyclization into compound 153. Using acetonitrile as a solvent is also essential because of its low ability to undergo proton transfer and the low solubility of benzimidazoline-2-thione in it. This combination of properties initially yields the kinetic product and then leads to activation of the second nucleophilic center. 

Billon, using acetonitrile as a solvent, carried out the first systematic investigations on the anodic oxidation of phenothiazine... 

Despite the favorable properties of acetonitrile as a solvent, its use for equilibrium acidity measurements has its definite limitations. The pK range that is tolerable is limited at the high end by onset of solvent deprotonation, and at the low end by substrate autodissociation, as has been implicated for HCo(CO)4 [14a] and TpCr(CO)3H [22b]. These limitations can be overcome by the choice of a less polar solvent, e.g. 1,2-dichloroethane (DCE), dichloromethane, or THE. To make reliable, quantitative comparisons of thermodynamic data obtained in different solvents, it is necessary to link the acidity scales and electrode potential references in the different solvents. This has all too often proven to be a far from trivial task. Although, in principle, 1 1 relationship between the acidity scales in different solvents never exists, pK differences between closely related compounds are often almost constant when compared in different solvents. This is because their solvation properties are similar, because of similarities in size and charge distribution. In less... 

DMF has an acceptable liquid range (—61 to 153" C), although the boiling point is near the upper limit for its convenient removal by distillation during the workup. DMF is inferior to acetonitrile as a solvent for UV spectroscopy. Contact with the skin and vapor concentrations over 10 ppm should be avoided. 

This type of method was used by Brus and co-workers in studies on CdS and ZnS [12, 13], which have led to the explosion of interest in solid samples of semiconductors which show quantum confinement effects. They [12] prepared CdS nanoparticles by a process involving the controlled nucleation of CdS in dilute aqueous solutions of cadmium sulfate and ammonium sulfide. The dynamic equilibrium between solvated ions and solid CdS in acetonitrile, as a solvent in the presence of a styrene or maleic anhydride copolymer, allowed the preparation of... 

It must be kept in mind that such symmetrical couplings are not inevitably favored. Thus, mesitylene yields (platinum anode, acetonitrile as a solvent containing tetrabutylammonium tetrafluorobo-rate) an aryl-aryl coupling product,... 

If the reaction is done with acetonitrile as a solvent under reducing conditions, the carbene intermediate 78 eliminates fluoride and reacts with the nitrile generating nitrilium ylide 83 as illustrated in Scheme 23. This intermediate, in turn, undergoes addition of isonitrile followed by subsequent cyclization to the imidazopyridinium intermediate 84 that is then reduced with sodium triacetoxyborohydride to give imidazopyridine 85 <05TL4487>. 

A good correlation holds between the substrate BDE and log k for oxidation. We note, however, that the reaction is performed in acetonitrile as a solvent. The BDE of acetonitrile (BDE< h = 94.8 kcal moh ) [65, 66] is less than that of cyclohexane (BDEc fj = 99.5 kcal moki), which is oxidized at an appreciable rate. The inertness of acetonitrile is all the more striking inasmuch as its concentration as a neat solvent is 10-10 times greater than the hydrocarbon substrate. The oxo complex does decompose slowly over time at a rate of 5.8 x 10 s k If one assumes that this decomposition rate is essentially equivalent to the rate of hydrogen atom abstraction of acetonitrile by the [(N4Py)Fe =0] +, then the Polanyi correlation for BDE is compromised (Fig. 17.7(a)). Conversely, acetonitrile as a substrate for oxi-... 

The benzo-l,2-selenazine (benzisoselenazine) ring system 144 can be prepared by copper(l)-promoted reaction of amine 143 with potassium selenocyanate in the presence of triethylamine (Equation 37) <2000JOC8152>. The ring closure also affords 3,3-dimethylindoline as a by-product, but a twofold excess of selenocyanate and acetonitrile as a solvent led to optimum formation of the desired selenazine. 

The additional effort of synthesizing a new special solvent can be rarely justified, especially in industrial research. Of course, this is not only tme for ionic liquids. It is very likely that nobody would use acetonitrile as a solvent in the laboratory if one had to synthesize it before use. 

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