Aprotic solvents acetonitrile

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). 

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 . 

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). 

What makes FHF an attractive species to investigate by nmr spectroscopy is that it consists of three nuceli each with spin 1/2 bonded directly. Also, the proton of the strong hydrogen bond should have an unusual chemical shift. Early work failed to detect the expected F doublet and H triplets (e.g. Soriano et al., 1969), and it was not until the importance of the solvent was appreciated that coupling was observed (Fujiwara and Martin, 1971, 1974a,b). Suitable media were found to be the dipolar aprotic solvents acetonitrile, nitromethane and dimethylformamide. 

Thus, the main products from quinaldine in aprotic solvent acetonitrile are quinolizine 280 and indolizine 281a (rather than pyridoazepine 282) in protic solvent methanol only indolizine 281a forms, but in both cases higher-fused products (1 3 and 1 4 adducts) are accompanying. Also the long-lasting discussion about the products obtained from 6-bromoquinaldine has been settled in favor of the two isomers 283 (76J(P1)692). 

In this section we mention several solvents that were not covered in the previous sections and which are of some importance to this field. Three important organic polar aprotic solvents—acetonitrile (AN), dimethyl sulfoxide (DMSO), and... 

I he third step is the coupling of the polymer-bonded deo.xynucleoside with a protected deoxynucleoside containing a phosphonmihlite group at its 3 position. [A phosphoramidite has the structure R2NP(OR)2. The coupling reaction takes place in the polar aprotic solvent acetonitrile requires catalysis by the heterocyclic amine tetrazole and yields a phosphite, as product. Note that one... 

In the absence of monopoles, molecules with large dipole moments dominate the multipole interaction energies, and such molecules are polar. The term polarity, does not refer directly to dipole moment, but polar molecules have the ability to solvate species that have regions of charge deficiency or excess. Water is a highly polar compound, yet it has a relatively small dipole moment compared with the dipolar aprotic solvents acetonitrile, formamide, A,A-dimethylformamide, and dimethylsulfoxide. 

Anodic fluorination has also been accomplished in aprotic solvents (acetonitrile, sulfolane, nitromethane) in the presence of fluorides in the form of HF, R3N HF, R4NF XHF and R4NBF4. Aromatic hydrocarbons (but not aliphatic ones as yet) have been oxidized by an ECE mechanism to partially fluorinated products. 

Examination of Solvent Effect on Nucleophilic Fluorination with KF/ dicvclohexano-18 crown-6. Using 1-bromodocosane (12) as substrate and KF/DC-18-C-6 as reagent system, solvent effect was examined. Solvents were chosen from common dipolar aprotic solvent [acetonitrile, hexa-methylphosphoric triamide (HMPT), dimethylsulfoxide (DMSO), diglyme], from weakly basic dipolar aprot c solvents (sulfolane, ethylene carbonate, propylene carbonate) " and from acid amide solvents [N,N-dimethylformamide (DMF), N,N-diethylacetamide (DEA), N-methyl-pyrrolidone (NMP), tetramethylurea]. ... 

Figure 14 Interactions of dipolar aprotic solvents (acetonitrile, N,iV-dimethylformamide, dimethyl sulfoxide) and water with fibrous cellulose I as measured by scavenging of trapped macrocellulosic radicals at 298 K...

As a rule it is best to carry out electrochemical generation in media where there is a single one-electron polarographic wave this occurs under conditions where the protonation of radical anions formed in the first electron transfer is either excluded or retarded, i. e., in polar aprotic solvents (acetonitrile, dimethylformamide, tetrahydrofuran, 1,2-dimethoxyethane, and others). 

It has been shown in a number of papers [10-13] that when surface-active substances are added to the polarographed solution, the four-electron diffusion waves for the reduction of a number of nitro compounds in weakly alkaline aqueous solution decrease to a one-electron level and that simultaneously, at a more negative potential, a new three-electron wave appears, so that the overall process corresponds to the reduction of the nitro compound to the respective hydroxylamine derivative. The decrease of the four-electron wave to the one-electron step has also been observed when switching from aqueous solutions to solutions in aprotic solvents acetonitrile, dime thylformamide [14-16]. This phenomenon is due to retarded protonation of the radical anion derived from the nitro compound in the first electron transfer the surface-active substances added to the aqueous solution displace the radical anions from the electrode surface [12, 13, 17], thereby preventing their protonation at the surface [18]. 

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