Acetonitrile polar, aprotic

Aluminum chloride dissolves readily in chlorinated solvents such as chloroform, methylene chloride, and carbon tetrachloride. In polar aprotic solvents, such as acetonitrile, ethyl ether, anisole, nitromethane, and nitrobenzene, it dissolves forming a complex with the solvent. The catalytic activity of aluminum chloride is moderated by these complexes. Anhydrous aluminum chloride reacts vigorously with most protic solvents, such as water and alcohols. The ability to catalyze alkylation reactions is lost by complexing aluminum chloride with these protic solvents. However, small amounts of these "procatalysts" can promote the formation of catalyticaHy active aluminum chloride complexes. 

Acetonitrile and hydrogen cyanide are hy-products that may he recovered for sale. Acetonitrile (CH3CN) is a high polarity aprotic solvent used in DNA synthesizers, high performance liquid chromatography (HPLC), and electrochemistry. It is an important solvent for extracting butadiene from C4 streams. Table 8-1 shows the specifications of acrylonitrile, HCN, and acetonitrile. ... 

In contrast with protic solvents, which decrease the rates of SN2 reactions by lowering the ground-state energy of the nucleophile, polar aprotic solvents increase the rates of Sn2 reactions by raising the ground-state energy of the nucleophile. Acetonitrile (CH3CN), dimethylformamide ((Chy NCHO,... 

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 higher solubility of several quaternary ammonium salts of glyphosate in polar aprotic organic solvents such as acetonitrile was discovered (2), which permitted their reaction in solution with various alkyl halides. For example, GLY(n-Bu4N)2H reacted with either o-xylylene dichloride or 1,5-dibromopentane to produce the interesting quaternary glyphosate derivatives 81 and 82, whose structures have been confirmed by x-ray analysis (2). 

In the Heck reactions discussed above it was essential to use polar aprotic solvents such as acetonitrile or DMF if high regioselectivity was to be achieved. In other Heck couplings the use of water as a solvent has recently gained attention. The advantages of water compared with standard organic solvents are many - it is, for example, cheap and nontoxic - but its usefulness extends only over a number of well-defined applications, partly because of problems with the solubility of the reactants and catalysts. The development of aqueous catalytic systems is, consequently, an important field [21]. 

Decomposition of sulfonyl azides was shown to be catalyzed by copper in 1967 (72, 73). In the presence of alkenes, the reaction provides both aziridines and the C-H insertion products, albeit in low yields (73). In 1991, Evans et al. (74, 75) illustrated that both Cu(I) and Cu(II) salts were effective catalysts for nitrenoid transfer from [A-(/Moluenesulfonyl)imino]phenyliodinane (PhI=NTs) to a variety of acceptor alkenes. In the absence of ancillary ligands, reactions proceed best in polar aprotic solvents such as acetonitrile. Similar results are observed using both Cu(MeCN)4C104 and Cu(acac)2 as precatalysts, Eq. 53. 

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). 

A term, usually referring to a solvent, describing a compound which act neither as a proton donor nor a proton acceptor. Examples of polar aprotic solvents include dimethylformamide, dimethylsulfoxide, acetone, acetonitrile, sulfur dioxide, and hexamethylphosphoramide. Examples of nonpolar aprotic solvents include benzene and carbon tetrachloride. Studies of reactions in protic and aprotic solvents have demonstrated the importance of solvation on reactants, leaving groups, and transition states. Degrees of nucleophilicity as well as acidity are different in aprotic solvents. For example, small, negatively charged nucleophiles react more readily in polar aprotic solvents. It should also be noted that extremely... 

Eurthermore, it was noted that the product ratio was also dependent on the nature of the solvent employed. Thus, the nitrone 186 (Equation 122) undergoes cyclization in nonpolar aprotic solvents such as benzene or toluene and polar aprotic solvents such as DMSO, DME, or acetonitrile to afford the five-membered ring cycloadduct 155 as the... 

Figure 7 shows the degradation quantum yield, d of a-guaiacoxyacetoveratrone in 7 deaerated solvents acetonitrile (ACN), dioxane (DIOX), 1,2-dimethoxyethane (DME), methanol (MeOH), ethanol (EtOH), isopropanol (iPrOH) and ethoxyethanol (EtOEtOH) (40,41). The 4 was significantly larger in alcohols, 0.34 to 0.52, than in pure aprotic solvents, < 0.1. There was very little difference in d in polar aprotic solvents, 0.08 in acetonitrile, compared to that in non-polar aprotic solvents,... 

The most effective solvents for this reaction are polar aprotic solvents such as acetonitrile, DMF, NMP, or DMSO. Addition of halide salts such as tetra-w-butyl-ammonium bromide strongly facilitates the reaction and enables the conversion of aryl iodides and activated bromides even in the absence of phosphines (Jeffery conditions) [19]. Under these conditions the presence of water was sometimes... 

The choice of solvent and temperature also plays a significant role in the selectivity between the formation of 96 and 98 in the reaction between the 2,5-dimethylpyrrole complex 22 and MVK (Table 7). For polar aprotic solvents such as acetonitrile or DMF, an approximate 1 1 ratio of the two products is obtained, while in protic solvents such as methanol or water, the formation of conjugate addition products is favored. 

You see the reason for this solvent effect when you look at lines 2 and 3 in Table 2.1. Ions are stabilized quite considerably by solvation. Heterolyses of alkylating agents, and consequently SN1 reactions, therefore, succeed only in highly solvating media. These include the polar protic solvents such as methanol, ethanol, acetic add, and aqueous acetone as well as the polar aprotic solvents acetone, acetonitrile, DMF, NMP, DMSO, and DMPU (Figure 2.16). Unfortunately, DMPU does not solvate as well as HMPA, which is a carcinogen. 

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... 

---