Nitromethane medium

Friedel-Crafts acylation. This salt in LiC104-nitromethane medium catalyzes the acylation of arenes at room temperature, usually in excellent yields (except benzene — acetophenone)... 

The value of the second-order rate constant for nitration of benzene-sulphonic acid in anhydrous sulphuric acid varies with the concentration of the aromatic substrate and with that of additives such as nitromethane and sulphuryl chloride. The effect seems to depend on the total concentration of non-electrolyte, moderate values of which (up to about 0-5 mol 1 ) depress the rate constant. More substantial concentrations of non-electrolytes can cause marked rate enhancements in this medium. Added hydrogen sulphate salts or bases such as pyridine... 

Thompson points out that there is no evidence that adducts give other than acetates on thermolysis. The exocyclic methylene intermediate (iv) postulated by Robinson could arise by proton abstraction from a Wheland intermediate analogous to (vll) above, rather than from the adduct (in). Similarly its decomposition does not necessarily require the intermediacy of the adduct (v). The fact that i -methyl-4-nitromethylnaphthalene is the product even when the nitrating medium is nitric acid and nitromethane would then require no separate explanation. 

The Nenitzescu process is presumed to involve an internal oxidation-reduction sequence. Since electron transfer processes, characterized by deep burgundy colored reaction mixtures, may be an important mechanistic aspect, the outcome should be sensitive to the reaction medium. Many solvents have been employed in the Nenitzescu reaction including acetone, methanol, ethanol, benzene, methylene chloride, chloroform, and ethylene chloride however, acetic acid and nitromethane are the most effective solvents for the process. The utility of acetic acid is likely the result of its ability to isomerize the olefinic intermediate (9) to the isomeric (10) capable of providing 5-hydroxyindole derivatives. The reaction of benzoquinone 4 with ethyl 3-aminocinnamate 35 illustrates this effect. ... 

Nitronium tetrafluoroborate has been prepared by interaction of nitric acid, hydrogen fluoride, and boron fluoride in nitromethane.5 However, mixtures of nitric acid and nitromethane are extremely explosive.6,7 The present modification of the procedure, in which the medium is methylene chloride instead of nitromethane, was developed to avoid this hazard. It has not been published before. 

To an ice-cold solution of the aldehydo sugar in CH,OH (ca. 25 mL per g) are added 3 equiv of nitromethane (or nitrocthane), followed by 2.9 equiv of sodium methoxide. After stirring for 2 h 45 min, the medium is neutralized by the addition of acidic Dowex 50, then filtered. Removal of the solvent by distillation and purification by chromatography on silica gel (Ei,0/hcxane) or on aluminum oxide (Et20) furnishes the product yield 85-99%. 

Some interesting results have been obtained by Akand and Wyatt56 for the effect of added non-electrolytes upon the rates of nitration of benzenesulphonic acid and benzoic acid (as benzoic acidium ion in this medium) by nitric acid in sulphuric acid. Division of the rate coefficients obtained in the presence of nonelectrolyte by the concentration of benzenesulphonic acid gave rate coefficients which were, however, dependent upon the sulphonic acid concentration e.g. k2 was 0.183 at 0.075 molal, 0.078 at 0.25 molal and 0.166 at 0.75 molal (at 25 °C). With a constant concentration of non-electrolyte (sulphonic acid +, for example, 2, 4, 6-trinitrotoluene) the rate coefficients were then independent of the initial concentration of sulphonic acid and only dependent upon the total concentration of non-electrolyte. For nitration of benzoic acid a very much smaller effect was observed nitromethane and sulphuryl chloride had a similar effect upon the rate of nitration of benzenesulphonic acid. No explanation was offered for the phenomenon. 

Further confirmation of the proposed mechanism is provided by the fact that the reaction rates in acetic acid and nitromethane are little affected by the addition of small amounts of water, but when larger amounts (ca. 5 %) are added (to the acetic acid medium) competition between water and the aromatic for... 

Lithium perchlorate in nitromethane (LP-NM) is sometimes a more effective reaction medium than LP-DE for certain Diels-Alder reactions. The cycloaddition of 2,3-dimethylbutadiene with nitrostyrenes (Scheme 6.24) occurs with low... 

The condensation of nitro compounds and imines, the so-called aza-Henry or nitro-Mannich reaction, has recently emerged as a powerful tool for the enantioselective synthesis of 1,2-diamines through the intermediate /3-amino nitro compounds. The method is based on the addition of a nitronate ion (a-nitro carbanion), generated from nitroalkanes, to an imine. The addition of a nitronate ion to an imine is thermodynamically disfavored, so that the presence of a protic species or a Lewis acid is required, to activate the imine and/or to quench the adduct. The acidic medium is compatible with the existence of the nitronate anion, as acetic acid and nitromethane have comparable acidities. Moreover, the products are often unstable, either for the reversibility of the addition or for the possible /3-elimination of the nitro group, and the crude products are generally reduced, avoiding purification to give the desired 1,2-diamines. Hence, the nitronate ion is an equivalent of an a-amino carbanion. 

A nitromethane/aluminium chloride complex had been prepared. A gaseous alkene was added to the complex the pressure reached 5.6 bar and the temperature 2°C. The medium had been stirred at the beginning of the operation and then intemupted. A temperature rise caused the autoclave to detonate and the medium to carbonise entirely. 

Nitromethane was treated with lithium aluminiumhydride in diethyl ether medium and at ambient temperature. This was followed by an explosion which pulverised the equipment. This accident can be explained by the fact that there was a redox reaction, but also by the formation of nitromethane lithium, unless... 

On the assumption that = 2, the theoretical values of the ion solvation energy were shown to agree well with the experimental values for univalent cations and anions in various solvents (e.g., 1,1- and 1,2-dichloroethane, tetrahydrofuran, 1,2-dimethoxyethane, ammonia, acetone, acetonitrile, nitromethane, 1-propanol, ethanol, methanol, and water). Abraham et al. [16,17] proposed an extended model in which the local solvent layer was further divided into two layers of different dielectric constants. The nonlocal electrostatic theory [9,11,12] was also presented, in which the permittivity of a medium was assumed to change continuously with the electric field around an ion. Combined with the above-mentioned Uhlig formula, it was successfully employed to elucidate the ion transfer energy at the nitrobenzene-water and 1,2-dichloroethane-water interfaces. 

The Michael reaction of benzylidene acetophenone and benzylidene acetone with ethyl acetoacetate, nitromethane, and acetylacetone was studied by Musaliar and co-workers in the presence of a cetyltrimethy-lammonium bromide-containing aqueous micellar medium.50 The Michael reaction of various nitro alkanes with electrophilic alkenes is performed in NaOH (0.025-0.1 M) in the presence of cetyltrimethylam-monium chloride (CTACI) without any organic solvent (Eq. 10.23).51... 

A method for determining the gamma isomer of benzene hexachloride by partition chromatography has been developed by Aepli et al. (1). Nitromethane and n-hexane are used as the partition solvents, and silicic acid is the supporting medium. The method appears to be useful for routine product analyses. An accuracy of about 2% of the actual gamma isomer present is claimed. 

In recent years, there has been increased recognition that water is an attractive medium for organic reactions from the environmental point of view. The Michael addition of various nitroalkanes to conjugated enones can be performed in NaOH (0.025 M) and in the presence of cetyltrimethylammonium chloride (CTAC1) as cationic surfactant in the absence of organic solvents (Eq. 4.109).146 The Michael addition of nitromethane to methyl acrylate is carried out in water using NaOH as a base to give the mono adduct (Table 4.2).147... 

It should be mentioned that medium effects do not usually change the characteristic shape of an absorption spectrum to such an extent that it can not be recognized. Thus the characteristic Bactrian camel shape of the absorption band of solutions of trityl chloride in sulfuric acid and in nitromethane leaves no doubt that essentially the same ion is present in both solvents. 

A different behavior is exhibited by naphthalene-1,8-dicarbocal-dehyde (73). No m-naphthane derivatives are obtained on reaction with nitromethane, nitroethane or other methylene components. The basic medium, required for aldol type additions, causes the dialdehyde to undergo Cannizzaro reaction to the naphthopyranon (74) via an intramolecular 1,5-hydride shift, which is sterically favoured by the peri-position of the two aldehyde functions 28). 

The Sowden homologation [21], based on the nitroaldol condensation (Henry reaction) [22] between the aldehydo sugar and nitromethane in basic medium, followed by the Nef decomposition [23] of the resultant nitronate in strongly acidic conditions, has been employed in a more limited number of cases than the cyanohydrin synthesis. A recent example in this area is shown by the stepwise homologation of (V-acetyl-D-mannosamine (11) into /V-acetylneuraminic acid (12) [24] (Scheme 4). Also, this procedure has found... 

Solvent effects on quantum yields have been studied to some extent. Yields for substitution fall precipitously and the nature of the reaction may change if the medium consists of a noncoordinating solvent. Thus tra s-[Cr(NCS)4(NH3)2] shows a 0 of about 0.3 in aqueous media (for thiocyanate aquation), but is photoinert in nitromethane. In a mixed solvent study, it was concluded that the photochemical behavior of this complex depended on the solvent composition of the solvation shell rather than on the stoichiometric composition.41 42... 

A major advance was devised by Pehr Edman (University of Lund, Sweden) that has become the standard method for N-terminal residue analysis. The Edman degradation is based on the chemistry shown in Figure 27.12. A peptide reacts with phenyl isothiocyanate to give a phenylthiocarbamoyl (PTC) derivative, as shown in the first step. This PTC derivative is then treated with an acid in an anhydrous medium (Edman used nitromethane saturated with hydrogen chloride) to cleave the amide bond between the N-terminal amino acid and the remainder of the peptide. No other peptide bonds are cleaved in this step as amide bond hydrolysis requires water. When the PTC derivative is treated with acid in an anhydrous medium, the sulfur atom of the C=S unit acts as... 

With a variety of different mechanisms available, it is not surprising that the characteristics of hydrochlorination depend on the reaction conditions. Thus, in nitromethane, a medium that gives extensive Wagner-Meerwein shifts during hydrochlorination, olefins react according to the third-order rate law,... 

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