Methylene chloride 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. 

Most thiirene dioxides (and oxides) have been prepared through a modified Ramberg-Backlund reaction as the last crucial cyclization step, as illustrated in equation 40 for the benzylic series . Synthesis of thiirene dioxides requires two major modifications of the originally employed reaction first, the inorganic base has to be replaced by the less basic and less nucleophilic triethylamine - and second, the aqueous media has to be substituted by an aprotic organic solvent (e.g. methylene chloride). Under these mild reaction conditions the isolation of aryl-substituted thiirene dioxides (and oxides) is feasible . In fact, this is the most convenient way for the preparation of the aryl-disubstituted three-membered ring sulfones and sulfoxides. ... 

The sulfonylated and acylated PPO presents solubility characteristics which are completely different from those of the parent PPO. Table V presents the solubility of some modified structures compared to those of unmodified PPO. It is very important to note that, after sulfonylation, most of the polymers become soluble in dipolar aprotic solvents like dimethyl sulfoxide (DMSO), N,N— dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC). At the same time it is interesting to mention that, while PPO crystallizes from methylene chloride solution, all the sulfonylated polymers do not crystallize and form indefinitely stable solutions in methylene chloride. Only some of the acetylated polymers become soluble in DMF and DMAC, and none are soluble in DMSO. The polymers acetylated with aliphatic acid chlorides such as propionyl chloride are also soluble in acetone. 

Solutions of dinitrogen pentoxide in aprotic solvents like methylene chloride, chloroform and carbon tetrachloride are efficient reagents for the iV-nitration of secondary amines. These reactions, known as nucleophilic nitrations , need excess amine present to react with the nitric acid formed during the reaction. Such nitrations are useful for the synthesis of secondary... 

If the metathesis polymerization is performed in solution, the preferred solvents are methylene chloride or chlorobenzene. Preferably, the solvent is aprotic in order to avoid ionic side reactions. The molecular weight is controlled by the addition of an acyclic olefin, such as 1-butene (13). 

Some of the salts were isolated in pure crystalline form and showed fairly high thermal stability, but many of the cations were observed only in solution. In certain cases, however, solid complexes are readily formed, like Me3NiMe3Si0S02CF3, although at ambient temperature in solution only unchanged reactants are observed (78). They are often easily soluble in aprotic solvents of high or moderate polarity like acetonitrile and methylene chloride. Some of these complexes are unstable at room temperature, decomposing reversibly to components, and may be observed only at a low temperature (78,242,252,255,256). Sometimes irreversible decomposition to other products takes place. An example is shown in Eq. (48). The majority of these complexes are hydrolytically very unstable... 

Dipolar aprotic organic solvents, e.g., acetonitrile, tetrahydrofurane, dimethylformamide, dimethylsulfoxide, sulfolane, methylene chloride, y-butyrolactonc, etc ... 

Photolysis of the arene complexes in the presence of monodentate ligands, e.g. carbon monoxide, leads to new complexes of the type CpFe(L) whereas in pure aprotic solvents, ferrocene and iron salts are formed Investigation of the photo-lytic reaction of an iron arene complex with excess ethylene oxide in methylene chloride solution (Meier and Rhis ) showed that a crystalline crown ether complex (structure shown in Fig. 9) was obtained in high yield. Only traces of dioxane could be detected. 

When methylene chloride solutions of the alkene and aluminium trichloride were mixed a yellow solid precipitated. The precipitate contained both alkene and aluminium trichloride. Except for the cyano absorption the IR spectrum of the alkene in the precipitate is unchanged. Aluminium trichloride has co-ordinated to the cyano groups but not broken the double bond - a betaine has not been formed. The complex appears to be polymeric, it will not dissolve in polar aprotic solvents. However, it will dissolve in chloroform without chemical reaction if a little methanol is added. Apparently, the polymeric structure is disrupted by methanol co-ordination. The HNMR (in CDC13) spectrum shows that one molecule of alkene dissolves per molecule of alcohol. Despite the proximity of an alcohol molecule to the strongly polarized alkene no chemical reaction takes place in this solvent. 

Solubility sol in both polar and nonpolar aprotic solvents like diethyl ether, THF, methylene chloride, pentane, hexane, etc. 

Both siloxane-polyimide copolymers and BPADA-derived copolymers exhibited excellent solubility in a variety of dipolar aprotic solvents, including tetrahydrofuran, n-methylpyrrolidone, and dimethyl sulfoxide, as well as chlorinated hydrocarbons such as o-dichlorobenzene and methylene chloride. The polymers and copolymers were typical thermoplastics exhibiting little elongation at failure. The tensile properties are summarized in Table II. 

Epoxidation. Mimoun et at. report that the M0O5 HMPT complex reacts with olefins to form epoxides in high yield. Alkyl substituents on the double bond increase the rate of epoxidation. Aprotic solvents also enhance the rate highest rates arc observed in methylene chloride. The reaction is very slow in DMF or THF. The epoxidation is stcreospecific with retention of configuration of the olefin. Thus dj-bulene-2 is convened into cu-2,3-epoxybulane and iran. -bulene-2 into /ran5-2,3-epoxybutane. The French chemists proposed the mechanism shown in scheme I. 

The protic solvents most widely used are methanol, ethanol, ethoxyethanol and methoxyethanol in which most organic molecules are soluble. Aprotic solvents that have found extensive use are diglyme, dimethoxyethane, tetrahydrofuran, methylene chloride and chloroform. 

It was in 1990 that Kratschmer et al. [217,218] reported the first macroscopic preparation of in gram quantities by contact-arc vaporization of a graphite rod in a 100 Torr atmosphere of helium, followed by extraction of the resultant soot with toluene. Fullerene ions could also be detected by mass spectrometry in low-pressure hydrocarbon flames [219]. The door was opened by, Kratschmer and co-workers preparative success to extensive studies of the electrochemical behavior of the new materials. Cyclic voltammetry of molecular solutions of Ceo in aprotic electrolytes, e.g., methylene chloride/quatemary ammonium salts, revealed the reversible cathodic formation of anionic species, the radical anion, the dianion, etc. (cf. [220,221]). Finally, an uptake of six electrons in the potential range of 1-3.3 V vs. SHE in MeCN/toluene at — 10°C to form the hexavalent anion was reported by Xie et al. [222]. This was in full accordance with MO calculations. A parametric study of the electroreduction of Cgo in aprotic solvents was performed [223]. No reversible oxidation of C o was possible, not even to the radical cation. However, the stability of di- and trications with special counterions, in the Li/PEO/C 3 MoFf cell, was claimed later [224]. 

Although the enhanced speed of reaction in the highly polar, aprotic solvent makes it possible to effect the reaction in the minimum time, if the optimum yield of product is also desired it is preferable for the concentration of ions in the solvent not to exceed 1 molar. Preferably the concentration of these ions is maintained as low as possible by slowly adding the catechol... to the reaction mixture. During the course of this slow addition the ions react as they are formed, and are therefore always present in a very high dilution. When the alkaline conditions needed for the reaction are provided by the addition of an alkali metal hydroxide to the reaction mixture, it is usually most convenient and satisfactory to add the catechol... and the alkali metal hydroxide separately, simultaneously and slowly to a solution of methylene chloride in the highly polar, aprotic solvent. 

Aprotic solvents—Include acetonitrile, dimethylformamide, N-methylpyrrolidone, hexame-thylphosphoramide, pyridine, dimethyl sulfoxide, sulfolane, nitromethane, propylene carbonate, and methylene chloride. 

The secondary deuterium kinetic isotope effect is comprised of two secondary p-deuterium kinetic isotope effects of 1.22/jg-D and a secondary -deuterium kinetic isotope effect of 1.02. This kinetic isotope effect is identical to those found in several protic and dipolar aprotic solvents such as sulphuric acid-water, trifluoroethanol and methylene chloride. As a result, it has been concluded that the phenyl diazonium salt decomposes by the same mechanism in all solvents. 

Dehydrohatogenatioa. This base in benzene, toluene, or methylene chloride is a satisfactory reagent for dehydrohalogenation of haloalkenes to form alkynes. One advantage over KOH or NaOH is that an aprotic solvent can be used. Examples ... 

The hexaazaisowurtzitane ring system SI is considerably more stable toward acids than is the related triazawurtzitane 40c, which undergoes very facile ring opening in the presence of acid catalysts, even weak ones. Also, in aprotic solvents such as chloroform-d and acetonitrile-ds, 40c is in equilibrium with its monocyclic form 39. On the other hand, hexabenzyl-hexaazaisowurlzitanes 51a-g show no evidence of equilibration nor of decomposition in aprotic solvents by NMR assay. Furthermore, they are rather stable toward acids in aprotic solvents. The hexabenzyl compound 51a, for example, forms stable hydrochloride and hydrobromide salts in benzene, from which Sla may be regenerated by treatment with sodium hydroxide, However, Sla is completely decomposed by heating in acetic acid at 50 C for an hour or by treatment with 10% acetic acid in methylene chloride for several hours at 25 C. The decomposition products are unidentified oils. 

As might be expected on the basis of the C NMR chemical shift data, 3-methoxycarbonyl-2-pyrone 33 is less reactive toward vinyl ethers than 3-chlorocarbonyl-2-pyrone. In fact, at room temperature in methylene chloride, no cycloadduct formation was observed with a number of different vinyl ethers. Marko and co-workers, however, coaxed these pyrone dienes into reacting with representative vinyl ethers at elevated temperatures (70°-80 C) in polar aprotic solvents, leading to bicyclic lactones 34-37. In all cases, each of these bicycloadducts is obtained as a single stereoisomer. 

A stereogenic center on the tether (44a), composed of a relatively small hydroxyl substituent, results in the four possible product isomers shown in Figure 16. The designations anti and syn isomers refer to the orientation of the tether substituent and the adjacent carbonyl group in the product. Alcohol 44a yields all four possible products, and trans is preferred over cis by a factor of 2.5 or 4.2, depending on the solvent. The primary difference in the product ratios comes from the solvent-dependent synlanti ratio. In the protic solvent methanol, the anti isomers comprise 85% of the product whereas in the aprotic methylene chloride the syn isomers are 56% of the mixture. The syn selectivity may result from an intramolecular hydrogen bond of the alcohol to the nearby carbonyl (see pro-trans-syn conformation). Steric enhancement of the alcohol as a /-butyldimethylsilyl ether (44b) results in a solvent independent anti-selective photoreaction. The amount of syn isomers produced with a t-butyldimethylsilyloxy substituent is less than 1%. ... 

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