Displacement reactions solvents

Polymerization and Spinning Solvent. Dimethyl sulfoxide is used as a solvent for the polymerization of acrylonitrile and other vinyl monomers, and as a reaction solvent for other polymeri7ations. Tt is also used as a solvent for displacement reactions, solvent for base-catalyzed reaclions, extraction solvent, solvent for electrolytic reactions, cellulose solvent, pesticide solvent, and clean-up solvent,... 

Condensation ofDianhydrides with Diamines. The preparation of polyetherknides by the reaction of a diamine with a dianhydride has advantages over nitro-displacement polymerization sodium nitrite is not a by-product and thus does not have to be removed from the polymer, and a dipolar aprotic solvent is not required, which makes solvent-free melt polymerization a possibiUty. Aromatic dianhydride monomers (8) can be prepared from A/-substituted rutrophthalimides by a three-step sequence that utilizes the nitro-displacement reaction in the first step, followed by hydrolysis and then ring closure. For the 4-nitro compounds, the procedure is as follows. 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

In interpreting many aspects of displacement reactions, particularly solvolysis, it is important to be able to characterize fee nucleophilicity of fee solvent. Assessment of... 

Various sources of fluoride ion have been investigated, of which highly nucleophilic tetraalkylammonium fluorides ate the most effective Thuf, fluoro alkyl halides and N (fluoroalkyl)amines are efficiently synthesized by treatment of the corresponding trifluoromethanesulfonic esters with tetrabutylammonium fluoride trihydrate in aprotic solvents [5fl] (equation 34) The displacement reactions proceed quantitatively at room temperature within seconds, but tail with hydrogen fluoride-pyridine and give reasonable yields only with hydrogen fluo ride-alkylamine reagents... 

Nucleophilic displacement reactions One of the most common reactions in organic synthesis is the nucleophilic displacement reaction. The first attempt at a nucleophilic substitution reaction in a molten salt was carried out by Ford and co-workers [47, 48, 49]. FFere, the rates of reaction between halide ion (in the form of its tri-ethylammonium salt) and methyl tosylate in the molten salt triethylhexylammoni-um triethylhexylborate were studied (Scheme 5.1-20) and compared with similar reactions in dimethylformamide (DMF) and methanol. The reaction rates in the molten salt appeared to be intermediate in rate between methanol and DMF (a dipolar aprotic solvent loiown to accelerate Sn2 substitution reactions). 

Synthesis of all these heterocycle activated polyethers is carried out in polar aprotic solvents, such as NMPs, by the K2CO3 method. The effective displacement reactions are reported at varied temperatures (140-190°C) and durations (3-24 h). 

Interests in the phase transfer catalysis (PTC) have grown steadily for the past several years [68-70]. The use of PTC has recently received industrial importance in cases where the alternative use of polar aprotic solvents would be prohibitively expensive [71-74]. Thus, the potential application of the phase transfer catalyzed aromatic nucleophilic displacement reactions between phenoxide or thiophenoxide and activated systems has... 

The advantage of the activated displacement polymerization is the facile incorporation of different and unconventional structural units in the polymer backbone. Most of the heteroarylene activated polyethers prepared by this route are soluble in many organic solvents. The solubility behavior of new polyethers is shown in Table 8. In contrast to many polyphenylenequi-noxalines, poly(aryl ether phenylquinoxalines) prepared by the quionoxaline activated displacement reaction are soluble in NMP. Solubility in NMP is important since it is frequently used for polymer processing in the microelectronics industry [27]. 

With bromine monochloride at 0°C in a variety of solvents, 1 was converted into addition products, the product distribution being a function of solvent. A change in halogenating agent also altered the product ratio. (Scheme 4) Nucleophilic displacement reactions between these products and silver fluoride was found to cause preferential bromine substitution (83G149). 

The photolysis of chlorinated aromatic compounds occurs by several processes which follow predictable routes 13). They frequently undergo photochemical loss of chlorine by dissociation of the excited molecule to free radicals or, alternatively, through a nucleophilic displacement reaction with a solvent or substrate molecule. Either mechanism is plausible, and the operation of one or the other may be influenced by the reaction medium and the presence of other reagents. 

Extractive alkylation is used to derivatize acids, phenols, alcohols or amides in aqueous solution [435,441,448,502]. The pH of the aqueous phase is adjusted to ensure complete ionization of the acidic substance which is then extracted as an ion pair with a tetraalkylammonium hydroxide into a suitable immiscible organic solvent. In the poorly solvating organic medium, the substrate anion possesses high reactivity and the nucleophilic displacement reaction with an alkyl halide occurs under favorable conditions. 

After extraction, the loaded solvent contains 6 g T1 zirconium as zirconium oxide with 0.2% hafnium oxide. The raffinate is left with 0.2 to 0.3 g l l of the oxides of zirconium and hafnium of this, 70-90% is hafnium oxide. This raffinate can act as a feed solution for the recovery of pure hafnium oxide. The loaded extractant, on the other hand, is subjected to a scrubbing operation with pure zirconium sulfate solution to eliminate any co-extracted hafnium. This scrubbing operation is essentially a displacement reaction ... 

Thus solvolysis of (+)C6HsCHMeCl, which can form a stabilised benzyl type carbocation (cf. p. 84), leads to 98% racemisation while (+)C6H13CHMeCl, where no comparable stabilisation can occur, leads to only 34% racemisation. Solvolysis of ( + )C6H5CHMeCl in 80 % acetone/20 % water leads to 98 % racemisation (above), but in the more nucleophilic water alone to only 80% racemisation. The same general considerations apply to nucleophilic displacement reactions by Nu as to solvolysis, except that R may persist a little further along the sequence because part at least of the solvent envelope has to be stripped away before Nu can get at R . It is important to notice that racemisation is clearly very much less of a stereochemical requirement for S l reactions than inversion was for SN2. 

Syntheses are limited to mercuric salts of weak acids (2,110). Generally, increasing the length of the straight alkyl chain decreases the extent of decarboxylation (e.g., Ref. 133). Electron-withdrawing substituents suppress decarboxylation. For example, mercurials are not formed with Me02C, Cl, and Me(CH2)nO substituents on the a carbon (137,148,149), but some decarboxylation occurs with these on the j8 carbon (135-137). Chain decarboxylation predominated in reactions in benzene, butyric acid [R = Me(CH2)2] (150), or acetic acid (R = Me) (124). The chain reaction was also observed for R = Me(CH2)2 in the absence of solvent and in ethylacetate or heptane solution, but in these media the radical displacement reaction was dominant (2,150). When benzene was used as solvent... 

These problems can be somewhat overcome by a study of reactions in solution where much greater densities are possible than in the gas phase and fast bimolecular reaction are diffusion limited [1,28,29]. However, since coordinatively unsaturated metal carbonyls have shown a great affinity for coordinating solvent we felt that the appropriate place to begin a study of the spectroscopy and kinetics of these species would be in a phase where there is no solvent the gas phase. In the gas phase, the observed spectrum is expected to be that of the "naked" coordinatively unsaturated species and reactions of these species with added ligands are addition reactions rather than displacement reactions. However, since many of the saturated metal carbonyls have limited vapor pressures, the gas phase places additional constraints on the sensitivity of the transient spectroscopy apparatus. 

Sigma (a) bonds Sigma bonds have the orbital overlap on a line drawn between the two nuclei, simple cubic unit cell The simple cubic unit cell has particles located at the corners of a simple cube, single displacement (replacement) reactions Single displacement reactions are reactions in which atoms of an element replace the atoms of another element in a compound, solid A solid is a state of matter that has both a definite shape and a definite volume, solubility product constant (/ p) The solubility product constant is the equilibrium constant associated with sparingly soluble salts and is the product of the ionic concentrations, each one raised to the power of the coefficient in the balanced chemical equation, solute The solute is the component of the solution that is there in smallest amount, solution A solution is defined as a homogeneous mixture composed of solvent and one or more solutes. 

The choice of the catalyst is an important factor in PTC. Very hydrophilic onium salts such as tetramethylammonium chloride are not particularly active phase transfer agents for nonpolar solvents, as they do not effectively partition themselves into the organic phase. Table 5.2 shows relative reaction rates for anion displacement reactions for a number of common phase transfer agents. From the table it is clear that the activities of phase transfer catalysts are reaction dependent. It is important to pick the best catalyst for the job in hand. The use of onium salts containing both long and very short alkyl chains, such as hexade-cyltrimethylammonium bromide, will promote stable emulsions in some reaction systems, and thus these are poor catalysts. 

A similar dependence of the first-order rate constants with respect to the quantity of added water has been reported for the reaction of sodium formate with 1,4-dichlorobutane and related displacement reactions, In these studies tetra- n-butylammonium hydrogen sulphate and tetra- n-butylammonium bromide were used as catalysts and chlorobenzene as the solvent. 

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