Methyl sulfoxide, solvent

The kinetics of polycondensation hy nucleophilic aromatic substitution in highly polar solvents and solvent mixtures to yield linear, high molecular weight aromatic polyethers were measured. The basic reaction studied was between a di-phenoxide salt and a dihaloaromatic compound. The role of steric and inductive effects was elucidated on the basis of the kinetics determined for model compounds. The polymerization rate of the dipotassium salt of various bis-phenols with 4,4 -dichlorodiphenylsulfone in methyl sulfoxide solvent follows second-order kinetics. The rate constant at the monomer stage was found to be greater than the rate constant at the dimer and subsequent polymerization stages. 

Various ratios of AA, IA and NVP monomers were copolymerized in water with potassium persulfate initiator ( 2 % by wt of combined monomers) with polymerization run under nitrogen for 9-10 hr at 95 °C. The copolymers prepared (Table 2) were recovered in high yields, using standard freeze-drying techniques. Several poly(AA-co-lA) and poly(AA-co-NVP) were also prepared for the study. For purification, the copolymers were dissolved in methyl alcohol and precipitated from diethyl ether, followed by drying under vacuum. The IR spectrum of the copolymers were obtained from cast films, using a MID AC FT IR Spectrometer. NMR ( H and C) spectra were obtained on a Bruker AM 250 MHz NMR analyzer, using deutrated methyl sulfoxide solvent and trimethylsilane (TMS) reference (Table I). 

The relative ease of H/D exchange of the methylene protons of benzyl methyl sulfoxide is markedly influenced by the nature of the base and the solvent used, as shown in Table 12. The data reveal that rather high stereoselectivities can be observed when alkyllithium-THF is used. 

Figure 3. Effect of temperature on the magnitude of the chemical shift difference between isopropyl methyl sulfoxide enantiomers in the presence of (-)-TFPE in CCI4. Molar ratio of alcohol to sulfoxide to solvent is 2 1 5. Symbols are as in Figure 2. Reprinted with permission from Tetrahedron Lett. 1974,2295-2298.

Before concentration, acid hydrolyzates are neutralized, most commonly with barium carbonate, although such organic bases as methyldioctylamine has been used.81 This step normally causes little loss, except by adsorption on, for example, barium sulfate,82 but the following points are of interest. Neutralization with ammonia has been recommended,83 as the neutral solution may be evaporated directly to dryness without filtration, and the ammonium sulfate formed is insoluble in methyl sulfoxide, a solvent used for trimethyl-silylation. The authors83 also found that, when hydrolyzates are neutralized with ion-exchange resins, the pH of the concentrated solutions may differ by as much as 2 units of pH. D-Fructose has been found to be epimerized by barium carbonate or pyridine, and lead... 

Solvents that have been less extensively used are N-methyl-2-pyrrolidinone and hexamethylphosphoric triamide.183 The author of this article183 also discussed the purification of chlorotrimethylsilane, and the anomalous results that may be obtained from the use of impure reagent have been commented on in the case of analyses of pentaerythritol.184 The various methods available for the bulk purification of methyl sulfoxide have been reviewed,185 and a symposium on this compound reviewed its use as a solvent in selected reactions.186... 

Methyl sulfoxide has been used, chiefly by Micheel and his coworkers, as an effective solvent for the acid-catalyzed polycondensation of sugars.93-101 In view of the good yields of material of high molecular weight, the methods developed offered considerable promise. Unfortunately, it was subsequently found 4 that, in acidic media, methyl sulfoxide undergoes a... 

It is clear, therefore, that polymers synthesized by polycondensation of sugars in acidic methyl sulfoxide are, actually, copolymers of sugars and formaldehyde in which some of the glycosyl residues are joined by glycosidic bonds, and others are linked by bridges of oxymethylene units. Nonetheless, because polycondensation of sugars can be effected in methyl sulfoxide, and because the methods developed for the polycondensation may be applicable to other solvent systems,10 the extensive studies reported by Micheel and his coworkers will be discussed. 

Other solvents may also be used with similar effects. Isopropyl alcohol has been used for fractionating a polyglucose.72 Examination of the fractions revealed that fractionation according to viscosity and immunological reactivity had occurred.240 The excellent solvent properties of methyl sulfoxide,241 tetramethylene sulfone, pyridine, N, TV-dimethylformamide, and formamide may also prove useful. 

Figure 4. Hydroxyl PMR signals (solvent, methyl sulfoxide-d6) for A) D-fructose after prior equilibration in water B) D-fructose at equilibrium in methyl sulfoxide-d6 C) leucrose, freshly dissolved crystals D) furanose, freslily dissolved crystals (arrows show the positions of signals that increase in intensity with time) G2-hydroxyl proton-2, F4-hydroxul proton-4 E) lactulose, freshly dissolved crystals. At the upper right are 13C-2 signals at 25.15 MHz for D-fructose in water (see Reference...

The preparation of 6.102 is carried out in a variety of solvents, such as DMF, DMA, dimethylsulfoxide (DMSO) and ethyl methyl sulfoxide, at 80°C and the yield of the carcerand is virtually quantitative. 

Note Colorless, odorless (when pure), hygroscopic liquid, powerful aprotic solvent dissolves many inorganic salts, soluble in water combustible readily penetrates the skin incompatible with strong oxidizers and many halogenated compounds (e.g., alkyl halides, aryl halides), oxygen, peroxides, diborane, perchlorates. Synonyms DMSO, methyl sulfoxide, sulfinylbismethane. 

Reagents. Para-Bis-A polymerization-quality bisphenol-A (Dow Chemical Co.) was recrystallized once from toluene. Pfaltz and Bauer s 4,4 -dichlorodiphenylsulfone was recrystallized three times from ethanol. Reagent phenol (Baker) and 4,4 -biphenol (Eastman s white label) were used as received. Spectroquality methyl sulfoxide, dimethyl acetamide, and dimethylformamide (Matheson, Coleman, and Bell) were used as solvents. 3,5,3, 5 -Tetramethyldiphenoquinone and hexamethylphosphor-amide (Aldrich) were used as received. 

The polymerization rate of several diphenoxide salts with 4,4 -di-chlorodiphenylsulfone has been measured in methyl sulfoxide and other solvents. The experimental data conforms to a second-order reaction model, which consists of a high reaction rate constant at the monomer stage, followed by a lower reaction rate constant at subsequent polymerization stages. Based on this kinetic model, the reaction rate constants and activation energies have been determined. 

There are fewer complications in the use of aprotic media as solvents for sugars, and a wide range of such media has been investigated for their potential utility. Several, in particular, methyl sulfoxide, N,N-dimethylformamide, and a number of nitrogenous, heterocyclic compounds, have proved to be exceptional solvents for the lower saccharides. 

One of the more important applications of methyl sulfoxide as a sugar solvent is for n.m.r. spectral studies, where, in conjunction with acetone-de, it has been used because exchange reactions are suppressed191 (see the n.m.r. section, p. 124). Methyl sulfoxide dissolves both amylose and amylopectin,192 and these can then be separated by the judicious use of co-solvents after dissolution.193 Ultracentri-... 

---