Solvent dioxolans

The cyclic diether, 1,3-dioxolane, is recommended by Ferro Corporation as a more benign solvent substitute for chlorinated organic solvents, such as methylene chloride, 1,2-dichloroethane, and 1,1,1-trichloroethane, and for ketones, such as methyl ethyl ketone (MEK). This ethylene glycol-based ether is a suitable solvent under neutral and basic conditions in several major-use areas. It is a powerful solvent for softening and dissolving polymers made from polar monomers, for example, polycarbonates, acrylates, cellulosics urethanes, phenoUcs, nitriles, urea-formaldehydes, and alkyds, as well as polyesters, vinyl epoxys, and halogen-containing polymers. As a reaction solvent it is added as a component to a special quaternary ammonium or phosphonium salt solution for preparation of a vesicular phenoxy resin. Other beneficial uses for the solvent dioxolane, include ... 

Tbe constraction of the Li/CuO button-type battery shown in Fig. 14.87a is similar to other conventional and lithium/solid-cathode cells. Copper oxide forms the positive electrode and lithium the negative. The electrolyte consists of lithium perchlorate in an organic solvent (dioxolane). 

The most commonly used protected derivatives of aldehydes and ketones are 1,3-dioxolanes and 1,3-oxathiolanes. They are obtained from the carbonyl compounds and 1,2-ethanediol or 2-mercaptoethanol, respectively, in aprotic solvents and in the presence of catalysts, e.g. BF, (L.F. Fieser, 1954 G.E. Wilson, Jr., 1968), and water scavengers, e.g. orthoesters (P. Doyle. 1965). Acid-catalyzed exchange dioxolanation with dioxolanes of low boiling ketones, e.g. acetone, which are distilled during the reaction, can also be applied (H. J. Dauben, Jr., 1954). Selective monoketalization of diketones is often used with good success (C. Mercier, 1973). Even from diketones with two keto groups of very similar reactivity monoketals may be obtained by repeated acid-catalyzed equilibration (W.S. Johnson, 1962 A.G. Hortmann, 1969). Most aldehydes are easily converted into acetals. The ketalization of ketones is more difficult for sterical reasons and often requires long reaction times at elevated temperatures. a, -Unsaturated ketones react more slowly than saturated ketones. 2-Mercaptoethanol is more reactive than 1,2-ethanediol (J. Romo, 1951 C. Djerassi, 1952 G.E. Wilson, Jr., 1968). 

Hydrogenation of enones in MeOH with Pd/C resulted in acetal formation. When ethylene glycol/THF is used as solvent, the related dioxolane is formed in 86% yield. 

Various cyclic ethers are reported to be superior solvents for secondary lithium metal batteries. 1,3-Dioxolane [94, 95] and... 

Dioxolane-l, 2-dimethoxyethane-Li2 B1()C11() exhibited chemical stability towards the components of a lithium-titanium disulfide cell and showed promise as an electrolyte in such cells [98], Among various systems composed of an ether-based solvent and a lithium salt, THF-LiAsF6 was the least reactive to lithium at elevated temperature and gave the best cycling efficiency [99, 100], Tetrahydrofu-ran-diethyl ether-LiAsF(i afforded lithium electrode cycling efficiency in excess of 98% [101],... 

The PGS obtained by Wang and coworkers was a kind of thermoset elastomer with the Young s modulus of 0.282 0.025 MPa, a tensile strain of at least 267 zE 59.4%, and a tensUe strength was at least 0.5 MPa. The mechanical properties of PGS were well consisted with that of some common soft tissues. Although PGS is a thermoset polymer, its prepolymer can be processed into various shapes by solving it in common organic solvents such as 1,3-dioxolane, tetrahydrofuran, isopropanol, ethanol, and iV,M-dimethylformamide. Porous scaffolds can be fabricated by salt leaching. 

Accordingly, the cyclopropenylidene anthrones 190/198 were converted by ferric chloride in hydroxylic solvents to the allene ketal 466, whose hydrolysis gives the allenic ketone 46 7288. The dioxolane 468 was obtained from the alkyl-substituted quinocyclopropene 190 in glycol and the ketone 467 in methanol. Apparently FeCl3 served not only as an oxidant, but also as a Lewis acid assisting solvent addition to C1 2 of the triafulvene. 

Aldehydes and ketones have been protected as acetals and dioxolanes using orthoformates, 1,2-ethanedithiol or 2,2-dimethyl-l,3-dioxolane by Hamelin and coworkers. This acid-catalyzed reaction proceeds in the presence of p-toluenesulfonic acid (p-TsOH) or KSF clay under solvent-free conditions (Scheme 6.2). The yields ob-... 

Unfortunately, the comparison is not reliable because the temperature was not measured in the domestic oven. Dioxolane formation by acid-catalyzed exchange between 2,2-dimethyl-l,3-dioxolane (DMD) and a ketone in a inert solvent, or simply in excess DMD, requires 4 to 7h under classical conditions [63], This reaction is readily achieved under microwave irradiation in high yields in 4 to 30 min (Scheme 8.43). 

Similarly, 39K nmr line-shape analysis has been applied to the study of the interaction of K+ with 18-crown-6 in a range of solvent mixtures (Schmidt Popov, 1983). In most instances, the cation exchange proceeds via a normal dissociative process (as found in water) however, in 1,3-dioxolane, metal exchange switches to a bimolecular exchange mechanism. 

The first two compounds have dipole moments which do not lie in the H—C-H plane. The C-2 methylene in (3) is geometrically similar to the methylene in (2) and is similarly substituted. However, in the dioxolane the permanent dipole moment must lie in or close to the H-C-H plane. The solvent invariance of VH H in (i) and (2) in contrast to the solvent dependence of 2/H H in (3) (Table 22) provides some support for this hypothesis. 

Table 22. Geminal H H coupling constant across C2 of 4-methyl-l, 3-dioxolane in various solvents...

Partial fluorination of 4-arylthio-l,3-dioxolan-2-ones occurs preferentially at the carbon atom adjacent to the thio group [67]. However, a remarkable solvent effect is encountered. In the more polar solvent, dimethoxyethane substitution occurs, while in the less polar dichloromethane a larger portion of the desulfurization with cleavage of the phenylthio group takes place. This is attributed to the fact that the intermediate radical cation is more stable in the polar solvent and undergoes deprotonation, while in the less polar solvent, the less stabilized radical cation dissociates into a dioxolane cation and a phenylthio radical. 

A further study of the aggregation state of PhLi in etheral solvents has resolved signals for the ipso carbon which firmly establish the tetramer and dimer structures in diethylether, and the dimer and monomer structures in THF. The effects of polar additives such as THF, DME, dioxolane, 2,5-dimethyltetrahydrofuran, TMEDA, PMDTA, HMTTA, HMPA, DMPU, and 12-crown-6 to solutions of PhLi in diethylether and/or THE have been studied by low-temperature multinuclear techniques. 

Cyclic formals react with dinitrogen pentoxide in chlorinated solvent to yield unstable but interesting ring-opened products, including hemiformal nitrates 1,3-dioxolane (44) reacts to yield a mixture of hemiformal nitrate (45) and formal ether (46) products. Similar products are formed from acyclic formals and dinitrogen pentoxide. ... 

Recent NMR study suggested that PhLi exists as a mixture of tetramer and dimer in diethyl ether and that the addition of a stoichiometric amount of a coordinating solvent such as THF, dioxolane, DME or TMEDA induces complete conversion of the mixture to dimeric solvates. In a THF solution PhLi exists as a mixture of dimer and monomer. It was noted that the addition of 12-crown or HMPA increases the reactivity and decreases the selectivity of PhLi in THF. 

Decomposition of 18 under thermal conditions in the presence of acetone in hydrocarbon solvent led to the formation of 23 and 24. These were shown to arise through rearrangement of the chloroepoxide (22) formed upon collapse of ylide 19. Thermolysis in the presence of excess acetone and a substituted benzaldehyde led to a 53% yield of 21, formed by an initial dipolar cycloaddition with the substituted benzaldehyde and ylide 19 to generate dioxolane 20. Dehydrochlorination of 20 yielded 21. 

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