Dimethyl sulfoxide stoichiometry

On the other hand, CH-acidic solvents such as acetylacetone, acetonitrile, nitro-methane, and dimethyl sulfoxide (Entries 25-28) yield stable crystal inclusions, each having a strict 1 1 stoichiometry. Finally, respective crystallization experiments using solvents of even less polarity or ability to form H-bonds have been carried out. The... 

The complications which result from the hydrolysis of alkali metal cyanides in aqueous media may be avoided by the use of non-aqueous solvents. The one most often employed is liquid ammonia, in which derivatives of some of the lanthanides and of titanium(III) may be obtained from the metal halides and cyanide.13 By addition of potassium as reductant, complexes of cobalt(O), nickel(O), titanium(II) and titanium(III) may be prepared and a complex of zirconium(0) has been obtained in a remarkable disproportion of zirconium(III) into zirconium(IV) and zirconium(0).14 Other solvents which have been shown to be suitable for halide-cyanide exchange reactions include ethanol, methanol, tetrahydrofuran, dimethyl sulfoxide and dimethylformamide. With their aid, species of different stoichiometry from those isolated from aqueous media can sometimes be made [Hg(CN)3], for example, is obtained as its cesium salt form CsF, KCN and Hg(CN)2 in ethanol.15... 

Simple 2,2-dibutyl-l,3,2-dioxastannolanes form solid complexes of monomer units with certain nucleophiles, such as pyridine and dimethyl sulfoxide, that have 1 1 stoichiometry and pentacoordinate tin atoms.62 Such complexes are less stable for more-substituted stannylene acetals, such as those derived from carbohydrates.62 Unfortunately, the precise structures of these complexes have not yet been defined. Addition of nucleophiles to solutions of stannylene acetals in nonpolar solvents has been found to markedly increase the rates of reaction with electrophiles,63 and transient complexes of this type are likely intermediates. Similar rate enhancements were observed in reactions of tributylstannyl ethers.57 Tetrabu-tylammonium iodide was the nucleophile used first,57 but a wide variety of nucleophiles has been used subsequently tetraalkylammonium halides, jV-methylimidazole,18 and cesium fluoride64,65 have been used the most. Such nucleophilic solvents as N,N-dimethylformamide and ethers probably also act as added nucleophiles. As well as increasing the rates of reaction, in certain cases the added nucleophiles reverse the regioselectivity from that observed in nonpolar solvents.18,19... 

In contrast to 2, the above derivatives incorporate four hydrogen bond donors. As a consequence, a favourable bonding situation is present in which the four secondary amine protons of each host can interact with the two charged carboxylate groups of the guest - see 4a and 4b. The proposed structure of the complex of the bis-urea derivative was supported by the existence of large NMR downfield shifts for both the inner and outer urea NH resonances in deutero-dimethyl sulfoxide and the observation of intramolecular H NOEs between the receptor aryl and the guest CH2 resonances in this solvent. A Job s plot confirmed the 1 1 stoichiometry of the product. 

Simple 2,2-dibutyl-l,3,2-dioxastannolanes form solid complexes of monomer units with nucleophiles, such as pyridine and dimethyl sulfoxide, that have 1 1 stoichiometry and pentacoordinate tinatoms. Such complexes are less stable for more substituted stannylene acetals, e.g., those derived from carbohydrates. Addition of nucleophiles to solutions of stannylene acetals in non-polar solvents has been found to markedly increase the rates of reaction with electrophiles and transient 1 1 complexes of this type are... 

First examples of second-sphere coordination adduct between a CD and such organometallic complexes were observed with the ferrocene and its derivatives. Thus, Breslow was the first to report in 1975 that ferrocene forms a 1 1 adduct with the /3-CD in both A/T-dimethylformamide and dimethyl sulfoxide. Nevertheless, the first crystalline inclusion complexes of ferrocene and its derivatives were prepared by Harada and Takahashi in 1984. The inclusion complexes were obtained by direct addition of crystals of ferrocene or its derivatives into aqueous solutions of CD. The stoichiometry of the inclusion complexes was found to be dependent on the sizes of the CD. The /3-CD and y-CD formed 1 1 stoichiometric inclusion complexes whereas a-CD formed a 2 1 (CD guest) complex with ferrocene. From induced circular dichroism experiments, three structures were proposed for these adducts as shown in Figure... 

Unusual control of host-guest stoichiometry in isostructural clathrates of mixed guests was recently re-ported. The diol 14 forms isostructural clathrates H-4A and H 4B (A=dimethylformamide, B=dimethyl sulfoxide). Investigation of the selectivity of H in mixtures of A and B spanning the entire concentration range 0 < Xa < 1 yielded the stepwise competition profile shown in Fig. 3,... 

Dimethyl sulfoxide is generally favored, particularly with processes using sodium hydroxide as base. In carbonate polymerizations, the presence of free phenolic hydroxyl groups at polymerization temperatures of 150-160°C leads to undesirable side reactions Involving acid catalyzed decomposition of OMSO which ultimately can lead to stoichiometry upsets. For polymerizations involving carbonate, dimethyl acetamide is often the solvent of choice [7], DMSO is limited by its 180 C boiling point to temperatures of 170 C or lower while DMAc is useful in the 150-160 C range. 

Oxidation of star polymethylene 6 affords 3 equiv. of a-hydroxy-co-(4-methoxyphenyl) polymethylene 5 with DP = n. The strict correspondence between stoichiometry and DP in these examples is consistent with a rapid initiation and the absence of termination or chain transfer reactions in the polymerization of ylide 1. The absence of a termination step is reasonable, since the living end of this polymer is a trialkylborane, which is stable under the reaction conditions. Dimethyl sulfoxide (DMSO), a byproduct that accumulates during the reaction does not inhibit the initiator/catalyst. 

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