K-DMSO System

The position of the intercalated DMSO molecule in the interlayer space of kaolinite is such that the first S-C group is almost parallel with the surface of kaolinite and the second S-C group is directed into the tetrahedral cavity of kaolinite [130, 131]. The S=0 group has 40.3° inclination to the basal surface of kaolinite. The methyl group of DMSO is influenced by both the opposing mineral surfaces. In addition, the intercalation of DMSO molecule results in the expansion of kaolinite from 7.2 to 11.19 A phase [132]. The formation of H-bonds between DMSO and surface OH groups of the octahedral side and weak H-bonds with the tetrahedral side of kaolinite was suggested [133-139]. 

The intercalated DMSO molecule has different orientations in low and high defect kaolinite [132, 140], This suggests different interactions between DMSO and these kinds of kaolinite. Heller-Kallai et al. [141] confirmed the same results. The authors have concluded that the way of placement of the DMSO molecule in the interlayer space of kaolinite depends on the number of defects in the structure of kaolinite. 

The value of the reaction enthalpy of decomposition of the kaolinite-DMSO intercalate is -12 kcal/mol [142] and the enthalpy of formation of hydrogen bonds is about -10 kcal/mol [143]. 

It is proposed that the intercalation of kaolinite with DMSO depends on the presence of water molecules in the interlayer space of mineral [132, 140, 144]. The water molecules are in well-defined positions within the intercalation structure. The evidence of the existence of two types of intercalated water in the DMSO-intercalation complex was obtained [132]. 

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BSSE corrected interaction energies (kcal/mol) of D-FA, D-MFA and K-DMSO systems calculated at the B3LYP/3-21G level of the theory, and using ONIOM(B3LYP/3-21G PM3) method [148,149] ... 

The adsorption and intercalation lead to more significant changes of geometrical parameters of the DMSO molecule in the K-DMSO system in comparison with intercalated and adsorbed FA and MFA molecules in dickite-FA and dickite-MFA systems [148, 150]. For example, the S=0 bond of the DMSO is enlarged about 0.035 A in the adsorbed system and 0.05 A in the intercalated system [148]. 

Fig. 5 The optimized structure of the DMSO intercalated molecule in the K-DMSO system calculated using cluster model at the B3LYP/3-21G level of theory [148], and periodic model calculated using the DFT method, PW91 potential and plane waves basis set [150] (K-DMSO(4) model).

The angle between the OH groups and the surface of kaolinite participating in the formation of hydrogen bonds with the DMSO molecule is 40-50° [150], Calculated geometry parameters of the octahedral OH groups of the intercalated K-DMSO system are in agreement with experimental data [134]. 

Calculated interaction energies for K-DMSO systems are significantly lower in comparison with two other studied systems (e.g., it is about 50 % comparing with the D-FA system) (see Table 3). It reflects the fact that the DMSO molecule is less stabilized with respect to the surface of the mineral than... 

Different interaction energies of the K-DMSO system were found using periodic models, depending on the number of DMSO molecules present [150]. The calculated values of interaction energies are as follows -21.69 kcal/mol (K-DMSO(l)), -17.90 kcal/mol (K-MSO(2)), -15.88 kcal/mol (K-DMSO(4)) (the interaction energies are recalculated per one DMSO molecule). The interaction energy that corresponds to mutual interactions of intercalated DMSO molecules in the interlayer space of kaolinite is about 2.43 kcal/mol. 

Notice that the base temperature in the methanol column is much higher in the DMSO system (468 K) compared to that in the water system (378 K). The temperature profile shown in Figure 11.18c shows a very large temperature change from the top to the bottoms of the methanol column (130 K differential). This feature will impact the control stmcture, as discussed later, requiring the use of an average temperature control structure. The acetone-DMSO separation is quite easy, so a very small reflux ratio is required to achieve high purities. The reflux ratio in the methanol column is heuristically fixed at 0.5 in this system as a reasonable minimum operational value. 

Trofimov has extended his previously reported heterocyclization of ketoximes 39 with acetylene to propyne or its isomer allene in superbase systems (MOR/DMSO M = K, Cs, R = H, t-Bu) to afford a facile synthesis of substituted pyrroles 40 and 41 . Due to a fast propyne to allene protropic isomerization under the reaction conditions, the product is the same regardless of which species is employed. 

In conjunction with the present review we have carried out AM1-SM4 calculations in solvent -hexadecane (e = 2.06) for the benzotriazole equilibrium. We find that 35 is better solvated than 34 by 0.9 kcal/mol, with all of the differential solvation being found in the AG pterm. Not surprisingly, PM3-SM4 results are very similar. This seems to be out of step with the data from CDCb, the most nonpolar solvent for which experimental results are available. It is not clear, however, whether this difference is attributable to (i) the smaller dielectric constant of -hexadecane compared to CDCb (for CHCb e = 4.8 at 293 K [240]), (ii) specific interactions between weakly acidic chloroform and the basic benzotriazole tautomers, (iii) inadequacies in the semiempirical electronic structure, (iv) inadequacies in the SM4 model, or (v) some combination of any or all of the above. When SM5 models are available for CHCI3 and DMSO, it will be interesting to revisit this system. 

An equilibrium and kinetic study of the iron(II) phthalocyanine/nitric oxide system in DMSO, at 293 K, showed that formation of [Fe(pc)(NO)] obeys a simple second-order rate law, like [Fe(pc)] plus CO but unlike [Fe(pc)] plus dioxygen. A rate constant for dissociation of [Fe(pc)(NO)] was derived from its formation rate and equilibrium constants. " ... 

It was later shown that one could reformat the log k vs mol% DMSO plot as a log k vs pX a plot , i.e. a Br0nsted-type plot. This transformation was effected through the effect of DMSO composition on pTsTa values, i.e. a novel Br0nsted-type plot , as illustrated in Figure 6 for the reaction of the Ox /T-ClCeHtO" pair with 4-nitrophenyl diphenylphos-phinate in the DMSO-H2O system. 

Figure 8.24a, for example, shows the FTIR spectrum before the photolysis of mixtures of DMS in air with h2o2 as the OH source and the residual spectrum after 5 min of photolysis (Barnes et al., 1996). The reactants, as well as the product S02 have been subtracted out in Fig. 8.24b. Dimethyl sulfoxide (DMSO) as well as dimethyl sulfone, CH3S02CH3 (DMS02), and small amounts of COS are observed as products. DMSO is so reactive that it is rapidly converted into DMS02 in this system and hence both are observed in Fig. 8.24b. However, Barnes and co-workers calculate that the DMSO yield corrected for secondary oxidation is about the same as the fraction of the OH-DMS reaction that proceeds by addition under these conditions, i.e., that the major fate of the adduct is reaction (47). Turnipseed et al. (1996) measured the yield of H02 from reaction (47) to be 0.50 + 0.15 at both 234 and 258 K, suggesting that there are other reaction paths than (47) as well. The mechanism of formation of COS is not clear but may involve the oxidation of thioformaldehyde (H2C=S). The implications for the global budget of COS are discussed by Barnes et al. (1994b, 1996).

A comparison of the suitability of solvents for use in Srn 1 reactions was made in benzenoid systems46 and in heteroaromatic systems.47 The marked dependence of solvent effect on the nature of the aromatic substrate, the nucleophile, its counterion and the temperature at which the reaction is carried out, however, often make comparisons difficult. Bunnett and coworkers46 chose to study the reaction of iodoben-zene with potassium diethyl phosphite, sodium benzenethiolate, the potassium enolate of acetone, and lithium r-butylamide. From extensive data based on the reactions with K+ (EtO)2PO (an extremely reactive nucleophile in Srn 1 reactions and a relatively weak base) the solvents of choice (based on yields of diethyl phenylphosphonate, given in parentheses) were found to be liquid ammonia (96%), acetonitrile (94%), r-butyl alcohol (74%), DMSO (68%), DMF (63%), DME (56%) and DMA (53%). The powerful dipolar aprotic solvents HMPA (4%), sulfolane (20%) and NMP (10%) were found not to be suitable. A similar but more discriminating trend was found in reactions of iodobenzene with the other nucleophilic salts listed above.46 Nearly comparable suitability of liquid ammonia and DMSO have been found with other substrate/nucleophile combinations. For example, the reaction of p-iodotoluene with Ph2P (equation (14) gives 89% and 78% isolated yields (of the corresponding phosphine oxide) in liquid ammonia and DMSO respectively.4 ... 

In more recent work (85ZOR406), important experimental details concerning heterocyclization of other ketoximes of the thiophene series with acetylene in the MOH/DMSO (M = Li, K) system have been reported (Scheme 14). 

POMs form by a self-assembly process, typically in an acidic aqueous solution and can be isolated as powder or crystals with counter-cations. Appropriate selection of counter-cations can control the solubility of POMs in various reaction media. For homogeneous system, alkylammonium cations, generally TBA, are selected as counter-cations of POM anions for the dissolution in organic solvents such as acetonitrile, DMF, DMSO and 1,2-dichloroethane. POMs with metal counter-cations such asNa +, K+,Rb+,Cs + and Ag + are not soluble in common organic solvents. 

Fig. 20. Dependence of the equilibrium association constant K of HAP (hexylammoniumpropionate) on the reciprocal dielectric constant e of the benzene-dg-DMSO-dg and DMSO-dg-DjO solvent system at 23.5 °C. [J. Phys. Chem. 79, 917 (1975) ...

Figure 1. Plots of In CJC0 against t for DMSO and isobutene obtained from a DMSO/isobutene/N02 photolysis system in 760 Torr synthetic air at 298 K.

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