Ether free systems

For more demanding applications, tetrabromophthalate ester is a thermally stable liquid fire-retardant additive with a bromine content of approximately 45wt%. Decabromodiphenyl ether is used for foamed soft PVC for thermal insulation even if diphenyl ether-free systems have been developed because of environmental concerns. 

When 1-methyl-2-nitrosoimidazole became available190 it was found that addition of excess GSH to solutions of l-methyl-2-nitrosoimidazole led to a rapid loss of the characteristic absorbance at 360 mn within a few seconds. Preliminary experiments suggested that formation of GSSG and the hydroxylamine was followed by formation of stable thio ethers. It should be noted, however, that detection of free hydroxylamine was unsuccessful57. In cell-free systems l-methyl-2-nitrosoimidazole reacted with excess GSH to form adducts in a 1 3 stoichiometric reaction191. 

The influence of solvating solvents, in our case THF, has been discussed previously (1). There is some ambiguity about the state of solvation of the initiator in polymerization in nonpolar solvents, in our case toluene. These systems, in which highly isotactic polymers are formed, are sometimes described as "ether-free" or "de-etherated". The basic procedure is to pump... 

Chromium complex 53 was also shown to efficiently catalyze the inverse electron-demand hetero Diels-Alder reaction of a,(3-unsaturated aldehydes with alkyl vinyl ethers (Scheme 17.19).26 Although the uncatalyzed process required elevated temperatures and pressures to give dihydropyrans in good yields but poor endo. exo selectivities, the reaction proceeded at room temperature in the presence of 5 mol% of ent-53 and 4A molecular sieves in dichloromethane of tert-butyl methyl ether with excellent diastereoselectivity (endo. exo >96 4) and promising enantioselectivities (72-78% ee). Optimal results were achieved using a solvent-free system and excess vinyl ether. 

In nonbiological cell-free systems, acrolein has been shown to form thiol ethers within seconds when reacted with glutathione or cysteine (Esterbauer et al. 1975, 1976). In cell systems in vitro, such as... 

The transfer free energy (as measured by the slope value) for any solute in an alcohol/water system should decrease as the chain length of the solvent alcohol is shortened. Of course the same effect ought to be observed if we hold the oil phase constant and make the aqueous phase less hydrophilic. The equations in Table V show that for a limited set of barbiturates partitioned between diethyl ether and a 50-50 mixture of water and dimethylformamide, the slope, compared with the octanol standard, is only 0.4 whereas the ether/water system gives a slope for the donor solute group of 1.13. Thus, a 50% reduction in the protic character of the polar phase reduces the sensitivity of the system by a factor of 2.8. 

Similar results were obtained with the chloroform-ether-amide system. As chloroform was foimd to be a somewhat less efficient hydrogen bond breaker than halothane, one would expect a free/associated ratio somewhat less favorable to the free species than in the case of the halothane-ether mixture. This is actually what has been observed. The system is another case of predictable antagonism. The dioxane-halothane-amide system also yielded similar results. 

The influence of alkali metal perchlorates on the photocyclisation of (34) has also been studied. The quantum yield for cyclization is reduced from 0.21 for the free system to 0.17 for irradiations in the presence of sodium perchlorate. The effect is even more dramatic with potassium and rubidium perchlorates when (j) is reduced to 0.02. The crown ether systems are obviously important since the overall shape can be controlled by the photochemical ring closure. 

The production of a stoichiometric quantity of hydrogen peroxide (in an O2-free system) provides strong evidence for the formation of HO- radical. Yields of 90% are observed from the combination of HOO and TEMPO via an iodide titration of the carbonate-buffered aqueous solution, with quantitative recovery of the TEMPO-free-radical product by ether extraction of the aqueous layer.41 The mass spectrum of the reaction products includes a peak at mass 34. 

Copper-containing mordenite catalysts have also been reported to be active for carbonylation of vapor-phase methanol [170]. Initially, the predominant reaction products were hydrocarbons resulting from methanol-to-gasoline chemistry, but after about 6 h on stream at 350 °C the selectivity of the catalyst changed to give acetic acid as the main product. A recent investigation was carried out with in situ IR and solid-state NMR spectroscopies to probe the mechanism by detecting surface-bound species. The rate of carbonylation was found to be enhanced by the presence of copper sites (compared to the metal-free system), and formation of methyl acetate was favored by preferential adsorption of CO and dimethyl ether on copper sites [171],... 

Smith, K., El-Hiti, G. A., Jayne, A. J., and Butters, M. 2003. Acetylation of aromatic ethers using acetic anhydride over solid acid catalysts in a solvent-free system scope of the reaction for substituted ethers. Org. Biomol. Chem. 1 1560-1564. 

Reduction of halides. Stephenson and co-workers have prepared a Zn-Cu couple by reaction of zinc dust, suspended in H2O, with CuClz dissolved in dilute hydrochloric acid (Oz-free system). The resulting black solid is washed with HzO, acetone, and finally ether. 

Unsaturated maleic/fumaric acid-containing polyesters (UPEs) dissolved in styrene, (2) acrylate/methacrylate systems, (3) thiol/ene systems, and (4) epoxide- or vinyl ether-containing systems. In the case of systems (l)-(3), free radical polymerizations are operative, while in case (4) cationic species are involved (see Chapter 10). Regarding thiol/ene systems, the mechanism of free radical thiol/aUcene polymerization outlined in Scheme 11.1 is assumed to be operative... 

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