Sodium isotopic exchange with

No exchange was detected between water and dimethylsulphoxide (48 R = CH3) (Leonard and Johnston, 1962) or diphenylsulphoxide (48 R = CeHs) in either 1-On hydrochloric acid or 1-0n sodium hydroxide at 100°C (Samuel and Weiss-Broday, unpublished results). Oae et al. (1961) found no exchange on pouring diphenyl sulphoxide in concentrated sulphuric acid into 0 -enriched water indicating that ionization to a doubly charged cation R2S++, did not occur. Diphenyl sulphone (49) does not undergo isotopic exchange with water even under fairly drastic acid or... 

When o-, m- and p-nitroanisole with 14C-labelled at the methoxy group were irradiated under identical conditions in methanol in the presence of sodium methoxide, only m-nitroanisole underwent methoxy exchange, with the limiting quantum yield (

labelled isotope experiments support a a complex intermediate and indicate an Sjv23Ar mechanism (direct substitution in the triplet state) for this reaction (equation 12) and for 4-nitroveratroles (equation 13). Further evidence from quenching and lifetime experiments also support a direct displacement SAr2Ar mechanism for the photosubstitution reaction of nitroaryl ethers with hydroxide ions13. 

Information regarding the distribution of the very commonly used detergent sodium lauryl sulfate (SLS) also appears in Table V. Twenty-four hrs. after injection of the form of SLS, most of it (65%) has been excreted in the urine of the shark. At the earlier time point, 4 hrs., the hepatic tissue has a higher concentration and quantity of the detergent than any other tissue. Muscle retained the isotope longer than did other tissues in this table and may represent sulfur exchange with endogenous substances. 

The first step of the analysis ensures isotopic exchange of the stable carrier and the radio-iodine in the sample. In this experiment, iodate carrier is added and then reduced to iodide with sodium sulfite to cause exchange among iodate, iodine, and iodide species. (Read the discussion in the Introduction to the Course on isotopic exchange.) The resulting iodide is purified by precipitation, first as silver iodide (Agl) and then, after dissolution, as palladium iodide (Pdl2). 

A method of determining airborne iodine has also been reported.241 Here, iodine is absorbed into 5% aqueous KI and spectrophotometrically determined at 590 nm in the form of its complex with starch. This method is selective with respect to bromine and chlorine, and the sensitivity of this method is 0.25 mg of I2 per m3 of air. The concentration of the, 31I isotope in water can be determined by a method involving isotope exchange in the starch-iodine complex.242 Flow-injection determination of ascorbic acid (0.1-40 mg/mL) has been proposed.243 Iodine is generated in the flow system as I3- ions, which are in turn exposed to starch to produce a steady signal at 350 and 580 nm. Ascorbic acid provides inversed maxima which are measured. This method is recommended for analysis of ascorbic acid in fruit juice, jam, and vitamin-C preparations. Use of the blue complex has also been reported for determination of sodium dichloro-isocyanurate in air.244 Obviously the blue reaction is applicable in the determination of amylose, amylopectin, and starch,245-252 as well as modified starches.245,253-255... 

The three different second-order processes thus exhibit widely different kinetic behaviour towards the varying base concentration at constant buffer ratio. In theory this dependence should provide a means of assigning the mechanism. An advantage over the isotopic exchange approach is that it should be possible to detect carbanion intermediates that eliminate more rapidly than they protonate. Unfortunately, the kinetics are not always clear-cut. The E2 mechanism can, under certain conditions, follow specific base catalysis, especially if one base is of much greater catalytic efficiency than the other bases present (e.g. the E2 reaction of l,l,l-trichloro-2,2-di-p-chlorophenyl-ethane with sodium thiophenoxide in methanol) . Alternatively, the base may be sufficiently powerful to produce a kinetically significant concentration of lyate ions (e.g. the E2 reaction of alkyl bromides with phenoxides in ethanol) " . 

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