Di-n-hexyl telluride (2), di-p-methoxyphenyl telluride (3), and (S)-2-(1-N,N-dimethylaminoethyl)phenyl phenyl telluride (4) catalyzed the oxidation of PhSH to PhSSPh with H(2)O(2) in MeOH. Telluride 2 displayed greater rate acceleration than the diaryltellurides 3 and 4 as determined by the initial velocities, v(0), for the rate of appearance of PhSSPh determined at 305 nm by stopped-flow spectroscopy. Rate constants for the oxidation of tellurides 2-4 (k(ox)), rate constants for the introduction of PhSH as a ligand to the Te(IV) center (k(PhSH)) of oxidized tellurides 5-7, and thiol-independent (k(1)) and thiol-dependent (k(2)) rate constants for reductive elimination at Te(IV) in oxidized tellurides 5-7 were determined using stopped-flow spectroscopy. Oxidation of the Te atom of the electron-rich dialkyl telluride 2 was more rapid than oxidation of diaryl tellurides 3 and 4. The dimethylaminoethyl substituent of 4, which acts as a chelating ligand to Te(IV), did not affect k(ox). Values of k(PhSH) for the introduction of PhSH to oxidized dialkyl tellurane 5 and oxidized diaryl tellurane 6 were comparable in magnitude, while the chelating dimethylaminoethyl ligand of oxidized telluride 7 diminished k(PhSH) by a fator of 10(3). Reductive elimination by both first-order, thiol-independent (k(1)) and second-order, thiol-dependent (k(2)) pathways was slower from dialkyl Te(IV) species derived from 2 than from diaryl Te(IV) species derived from 3. The chelating dimethylaminoethyl ligand of Te(IV) species derived from 4 diminished k(1) by a factor of 50 and k(2) by a factor of 3 (relative to the 3-derived species).

We report on a new sensor strategy that we have termed site selectively templated and tagged xerogels (SSTTX). The SSTTX platform is completely self-contained, and it achieves analyte recognition without the use of biomolecules. To illustrate the SSTTX scheme's potential, we present results for the selective detection and quantification of a model compound, 9-anthrol. The first-generation SSTTX shows the following: (i) exhibits an apparent dissociation constant of (1.8 +/- 0.3) x 10(-4) M for 9-anthrol; (ii) provides 0.3 muM detection limits for 9-anthrol; (iii) yields a 45-s response time (2-mum-thick film); (iv) is completely reversible (6% relative standard deviation after 25 cycles); (v) yields a selectivity factor for 9-anthrol over several structurally similar analogues/interferences (e.g., anthracene, 9,10-anthracenediol, benzophenone, 2-naphthol, phenol, and pyrene) of between 290 and 520; and (vi) is stable (<2% drift in performance) for at least 10 months when stored under ambient conditions in the dark. The results also suggest SSTTXs as new sensor elements for glycoside, pharmaceutical, prostaglandin, and steroid sensors.

Dendrimeric polyorganotellurides are prepared in high yield using propyloxy spacers to connect the organotelluride groups to the core molecules. The polyorganotellurides catalyze the oxidation of thiophenol with hydrogen peroxide to give diphenyl disulfide in homogeneous solutions (5% CH 2 Cl 2 /MeOH or 46% CH 2 Cl 2 /MeOH). The polyorganotellurides with two, three, four, and six catalytic groups show roughly statistical increases for the number of catalytic groups relative to the corresponding monotellurides. Catalysts containing [4-(dimethylamino)-phenyl]telluro groups and n-hexyltelluro groups are oxidized more rapidly by hydrogen peroxide and also show greater catalytic activity than the corresponding catalysts containing phenyltelluro groups. A combination of statistical effects and stereoelectronic effects give a 26-fold increase in catalytic activity from 1-phenoxy-3-(phenyltelluro)propane (23a; ν 0 ) 12 µM min -1 ) to dendrimer 22c with six n-hexyltelluro groups (ν 0 ) 312 µM min -1 ) for the oxidation of 1.0 × 10 -3 M PhSH with 3.75 × 10 -3 M H 2 O 2 in the presence of 1.0 × 10 -5 M catalyst. The rate of appearance of PhSSPh, with a molar extinction coefficient, , of 1.24 × 10 -3 L mol -1 cm -1 at 305 nm, was monitored at 305 nm.While H 2 O 2 is a powerful oxidant thermodynamically, many of the reactions of H 2 O 2 are limited by the kinetics of reaction, as illustrated by the oxidation of halides to the corresponding halogen/hypohalous acid 1 and the oxidation of thiols to disulfides. 2 Nature has developed a variety of peroxidase enzymes to accelerate these reactions of H 2 O 2 and other peroxy compounds, and chemists have designed synthetic catalysts to mimic the peroxidase enzymes. 3 Among these latter catalysts, diorganotellurides have been excellent catalysts for the activation of H 2 O 2 in these particular reactions. 2,4 The diorganotellurides undergo two-electron redox processes at the Te atom during the catalytic cycle, as shown in Scheme 1. 2,4,5 Peroxide oxidation of the diorganotelluride gives the corresponding oxide (or its hydrate), which then acts as an oxidant (kinetically superior to H 2 O 2 ) for a variety of substrates (Sub-H). The diorganotelluride is regenerated in the process to resume the catalytic cycle. The rate-limiting step in the catalytic process is the rate of oxidation of the diorganotelluride. 4a,5b For the diorganotellurides, catalytic activity with H 2 O 2 will be a balance between the rate of oxidation of the Te atom with H 2 O 2 and the rate of reductive elimination to form product and to regenerate catalyst. Traditionally, the molar activity of catalysts has been optimized through structure-activity relationships derived from substituent changes. However, stereoelectronic effects can only go so far with respect to increasing rates of oxidation of the Te atom. We have shown enhanced catalytic activity in dendrimeric 6 diorganotelluride catalysts 7 in which statistical increases in catalytic activity in two-phase systems were noted by (1) Mohammed, A.; Liebhafsky, ...

The level of stereocontrol obtained in the reduction of the free radical derived from the intramolecular addition of an acyl radical to an alpha-branched vinylogous carbonate is dependent upon the ring-size of the cyclic ether.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.