RESUMEN
Equilibrium sorption and desorption experiments were conducted with clinoptilolite to evaluate the potential sorption/desorption of iron during different pH conditions. Sorption experiments indicated a partitioning of 0% to 17% of the iron in solution given pH of 2 to 4. The pH 2 solution was able to desorb 70% of the iron that was captured from a pH 3 solution. The largest desorption and sorption of iron and corresponding pH represent the end points of iron capture primarily by sorption/exchange. These endpoints are the estimated pHpzc of 2.5 and the initial precipitation point of iron(II) at pH ~3.5. This acidity range is where clinoptilolite is able to capture iron without precipitation or the occurrence of full surface protonation. The inability of the highest acidity to remove all sorbed iron represents the greater bound iron that will not readily desorb with a change in pH. This retained iron creates a metastable state of the clinoptilolite that has a lower sorption capacity but reflects the ability of clinoptilolite to retain a sorbed transition metal with changes in pH. As pH varies, clinoptilolite may evolve in a sequence of metastable states reflective of its ability to capture or retain metals. PRACTITIONER POINTS: Clinoptilolite is a capable reactive substrate, but its sorption/exchange effectiveness at low and variable pH and ability to retain captured metals was unknown. Clinoptilolite retains its metal capture properties to a pH of 2.5 where surface protonation and mineral degradation likely occurs. The ability of clinoptilolite to retain captured iron under greater acidity reflects an evolution of its sorption/retention capacity.
Asunto(s)
Hierro , Zeolitas , Adsorción , Concentración de Iones de HidrógenoRESUMEN
The coupling of enyne carbonyl compounds that contain pendant alkene groups with Fischer carbene complexes to afford furans that contain pendant alkene groups is described. Subsequent intramolecular Diels-Alder reactions are effective in select cases, resulting in hydronaphthalene systems after dehydration. Although the Diels-Alder event is thermodynamically unfavorable, the overall transformation of alkene-furans to dihydronaphthalenes is a favorable process.
RESUMEN
The reaction of Fischer carbene complexes with conjugated enediynes that feature a pendant alkene group has been examined. The reaction proceeds through carbene-alkyne coupling to generate an enyne-ketene intermediate. This intermediate then undergoes Moore cyclization to generate a chromium complexed arene diradical, which then undergoes cyclization with the pendant alkene group. The radical cyclization prefers the 6-endo mode unless radical-stabilizing groups are present to favor the 5-exo mode. The intermediate diradical species were evaluated computationally in both the singlet and triplet configurations. Arene triplet diradicals feature minimal spin density at oxygen and delocalization to chromium. The 6-endo cyclization product was kinetically and thermodynamically favored.
RESUMEN
Fluoride-based deprotection of silylated 2-alkynylbenzyl alcohol derivatives featuring carbonyl-substituted alkynes results in the direct synthesis of alkylidenephthalan vinylogous esters. The reaction is selective for the Z alkylidenephthalans in a thermodynamically controlled process. Similar compounds are also produced in the coupling of Fischer carbene complexes with 2-alkynylbenzoyl derivatives in an aqueous solvent system. Subsequent acid-catalyzed inter- or intramolecular Diels-Alder reactions lead to hydronaphthalene or hydrophenanthrene derivatives.