Xerogel-Sequestered Silanated Organochalcogenide Catalysts for Bromination with Hydrogen Peroxide and Sodium Bromide

Abstract

While H2O2 is a powerful oxidant, decomposing into environmentally benign H2O and O2, a catalyst is often required for reactions with H2O2 to proceed at synthetically useful rates. Organotellurium and organoselenium compounds catalyze the oxidation of halide salts to hypohalous acids using H2O2. When sequestered into xerogel monoliths, the xerogel-chalcogenide combinations have demonstrated increased catalytic activity relative to the organochalcogen compound alone in solution for the oxidation of halide salts to hypohalous acids with H2O2. Diorganotellurides, diorganoselenides, and diorganodiselenides bearing triethoxysilane functionalities were sequestered into xerogel monoliths and their catalytic activity and longevity were investigated. The longevity of the catalyst-xerogel combinations was examined by isolating and recycling the catalyst-xerogel combination. It was found tellurium-containing catalyst 3 and selenium-containing catalyst 8 maintained their catalytic activity through three recycling trials and adding electron-donating substituents to catalyst 3 also increased the catalytic rate. The presence of organotellurium and organoselenium groups in the +4 oxidation state was determined by X-ray photoelectron spectroscopy.

Functional Enzyme Mimics for Oxidative Halogenation Reactions that Combat Biofilm Formation

“…The haloperoxidase‐like activity of selenium and tellurium compounds is not limited to homogenous reactions . Organo‐Se or organo‐Te complexes stabilized in “xerogels” displayed oxidative bromination activity for 4‐pentenoic acid (Table , entries 56 and 57) . The product, 4,5‐dibromopentanoic acid, reacted to the corresponding bromolactone ( Figure a).…”

“…a) Synthesis of chalcogenide xerogel (M = Se or Te) 31 and the oxidative bromination of 4‐pentoic acid 32 to bromofurane 34 with modified xerogel 31 . b,c) Proposed Se and Te intermediates .…”

“…b,c) Proposed Se and Te intermediates . d) Proposed inactivation mechanism of the xerogel 31 (Nu = e.g., H 2 O 2 , OH, Cl) …”

“…The use of modified xerogel coatings combines the physical and chemical antifouling characteristics of porous silica coatings with the haloperoxidase‐like activity of the organo‐selenium compounds . Leaching was observed for phenylchalocogenic acids, and phenylchalcogenic chloride formed for low molecular weight organo‐selenium or tellurium compounds (Figure c).…”

“…Leaching was observed for phenylchalocogenic acids, and phenylchalcogenic chloride formed for low molecular weight organo‐selenium or tellurium compounds (Figure c). However this may turn into an advantage because active components can be released during the defense process . A similar xerogel containing hydrogen peroxide and artificial sea water (with halides) was successfully tested as a “hybrid” coating against the settlement of cypris larvae of the barnacle Balanus amphitrite , larvae of the tubeworm H. elegans and of Ulva zoospores .…”