octan-2-ol

ChEBI · EMBL-EBI ↗ · Källdatum saknas · Källans villkor

An octanol carrying the hydroxy group at position 2.

BednarzSzczepan; RyśBarbara; BogdałDariusz · Application of Hydrogen Peroxide Encapsulated in Silica Xerogels to Oxidation Reactions ↗ · 4 juli 2012 · Källans villkor

2-Octanol was successfully oxidized in nearly quantitative yield both by the composite and 30% aqueous H2O2 (Table 2). The application of UHP as an oxidant lowers the yield of the reaction to 69%. Moreover, when the reaction temperature was decreased to 70 °C, UHP exhibited low reactivity manifested only 6% yield of 2-octanone with comparison to 64% and 56% for aqueous H2O2 and the xerogel, respectively. Oxidation under microwave conditions gave very good results only when 30% H2O2 was applied.

BednarzSzczepan; RyśBarbara; BogdałDariusz · Application of Hydrogen Peroxide Encapsulated in Silica Xerogels to Oxidation Reactions ↗ · 4 juli 2012 · Källans villkor

Silica xerogel–hydrogen peroxide composites stabilized by addition of small amounts of H3PO4 can be stored at 3 °C for 2 months without significant loss of H2O2 [7]. However, we have used unstabilized composites. We have found that after 2 weeks of storing at 5 °C, the composite loses about a half amount of H2O2 probably because slow decomposition of H2O2 catalyzed by heavy metals impurities presented in the silica matrix (probably, traces of Fe2+ from “water glass”). Relative instability of the composite could be a reason of its activity in oxidation reactions. In contrast, UHP is a stable H2O2 complex and such a high stability could be considered, to be a drawback to its potential chemical reactivity. An oxidation yield might by higher if dissociation of the adduct, i.e., dissolving or melting (m.p. 82 °C [15]) took place. UHP/hexafluoro-2-propanol (HFIP) system was investigated in epoxidation of olefins, and it was concluded that the fluoroalcohol has the unique ability to combine the two requirements: dissociation (dissolving) of the UHP adduct and activation of H2O2 [16]. We have observed similar effect of TFE on the epoxidation yield of cyclooctene with UHP as an oxidant (Table 3). The temperature effect on UHP and the silica xerogel–H2O2 composite activity was investigated in 2-octanol oxidation (Table 2). At the temperature 70 °C (below melting point of UHP) a conversion of the alcohol was very low and was significant increased when the temperature risen to 80 °C. In opposition, oxidation with 30% H2O2 and also with the composite did not show such high yield–temperature dependency.

BednarzSzczepan; RyśBarbara; BogdałDariusz · Application of Hydrogen Peroxide Encapsulated in Silica Xerogels to Oxidation Reactions ↗ · 4 juli 2012 · Källans villkor

We have found that silica xerogel–H2O2 composite is more suitable oxidant to microwave assisted reactions than UHP. The composite is easily heated by microwave irradiation probably because they contain c.a. 80% of polar components: H2O2 and H2O. These molecules are relatively weakly bonded to silica matrix and can undergo reorientation in microwave field, resulting in heat generation. Silica matrix is almost transparent for microwave irradiation (ε” < 0.001 2.5 GHz [17]) and does not heated directly by the radiation. For this reason, undesired superheating effect of the xerogel under microwave condition is much less probably than for solids strongly interacted with microwaves such as chromium dioxide (Magtrieve™) [18]. UHP is a crystalline complex formed by hydrogen bonding between urea and H2O2 [15], thus the molecules are locked together in a crystal structure. From that reason solid UHP weakly interacts with microwave irradiation in contrast to the melted one, which strongly absorbs microwave energy. It could cause overheating, thermal decomposition of H2O2 and even thermal degradation of urea. This might explain rather poor yields of reactions conducted under microwave condition where UHP were used as an oxidant in the solid state (Table 1 and Table 2). A presence of polar solvent could overcome mentioned limitations, e.g., high yields of oxidation with UHP in methanol [19] or 1,4-dioxane-water [20] were obtained in microwave assisted reactions.