No abstract

No abstract

Sulfonated carbons were prepared from carbonized rice husk and further treatment with sulfuric acid (TC-6M, sulfuric acid 6 mol L–1 under reflux, TC-L, concentrated 96% sulfuric acid under reflux, TC-V, vapor of concentrated 96% sulfuric acid). The catalytic activity of carbons was evaluated in esterification of glycerol with acetic acid (AA) and etherification of glycerol with tert-butyl alcohol (TBA). Only the TC-L carbon showed a significant amount of sulfur in its composition (2.2 mmol g–1). This catalyst also had the highest total acidity (5.8 mmol g–1) and improved the best catalytic performance in glycerol esterification and etherification. In the esterification reaction of glycerol, 90% conversion was observed after 5 h of reaction, with selectivities of 11%, 52%, and 37% to mono-, di-, and tri-glycerides, respectively. In the etherification of glycerol, after 4 h of reaction a conversion of 53% was achieved, with 25% selectivity to di- and tri-tert-butylglycerol. Thus, the use of sulfonated carbons in glycerol conversion proved to be an interesting alternative to add value to the production chains of rice and biodiesel by using their byproducts: rice husk and glycerol.

Sulfonated carbon-based catalysts were prepared from agroindustrial wastes (sugar cane bagasse, coconut husk, and coffee grounds). These catalysts showed high activity for glycerol etherification with tert-butyl alcohol. Yields of mono-tertbutyl glycerol (MTBG), di-tert-butyl glycerol (DTBG), and tri-tert-butyl-glycerol (TTBG) were higher than that obtained using Amberlyst-15 commercial resin. At 393 K and 5 wt % catalyst loading, glycerol conversion and selectivity to DTBG+TTBG after 4 h reaction time were 80.9% and 21.3%, respectively, with the sugar cane bagasse-based catalyst. Both catalytic activity and selectivity were affected by the presence of water in the reaction medium. However, the flexible and hydrophilic structure of the oxidized carbon allows the adsorption of water without compromising the activity of acid sites.

Triosmium dodecacarbonyl catalyzes a very efficient oxidation of alkanes by H(2)O(2) in MeCN to afford alkyl hydroperoxides (primary products) as well as alcohols and ketones (aldehydes) at 60 degrees C if pyridine is added in a low concentration. Turnover numbers attain 60,000, and turnover frequencies are up to 24,000 h(-1).