Selective Oxidation Of Diols And Nitriles Catalyzed By Na₂WO₄

The oxidation is a significant reaction in organic chemistry and a core technology for conversion of hydrocarbon to intermediate of organic synthesis. The oxidation is traditionally carried out with stoichiometric amounts of oxidants such as permanganates, chromium reagents, nitric acid, halogen oxyacid and organic peroxide acid, but the atomic utilization of these oxidizers is very low because the formation of various byproducts. In order to realize clean production, the studies on green oxidant and oxidation process have become the common ground of academia and industry. Aqueous H₂O₂ is safe, no poisonous, low price, thus is an ideal oxidant, however, its application efficiency in many reactions was low. Therefore looking for a new catalyst system which made the H₂O₂ became more active and more efficient oxidant has been an important subject in recent years. In the thesis the oxidations of diols and nitrils catalyzed by sodium tungstate, sodium molybdate and heteropoly acid using H₂O₂, Na₂CO₄-H₂O₂, and sodium percarbonate as oxidants were studied. The results of catalytic oxidation of 1,2-propanediol and butanediol using Na₂WO₄·2H₂O as catalyst and hydrogen peroxide (30%) as oxidant showed that the conversion of substrate increased with the increase of reaction time and temperature, but the selectivity forming hydroxyketone decreased. The increase of amount of catalyst or oxidant would lead to the formation of more by-products acetic acid and formic acid. The increase of acidity of the auxiliary additive would be favorable for the conversion of 1,2-propanediol, but the selectivity forming hydroxyacetone decreased. When Na₂WO₄ was used as catalyst, under the optimized reaction conditions: temperature 55 ℃, time 60 min, n(Na₂WO₄·H₂O)/(2-hydroxyl phenol)=1, the conversion of 1,2-propanediol was 13 % and the selectivity of hydroxyacetone could achieve 92.3 %. Under similar conditions, the conversions of 1,2-butanediol and 1,3-butanediol were 29.2 % and 77.5 %, and the selectivities forming 1-hydroxyl-2-butanone and 4-hydroxy-2-butanone were 65.8 % and 85.3 %, respectively. The mechanism of diol oxidation was discussed. The preparation of amides from aryl nitriles and aliphatic nitriles was studied in the presence of sodium tungstate catalyst using sodium percarbonate or sodium carbonate-hydrogen peroxide as oxidant in the solution of methanol and water mixture. The effect of the concentration of sodium tungstate, sodium carbonate and H2O2 were studied. The results indicated that aryl nitriles and aliphatic nitriles could transfer to aryl amides with very high selectivity of 95 %-100 % at room temperature. The comparing study of two oxidants suggested that when sodium carbonate-hydrogen peroxide was used as oxidant, the oxidation rate of nitrile and the selectivity forming amide were better than that percarbonate was used. The reactivities of nitriles would decrease with the increase of their branched chain length. In the oxidation of tolunitriles, the oxidation rates of p-tolunitrile and m-tolunitrile were very fast, but the oxidation of o-tolunitrile was very slow. The oxidation rates of p-haloid aryl nitrile and p-nitro aryl nitrile decreased according to the order p-nitrobenzonitrile>p-chlorobenzonitrile>p-brombenzonitrile, the selectivities to form aryl amides could keep 98 %-100 %. A suggestion mechanism of aryl nitrile oxidation was proposed to explain the observed results.