Yang Xiyun

Effect of Bromide Ions on the Pitting Corrosion of Hafnium in Anhydrous t-Butanol and Acetonitrile

Pitting of Hf in Et4NBr t-butanol and acetonitrile (ACN) solutions was studied by means of cyclic voltammetry, potentiodynamic anodic polarization, galvanostatic, potentiostatic and impedance techniques. The potentiodynamic anodic polarization curves did not exhibit an active dissolution region near corrosion potential due to the presence of an oxide film on the electrode surface, which was followed by pitting corrosion resulting from the passivity breakdown by the aggressive attack of bromide (Br−) ion. The pitting potential (E pit) increased with increasing potential scanning rate but decreased with increasing temperature and Br− concentration. Cyclic voltammetry and galvanostatic measurements allowed the pitting potential (E pit) and the repassivation potential (E p) to be determined. Analysis of the potential/time transients revealed that the applied anodic current density had a significant influence on the values of E pit. On the other hand, the E p values were independent on the applied current density. The current/time transients indicated that the incubation time (t i) for passivity breakdown decreased slightly with increasing potential and solution temperature. The impedance spectra showed that the resistance of passive layer decreased with increasing potential.

Asymmetric synthesis of 3β-acetoxy-17, 17-ethylendioxy-15β, 16β-methylene-5-androsten-7β-ol

Abstract3β-acetoxy-17, 17-ethylendioxy-15β, 16β-methylene-5-androsten-7β-ol(I) was prepared by 3 steps from 3β-acetoxy-15β, 16β-methylene-5-androsten-17-one (II) with overall yield of 52.7%. Thus, interaction of ethylene glycol and material (II) gave 3β-acetoxy- 17, 17-ethylendioxy-15β, 16β-methylene-5-androsten (III) which was subsequently oxidated and stereoselectively reduced to produce compound(I). The normal influencing factors, such as the types of oxidants and reductives, the mole ratio of reactants, the reaction temperature, and the addition ways of reactants, in oxidation and reduction were discussed. The results show that the oxidation rate order is CrO3-C5H5N (1:1, mole fraction)>CrO3-C5H5N(1:2)>(C5H5NH)2Cr2O7 in terms of the oxidant, the yield of the oxidation becomes higher with increasing the oxidant stoichiometry and raising the reaction temperature. And the optimum condition is that the reaction temperature is at 30 °C, and n(III)/n(CrO3-C5H5N(1:2))=1:20. The yield of the −7β alcohol order with Li[Al(OC(CH3)3)3H] (e. g. 78.6%) is more than that with NaBH4 (e. g. 14.5%) in terms of the reductive agent and the reduction rate decreases in the course of reaction. The compound (I) is characterized by IR and MS.