Palladium-catalyzed ring expansion reaction of 1-alkynylcyclobutanols with aryl iodides: an efficient route to 2-disubstituted methylenecyclopentanones

The reaction of 1-alkynylcyclobutanols with aryl iodides in the presence of Pd(OAc)₂ and Et₃N in acetonitrile at 80°C for 24 h gives 2-disubstituted methylenecyclopentan-1-ones in modest to good yields. The tandem insertion-ring expansion process proceeds via the formation of an alkynyl π-complex, followed by migration of a carbon-carbon bond of the tert-alkanol to form the cyclopentanones stereoselectively.     

Synthesis of meso-tetra-(3,5-dibromo-4-hydroxylphenyl)-porphyrin and its application to second-derivative spectrophotometric determination of lead in clinical samples

A new very sensitive and selective chromogenic reagent, meso-tetra-(3,5-dibromo-4-hydroxylphenyl)porphyrin [T(DBHP)P], was synthesized and studied for the determination of trace lead in detail. In 0.10 mol l-1 NaOH medium, lead reacts with T(DBHP)P to form a 1:2 yellow complex, which gives a maximum absorption at 479 nm; 0-0.48 microgram ml-1 Pb(II) obeyed Beer's law. The molar absorptivity of the complex and Sandell's sensitivity are 2.5 x 10(5) 1 mol-1 cm-1 and 0.000812 microgram cm-2, respectively. Second-derivative spectrophotometry is better than conventional spectrophotometry in sensitivity and selectivity, and its limit of quantification, limit of detection and relative standard deviation are 0.70 ng ml-1, 0.21 ng ml-1 and 1.0%, respectively. Ca (3250-fold), Mg (2000-fold), Sr (1000-fold), Ba (750-fold), Al (1000-fold), Bi (500-fold), Fe (2000-fold), Co (750-fold), Ni (1000-fold), Cu (750-fold), Zn (1250-fold), Cd (2500-fold) and Ag (550-fold) do not interfere with the determination of lead. The chromogenic system is remarkably superior to other reagents, especially porphyrin compounds. The influence caused by oxygen in air or in solution can be easily eliminated by adding Na2SO3. The reaction is very stable, the stability constant of the complex being 1.2 x 10(45). The chromogenic reaction is completed within 1 min at room temperature when 8-hydroxylquinoline is used as catalyst. The proposed method has been applied to the direct determination of trace lead in clinical samples. The accuracy and precision are both very satisfactory.     

武汉味精市场给本地生产企业带来的挑战

阐述了武汉味精市场的概况以及本地生产企业的特点,在此基础上分析了武汉市场味精企业面临的种种挑战.     

利用攀钢钛矿渣生产混凝土空心砌块的试验研究

运用正交试验的方法对利用攀钢钛矿渣生产混凝土空心砌块进行了研究。研究结果表明：钛矿渣取代砂、石和部分水泥后，可以生产出性能满足GB8239-1997《普通混凝土小型空心砌块》要求的混凝土空心砌块。所开发的砌块强度达到MU10等级，确定了生产混凝土空心砌块的最佳配方。     

激光辐照SnO2超微粒薄膜的AES,热电动势率及阻抗谱

研究ＹＡＧ脉冲激光辐照对ＳｎＯ２超微业薄膜的改性作用，由ＡＥＳ分析表明，在大气环境中激光束的轰击可使薄膜表面碳吸量明显减少，并有一定的氧化作用。在３００－６００Ｋ范围内测量激光辐照前后样品的热电动热率（ＴＥＰ），发现激光辐照后ＴＥＰ值明显减小，薄膜发生晶化。激光辐照对超微粒薄膜的电学性质、晶界效应也有影响，表明激光束作用使薄膜粒间效应减弱     

E8010纤维素型全位置立向下电焊条的配方设计

根据全位置立向下焊接的特点和要求，在对现有各类焊条渣系的物理性能及工艺性能进行试验分析的基础上，通过大量的试验，确定了具有短渣特性的高氧化钛渣系及高发气量的微晶纤维作为电焊条的基本配方，并加入适量的铁砂，利用其在焊接时冶金化学反应中的放热反应，提高电焊条的熔敷效率。