Reaction of 2,3-diphenylpyrazine 1-oxides with acetic anhydride

Some 2,3-diphenylpyrazine 1-oxides were heated with acetic anhydride to give the corresponding 2,3-di-acetoxy-2,3-dihydro-5,6-diphenylpyrazines. By X-ray diffraction analysis, the configuration of two acetoxyl groups was determined to be trans.     

Diversified synthetic approaches to the carbapenem antibiotics based on symmetrization-asymmetrization concept

cis-Fused bicyclic β-lactam compound 9, a key intermediate to cis-substituted carbapenem antibiotics, has been synthesized in optically pure form based on symmetrization-asymmetrization concept.     

Laser isotope separation of tritium using CF3CTBrF/CF3CHBrF

A new working molecule 2-bromo-1,1,1,2-tetrafluoroethane is reported for laser isotope separation of tritium. The multiphoton dissociation rate of CF₃CTBrF is studied as a function of irradiation wavenumber, using a CO₂ or NH₃ laser. In a tightly focused irradiation geometry where the dissociation saturates both for CF₃CTBrF and CF₃CHBrF, their threshold fluences of dissociation and the geometrically biased selectivity are measured near the maximum of the dissociation rate of CF₃CTBrF. When the irradiation geometry is optimized, a high selectivity exceeding 2700 is obtained.     

f-Element/crown ether complexes 2. The synthesis and crystal structure of Y(NO3)3(12-crown-4)

Y(NO₃)₃(12-crown-4) was prepared via reaction of the crown ether and Y(NO₃)₃·nH₂O in acetonitrile. Y(NO₃)₃(12-crown-4) crystallizes in the monoclinic space groupP2₁/c witha=12.084(5),b=8.524(4),c=15.150(6) Å, =91.62(3)⁰ andD _calc=1.92 g cm^–3 forZ=4. The structure was refined by least-squares to a final conventionalR value of 0.105 using 1249 independent observed reflections [I3(I)]. The title compound is isostructural with its Eu(III) analog. The yttrium ion is ten-coordinate, bonded to three bidentate nitrate groups and to the four oxygens of the crown ether. The coordination polyhedron is best described as a 4A, 6B-extended dodecahedron. The Y-O(nitrate) and Y-O(ether) separations average 2.44(5) and 2.46(4) Å, respectively.Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82040 (10 pages).For Part 1 see reference [6]     

A facile cleavage of oxirane with hydrazoic acid in dmf A new route to chiral β-hydroxy-α-amino acids

Chiral β-hydroxy-α-amino acids such as erythro-β-hydroxy-L-aspartic acid and erythro-β-hydroxymethyl-L-serine derivatives have been synthesized in optically pure form from L- and D-tartaric acids through a novel oxirane ring-opening reaction and a selective reduction of α-hydroxy ester as key steps.     

Potentiometric flow titration of iron(II) and chromium(VI) based on flow rate ratio of a titrant to a sample

A new potentiometric flow titration has been proposed based on the relationship of the flow rates between titrant and sample solutions. A sample solution is pumped at a constant flow rate. The flow rate of the titrant solution is gradually increased at regular time intervals and a flow rate for the titrant solution in the vicinity of the equivalence point is obtained. The concentration of the sample is calculated by C(S) (mol l(-1))=(R(T) (ml min(-1))xC(T) (mol l(-1)))/R(S) (ml min(-1)), where C(S), C(T), R(S), and R(T) denote the unknown sample concentration, titrant concentration in the reservoir, the flow rate of the sample solution which is a constant rate, and the flow rate of the titrant solution at an inflection point, respectively. The potentiometric flow titration of iron(II) with cerium(IV) and of chromium(VI) with iron(II) has been presented. The titration time of the proposed method is about 10 min per sample. An R.S.D. of the method is 0.77% for seven determinations of 1x10(-3) mol l(-1) iron(II). Similarly, the flow titration of chromium(VI) with iron(II) is carried out over the range 1x10(-4)-1x10(-3) mol l(-1) chromium(VI) and is successfully applied to the determination of chromium in high carbon ferrochromium.