Aromatic polycarbonates by direct synthesis from bisphenol a and carbon monoxide

Oxidative carbonylation of bisphenol A to polycarbonates has been studied using mixtures of carbon monoxide and oxygen in the presence of a host of catalytic systems. Catalysts containing palladium compounds and selenium, as well as PdCl₂/Fe/I₂ and Pd/Fe/I₂ catalytic systems, exhibit different selectivity and activity towards the products obtained. This revised version was published online in June 2006 with corrections to the Cover Date.     

On the nature of growth hillocks on sodium chlorate crystals

Optical examination of as-grown {100} surfaces of sodium chlorate crystals grown from aqueous solution revealed the presence of elliptical growth hillocks. The hillocks were present on both enantiomorphous forms and originated from dislocations, inclusions, and microcrystals attached to the growing surface. The value of the surface entropy factor equal to 4.55 at 313 K suggests that crystals grow via/or with the participation of dislocation mechanism, and the hillocks are dislocation growth centers. Compound mechanism controlled growth of some crystals because edge nucleation and dislocation centers operated simultaneously on the same surfaces.     

Enantiomorphism in sodium chlorate crystals

Creation of enantiomorphous forms in sodium chlorate and enantiomorphous nature of surface micromorphology were studied by optical microscopy. It was shown that when the small number of crystals nucleates spontaneously in unstirred, unseeded solutions then exclusively left- (L) or right-handed (D) crystals can be formed. At the large number of nucleated crystals the probability of the creation of L and D form is nearly the same. L and D crystals can be distinguished by the shape of growth or dissolution centers.     

Chiral Symmetry Breaking in Sodium Chlorate Crystallization from Unstirred Solution

Statistics of nucleation of chiral forms of sodium chlorate from unstirred, achiral solutions was studied. The trimodal distribution of enantiomers was obtained in which apart from the peak for the same probability of the creation of L and D crystals, two other maxima for the large enantiomeric excesses of L and D forms were present. The first nucleated crystals govern the handedness of the secondary crystals and the formation of pure enantiomers and high enantiomeric excesses in crystallization from unstirred, unseeded solutions are caused by the process of chiral symmetry breaking rather than statistical fluctuations.