Synthesis of colloidal aluminosilicate for light-scattering investigations

To develop a binary colloidal system with a slight index of refraction mismatch suitable for light scattering studies, pure silica particles synthesized by the method of St?ber were mixed with aluminosilicate colloids synthesized using a novel approach. With this, index-matching for one component allowed extraction of the spatial distribution of the other. In addition, it was observed that by varying the solvent, interactions between colloids could be tuned from purely repulsive to weakly attractive.     

Pseudo-steady-state solutions for solidification in a wedge

Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially.     

Phenylphosphatrioxa-adamantanes: bulky, robust, electron-poor ligands that give very efficient rhodium(I) hydroformylation catalysts

The cage phosphines 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6-phosphaadamantane (1a) and 1,3,5,7-tetraethyl-6-phenyl-2,4,8,trioxa-6-phosphaadamantane (1b) have been made by the acid catalysed addition of PhPH(2) to the appropriate beta-diketones; the acid used (HCl, H(3)PO(4) or H(2)SO(4)) and its concentration affect the rate and selectivity of these condensation reactions. Phosphines 1a and 1b react with [PdCl(2)(NCPh)(2)] to form complexes trans-[PdCl(2)(1a)(2)](2a) and trans-[PdCl(2)(1b)(2)](2b) as mixtures of rac and meso diastereoisomers. The platinum(II) chemistry is more complicated and when 1a or 1b is added to [PtCl(2)(cod)], equilibrium mixtures of trans-[PtCl(2)L(2)] and [Pt(2)Cl(4)L(2)](L = or ) are formed in CH(2)Cl(2) solution. Meso/rac mixtures of trans-[MCl(CO)(1a)(2)] M = Ir (6a) or Rh (7a) are formed upon treatment of MCl(3).nH(2)O with an excess of 1a and the anionic cobalt complex [NHEt(3)][CoCl(3)(1a)](9) was isolated from the product formed by CoCl(2).6H(2)O and 1a. The nu(CO) values from the IR spectra of 6a and 7a suggest that 1a resembles a phosphonite in its bonding to Rh and Ir. Crystal structures of meso-2a, meso-2b, rac-6a and 9 are reported and in each case a small intracage C-P-C angle of ca. 94 degrees is observed; this may partly explain the bonding characteristics of ligands 1a and 1b. The cone angles for 1a and 1b are similar and large (ca. 200 degrees). Rhodium complexes of ligands 1a and 1b are hydroformylation catalysts with similarly high activity to catalysts derived from phosphites. The catalysts derived from 1a and 1b gave unusually low linear selectivity in the hydroformylation of hexenes. This feature has been further exploited in quaternary-selective hydroformylations of unsaturated esters; catalysts derived from 1a give better yields and regioselectivities than any previously reported catalyst.     

The ferrocene analogues of salicylic acid and aspirin

The reaction of hydroxyferrocene with 2,3-dihydropyran gave (ferrocenyloxy)-2-tetrahydropyran which on lithiation gave the corresponding 2-lithiated ferrocene which was used to prepare 1-carboxy-2-hydroxyferrocene and 1-carboxy-2acetoferrocene.     

Microdetermination of molybdenum in organometallic compounds by molecular emission and atomic absorption spectrometry

A direct method is described for the determination of molybdenum in mg amounts of organomolybdenum compounds by flame emission or atomic absorption spectrometry. Air/acetylene, air/hydrogen and dinitrogen oxide/acetylene flames were used. The emission of molybdenum oxide is found to be analytically useful in the hydrogen-based flames while the acetylene-based flames are better for atomic absorption. Various organomolybdenum compounds were analysed by both methods as well as by an alternative spectrophotometric method, with satisfactory agreement. The procedure involves simply dissolving the sample in a mixed solvent and aspirating the solution into the flame.     

Synthesis and structure of 1,4:3,6-dianhydro-2-O-p-tosyl-D-mannitol

1,4:3,6-Dianhydro-2-O-p-tosyl-D-mannitol (3) has been isolated from the reaction of 1,4:3,6-dianhydro-D-mannitol (2) andp-toluenesulfonyl chloride (1:2 mole ratio) in pyridine in 19% yield after fractional crystallization. It crystallizes in the orthorhombic space groupP2₁2₁2₁ (Z=4) witha=6.064(2),b=8.347(1) andc=26.455(16) Å. Disorder associated with the unsubstituted furanose ring provides two arrangements, rings B and C, with two sets of sites for both the hydroxyl group and a ring carbon atoms: the relative occupancy of ring B: ring C=0.53(1):0.4791). Distinct H-bonding situations (both intra-and inter-molecular) are associated with the two arrangement. The conformations of the unsubstituted furanose ring with the weaker intramolecular H-bonding (ring B) and the tosyl-substituted ring (ring A) are very similars, being 1:2 mixtures of envelope [³ E] and twist forms [³ T ₄]: the stronger H-bonding in ring C results instead in a conformation made up from a 30:70 mixture ofE ₀ and⁴ T ₀ forms. The¹H-NMR spectrum for3 indicates that the average solution conformation is also a mixture of envelope and twist forms and is similar to that of the A/B solid-state arrangement.