Philip R. Rudolf

A simple and convenient synthesis of β-amino alcohol chiral auxiliaries based on limonene oxide

Abstract A series of chiral β-amino alcohols was prepared by the reaction of secondary amines with a 1:1 mixture of cis - and trans -limonene oxide in the presence of water as a catalyst. The β-amino alcohol obtained was derived from the trans -limonene oxide, and the unreacted cis -limonene oxide was recovered from the reaction mixture. The β-amino alcohols are useful chiral auxiliaries for the addition of diethylzinc to benzaldehyde.

Structure refinement and water location in the very large-pore molecular sieve VPI-5 by X-ray Rietveld techniques

Abstract The structure of the very large pore molecular sieve VPI-5 was solved based on a combination of X-ray power diffraction measurements and modeling techniques. The original structure refinement was hampered by the fact that the water molecules, which represent 25% of the scattering material, could not be located. In the present work, one VPI-5 family member was analyzed using X-ray Rietveld refinement. Rietveld refinement results show that the reported structure is correct. All the water molecules were located and refined in the 18—ring pore. The water molecules form weakly associated layers within the pore, in a manner not unlike that of liquid water. VPI-5, AlPO4·2 H2O, is hexagonal with space group P63cm and cell parameters of a = 18.9777(3), c = 8.1155(1) A ; V = 2531.4(1) A 3 ; D calc = 1.243 g cm −3 . Small errors in the refinement were found to be caused by a second phase of a slightly dehydrated VPI-5. This was the reason for a high final refinement residual, Rwp, of 0.31.

Rietveld refinement of several structural models for mordenite that account for differences in the X-ray powder pattern

The zeolite mordenite is becoming increasingly important in several catalytic processes that include paraffin isomerization, alkylations, dewaxing of heavy petroleum fractions, and shape-selective reactions of polynuclear aromatics. The catalytic activity of mordenite is related to the synthesis method and appears to be related to the X-ray powder diffraction (XRPD) pattern of the Na mordenite precursor. The differences in the XRPD pattern have been attributed to stacking errors and other effects, but the structural details are unknown. This work was conducted to define the source of these differences. Several theoretical models were developed to account for the XRPD changes. These include ordering of the cations and water molecules, c-axis faulting, and intergrowths of two different crystal forms. Rietveld refinement was used to fit the models to the experimental X-ray powder patterns. Three mordenite samples, with Si:AI ranging from 6:1 to 9.5:1, exhibit the range of differences observed in the X-ray pattern. Results indicate that a c-axis faulted structure is the best model to account for the observed XRPD behavior. The Rietveld refined fault contribution of 9–20% is consistent with other analytical and chemical evidence.

Boranes in synthesis — VII. Synthesis of 2-dialkylamino-6,6-dimethylbicyclo[3.1.1]heptan-3-ols from (R)-(+)-nopinone. Chiral auxiliaries for the addition of diethylzinc to aromatic aldehydes

Abstract The reaction of (1 R ,5 S )-(+)-nopinone with secondary amines in cyclohexane with the azeoptropic removal of water afforded excellent yields of the correspondin enamines. Hydroboration of these enamines with BMS followed by methanolysis and oxidation with basic hydrogen peroxide gave the corresponding (1 R ,2 S ,3 S ,5 R )-2-dialkylamino-6,6-dimethylbicyclo[3.1.1]heptan-3-ols. These amino alcohols, in spite of their trans geometry, served as chiral auxiliaries for the addition of diethylzinc to aromatic aldehydes to give nearly quantitative yields of the corresponding ( R )-1-aryl-1-propanols with 52 to 80% ee.

Nonaqueous Synthesis of Large Zeolite and Molecular Sieve Crystals

Here we present a novel method for the growth of uniformly large and morphologically well defined single crystals of all-silica, aluminosilicate and aluminophosphate molecular sieves with dimensions in the size range of 0.4-5mm. The synthesis mixtures were comprised of pyridine or other organic solvents, a hydrogen fluoride containing mineralizer, reagent amounts of water, an optional nitrogen-containing organic additive and sources of framework-building species. The identity, morphologies and crystal sizes of the synthesis products were found to depend critically on the basicity, hydrogen-bonding ability and viscosity of the organic solvent as well as on the reagent composition of the reaction mixture, especially on the amount of water. Using this method, molecular sieves of MFI, FER and MTN structure types along with the porous macroanionic Al3P4O163-AlPO4-5 like sheet structure have been obtained in our laboratory.

Techniques for ab initio structure determination from X-ray powder diffraction data

Abstract The ab initio structure determination of new materials using X-ray powder diffraction data is still in its infancy when compared with the advances that have been made in single crystal diffraction techniques. Although the powder diffraction data contain all the information that is measurable in a single crystal experiment, getting at even a small part of this information is not trivial. The ab initio structure determination requires an accurate and precise decomposition of the (usually highly) overlapped peaks in the powder pattern. The peak position information is then used for unit cell indexing, and once this is accomplished the resultant integrated intensities can be used for the structure solution. At best, the powder data are normally limited to specific zones of hkl data, only the strongest of which are represented in the powder pattern. This can translate to problems in building the structure model. An overview of the procedures, from data acquisition through to the final refined structure, will be examined.