Thermal studies on Zirconium hydroxide gel formed by aqueous gelation

Zirconium hydroxide gel has been prepared by a novel aqueous gelation process by the controlled hydrolysis of zirconium oxychloride in the presence of sodium acetate. The gel thus formed has been subjected to thermal analysis: TG, DTG, and DSC. Thermal analysis shows that the gel is continuously dehydrated in the temperature range between room temperature and 500?°C. The total mass loss relative to the initial mass is about 44.1%. Thermal analysis shows that the decomposition takes place in three stages. The gel contains absorbed and coordinated water. In the second stage of dehydration, dehydration of the Zr(OH)₄ gel also takes place along with the removal of the coordinated water. The DSC analysis coupled with TG and structural information, indicate that the exothermic processes between 349 and 460?°C can be attributed to the nucleation process of the formation of tetragonal zirconia, with phase transformation at 460?°C.     

Scalable total synthesis of (-)-berkelic acid by using a protecting-group-free strategy

Supply chain: the polycyclic core of (-)-berkelic acid (1) was constructed in just one step from very simple starting materials. The total synthesis of 1 involves a seven-step linear sequence. Protection/deprotection steps were avoided and all but the last step were performed on a gram scale. This synthesis could solve the supply problem associated with the exhaustion of the natural source.     

Alternating droplet generation and controlled dynamic droplet fusion in microfluidic device for CdS nanoparticle synthesis

A multifunctional and high-efficiency microfluidic device for droplet generation and fusion is presented. Through unique design of the micro-channels, the device is able to alternately generate droplets, generating droplet ratios ranging from 1 ratio 5 to 5 ratio 1, and fuse droplets, enabling precise chemical reactions in several picoliters on a single chip. The controlled fusion is managed by passive control based on the channel geometry and liquid phase flow. The synthesis of CdS nanoparticles utilizing each fused droplet as a microreactor for rapid and efficient mixing of reagents is demonstrated in this paper. Following alternating droplet generation, the channel geometry allows the exclusive fusion of alternate droplets with concomitant rapid mixing and produces supersaturated solution of Cd2+ and S2- ions to form CdS nanoparticles in each fused droplet. The spectroscopic properties of the CdS nanoparticles produced by this method are compared with CdS prepared by bulk mixing.     

A DFT computational study of spin crossover in iron(III) and iron(II) tripodal imidazole complexes. A comparison of experiment with calculations

B3LYP* functionals were used to model the sixteen iron(II) (1A, LS and 5T, HS) and iron(III) (2T, LS and 6A, HS) complexes of the 1:3 Schiff base condensate of tris(2-aminoethyl)amine and imidazole-4-carboxaldehyde, H3L1, and its deprotonated forms, [H2L1]1-, [HL1]2-, and [L1]3-. This ligand system is unusual in that [FeH3L1]3+, [FeH3L1]2+ and [FeL1]- all exhibit a spin crossover between 100-300 K. This makes these complexes ideal for a hybrid DFT computational approach and provides an opportunity to refine the value of the exact exchange admixture parameter, c3, and to predict properties of partially protonated complexes that are not experimentally available. The accepted value of 0.20 is larger than the value of approximately 0.13 that was found to best reproduce experimental data in terms of spin state predictions. With iron(III) B3LYP calculations showed that all of the complexes were low spin at 298 K with the exception of [FeH3L1]3+ which is spin crossover in agreement with experimental results. It was also shown for iron(III) that the ligand field increased as the number of protons decreased. In contrast all of the iron(II) complexes were close to the spin crossover region regardless of protonation state. Experimental structures are fairly well modeled by this system in regard to the key structural indicators of spin state, which are the bite and trans angles. The calculated iron to nitrogen atom distances are always larger in the high spin form than the low spin form but all iron to nitrogen bond distances are larger than the experimental values. In general non-bonded interactions are not well modeled by this methodology.     

High-resolution electron tomography study of an industrial Ni-Mo/gamma-Al2O3 hydrotreating catalyst

The growing demand for high-quality transportation fuels requires their cost-effective production by hydrodesulfurization of crude oils using heterogeneous catalysts. To study the three-dimensional (3D) structure of such a commercial, sulfided Ni-Mo/gamma-Al2O3 catalyst, electron tomography was applied. The MoS2 particles form an interconnected complex structure within the mesopores of the alumina support. Spatial organization, morphology, and orientation of the MoS2 particles in the pores were resolved with sufficient accuracy to display the 6-A-spaced MoS2 crystal planes. The proximity of the MoS2 edge planes and more loosely interacting MoS2 basal planes to the alumina support showed the presence of pores smaller than 3 nm, which was confirmed by physisorption experiments. The actual shape of the MoS2 particles cannot be described by simple models as derived from studies on model catalysts. Electron tomography is a unique tool to study the actual 3D structure of complex industrial catalysts with sub-nanometer resolution.     

Hydroxy-1-aminoindans and derivatives: preparation, stability, and reactivity

The chemical stability and reactivity of hydroxy-1-aminoindans and their N-propargyl derivatives are strongly affected by the position of the OH group and its orientation relative to that of the amino moiety. Thus, the 4- and 6-OH regioisomers were found to be stable, while the 5-OH analogues were found to be inherently unstable as the free bases. The latter, having a para orientation between the OH and the amino moieties, could be isolated only as their hydrochloride salts. 7-Hydroxy-1-aminoindans and 7-hydroxy-1-propargylaminoindans represent an intermediate case; while sufficiently stable even as free bases, they exhibit, under certain experimental conditions, unexpected reactivity. The instability of the 5- and 7-hydroxy-aminoindans is attributed to their facile conversion to the corresponding, reactive quinone methide (QM) intermediates. The o-QM obtained from 7-hydroxy-aminoindans was successfully trapped with ethyl vinyl ether via a Diels-Alder reaction to give tricyclic acetals 32a,b.