Hydrotalcite Interlayer Research Articles

Molecular Alignment and Photodimerization of 4‘-Chloro-4-stilbenecarboxylic Acid in Hydrotalcite Clays: Bilayer Formation in the Interlayers

It was observed that the photolysis of 4‘-chlorostilbenecarboxylic acid (CSC) in N,N-dimethylformamide (DMF) yielded mainly a syn head-to-head dimer. The molecular alignment in hydrotalcite interlayers has been investigated by electric linear dichroism (ELD) at room temperature in order to clarify the correlation between the photocyclodimerization and the molecular alignment of CSC intercalated in hydrotalcite interlayers in DMF. ELD analysis in combination with X-ray diffraction analysis of this hydrotalcite complex involving CSC revealed the CSC molecules to be intercalated as a double layer, the tilt angle of the molecular plane being ca. 39.4°. The suggested molecular parallel packing model was found to be in good agreement with the stereochemistry of the photodimerization.

Photopolymerization of 4-vinylbenzoate and m- and p-phenylenediacrylates in hydrotalcite interlayers

Photopolymerizations of intercalated 4-vinylbenzoate (VBA) and p-(or m-) phenylenediacrylates (PDA) were investigated in the presence of an anion exchange clay, hydrotalcite. UV irradiation of clay powder adsorbing VBA and 4-benzoylbenzoate (BBA) ions gave rise to the cyclodimerization of the olefin and a radical polymerization to form polyvinylbenzoate. The degree of the polymerization was 10–10 3. The stereoregularity was investigated by NMR analysis and is discussed in relation to the state of molecular aggregation in the clay interlayers. In contrast to VBA, photoreaction of the intercalated PDAs resulted in the formation of oligomers in [2+2] cycloaddition manner, of which the polymerization degrees were rather low (up to ten at most). The stereochemistry of the oligomer was revealed to be of a syn-head-to-head structure by NMR analysis. Dianionic molecules such as PDAs showed an interesting intercalation behavior in contrast to monoanions, i.e. just one double-negatively charged molecule was estimated to occupy three anion exchange sites of the hydrotalcite layer. Also, the relatively low polymerization degrees of the PDAs were found to be due to the above intercalation characteristics. Powder X-ray diffraction analysis showed that the molecular aggregation state was remarkably changed by desiccating the clay composite in vacuum, thus suppressing the efficiency of the photoreaction.

ChemInform Abstract: Stereoselectivity Control of (2 + 2) Photocycloaddition by Changing Site Distances of Hydrotalcite Interlayers.

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Stereoselectivity control of [2 + 2] photocycloaddition by changing site distances of hydrotalcite interlayers

Stereoselectivity of photocyclodimers of unsaturated carboxylates is shown to be controlled by changing the site distance of clay interlayers.

Uptake of benzenecarboxylate ions by magnesium aluminium oxides

AbstractThe behaviour of uptake of the benzenecarboxylate ions, C6H6‐n(COO)nn (n = 1–6), in aqueous solutions by rock‐salt type magnesium aluminium oxide, Mg(1‐x)(2+x)Al2x/(2+x)O (x = 0.17, 0.30, 0.33) was investigated at 0.70°C. All the benzenecarboxylate ions were taken up from solution competitively with OH‐ to form the hydrotalcite‐like layered double hydroxides. The uptake rate could be adequately described by a surface chemical reaction controlled shrinking core model, and the apparent activation energy was c. 60 kJ mol−1. The selectivity of anion uptake increased with increasing the charge density of the benzenecarboxylate ions. The amount of benzenecarboxylate ions incorporated in the interlayer of hydrotalcite and the selectivity of uptake for benzenecarboxylate possessing higher electric change increased with increasing aluminium content in the magnesium aluminium oxide.

Intercalation of benzenecarboxylate ions into the interlayer of hydrotalcite

Intercalation behaviour of benzenecarboxylic acids in the interlayer of hydrotalcite was investigated by using the chemical reaction of rock-salt type magnesium aluminum oxide, Mg 0.61Al 0.26O, and various benzenecarboxylates in aqueous solutions at 50–70°C. Magnesium aluminum oxide hydrated and combined with benzenecarboxylate ions and hydroxyl ion competitively to form hydrotalcite-like compounds. The amount of benzenecarboxylate ions incorporated in the interlayer of hydrotalcite and the selectivity of anion uptake increased with increasing charge density of the ions.

Preparation and photochemical properties of cadmium sulphide-zinc sulphide incorporated into the interlayer of hydrotalcite

Semiconductor particles composed of mixed CdS and CdS-ZnS were incorporated into an interlayer of hydrotalcite by chemical reaction between Cd(edta) 2− and S 2− in the interlayer. The incorporated particles seemed to be very small, less than 0.4 nm thick. The band gap energies of CdS and sequentially precipitated CdS followed by ZnS in the interlayer were slightly larger than that of normal-crystalline CdS. On the other hand, the band gap energy of CdS-ZnS mixture coprecipitated in the interlayer was almost equal to the average value of those of normal-crystalline CdS and ZnS. The CdS and CdS-ZnS mixture incorporated into hydrotalcite were capable of efficient hydrogen evolution following irradiation with visible light in the presence of Na 2S and/or Na 2SO 3 as a sacrificial donor. The hydrogen production activities of the catalyst incorporated in hydrotalcite were in the order of sequentially precipitated CdS followed by ZnS > simultaneously precipitated CdS-ZnS mixture ⪢ CdS. The difficulty of mass transfer of the hydrogen evolved in response to visible light through the interlayer restricted the efficiency of the semiconductor incorporated into hydrotalcite. Almost equal amounts of S 2O 6 2− and SO 4 2− were formed by the photochemical oxidation of SO 3 2− in aqueous solution catalysed by unsupported CdS/ZnS, but the amount of S 2O 6 2− produced in the same reaction with CdS/ZnS incorporated into hydrotalcite was significantly less.