Kaolinite irradiation

BDE-209 debromination during photolysis leads to the formation of less bro-minated congeners. The appearance of these photo-induced products is faster under UV irradiation than under sunlight. Figure 16.19 shows gas chromatograms over time of BDE-209 adsorbed on montmorillonite, during 101 days of irradiation by sunlight, and compared to a control held in darkness. Over time, the areas of peaks for nona-, octa- and heptabromodiphenyl ethers increased in the irradiated samples and remained at trace values in the dark control. Ahn et al. (2006) note a comparable but slower time trend for BDE-209 adsorbed on kaolinite. 

A common and effective direct approach to unsubstituted or multiply substituted oxazolines is the Lewis acid catalyzed reaction of nitriles with amino alcohols in an alcoholic or aromatic solvent (chlorobenzene) at reflux. The most common Lewis acids employed include ZnCl2, ZnBr2, NiBr2, CuCl2, and kaolinitic clay. Microwave irradiation has also been reported to facilitate the transformation. Alternatively, the condensation can be carried out in the presence of catalytic amounts of potassium carbonate. The method works well for both aliphatic and aromatic nitriles, with retention of stereochemistry. Some representative examples from the recent literature are listed in Table 8.16 (Scheme 3 40),2 35.2oi-2i3... 

Keywords 2-hydroxybenzaldehyde, 2-hydroxyacetophenone, Meldrum s acid, kaolinitic clay, microwave irradiation, 3-carboxycoumarin... 

Table I. Treatment of Kaolinite with Caustic and Microwave Irradiation, Followed by Water or 10% HCl Wash...

Illite, a mineral that forms in alkaline solutions (15), is more stable than kaolinite in 30% NaOH. The experiments (Table II) in which illite was reacted either at room temperature or at 105 C with 30% NaOH showed that no discernible reaction took place. In the microwave irradiated experiments, however, considerable changes occurred. Illite strongly absorbed the microwave energy, causing considerable heating of the sample. When illite was irradiated for... 

Montmorillonite began to break down in 30% NaOH solutions at room temperature (Table III). The first change noted, as with kaolinite, was that the peak intensities decreased in the XRD pattern. A decrease in peak intensities was also seen in the XRD patterns for samples heated to 105 C. Microwave irradiation of montmorillonite caused heating of the sample and some changes in the XRD pattern. 

The reactions between clay minerals, NaOH solutions, and micro-wave irradiation showed that the clay mineral structures began to break down, and the released Al and Si (and some K) combined with Na from the solution to form new minerals. The exact reaction path could not be determined from the present experiments. Since the new minerals formed had approximately the same Al Si ratio as the clay minerals, no excess Al (as AI2OJ or Al(OH)g) or quartz was expected, nor was any found in the XRD pattern. The following equations, arranged with increasing time, seem most reasonable to describe the reactions observed for kaolinite and illite ... 

Bandgar et al. (1999) investigated the conversion of aldoximes into nitrile using natural kaolinitic clay EPIC, EPZG or EPZlO as a heterogeneous catalyst and microwave irradiation under solvent-free condition. This reaction provides 52-95% yield. 

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