Montmorillonite transformation

A diverse group of organic reactions catalyzed by montmorillonite has been described and some reviews on this subject have been published.19 Examples of those transformations include addition reactions, such as Michael addition of thiols to y./bunsatu rated carbonyl compounds 20 electrophilic aromatic substitutions,19c nucleophilic substitution of alcohols,21 acetal synthesis196 22 and deprotection,23 cyclizations,19b c isomerizations, and rearrangements.196 24... 

Glycals can be transformed into 1,6-anhydro sugar derivatives by intramolecular cyclization in the presence of Lewis and Brpnsted acids, a reaction that has been termed the intramolecular Ferrier glycosylation.168 Sharma el al.169 showed that a montmorillonite clay-supported silver reagent can be an efficient catalyst for this transformation. The 1,6-anhydro-2,3-dehydro sugars obtained were then selectively dihydroxylated to furnish 1,6-anhydro saccharides. 

A new synthetic route for functionalized polyhydroxyalkyl-pyrimidines starting from unprotected aldoses and based on montmorillonite K-10 catalysis and solvent-free microwave irradiation conditions, has been reported by Yadav et al,m Thus, reaction of D-glucose and D-xylose with semicarbazide or thiosemicarbazide (186) in the presence of montmorillonite K-10, under microwave irradiation, proceeded via domino cycloisomerization, dehydrazination, and dehydration of the intermediate semi- or thiosemicarbazones (187) to afford l,3-oxazin-2-ones or l,3-oxazine-2-thiones (188) in one single step and in yields between 79% and 85% (Scheme 34). Other mineral catalysts tested, such as silica gel and basic alumina, were far less effective for this transformation and only silica gel was active at all, giving low yields (15-28%) of compounds 188a-d. The l,3-oxazin-2-ones(thiones) thus synthesized were subsequently converted into the target pyrimidines by reaction with aromatic... 

This conclusion is in agreement with the kinetic results from Radoiu et al. [86] obtained for the transformation of 2- and 4-tbutyl phenols in the liquid phase in the presence of montmorillonite KSF as catalyst either under the action of MW or A (Eq. (31) and Tab. 3.12). 

It was found that in the catalytic transformation of 2- and 4-t-butylphenol in the liquid phase on heterogeneous KSF and K10 montmorillonite catalysts under micro-wave and conventional conditions the microwaves affected both the rate and the selectivity of the reaction. 

Reaction of 218 with aromatic aldehydes to give the ring-closed product 220 takes place in boiling ethanol in excellent yield (Scheme 44) <2001PHA376>. The transformation obviously proceeds via formation of a dihydro thiadiazole 219, as also suggested for the transformation of 218 under microwave irradiation in the presence of montmorillonite <2002PS2399>. 

Cruz M, Kaiser A, Rowxhat PG, et al. 1974. Absorption and transformation of HCN on the surface of copper and calcium montmorillonite. Clays Clay Mineral 22 417-425. 

The kinetics of PAA, synthesized from 4,4 -oxydianiline and pyromellitic dianhydride, solid-state imidization both in filler absence and with addition of 2 phr Na+-montmorillonite was studied [1], The nanofiller was treated by solution of P-phenylenediamine in HC1 and then washed by de-ionized water to ensure a complete removal of chloride ions. The conversion (imidization) degree Q was determined as a function of reaction duration t with the aid of Fourier transformation of IR-spectra bands 726 and 1014 cm 1. The samples for FTIR study were obtained by spin-coating of PAA/Na+-montmorillonite mixture solution in N,N-dimethylacetamide on KBr disks, which then were dried in vacuum for 48 h at 303 K. It was shown, that the used in paper [1] method gives exfoliated nanocomposites. The other details of nanocomposites polyimid/Na+-montmorillonite synthesis and study in paper [1] were adduced. The solid-state imidization process was made at four temperatures 7) 423, 473, 503 and 523 K. 

Fig. 7 shows the progressive transformation of montmorillonite to iliite/smectite interlayers by the gradual development of both the characteristic Cs and Rb high selectivity profiles observed for pure illite and the high Cs-Rb selectivity at+ race fadings. The data can be simulated (see table VI for the Ca - Cs case) using a consistent set of intrinsic selectivity coefficients and identical site group capacities for the Ca-Cs and... 

The use of heterogeneous catalysts in this reaction has also been achieved palladium-montmorillonite clays [93] or palladium/activated carbon [94] in the presence of dppb transformed 2-allylphenols into lactones, the regiose-lectivity of the reaction being largely dependant on the nature of the support. Very recently, palladium complexes immobilized onto silica-supported (polyaminoamido)dendrimers were used as catalysts in the presence of dppb for the cyclocarbonylation of 2-allylphenols, 2-allylanilines, 2-vinylphenols, and 2-vinylanilines affording five-, six-, or seven-membered lactones and lactams. Good conversions are realized and the catalyst can be recycled 3-5 times [95]. 

In contrast to these transformations, Michael additions of simple enolates to acceptor-substituted dienes often yield mixtures of 1,4- and 1,6-addition products27-30. For example, a 70 30 mixture of 1,4- and 1,6-adducts was isolated from the reaction of the lithium enolate of methyl propionate with methyl sorbate30. This problem can be solved by using the corresponding silyl ketene acetal in the presence of clay montmorillonite as acidic promoter under these conditions, almost exclusive formation of the 1,4-addition product (syn/anti mixture) was observed (equation ll)30. Highly regioselective 1,4-additions... 

Onium salts, such as tetraethylammonium bromide (TEAB) and tetra-n-butylammonium bromide (TBAB), were also tested as PTCs immobilized on clay. In particular, Montmorillonite KIO modified with TBAB efficiently catalyzed the substitution reaction of a-tosyloxyketones with azide to a-azidoketones, in a biphasic CHCI3/water system (Figure 6.13). ° The transformation is a PTC reaction, where the reagents get transferred from the hquid to the solid phase. The authors dubbed the PTC-modified catalyst system surfactant pillared clay that formed a thin membrane-hke film at the interface of the chloroform in water emulsion, that is, a third liquid phase with a high affinity for the clay. The advantages over traditional nucleophilic substitution conditions were that the product obtained was very pure under these conditions and could be easily recovered without the need for dangerous distillation steps. 

A striking example of iron-enrichment of a detrital silicate material is presented by Giresse and Odin (1973). Recent, kaolinite-rich sediments containing about 8% Fe total on the West African Continental Shelf, are transformed into pellets rich in montmorillonite which contain 16-21% total iron. This material is then progressively enriched in potassium to form glauconite. 

Tomita, et al., 1970 Meilhac and Tardy, 1970.) The prevalence of montmorillonites, in river sediments and those studied as deep-sea cores in the numerous JOIDES reports leads one to believe that montmorillonite is a very common weathering product. Certainly a portion of it is derived from degraded micas but if one considers that the next most common sedimentary mineral is illite, one is forced to conclude that either continental rocks are for the major part made of micas or that many other minerals are transformed into montmorillonite during the weathering process. 

It is evident that such theoretical constructions find form in real situations, since the transformation of montmorillonites to mica (potassic) or... 

A very interesting beginning has been made in experimental determinations of the behavior of fatty acids in a water-montmorillonite system at one atmosphere pressure (Johns and Shimoyama, 1972). The basis of the study is the transformation of a long chain molecule to smaller units by breaking specific carbon-carbon bonds. The energy necessary to do this is estimated to be about 46 Kcal/mole in a montmorillonite system, whereas calculations put the value at 56-58 Kcal in a uniquely hydrocarbon... 

Khanna, M. Stotzky, G. (1992). Transformation of Bacillus subtilis by DNA bound on montmorillonite and effect of DNase on the transforming ability of bound DNA. Applied and Environmental Microbiology, 58, 1930-9-... 

---