The roles of different forms of Fe(III) impurities in a hectorite with respect to the oxidation of benzidine in aqueous suspension have been evaluated using electron spin resonance and UV-visible spectroscopy. Natural surface-adsorbed Fe(III) showed no detectable activity in the oxidation process, while very small quantities of structural octahedral Fe(III) apparently promoted a relatively rapid conversion to the radical cation. However, extremely small quantities of benzidine were oxidized in comparison to the exchange capacity of the clay. Freshly adsorbed Fe3+ cations effectively oxidized benzidine, but lost much of this ability upon aging. The Fe(III)-benzidine electron transfer could be distinguished from an O2-benzidine reaction, since the latter reaction was slow and limited by the rate of O2 diffusion into the clay-water system. The O2-benzidine reaction was also inhibited at high pH. The existence of two reaction mechanisms and the involvement of only a small fraction of the total structural iron, as shown by comparison of the hectorite and a montmorillonite, may explain the conflicting interpretations in the literature. The benzidine blue reaction not only requires an oxidizing agent to form the radical, but also a clay surface to adsorb and stabilize it against further oxidation.

The role of adsorbed and structural Fe3+ in palygorskite and sepiolite with respect to the oxidation of hydrocortisone in aqueous suspension has been evaluated using electron spin resonance and UV-visible spectroscopy. Natural surface-adsorbed Fe3+ showed an important activity in the oxidation process, although smaller than octahedral Fe3+. The kinetics of oxidative degradation of hydrocortisone by palygorskite appear to be composed of two apparent first order reactions which may be associated with two kinds of sites for Fe in palygorskite. The lower oxidizing power of sepiolite for hydrocortisone degradation is due to its very low Fe3+ content.

Pillared bentonites were found to be efficient catalysts for the O-methyl bond cleavage of anisoles (e.g., m-methylanisole, guaiacol, and creosol) under very mild, static conditions (150°C, a few hours, inert atmosphere). The O-methyl bond cleavage led to phenolic products. Gas chromatographymass spectrometry and solid-state 13C nuclear magnetic resonance (NMR) techniques used to probe 13C-labeled anisoles revealed that dealkylation and transalkylation reactions occurred to a large extent, and that conversion was efficient at >95% after two days. Ortho- and para-isomers were observed exclusively, without any evidence of meta-substitution. Volatile products were determined by mass spectrometry to be 13CH3OH and (13CH3)2O. Magic-angle spinning 13C NMR experiments showed that the molecules were fairly mobile in the clay micropores prior to catalysis. After catalysis, cross-polarization NMR showed that molecular motion had decreased markedly. Ultraviolet-visible spectroscopy of the colored complexes suggested some quinone formation. The trend of clay reactivity was found to be: pillared bentonite ≫ acid-washed montmorillonite > untreated bentonite > pillared fluorhectorite ≃ untreated fluorhectorite.

The reactions of simple conjugated dienes over divalent and trivalent transition metal-exchanged montmorillonites yield, in the absence of nucleophiles, a variety of products. Some of these products are a result of Diels-Alder cycloaddition reactions, whereas others are indicative of carbocation intermediates, i.e., other dimers, oligomers, and isomerization products of these intermediates. The reactions in sealed cells between 20° and 150°C show trends in the yields of the various product groups. Dimers of butadiene and isoprene formed by cycloaddition (i.e., 4-vinylcyclohexene and the monoterpene p-menthadiene (limonene)) were formed at low temperatures (20–50°C). As the temperature was raised, the total yield of dimers increased and higher oligomers were formed along with isomerization products of the dimers and oligomers. The products of cycloaddition, however, did not increase markedly. The type of solvent used for the reaction was found to influence the reactivity, e.g., the use of 1,4-dioxan rather than chloroform led to a reduction in total conversion and also to a markedly higher degree of selectivity. In the presence of a suitable nucleophile (methanol), both dienes gave the 1,4-addition product predominantly, which suggests that an allylic carbocation intermediate was involved. The use of an interlayer-supported nickel complex, [HNi(P(OEt)3)4]+, produced the only large scale polymerization observed in this work.

Infrared spectra of adsorbed pyridine have been used to obtain qualitative information on the nature of the interaction of pyridine with different rhodium catalysts supported on palygorskite and silica. Based on these data, qualitative definitions of the adsorption sites of these catalysts have been deduced. The catalysts were prepared with natural palygorskite, and palygorskite dehydrated in vacuo at 150°C and 400°C. In this way, catalysts were obtained that had different water contents and, therefore, different acidities. Lewis-bound pyridine was detected by infrared spectroscopy from room temperature to 500°C. The greatest acidity was found in a catalyst prepared with the palygorskite support dehydrated at 150°C before preparation of the catalyst. With this catalyst, strongly hydrogen-bound pyridine was observed when evacuation was carried out at temperatures between 150°C and 300°C. Catalysts prepared with the palygorskite support pretreated at 400°C did not exhibit strongly hydrogen-bound pyridine, and Lewis acidity decreased significantly. As expected, hydrogen-bound pyridine was also detected for rhodium supported on silica. However, it was desorbed at temperatures below 150°C. The results of the acidity studies follow the same pattern as those for 1 -hexene double-bond migration under hydrogénation reaction conditions.

Volatiles formed on heating clay minerals contain a variety of cations and anions and are highly reactive. Gas chromatograph-mass spectrometer analysis of long-chain n-alkanes exposed to such volatiles showed that some decomposition occurred even <250°C. Reactions with anions donated by the volatiles led to compounds containing atoms other than C and H, e.g., Cl. The products obtained from n-alkanes heated in a stream of clay volatiles to 500°C resembled those produced by corresponding alkane-clay mixtures heated to 250°C. At higher temperatures contact between the alkanes and montmorillonite or halloysite led to changes in the assemblages formed, whereas kaolinite or sepiolite had no effect. Thus, the first reactions that occurred when clays were heated with n-alkanes were apparently induced by the volatiles; at higher temperatures catalysis due to direct contact came into play with some of the clay minerals.

Clays may catalyze chemical reactions by acting as Brönsted acids, Lewis acids, and/or Lewis bases. The changes occurring when limonene (p-menthadiene) is heated in the presence of montmorillonite illustrate how Brönsted and Lewis acidity may operate competitively, the nature of the interlayer cations determining which reaction dominates. The rate at which the starting material disappears increases with the acidity of the clay, which depends upon the interlayer cations (Na < Mg < Al < H). The concentration of disproportionation and isomerization products reaches a maximum after reaction times which decrease with increasing surface acidity of the clay, p-cymene is produced by oxidation in concentrations inversely related to the surface acidity of the clay. The course of the chemical reaction can thus be steered in the preferred direction by an appropriate choice of interlayer cations.

The catalytic power of Ca-nontronite (0.2–2 μm) for the polycondensation of phenols and glycine and the associated reactions that involve the ring cleavage of phenols and the decarboxylation and deamination of glycine was studied in systems free of microbial activity. At the end of a 90-hr reaction period, the amount of CO2 released from the Ca-nontronite-glycine-pyrogallol, Ca-nontronite-glycine-eatechol, and Ca-nontronite-glycine-hydroquinone systems were 5.1, 8.7, and 11.6 times higher, respectively, than those from the respective nontronite-free systems, showing the catalytic role of Ca-nontronite in the ring cleavage of phenols and the decarboxylation of glycine. The release of CO2 and NH3 from the Ca-nontronite-glycine system revealed that Ca-nontronite can catalyze decarboxylation and deamination of glycine. The ability of Ca-nontronite to catalyze the deamination of glycine was substantially enhanced by the presence of a phenol. The visible absorbances at both 472 and 664 nm of the supernatants, the total yields of N-containing humic polymers, and the fractions of glycine converted to nitrogenous polymers indicated that polycondensation of glycine and phenol was greatly catalyzed by Ca-nontronite. The total N-containing humic polymers formed in the systems decreased in the order: Ca-nontronite-glycine-pyrogallol > Ca-nontronite-glycine-cateehol > Ca-nontronite-glycine-hydroquinone > glycine-pyrogallol > glycine-hydroquinone > glycine-catechol. The infrared and electron spin resonance spectra of humic acid (HA) and fulvic acid (FA) formed in the supernatants of the reaction systems were quite similar to those of soil HA and FA. The catalytic power of Ca-nontronite in affecting the ring cleavage of phenols, deamination and decarboxylation of amino acids, and formation of humic substances derived from phenols with amino acids in soils and the related environments thus merits attention.

With the current interest in the use of transition metal-exchanged phyllosilicates as catalysts for novel organic syntheses, investigations into the factors which affect the movement of reactant, product, and solvent molecules into and out of their interlamellar region are of considerable importance. Mixed organic-water intercalates of a Wyoming montmorillonite, exemplified by the Na-montmorillonitepyridine-water system which can form four different intercalates exhibiting basal spacing of 29.3, 23.3, 19.4, and 14.8 Å depending on the pyridine: water ratio, have been used as a model system. X-ray and neutron diffraction and quasielastic neutron scattering data relating to the interconversion of interlayer species indicate that access to and exit from the interlayer space is hindered at high partial pressures of water by a water-film diffusion barrier in the interparticulate voids which exist between the aggregated silicate layers. At lower water vapor pressures the rate-limiting step for interconversion from one intercalate to another is the rate of transport of reagents and products to and from the clay particles. Under conditions where these rates are fixed, the rate-limiting step is the rate of diffusion of the pyridine molecule in the lower-spacing intercalate. Processes which involve a change in basal spacing do not necessarily proceed via a single discrete step, but are also affected by the amount of water made available to the system. In organic reactions catalyzed in the interlamellar space of various cation-exchanged montmorillonites (e.g., the conversion of alk-1-enes to di-2,2’-alkyl ethers and the reaction of alcohols to form ethers), rate-determining steps similar to those found above are likely to be operative. In particular, for reactions carried out in the liquid phase, where mass transport is facile and where phase-transfer problems are avoided, such reactions are likely to be diffusion controlled.

The acid-catalyzed reaction between methanol and isobutene to give methyl-t-butyl ether may be carried out using a cation-exchanged smectite as the catalyst. In 1,4-dioxan solvent at 60°C smectites exchanged with Al3+, Fe3+, or Cr3+ give yields of ∼60% after 4 hr, whereas smectites exchanged with Cu2+, Pb2+, Ni2+, Co2+, Ca2+, and Na+ give less than ∼8% yield. The reaction is efficient only when certain solvents are used, e.g., with Al3+-smectite the yield is ∼5% when using 1,2-dimethoxyethane, diethyleneglycol diethylether, n-pentane, tetrahydropyran, N-methylmorpholine, or tetrahydrofuran solvents compared with ∼60% using 1,4-dioxan solvent (4 hr). Moreover, the effective solvents depend somewhat on the clay interlayer cation. The use of tetrahydrofuran and tetrahydropyran gives ∼35% yields at 60°C (4 hr) with Fe3+- or Cr3+-smectites but ∼4% yield with Al3+-smectite.

The catalytic activity of sepiolite from Amboseli, Tanzania, for the dehydration and dehydrogenation of ethanol at 150°–300°C has been studied using a flow reactor. Both reactions occur, but the catalyst activity decreases with use. The products include water, carbon dioxide, ethene, ethanal (acetaldehyde), diethyl ether, but-1,3-diene, but-2-enal (crotonaldehyde), and an unidentified aromatic compound. The proportions change with temperature, the dehydrogenation reaction being favored at the higher temperatures. The BET surface areas of the sepiolite are 316 m2/g (nitrogen adsorption at — 197°C) and 212 m2/g (ethanol vapor adsorption at 25°C, assuming a molecular cross-sectional area of 24.6 Å2), indicating a possible greater penetration of pores and channels by nitrogen compared with ethanol vapor under these conditions. The pore-size distribution reveals that approximately 55% of the surface area measured by nitrogen adsorption is contributed by micropores.

By ion exchanging expandable clay minerals with large, cationic oxyaluminum polymers, “pillars” were introduced that permanently prop open the clay layers. On the basis of thermal, infrared spectroscopic, adsorption, and X-ray powder diffraction (XRD) analysis, the interlayering of commercial sodium bentonite with aluminum chlorohydroxide, [Al13O4(OH)24(H2O)12]+7, polymers appears to have produced an expanded clay with a surface area of 200–300 m2/g. The pillared product contained both Brönsted and Lewis acid sites. XRD and differential scanning calorimetry measurements indicated that the micropore structure of this interlayered clay is stable to 540°C. Between 540° and 760°C, the pillared clay collapsed with a corresponding decrease in surface area (to 55 m2/g) and catalytic cracking activity for a Kuwait gas oil having a 260°-426°C boiling range.

Montmorillonite-based catalysts were compared with an acidic ion-exchange resin of the type used industrially for the production of methyl t-butyl ether (MTBE) from methanol and isobutene or t-butanol. When 1,4-dioxan was used as solvent, Al3+-exchanged montmorillonites had about half the efficiency of the resin Amberlyst 15 at 60°C; they were, however, about twice as efficient at this temperature at Ti3+-montmorillonite or K10, a commercially available acid-treated bentonite. Montmorillonite exchanged with Chlorhydrol solutions to give interlayer [Al13O4(OH)2(H2O)12]7+ ions and pillared clays derived from such materials were poor catalysts, as was K306, a more drastically acid-treated bentonite- based commercial catalyst. Freeze-drying of the Al3+-clay before reaction to produce a more open, porous structure had no effect on its catalytic efficiency. The activation energy for the reaction of isobutene and methanol in dioxan was 44 kj/mole for an Al3+-clay catalyst compared with 25 kJ/mole for reactions catalyzed by Amberlyst 15. With no solvent (as in industrial processes), the rates of reaction were considerably slower for both the clay- and resin-catalyzed reactions. As has been found previously for resin-catalyzed reactions using stoichiometric amounts or an excess of methanol, the rate was proportional to the isobutene concentration, and the rate-determining step appeared to be protonation of the alkene. The performance of the Al3+-clay catalyst was increased by reducing the water content of the clay. In most reactions the clay catalysts were equilibrated at 12% relative humidity. Exposure of the clay to a low vacuum (10−1 torr) before use increased its catalytic activity from 50 to 60% of that of Amberlyst 15.

The catalytic power of Ca-nontronite, Ca-bentonite, and Ca-kaolinite in promoting the abiotic ring cleavage of pyrogallol (1,2,3-trihydroxybenzene) and the associated formation of humic polymers was studied in systems free of microbial activity. The presence of Ca-kaolinite and especially Ca-nontronite in the pyrogallol solutions at pH 6.00 greatly enhanced the absorbance at both 472 and 664 nm of the supernatants. At an initial pH of 6.00 and at the end of a 90-hr reaction period, the amounts of CO2 released from the ring cleavage of pyrogallol and the yields of the resultant humic polymers formed in the reaction systems followed the same sequence: Ca-nontronite > Ca-kaolinite > Ca-bentonite. The data indicate that the catalytic power of Fe(III) on the edges and in the structure of nontronite was substantially greater than that of Al on the edges of kaolinite and montmorillonite and of a small amount of Fe(III) in the structure of montmorillonite in promoting the reactions. The infrared and electron spin resonance spectra and the solid-state, cross-polarization magic-angle-spinning 13C nuclear magnetic resonance spectra of humic polymers formed in the reaction systems resembled those of natural humic substances.

The exchange of Rh(NBD)(Pϕ3)2+, Rh(NBD)(PMe2ϕ)3+, Rh(COD)(Pϕ3)2+, and Rh(PMe2ϕ)4+ on hectorite was studied in methanol/dichloromethane, acetone, dimethylformamide, and acetonitrile. At low initial Rh+ concentration and short contact times, ion exchange was the predominant process, and its selectivity and maximum capacity were solvent-dependent. High initial Rh+ concentrations, long contact times, and the most polar solvents favored intersalation and salt precipitation. In all experiments monolayers of complex formed in the interlamellar space and were very tightly held. The complexes retained their integrity on the surface even after removal of all solvent molecules.

Hydroxychromium montmorillonites were prepared from solutions containing chromium nitrate and varying amounts of NaOH. The reactant Cr ions were hydrolyzed and, in some experiments, were dimerized to a significant extent. The extent of polymerization in the product formed from a solution containing a maximum amount of [Cr2(H2O)8(OH)2]4+ was compared with that in products obtained from solutions containing monomer, [Cr(H2O)5OH]2+, and lesser amounts of the dimer. Despite the uncertainty about the nature and amounts of product interlamellar species, the catalytic effect of the montmorillonite interlayer on the hydrolysis and polymerization of Cr(III) appears to be independent of the nature of the reactant species. The validity of this conclusion depends to a large extent on the reliability of water determination in the clay mineral species, which is estimated to be no better than 5%. The assumption that H2O+ is 'combined’ and H2O— is 'free’ water is shown to be partially true, thereby causing some uncertainty in the interpretations of interlayer compositions.

When 1-hexene was adsorbed by Cr3+-montmorillonite at room temperature, all evidence of C=C(str) vibrations was lost. Protonation of the alkene occurred, and the secondary carbocation formed was bound at a site on the primary coordination sphere of the interlayer cation. Some of the hydrogen atoms of these primary-sphere water molecules were involved in strong hydrogen bonds to the silicate sheets, whereas others did not form such bonds, but were free and directed into the interlayer space. These latter hydrogen atoms were labile and protonated the alkene molecules.