Cation-exchanged Montmorillonite Research Articles

Mechanism of cellulose polymer reactions with some cation-exchanged montmorillonite catalysts

The degradation of cotton cellulose polymer by Li+-, K+- and NH4+-exchanged montmorillonite has been studied. A general reaction scheme is proposed. The mechanism of this reaction would most probably involve chain breaking and increasing the reducing power of cellulose polymer by dissociation of water molecules coordinated to the central metal ion.

Ce3+-Exchanged Montmorillonite (Ce3+-Mont) as a Useful Substrate-Selective Acetalization Catalyst

Cation-exchanged montmorillonite (M{sup n+}-mont; M{sup n+} = Ce{sup 3+}, Zr{sup 4+}, Fe{sup 3+}, Al{sup 3+}, Zn{sup 2+}, H{sup +}, and Na{sup +}) was evaluated as a catalyst for the acetalization of carbonyl compounds with methanol. Cyclohexanones, benzaldehydes, and acid-sensitive 2-furancarboxaldehyde were efficiently acetalized in methanol in the presence of Ce{sup 3+}-mont. 30 refs., 2 tabs.

Cation-Exchanged Montmorillonite-Catalyzed Friedel–Crafts Transannular Alkylation with (Z,Z)-1,5-Cyclooctadiene

Abstract The five isomers of phenylbicyclooctanes were produced by Friedel–Crafts transannular alkylation of benzene with (Z,Z)-1,5-cyclooctadiene (1,5-COD) in the presence of a cation-exchanged montmorillonite (Mn+-mont). Mn+-Mont could be used repeatedly to provide the same products in good yields.

Rearrangement of alkyl phenyl ethers to alkylphenols in the presence of cation-exchanged montmorillonite (M n+-mont)

The rearrangement of alkyl phenyl ethers such as 4-phenoxybutan-2-one 1,1-phenoxybutane 2a, 2-phenoxybutane 2b, 2-methyl-2-phenoxypropane 2c and phenoxycyclohexane 2d have been investigated in the presence of cation-exchanged montmorillonite (Mn+-mont; Mn+= Zr4+, Al3+, Fe3+ and Zn2+). The ether 1 rearranged to 4-(4-hydroxyphenyl)butan-2-one 3(raspberry ketone), the odour source of raspberry, in 16–34% GLC yield, where Zn2+-mont was the most effective catalyst. Similarly, other ethers 2a–d rearranged to the corresponding alkylphenols in up to 75% isolated yield with good product selectivity, Al3+-mont being the catalyst of choice. Al3+-Mont was regenerated and reused in the rearrangement of 2b, 2c and 2d.

Swelling behavior of montmorillonite cation exchanged for ω-amino acids by ∊-caprolactam

Natural Na-montmorillonite was cation exchanged for the ammonium cations of various ω-amino acids [H3N+(CH2)n−1 COOH, n = 2, 3, 4, 5, 6, 8, 11, 12, and 18]. X-ray diffraction (XRD) results suggested that the chain axes of ω-amino acids with a carbon number of eight or less were parallel to the silicate layers, and that the chain axes of those with a carbon number of 11 or more were slanted to the layers. The cation-exchanged montmorillonites form intercalated compounds with ∊-caprolactam at 25 °C. The montmorillonites intercalated with both ω-amino acid and ∊-caprolactam were studied by XRD measurement at room temperature and 100 °C. We propose a model where amino acid molecules were arranged perpendicular to silicate layers and ∊-caprolactam molecules filled the space between them. When the ∊-caprolactam was melted at 100 °C, the basal spacing for the montmorillonite increased, in which the carbon number exceeds 11. This phenomenon will be applicable to obtaining the nylon 6-clay hybrid, a molecular composite of nylon 6 and montmorillonite.

ChemInform Abstract: Cation‐Exchanged Montmorillonite Clays as Lewis Acid Catalysts in the Fries Rearrangement of Phenyl p‐Toluenesulfonate.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Use of Inorgano-Organo-Clays in the Removal of Priority Pollutants from Industrial Wastewaters: Adsorption of Benzo(a)Pyrene and Chlorophenols from Aqueous Solutions

AbstractBenzo(a)pyrene (B(a)P), and chlorophenols were sorbed from their respective aqueous solutions onto inorgano-organo-clays (IOCs). Cetyl pyridinium hydroxy-Al montmorillonite (CPC-hydroxy-Al montmorillonite), an IOC, containing only 11–12% surface organic carbon by weight, bound pentachlorophenol strongly, with an observed monolayer capacity of 0.08 mmole/g. The comparable value for granulated activated carbon (GAC) was found to be 0.12 mmole/g. On the other hand, cetyl pyridinium cation-exchanged montmorillonite (CPC-montmorillonite), containing 19.2% surface organic carbon by weight, did not bind pentachlorophenol as efficiently as did IOCs. For benzo(a)pyrene, CPC-hydroxy-Al montmorillonite was found to be a better adsorbent than GAC and CPC-montmorillonite. The significant difference in the sorption potential of the two types of surfactant-laden clays for pentachlorophenol and benzo(a)pyrene was probably due to the surface orientation of the adsorbed organic carbon. For 3,5-dichlorophenol, however, both types of organo-clays exhibited weak binding, which was probably due to the greater aqueous solubility of the dichlorophenol.

Deuterium Nuclear Magnetic Resonance Studies of Water Molecules Restrained by Their Proximity to a Clay Surface

AbstractObservation of quadrupolar splittings for 2H and 17O nuclei from D2O solvent molecules in suspensions of the Ecca Gum BP bentonite points unambiguously to the ordering of water molecules with respect to a static magnetic field. The application of the magnetic field apparently orients the clay platelets as tactoids. Some water molecules adhere to the platelets and are oriented. The magnitude of the quadrupolar splitting depends strongly on the nature of the interstitial cations. The sign of the splitting changes as the ratio of divalent to monovalent cation increases, reflecting a switch in the microdynamics of water molecules next to the plates. With the entry of divalent cations, the clay becomes more cohesive due to the vertical electrostatic attraction of the counterions to the charged plates. More of these hydrated divalent ions compared with monovalent ions condense onto the charged sheet, thereby increasing metal coordination to those water molecules in contact with the clay surface. The dominant reorientation mode of the water molecules switches from rotation of water molecules around hydrogen bonds to the charged sheets to rotation around the electrostatic bond to the divalent metal cation. The effect is spectacular and important in understanding the chemical properties of cation-exchanged montmorillonites.

The acidity of trivalent cation-exchanged montmorillonite. II. Desorption of mono- and di-substituted pyridines

AbstractTemperature programmed desorption (TPD) and IR spectroscopy were used to examine the desorption of pyridine, 2-methyl-, 4-methyl- and 2,6-dimethylpyridine from Al3+- and Cr3+-montmorillonite. Pyridine desorbed from Lewis sites at 150°C and from Bronsted sites at 340°C. 4-methylpyridine desorbed from Lewis and Bronsted centres at 210°C and 410°C respectively, some 60°C higher than pyridine due to its higher basicity. Conversely, the 2-methyl- and 2,6-dimethylpyridine, which are sterically hampered with respect to their coordination to Lewis centres, desorbed from these sites near 100°C, but due to their greater basicity desorbed from Bronsted sites at higher temperatures. These interpretations were confirmed by IR spectroscopy.

Acylation over cation-exchanged montmorillonite

The Friedel-Crafts acylation of aromatic compounds (benzene, toluene, xylene) with carboxylic acids (CH 3(CH 2) n COOH, n = 0–14) was performed over cation-exchanged montmorillonites (H +, Al 3+, Ni 2+, Zr 4+, Ce 3+, Cu 2+, La 3+). Yields in ketones were found to be dependent upon the nature of the interlayer cation and on the acid chain length.

The catalytic conversion ofn-pentanol to dialkylether by some cation-exchanged montmorillonite catalysts

The heterogeneous catalytic conversion ofn-pentanol to dialkylether was carried out using untreated cation-exchanged montmorillonites and using samples which had been preheated at 300°C in an atmosphere of air, hydrogen or nitrogen. The catalyst has been characterized by applying thermogravimetric analysis, X-ray diffraction and cation exchange capacity tests. Gas-chromatographic analysis of the products showed that the catalytic reactivity of the exchanged montmorillonite is related to the cation radius.

Review of the Diffusion of Water and Pyridinein the Interlayer Space of Montmorillonite: Relevance to Kinetics of Catalytic Reactions in Clays

AbstractWith 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.

ChemInform Abstract: SHEET SILICATES: BROAD SPECTRUM CATALYSTS FOR ORGANIC SYNTHESIS

Abstract Although montmorillonites have been found to have little catalytic activity in their natural Na+ form, various cation-exchanged montmorillonites have proved to be effective catalysts for a wide variety of organic reactions. Alkenes can be induced to add (a) water, (b) alcohols, (c) thiols and (d) carboxylic acids to furnish ethers, thioethers and esters in the presence of these cation-exchanged sheet silicates, but amines failed to undergo addition with alkenes under similar conditions. The number of products obtained in each reaction depended upon the ease of rearrangement of the carbocation intermediates. High yields were obtained in those cases where a single carbocation intermediate was involved. The cation-exchanged sheet silicates also catalysed a variety of elimination reactions. Water was eliminated from alcohols to produce ethers, ammonia was eliminated from amines to make secondary amines and hydrogen sulphide was eliminated from thiols to give dialkyl sulphides. Cation-exchanged bentonites were also effective catalysts in the production of dioxan from ethylene oxide and in the preparation of acetals with orthoformates. Analysis of the products from the reactions suggested that the cation-exchanged montmorillonites reacted, in nearly all cases, as acidic heterogeneous catalysts.

Sheet silicates: broad spectrum catalysts for organic synthesis

Although montmorillonites have been found to have little catalytic activity in their natural Na + form, various cation-exchanged montmorillonites have proved to be effective catalysts for a wide variety of organic reactions. Alkenes can be induced to add (a) water, (b) alcohols, (c) thiols and (d) carboxylic acids to furnish ethers, thioethers and esters in the presence of these cation-exchanged sheet silicates, but amines failed to undergo addition with alkenes under similar conditions. The number of products obtained in each reaction depended upon the ease of rearrangement of the carbocation intermediates. High yields were obtained in those cases where a single carbocation intermediate was involved. The cation-exchanged sheet silicates also catalysed a variety of elimination reactions. Water was eliminated from alcohols to produce ethers, ammonia was eliminated from amines to make secondary amines and hydrogen sulphide was eliminated from thiols to give dialkyl sulphides. Cation-exchanged bentonites were also effective catalysts in the production of dioxan from ethylene oxide and in the preparation of acetals with orthoformates. Analysis of the products from the reactions suggested that the cation-exchanged montmorillonites reacted, in nearly all cases, as acidic heterogeneous catalysts.

Catalyzed reactions of organic molecules at clay surfaces: Ester breakdown, dimerizations, and lactonizations

The use of montmorillonites as Brønsted acid catalysts has been investigated for a range of reactions: (i) decomposition of cyclohexyl esters, (ii) dimerization of propenylbenzenes, and (iii) the lactonization of cyclooctene-5-carboxylic acid. The ester cracking can be accomplished with a wide range of ion-exchanged clays, with conversions of up to 98% after 7 hr at 140 °C (Al 3+-montmorillonite). Although the cracking rate is dependent upon the interlayer cations in the clay, at least some of the activity is due to sites on the external surfaces of the clay particles. The dimerization of anethole (1-(4-methoxybenzene)-prop-1-ene) is efficient when using either di- or trivalent cation-exchanged montmorillonites, e.g., 44% recoverable yield of metanethole is attainable in 1 hr at 126 °C compared with literature procedures giving 24% yields in 7 hr. For a second propenylbenzene, isohomogenol (1-(3,4-dimethoxybenzene)-prop-1-ene), dimerization could only be effected using the very acidic trivalent ion-exchanged montmorillonites. Yields were typically 60% after 5 hr at 69 °C. It is not apparent why there are large differences in reactivity between anethole and isohomogenol, which are closely related structurally. Cation-exchanged montmorillonites can also catalyze the conversion of cyclooctene-5-carboxylic acid initially to 4-cyclooctane carbolactone and then to a variety of other lactone products. The rate of consumption of the acid is similar with a variety of ion-exchanged clays, but the subsequent rate of isomerization is cation dependent. For the lactonizations the clay acid catalysts proved no better than liquid phase catalysts in producing a high percentage of one particular lactone.

Selective chemical conversions using sheet silicate intercalates: Low-temperature addition of water to 1-alkenes

By refluxing hex-1-ene, hept-1-ene, or oct-1-ene in hexane solution with one of a range of cation-exchanged montmorillonites, the alkenes are converted to the corresponding bis-sec-alkyl ethers. The structures of the ethers may be demonstrated by a combination of gas-liquid chromatography and spectroscopy, but they cannot practicably be prepared by any other method. A number of cations facilitate conversion, the most efficient being Cu 2+, Fe 2+ and Fe 3+, Cr 3+, and Al 3+: Intercalation is a prerequisite for the reaction which involves transfer of oxygen from hydration shell water held in the interlamellar region to the alkene. Collapsed (strongly dehydrated) montmorillonites do not facilitate the conversion which, for the expanded silicates, is characterized by an optimal water content for a given cation. Thus for Cu 2+-exchanged bentonite the optimal metal-water ratio is 1:12 and under these circumstances 100% conversion of usable interlamellar water to ether is achieved. Use of other sheet structures, e.g., Cu(UO 2) 2(PO 4) 2 · 6H 2O, failed to convert the alkenes, while with Cu 2+-exchanged synthetic hectorites and fluorohectorites the reaction was not clean, the ether being only one of a number of products. It has not yet proved possible to make the reaction self-sustaining by constant addition of water.

Comparison of gas—solid chromatography properties of tris(ethylenediamine)chromium(III) cation-exchanged montmorillonite, hectorite and attapulgite

Comparison of gas—solid chromatography properties of tris(ethylenediamine)chromium(III) cation-exchanged montmorillonite, hectorite and attapulgite

ChemInform Abstract: CHEMICAL CONVERSIONS USING SHEET SILICATES‐ READY DIMERIZATION OF DIPHENYLETHYLENE

Cation-exchanged montmorillonites function as efficient catalysts for the production of 1-methyl-1,3,3-triphenylindan from 1,1-diphenylethylene at low temperature.

Azobenzene Intercalates of Montmorillonite

AbstractA study has been made of the interaction of azobenzene vapor with a series of cation-exchanged montmorillonites. Cu2+- and Ag+-clays give basal spacings ≥ 20Å. The azobenzene retains its trans conformation in the clay and can be extracted with ether. If the intercalate is heated above 120°C then there is catalytic decomposition leaving a black product. Infrared spectra of an extract from this product suggests that it might be made up of a mixture of amines. A photo-electron spectroscopic study shows that the nitrogen is in two distinct chemical environments both in the initial and in the blackened intercalates. The C:N ratio remains at 6:1 throughout.

Chemical conversions using sheet silicates: ready dimerization of diphenylethylene

Cation-exchanged montmorillonites function as efficient catalysts for the production of 1-methyl-1,3,3-triphenylindan from 1,1-diphenylethylene at low temperature.