Canadian Science Publishing

The adsorption of the cationic dye rhodamine 6G by montmorillonite (Wyoming bentonite) and laponite (synthetic hectorite) was studied by visible and fluorescent spectroscopy and by X-ray diffraction methods. Adsorption of the dye takes place by the mechanism of cation exchange. X-ray data indicate that the adsorbed cationic dye is located in the interlayer spaces of both minerals. It was found that adsorption prevents the dimerization of the dye, and gives rise to red shifts of the principal absorption band of the dye. A study of the effect of varying concentration of dye or clay on the location and intensity of this band proved to be useful in determining the adsorption capacity of the clay. The observed spectral changes are linked to surface polarity and to clay flocculation. At concentrated suspensions of montmorillonite, an additional weak absorption shoulder is obtained at 470–490 nm, which may be attributed to aggregated dye molecules, probably trapped within the cavities of book-house structured flocs. Due to steric hindrance rhodamine 6G does not give π interactions with the oxygen plane of the silicate layer. Therefore the adsorption of the dye by expanding clay minerals does not give rise to metachromasy. Fluorescence of the adsorbed dye is reported: it is red shifted and quenched relative to aqueous solutions. The use of fluorescence spectra to determine the saturation point is described, and aging and ultrasonic effects on spectral features are presented and discussed.

A simple method was explored for the preparation of methyl 4,6-O-benzylidene-hex-2-enopyranosides. Methyl 2,3-anhydro-4,6-O-benzylidene-D-hexopyranosides were converted to diaxial iodohydrins using sodium iodide in acetone which contained sodium acetate and acetic acid. Treatment of the iodohydrins with either methane- or p-toluenesulfonyl chloride in refluxing pyridine yielded the 2,3-unsaturated derivative in excellent yield. The four isomers for methyl 4,6-O-benzylidene-D-hex-2-enopyranoside were thus prepared. The rotations of the anomeric pairs followed Hudson's rules of isorotation. Evidence is provided that, in the absence of strong destabilizing interactions in the product, the epoxide ring of one of the above-mentioned 2,3-anhydroglycosides is opened by lithium iodide in ether to form the iodohydrin as the lithium alkoxide in high yield. This observation provides an explanation for the reduction of methyl 2,3-anhydro-4,6-O-benzylidene-α-D-allopyranoside to 4,6-O-benzylidene-D-allal. Reaction of methyl 4,6-O-benzylidene-2-deoxy-2-iodo-α-D-idopyranoside with methyl lithium provided 4,6-O-benzylidene-D-gulal. The conformational properties of a number of the compounds prepared and of acetylated methyl pentopyranosides, as derived from their nuclear magnetic resonance parameters, are discussed with particular reference to the role that geminal coupling constants may play in the determination of configuration and conformational equilibria.

The [3,3]-sigmatropic rearrangements of silyl ketene acetals obtained from aliphatic esters of furanoid and pyranoid glycals is described. The heterocyclic γ,δ-unsaturated carboxylic acids II are produced in good yields. A new preparation of furanoid and pyranoid glycals is described.

Dimethylsulfoxide is reduced by molecular hydrogen under mild conditions to dimethylsulfide and water in the presence of rhodium(III) complexes as catalysts. The kinetics of the systems using RhCl₃.3H₂O and cis-RhCl₃(Et₂S)₃ have been investigated, and a mechanism involving reduction of coordinated dimethylsulfoxide in a rhodium(III) hydride complex is postulated. The catalytic efficiency of the systems decreases slowly due to the production of inactive rhodium(I) species.

Kinetics of methane hydrate formation with different ratios of silica sand and clay and different water saturations were studied. At suitable temperature and methane gas pressure, water in the void spaces of silica sand packing and intercalated area of clay were converted into hydrate. It was observed that the rate of hydrate formation increases with higher void space in the packing, and addition of clay in test sediment decreases water to hydrate conversion as well as rate of hydrate formation. Maximum water to hydrate conversion of 60.0% was achieved in pure silica sand bed at 75% water saturation. Presence of fine clay particles is expected to reduce the void spaces and thus may hinder effective mass transfer of hydrate forming gases in the bed. However, it is also possible that the bentonite clay used in this work may actually inhibit hydrate growth. Additional experiments in stirred tank reactor were carried out to understand the inhibiting effect of bentonite clay for hydrate formation.

The title compounds, natural coumarins or their racemic modifications, were synthesized via malonic acid condensations with appropriate salicylaldehydes. Oxidation of 2,4-dihydroxy-5-(3-methyl-2 butenyl)benzaldehyde with DDQ, peracid, and acid–peracid gave the aldehydes for xanthyletin, marmesin, and decursinol, respectively. Some ¹⁴C-labelled coumarins were prepared similarly. The n.m.r. spectral data for the products are presented.

Cyclopropylbenzene was subjected to whole-cell fermentation with either Escherichia coli JM109 (pDTG601) or E. coli JM109 (pDTG602), expressing toluene dioxygenase and toluene dioxygenase – dihydrodiol dehydrogenase enzymes, respectively. The corresponding metabolites, 3-cyclopropylcyclohexa-3,5-diene-1,2-diol (3) and 3-cyclopropylbenzene-1,2-diol (5) have been isolated in yields of 2.5 and 1 g L^–1, respectively. The absolute stereochemistry correlation for 3 is provided, along with a preliminary discussion of its potential in asymmetric synthesis. Possible mechanistic implications are indicated for the enzymatic oxygenation through the use of calculations. Experimental data are provided for all new compounds.Key words: cyclopropylbenzene, bio-oxidation, cis-diene diol, catechol, JM109 (pDTG601), JM109 (pDTG602), dioxygenase.

New competition kinetic studies of electron reactions in HCl and HBr in the 10¹⁸ to 10²⁰ molecule cm⁻³ concentration region are reported and shown to support the findings of earlier investigations. The capture of thermal electrons by (HX)₂ dimers is examined from a kinetic and thermodynamic point of view. The (HX)₂⁻* intermediate previously proposed by several groups is considered to be involved in both systems. Differences in the magnitudes and concentration dependences of the rates can be explained, if reaction 5b is fast [Formula: see text] in[Formula: see text]HBr but relatively slow in [Formula: see text] where [6a] and [6b] are the major product-forming reactions. Thermochemical data show [5b] to be strongly favoured energetically in[Formula: see text]HBr, and close to thermoneutral in HCl. Reaction 6b is energetically favourable in HCl. The present data require an autoionisation life-time of ∼10⁻¹² s for (HX)₂⁻*. From other considerations that of HX⁻* is expected to be [Formula: see text] This means that formation of (HX)₂⁻* must take place by collisions of electrons with HX molecules which are in effect already interacting. Production of stabilised HX⁻ from (HX)₂⁻* does not appear to contribute in HCl, but[Formula: see text]may occur in other HX Systems. The general implications of the mechanism for electron capture in HF and HX mixtures with other polar vapours are mentioned.

It was discovered that olefinic double bonds are readily oxidized in an aqueous solution of periodate which contains only catalytic amounts of permanganate. The data suggest that in the effective pH range of 7 to 10 the permanganate is not reduced at once beyond the manganate state and that it is regenerated from this state by periodate action. Evidence was obtained that the main course of the oxidation of an olefin of type —CH=CH— involves first permanganate oxidation to hydroxyketones which are then rapidly cleaved by periodate to products which may subsequently be oxidized by the permanganate.

Thermal decomposition of 1.1–6.6 m aqueous perchloric acid at 295–322° yields oxygen, chlorine, and a small quantity of hydrochloric acid. The initial rates of decomposition have been measured, using a perchlorate ion activity electrode, and show 3.5 order dependence on the stoichiometric perchloric acid concentration; the corresponding rate coefficient and activation energy at 300.0° are 3.1 × 10^-7 m ^−2.5 s⁻¹ and 84 kcal mole⁻¹, respectively. The order of reaction with respect to time is less than 3.5 and depends upon the initial perchloric acid concentration; this effect is due to acceleration of the decomposition by the reaction products, notably chloride ion. It is suggested that the rate-determining step in the decomposition of aqueous perchloric acid is the reaction of two undissociated HClO₄ molecules to give H₂O, ClO₃, and ClO₄.