The kinetics of formation of the silicate cubic octamer, Q(3)(8), in aqueous tetramethylammonium (TMA) silicate solutions was investigated by (29)Si NMR. The rate equation for solutions at pH 13.2-13.6 is d[Q(3)(8)]/dt = k(f) [H(+)](1.6)(+/-)(0.1)[TMA(+)](0.36)(+/-)(0.08)[Si](0.8)(+/-)(0.3) where k(f) = (2.2 +/- 0.8) x 10(16) mol(-)(1.8) kg(1.8) s(-)(1) at 296 K. The findings prove unequivocally that alkylammonium cations participate directly in the formation and subsequent stabilization of cagelike polysilicate anions. This implies a radically different mechanistic role than "templating" for alkylammonium cations in the synthesis of molecular sieves.

The addition of tetraalkylammonium cations to aqueous silicate solutions enhances the abundance of symmetric, cagelike, polysilicate anions including the cubic octamer, Si(8)O(20)(8)(-). The equilibrium ratio of tetramethylammonium (TMA) cations to the octameric silicate anion is 8:1 for solutions with a concentration ratio [OH(-)]:[Si] >/= 1:1. Evidence indicates that organocations directly associate with cagelike polyanions to form a protective shell of hydrophobic hydration that impedes hydrolysis of the central anion.

The adsorption of Athabasca and Cold Lake C 7 -asphaltenes on stainless steel (304L), iron, and aluminum powders was measured using UV-vis spectrophotometry. The effects of resins, temperature, and n-heptane-to-toluene ratio were also investigated. In all cases, Langmuir (type I) isotherms were observed, indicating that asphaltenes saturated the available surface area for adsorption. The saturation adsorptions of the asphaltenes on metals (0.25-2.7 mg/m 2 ) were of the same order of magnitude as adsorption of asphaltenes on minerals. The saturation adsorptions were less than the monolayer surface coverage observed on water-in-hydrocarbon emulsion interfaces, indicating that there are a limited number of adsorption sites on the metals. Higher molar saturation adsorptions were observed for resins and low molar mass asphaltenes, suggesting that adsorption was limited by the morphology of the metal surface. In general, higher mass saturation adsorptions were observed when asphaltenes self-associated to greater extents and consequently larger molecules adsorbed on the surface.

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Dimethoxycarbene (la) and methoxy(2,2,2-trifluoroethoxy)-carbene (lb) were generated in benzene solution by thermolysis of the corresponding 2,2-dialkoxyoxadiazolines 7. The carbenes were trapped by intermolecular reaction with a variety of cyclic anhydrides 8. The products 9 are formally the result of carbene insertion into the bond between the carbonyl carbon and the ring oxygen atoms. The results of a competition between dimethylmaleic and dichloromaleic anhydrides for dimethoxycarbene suggests that this reaction proceeds by nucleophilic attack of dialkoxycarbene onto the carbony1 carbon atom of the anhydride.Dioxycarbenes have become a focus of interest for both physical organic and theoreticalThe oxy substituents strongly influence the physical properties of the carbene, giving it a strikingly low reactivity and high nucle~philicity['-~l. The geometry of the transition states calculated for cyclopropanation of dihydroxycarbene with substituted alkenes reflects this nucleophilicity. For instance, bond formation to the P-carbon of acrolein precedes bond formation to the a -~a r b o n [~~] .The high stabilization energy (83 kcal/m01)~~"1 for the singlet state of dihydroxycarbene relative to the singlet state of methylene accounts for the low reactivity of dioxycarbenes. This contrasts with the comparatively omnivorous reactivity and electrophilicity of more conventional carbenes.It has become evident that singlet dioxycarbenes have a tendency to react according to stepwise ionic mechanisms. This is contrary to the general notion that singlet carbenes undergo concerted reactions. In their studies, Hoffmann and co-workers have found a variety of reactions of dimethoxycarbene which are governed by nucleophilic attack of the carbene onto a For instance, H~ffmannL~~] performed a detailed study of the addition of dimethoxycarbene (la) to phenyl isocyanate and postulated the zwitterion 2 as an intermediate in the reaction. This intermediate results from nucleophilic attack of dimethoxycarbene onto the carbon of the isocyanate group (Scheme 1). The zwitterion 2 adds to a second molecule of isocyanate to yield the observed product 3 with excellent regioselectivity.Seitz and co-worker~[~] have also performed additions of dimethoxycarbene onto tetrazine substrates and have found evidence of step-wise chemistry. Tetrazine 4 is thought to intercept dimethoxycarbene (la, Scheme 2) to yield a zwitterion 5 which closes to yield 6, the product of overall 1,4-addition.The convenience of 2,2-dioxyoxadiazolines 7 as thermal precursors of dioxycarbenes[61 provides the opportunity to investigate some new chemistry of these interesting reactive intermediates. While some of the chemistry of dimethoxy~a r b e n e [~*~-~] and methoxy(2,2,2-trifluoroethoxy)carbene~7~ has been investigated, anhydrides have never been used as dialkoxycarbene traps. We now report on the reaction of two dialkoxycarbenes with a series of cyclic anhydrides 8 to afford the novel products of ring expansion 9. Results and Discussion Dimethoxycarbene (la) and met...