A. Sinnema

New acid catalyst comprising heteropoly acid on a mesoporous molecular sieve MCM-41

New solid acid catalysts, consisting of heteropoly acid (HPA) H3PW12O40 (PW) supported on a mesoporous pure-silica molecular sieve MCM-41, have been prepared and characterized by nitrogen physisorption, X-ray diffraction, FT-IR, and31P magic angle spinning NMR. The PW/MCM-41 compositions with PW loadings from 10 to 50 wt% have ∼ 30 Å uniformly-sized mesopores. HPA retains the Keggin structure on the MCM-41 surface and forms finely dispersed HPA species. No HPA crystal phase is developed even at HPA loadings as high as 50 wt%. PW/MCM-41 exhibits higher catalytic activity than H2SO4 or bulk PW in liquid-phase alkylation of 4-t-butylphenol (TBP) by isobutene and styrene. In the alkylation of TBP by styrene, PW/MCM-41 shows a size selectivity compared to bulk PW and PW/SiO2, providing higher yields of a 2-(1-phenylethyl)-4-t-butylphenol, at the expense of the more bulky 2,6-bis-(1-phenylethyl)-4-t-butylphenol. The PW/MCM-41 compositions, having strong acid sites and a regular mesoporous system, are promising catalysts for the acid-type conversion and formation of organic compounds of large molecular size.

Study of catalysts comprising heteropoly acid H3PW12O40 supported on MCM-41 molecular sieve and amorphous silica

With the aim of obtaining pure Keggin-type heteropoly acid (HPA) species on siliceous surfaces, the preparation of HPA catalysts, comprising of 10 to 50 wt.% H3PW12O40 (PW) supported on an amorphous silica or a mesoporous all-silica molecular sieve MCM-41, was studied. The state of HPA on the siliceous surface was characterized by 31P NMR, XRD and TEM. Impregnating MCM-41 or amorphous SiO2 with an aqueous solution of PW gave catalysts with, in general, two HPA species: one with intact Keggin structure (A) and the other with a different structure (B), supposedly, H6P2W18O62 (P2W18) and/or H6P2W21O71 (P2W21). The relative amount of species A and B depends on HPA loading, with A dominating. At higher loadings, 30–50 wt.%, A is practically the only one present on the surface; at lower loadings, both species exist, the amount of B increasing as the HPA loading decreases. In contrast, catalysts prepared by impregnation with a methanol solution of HPA contained exclusively Keggin-type A over the whole range of PW loading. In the PWMCM-41 catalysts, as shown by TEM, the PW species are mainly located inside the MCM-41 pores. The B species was about 8 times as active as A in the liquid-phase trans-de-t-butylation of 2,6-di-t-butyl-4-methylphenol.

17O NMR determination of proton sites in solid heteropoly acid H3PW12O40.31P,29Si and17O NMR, FT-IR and XRD study of H3PW12O40 and H4SiW12O40 supported on carbon

Abstract17O MAS NMR spectra for solid heteropoly acid (HPA) H3PW12O40 are reported. Comparison of solid-state and solution17O resonances shows that in the solid dehydrated H3PW12O40 terminal W=O oxygen atoms are the predominant protonation sites. H3PW12O40 and H4SiW12O40 supported on chemically activated carbon have been studied by means of NMR, FT-IR and XRD. The carbon-supported HPAs retain their Keggin structure and form finely dispersed HPA species. No HPA crystal phase is developed even at an HPA loading as high as 45 wt%.31P,29Si and17O MAS NMR spectra for bulk and carbon-supported HPAs indicate interaction of the HPA Keggin units with the carbon surface, causing large line broadening in the NMR spectra.

Proton sites in Keggin heteropoly acids from17O NMR

The structure of the bulk proton sites in dehydrated solid Keggin-type heteropoly acids (HPA) H3PW12O40 and H4SiW12O40 was determined by17O NMR. The terminal W=O oxygen atoms in Keggin heteropolyanions were found to be the predominant protonation sites. The protonation of HP As in solution is also discussed on the basis of17O NMR data.

Hydration and acetoxylation of dihydromyrcene catalyzed by heteropoly acid

The liquid-phase hydration and acetoxylation of the monoterpene dihydromyrcene (DHM, 3,7-dimethyl-1,6-octadiene) are efficiently catalyzed by Keggin-type heteropoly acid H3PW12O40 (HPA) at 14–30°C to yield dihydromyrcenol (DHMOH, 2,6-dimethyl-7-octen-2-ol) and dihydromyrcenyl acetate (DHMOAc). Homogeneous, biphasic (DHMAcOH-H2O-HPA) and heterogeneous (with HPASiO2 catalyst) reactions have been studied. HPA has a much higher catalytic activity than conventional acid catalysts such as H2SO4 and Amberlyst-15. A synthetically useful biphasic acetoxylation/hydration of DHM has been developed. The method provides a 90% selectivity to the sum of DHMOH and DHMOAc at 21% DHM conversion and allows for easy and clean catalyst recycling without loss of activity.

Synthesis and proton magnetic resonance studies of some 1,2-dialkyl-1,2-bis(2,6-dimethyl-phenyl)ethanes

Abstract Compounds of the type R1R2CH-CHR2R1, in which R1 is 2,6-dimethylphenyl and R2 is hydrogen, methyl, or t-butyl, were synthesized and the meso and racemic isomers separated. A study of these compounds by PMR spectroscopy, including 13C-satellites and the effects of temperature variation, yielded information about the configurations, the preferential conformations, and the barriers to rotations about the R1CH bonds.

Chemistry of neopentyl derivatives—II : Restricted rotation in 2,6-disubstituted neopentylbenzenes

Abstract A series of neopentylbenzene derivatives with substituents in 2- and 6-positions has been synthesized. A number of compounds were investigated by dynamic NMR spectroscopy. Restricted rotation was observed in 3-methyl-2-neopentylbenzoic acid and its derivatives. Thermodynamic and Arrhenius parameters were obtained for the restricted rotation of the neopentyl group. An additional Me group in 3-position causes a COOMe group in 2-position to rotate out of the plane of the aromatic ring, and this change is effective in reducing the barrier to rotation of the neopentyl group by about 1 kcal mole−1.

Reactions of hydroxyglycines. New synthetic routes to 4-phenylquinazoline derivatives

Abstract Reaction of hydroxyglycine with 2-aminobenzophenones gives 1,2-dihydro-4-phenyl-quinazoline-2-carboxylic acids in high yields and under mild conditions. These can be smoothly converted into the corresponding 3,4-dihydro isomers and into quinazoline derivatives via rearrangement and oxidation by air, respectively. The X-ray crystallographic structure of 6-chloro-1,2-dihydro-1-methyl-4-phenylquinazoline-2-carboxylic acid shows the carboxylate group at C(2) and the methyl group at N(1) to be in axial positions.

Thermally induced skeletal inversion and ring opening of hexamethylbicyclo[2.2.0]hexanes☆

Abstract Hexamethylbicyclo[2.2.0]hexanes underwent endo,exo isomerization (skeletal inversion) and stereoselective supra, antara cleavage at 140–250°. The kinetics were studied and the products isolated and identified. The reactions are discussed in terms of a common 1,4-π-bonded intermediate which evolves to the invertomer or opens conrotatorially to methyl-substituted hexadienes.

17O MAS NMR study of 12-molybdophosphoric acid

Abstract17O MAS NMR spectra for17O enriched solid heteropoly acid H3PMo12O40 are reported. The oxygen exchange between solid H3PMo1217O40 and H216O vapor at 200–250°C is shown to be accompanied by fast mixing of terminal Mo=O and bridging Mo-O-Mo oxygens in the Keggin unit. The oxygen exchange in H3PMo1217O40 is much faster than in H3PW1217O40 in solution as well as in the gas phase.