Reduction Of Carbonates Research Articles

Diastereoselective Palladium‐Catalyzed Formate Reduction of Allylic Carbonates as a New Entry into Propionate Units.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Use of malachite green as photocatalyst in reduction of sodium and potassium carbonates

The photoreduction of aqueous sodium and potassium carbonates has been performed in the presence of a malachite green (MG) solution (which is a photocatalyst also). The photocatalytic formation of formic acid and formaldehyde were measured spectrophotometrically using Nash reagent. The effects of variations of various parameters, like pH, amount of photocatalyst (MG concentration), concentration of Na 2CO 3 and K 2CO 3, light intensity etc., on the yield of photoproducts were also investigated. A tentative mechanism for this reduction has been proposed.

Diastereoselective palladium-catalyzed formate reduction of allylic carbonates as a new entry into propionate units.

[reaction: see text] The diastereoselective palladium-catalyzed formate reduction of allylic carbonates is described. Reduction of allylic carbonates under mild conditions (Pd(OAc)(2) (2.5-5 mol %), [n-Bu(3)PH]BF(4) (2.5-5 mol %), HCO(2)H/Et(3)N (1:2) (3 equiv), CH(3)CN (0.05M), 40 degrees C) affords the terminal olefin as the syn isomer in good yields and modest to excellent diastereoselectivity. These compounds, which are useful building blocks for the synthesis of polypropionate units, are the synthetic equivalent of the products obtained from an aldol reaction of an alpha-methyl-beta,gamma-unsaturated aldehyde.

Electrochemical and Infrared Studies of the Reduction of Organic Carbonates

The reduction potentials of five organic carbonates commonly employed in lithium battery electrolytes, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and vinylene carbonate (VC) were determined by cyclic voltammetry using inert (Au or glassy carbon) electrodes in tetrahydrofuran/ supporting electrolyte. The reduction potentials for all five organic carbonates were above 1 V (vs. PC reduction was observed to have a significant kinetic hindrance. The measured reduction potentials for EC, DEC, and PC were consistent with thermodynamic values calculated using density functional theory (DFT) assuming one-electron reduction to the radical anion. The experimental values for VC and DMC were, however, much more positive than the calculated values, which we attribute to different reaction pathways. The role of VC as an additive in a PC-based electrolyte was investigated using conventional constant-current cycling combined with ex situ infrared spectroscopy and in situ atomic force microscopy (AFM). We confirmed stable cycling of a commercial li-ion battery carbon anode in a PC-based electrolyte with 5 mol % VC added. The preferential reduction of VC and the solid electrolyte interphase layer formation therefrom appears to inhibit PC cointercalation and subsequent graphite exfoliation. © 2001 The Electrochemical Society. All rights reserved.

Diamonds from the asthenosphere and the transition zone

Over the last two decades inclusions in diamonds have been recognised from a number of mines which represent chemically pristine samples of the sublithospheric mantle. X-ray diffraction studies show that isochemical phase transitions occurring in the plastic deformation field of diamond have completely eliminated crystal structures which are stable at transition zone and lower mantle pressures only. In the case of lower mantle inclusions ultra-deep parageneses may nevertheless be readily recognised by their unique chemical composition. For the chemically much less distinct asthenospheric and transition zone parageneses, majorite garnet is the only reliable indicator. From the majorite garnet record, the deeper upper mantle and transition zone appear to be dominated by basaltic material. Apart from elevated Si contents, the major element composition of majorite garnets is not significantly different from lithospheric eclogitic garnets, although there is a bias to higher Na and Ti and lower Fe contents. Coexisting clinopyroxene completely falls within the compositional ranges of the normal eclogitic suite. Trace element studies indicate that the majoritic source rocks have REEN patterns which range from MORB type to strongly LREE enriched. As petrological data are not consistent with a basaltic asthenosphere and transition zone, deep diamonds may represent either an exceptional sampling bias or, more likely, preferential diamond formation in eclogitic environments. This may be due to the pyrolitic parts of the transition zone being too reducing for diamond formation. It is speculated that sublithospheric eclogitic diamonds originated in subducted oceanic crust, which is relatively oxidised compared to pyrolite mantle due to sea water alteration. In such a scenario diamonds may originate either from redox reactions involving reduced mantle fluids and slab material or from reduction of carbonates which occurs invariably with increasing depth as pressure promotes the formation of ferrous iron rich minerals and therefore decreasing f O2. The latter process may explain the isotopically heavy composition (δ13C up to +0.9%) of some asthenospheric and transition zone diamonds. Isotopically light diamonds (δ13C down to −24.4 %) are probably related to chemical fractionation processes since subducted organic matter which is frequently invoked to cause such signatures should convert to diamond at much shallower depth.

Photocatalytic reduction of carbonates and formation of some energy rich systems in the presence of Toluidine Blue

Photocatalytic reduction of carbonates and formation of some energy rich systems in the presence of Toluidine Blue

Photocatalytic reduction of carbonates and formation of some energy rich systems in the presence of Toluidine Blue

Aqueous sodium and potassium carbonates have been photoreduced in the presence of Toluidine Blue solution (which is also the photocatalyst). The photocatalytic formation of formic acid and formaldehyde was measured spectrophotometrically using Nash reagent. The effect of variation of various parameters like pH, amount of photocatalyst (Toluidine Blue concentration), concentration of Na2CO3 and K2CO3, light intensity, etc., on the yield of photoproducts was also investigated. A tentative mechanism for this reduction has been proposed. Copyright © 2001 John Wiley & Sons, Ltd.

99/02814 Photocatalytic reduction of some alkali carbonates in the presence of methylene blue

99/02814 Photocatalytic reduction of some alkali carbonates in the presence of methylene blue

Photocatalytic reduction of some alkali carbonates in the presence of methylene blue

The photoreduction of aqueous sodium and potassium carbonates has been carried out in the presence of methylene blue solution (which is a photocatalyst also). The photocatalytic formation of formic acid and formaldehyde were measured spectrophotometrically using Nash reagent. The effect of variation of various parameters like pH, amount of photocatalyst (methylene blue concentration), concentration of Na2CO3 and K2CO3, light intensity, etc. on the yield of photoproducts was also investigated. A tentative mechanism for this reduction has been proposed. Copyright © 1999 John Wiley & Sons, Ltd.

Palladium-Catalyzed asymmetric reduction of allylic esters with a new chiral monodentate ligand, 8-diphenylphosphino-8′-methoxy-1,1′-binaphthyl

A new chiral monodentate ligand, 8-diphenylphosphino-8′-methoxy-1,1′-binaphthyl (8-MeO-MOP), was used for palladium-catalyzed reduction of allylic carbonates with formic acid. Various methylcarbonates of 3,3′-disubstituted allylic alcohols were converted to the corresponding optically active 1-olefins with this ligand.

Assessment of the Activity of 8-Diphenylphosphino-8'-methoxy-1,1'- binaphthyl as a Ligand for Palladium-Catalyzed Reactions.

A monodentate phosphine, 8-diphenylphosphino-8'-methoxy-1, 1'-binaphthyl, was shown to be active as a ligand in palladium-catalyzed reactions, including the reduction of allylic carbonates with formic acid, hydrosilylation of a terminal olefin, and hydroboration of but-1-en-3-yne, even though it has a highly hindered lone pair.

ChemInform Abstract: Optically Active Allylsilanes. Part 19. Asymmetric Synthesis of Allylsilanes by Palladium‐Catalyzed Asymmetric Reduction of Allylic Carbonates with Formic Acid.

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Asymmetric synthesis of allylsilanes by palladium-catalyzed asymmetric reduction of allylic carbonates with formic acid

Reduction of 3-alkyl-3-trialkylsilyl-2-propenyl methyl carbonates with formic acid and 1,8-bis(dimethylamino)naphthalene in the presence of a palladium catalyst (3 mol %) coordinated with ( R)-3-diphenylphosphino-3′-methoxy-4,4′-biphenanthryl (MOP-phen) gave optically active allylsilanes (3-alkyl-3-trialkylsilyl-1-propenes) of up to 91 % ee.

Surface reactions of adhesives on dentin

The purpose of this study was to characterized changes in the surface chemistry of dentin following various adhesive treatments. The coronal parts of sound freshly extracted third molars were cross-sectioned over the pulp chambers, each producing a pair of dentin samples which were polished to 600 grit and cleaned with 3% H 2O 2. The first sample of each pair was used as a control, while the second one was subjected to one of the following adhesive treatments: (a) Gluma Cleanser, (b) Tenure Conditioner, (c) Scotchprep, (d) Gluma Cleanser/ Gluma Primer, (e) Tenure Conditioner/ Tenure Solution A&B, or (f) Scotchprep/ Scotchbond 2 Adhesive. The treated samples paired with their respective controls were studied by small-area ESCA spectroscopy. Three areas of 1.0 mm in diameter randomly chosen on each sample were analyzed by survey and C1s, O1s, N1s high-resolution spectra. The samples from groups d, e, and f were additionally subjected to argon-ion-depth profilling of the uppermost 2-nm layer at 0.5-nm intervals. According to the results, treatment modes a, b, and c caused the reduction of carbonates and increased the -NH/NH 2 ratio. Treatments a and c increased the alcohol groups, while treatments b and c increased the carbonyl and ether groups. All these changes were in comparison to the reference dentin specimens. Dentin treatment with d, e, and f induced a complex in depth distribution of the C, N, O binding states. The energy shifts detected do not indicate primary bonding of the tested adhesives to the dental substrate.

Significance of the reduction of alkali carbonates in catalytic carbon gasification

The catalytic effect of alkali carbonates on carbon gasification depends not only on the initial catalyst loading but also on how these carbonates are reduced to surface complexes during the initial heating of the samples. This effect is primarily due to three important processes which take place simultaneously during the initial heat treatment: 1, catalyst re-distribution on the surface; 2, catalyst loss by vaporization; and 3, change in the substrate surface area due to carbon conversion.

Stable Isotope Geochemistry of the Beishan Stratabound Sphalerite‐Pyrite Deposit, Guangxi

AbstractBased on lead isotope data, it has been shown that lead in the Beishan stratabound sphalerite‐pyrite deposit came mainly from the oldland and its underlying basement rocks and, subordinately, the Devonian itself or the sea water at that time. As to its primary source, upper crust lead was predominant, while lower crust lead or upper mantle lead was subordinate. Sulfur was formed mainly through bacterial reduction of marine carbonates. The carbon and oxygen isotopic analyses for carbonate rocks and minerals have demonstrated that carbonate rocks in the Beishan area are normal marine sediments. The isotopic characteristics of the carbonate rocks are intermediate between those of the northern Guangdong and central Hunan, but closer to those of the central Hunan basin. The formation of the Beishan deposit underwent: a depositional‐diagenetic mineralization stage and a successive post‐diagenetic enrichment‐remoulding one.