Barium carbonate, formation

All of these complexes decompose cleanly at low temperature to produce acetonitrile, carbon dioxide, and initially, the metal hydroxide (equation 45). The decomposition temperatures are 144,176, and 198 °C for Ba, Cu, and Y, respectively. In the case of copper and yttrium, the final product is the metal oxide produced by the dehydration of the hydroxide, while barium hydroxide recombines with carbon dioxide to yield the carbonate. Barium carbonate formation can be avoided, however, by use of a different ligand that avoids carbon dioxide formation. Benzoin a-oxime (Hbo) (13) has been found to be a quite suitable diprotic ligand for this purpose. The barium salt is easily prepared by reaction of the oxime with the metal dihydride (equation 46), and it decomposes cleanly to barium oxide by loss of benzaldehyde and benzonitrile at 250 °C (equation 47). 

Alkali moderation of supported precious metal catalysts reduces secondary amine formation and generation of ammonia (18). Ammonia in the reaction medium inhibits Rh, but not Ru precious metal catalyst. More secondary amine results from use of more polar protic solvents, CH OH > C2H5OH > Lithium hydroxide is the most effective alkah promoter (19), reducing secondary amine formation and hydrogenolysis. The general order of catalyst procUvity toward secondary amine formation is Pt > Pd Ru > Rh (20). Rhodium s catalyst support contribution to secondary amine formation decreases ia the order carbon > alumina > barium carbonate > barium sulfate > calcium carbonate. 

Barium carbonate prevents formation of scum and efflorescence in brick, tile, masonry cement, terra cotta, and sewer pipe by insolubilizing the soluble sulfates contained in many of the otherwise unsuitable clays. At the same time, it aids other deflocculants by precipitating calcium and magnesium as the carbonates. This reaction is relatively slow and normally requites several days to mature even when very fine powder is used. Consequentiy, often a barium carbonate emulsion in water is prepared with carbonic acid to further increase the solubiUty and speed the reaction. 

Barium sulfide solutions undergo slow oxidation in air, forming elemental sulfur and a family of oxidized sulfur species including the sulfite, thiosulfate, polythionates, and sulfate. The elemental sulfur is retained in the dissolved bquor in the form of polysulfide ions, which are responsible for the yellow color of most BaS solutions. Some of the mote highly oxidized sulfur species also enter the solution. Sulfur compound formation should be minimized to prevent the compounds made from BaS, such as barium carbonate, from becoming contaminated with sulfur. 

In humans, inhaled insoluble barium salts are retained in the lung (47,49). Inhalation of high concentrations of the fine dusts of barium sulfate can result in the formation of harmless nodular granules in the lungs, a condition called baritosis (49). Baritosis produces no specific symptoms and no changes in pulmonary function. The nodulates disappear upon cessation of exposure to the barium salt. However, it is possible that barium sulfate may produce benign pneumoconiosis because, unlike barium carbonate, barium sulfate is poorly absorbed (21). 

Palladium catalysts have been prepared by fusion of palladium chloride in sodium nitrate to give palladium oxide by reduction of palladium salts by alkaline formaldehyde or sodium formate, by hydrazine and by the reduction of palladium salts with hydrogen.The metal has been prepared in the form of palladium black, and in colloidal form in water containing a protective material, as well as upon supports. The supports commonly used are asbestos, barium carbonate, ... 

In a study on the influence of supports on rhodium, the amount of dicyclohexylamine was found to decrease in the order carbon > barium carbonate > alumina > barium sulfate > calcium carbonate. Plain carbon added to rhodium-on-alumina-catalyzed reactions was found to cause an increase in the amount of dicyclohexylamine, suggesting that carbon catalyzes the formation of the intermediate addition product (59). 

Current views (100) on the mechanism of bromination by NBS invoke the formation of molecular bromine and bromine atoms in low concentration, which subsequently act as the brominating agent. The bromination reaction was studied in detail in this laboratory under a variety of conditions using 93 (R = Ms) as a model. The product 94 (R = Ms) was indeed formed (42%) when NBS was substituted by 1.1 equivalents of bromine which was added at a slow rate to the reaction mixture. The yield was 68% when benzoyl peroxide was used as a catalyst. Using NBS alone or in the presence of reagents such as barium carbonate, pyridine, or s-trinitrobenzene, the yield was 60-70%. 

By hydrolysis under very mild alkaline conditions (with a boiling suspension of barium carbonate), ribonucleic acids have been shown to yield small quantities of cyclic phosphates as well as the normal nucleotides.96 These materials were identical electrophoretically with synthetic cyclic phosphates and were readily hydrolyzed to mixtures of 2- and 3-phosphates. Their formation in this way constitutes strong support for Brown and Todd s theory. The precise way in which the alkaline hydrolysis of the polynucleotide occurs has been studied using isotopically labeled water, and the results are in agreement202 with the scheme outlined above. 

Steier, H.P. Requema, J. Moya, J.S. (1999) Transmission electron microscopy study of barium hexaferrite formation from barium carbonate and hematite. J. Mat. Res. 14 3647-3652... 

In another study,125 methyl 5-0-benzoyl-2,3-dideoxy-/8 D-g(t/cero-pent-2-enofuranoside (81) was treated with bromine in methanol in the presence of silver acetate and barium carbonate the two monobenzoates (shown as 84) of methyl 2-bromo-2-deoxy-j8-D-xylofurano-side were obtained. A rationalization for this reaction involves formation of an intermediate bromonium ion (82), produced by attack of Br on the less-hindered side of the double bond, which then undergoes trans-attack by the benzoate group at C-5 to give the benzoxonium intermediate (83) the monobenzoates (84) are obtained on processing of the reaction mixture with water. 

E. W. Hilgard verified the conclusion and suggested the reaction as an explanation of the formation of natural soda but G. Lunge showed that dil. soln. are required, and on evaporation, the reaction is reversed. H. Taylor (1851) used barium bicarbonate under similar conditions and R. von Wagner showed that a clear soln. of barium bicarbonate decomposes sodium sulphate, forming barium sulphate and sodium bicarbonate, and that a comparatively small proportion of the bicarbonate will complete the reaction between barium carbonate and sodium sulphate. 

Fithium tetrahydroaluminate, Fluoroamides, 0075 Lithium tetrahydroaluminate, Water, 0075 Lithium, 1,2-Diaminoethane, Tetralin, 4675 Magnesium, Barium carbonate, Water, 4685 Maleic anhydride, Bases, or Cations, 1400 Mercaptoacetonitrile, 0763 t Methanol, Hydrogen, Raney nickel catalyst, 0482 4-Methoxy-3-nitrobenzoyl chloride, 2911 Methoxyacetyl chloride, 1161 t Methyl formate, Methanol, Sodium methoxide, 0830 3-Methyl-2-penten-4-yn-l-ol, 2378 Nitric acid, 4430... 

An efficient procedure for the formation of primary bromides is the reaction of 4,6-O-benzylidene hexopyranosides with A-bromosuccinimide (NBS) in the presence of barium carbonate. This reaction leads to the corresponding 4-0-benzoyl-6-bromide-6-deoxy-glycoside (Scheme 3.4a).17 Probably, the reaction proceeds by the radical bromination of the benzylic carbon atom followed by rearrangement to the 6-deoxy-6-bromo derivative. The application of this method is very efficient since the benzylidene functionality can act as a protecting group but can be oxidatively cleaved to give a 6-deoxy-6-bromo derivative. 

The barium carbonate is insoluble. Double substitution reactions occur with the formation of an insoluble substance or a covalent substance. Because barium carbonate is not covalent, it must be insoluble. 

Although the superoxide ion was also successful in destroying some aliphatic and aromatic halogenated hydrocarbons, resulting in the formation of barium carbonate, soluble halides, and water, it was unsuccessful in destroying nitroaromatic compounds, or aliphatic compounds having an amine or a nitrile group attached to them... 

Positive proof is given that thermal ions or chemi-ions accelerate the nucleation process of carbon formation. On the other hand, metals which easily produce hydroxides can inhibit carbon formation, and of these, barium is the most eflBcient. Transition metals such as manganese do not seem to play a role either in the formation phase of small soot particles or in their oxidation phase. We suggest that in industrial combustion devices, their intervention occurs in the agglomeration phase from involatile oxides formed in poor combustible zones. These oxides produce positively charged solid particles which can transfer their charges to the small soot particles, and consequently they prevent the agglomeration process. 

The first examples reported by Sandmeyer date back to 1884. The many various preparative procedures differ mainly in the type and the preparation of the copper-cyanide complex which is used. In the Gattermann procedure KCN in the presence of Cu powder is used. Generally one tries to avoid the formation of HCN on the addition of alkali metal cyanide to the acidic medium by neutralizing the diazo-nium salt solution in advance with sodium or barium carbonate. Cyanogen, which is formed from CN ions on treatment with Cu" salts, is also a harmful by-product. In this case the addition of sodium hydrogen sulfite (equation 19) proved to be of great value. 

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