Titanium chemical equivalents

English chemist and physicist Discoverer of palladium and rhodium Inventor of a process for making platinum malleable. Famous for his researches on force of percussion, gout, diabetes, columbium (niobium), tantalum, and titanium, and his scale of chemical equivalents. 

Dr. Wollaston was a man of very broad interests, as a list of his publications will show. His papers were on such diverse subjects as force of percussion, fairy rings, gout, diabetes, seasickness, metallic titanium, the identity of columbium (niobium) and tantalum, a reflection goniometer, micrometers, barometers, a scale of chemical equivalents, and the finite extent of the atmosphere. He died in London on December 22,1828 (13). 

Chemical equivalents. In practice, empirical parameters, called the aluminum, oxygen, and molybdenum equivalents, are utilized to assess the type and quantity of phases that are formed during processing. These chemical equivalents for titanium alloys are defined as follows ... 

An important use in flexible PVC is in roofing. Such compounds typically are formulated either with titanium dioxide or fine-particle carbon black (e.g., ASTM grade N110) for UV light absorption. Performance fife is improved by addition of 0.3-0.5 phr of a polymeric HALS such as listed above. Clear flexible sheet, as in pond or swimming pool liners, should use a combination of 0.2-0.3 phr each of a benzotriazole and a polymeric HALS. In FDA applications, use is again restricted to a maximum of 0.25 phr of Tinuvin P or chemical equivalent. Note that suppliers literature should be checked for new approvals. 

Chemical deoxygenation of sulfoxides to sulfides was carried out by refluxing in aqueous-alcoholic solutions with stannous chloride (yields 62-93%) [186 Procedure 36, p. 214), with titanium trichloride (yields 68-91%) [203], by treatment at room temperature with molybdenum trichloride (prepared by reduction of molybdenyl chloride M0OCI3 with zinc dust in tetrahydrofuran) (yields 78-91%) [216], by heating with vanadium dichloride in aqueous tetrahydrofuran at 100° (yields 74-88%) [216], and by refluxing in aqueous methanol with chromium dichloride (yield 24%) [190], A very impressive method is the conversion of dialkyl and diaryl sulfoxides to sulfides by treatment in acetone solutions for a few minutes with 2.4 equivalents of sodium iodide and 1.2-2.6 equivalents of trifluoroacetic anhydride (isolated yields 90-98%) [655]. 

Asymmetric epoxidation of ailylic alcohols.1 Epoxidation of allylic alcohols with r-bulyl hydroperoxide in the presence of titanium(lV) isopropoxide as the metal catalyst and either diethyl D- or diethyl L-tartrate as the chiral ligand proceeds in > 90% stereoselectivity, which is independent of the substitution pattern of the allylic alcohol but dependent on the chirality of the tartrate. Suggested standard conditions are 2 equivalents of anhydrous r-butyl hydroperoxide with 1 equivalent each of the alcohol, the tartrate, and the titanium catalyst. Lesser amounts of the last two components can be used for epoxidation of reactive allylic alcohols, but it is important to use equivalent amounts of these two components. Chemical yields are in the range of 70-85%. 

Uemura et al. [49] found that (R)-1,1 -binaphthol could replace (7 ,7 )-diethyl tartrate in the water-modified catalyst, giving good results (up to 73% ee) in the oxidation of methyl p-tolyl sulfoxide with f-BuOOH (at -20°C in toluene). The chemical yield was close to 90% with the use of a catalytic amount (10 mol %) of the titanium complex (Ti(0-i-Pr)4/(/ )-binaphthol/H20 = 1 2 20). They studied the effect of added water and found that high enantioselectivity was obtained when using 0.5-3.0 equivalents of water with respect to the sulfide. In the absence of water, enantioselectivity was very low. The beneficial effect of water is clearly established here, but the amount of water needed is much higher than that in the case of the catalyst with diethyl tartrate. They assumed that a mononuclear titanium complex with two binaphthol ligands was involved, in which water affects the structure of the titanium complex and its rate of formation. 

Asymmetric conjugate addition of thiols to chiral -substituted 7V-enoylsultams 19, catalyzed by 1.5 equivalents of titanium(IV) chloride, affords the adducts 20 in good chemical yields and variable diastereoselectivities 3S. 

Table 1 lists the support used in the present study. TIO is a Reference Catalyst of the Catalysis Society of Japan (JRC-TIO-4, equivalent to P-25) [9]. ST (supplied from Catalysts and Chemicals Ind. Co., Ltd.) was prepared by the coprecipitation method. GT and XG were prepared by the thermal reaction of titanium tetraisopropoxide and tetraethylorfriosilicate in glycols (glycothermal reaction) [7]. HT was prepared by the hydrolysis of titanium alkoxide in toluene with water that was dissolved from gas phase at high temperature [8]. 

The PCHE was chosen because space constraints were critical (see Figure 9.2) and the above ground location favoured the 1 tonne PCHE rather than the 20 tonne equivalent shell and tube exchanger. Prior to installation, a series of trials on the prevention of biofouling in narrow channel heat exchangers carried out at another BP Amoco terminal showed that control by chemical injection was acceptable in the titanium PCHE (Anon, 1998 Reay, 1999). 

The chemical processes occurring in the cell are equivalent to those for the pure electrolytic case as described by Van Tamelen et al. Titanium (IV) isopropoxide is first reduced to a state wherein molecular N2 can be bound this is evidenced by the development of an intense blue-black color which is attributed to a Ti(II) com-... 

The relative ease with which hydrogen chemisorbs on the surface of a metal oxide surface mainly depends on the chemical nature of the oxide and on the O-vacancies. Thus, hydrogen adsorbs dissociatively on a perfect titanium oxide surface [10,11]. The energetically most favorable mode for the adsorption of atomic hydrogen is the adsorption on the outermost O atom, accompanied by the reduction of a Ti atom. In this mode, protons are formally adsorbed while an equivalent amount of Ti(IV) atoms are reduced to Ti(III). Theoretical calculations have demonstrated that H adsorption is less favorable on a defective surface than on a perfect surface. However, the best adsorption mode for the atomic chemisorption on a defective surface is heterolytic adsorption, which involves two different adsorption sites one H+/0= and one H on the surface. This adsorption mode is best on irreducible oxides such as MgO however, it is less favorable than adsorption on the perfect Ti02 surface [10]. The heat of atomic adsorption in all cases is very weak and dissociation onto the surface is unlikely. The molecular adsorption (physisorption), thus, remains the most stable system. 

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