Titanium salts reduction

Redox titrants (mainly in acetic acid) are bromine, iodine monochloride, chlorine dioxide, iodine (for Karl Fischer reagent based on a methanolic solution of iodine and S02 with pyridine, and the alternatives, methyl-Cellosolve instead of methanol, or sodium acetate instead of pyridine (see pp. 204-205), and other oxidants, mostly compounds of metals of high valency such as potassium permanganate, chromic acid, lead(IV) or mercury(II) acetate or cerium(IV) salts reductants include sodium dithionate, pyrocatechol and oxalic acid, and compounds of metals at low valency such as iron(II) perchlorate, tin(II) chloride, vanadyl acetate, arsenic(IV) or titanium(III) chloride and chromium(II) chloride. 

Asymmetric pinacol coupling reactions with a stoichiometric amount of titanium salts have been observed using a combination of TiGL and chiral amines such as A,A,A,A-tetramethyl-l,2-cyclohexanediamine and 2-methoxy-methylpyrrolidine. " " In these reports, the titanium salt is considered to be TiGl2- However, the titanium salt prepared by reduction of TiGU with McsSiSiMcs has proved to be TiGL. The enantioselectivities of the reactions using the chiral amines are modest (Table 2). 

A number of low-valent metal ions have been shown to reduce a-halocarbonyl compounds. The most commonly used species for this purpose have been chromium(II) and low-valent titanium " salts, although vanadium(II), samarium(II), iron(II) and tin(II) salts have also been used. 7 222 chloro, bromo and iodo ketones can all be reduced by chromium(II) and titanium(III) salts. Selective reductions are possible axial halides are reduced in preference to equatorial, and a,a-dihalo ketones can be selectively reduced to the corresponding monohalides (equation 10). 7 The use of samarium(II) iodide has recently been advocated for such a-cleavages.72 a-Halo esters and ketones are reduced instantaneously at -78 °C in excellent yields. a-Acetoxy esters are stable to this reagent. 

Macro quantities of selenium can be determined gravimetrically after reduction to the elemental form by various reagents such as tin (II) chloride, potassium iodide, or ascorbic acid (I). Ooba described a technique whereby the element is precipitated from perchloric acid solution with hydrazine (2). Selenium may be titrated with standard solutions of sodium thiosulfate, iodide, and ferrous, chromous, or trivalent titanium salts after oxidation to Se(VI) (I). Photometric and fluorometric methods based on formation of the piaselenol with diaminobenzidine or 2,3-diaminonaphthalene has been used for the determination of selenium (I, 3,4,5). Interfering elements such as As, Co, Cr, Cu, Fe, Hg, and Ni, are masked with EDTA or other chelating agents. 

Potassium fluotitanate, K2TiFe, is a convenient source for the preparation of other titanium salts. It can easily be obtained pure because it is sparingly soluble (0.6 gram in 100 grams of water at 0°), and it is therefore used as a primary standard in oxidation-reduction titrations. Its existence and stability illustrate the power of the fluoride ion to form stable C9mplex ions and to bring out the highest coordination number of an element. 

Synthesis of 3-substituted benzo[fc]furans was realized from a combination of benzotiiazole chloride mediated intramolecular cyclization and low-valent titanium promoted reduction. Thus, the sodium salt of 2-hydroxybenzophenone was first allowed to react with a 1-benzotriazol-l-ylalkyl chloride to give a ketone which was cyclized by LDA. Eventually, A titanium promoted elimination led to the desired 3-phenylbenzo(I>]furan in good yield <01JOC5613>. 

Abstract - The standard potentials of the reaction steps for the reduction of TiCLi in alkali chlorides were calculated from transient electrochemical techniques. It is shown that the stability ranges of the various oxidation states of titanium depend on the composition and temperature of the solvent. The presence of strong chloride ion donors, such as cesium chloride, enhances the stability of the high oxidation states. The results are interpreted in terms of formation of chlorocomplexes. The thermodynamic properties of solutes were calculated and the Gibbs energy of dissolution of the titanium salts determined. 

Probably the most popular carbon-carbon double-bond-forming reaction involving sulphur proceeds via the elimination of a sulphur-oxygen species. This is illustrated by a synthesis of 1,5-unsaturated dicarbonyl compounds (236) which proceeds by phenylthioalkylation of enolates (236a), using the phenyl-thioalkene (237), followed by ozonolysis and elimination of the sulphoxide moiety to provide the double bond. An alternative method for double-bond formation is shown in the preparation of alkenes R CH=CHR by reductive cleavage of the sulphide (238) with titanium salts, and demonstrates the versatility of sulphur in such double-bond formations. In the latter example... 

The problem about the aging period for preparation of reactive species 3, argued by Lombardo, should not be attributed only to the formation of gem-dizinc species. As titanium(IV) chloride is also reduced with zinc powder, [17] the titanium salt that works as a mediator would be the low-valent one. The reduction process of titanium(IV) may also sometimes cause the problem of reproducibility of methylenation reaction. In 1998, Matsubara and coworkers reported a general... 

Reductive coupling of carbonyl compounds to yield olefins is achieved with titanium (0), which is freshly prepared by reduction of titanium(III) salts with LiAIH4 or with potassium. The removal of two carbonyl oxygen atoms is driven by T1O2 formation- Yields are often excellent even with sensitive or highly hindered olefins. (J.E. McMurry, 1974, 1976A,B). 

Aluminum. All primary aluminum as of 1995 is produced by molten salt electrolysis, which requires a feed of high purity alumina to the reduction cell. The Bayer process is a chemical purification of the bauxite ore by selective leaching of aluminum according to equation 35. Other oxide constituents of the ore, namely siUca, iron oxide, and titanium oxide remain in the residue, known as red mud. No solution purification is required and pure aluminum hydroxide is obtained by precipitation after reversing reaction 35 through a change in temperature or hydroxide concentration the precipitate is calcined to yield pure alumina. 

Other Metals. AH the sodium metal produced comes from electrolysis of sodium chloride melts in Downs ceUs. The ceU consists of a cylindrical steel cathode separated from the graphite anode by a perforated steel diaphragm. Lithium is also produced by electrolysis of the chloride in a process similar to that used for sodium. The other alkaH and alkaHne-earth metals can be electrowon from molten chlorides, but thermochemical reduction is preferred commercially. The rare earths can also be electrowon but only the mixture known as mischmetal is prepared in tonnage quantity by electrochemical means. In addition, beryIHum and boron are produced by electrolysis on a commercial scale in the order of a few hundred t/yr. Processes have been developed for electrowinning titanium, tantalum, and niobium from molten salts. These metals, however, are obtained as a powdery deposit which is not easily separated from the electrolyte so that further purification is required. 

Titanium Sulfates. Solutions of titanous sulfate [10343-61-0] ate readily made by reduction of titanium(IV) sulfate ia sulfuric acid solutioa by electrolytic or chemical means, eg, by reduction with ziac, ziac amalgam, or chromium (IT) chloride. The reaction is the basis of the most used titrimetric procedure for the determination of titanium. Titanous sulfate solutions are violet and, unless protected, can slowly oxidize ia coatact with the atmosphere. If all the titanium has been reduced to the trivalent form and the solution is then evaporated, crystals of an acid sulfate 3 Ti2(S0 2 [10343-61-0] ate produced. This purple salt, stable ia air at aormal temperatures, dissolves ia water to give a stable violet solutioa. Whea heated ia air, it decomposes to Ti02, water, sulfuric acid, and sulfur dioxide. 

These facts would suggest that die electrolysis of molten alkali metal salts could lead to the inuoduction of mobile elecU ons which can diffuse rapidly through a melt, and any chemical reduction process resulting from a high chemical potential of the alkali metal could occur in the body of the melt, rather than being conhned to the cathode volume. This probably explains the failure of attempts to produce tire refractoty elements, such as titanium, by elecU olysis of a molten sodium chloride-titanium chloride melt, in which a metal dust is formed in the bulk of the elecU olyte. 

Reductant equivalent weights of, 847 Reduction 409 by chromium(II) salts, 409 by hydrogen sulphide, 416 by Jones reductor (zinc amalgam), 410 by liquid amalgams, 412 by silver reductor, 414 by sulphurous acid, 416 by tin(II) chloride, 415 by titanium(II[), 410 by vanadium(II), 410 see also Iron(III), reduction of Reduction potentials 66 Reference electrodes potentials, (T) 554 Relative atomic masses (T) 819 Relative error 134 mean deviation, 134... 

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

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