Titanium trichloride forms

Li3(BN2) have already demonstrated the decomposition of (BN2) ions into boron nitride. The remaining nitride can lead to the formation of a binary metal nitride or reduce the transition metal ion under the formation of N2. Both mechanisms have been obtained experimentally, depending on the stability of the metal nitride. For instance niobium pentachloride forms NbN, titanium trichloride forms TiN, and nickel dichloride forms Ni, plus BN and nitrogen, respectively, in reactions with Li3(BN)2 (at 300-600°C) [24]. 

Titanium Dichloride. Titanium dichloride [10049-06-6] is a black crystalline soHd (mp > 1035 at 10°C, bp > 1500 at 40°C, density 31(40) kg/m ). Initial reports that the titanium atoms occupy alternate layers of octahedral interstices between hexagonaHy close-packed chlorines (analogous to titanium disulfide) have been disputed (120). TiCl2 reacts vigorously with water to form a solution of titanium trichloride andUberate hydrogen. The dichloride is difficult to obtain pure because it slowly disproportionates. 

Titanium Trichloride. Titanium trichloride [7705-07-9] exists in four different soHd polymorphs that have been much studied because of the importance of TiCl as a catalyst for the stereospecific polymerization of olefins (120,124). The a-, y-, and 5-forms are all violet and have close-packed layers of chlorines. The titaniums occupy the octahedral interstices between the layers. The three forms differ in the arrangement of the titaniums among the available octahedral sites. In a-TiCl, the chlorine sheets are hexagonaHy close-packed in y-TiCl, they are cubic close-packed. The brown P-form does not have a layer stmcture but, instead, consists of linear strands of titaniums, where each titanium is coordinated by three chlorines that act as a bridge to the next Ti The stmctural parameters are as follows ... 

Titanium trichloride is almost always prepared by the reduction of TiCl, most commonly by hydrogen. Other reduciag agents iaclude titanium, aluminum, and 2iac. Reduction begias at temperatures of ca 500°C and under these conditions a-TiCl is formed. The product is cooled quickly to below 450°C to avoid disproportionation to the di- and tetrachlorides. P-TiCl is prepared by the reduction of titanium tetrachloride with aluminum alkyls at low (80°C) temperatures whereas y-TiCl is formed if titanium tetrachloride reacts with aluminum alkyls at 150—200°C. At ca 250°C, the P-form converts to d. d-TiCl is made by prolonged grinding of the d- or y-forms. 

The last reaction is the most favored of these three. The actual occurrence of the reactions with elemental phosphorus or phosphorous trichloride as products has been explained to be due to kinetic reasons. The thorium present in the ore volatilizes in the form of thorium tetrachloride (ThCl4) vapor other metallic impurities such as iron, chromium, aluminum, and titanium also form chlorides and vaporize. The product obtained after chlorination at 900 °C is virtually free from thorium chloride and phosphorous compounds, and also from the metals iron, aluminum, chromium, and titanium. 

An equilibrium mixture of the cyclohexane- 1,3-dione (42) and its enol form (43) was irradiated in the presence of cyclopentene in MeOH to afford the intermediate (44), which was readily transformed to the tricyclic intermediate (45) and subsequently followed an retroaldolization sequence to give the cyclooctanedione (46) in 90 % yield. When refluxed with titanium trichloride and K metal in THF for 5 min., compound (46) gave the diol (47) 21K... 

The active component of the catalyst mixture is a complex which gets formed between titanium trichloride and triethylaluminium. The structure of the complex may be put as follows ... 

Reduction of aromatic aldehydes to pinacols using sodium amalgam is quite rare. Equally rare is conversion of aromatic aldehydes to alkenes formed by deoxygenation and coupling and accomplished by treatment of the aldehyde with a reagent obtained by reduction of titanium trichloride with lithium in dimethoxyethane. Benzaldehyde thus afforded /ra/is-stilbene in 97% yield [206, 209]. 

An interesting deoxygenation of ketones takes place on treatment with low valence state titanium. Reagents prepared by treatment of titanium trichloride in tetrahydrofuran with lithium aluminum hydride [205], with potassium [206], with magnesium [207], or in dimethoxyethane with lithium [206] or zinc-copper couple [206,209] convert ketones to alkenes formed by coupling of the ketone carbon skeleton at the carbonyl carbon. Diisopropyl ketone thus gave tetraisopropylethylene (yield 37%) [206], and cyclic and aromatic ketones afforded much better yields of symmetrical or mixed coupled products [206,207,209]. The formation of the alkene may be preceded by pinacol coupling. In some cases a pinacol was actually isolated and reduced by low valence state titanium to the alkene [206] (p. 118). 

Titanium in a low valence state, as prepared by treatment of solutions of titanium trichloride with potassium [206] or magnesium [207] in tetrahydro-furan or with lithium in dimethoxyethane [206], deoxygenates ketones and effects coupling of two molecules at the carbonyl carbon to form alkenes, usually a mixture of both stereoisomers. If a mixture of acetone with other ketones is treated with titanium trichloride and lithium, the alkene formed by combination of acetone with the other ketone predominates over the symmetrical alkene produced from the other ketone [20(5] Procedure 39, p.215). 

Hydrazones treated with alkalis decompose to nitrogen and hydrocarbons [845, 923] Woljf-Kizhner reduction) (p. 34), and p-toluenesulfonylhydra-zones are reduced to hydrocarbons by lithium aluminum hydride [812], sodium borohydride [785] or sodium cyanoborohydride [813]. Titanium trichloride hy-drogenolyzes the nitrogen-nitrogen bond in phenylhydrazones and forms amines and ketimines which are hydrolyzed to the parent ketones. Thus 2,4-dinitrophenylhydrazone of cycloheptanone afforded cycloheptanone in 90% yield [202]. 

This sequence bears an interesting resemblance to a one-step couphng reaction developed many decades later, a transform that would seem apphcable to the synthesis of DES if that were still an important drug. Thus, treatment of acetophenone (4-1) with titanium trichloride has been demonstrated to yield initially the pinacol product (4-2) if a reducing agent such as potassium metal is present, the glycol is eliminated to form a double bond. The product (4-3) consists predominantly ( 90%) of the tmns isomer [4]. 

It has also been found that the polymer formed from the beginning of the reaction is already prevaiUngly isotactic. This means that, from the start of the reaction, there exist a certain number of active centers on the solid a-TiCU surface which immediately yield iso tactic polymer consequently, it can be excluded that, at least for the active centers present on the initial free surface of a-titanium trichloride, there is an initial activation process, whose rate is slow enough to be observed even when operating at low temperature (30°). 

There is some evidence that the faces on which titanium atoms may exist, e.g., lateral faces (thus, not the 001 faces supposed free from fault), show a greater catalytic activity. From adsorption measurements of radioactive triethylaluminum on an a-titanium trichloride sample having well developed crystals (sample B, see Fig. 7), one may observe that the total amount of alkylaluminum which can be adsorbed (Table X, last line) is remarkably greater than the one sufficient to form a monomolecular layer on the lateral faces of the crystals (38). It is most likely that the alkyl-... 

Titanium forms three series of salts in which the element is respectively tetra-, tri-, and mono-valent. Thus, titanium and chlorine form titanium tetrachloride, TiCl4, titanium trichloride, TiCl3, and titanium monochloride, TiCl. The two last are unstable and readily pass into the higher chloride. Titanium tetrachloride shows a marked resemblance to tin tetrachloride it unites easily with hydrochloric acid in solution, with formation of the complex acid, ehloro-titanic acid, [TiCl6]tI2, and forms many crystalline products with other chlorides. It also unites with ammonia, forming ammines. 

Natta (67) has studied the effect of two isomeric forms of titanium trichloride on the polymerization of dienes and of isotactic polypropylene. He has found that the alpha isomer, which gave the higher isotactic polypropylene, gave greater amounts of trans 1.4-polydiene than the beta, which gave cis 1.4-diene. 

The first process was that of P. Spence and Sons1 in 1903, in which the sulphite was reduced by mixing it with titanium trichloride. The mixture was subsequently poured into caustic soda solution and stable sodium hydrosulphite formed, whilst the titanium was precipitated as titanic hydroxide Ti(OH)4. This hydroxide was afterwards dissolved in hydrochloric acid and reduced by electrolysis... 

Shimoishi and Toei [766] have described a gas chromatographic determination of selenium in non saline waters based on l,2-diamino-3,5-dibromobenzene with an extraction procedure that is specific for selenium (IV). Total selenium is determined by treatment of non saline water with titanium trichloride and with a bromine-bromide redox buffer to convert selenide, elemental selenium and selenate to selenious acid. After reaction, the 4,6-dibromopiazselenol formed from as little as lng of selenium can be extracted quantitatively into 1 ml of toluene from 500ml of natural water up to 2ng L 1 of selenium(IV) and total selenium can be determined. The percentage of selenium(IV) in the total selenium in river water varies from 35 to 70%. 

Titanium trichloride is an extremely easily oxidized material which dissolves in water to form a violet solution. On oxidation, it is converted to the colorless titanic acid, Ti(OH)4. Using a titanium trichloride solution of known strength, it is possible to reduce quantitatively dyes of various classes, the endpoint being taken as the point where the color of the dye disappears. 

The reactions described in Equation (20) are, however, only known for heterogeneous catalysts. For example, formaldehyde was formed selectively by a four-electron reduction of CO2 by an aluminum amalgam in the presence of titanium trichloride, even at room temperature and atmospheric pressure. The reaction is catalytic wiih respect to titanium [117,118]. 

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