Titanium acetic acid system

The nonhydrolytic M—O—M bond formation via ester elimination between metal alkoxides and carboxylic acids is a well-known approach in sol-gel chemistry. In this direction, titanium -butoxide and acetic acid were used for the nonhydrolytic synthesis of anatase Ti02 nanopartides at 100 °C [92]. Moreover, spindle-shaped nanoporous anatase Ti02 mesocrystals with a single-crystal-like structure and tunable sizes were synthesized in the tetrabutyl titanate and acetic acid system without any additives imder solvothermal conditions [93]. A complex mesoscale assembly process, involving oriented aggregation of tiny anatase nanocrystals and entrapment of in situ produced butyl acetate as a porogen, was proposed for the formation of the mesocrystals. They exhibited a good performance as anode material for lithium ion batteries [93]. 

Catalysts. Iodine and its compounds ate very active catalysts for many reactions (133). The principal use is in the production of synthetic mbber via Ziegler-Natta catalysts systems. Also, iodine and certain iodides, eg, titanium tetraiodide [7720-83-4], are employed for producing stereospecific polymers, such as polybutadiene mbber (134) about 75% of the iodine consumed in catalysts is assumed to be used for polybutadiene and polyisoprene polymeri2a tion (66) (see RUBBER CHEMICALS). Hydrogen iodide is used as a catalyst in the manufacture of acetic acid from methanol (66). A 99% yield as acetic acid has been reported. In the heat stabiH2ation of nylon suitable for tire cordage, iodine is used in a system involving copper acetate or borate, and potassium iodide (66) (see Tire cords). 

This catalyst system is used in about 70% of the -xylene oxidations, and the percentage is increasing as new plants almost invariably employ it. Process conditions are highly corrosive owing to the acetic acid and bromine, and titanium must be used in contact with some parts of the process. 

Reduction. Just as aromatic amine oxides are resistant to the foregoing decomposition reactions, they are more resistant than ahphatic amine oxides to reduction. Ahphatic amine oxides are readily reduced to tertiary amines by sulfurous acid at room temperature in contrast, few aromatic amine oxides can be reduced under these conditions. The ahphatic amine oxides can also be reduced by catalytic hydrogenation (27), with 2inc in acid, or with staimous chloride (28). For the aromatic amine oxides, catalytic hydrogenation with Raney nickel is a fairly general means of deoxygenation (29). Iron in acetic acid (30), phosphoms trichloride (31), and titanium trichloride (32) are also widely used systems for deoxygenation of aromatic amine oxides. 

Addition compounds form with those organics that contain a donor atom, eg, ketonic oxygen, nitrogen, and sulfur. Thus, adducts form with amides, amines, and A/-heterocycles, as well as acid chlorides and ethers. Addition compounds also form with a number of inorganic compounds, eg, POCl (6,120). In many cases, the addition compounds are dimeric, eg, with ethyl acetate, in titanium tetrachloride-rich systems. By using ammonia, a series of amidodichlorides, Ti(NH2) Cl4, is formed (133). 

Titanium Silicides. The titanium—silicon system includes Ti Si, Ti Si, TiSi, and TiSi (154). Physical properties are summarized in Table 18. Direct synthesis by heating the elements in vacuo or in a protective atmosphere is possible. In the latter case, it is convenient to use titanium hydride instead of titanium metal. Other preparative methods include high temperature electrolysis of molten salt baths containing titanium dioxide and alkalifluorosiUcate (155) reaction of TiCl, SiCl, and H2 at ca 1150°C, using appropriate reactant quantities for both TiSi and TiSi2 (156) and, for Ti Si, reaction between titanium dioxide and calcium siUcide at ca 1200°C, followed by dissolution of excess lime and calcium siUcate in acetic acid. 

PZN-PT, and YBa2Cug02 g. For the preparation of PZT thin films, the most frequently used precursors have been lead acetate and 2irconium and titanium alkoxides, especially the propoxides. Short-chain alcohols, such as methanol and propanol, have been used most often as solvents, although there have been several successful investigations of the preparation of PZT films from the methoxyethanol solvent system. The use of acetic acid as a solvent and chemical modifier has also been reported. Whereas PZT thin films with exceUent ferroelectric properties have been prepared by sol-gel deposition, there has been relatively Httle effort directed toward understanding solution chemistry effects on thin-film properties. 

Allyl silanes react with a wide variety of electrophiles, rather like the ones that react with silyl enol ethers, provided they are activated, usually by a Lewis acid. Titanium tetrachloride is widely used but other successful Lewis acids include boron trifluoride, aluminium chloride, and trimethylsilyl tri-flate. Electrophiles include the humble proton generated from acetic acid. The regiocontrol is complete. No reaction is observed at the other end of the allylic system. All our examples are on the allyl silane we prepared earlier in the chapter. 

Trost first introduced the di-fe/7-butylsilylene derivative as a means for protecting 1,2- and 1,3-diols during a synthesis of PiUaromycinone derivatives.213 Di-ferf-butylsilylene derivatives are not as robust as isopropylidene or benzylidene acetals and their use is best reserved for systems requiring deprotection under very mild conditions. Di-isopropylsiiylene derivatives are occasionally used but they usually only survive in highly crowded environments.214 Di-feri-butylsily-lene derivatives survive hydroboration with 9-BBN, mild oxidation (e g the Dess-Martin, ozone), Lewis acids such as trifluoroborane e the rate and titanium tetrachloride, mild acids (pyridinium p-toluenesulfonate). camphorsulfonic acid, strong bases such as feri-butyllithium (THF, -50 °C), DDQ, and sodium meth-oxide in methanol at 0 C — conditions used to cleave acetate esters. 

Titanium trichloride fimctions as an excellent reductive Nef alternative reagent. This aqueous reagent is very acidic, so that acid sensitive groups such as ketals and esters do not survive unless an acetate buffer is used. Systems prcme to acid-catalyzed rearrangements may then successfully undeigo the reaction (equation 10).Some veiy sensitive multifunctional compounds have been obtained using this modified Nef procedure (equation 11). A related process is the formation of 1,4-diketones via in situ generation of a nitronatc anion by the Lewis acid catalyzed addition of an enol silyl ether to a nitroalkene (equation 12). ... 

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