Titanium alkoxides determination

Abstract—The effects of metal alkoxide type and relative humidity on the durability of alkoxide-primed, adhesively bonded steel wedge crack specimens have been determined. Aluminum tri-sec-butoxide, aluminum tri-tert-butoxide, tetrabutyl orthosilicate, and titanium(IV) butoxide were used as alkoxide primers. Grit-blasted, acetone-rinsed mild steel adherends were the substrates bonded with epoxy and polyethersulfone. The two aluminum alkoxides significantly enhanced the durability of the adhesively bonded steel, while the titanium alkoxide showed no improvement in durability over a nonprimed control. The silicon alkoxide-primed samples gave an intermediate response. The failure plane in the adhesively bonded samples varied with the relative humidity during the priming process. 

The electrochemical reduction of Ti02 is known to be accompanied by the intercalation of small cations. This finding has been explored in sensitizing anatase films for battery applications [149]. Cation coordination to titanium alkoxide sol-gel precursors is also well known [150]. Lyon and Hupp used quartz crystal microbalance techniques to determine the mass of intercalating cations as the TiOa film is reduced [151]. Hagfeldt and co-workers have studied Li+ and Na intercalation into anatase Ti02 both theoretically and experimentally [152, 153). They found that the diffusion constants for Li and Na+ are temperature dependent with an activation barrier of 0.4 eV for insertion and 0.5 eV for extraction. The Li+ diffusion coefficient at 25 °C into the nanoporous structure was approximately 2 X 10 cm s for insertion and 4 x 10 cm s for extraction. 

In a very comprehensive study by Finn and co-workers the synthesis, properties and reactions of several titanium-substituted ylides are described. The complexes were prepared from titanium alkoxides and (Me2N)3P=CH2 (scheme 9). The structure of one of the complexes was determined crystallographically which showed it to exist as a chloride bridged dimer (53). The ylidic P-C distance and /pc coupling constant are charactersitic of a P-C single bond which, together with the six-coordinate nature of the Ti centres, verify the zwitterionic nature of the species in both the solid state and in solution. The titanium ylide... 

In general, the facility for interchange of alkoxy groups increases from tertiary to secondary to primary groups. Verma and Mehrotra tried to determine the extent of such equilibria in the case of titanium alkoxides, Ti(OR)4 and found the following order in the interchangeability of alkoxo groups in alcoholysis reactions MeO > EtO > Pr 0 > Bu 0. ... 

The oxidation of alkanes by r-butyl hydroperoxide (TBHP) has been catalysed by titanium alkoxides, producing the corresponding alcohols and ketones. A radical mechanism is proposed in which r-butoxyl radical formed from TBHP and titanium alkoxide initiates the reaction. The evolution of oxygen (from the decomposition of peroxide) and the abstraction of hydrogen from alkane to form alkyl radical occur competitively. A method for the determination of both the primary and secondary KIEs at a reactive centre based on starting-material reactivities allows the determination of the separate KIEs in reactions for which neither product analysis nor absolute rate measurements are applicable. It has been applied to the FeCls-catalysed oxidation of ethylbenzene with TBHP, which exhibits both a primary KIE and a substantial secondary KIE the findings are in accordance with previous mechanistic studies of this reaction. The oxidation of two l-arylazo-2-hydroxynaphthalene-6-sulfonate dyes by peroxy-acids and TBHP catalysed by iron(III) 5,10,15,20-tetra(2,6-dichloro-2-sulfonatophenyl)porphyrin [Fe(ni)P] is a two-step process. In single turnover reactions, dye and Fe(in)P compete for the initially formed OFe(IV)P+ in a fast reaction and OFe(IV)P is produced the peroxy acid dye stoichiometry is 1 1. This is followed by a slow phase with 2 1 peroxy acid dye stoichiometry [equivalent to a... 

The first X-ray crystal structure determination of a tetraalkoxide was of the centrosym-metric tetranuclear ethoxo compound [Ti4(/i3-OEt)2(/i-OEt)4(OEt)io]. Each titanium atom is in a distorted octahedral coordination as indicated in Fig. 4.35. Since solution molecular weight measurements showed that the trimer [Ti3(OEt)i2] is present, the crystal structure determination clearly emphasized that it is unwise to attempt to predict crystal structures from solution data. Various attempts have been made to deduce the structure of the trimer and a recent X-ray absorption study (XANES and EXAFS) inclines to the view that five-coordinated (TBP) titanium is present in a symmetrical molecule [Ti3(/z-OEt)3(OEt)9]. The tetranuclear structure in the crystalline state was reinforced by the partial structure of the mixed alkoxide [Ti4(OMe)4(OEt)i2] which had the same Ti40i6 framework as in Fig. 4.35. The same structure was also found for the tetramethoxide [1i4(/i3-OMe)2(M-OMe)4(OMe)io]. ... 

A few organotitanium alkoxides have been structurally determined. In bis-benzyl titanium diethoxide a centrosymmetric dimer [(C6H5CH2)4Ti2(/r-OEt)2(OEt)2] is formed involving five-coordinated Ti in a distorted TBP configuration. In bis-methyl titanium tritox methoxide (tritox = tri-tert-butyl carbinolate, BU3CO) the methoxo... 

The chemical composition of the products is determined by a number of important factors, such as the nature of metal atoms involved, the nature of alkoxide groups, the ratio of homometallic reactants applied and, in certain cases, even on the solvent in which the reaction is carried out. For example, the reaction of barium ethoxide and titanium ethoxide in 1 (where x>2) ratio in oxygen-free solutions provides different products in alcohol and in hydrocarbon media (Yanovsky, 1995 Kessler, 1994) ... 

Sol-gel routes for binary titanium dioxide, tertiary titanates, and other mbced metal oxide systems not only employ various Ti(lV) alkoxides and modified alk-oxides but also Ti(IV) chlorides, oxychlorides, oxynitrates, and so on. The microstructure of the resulting titania and titanates depends on the morphology and interactions between primary particles (clusters) forming upon hydrolysis-condensation of Ti(IV) precursors. An apparent lack of crystalline order and very small size of primary particles and clusters (<1 nm) is observed in the early stages of reaction. At a more advanced stage, the morphology is determined by interparticle interactions and aggregation mechanisms. 

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