Alkoxide acetates, mixed

In an early paper, the formation of products of lower chloride zirconium ratios, as compared to the moles of acetyl chloride employed with zirconium tetra-tert-butoxide, was ascribed to steric effects. However, in a careful re-examination, the reactions between metal fert-butoxides and acetyl halides have been found " to follow an entirely different course. For example, the reaction between zirconium tertiary butoxide and acetyl chloride was slow, and complete replacement of even one mole of tertiary butoxo group was not achieved the equimolar reaction product had the average composition, ZrClo.7(OBu )3 3. On the basis of further reaction of zirconium chloride tertiary butoxide with acetyl chloride it appeared that a side reaction occurred and instead of higher chloride alkoxides, mixed-alkoxide acetates were formed ... 

Contrary to the facile straightforward reactions of ethoxides and isopropoxides of different metals according to Eq. (2.268), an entirely different comse of reaction, resulting in the final formation of metal acetate, can be further illustrated by the reaction of aluminium tertiary butoxide with acetyl chloride. In this case, the first stage of the reaction is fast, but the aluminium monochloride di-fert-butoxide formed initially reacts with tertiary butylacetate also formed during the reaction, to produce the corresponding mixed alkoxide-acetate ... 

Titanium—Vanadium Mixed Metal Alkoxides. Titanium—vanadium mixed metal alkoxides, VO(OTi(OR)2)2, are prepared by reaction of titanates, eg, TYZOR TBT, with vanadium acetate ia a high boiling hydrocarbon solvent. The by-product butyl acetate is distilled off to yield a product useful as a catalyst for polymeri2iag olefins, dienes, styrenics, vinyl chloride, acrylate esters, and epoxides (159,160). 

Transition-metal mixed oxides active in combustion catalysis have been prepared by two main procedures i) classical coprecipitation / calcination procedures starting from metal nitrates and/ or alkoxides ii) preparation based on the supercritical drying of gels prepared from organic complexes (alkoxides, acetylacetonates or acetates), producing aerogels . Details on the second preparation can be found in Ref. 13. 

Transesterification reactions have been extensively used for the preparation of further alkoxides.158-165 Mixed alkoxides [M(OR)5. r(OR )j ] were obtained from the same alcoholysis reactions.166,167 Exchange reactions between [Nb(OEt) ] or [Nb(OPr )s] and organic acetates have also been exploited for the preparation of higher alkoxides. 

Reaction of [Mo(NO)(Me2pzb)I(OR)] with silver acetate in the presence of the alcohol ROH leads to the bis(alkoxides) [Mo(NO)(Me2pzb)(OR)2]. The mixed alkoxides were similarly prepared.126 The structures of several dialkoxides (Et, Pr Pr , Pr Et, Et) have been investigated in detail in view of the rather bulky character of the ligands at molybdenum. 

Modification by acetylacetone is a powerful route, that allows precursor solutions to be stabilized. Interaction of titanium alkoxides with acetylacetone was extensively studied and reviewed in [1391,86]. Study ofreactions, occurring on interaction of Zr(OPrn)4 and Ti-Zr alkoxide mixture with acetylacetone, was performed in [1448] and allowed the authors to simplify the technique for preparation of precursor solution for PZT films application and to overcome the requirement of prolonged refluxing, which certainly decreases reproducibility. After dissolution of titanium and zirconium alkoxides in methoxyethanol, acetylacetone is added to form stable zirconium and titanium stock solutions. The introduction of acetylacetone allowed aqueous lead acetate (and lanthanum acetate for PLZT films) solutions to be added to mixed titanium and zirconium solutions. No reaction steps involving elevated temperatures or distillation or long reaction times are required. The solution could be used both immediately on mixing or after storage for several months. Such solutions were successfully used for application of ferroelectric films. 

The metathesis reaction of metal chloride with alkali alkoxides (method 5) was historically the first approach applied, and it remains the main route to both mono- and bimetallic derivatives of Mn(H). The most efficient approach to Mn(II) derivatives is, however, provided by the alcoholysis of the corresponding silylamide (method 4). The derivatives of Mn(IH) and mixed-valence Mn(H,IH) were obtained by alcoholysis ofMn(III) acetate by polyatomic phenols in the presence of 2,2 -dipyridil accompanied by reduction in the latter case (methods 4 and 4+7). 

Titanium salts nicely promote acetalization, transacetalization, and deacetalization, etc. Acetals and related compounds are prepared from the parent carbonyl compounds or other acetals in the presence of a titanium salt. In addition to ordinary acetals, N,Oy or (5, 5)-acetals could be prepared by this method. Equation (234) illustrates the preparation of a mixed acetal with different alkoxide groups [533]. Table 20 shows the preparation of different acetals in the presence of titanium salts. 

Mixed-ligand precursors are also frequently employed in CSD processing. For example, titanium tetraisopropoxide, which is too reactive to be directly employed in most CSD routes, may be converted into a more suitable precursor by a reaction with either acetic acid or acetylacetone (Hacac). Such reactions are critical in dictating precursor characteristics and have been studied extensively. - Using these reactions, crystalline compounds of known stoichiometry and structure have been synthesized that may subsequently be used as known precursors for film fabrication.Mixed-hgand molecules (carboxylate-alkoxide and diketonate-alkoxide ) represent complexes that are not easily hydrolyzed. A typical structure for one of these compounds is shown in Figure 27.3e. 

A variety of mixed ligand/alkoxide uranium(V) products are also isolable. Substitution compounds (U(0R)4L, U(0R)3L2, U(0R)2L3) were prepared from the reactions of U(OCH2CH3)5 with FlCl, /3-ketoesters (2,2,2,-trifiuoroaceto acetate, methyl acetate, ethyl acetate), acetyl chlorides... 

With most of the R groups, the above reactions can be pushed to completion if the liberated isopropanol or acetate is removed azeotropically with a solvent such as benzene or cyclohexane. Alternatively, the reactions lead to the isolation of mixed alkoxides, many of which can be distilled without apparent disproportionation (6). For the replacement of isopropoxide by rcrr-butoxide groups, transesterification with rerf-butyl acetate is generally preferred (6) because of a larger difference in the boiling points of ferf-butyl and isopropyl acetate. 

The sulfonium fluorosulfonates 45 are very useful precursors for functionalized cyclopropyl sulfides. The reaction of these salts with aliphatic alcohols gave mixed acetals (e.g. 47) in quantitative yield, while phenol reacted as both an oxygen and carbon nucleophile. Benzenethiol and potassium fluoride provide the expected substitution products (e. g. 50 and 51, respectively), however, these are accompanied by side products such as methylated reagent [(methylsul-fanyl)benzene] or l,l-bis(methylsulfanyl)cyclopropane. Quite surprisingly, these substitution reactions fail with strong nucleophiles such as alkoxides, thiolates and azide. 

The generally accepted mechanism for the Perkin reaction is shown in Scheme 2. Much of the early woik leading to this view, which was the result of numerous investigations spanning a period of greater than SO years, has been reviewed in some detail. Formation of the anhydride enolate (1) and aldol-type condensation generates the alkoxide anhydride (2). Intramolecular acylation provides an acetoxycaibox-ylate (3), which forms a mixed anhydride elimination of acetic acid and hydrolysis affords the unsatu-... 

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