Metal alkoxides reactions with esters

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). 

Alkali metal alkoxides, r-butyl acetate neat, 45°, 30 min, 98% yield of r-butyl ester from methyl benzoate. The rate constant for the reaction increases with increasing ionic radius of the metal and with decreasing polarity of the solvent. Equilibrium for the reaction is achieved in <10 sec. Other examples eire presented. " ... 

This scheme is remarkably close to the coordination insertion mechanism believed to operate in the metal alkoxide-catalyzed ring-opening polymerization of cyclic esters (see Section 2.3.6). It shares many features with the mechanism proposed above for the metal alkoxide-catalyzed direct polyesterification (Scheme 2.18), including the difficulty of defining reaction orders. 

A similar steric effect was observed in the reaction of benzyl carboxylate (44). When 44a-d were treated with Bu OK under solvent-free conditions at around 100 °C for 30 min, the corresponding condensation products 45a (75%), 45b (66%), 45c (64%), and 45d (84%) were obtained in the yields indicated [9] (Scheme 6). When the same reactions of 44a-d and Bu OH were carried out in toluene under reflux for 16 h, no condensation product was obtained and 44a-d were recovered unchanged. In solution reactions, exchange of the alkoxy group occurs among the substrate, reagent, and solvent. Therefore, the alkoxy groups of the ester, metal alkoxide, and alcohol used as a solvent should be identical. 

The preferential -configuration of the enol esters, derived from p-dicarbonyl compounds under phase-transfer conditions, contrasts with the formation of the Z-enol esters when the reaction is carried out by classical procedures using alkali metal alkoxides. In the latter case, the U form of the intermediate enolate anion is stabilized by chelation with the alkali metal cation, thereby promoting the exclusive formation of the Z-enol ester (9) (Scheme 3.5), whereas the formation of the ion-pair with the quaternary ammonium cation allows the carbanion to adopt the thermodynamically more stable sickle or W forms, (7) and (8), which lead to the E-enol esters (10) [54],... 

Alkyl halides undergo Sn2 reactions with a variety of nucleophiles, e.g. metal hydroxides (NaOH or KOH), metal alkoxides (NaOR or KOR) or metal cyanides (NaCN or KCN), to produce alcohols, ethers or nitriles, respectively. They react with metal amides (NaNH2) or NH3, 1° amines and 2° amines to give 1°, 2° or 3° amines, respectively. Alkyl halides react with metal acetylides (R C=CNa), metal azides (NaN3) and metal carboxylate (R C02Na) to produce internal alkynes, azides and esters, respectively. Most of these transformations are limited to primary alkyl halides (see Section 5.5.2). Higher alkyl halides tend to react via elimination. 

The generation of dichlorocarbene for addition to olefins has been realized by the use of chloroform and alkali metal alk-oxides4 6 (preferably potassium feri-butoxide), sodium trichloro-acetate,6 butyllithium and bromotrichloromethane,7 and the reaction of an ester of trichloracetic acid with an alkali metal alkoxide.2,8 The latter method, which is here illustrated by the preparation of 2-oxa-7,7-dichloronorcarane, generally gives higher yields of adducts. 

The insertion of carbon dioxide into a transition metal-oxygen bond, e.g., a metal alkoxide, results in an organic carbonate ester, coordinated in either a monodentate or bidentate manner. Only a limited number of such reactions have been observed, and little mechanistic information is available. The reactions may proceed by interaction of C02 with ROH or RO in solution followed by metal coordination, in a manner similar to the C02 reactions with the early transition metal dialkylamides. Alternatively, direct attack of C02 on the alkoxide oxygen might occur, or a C02 adduct may form as an intermediate. 

Although formally involving the reaction with a C—H bond, metal alkoxides will react with /1-diketones and / -keto esters to form six-membered chelates and alcohols. Hence the acetyl-acetonate (acac) derivatives of aluminum can be obtained (equation 63).238... 

In [1677] complex alkoxides and alkoxide-carboxylates were compared as precursors for preparation ofBST films. In contrast to the introduction of alkaline earth carboxylates in the form of preliminary isolated salts, in this work metal alkoxide solution in methoxyethanol containing titanium and alkaline-earth metal was modified by addition of 2-ethylhexanoic acid with subsequent slow distilling off the solvent and repeated dilutions with fresh portions of methoxyethanol. During the distillation process, part of the alkoxide groups are substituted by the 2-ethylhexanoate ligands. The exchange reaction of Ti(OPr )4 with acid was studied in different solvents, and it was demonstrated that in the course of distillation the titanium oxoisopropoxy-2-ethylhexanoate is formed with elimination of ester ... 

Now for some of the reactions you have seen in the last few chapters. Starting with carbonyl substitution reactions, the first example is the conversion of acid chlorides into esters. The simplest mechanism to understand is that involved when the anion of an alcohol (a metal alkoxide RO ) reacts with an acid chloride. The kinetics are bimolecular rate = fc[MeCOCl] [RO ]. The mechanism is the simple addition elimination process with a tetrahedral intermediate. 

Transesterifications of aliphatic carbonate esters with glycols are catalysed by alkali metal alkoxides. No catalyst is needed for the transesterification of diaryl carbonates with aliphatic diols. Alkyl carbonate esters and p-xylylene glycol undergo transesterification reactions when certain titanium compounds are used as catalysts. The preparation of aromatic polycarbonates by transesterification is best... 

Functionally substituted benzylic, allylic, and vinylic compounds containing alkoxides, esters, ethers, nitriles, or amides can be reacted with halosilanes under Barbier conditions using HMPT to yield C- and O-silylated products, 1,2- or 1,4-addition products, as well as reductive dimers. Radical and anionic intermediates are postulated, based on SET reactions from the metal, and multiple silated species can be obtained. The use of the TMSCl-Mg-HMPT system has been extensively investigated by Galas group [85] at the University of Bordeaux, and their work has greatly advanced the science of the Barbier reaction with silanes. 

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