Alkali metal alkoxides, reactions with

Anhydrous halogen derivatives of metals can be converted into metal alkoxides via reaction with either alkali metal alkoxides or with alcohols in the presence of ammonia. The reaction is usually carried out in other solvents than alcohols (hydrocarbon or ether ones) on cooling and with the amoimts of alcohols only slightly exceeding the stoichiometry. The reason is that oxo-alkoxides or oxo-alkoxide halides can otherwise be formed as impurities. This approach can be used successfully for synthesis of, for example, alkoxides of Sn(IV) [87], Bi (III) [114], and Fe(III) [82] ... 

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. " ... 

Zinc phthalocyanine (PcZn) is prepared from phthalonitrile in solvents with a boiling point higher than 200 C, e.g. quinoline277,278 or 1-bromonaphthalene,137 or without solvent in a melt of phthalonitrile.83,116 The zinc compound normally used is zinc(ll) acetate or zinc powder. The reaction of zinc(II) acetate with phthalic acid anhydride, urea and ammonium mo-lybdate(VI) is also successful.262 The metal insertion into a metal-free phthalocyanine is carried out in an alcohol (e.g.. butan-l-ol).127,141,290 This reaction can be catalyzed by an alkali metal alkoxide.112,129... 

Alkali-immobile dye-releasing quinone compounds, 19 293-294 Alkali lignins, 15 19-20 Alkali manganate(VI) salts, 15 596 Alkali manganates(V), 15 592 Alkali-metal alkoxide catalysts, 10 491 Alkali-metal alkoxides, effects of, 14 252 Alkali-metal alkylstannonates, 24 824 Alkali-metal fluoroxenates, 17 329-330 Alkali-metal hydrides, 13 608 Alkali-metal hydroxides, carbonyl sulfide reaction with, 23 622 Alkali-metal metatungstates, 25 383 Alkali-metal perchlorates, 18 211 Alkali-metal peroxides, 16 393... 

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],... 

Modified MPV-type reductions carried out with chiral magnesium alkoxides and with chiral Grignard reagents have been discussed in detail (1). These reagents differ from the aluminum alkoxides since the Grignard reaction is essentially irreversible. Chiral alkali metal alkoxides have also been used to effect asymmetric reductions (1). 

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. 

Double alkoxides with alkali metals A[M(OR)6] (Table 8) were formed from the reaction of the pentaalkoxides with alkali metal alkoxides. The double alkoxides of Mg, Ca, Sr and Ba with Nb and Ta have been synthesized in the presence of MgCl2 as a catalyst.169 Refluxing M(OPri)5 and A(OPri)3 (A = A1 or Ga) in isopropyl alcohol afforded double isopropoxides of the type [MA(OPr )8J and [MA2(OPr1)n]170. [NbTa(OMe)10] appears to be the first mixed transition metal alkoxide isolated.171 NMR showed it to be in dynamic equilibrium with the symmetrical M2(OMe)i0 dimers in solution, with close to random distribution of the three species. 

There have been few investigations of the reactions of polyhydroxy compounds with alkali metal alkoxides in nonaqueous media at room temperature.. Percival" reported the preparation of D-glucose-NaOEt and D-glucose NaOMe by treating d-glucose with sodium ethoxide, and penta-O-acetyl-D-glucopyranose with sodium methoxide, respectively. The adducts were dried under vacuum at 60° for 24 hours, a treatment which would make the presence of any significant proportion of alcohol of solvation unlikely. Any traces of moisture in the preparative medium preclude the formation of an aJkoxide adduct. 

In summary, the reaction between an alkali metal alkoxide and a poly-hydroxy compound in hot alcoholic media produces an alcoholate and, possibly, a small proportion of alkoxide adduct however, the conditions governing the ratio of alcoholate to adduct have not yet been well defined. Reactions with alkali metal hydroxides and cyanides produce mixtures (of alcoholate and adduct) that consist mainly of alcoholate. Occurrence of reactions between alkaline-earth metal hydroxides and polyhydroxy compounds in anhydrous alcoholic media has not been reported. 

By reactions with alkali metal alkoxides and phenoxides 338... 

On the other hand, application of alkali metal amalgam permits the slowing down of the reaction of metals with alcohols, which is used in the industrial production of alkali metals alkoxides. Production of NaOR by Mathieson Alkali Works is based, for instance, on the reaction of sodium amalgam (formed as a result of the electrolysis of aqueous NaCl solution with the mercury cathode) with alcohol NaOR ROH is isolated from the solutions. Na residue in the amalgam is hydrolyzed, the obtained mixture is returned to the electrolyz-... 

The most usual synthetic routes to the derivatives of platinum group metals are the exchange reactions of the complexes containing halide ligands with alkali metal alkoxides (method 5), alcoholysis of the same kind derivatives (usually by phenols, method 4), alcoholysis of hydroxide complexes (method 3), and redox reactions — reduction of chlorides or 0s04 in alcohol media (method 7) (Table 12.25). 

The study of the reaction of alkali metal alkoxides in absolute EtOH with nitrophenyl... 

The study of the reaction of alkali metal alkoxides in absolute EtOH with nitrophenyl 2-thiophenecarboxylates (349) shows that the reactivity depends on the size of the alkali metal ions.315 The ions form complexes at the TS more strongly than in the ground state. 

Alkali metal alkoxides such as KOH, NaOH, and CH3ONa are the most effective catalysts in alkali-catalyst transesterification. When using KOH, NaOH, and CH3ONa alkali-catalyst for FAME conversion, the active catalytic species were the methoxide anion (CH 0 ), formed by the reaction between methanol and hydroxide ions of KOH and NaOH. In addition, the methoxide anion was formed by dissolution of sodium methoxide. Sodium methoxide causes the formation of several byproducts, mainly sodium salts, that have to be treated as waste and additionally require high-quality oil (16). However, KOH has an advantage because it can be converted into KOH by reaction with phosphoric acid, which can serve as a fertilizer. Since KOH is more economical than sodium methoxide, it is the preferred choice for large-scale FAME production process. 

The reactions of carbonyl metal cations with alkali metal alkoxides, whereby carboalkoxycarbonyls are formed (54), warrant special mention, e-g-,... 

The reaction of Rh6(CO)i6 with a primary amine gives the monoanionic derivative containing a carboamide group, whereas the analogous carbo-alkoxy derivatives have been obtained by reduction with alkali metal alkoxides in anhydrous alcohol (45) ... 

Question 4.15 Three routes for the synthesis of alkoxides involve (i) the reaction of LnCb with an alkali metal alkoxide, (ii) reaction of an alkali metal with an alcohol, (iii) the reaction of a silylamide [Ln N(SiMe3)2 3] with an alcohol. What are the advantages and disadvantages of each ... 

Answer 4.15 (i) The chemicals are readily available. The chloride is fairly insoluble in organic solvents and it is possible that chlorine is retained in the product, (ii) There is no need to make the alkali metal alkoxide, as the alcohol is the starting material. The metal may need careful cleaning and there may be the need for heating and a catalyst. One product is a gas. (iii) The lanthanide silylamide has to be prepared first. Because of the bulky nature of the ligand, it may be inert to substimtion, but there are no problems with chloride retention and the reaction should be clean. 

The reaction of metal halides with an alkoxide or aryloxide (most commonly an alkali metal alkoxide), can resnlt in metathetic exchange to give the required complex (equation 6). Such reactions can also result in the formation of heterometallic species (such as NaZr2(OR)4) this can be a problem when homometallic aUcoxides are desired, but it is an important route to heterometallic alkoxides and aryloxides. The nature of the product can be influenced by the alkali metal, the alkoxide ligand, and the relative amounts of the reactantsd ... 

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