Alkali alkoxide

The first step for the synthesis of a melt spinnable polysilane is the alkoxylation and distillation of the residue (Figure 1). 1,2-dimethyltetramethoxydisilane and 1,1,2-trimethyltrimethoxydisilane are mixed in a special ratio and a poly silane will be obtained by a catalytic redistribution reaction. Catalysts for this reaction are alkali alkoxides like sodium methoxylate. Phenylmethoxydisilanes [22] or phenylchloride are used as additives. A mixture of methyltrimethoxysilane and dimethyldimethoxy-silane distils off as a byproduct of the redistribution reaction. Figure 2 shows the mechanism of the catalytic redistribution. 

Association of sodium hydride and alkali alkoxides with nickel salts has been reported to be effective in many hydrogenations and selective reductions of organic halides (211, 221). 

Cyclic alkenes with alkali alkoxides give almost exclusively products of nucleophilic substitution of one or more vinylic or allylic fluorine or halogen atoms. The preference of the attack is expressed by the sequence fluorine > chlorine > bromine.68... 

The appearance of the alkali alkoxide can lead to formation of bimetallic alkoxides or bimetallic alkoxide halides as impurities. For example, lithium oxoalkoxocomplexes were isolated as side products of the anodic dissolution of Mo and W when LiCl was used as conductive additive [908],... 

The metatheis of acetates with the alkali alkoxides (method 5) can be used for the preparation of the methoxides and ethoxides of all three elements and is the only reaction leading to Hg(OR)2 [1623]. The trans-esterification of Zn(OMe)2 (method 6), according to [1121], can be carried out only in the presence of LiOR (forming soluble bimetallic complexes). The direct electrochemical synthesis on the anodic oxidation of metals in alcohols has been described for Zn(OEt)2 and a series of cadmium derivatives (Cd(OR)2 — obtained in the presence of such donor ligands as Dipy, Phen, and Dmso [98]) (method 2). 

The classic study of Al(OR)3 was carried out by Tishchenko [1585] at the end of nineteenth century. His dissertation, entitled On the Action of Amalgamated Aluminum on Alcohols (Aluminum Alkoxides, Their Properties and Reactions), became a great resonance for the chemistry of alkoxides (see also Chapter 1). The synthetic approaches, that he developed are still in use the purity of the samples obtained by Tishchenko, taking into account the data he reported, was definitely not worse than that of those described at present. In 1929 Meerwein and Bersin [1101], performing the acidimetric titration of Al(OR)3 solutions by solutions of alkali alkoxides, discovered the existence of bimetallic alkoxides (Meerwein salts), which play an important role in the modern chemistry of metal alkoxides. 

The alkoxides of both oxidation states were obtained by metathesis of germanium halides (chlorides and iodides) with alkali alkoxides [1488, 1142, 857, 1535]. The yields can be increased by application of GeCl4 solvates with Py or NH3 or amines [3, 222] (method 5) and also by alcohol interchange of ethoxides (method 6) or alcoholysis of Ge[Si(NR3)2]2 [568, 1543] (method 4). The application of alkali alkoxides in the preparation of Ge(OR)4is possible in contrast to that of analogous derivatives of Sn(IV) and Zr due presumably to the much lower stability of corresponding alkoxogermanates the intermediate products of the corresponding reactions because of stability — of the tetrahedral coordination for Ge. The direct electrochemical preparation of Ge(OEt)4... 

Application of alkali alkoxides is impossible in this reaction because of formation of rather stable alkoxozirconates [115]. 

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). 

The main route to rhenium alkoxides is the interaction of halids and oxy-halids with alkali alkoxides or alcohols in presence of amines (method 5). As the important starting reagents can serve also Re2(CO),0 and Re207 (method 3) The preparation ofrhenium (V) and (VI) oxoderivatives by the anodic oxidation of metal in alcohols has also been described (method 2) (see Table 12.22). The bimetallic alkoxides ofrhenium and heavy transition metals can most efficiently be obtained by interaction ofrhenium (VII) oxide with the alkoxides ofthese elements in refluxing toluene ... 

In addition to the bimetallic complexes of rhenium and alkaline metals formed as byproducts in the exchange reactions of rhenium halids with alkali alkoxides (such as, for example, LiReO(OPr )5 xLiCl(THF)2 [519]) there has been recently prepared a number ofbimetallic complexes ofrhenium and molybdenum, rhenium and tungsten, and rhenium and niobium [904, 1451]. The latter are formed either due to the formation of a metal-metal bond, arising due to combination of a free electron pair on rhenium (V) and a vacant orbital of molybdenum (VI) atom or via insertion of molybdenum or tungsten atoms into the molecular structure characteristic of rhenium (V and VI) oxoalkox-ides. The formation of the compounds with variable composition becomes possible in the latter case. 

Arulsamy, N. et al., J. Amer. Chem Soc., 2001, 123(44), 10860 Reaction of acetone with nitric oxide in presence of alkali alkoxides gives various diazene A-oxide- A -hydroxylate salts (RN(0)=N0Met, also called diazenediolates), such as the disodium methanebis- or trisodium methanetris- compounds according to nitric oxide pressure. Potassium alkoxides behaved similarly, but lithium only formed a bis- compound. These compounds are explosive. The sodium bis- hydrate shattered a DSC apparatus. 

The mechanism of this type of reaction, originally elucidated by Kruck (94), is related to the simple addition of the nucleophile observed with alkali alkoxides. In the present case the following reactions, in which the saponification step is also of preparative significance (99, 102), have been observed (45) ... 

The regenerated KOH works as a catalyst once again. If alkali alkoxides are used as catalysts instead of alkali hydroxides, the exchange of protons between the growing polymer and the dead polymer is ... 

Silacyclobutanes as well as silacyclopropanes undergo aldehyde insertion under catalysis by /-BuOK (Equation (77)).292 The reaction of silacyclobutanes with lithium carbenoids such as dihalomethyllithium and oxiranyllithium gives 2-substituted silacyclopentanes (Equation (78)). Treatment of l-(l-iodoalkyl)- and 1-oxiranyl-silacyclobutanes with a stoichiometric amount of an alkali alkoxide leads to silacyclopentanes by anionic 1,2-shift of the ring carbon adjacent to silicon. These ring-expansion reactions proceed probably via a pentacoordinate silane intermediate. 

Table IV gives an example of our own work on the polymerization of a number of higher aldehydes. Potassium triphenylmethoxide—a soluble initiator—polymerized a number of higher aldehydes to crystalline isotactic poly aldehydes. Table V lists a number of alkali alkoxides and other related compounds used as initiators for the n-butyraldehyde polymerization. Neither the type of the alkoxide nor the cation is of any great importance for the polymerization rate, the polymer yield, and stereoregularity of the resulting polyaldehyde as long as the initiator is adequately soluble in the reaction mixture.

The ready ring fission which is characteristic of 3-unsubstituted derivatives of the fully unsaturated compounds is also found here. Strong bases (alkali alkoxides) convert them into cyclic /9-ketonitriles (67, R = H) 84,85 88 90,91 if methyl iodide is present, a methyl group is introduced into the molecule (67, R = CH3).87,89... 

In early work, vinyl chloride had been heated with stoichiometric amounts of alkali alkoxides in excess alcohol as solvent, giving vinyl ethers as products (210). Supposedly this involved a Williamson ether synthesis, where alkali alkoxide and organic halide gave an ether and alkali halide. However, it was observed that small amounts of acetylene were formed by dehydrohalogenation of vinyl chloride, and that this acetylene was consumed as the reaction proceeded. Hence acetylene was substituted tor vinyl chloride and only catalytic amounts of alkali were used. Vinylation proceeded readily with high yields... 

Michael condensations are catalyzed by alkali alkoxides, tertiary amines, and quaternary bases and salts. Active methylene compounds and aliphatic nitro compounds add to form p-substituted propionates. These addition reactions are frequently reversible at high temperatures. Exceptions are the tertiary nitro adducts which are converted to olefins at elevated temperatures (24). 

The heavier alkali amides have yet to find widespread nse in synthesis owing to the inferior selectivity imparted by then-greater reactivity. However, in situ mixtures of heavy alkali alkoxides and lithium amides are finding increasing nse as very strong bases. The nature of the reactive species is as yet unclear. 

The reaction has been extended to nitrogen-containing compounds by the use of an alkali alkoxide, such as potassium t-butoxide. ... 

Once the alkali alkoxide solutions have been added and the dispersed precipitate has been homogenized, the remaining alkoxides are precipitated by addition of methanol to form insoluble methoxides. Care must be taken to avoid segregation during precipitation due to differing solubilities and reactivities between the various metal alkoxides. When the desired precipitate is heated, the A phase is again the first crystalline phase to form at temperatures below 600°C. The lambda-to-beta transition occurs at 700°C. No p" phase formation occurs below 1200°C. 

Williamson ether synthesis Alkylation of alkali alkoxides with primary or secondary alkyl halides to form ethers. 484... 

Although so far utilized (64a) only for the preparation of aryloxide derivatives, ether adducts of the lanthanide nitrates, such as [Ln(N03)3-Me0(CH2CH20)4Me], may also prove to be convenient starting materials for their alkoxide analogues by reactions with alkali alkoxides. 

These alkoxometalate chloride derivatives, EC1XL x, can be converted into their alkoxometalate alkoxide or /3-diketonate analogues by their reaction with alkali alkoxide or /3-diketonate in the appropriate molar ratios. 

Lewis acid-base reactions between component alkoxides have been used primarily for the synthesis of bimetallic alkoxides involving (1) alkali alkoxides and less basic alkoxides, and (2) between binary alkoxides of other metals. 

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