2-Propoxide

A heterogeneous olefin epoxidation catalyst containing both V and Ti in the active site was prepared by sequential non-hydrolytic grafting. The silica was exposed first to VO(OiPr)3 vapor followed by Ti(0 Pr)4 vapor. Formation of propene is evidence for the creation of Ti-O-V linkages on the surface. Upon metathesis of the 2-propoxide ligands with BuOOH, the catalyst becomes active for the gas phase epoxidation of cyclohexene. The kinetics of epoxidation are biphasic, indicating the presence of two reactive sites whose activity differs by approximately one order of magnitude. 

Formation of 2-propanol and propene was confirmed by GC/MS. Chemisorption of Ti(0 Pr)4 is therefore suggested to be a consequence of nonhydrolytic condensation of the 2-propoxide ligands, which generates V-O-Ti bridges in the absence of surface hydroxyl groups. After removal of volatiles and desorption of physisorbed metal complexes, analysis reveals the presence of two equiv. Ti per V site on the surface, Table 1 (experiments 3 and 4). 

The 2-propoxide ligands of 2 undergo quantitative exchange in the presence of excess fer/-butylhydropeioxide, eq 3 ... 

This in accordance with the mechanism shown in Figure 14.5. In a preequilibrium two 2-propoxide anions are replaced by a tertiary-butylperoxy anion and an allyloxy anion, as follows clearly from the kinetic equation. This intermediate has a very low concentration and has not been observed directly. From here on we can only speculate on the interactions leading to a preferred attack on either of the enantiotopic faces of the alkene. 

Aryl fluoroalkyl ethers have been prepared from the reaction, at room temperature in HMPA, of fluo-ro-substituted alkoxides with activated fluoro-,149 nitro-,149 and, at 150 °C, also chloro-arenes150,151 and some chloro-substituted pyrazines (equation 15), pyrimidines, quinolines,150,152 and pyridines.152 Disubstitution was observed in die presence of comparably activated leaving groups such as in 2,4- and 2,6-di-chloronitro- or cyano-benzenes, whereas regiospecific substitution took place at position 4 in 3,4-dichloronitro- or cyano-benzene and at position 2 in 2-fluoro-6-chlorocyanobenzene.151 Steric hindrance and the number of fluorine substituents in the alkoxide pose limits to the reactivity. Thus, tertiary alkoxides, or alkoxides containing more than four fluorine substituents, displace activated nitro and fluoro, but not chloro substituents.149,150 The secondary hexafluoro-2-propoxide anion does not react even with the more reactive nitro and fluoro derivatives.149... 

Meerwein-Ponndorf-Verley-Type Reduction Reduction of ketones by 2-propanol or related alcohols, known as Meerwein-Ponndorf-Verley (MPV) reduction, is promoted by various metal alkoxides, typically aluminum 2-propoxide [2a,d,281]. The C2 hydrogen of 2-propanol is transferred directly to the carbonyl carbon through a six-membered pericyclic transition state [284], Earlier, a stoichiometric quantity of a metal alkoxide was required for this purpose, but recently, lanthanide [285] and aluminum [286] complexes acting as excellent catalysts have been reported. 

Sodium 2-Methyl-2-propoxide, see Sodium fert-butoxide, 1661b... 

Biirgi T, Bieri M (2004) Time-resolved in situ ATR Spectroscopy of 2-propanol oxidation over Pd/A1203 evidence for 2-propoxide intermediate. J Phys Chem B 108 13364-13369... 

It can be said that not only the above mentioned nano-structure but also other ordinary physical or structural properties measured for photocatalysts have not been proved to be decisive factors for the photocatalytic activities. It is true that photocatalytic activities of photocatalysts of certain components prepared or treated in different ways or under different conditions may be different and this is because physical and structural properties of those photocatalysts differ depending on the preparation/treatment conditions, that is, physical and structural properties must control the photocatalytic activity 49). A problem is we, at least the author, do not know how properties affect photocatalytic activity. A possible reason is that those properties, though we do not know how many properties are required for analysis, are changed at the same time. For example, when titania photocatalysts are prepared by hydrolysis of a titanium compound such as titanium(IV) sulfate or tetra (2-propoxide) followed by calcination in air, higher-temperature... 

Westin, G, Moustiakimov, M., and Kritikos, M. (2002) Synthesis, characterization and properties of three europium 2-propoxides [Eu4(OPr )io(HOPr )3]-2HOPr EusOOPrjj and EuAEOPPij. Inorganic Chemistry, 41, 3269-3258. 

Okano, T., Matsuoka, M., Konishi, H., Kiji, J. Meerwein-Ponndorf-Verley reduction of ketones and aldehydes catalyzed by lanthanide tri-2-propoxides. Chem. Lett. 1987, 181-184. 

Lastly, 2-propoxide intermediates undergo a p-hydride elimination step above 300 K to yield the final acetone product. The selectivity of this step is best illustrated by the acetone TPD traces shown in Figure 5, which were obtained with the partially labelled CD3CHICD3 isotopomer of 2-propyl iodide. The only acetone detected in these experiments is the perdeutero species, which means that the hydrogen-removing step is regiospecific and involves only the secondary middle hydrogen. These experiments also confirm that propene is not involved in the production of acetone in this system. 

Fig. 5. Acetone TPD traces for the main isotopomers expected from the reaction of CD3CHICD3 with oxygen on Ni(lOO) surfaces. The exclusive formation of perdeutero acetone in this case indicates the high selectivity towards a P-hydride elimination step from the 2-propoxide intermediate, and rules out a mechanism where an initial P-hydride elimination from 2-propyl groups on Ni sites is followed by oxygen incorporation.

Reduction of ketones using 2-propanol or related alcohols is referred to as Meerwein-Ponndorf-Verley (MPV) reduction [2a, 2d, 87]. Historically, metal alkox-ides, typically aluminum 2-propoxide, have been used as stoichiometric promotors for this purpose. The hydrogen migration is conceived to occur through a direct, pericyclic mechanism involving a metal alkoxide and ketonic substrate... 

Starting material for 2.55 is 4-methyIpent-4-en-2-one (mesityl oxide), which is nitrosated after nucleophilic addition of ethylamine to the ethylenic double bond. Diazoethane is obtained in 50 0 yield by alkaline cleavage with sodium 2-propoxide in 2-propanol and ether. The method of Adamson and Kenner (1935, 1937) is also applied for higher homologs, but the yields decrease (1-diazooctane 16 0) due to the higher instability of these compounds (see Sect. 2.2). As shown in (2-20), mesityl oxide is regenerated in the reaction. 

C-allylation of PhO" Na with H2C=CHCH2C1 in a variety of solvents in the presence of different crown ethers is most effective in each case when using poly(vinylbenzo-15-crown-5)polyether. Only in the presence of the crown ethers 15-crown-5 and 18-crown-6 are the anions in potassium phthalimide and sodium saccharinate, respectively, sufficiently activated to bring about nucleophilic aromatic substitution of the 4-fluorine in pentafluoropyridine. The formation of 2,4-dinitrophenol, in addition to the expected ether, from 2,4-dinitrochlorobenzene and potassium 2-propoxide in 2-propanol-benzene (1 1), in the presence of dicyclohexyl-18-crown-6 polyether, has been accounted for on the basis of a nucleophile-radical reaction (5rn1)/ ... 

In contrast to its a anomer 50, the p-glucoside 56 yielded oxazoline 62 on treatment with sodium methoxide (later Meyer zu Reckendorf isolated 2-3% of the corresponding aziridine ). The action of sodium 2-propoxide in boiling... 

Alkyl anions have been implicated as intermediates stabilized by a neutral molecule. Alkoxide ions when photolysed in a pulsed ICR spectrometer dissociate into alkanes and enolate anions The intermediate 19 in equation 25 can be represented by two possible extremes. In 19a the alkyl anion R is solvated by a ketone and inl9b the radical anion of the ketone is solvated by the radical R. The structure of this intermediate will then depend on the relative electron affinities of the alkyl group R and the ketone. Brauman and collaborators photolysed a series of 2-substituted-2-propoxides (18 with R = CH3, R" = H and R varied). For substituents R = CF3, H, Ph and H2C=CH, the C—R bond dissociation energies for homolytic fission are larger than the C—CH3 bond energy, i.e. if the intermediate complex has the structure 19b then methane would be expected to be produced. Conversely, since these R groups form more stable anions than CH3, decomposition via 19a should result in RH. The experimental observation that only RH is formed led to the conclusion that 19 is best described by the solvated alkyl anion structure 19a. 

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