Aluminum phenoxide catalyst

To vessel with flushed nitrogen at an elevated temperature to 165°C 490 parts of phenol was placed, then 4.5 parts of aluminum turnings were added in small increments.The reaction mixture was accompanied by evolution of hydrogen for 15 min, then the mixture was allowed to cool to about 60°C and agitation discontinued. Aluminum phenoxide catalyst mixture was ready. 

Recently, in a Union Carbide Corporation patent, it was shown that the aluminum phenoxide catalysts and particularly... 

The most important appHcation of metal alkoxides in reactions of the Friedel-Crafts type is that of aluminum phenoxide as a catalyst in phenol alkylation (205). Phenol is sufficientiy acidic to react with aluminum with the formation of (CgH O)2Al. Aluminum phenoxide, when dissolved in phenol, greatiy increases the acidic strength. It is beheved that, similar to alkoxoacids (206) an aluminum phenoxoacid is formed, which is a strong conjugate acid of the type HAl(OCgH )4. This acid is then the catalyticaHy active species (see Alkoxides, metal). 

The choice of catalyst is based primarily on economic effects and product purity requirements. More recentiy, the handling of waste associated with the choice of catalyst has become an important factor in the economic evaluation. Catalysts that produce less waste and more easily handled waste by-products are strongly preferred by alkylphenol producers. Some commonly used catalysts are sulfuric acid, boron trifluoride, aluminum phenoxide, methanesulfonic acid, toluene—xylene sulfonic acid, cationic-exchange resin, acidic clays, and modified zeoHtes. 

ButylatedPhenols and Cresols. Butylated phenols and cresols, used primarily as oxidation inhibitors and chain terrninators, are manufactured by direct alkylation of the phenol using a wide variety of conditions and acid catalysts, including sulfuric acid, -toluenesulfonic acid, and sulfonic acid ion-exchange resins (110,111). By use of a small amount of catalyst and short residence times, the first-formed, ortho-alkylated products can be made to predominate. Eor the preparation of the 2,6-substituted products, aluminum phenoxides generated in situ from the phenol being alkylated are used as catalyst. Reaction conditions are controlled to minimise formation of the thermodynamically favored 4-substituted products (see Alkylphenols). The most commonly used is -/ fZ-butylphenol [98-54-4] for manufacture of phenoHc resins. The tert-huty group leaves only two rather than three active sites for condensation with formaldehyde and thus modifies the characteristics of the resin. 

Among metal alkoxides, aluminum phenoxide is one of the most important Friedel-Crafts catalysts in the alkylation of phenol. ... 

Modifications of these resins are also known. For example, aluminum phenoxide bonded to an acidic E)owex resin has been used as a heterogeneous catalyst for alkylation and transalkylation of phenols and polysubstituted phenols, respectively. ... 

Alkylation of phenols with isobutene has also been accomplished using a heterogeneous catalyst system comprising an aluminum phenoxide bonded to a solid polymeric resin having acidic functional... 

Tsuji and coworkers have developed diisobutylaluminum phenoxide-pyridine as an effective aldol condensation catalyst and applied it to the macrocyclization of 2,15-hexadecanedione (equation 132). Addition of the diketone at high dilution to a solution of the catalyst in hexane provides a mixture of cis and trans isomers of the and A enones. Catalytic hydrogenation of the mixture affords ( )-muscone. The authors explain the regioselectivity of the process by assuming that the aluminum phenoxide functions as a Lewis acid, coordinating to the carbonyl group. Pyridine functions as a base to remove a proton from the less hindered methyl group. 

Aluminum chloride, 60, 61 Diels-Alder catalyst, 144 Friedel-Crafts acylation catalyst, 91-100 MA complex, 212 Aluminum, diethyl chloride, 345 Aluminum oxide, dehydrating catalyst, 87 Aluminum phenoxides, MA polymerization reactant, 273... 

The cycloaddition of functionalized cyclopentadiene and dienophile 83 was better performed by use of an entirely different, non-phenoxide-type aluminum complex (Scheme 6.53). Thus a chiral catalyst endowed with the more electron-with-drawing bis (sulfonamide) ligand was explored by Corey and coworkers [73]. The reaction of the trons-crotyl derivative 83 and cyclopentadiene with 20 mol% 84 as catalyst at -78 °C for 16 h provided adduct 85 in 88% yield and 94% ee. The ad-... 

The most extensive application of the Oppenauer oxidation has been in the oxidation of steroid molecules. The most common aluminum catalysts are aluminum /-butoxide, i-propoxide, and phenoxide. While only catalytic amounts of the aluminum alkoxide are theoretically required, in practice at least 0.25 mole of alkoxide per mole of alcohol is used. Acetone and methyl ethyl ketone have proved valuable hydride acceptors due to their accessibility and ease of separation from the product, whereas other ketones such as cyclohexanone and p-benzoquinone are useful alternatives, due to their increased oxidation potentials.4 Although the reaction can be performed neat, an inert solvent to dilute the reaction mixture can reduce the extent of condensation, and, as such, benzene, toluene, and dioxane are commonly utilized. Oxidation of the substrate takes place at temperatures ranging from room temperature to reflux, with reaction times varying from fifteen minutes to twenty-four hours and yields ranging from 37% to 95%. 

A timeline for the development of olefin metathesis, adapted from a review by Grubbs, is shown in Figure 21.3. Olefin metathesis is more than 50 years old. " It was first conducted with ill-defined rhenium, molybdenum, and tungsten systems generated from perrhenate, aluminum oxide, - and tetraethyl lead as additive, from molybdenum oxide on p-TiO and tetramethyltin as additive, ° or from tungsten phenoxides supported on niobium oxide and silicon oxide activated with alkylaluminum reagents. The temperatures for these processes are hi, but the catalysts are relatively inexpensive and can be long lived. These are the types of catalysts that have been used for the synthesis of commodity chemicals by olefin metathesis. 

Methyl aluminum complex 99 has been tested as a catalyst for ROP of LA in the presence of isopropyl alcohol as an initiator and found that in all cases narrow PDl ranging from 1.01 to 1.04 was observed [74], The binuclear aluminum complexes 100-101 coordinated with sterically hindered benzotriazole phenoxide ligands are illustrated in Scheme 6.24 [75]. 

Classical MPV reduction (Al(Oi-Pr)3 and i-PrOH system) has several disadvantages. That is, stoichiometric amount of Al(Oi-Pr)3 and excess amount of 2-propanol as hydride donor are needed for smooth reaction. In addition, reaction rate is relatively slow. Since these reasons, development of effective catalysts for MPV reduction and/or Oppenauer oxidation is an important task in synthetic organic chemistry. Recently, to solve these problems highly active aluminum catalysts were reported. Maruoka and coworkers reported that bidentate Lewis acids (75a) and (75b) derived from bis-aluminated phenoxide (17) and various secondary alcohols effectively catalyze MPV reductions (Scheme 6.58). In these catalysts, bis-aluminated structure, which is coordinated by one carbonyl oxygen in a double coordination manner, is crucial for high catalytic activity [76]. 

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