Isopropoxides

In the following preparation to illustrate the Meen.vein-Pormdorf-Verley reduc tion, a solution of benzophenone in isopropanol is rapidly reduced in the presence of aluminium isopropoxide to benzhydrol (CaHs)2CO (C Hj)jCH OH. It is clear that the aluminium isopropoxide must take some essential part in this reaction, for benzophenone when dissolved even in cold isopropanol with a trace of acetic acid is reduced to tetraphenylethyleneglycol (p. 150). 

The mechanism of the reduction remains uncertain. The work of E. D. Williams, K. A. Krieger and A. R. Day (1953) using deuterium-labelled aluminium isopropoxide, shows that hydrogen atoms are transferred predominantly from the central carbon atom of an isopropoxide group to the carbon atom of the carbonyl group undergoing reduction, the process probably involving a cyclic complex ... 

Aluminium isopropoxide can be obtained as a fine powder from technical sources. When the bottle has once been opened however, the stopper should be firmly replaced and covered with wax more conveniently, the stoppered bottle can be kept in an atmospheric desiccator over calcium chloride or sodium hydroxide, preferably in the dark. 

It is advisable in any case before an experiment to place the weighed aluminium isopropoxide overnight in a shallow dish in a vacuum desiccator over sodium hydroxide. The isopropanol should be dried over anhydrous sodium sulphate, and the clear liquid decanted off before use. 

The powdered isopropoxide and the isopropanol must be dried as described above. 

Place in the flask 2 g. of benzophenone, 15 ml. of isopropanol and 2 5 g. of aluminium isopropoxide. This mixture has now to be heated gently under reflux so that the temperature registered by the thermometer in the column does not exceed 80°, i.e., so that only acetone distils. For this purpose, the flask should preferably be heated in an oil-bath direct heating, even over an asbestos sheet, may cause local overheating and decomposition the use of a water-bath on the other hand may make the column undesirably damp. 

The reagent is conveniently stored as a solution in isopropyl alcohol. The molten (or solid) alkoxide is weighed out after distillation into a glass-stoppered bottle or flask and is dissolved in sufficient dry isopropyl alcohol to give a one molar solution. This solution may be kept without appreciable deterioration provided the glass stopper is sealed with paraffin wax or cellophane tape. Crystals of aluminium isopropoxide separate on standing, but these may be redissolved by warming the mixture to 65-70°. 

Prepare a solution of aluminium isopropoxide from 23 -5 g. of aluminium, 0-5 g. of mercuric chloride and 250 ml. of dry isopropyl alcohol ... 

Carbonylation of allylic alcohols requires severe conditions[248]. The carbonylation of allylic alcohols proceeds smoothly in the presence of LiCl and Ti(IV) isopropoxide[249j. The allylic methyl ether 394 can be carbonylated with the use of PdCl2[250] or 7r-allylpalladium coordinated by BF4, PF, and... 

It is possible to reduce thiazole carbonyl derivatives with aluminium isopropoxide (56, 57). For example, 4-methyl-5-acetylthiazole gives 4-methyl-5-(a-hydroxyethyl)thiazole. With aluminium amalgam one obtains a duplication like to the pinacol reaction, and the yield is genaally poor... 

The reduction of thiazole carboxaldehydes with isopropanol and aluminium isopropoxide gives the corresponding alcohols (37, 107, 108). 

Reduction with aluminium isopropoxide by the Meerwein-Pondorf procedure yields the alcohol (56, 57, 112). 

Secondary and tertiary alkyl halides are not suitable because they react with alkox ide bases by E2 elimination rather than by 8 2 substitution Whether the alkoxide base IS primary secondary or tertiary is much less important than the nature of the alkyl halide Thus benzyl isopropyl ether is prepared m high yield from benzyl chloride a pri mary chloride that is incapable of undergoing elimination and sodium isopropoxide... 

These reversible reactions are cataly2ed by bases or acids, such as 2iac chloride and aluminum isopropoxide, or by anion-exchange resias. Ultrasonic vibrations improve the reaction rate and yield. Reaction of aromatic aldehydes or ketones with nitroparaffins yields either the nitro alcohol or the nitro olefin, depending on the catalyst. Conjugated unsaturated aldehydes or ketones and nitroparaffins (Michael addition) yield nitro-substituted carbonyl compounds rather than nitro alcohols. Condensation with keto esters gives the substituted nitro alcohols (37) keto aldehydes react preferentially at the aldehyde function. 

Zirconium alkoxides behave similarly in regard to thermal stability. The series zirconium methoxide [28469-78-5] zirconium ethoxide [18267-08-8] zirconium isopropoxide [2171 -98 ] zirconium /r /f-butoxide [2081 -12-1] shows decreasing thermal stability. 

Titanium Alkoxides. Titanium alkoxides are made from titanium tetrachloride and the corresponding alcohols in the presence of ammonia. Higher titanium alkoxides are manufactured from lower alkoxides by alcoholysis. Titanium isopropoxide and -butoxide are commercially available in barrels. Annual production of titanium alkoxides is estimated at 3000—4000 metric tons at an average price of about 4/kg. 

The estimation of alkoxy groups is not such a simple task. One method (26,68) involves hydrolysis and oxidation of the Hberated alcohol with excess standard potassium dichromate solution. The excess may then be estimated iodometrically. This method is suitable only for methoxides, ethoxides, and isopropoxides quantitative conversion to carbon dioxide, acetic acid, and acetone, respectively, takes place. An alternative method for ethoxides is oxidation followed by distillation, and titration of the Hberated acetic acid. 

Aluminum acetylsaHcylate is a tasteless, nonbasic, stable, alternative therapeutic salt to aspirin (83). Also called aluminum aspirin, it is an insoluble white to off-white powder prepared by reaction of aluminum isopropoxide with sodium acetylsaHcylate in an organic solvent. The product precipitates from the reaction mixture (83). Standards requke that aluminum aspirin contain not less than the equivalent of 80% aspirin, corresponding to 90% purity on an anhydrous basis. The aluminum oxide assay must be 12—17% (81). 

Catalytic amounts of mercuric chloride are usually employed in this preparation. Aluminum isopropoxide is a useful Meerwein-Potmdorf-Verley reducing agent in certain ester-exchange reactions and is a precursor for aluminum glycinate, a buffering agent (see Alkoxides, metal). 

DOT 17E phenolic-lined steel pails and dmms, respectively. Plain steel is not suitable for isopropyl alcohol containing water because msting can result. Instead, baked phenolic-lined steel tanks are used. Aluminum is also unsuitable. It is attacked by isopropyl alcohol, especially the anhydrous grade, resulting ia the formation of aluminum isopropoxide. Containers must comply with DOT specifications. Tanks, piping, and equipment can be made of similar material. 

Fig. 8. Gelation behavior of alumina sols prepared from hydrolysis of aluminum isopropoxide at ( ) 90°C and (-) room temperature (49).

AH (A)-menthol is made by synthetic methods. One method involves the cyclization of (+)-citroneIlal (68). Using a mild acid catalyst, (+)-citroneIlal [2385-77-5] undergoes an ene-reaction to produce a mixture of isopulegols (142). Catalytic hydrogenation of the isopulegol mixture gives a mixture of menthol and its isomers. The (A)-menthol is obtained after efficient fractional distillation and the remaining isomers can be equilibrated, usually with sodium menthol ate or aluminum isopropoxide. An equilibrium mixture is obtained, comprised of 62 wt % (A)-menthol, 23 wt % (+)-neomenthol, 12 wt % (+)-isomenthol, and 3 wt % (+)-neoisomenthol. The equilibrium mixture can be distilled to recover additional (+)-mentbol. 

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