Aluminium homogenization

DETERMINATION OF ALUMINIUM AS THE 8-HYDROXYQUINOLATE, AI(C,H60N)3> WITH PRECIPITATION FROM HOMOGENEOUS SOLUTION... 

First spray the dried chromatogram homogeneously with reagent 1. Then remove excess reagent in a stream of cold air in the fume cupboard (ca. 30 min for silica gel and 3 h for aluminium oxide layers). Then spray the chromatogram lightly with reagent 2. 

The plate should be heated as rapidly and homogeneously as possible after the first spraying step this is best done on a thick preheated aluminium plate in a drying cupboard equipped with ventilation allowing the nitric acid vapors to be removed using a water pump vacuum [1]. 

HAT [Homogeneous alkylation technology] An alkylation process using an alkyl aluminium catalyst. Developed by Kerr-McGee in 1994. 

By careful control of these parameters aluminium may be separated, and few interferences are observed if the precipitation is carried out from an ammoniacal-cyanide-EDTA solution. When large amounts of Ca or Mg are present the homogeneous precipitation procedure (Table 5.18) is usefully employed at pH = 5. The precipitate is readily filtered and may be weighed after drying at 150°C as the anhydrous compound. 

Aluminium distribution in A and B1 intermediate and final phases Various compositional zonings have been reported in silica-rich ZSM-5 zeolites prepared under particular conditions (11-13,19,26, 27,31,32,59,68) while other studies provided evidence for homogeneous A1 distribution throughout the crystallites (69-71). Obviously, the distribution of aluminium in ZSM-5 must depend on its mechanism of crystallization. 

The thermal decomposition of trimethyl aluminium has been investigated by Yeddanapalli and Shubert117 and by Ouimet118. In both investigations the decomposition was found to occur by a predominantly homogeneous chain reaction and methane was the major gaseous product (CH4 > 91 % above 400 °C and 100 torr pressure CH4 99 %). 

Polymerisations in n-pentane. Kennedy and Thomas, wishing to study the polymerisation of isobutene by aluminium chloride under homogeneous conditions, i.e., in a solvent in which even the highest polymers remained in solution at low temperatures, chose n-pentane [54]4. The specimen they used was stated to contain approximately 0.1 mole/1 of branched and olefinic impurities which are known to reduce the DP and therefore the DPs obtained must be (slightly) lower than those which would have been obtained in pure n-pentane. 

An important requirement for such vapor pressure measurements with Knudsen cells is the temperature distribution in and around the cell. If the temperature is not homogeneous within the cell, condensation and crystallization of the vaporized species may occur in the colder regions. This was observed e.g. with gold. In other cases the orifice was reduced in diameter up to complete blockage when vaporized metals like aluminium where oxidized due to the partial pressure of oxygen. To prevent these deposits, ultra high vacuum is necessary or the use of graphite cells instead of alumina cells. 

Cyclopentadienyl ligands have become extremely important in catalysis for metal such as Ti, Zr, and Hf (Chapter 10) and in academic studies of related elements such as Ta. Ethylene polymerisation with the use of CpiTiCE (alkylated with aluminium alkyl compounds) has been known for many decades, but the intensive interest in derivatives of these compounds started in the early 1980 s following the discovery of MAO (methaluminoxane - see chapter 10) which boosted metallocene catalyst activities by several orders of magnitude. Commercial interest focussed on ethylene copolymers (LLDPE where more homogeneous comonomer incorporation resulted in greatly improved copolymer properties) and in enantiospecific polymerisations for propene, styrene, etc. 

Meerwein-Pondorf-Verley reduction, discovered in the 1920s, is the transfer hydrogenation of carbonyl compounds by alcohols, catalyzed by basic metal compounds (e.g., alkoxides) [56-58]. The same reaction viewed as oxidation of alcohols [59] is called Oppenauer oxidation. Suitable catalysts include homogeneous as well as heterogeneous systems, containing a wide variety of metals like Li, Mg, Ca, Al, Ti, 2r and lanthanides. The subject has been reviewed recently [22]. In this review we will concentrate on homogeneous catalysis by aluminium. Most aluminium alkoxides will catalyze MPV reduction. 

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