Alumina grades

Rapid purification Pass through a column of basic alumina (Grade 1, lOg/mL of CHCI3), and either dry by standing over 4A molecular sieves, or alternatively, distil from P2O5 (3% w/v). Use immediately. 

For many years the most common catalyst was an amorphous or noncrystalline type called 3A. Initially, all 3A catalyst contained 13% alumina and 87% silica. To improve activity maintenance, the alumina content was increased to 25%. Both 13 and 25% alumina grades continue to be used the choice at a given refinery is based on the specific situation. Another amorphous type catalyst, containing silica-magnesia and called 3E, is also used. 

Vz grams of the residue were dissolved in 10 ml of benzene, and the solution was passed over a chromatographic adsorption column containing 50 grams of alumina (Alcoa activated alumina. Grade F-20) which had previousiy been shaken for about 20 minutes with a mixture of 100 ml of benzene containing 1.5 ml of 10% acetic acid. 

Alumina chromatography The butanol extract containing F is poured onto a column of alumina (2.6 x 9 cm Woelem basic alumina Grade 1), and F adsorbed is eluted with 50% ethanol containing 0.6% ammonium hydroxide. The fractions containing F are combined (a trace of Tris is added) and concentrated to about 5 ml, and mixed... 

To an orange solution of 11.78 g (25.9 mmol) of 1 (R1 = H) in 400 mL of THF under nitrogen at —78°C are added 25.1 mL (40.2 mmol) of butyllithium and the resulting dark-red mixture is stirred at this temperature for 3.5 h. Then 8.0 mL (63.1 mmol) of chlorotrimethylsilane, freshly distilled from calcium hydride, are added in one portion, the mixture stirred at —78 C for 1 h and then warmed to r.t. over 2 h. The solvent is removed and the residue extracted with three 20-mL portions of CH2C12. The combined extracts are filtered through alumina (grade V) to give, upon removal of the solvent, pure product yield 13.35 g (98%)28. 

The catalyst employed was Alcoa Activated Alumina (Grade F-l, 4- to 8-mesh) from the Aluminum Company of America. A fresh catalyst is brought to a condition of maximum activity by passing a slow stream of air through the catalyst bed for 94 hours at 390-405°. Without this pretreatment, yields are 5-10% lower than those reported here. The catalyst is reactivated after each run by passing air through it for 39 hours at 390-405°. 

More recently a convenient method of purification has been recommendedt which is to decant the solvent, previously treated with sulphuric acid, directly on to a basic alumina (Grade I) column using about 50 g of adsorbent for each 100 ml of solvent the first 5 per cent of eluate is discarded. The column receiver should be suitably protected from the ingress of moisture by the attachment of a calcium chloride tube. This method also removes any peroxides which may be present. 

The cellosolve and carbitol solvents may contain traces of peroxide. These can be removed either by heating under reflux over anhydrous tin(n) chloride (see 11. Propan-2-ol) or by filtration under slight pressure through a column of activated basic alumina (Grade I) the used alumina should be saturated with water before being discarded. 

Commercial grades of DMF may be purified initially by azeotropic distillation with benzene (CAUTION). Distil a mixture of 1 litre of DMF and 100 ml of benzene at atmospheric pressure and collect the water benzene azeotrope which distils between 70 and 75 °C. Shake the residual solvent with powdered barium oxide or with activated alumina (Grade I), filter and distil under nitrogen at reduced pressure collect the fraction having b.p. 76°C/39mmHg or 40°C/10mmHg. The distillate is best stored over a Type 4A molecular sieve. 

The mixture was allowed to stand for 70 hours and then concentrated to a small volume under reduced pressure. The residue was dissolved in 100 ml of methylene chloride, washed with 75 ml of water, three times with 50 ml of saturated brine solution each time and filtered over neutral alumina (grade 1). The filtrate was evaporated to dryness and the resulting colorless oil taken up in ether, which was then saturated with hydrogen chloride. The pale yellow precipitate was filtered off and recrystallized from methanol/ether yielding 1-[2-(diethylamino)ethyl]-5-(2-fluorophenyl)-7-chloro-2,3-dihydro-1H-1,4-benzodiazepinone-(2) dihydrochloride as pale yellow rods melting at 190° to 220°C with decomposition, (from British Patent 1,040,548). 

The purity of the hemin ester can be checked by tic (silica gel, with CHC13/ methanol = 5 1), or by visible spectroscopy. A small amount of the hemin ester dissolved in pyridine can be reduced by sodium dithionite in a cuvette.1 2 The resultant hemochrome should exhibit two absorption maxima at 557 and 526 nm. If necessary, the product can be further purified by chromatography on an alumina (grade III) column (1X10 cm) using a mixture of chloroform and methanol (10 1) as eluent. However, the iron prophyrin compound obtained after chromatography exists as the p-oxo dimer, [Fe(III)-O-Fe(III)], which may be converted back to the chloride by treatment in CHC13 with dry HO followed by crystallization from chloroform/methanol. 

Toxic) Perhaps the simplest procedure is to pass the chloroform through a column of basic alumina (grade I, lOg per 14ml). This removes traces of water and acid and also removes the ethanol which is present as a stabiliser. Carbon tetrachloride may be purified in the same way. Larger volumes of either solvent can be dried with 4A sieves, or by distillation from phosphorus pentoxide (3% w/v). Distilled chloroform should be stored in the dark to prevent formation of phosgene. 

The products were isolated and purified by column chromatography on alumina grade III, then distilled (high vacuum) at rt all pure materials must be stored under argon below -25°C. 

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