Basic operations dissolving

The preparation of oral liquids generally follows the basic operations such as dissolving, mixing and dispersing described in Chap. 29. The method depends on the characteristics of the formulation solution, suspension, emulsion. This section discusses as well the increasing non-availability of the active substance as a raw material. 

The process operated by ACl is outlined in Figure 7. Bales of cotton linter are opened, cooked in dilute caustic soda, and bleached with sodium hypochlorite. The resulting highly purified ceUulose is mixed with pre-precipitated basic copper sulfate in the dissolver, and 24—28% ammonium hydroxide cooled to below 20°C is added. The mixture is agitated until dissolution is complete. If necessary, air is introduced to aUow oxidative depolymerization and hence a lowering of the dope viscosity. 

As a result of these more exacting operational demands and the reduction in MU water dissolved impurities, basic waterside problems... 

Substituted benzyl chlorides were carbonylated using a Pd/tppts catalyst in aqueous/organic two phase systems under basic reaction conditions to afford the sodium salts of the corresponding phenylacetic acids. After acidification the phenylacetic acid dissolved in the organic phase and could be readily separated from the Pd/tppts catalyst contained in the aqueous phase (Figure 12) 466-468 TOFs up to 21 h 1 (turnover number, TON=165) and phenylacetic acid yields up to 94% were obtained at 70°C, 1 bar CO, tppts/Pd=10, NaOH/substrate=3/2 in an aqueous/toluene (1/1) two phase system in a batchwise procedure.466 The TOFs were improved to a maximum of 135 h 1 (TON=1560) in a continuous operation mode. Palladium catalysts modified with binas (Table 2 25) exhibited low catalytic activity (TONs up to 140) in the carbonylation of benzyl chloride 466 In strongly acidic media (pH=l) the Pd/25 catalyst was active and remained stable during the reaction which contrasts with Pd/tppts where palladium black was observed. However, the catalyst was completely deactivated after three cycles.466... 

Its laboratory method of ptepn, given in Ref 8, p 192 and in PATR 1448, p 9, consists of two steps prepn of Pb hydroxide and of LDNR, Basic. To a soln of 18.96g of pb acetate in 67 ml of warm distd w add gradually, with stirring, 4.0 g of NaOH dissolved in 67 ml of w and continue stirring for 5 mins. After allowing to settle, wash the white ppt of Pb hydroxide, by decantation three times with 100ml of distd w, and use immediately for the next operation... 

Acid chlorides. The corresponding acid and hydrogen chloride are the most likely impurities. Usually these can be removed by efficient fractional distillation. Where acid chlorides are not readily hydrolysed (e.g. aryl sulphonyl chlorides) the compound can be freed from contaminants by dissolving in a suitable solvent such as alcohol-free chloroform, dry toluene or petroleum ether and shaking with dilute sodium bicarbonate solution. The organic phase is then washed with water, dried with sodium sulphate or magnesium sulphate, and distilled. This procedure is hazardous with readily hydrolysable acid chlorides such as acetyl chloride and benzoyl chloride. Solid acid chlorides are satisfactorily crystallised from toluene, toluene-petroleum ether, petroleum ethers, alcohol-free chloroform/toluene, and, occasionally, from dry ethyl ether. Hydroxylic or basic solvents should be strictly avoided. All operations should be carried out in a fume cupboard because of the irritant nature of these compounds. 

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