Stirrers air-driven

Toward the end of the acid chloride addition, TEA hydrochloride precipitated, and the solution became quite viscous, making stirring and removal of reaction heat more difficult. Hence, a large stirring paddle and a strong stirring motor (e.g., an air-driven stirrer) were used. 

B. 2-( 1,3-Dibenzoyl-4-imidazolin-2-yl)imidazole hydrochloride. 3 Into a 3-L beaker equipped with an air-driven stirrer are successively introduced 150 g (0.335 mol) of dry, unrecrystallized... 

L, wide-mouthed, round-bottomed vessel fitted with an efficient air-driven stirrer and thermometer is charged with 68 g (1.0 mol) of imidazole (Note 1), 202 g (2 mol) of triethylamine (Note 2), and 1000 mL of acetonitrile (Note 3). To the mixture is added dropwise over a 1-hr period and with external cooling 281 g (2.0 mol) of benzoyl,chloride (Note 2) the temperature is maintained at... 

The original standard bench-scale kettle was a 600-ml stainless-steel beaker, temperature was controlled by immersion in a water bath, and agitation was effected with a 2-in.-wide, oval-shaped, flat-bladed, air-driven stirrer. Operations were performed semiremotely behind a shield in a fume hood. However, considerable exposure of the operator s hands and forearms took place even when tongs and other tools were used. 

A dry, 5-L, four-necked, round-bottomed flask is equipped with an air-driven stirrer (Note 1), 250-mL pressure-equalizing dropping funnel,... 

Hydrolysis of racemic epoxide 18 was carried out using cells of R. glutinis. The cells (150 g) were suspended in 500 ml of 100 mM phosphate buffer pH 8.0 in a jacketed three-necked flask fitted with an air driven stirrer, condenser and stopper. A solution of 2.5 g racemic epoxide 18, in 50 ml of methyl tertbutyl ether was added to the stirred cell suspension. After 5.5 h at 28°C, the reaction was stopped. NaCI (180 g) was added and the mixture was extracted twice with an equal volume of ethyl acetate. The combined ethyl acetate layers were dried over anhydrous Na SO, filtered and the solvent was removed by a rotary evaporator to provide (S)-epoxide 18a in 48% solution yield. A portion (2.2 g) of the reaction product was dissolved in a mixture of heptanerethyl acetate (1 1) and repeatedly extracted with 0.10 M solution of Na B Oj in water. The organic layer provided 0.95 g of (S)-epoxide 18a with ee of >99% while the aqueous layer provided 1.02 g of (R)-diol 20 with ee of 79% [59]. 

Lobucavir 39 (7.00 g, 26.39 mmol), N-Cbz-t-valine p-nitrophenyl ester (35 g) and 10.5 g Chiro-CLEC BL (immobilized enzyme) were added to a jacketed 1 L three-necked round-bottom flask equipped with an air-driven stirrer and a condenser maintained at 5°C by a circulating water bath. Acetone (490 mL) followed by 210 mL DMF were added and the reaction was carried out at 45°C. The recovered immobilized enzyme was reused. The reaction was scaled up to a 4.5 Kg batch and excess p-nitrophenyl ester of CBz-L-valine was also recovered [95]. 

Add 1 ml of 2 M KNOg to the sample in the 125 ml cylindrical separatory funnel. Dilute to the 30 ml mark with 4 N HNO and stir the solution briefly. Add 30 ml of 5Q ( TBF In n-tetradecane. Agitate the solution vigorously for 4 min with an air-driven stirrer. Discard the acid portion (lower layer). Wash the TBP portion with 4 ilNO and again discard the acid portion. Back extract with seven 15 ml portions of distilled water, collecting the strip solution In a 150 ml beaker. Evaporate the conO lned aqueous portions to 10-15 ml, then quantitatively transfer the solution to a flamed stainless steel planchet. Allow to dry under a heat lamp, flame the planchet to burn off organic residue, and count on an o-counter. Retain for pulse-height analysis If the o-count exceeds a specified level. 

Vigorous shaking is essential. An ordinary motor-driven stirrer proved to be inadequate. Phenylbromoethyne gradually darkens when exposed to light or air. The product is best stored under nitrogen in a refrigerator and should be distilled within a few days of its preparation. 

B. Azetidine. A stirred mixture of 38 g. (0.68 mole) of potassium hydroxide pellets in 100 ml. of white mineral oil (Note 8) is heated to 140-150° in a four-necked 500-ml. round-bottomed flask, fitted with an air-driven Hershberg stirrer, a thermometer, a dropping funnel, and a 6-in. Vigreux column fitted with a vacuum-distillation head. The flask is removed from the heat source, and 50 g. (0.32 mole) of purified l-(2-carbethoxyethyl)azetidine is added dropwise at a rate sufficient to maintain the reaction temperature at 150° (Note 9). After addition is complete, the reaction mixture is heated to 200° at 50 mm. to remove all traces of ethanol (Note 10). The flask is fitted with a distillation head and a nitrogen bubbler, and the distillation is resumed at atmospheric pressure until azetidine distills (210° maximum pot temperature) (Note 11). The resulting product (19.6 g., 85% purity) is dried over potassium hydroxide and redistilled through a short Vigreux column to furnish 14.5-15.8 g. (80-87%) of purified azetidine, b.p. 62-63° (Note 12). 

The stirrer should be smooth running and gas-tight. The stirring motor (air-driven) should have a high torque because the reaction mixture tends to agglomerate as the reaction proceeds. 

In practice the oxidation of Stretford solution by Reaction 9 is ki-netically limited so that a substantial improvement in performance can be obtained by staging the process. It is estimated that the overall residence time in the oxidizer can be decreased by as much as 50% when three oxidizer stages are used in place of a single stage. Commercially, a three-stage oxidizer is used in which power-driven stirrers churn air into small bubbles. An analysis of commercial oxidizer performance indicates that mass transfer is not a significant factor. Hence the bubble size is suitably small. 

The apparatus consists of a 3-1. three-necked round-bottomed creased flask, with standard ball joints and an indented cone-shaped bottom (Note 1), which is heated by means of an electric mantle and is equipped with a high-speecT stirrer of stainless steel driven by a 10,000 r.p.m. motor (Note 2). One side neck is fitted with a bulb-type air-cooled condenser (Note 3), on top of which fits a 1-1. pressure-equalizing Hershberg dropping funnel (Note 4). The top of the dropping funnel is to be connected in turn to a U-tube containing a 1-cm. head of mercury. The entire apparatus is securely fastened to a sturdy support. 

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