Yield from Evaporative Cooling

Example 2 Yield from Evaporative Cooling Starting with 1000 lb of water in a solution at H on the solubility diagram in Fig. 18-57, calculate the yield on evaporative cooling and concentrate the solution back to point H so the cycle can be repeated, indicating the amount of NaCl precipitated and the evaporation and dilution required at the different steps in the process. 

Air Temperature A simple thermocouple can be used in most cases, but in some cases special care must be taken to ensure that wet or sticky material does not build up on the thermocouple. A wet thermocouple will yield a low temperature from evaporative cooling. 

Solution. The yield from a cooling and evaporating crystallizer is given by Eq. (11.3-5) ... 

Add 4 0 g. (4 0 ml.) of pure anihne dropwise to a cold solution of ethyl magnesium bromide (or iodide) prepared from 1 Og. of magnesium, 5 0 g. (3-5 ml.) of ethyl bromide (or the equivalent quantity of ethyl iodide), and 30 ml. of pure, sodium-dried ether. When the vigorous evolution of ethane has ceased, introduce 0 02 mol of the ester in 10 ml. of anhydrous ether, and warm the mixture on a water bath for 10 minutes cool. Add dilute hydrochloric acid to dissolve the magnesium compounds and excess of aniline. Separate the ethereal layer, dry it with anhydrous magnesium sulphate and evaporate the ether. Recrystallise the residual anihde, which is obtained in almost quantitative yield, from dilute alcohol or other suitable solvent. 

In a typical procedure, a solution of 0.175 mmol of L- -amino acid and 0.175 mmol of NaOH in 1 ml of water was added to a solution of 0.100 mmol of Cu(N03)2in 100 ml of water in a 100 ml flask. Tire pH was adjusted to 6.0-6.5. The catalyst solution was cooled to 0 C and a solution of 1.0 mmol of 3.8c in a minimal amount of ethanol was added, together with 2.4 mmol of 3.9. The flask was sealed carefully. After 48 hours of stirring at 0 C the reaction mixture was extracted with ether, affording 3.10c in quantitative yield After evaporation of the ether from the water layer (rotary evaporator) the catalyst solution can be reused without a significant decrease in enantioselectivity. 

Example 1 Yield from a Crystallization Process A 10,000-lh batch of a 32,5 percent MgS04 solution at 120°F is cooled without appreciable evaporation to 70°F, What weight of MgS04-7H20 crystals will be formed (if it is assumed that the mother liquor leaving is saturated) ... 

The contents of the flask are transferred to a separatory funnel while still hot and washed three times with 200-cc. portions of hot water to remove the sodium laurate (Note 7). The lauryl alcohol is extracted with ether from the cooled mixture and the washings. The combined ether extracts are washed with water, sodium carbonate solution, and again with water, and dried over anhydrous magnesium sulfate. The ether is evaporated and the lauryl alcohol distilled under diminished pressure. The yield is 60-70 g. (65-75 per cent of the theoretical amount) of a product boiling at i43-i46°/i8 mm. or i98-2oo°/i35 mm. (Note 8). 

Solvent evaporation in a rotary evaporator afforded the amino alcohol product (4.14g, 90% yield). The purity of the crude product is high enough to be used in the catalysis experiments, but it can be purified further by vacuum distillation in a Kugelrohr [90-100 °C, 0.030-0.035 mbar] cooling the recipient flask with dry ice (84% yield from the amino ester, as white needles). 

Method C (dichlorination) TMBA-IC14 (4.18 g, 10 mmol) is stirred with the acetophenone (5 mmol) in AcOH (50 ml) at 70°C for 5 h. BTMA-IC12 is collected by filtration from the cooled mixture and aqueous NaHS03 (5%, 10 ml) and NaHC03 (5%, 80 ml) are added to the concentrated filtrate. The aqueous mixture is extracted with Et20 (4 x 40 ml) and the dried (MgS04) extracts are evaporated to yield the dichloroacetyl derivative (Table 2.17). 

B. 1,4-Cyclohexanedione. The purified 2,5-dicarbethoxy-l,4-cyclohexanedione (170 g., 0.66 mole) (Note 5) and 170 ml. of water are placed in a glass liner (vented) of a steel pressure vessel of 1.5-1. capacity (fitted with a pressure-release valve). The vessel is sealed, heated as rapidly as possible to 185-195°, and kept at this temperature for 10-15 minutes (Note 6). The reaction vessel is immediately removed from the heater, placed in a large tub of ice water, and cooled to room temperature. The gas pressure then is carefully released. The resulting yellow to orange liquid is transferred to a distillation flask with the aid of a minimum volume of ethanol, and most of the water and ethanol is removed under reduced pressure by means of a rotary evaporator. The flask is attached to a short heated column fitted with a short air condenser. The remainder of the water and ethanol is removed under reduced pressure, and the 1,4-cyclohexanedione is distilled, b.p, 130-133° (20 mm.). The product solidifies to a white to pale-yellow solid, m.p. 77-79°, deld 60-66 g. (81-89% yield from 2,5-dicarbethoxy-l,4-cyclohexanedione). The compound may be conveniently recrystallized from carbon tetrachloride (7 ml. per gram of dione) the purified product is obtained as white plates, m.p. 77-79° (90% recovery). 

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