Potassium hydroxide brines

At present about 77% of the industrial hydrogen produced is from petrochemicals, 18% from coal, 4% by electrolysis of aqueous solutions and at most 1% from other sources. Thus, hydrogen is produced as a byproduct of the brine electrolysis process for the manufacture of chlorine and sodium hydroxide (p. 798). The ratio of H2 Cl2 NaOH is, of course, fixed by stoichiometry and this is an economic determinant since bulk transport of the byproduct hydrogen is expensive. To illustrate the scde of the problem the total world chlorine production capacity is about 38 million tonnes per year which corresponds to 105000 toimes of hydrogen (1.3 x I0 m ). Plants designed specifically for the electrolytic manufacture of hydrogen as the main product, use steel cells and aqueous potassium hydroxide as electrolyte. The cells may be operated at atmospheric pressure (Knowles cells) or at 30 atm (Lonza cells). 

The apparatus consists of a 3-]. three-necked flask fitted with a mercury-sealed mechanical stirrer, a reflux condenser, a dropping funnel, and a thermometer which reaches almost to the bottom of the flask. Five hundred grams of potassium hydroxide pellets (85 per cent potassium hydroxide) (7.5 moles) and 750 cc. of commercial absolute methyl alcohol (free from acetone) are placed in the flask and stirring begun. The bulk of the alkali dissolves in a few minutes, with the evolution of heat. The flask is now surrounded by an ample cold-water bath, and, when the internal temperature drops to 6o°, addition of a mixture of 360 g. (353 cc., 3 moles) of -tolualdehyde (Note 1), 300 cc. of formalin (3.9 moles) (Note 2), and 300 cc. of absolute methyl alcohol is begun at such a rate that the internal temperature remains at 60-70°. This addition requires about fifteen minutes. The internal temperature is then maintained at 60-70° for three hours, after which the reflux condenser is replaced by a downward condenser, and the methyl alcohol distilled with the aid of a brine bath until the internal temperature reaches ioi°. Nine hundred cubic centimeters of cold water is then added to the warm residue, and the mixture cooled. The resulting two layers are separated at once (Note 3), and the aqueous layer extracted with three 200-cc. portions of benzene. The combined oil and extracts are washed with five or six 50-cc. portions of water (Note 4), and the combined washings extracted... 

Acetanilide (13.5 g), (substituted) aromatic bromide (25 g), potassium carbonate (13.2 g), and copper iodide (1.9 g) were heated (190°C) and stirred overnight. After cooling to room temperature toluene was added and the precipitate filtered. The solution was concentrated and the excess of bromide removed by distillation under reduced pressure. The residue was dissolved in ethanol (200 mL), potassium hydroxide (10.3 g) was added, and the mixture refluxed overnight. Ethanol was evaporated, the residue dissolved in dichloromethane, and washed with brine. The organic layer was dried over MgS04 and concentrated to obtain the crude diphenylamine. 

Potassium hydroxide is produced commerically by electrolysis of a saturated solution of potassium chloride in brine using mercury cells consisting of a titanium anode and mercury cathode. Potassium reacts with mercury forming the amalgam which, on treatment with water, forms potassium hydroxide and hydrogen. 

The acidic aqueous layer from the aqueous acetic acid/sodium acetate/pentane hydrolysis of 2-alkylcyclo-hexanonc imines is neutralized with solid potassium hydroxide to pH 14, and then saturated with sodium chloride. This aqueous solution is extracted with four portions of diethyl ether, and the combined ethereal layer is washed with brine. Drying over potassium carbonate and concentration gives an oil which is distilled 85% recovery bp 57-59 °C/0.02 Torr [x]D — 13.75 (c = 5.8, benzene). If the rotation of the distilled amine is lower than 13.40, it is purified via its hydrochloride. Thus, a solution of the amine in ice-cold diethyl ether is treated with dry hydrogen chloride by bubbling through a fritted disk. The amine hydrochloride is collected by filtration and recrystallized from ethanol mp 151-152°C. 

To a stirred solution of benzoyloxy(tcrt-butyl)methylphosphine-borane (99% ee, 6.06 g, 24 mmol) in acetone (25 mL) was added a solution of potassium hydroxide (4.0 g, 72 mmol) in water (15 mL) dropwise. After completion of the hydrolysis (ca. 1 h), the reaction mixture was diluted with water (lOOmL) and extracted three times with diethyl ether. The combined extracts were washed with brine and dried over Na2S04. The solvent was evaporated and the resulting crude (/f)-tert-butyl(hydroxymethyl)methylphosphine-borane was dissolved in acetone (70 mL). The solution was added to a vigorously stirred, cooled (0°C)... 

The step 5 product (9.33 mmol) was dissolved in 80 ml THF and 20 ml methanol and treated with concentrated hydrochloric acid (25 drops) and stirred at ambient temperature for 2 hours. Potassium hydroxide (334 mmol) dissolved in 100 ml water was added to the solution, which was stirred vigorously at 80°C for 5 hours. The basic solution was neutralized with hydrochloric acid to pH 8 and the solution concentrated to a brown oil. The oil was treated with 100 apiece of ethyl acetate and brine and the organic layer collected. The brine layer was washed twice with 100 ml ethyl acetate. Combined organic layers were washed once with 100 ml brine, dried over MgS04, and a white solid isolated after the mixture was concentrated. The solid was triturated with hot CHC13 for 5 minutes, filtered, washed with additional hot CHC13, dried under vacuum overnight at 80°C, and the product isolated. 

A. Trimethyl 2-chloro-2-cyclopropylidenorthoacetate. A 1-L, two-necked, round-bottomed flask equipped with a mechanical stirrer and a reflux condenser is charged with 40.0 g (0.19 mol) of 1-chloro-1-(trichloroethenyl)cyclopropane (Note 1), 120 g of potassium hydroxide, and 300 mLof methanol (Note 2). The mixture is stirred for 16-18 hr in an oil bath at 85°C. After the solution is cooled to room temperature, it is diluted with 1 L of ice water. The mixture is then transferred to a 3-L separatory funnel and extracted with three 200-mL portions of ether. The combined ether phases are washed with three 150-mL portions of saturated brine, dried over anhydrous magnesium sulfate, and filtered. The solvent is removed from the filtrate by distillation at atmospheric pressure, and the residue is distilled through a short-path column under water-aspirator vacuum to give 14.5-15.4 g (39-41%) of trimethyl 2-chloro-2-cyclopropylidenorthoacetate, bp lOS-IOS C (20 mm) (Notes 3 and 4). 

The chiral methoxyamine is recovered from the aqueous solution by neutralisation with solid potassium hydroxide and extraction with ether. The ethereal extract is washed with brine, dried over potassium carbonate and concentrated to give the crude chiral amine in 80-88 per cent yield. Distillation affords the pure amine (70-75% recovery) with [a] values which indicate that no racemisation has occurred. 

The manufacture of potassium hydroxide by the diaphragm methode starts from a solution containing some 370 g KC1 per litre the hydroxide solution thus obtained will contain some 180 g KOH per litre. The amalgam electrolysis uses a solution containing 350 g KC1 per litre, the depleted spent brine usually contains about 290 g KC1 per litre. 

The technological process for purifying brine is almost identical with both diaphragm and mercury cell methods of the manufacture of either sodium or potassium hydroxide. Therefore, it is sufficient to describe only the preparation of brine in the manufacture of sodium caustic by the amalgam method. 

Particular attention must be paid to the purification of brine when manufacturing potassium hydroxide, as potassium amalgam is much more sensitive to impurities (Mg, Ca, heavy metals) than sodium amalgam. 

Potassium hydroxide (4.0 mmol) dissolved in 4 ml water was added to an optically active imine (1.0 mmol) dissolved in 5 ml THF and the mixture stirred at ambient temperature 20 hours. Thereafter, 2 ml 10% HCl was added, the solution made acidic, and the mixture extracted with diethyl ether. The organic layer was washed with brine, dried, concentrated, the residue either recrystallized from pentane or purified by chromatography using hexane/EtOAc, 10 1, and the product isolated. 

The first electrolytic production of chlorine was by the electrolysis of a potassium chloride brine with coproduction of potassium hydroxide by the... 

The cell was loaded with saturated potassium chloride brine, indirectly heated to 80-90°C with steam pipes, and then a current of about 3500 A was passed through the cell for a period of 3 days. During this time, the chlorine and hydrogen produced were collected, and the potassium hydroxide concentration in solution rose to about 7% (Eqs. 8.9 and 8.11). 

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