Sodium hydroxide solutions carbon dioxide removal with

Chill the concentrated solution of the amine hydrochloride in ice-water, and then cautiously with stirring add an excess of 20% aqueous sodium hydroxide solution to liberate the amine. Pour the mixture into a separating-funnel, and rinse out the flask or basin with ether into the funnel. Extract the mixture twice with ether (2 X25 ml.). Dry the united ether extracts over flake or powdered sodium hydroxide, preferably overnight. Distil the dry filtered extract from an apparatus similar to that used for the oxime when the ether has been removed, distil the amine slowly under water-pump pressure, using a capillary tube having a soda-lime guard - tube to ensure that only dry air free from carbon dioxide passes through the liquid. Collect the amine, b.p. 59-61°/12 mm. at atmospheric pressure it has b.p. 163-164°. Yield, 18 g. 

Manufacture. Aqueous sodium hydroxide, sodium bicarbonate, sodium carbonate, or sodium sulfite solution are treated with sulfur dioxide to produce sodium metabisulfite solution. In one operation, the mother Hquor from the previous batch is reinforced with additional sodium carbonate, which need not be totally in solution, and then is treated with sulfur dioxide (341,342). In some plants, the reaction is conducted in a series of two or more stainless steel vessels or columns in which the sulfur dioxide is passed countercurrent to the alkaH. The solution is cooled and the sodium metabisulfite is removed by centrifuging or filtration. Rapid drying, eg, in a stream-heated shelf dryer or a flash dryer, avoids excessive decomposition or oxidation to which moist sodium metabisulfite is susceptible. 

To a flame-dried, three-neck, 1-1 flask were added, in order, p-xylene (107 g, 1.0 mol), phosphorus trichloride (412 g, 3.0 mol), and anhydrous aluminum chloride (160 g, 1.2 mol). The reaction mixture was slowly heated to reflux with stirring. After 2.5 h at reflux, the reaction was allowed to cool to room temperature and the volatile components distilled at reduced pressure. The residual oil was slowly added to cold water (1 1) with stirring, and a white solid formed. The solid was removed by filtration, washed with water, and air dried. The solid was suspended in water (1 1) to which was added 50% sodium hydroxide solution (90 ml) to cause dissolution. The solution was saturated with carbon dioxide and filtered through Celite . The basic solution was washed with methylene chloride (200 ml) and acidified with concentrated hydrochloric acid (200 ml). The white solid that separated was isolated by extraction with methylene chloride (3 x 250 ml). The extracts were dried over magnesium sulfate, filtered, and evaporated under reduced pressure to give the pure 2,5-dimethylbenzenephosphinic acid (99 g, 60%) as an oil, which slowly crystallized to a solid of mp 77-79°C. 

To the crude diethyl o-nitrobenzoylmalonate is added a solution of 60 ml. of glacial acetic acid, 7.6 ml. of concentrated sulfuric acid, and 40 ml. of water, and the mixture is heated under reflux for 4 hours (Note 4) or until no more carbon dioxide is evolved. The reaction mixture is chilled in an ice bath, made alkaline with 20% sodium hydroxide solution, and extracted with several portions of ether. The combined ethereal extracts are washed with water and dried with anhydrous sodium sulfate followed by Drierite, and the solvent is removed by distillation. On fractional distillation of the residue, 27.0-27.4 g. (82-83%) of light-yellow o-nitroacetophenone boiling at 158-159°/16 mm. is obtained n 1.548, wg 1.551, df 1.236) (Note 5). 

In the AOAC procedure, a container s cap is punctured with a strong needle. The gas is then shaken out of the product and collected in a gas burette. The pressure is finally adjusted to atmospheric before the volume is read off the burette. Carbon dioxide can also be removed by dissolving it in sodium hydroxide solution any other gases in the container can also be measured in this way. 

While the distillation is continuing, two or three crystals of barium chloride are added to the distillate in the first Erlenmeyer flask. This distillate is then boiled gently for several seconds to remove carbon dioxide as well as to ascertain if any turbidity appears (Note 6). If the distillate remains clear, it is titrated with standard 0.01 N sodium hydroxide solution after addition of four to five drops of the phenolphthalein solution (Note 7). All further distillates are treated as described above. If less than 4ml of the standard alkali solution are required for the titration of the first distillate, the next 10ml of distillate is similarly titrated. If the acetic acid in the initial distillate consumes more than 4ml of standard alkali then three additional 5-ml distillates are collected and individually titrated as described above. When the indicator changes color upon the addition of the first drop of the alkaline solution, the analysis is complete. 

An example of this type of calculation is the assay of Lithium Carbonate Tablets BP. Lithium carbonate is used as an antidepressant in 250 mg and 400 mg strengths. The BP assay is to weigh and powder 20 tablets. Add a quantity of the powder containing 1 g of lithium carbonate to 100 mL of water add 50 mL of 1 M hydrochloric acid and boil for 1 minute to remove carbon dioxide. Cool and titrate the excess acid with 1 m sodium hydroxide solution using methyl orange as indicator. The assay is then repeated omitting the sample. 

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