Acetic acid sulfur dioxide removal

Lead acetate is more satisfactory than sulfur dioxide for the removal of selenious acid, provided that the solution is kept cool and a large excess is avoided. 

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). 

The current method (3, 4, 6, 22) involves steam distillation to separate the volatile (primarily acetic) acids from the non-volatile (fixed) acids. Special equipment has been devised for this separation (6). Sulfurous and sorbic acid content can be corrected, or the sulfurous acid may be removed (33). Carbon dioxide must be removed so that it does not interfere with the test (6, 33). An automated procedure is also available (34) which measures the volatile acids in the distillate at 450 nm using bromophenol blue. 

A more detailed study of the reaction showed that direct iodination takes place when the hydriodic acid formed in the reaction is neutralized by the addition of alkali,280 hypoiodous acid,559-570 or sodium acetate.671, 572 In order to introduce a second iodine atom, Derbyshire and Waters573 used excess iodine in the presence of silver nitrate and nitric acid and obtained 1,4,5-triiodopyrazole. The iodine atom in the 1-position was readily removed by the action of sulfur dioxide or hydriodic acid. Further treatment of 4,5-diiodopyrazole gave 1,3,4,5-tetraiodopyrazole and hence 3,4,5-triiodopyrazole. Methylation of the nitrogen atom facilitates iodination of the ring.571... 

A) Preparation of Ethyl Acetate (Sm.). Place in an eight-inch tube 5 ml of ethanol, 5 ml of glacial acetic acid, and 0.5 ml (7-8 drops) of sulfuric acid. Insert a micro condenser in the tube arranged for reflux, and heat for 0.5 hours. Remove the reflux condenser and distill from a water bath until no more distillate passes over. The distillate consists of ethyl acetate and small amounts of acetic acid, ethanol, water, and sulfur dioxide. The latter was formed by the oxidizing action of the sulfuric acid. Add 2 ml of a saturated solution of sodium carbonate to the mixture in the re-... 

The distillate contains ethyl acetate, and small amounts of alcohol, acetic acid, ether, water, and sulfur dioxide. Transfer the distillate into a separatory funnel, and add small amounts of a saturated solution of sodium carbonate until the upper layer is no longer acid (test with litmus). Remove the lower aqueous layer. The remaining layer contains the ester and a small amount of ethanol. Shake with 10 ml of concentrated calcium chloride solution to remove traces of alcohol. Dry the ester with 6 g of anhydrous magnesium sulfate, then transfer to a distilling flask and fractionate. The portion which boils below 73° is rejected. The fraction boiling at 73-80° is collected. The yield is about 40-50 g. 

Removal of selenium and selenious acid. Use of selenium dioxide or selenious acid as an oxidant is attended with the difficulty of freeing the reaction mixture of colloidal selenium and of excess oxidant. A procedure for the oxidation of paraldehyde to glyoxal and isolation of the product as the bis-bisulfite addition compound specifies use of lead acetate as more satisfactory for the removal of selenious acid than sulfur dioxide, provided that the solution is kept cool and a large excess is avoided. A... 

Dimethylketene Acetic anhydride (25 g), dimethylmalonic acid (6.5 g), and concentrated sulfuric acid (1 drop) are placed in a dry Claisen flask dissolution occurs when the mixture is shaken. The solution is set aside at room temperature for 2 days, then a little powdered barium carbonate is added and the acetic acid and anhydride are removed by gentle heating in a vacuum. A new receiver is then attached and this is cooled in ice. The temperature is then gradually raised to about 100°, whereupon the dimethylmalonic anhydride decomposes with evolution of carbon dioxide and distillation of the dimethylketene produced. The yield is 65% (2.3 g) and the b.p. 34°. 

The above substitutes for the iodometric determination with one or two exceptions have not been tested for specificity for free SO2. Mathers (1949) on the basis of the fact that free sulfur dioxide is removed early in the distillation of wine proposed that 10 ml. of the distillate from the alcohol determination be mixed with 0.5 ml. of 5% neutral lead acetate and the turbidity of the suspension formed be used to correct volatile acidity for sulfur dioxide. La Rosa (1950) assumed that the color formed on mixing the fuchsin-sulfuric acid-formaldehyde reagent with white wine was a measure of free SO2 but did not give any data to confirm this. The fuchsin procedure and the lead sulfite procedures are very sensitive, the former more so, and can be applied only to very small aliquots or to dilute solutions. 

In pyridine and with a suitably blocked derivative, the same reagent can be used selectively to introduce sulfate acid ester groups thus, 1,2 5,6-di-O-isopropylidene-D-glucose can be sulfated, and, on removal of the cyclic acetal groups, D-glucose 3-sulfate can be obtained as a suitable salt. Sulfur trioxide or chlorosulfonic acid in liquid sulfur dioxide, and sulfur trioxide in halogenated hydrocarbon solvents, pyridine, or iV,A -dimethylforma-mide, can also be employed for sulfation. 

The following acids are recommended for this type of catalyst removal sulfuric acid [9, 765], carbon dioxide [154, 155] and carboxylic acids such as oxalic acid [156, 766, 767], formic acid [157-160, 768, 769, 780] acetic acid [160, 769-772], propionic acid, fumaric acid and maleic acid [775, 776]. 

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