Synthesis of anhydrous acetic acid
Entry posted by crazyboy25
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Anhydrous acetic acid often referred to as glacial acetic acid or ethanolic acid is a useful acid that is found in vinegar. Glacial acetic acid (GAA) can be made by oxidizing ethanol with a mixture of potassium dichromate and sulfuric acid (also known as chromic acid) but it is much easier to make it by distillation of an acetate salt and an acid. Sodium acetate is used as a source of acetate ions because it is cheap and easy to make. Sulfuric acid is used as a source of hydrogen ions because it has a high boiling point and won’t contaminate the product.
Step 1: synthesis if sodium acetate
Step 2: synthesis of acetic acid by distillation of sulfuric acid and sodium acetate
Step 3: desiccation of acetic acid to yield GAA
Step 1: synthesis if sodium acetate
Sodium acetate is easily made by slowly adding sodium bicarbonate to vinegar until it stops foaming. An excess of vinegar is used because it will boil away and not contaminate the product. When all the sodium bicarbonate has been reacted with the vinegar and the solution is slightly acidic the mixture is boiled until it begins to crystallize. The wet crystals are placed in a glass tray and heated in the oven at about 500 F until they are completely dry. The now anhydrous sodium acetate is powdered and sealed in an airtight container.
Step 2: synthesis of acetic acid by distillation of sulfuric acid and sodium acetate
2NaCH3COO+H2SO4=2CH3COOH+Na2SO4
The stochimetric amount of sodium acetate to sulfuric acid is 50g sodium acetate to 29.7g sulfuric acid. But this mixture was found to produce lower yields over long periods of time so the amount of sulfuric acid was changed to 50g.
50g of powdered sodium acetate are added to a 500ml round bottom flask.
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To this is added 50 grams concentrated sulfuric acid. Dense white fumes smelling strongly of acetic acid are evolved.
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The flask is attached to a distillation set up to which heat is applied until the white fumes dissipate and a clear liquid begins to distill over at about 110 C.
Soon all that remains in the flask is charred organic material from the sodium acetate and sodium sulfate.
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Step 3: desiccation of acetic acid to yield GAA
40ml of acetic acid from the previous step were added to a 500ml round bottom flask to which was added a small spoonful of anhydrous magnesium sulfate (formed by heating Epsom salt at 500 F for 2-3 hours).
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The mixture was distilled almost to dryness and the distillate was collected. I store the GAA in my freezer.
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