Jump to content
APC Forum

Madscience workshop

  • entries
    4
  • comments
    13
  • views
    28821

Synthesis of anhydrous acetic acid


crazyboy25

5504 views

Do you like the new board better? Worse?  

65 members have voted

  1. 1. Do you like the new board better? Worse?

    • Its much better.
      30
    • Its a little better.
      13
    • There very similar.
      1
    • The old one was a little better.
      1
    • This one sucks.
      2

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.

 

http://i179.photobucket.com/albums/w318/crazyboy25/IMG_0102.jpg

 

To this is added 50 grams concentrated sulfuric acid. Dense white fumes smelling strongly of acetic acid are evolved.

 

http://i179.photobucket.com/albums/w318/crazyboy25/IMG_0103.jpg

 

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.

 

http://i179.photobucket.com/albums/w318/crazyboy25/IMG_0116.jpg

 

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).

 

http://i179.photobucket.com/albums/w318/crazyboy25/IMG_0135.jpg

 

The mixture was distilled almost to dryness and the distillate was collected. I store the GAA in my freezer.

 

http://i179.photobucket.com/albums/w318/crazyboy25/IMG_0137.jpg

6 Comments


Recommended Comments

You've got some really nice organic chemistry glassware... the condenser, heating mantles, round bottom flasks, etc. Did you buy these new or surplus? I've got a basic glassware set, but I definitely need to expand it a bit. Do you have any sources that you can recommend?
Link to comment
You've got some really nice organic chemistry glassware... the condenser, heating mantles, round bottom flasks, etc. Did you buy these new or surplus? I've got a basic glassware set, but I definitely need to expand it a bit. Do you have any sources that you can recommend?

 

Thanks. Beakers and flasks I got from Cynmar. All the rest I got on eBay (new), its not cheap but you can all the components of a distillation set up except a heating mantle for about $90. LabX, Chemglass and Ace glass all have a wide selection of products but the prices are outrageous.

Link to comment
Crazyboy, the very last picture... what is it? The remnants of the magnesium sulfate and GAA from the last distillation? Thanks for posting these processes; cool stuff!
Link to comment
crazyboy25

Posted

Crazyboy, the very last picture... what is it? The remnants of the magnesium sulfate and GAA from the last distillation? Thanks for posting these processes; cool stuff!

 

 

GAA, it has a very low freezing point and I find it easy to store in the freezer or refrigerator with some plastic wrap.

Link to comment
Mumbles

Posted

The dryest of the dry GAA should freeze on a cool day, about 60F (16C). It might even be getting slushy in my house right now.
Link to comment
oldmanbeefjerky

Posted

i cant imagine why anyone would need anhydrous acetic acid.
Link to comment
×
×
  • Create New...