Acetylsalicylic acid

 

Acetylsalicylic acid
aka Aspirin

Chemical formula	C9H8O4
OTP appearance	white solid
Density(g/cc)	1.4
Melting Point(°C)	135
Boiling Point(°C)	140
Immediate Danger to Life and Health	150mg/kg
NFPA 704	0 0 0

Acetylsalicylic acid is included in WHO, DHS, and EMS and is used to treat pain, fever, and/or inflammation. Specific inflammatory conditions which aspirin is used to treat include Kawasaki disease, pericarditis, and rheumatic fever. Aspirin given shortly after a heart attack decreases the risk of death. Aspirin is also used long-term to help prevent further heart attacks, ischaemic strokes, and blood clots in people at high risk. It is usually administered orally.

Uses

Primary

• Pharm: Used in the medication aspirin on multiple formularies

Natural Occurrence

• Related compounds occur naturally

Hazards

• 150 mg/kg of body mass is toxic.
• 500 mg/kg is deadly

Production

Synthesis

From methyl salicylate

• React Methyl salicylate with sodium hydroxide giving sodium salicylate, methanol and water.

  C₈H₈O₃ + NaOH → NaC₇H₅O₃ + CH₃OH

• React sodium salicylate with acetyl chloride producing acetysalicylic acid and salt

NaC₇H₅O₃ + C₂H₃OCl → C₉H₈O₄ + NaCl

The aspirin can be separated by precipitating it, since salt is 100x more soluble in water. (359g/L vs 3g/L)

From salicylic acid

via acetic acid

• React salicylic acid with a large excess of dry acetic acid in the presence of a dehydrating agent, such as sulfuric acid, giving acetylsalicylic acid and acetic acid.

  C₆H₄(OH)COOH + CH₃COOH

  {H₂SO₄

  →

  50-70°C}

  C₉H₈O₄ + H₂O

• Add cold water and place in an ice bath to crystallize the acetylsalicylic acid
• Filter
• Retain residue (acetylsalicylic acid)
• Retain filtrate for other batches (recycle mother liquor)

via acetic anhydride

• React salicylic acid with acetic anhydride, giving acetylsalicylic acid and acetic acid. Small amounts of sulfuric acid (and occasionally phosphoric acid) are often used as a catalyst.

  C₆H₄(OH)COOH + (CH₃CO)₂O

  {H₂SO₄

  →

  }

  C₉H₈O₄ + CH₃COOH

Purification

1. Dissolve in minimal hot ethanol
2. Add 3-4 volumes of cold water
3. Filter, discard filtrate

Testing

• Melting point
• For the FeCl3 test, the samples do not have to be dry. To do the test, get 4 test tubes. Place 1 mL of ethanol and 2 drops of FeCl3 solution in each tube. Add a few crystals of salicylic acid to one test tube. Add a few crystals of your crude aspirin product to the second tube. In the third tube, place a few crystals of the recrystallized aspirin. Don’t add anything else to the fourth tube – it will be your control. Shake each of the tubes and record your observations.

See Also

• Paracetamol
• Ibuprofen