Hard to swallow dry: Kinetics and mechanism of the anhydrous thermal decomposition of acetylsalicylic acid

The methods of thermal analysis and mass spectrometry have been used to study the kinetics and mechanism of the anhydrous thermal decomposition of acetylsalicylic acid. Both thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) show that decomposition occurs in two steps. Mass...

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Bibliographic Details
Published in:Journal of pharmaceutical sciences 2002-03, Vol.91 (3), p.800-809
Main Authors: Long, Gregory T., Vyazovkin, Sergey, Gamble, Nicoleigh, Wight, Charles A.
Format: Article
Language:English
Subjects:
acetylsalicylic acid
Algorithms
Analgesics
Anti-Inflammatory Agents, Non-Steroidal - administration & dosage
Anti-Inflammatory Agents, Non-Steroidal - chemistry
aspirin
Aspirin - administration & dosage
Aspirin - chemistry
Biological and medical sciences
Calorimetry, Differential Scanning
decomposition
Drug Stability
Excipients
Humidity
isoconversional method
Kinetics
mechanism
Medical sciences
Neuropharmacology
Pharmacology. Drug treatments
Pressure
shelf-life
Starch
Stearic Acids
Tablets
Temperature
thermal analysis
Thermodynamics
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Summary:The methods of thermal analysis and mass spectrometry have been used to study the kinetics and mechanism of the anhydrous thermal decomposition of acetylsalicylic acid. Both thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) show that decomposition occurs in two steps. Mass‐spectrometric analysis of the residue left after the first decomposition step (≈60% mass loss) suggests that in the condensed phase, acetylsalicylic acid decomposes by first forming linear oligomers that are further converted into cyclic oligomers. Model‐free isoconversional kinetic analysis of TGA traces has been used to determine global activation energies as a function of the extent of reaction. This method of analysis has also been used to make kinetic predictions of shelf life at ambient temperatures (20–40°C) under anhydrous conditions for acetylsalicylic acid. Our estimate of a shelf life of 876 days (≈2.4 years) for 5% decomposition at 30°C is in good agreement with shelf lives of 2–3 years that are stamped on over‐the‐counter aspirin bottles. Hence, this approach can be used to systematically study the factors that determine the decomposition kinetics of aspirin and may be used for express screening of pharmaceuticals in order to identify those with desirable thermal stabilities. © 2002 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:800–809, 2002
ISSN:0022-3549
1520-6017
DOI:10.1002/jps.10029