Chemical Stability 2 Flashcards
What is oxidation defined as?
Addition of O
Removal of H
Loss of e-
What is reduction refined as?
Removal of O
Addition of H
Addition of e-
What is autooxidation?
Molecular oxygen (O2) is the ultimate source
Formation of reactive oxygen species (ROS)
What does activation of ground state molecular O produce?
Range of ROS
What is a free radical?
Has unpaired e-
What are the 2 key reactions of radicals?
Fenton
Udenfriend
What is a Fenton reaction?
Generated .HO radicals
What is a Udenfriend reaction?
Complex multistep process
What can hydrogen peroxide undertake oxidation reactions on?
Povidone
PEG
What is the original component in Udenfriend reaction?
Fe2+
EDTA (metal chelator)
Ascorbic acid (reducing agent)
What is phenol/catechol oxidised to?
Quinone
What is phenol oxidised to?
Dimeric products
What is amines oxidised to?
N-oxides
What is thioether oxidised to?
S-oxide
What is thiol oxidised to?
Disulphide
What does a “fish hook” arrow show?
1 e- going to A + other goes with B
Describe 7 valence electrons
(radical)
Same as carbocation = sp2
Describe the stability of radicals from methyl to tertiary
Increase
What are the steps in radical formation?
Initiation
Propagation
Termination
What is a good oxidation initiation?
Light, UV light
What are susceptible to C-H oxidation?
Ethers
Aliphatic amines
Aldehydes
What are susceptible to O-H + N-H oxidation?
Phenols
Aromatic amines
How can you minimise oxidation by preventing inititation?
Protect from light
Limit peroxides
Use optimum pH
Add chelating agent to remove metal ions
How can you minimise oxidation by stopping oxidation?
Pack under inert gas - eg. nitrogen
Add antioxidant
What is oxidation via atmospheric oxygen a significant issue for?
Proteins
Proteins in solution
Freeze-dried samples
Amino acids
Describe no-radical reactions of peroxides
H2O2 can act as a precursor
To hydroxyl radical
BUT can also directly oxidise amines + sulphides
SN2 reaction
When is oxidation observed with aromatic amines?
X = H = oxidation
X = EDG = oxidation
X = EWG = NO oxidation
What do COOH produce under hydrogen peroxide?
Carboxyl peracids
What do bicarbonate produce under hydrogen peroxide?
Peroxymonocarbonate
What do nitriles produce under hydrogen peroxide?
Peroxycarbimidic
Describe the oxidation of thioethers by hydrogen peroxide
Nu- attack by sulphur on peroxide
Yields sulfoxide