Chemical Stability 2

Question 1

What is oxidation defined as?

Answer 1

Addition of O
Removal of H
Loss of e-

Question 2

What is reduction refined as?

Answer 2

Removal of O
Addition of H
Addition of e-

Question 3

What is autooxidation?

Answer 3

Molecular oxygen (O2) is the ultimate source
Formation of reactive oxygen species (ROS)

Question 4

What does activation of ground state molecular O produce?

Answer 4

Range of ROS

Question 5

What is a free radical?

Answer 5

Has unpaired e-

Question 6

What are the 2 key reactions of radicals?

Answer 6

Fenton
Udenfriend

Question 7

What is a Fenton reaction?

Answer 7

Generated .HO radicals

Question 8

What is a Udenfriend reaction?

Answer 8

Complex multistep process

Question 9

What can hydrogen peroxide undertake oxidation reactions on?

Answer 9

Povidone
PEG

Question 10

What is the original component in Udenfriend reaction?

Answer 10

Fe2+
EDTA (metal chelator)
Ascorbic acid (reducing agent)

Question 11

What is phenol/catechol oxidised to?

Answer 11

Quinone

Question 12

What is phenol oxidised to?

Answer 12

Dimeric products

Question 13

What is amines oxidised to?

Answer 13

N-oxides

Question 14

What is thioether oxidised to?

Answer 14

S-oxide

Question 15

What is thiol oxidised to?

Answer 15

Disulphide

Question 16

What does a “fish hook” arrow show?

Answer 16

1 e- going to A + other goes with B

Question 17

Describe 7 valence electrons
(radical)

Answer 17

Same as carbocation = sp2

Question 18

Describe the stability of radicals from methyl to tertiary

Answer 18

Increase

Question 19

What are the steps in radical formation?

Answer 19

Initiation
Propagation
Termination

Question 20

What is a good oxidation initiation?

Answer 20

Light, UV light

Question 21

What are susceptible to C-H oxidation?

Answer 21

Ethers
Aliphatic amines
Aldehydes

Question 22

What are susceptible to O-H + N-H oxidation?

Answer 22

Phenols
Aromatic amines

Question 23

How can you minimise oxidation by preventing inititation?

Answer 23

Protect from light
Limit peroxides
Use optimum pH
Add chelating agent to remove metal ions

Question 24

How can you minimise oxidation by stopping oxidation?

Answer 24

Pack under inert gas - eg. nitrogen
Add antioxidant

Question 25

What is oxidation via atmospheric oxygen a significant issue for?

Answer 25

Proteins Proteins in solution Freeze-dried samples Amino acids

Question 26

Describe no-radical reactions of peroxides

Answer 26

H2O2 can act as a precursor To hydroxyl radical BUT can also directly oxidise amines + sulphides SN2 reaction

Question 27

When is oxidation observed with aromatic amines?

Answer 27

X = H = oxidation X = EDG = oxidation X = EWG = NO oxidation

Question 28

What do COOH produce under hydrogen peroxide?

Answer 28

Carboxyl peracids

Question 29

What do bicarbonate produce under hydrogen peroxide?

Answer 29

Peroxymonocarbonate

Question 30

What do nitriles produce under hydrogen peroxide?

Answer 30

Peroxycarbimidic

Question 31

Describe the oxidation of thioethers by hydrogen peroxide

Answer 31

Nu- attack by sulphur on peroxide Yields sulfoxide