1. Antioxidants

2. Anti-oxidant “ They are the reducing agents which are added to the drugs or other pharmaceuticals to prevent their oxidation through oxidative processes.” Anti-oxidants undergo oxidation more readily than the drugs or other pharmaceuticals with which they are present. The anti-oxidant usually prevents oxidation of active compounds and in place gets oxidised itself. Anti-oxidants are mainly used in pharmaceutical preparations containing readily oxidisable substances to present them in their original form.

3. Antioxidants or Preservatives ? ? ?

4. Criteria for Anti-oxidants The anti-oxidants themselves or their reduction products should not be toxic and harmful to the human body. In order to attain prolonged stability, the anti-oxidants should undergo oxidation quite slowly but more readily than the drugs which are to protect from oxidation. They should be physiologically and chemically compatible. They should be chemically inert. They should not pose any solubility problem in either reduced or oxidized form. A strong anti-oxidant will protect the material when used in small amount and for longer period.

5. What is an ION? Ion: An atom or molecule that has acquired an electrical charge by either gaining or losing electrons.atommoleculeelectrical charge electrons - A cation is an ion that has lost electrons and acquired a positive charge.cationelectrons - An anion is an ion that has gained electrons and acquired a negative charge.anionelectrons

6. Mechanism of action The mechanism of action of inorganic anti- oxidants happens to be the same as it is involved in redox chemical reaction. In redox reaction there occurs transfer of electron from one compound to other. – An oxidation involves the loss of electrons from chemical species and reduction involves the gain of electrons. – The overall reaction can be shown as: OX + e -  RED Contd…

7. It is possible to determine the efficacy of chemical substance to undergo oxidation-reduction by electrode system. The electrical potential developed in cell can be measured by voltmeter and the measurement of electrode potential can be done by the Nernst equation: E cell = E ͦ cell - 0.0591 log [OX] n [Red] Where, E cell is potential of cell in volts E° cell is standard potential n is number of electrons involved [OX]/[Red] is ratio of concentration of oxidant and reductant respectively.

8. Hypophosphorus acid Formula: H 3 PO 2 Preparation: (1)Ba(H 2 PO 2 ) 2 + H 2 C 2 O 4  BaC 2 O 4 + 2H 3 PO 2 Barium oxalic acid hypophosphite (2) Ca(H 2 PO 2 ) 2 + H 2 SO 4  CaSO 4 + 2H 3 PO 2 (3) For pure Hypophosphorus acid: KH 2 PO 2 + C 4 H 6 O 6  H 3 PO 2 + KHC 4 H 4 O 6 potassium tartric acid potassium hypophosphite bitartrate

9. Properties: - Clear yellowish liquid having slight acidic odour & taste - Syrupy in nature but forms crystalline solid at 17.4°C. - It is miscible with water and alcohol - It exhibits 2 important chemical properties: (i) Acidic properties: It acts as monobasic acid because only one hydrogen is ionizable. HPH 2 O 2 + H 2 O  H 3 O + + PH 2 O 2 - The acid can be neutralised with alkali hydroxides or carbonates e.g. 2HPH 2 O 2 + Na 2 CO 3  2NaPH 2 O 2 + H 2 O + CO 2

10. (ii) Reducing properties: It is able to reduce many compounds to form phosphorus acid H 2 PHO 3 and finally to phosphoric acid (H 3 PO 4 ). Thus, with iodine it forms iodide ions and it is able to decolourise acidic solution of KMnO 4. HPH 2 O 2 +2I 2 + 2H 2 O  4HI + H 3 PO 4 Assay: Acid-base titration method An accurately weighed amount (5g) of the sample is diluted with 50ml of water. Then, it is titrated with 0.5N NaOH using methyl orange as an indicator.

11. Uses: -It do not possess any significant pharmacological actions, so it finds use as an antioxidant (0.5-1%) in p’ceutical preparations. -It is mainly used in syrup of ferrous iodide where it does not allow the formation of ferric ions and colouration. -Hypophosphates are a source of phosphorus and regarded to be a brain tonic. Storage: - It should be stored in well closed container.

12. Sodium metabisulphite Formula: Na 2 S 2 O 5 Preparation: NaOH + SO 2(g)  NaHSO 3 2NaHSO 3  Na 2 S 2 O 5 + H 2 O When SO 2 is passed through a hot strong solution of NaOH until saturation, this compound is formed. Initially sodium bisulphite is formed which loses water and yields the metabisulphite on cooling. Because of the initial heat treatment, the product is also called pyrosulphite.

13. Properties: -Colourless, prismatic crystals or white powder which may become yellowish on keeping. -Sulphurous odour -Saline taste -Freely soluble in water forming sodium bisulphite -Slightly soluble in alcohol -The aqueous solution is acidic in nature and neutralises bases like Na 2 CO 3. -Strong reducing agent -Decolourises solutions of KMnO 4.

14. Assay: Basis: Oxidation-reduction mechanisms (Back titration) Burette:0.1N Na 2 S 2 O 3 Iodine flask:Sample solution + Excess (50ml) of I 2 solution + 1 ml HCl Indicator:Starch mucilage End-point:Blue-colourless

15. Action and uses: - As an antioxidant in the preservation of food materials. (Potassium salt is more preferred) - As a stabilizer in many injections to prevent oxidation of phenols, catechols and related compounds.(0.1%) -It is also used in oral preparations like syrup. -It may be inactivated by metal ions. A small amount of Na-EDTA may be added to it prevent such deterioration and make it more effective. -As it is a strong reducing agent, this is incompatible with many compounds which undergo reduction.

16. Sodium suphite Sodium bisulphite Sulphur dioxide Carbon dioxide