Chapter 3 Pharmaceutical Aids and Necessities Official Antioxidants

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Question Answer
Standard buffer systemsdesigned to provide a solution having a specific pH for analytical purposes
Actual pharmaceutical buffersdesigned to maintain pH limits in drug preparations.
Standard Buffer SystemsDefinite pH, pH ranges from 1.2 to 10.0
Actual Buffer Systems • Designed to maintain pH limits
AntioxidantReducing Agents
Either the antioxidant is oxidized in place of the active constituent – If the active component is oxidized, the antioxidant reduces it back to its normal oxidation stateMechanisms of Action:Antioxidant

Hypophosphorus Acid, NF XIII

Question Answer
At ordinary temp, colorless, syrupy liquid or slightly yellow, odorless containing not less than 30% and not more than 32% of HPH2O2Physical Properties Hypophosphorus Acid
– Acidic properties (reaction?) – Reducing Properties • Readily oxidized to phosphoric acid. • Eg. Reaction with HI and water • Eg. Reaction with KMnO4 + H2SO4 – Decomposition of acid • When heated between 130o and 140oC, it decomposes into phosphorous acid and hydrogen phosphide (phosphine) (chemical equation?)Chemical Properties Hypophosphorus Acid
When heated between 130o and 140oC, it decomposes into phosphorous acid and hydrogen phosphide (phosphine) (chemical equation?) Decomposition of acid Hypophosphorus Acid
– When heated, it liberates spontaneously inflammable phosphine. – Yields white precipitate with HgCl2 TS. The precipitate becomes gray with an excess of hypophosphorus acid (?) – Gives red precipitate of Cu2H2 when warmed with CuSO4 TS.ID Tests Hypophosphorus Acid
– Hypophosphorus and its salts (hypophosphites) have no pharmacological actions – Antioxidant (0.5 to 1%): HI Syrup and FeI2 syrup – Preservatives in certain foodsUses Hypophosphorus Acid

Sulfur Dioxide, USP XVIII

Question Answer
– Colorless, nonflammable gas with strong suffocating, irritating, pungent odorPhysical Properties Sulfur Dioxide
Strong reducing agent (Oxidation state?) SO2 + I2 + H2O ? SO2 + KMnO4 + H2O ? – As the pH approaches neutral to alkaline values, SO2 is converted almost totally to bisulfite and sulfite.Chemical Properties Sulfur Dioxide
– Preservatives – Because of its gaseous state, it is usually used in injectable preparations enclosed in a single-dose ampules or multiple-dose vials. – Usual concentration: 0.1 – 1.0%Uses Sulfur Dioxide

Sulfur Bisulfite, USP XVIII

Question Answer
Sodium BisulfiteSodium Hydrogen Sulfite, Sodium Acid Sulfite
– USP: mixture of NaHSO3 and Na2S2O5 – White or yellowish crystals or a granular powder – Unstable to air, giving off SO2Physical Properties :Sodium Bisulfite
– Neutralized by acids (e.g. HCl) yielding sulfurous acid – Reducing AgentChemical Properties :Sodium Bisulfite
Metabisulfite (Na2S2O5) + waterCommercial Bisulfite (Preparation):
– Na – SulfiteOfficial ID Tests:Sodium Bisulfite
sulfites and bisulfites yield sulfur dioxide, which blackens filter paper moistened with mercurous nitrate.Sodium Bisulfite + With HCl, SO32- + 2HCl → SO2↑ + H2O + 2Cl- SO2↑ + (Hg)2(NO3)2 + 2H2O → 2Hg↓ + 2HNO3 + H2SO4
– Externally used against parasitic skin diseases – Internally used as antiseptic in gastric fermentationUses:Sodium Bisulfite

Sodium Metabisulfite, NF XIII

Question Answer
Sodium MetabisulfiteDisodium Pyrosulfite
– White crystal or white to yellowish crystalline powder – Contains an amount of Na2S2O5 not less than 66.0% and not more than 67.4% of SO2.Physical Properties
– Usually found in solutions of drugs that contain the phenol or catechol nucleus (phenylephrine and epinephrine) to prevent oxidation of these compounds to quinones. – Usual concentration: 0.1%Uses

Sodium Thiosulfate, USP XVIII

Question Answer
Sodium Thiosulfate• Sodium hyposulfite (misnomer) • Sodium hydrosulfite
– Odorless and has a cooling, bitter taste. – Efflorescent at above 23C – Deliquescent at moist air.Physical Properties :Sodium Thiosulfate
– Redox reaction (manifestation: decolorization)Chemical Properties:Sodium Thiosulfate
[1]S2O32- + 2HCl → S↓ + SO2↑ + H2O + 2Cl- [1-1]SO2↑ + (Hg)2(NO3)2 + 2H2O → 2Hg↓ + 2HNO3 + H2SO4 [2]2S2O32- + FeCl3 → [Fe(S2O3)2]- + 3Cl-Official ID Tests:Sodium Thiosulfate
it gives a white precipitate that soon turns yellow, and sulfur dioxide, which blackens filter paper moistened with Hg2(NO3)2 TS.Sodium Thiosulfate + With HCl
it produces a dark violet color that quickly disappears.Sodium Thiosulfate + With FeCl3 TS,
– Antidote for cyanide poisoning – Antidote for arsenical and heavy metal poisoning (without sound experimental basis)Pharmacology:Sodium Thiosulfate
– Infrequently used as a cathartic and as an antiseptic wash to combat ringworm and other parasitic skin diseases.Uses:Sodium Thiosulfate

Sodium Nitrite, USP XVIII

Question Answer
– Deliquescent when exposed to atmosphere and subsequently converted to sodium nitrate.Physical Properties:Sodium Nitrite
– Reducing Agent (KMnO4 + H2SO4) (nitric acid is the product) – Oxidizing Agent (acidified with H2SO4 + KI) (liberates iodine and NO) – Assay: • PermanganometryChemical Properties:Sodium Nitrite
evolve brownish-red fumes. The solution colors starch-iodide paper blue.Sodium Nitrite + Wit dil. mineral acids or with acetic acid, nitrites
[1]NO2- + HCl → HNO2 + Cl- 3HNO2 → HNO3 + 2NO↑ + H2O 2NO↑ + O2↑ → 2NO2↑ [2]NO2- + CH3COOH → HNO2 + CH3COO- 3HNO2 → HNO3 + 2NO↑ + H2O 2NO↑ + O2↑ → 2NO2↑ [3]HNO2 + starch-iodide → starch-iodo complexOfficial ID Tests:Sodium Nitrite
– Relaxes smooth muscle (esp smaller blood vessels) – Antidote for cyanide poisoningPharmacology:Sodium Nitrite
– Anti-Rust Tablets – Hypotensive Uses:Sodium Nitrite

Nitrogen, USP XVIII

Question Answer
NitrogenInert gas
• Can be used to protect chemicals, reagents, and pharmaceuticals from air oxidation by displacing the air in reaction vessels and containers.Properties:Nitrogen
– Retards oxidation of sensitive products (oil, vitamins, etc)Uses:Nitrogen