Dr.D.Panda – Inorganic Pharm.Chem. – Poisons and Antidots

Poisons And Antidotes Poisoning of the body takes place due to various reasons which are as follows; 1) The most common poisoning is due to intake of heavy metals through food and water. 2) Sometimes, the metals get leached from the used utensils (for cooking and eating) which ultimately poisons our body in long run. 3) The poisoning can also occur because of use of insecticides and pesticides. 4) The poisoning can also occur because of excessive use of drugs. Antidotes : These are the chemical agents which react with the ingested toxic or poisonous substances and either neutralise them or chemically convert them to non-toxic / less-toxic forms. Here, we will get to know about the heavy metals poisoning and cyanide poisoning and the antidotes used to act against those poisons.

Heavy metals Poisoning The heavy metal poisoning takes place due to intake and incomplete metabolism of the salts of arsenic, lead, mercury, iron and cadmium in our body. Depending upon the content and type of heavy metals, the toxic effects can be seen in the patients. This kind of poisoning can be treated with initial administration of activated charcoal (for absorbing heavy metals) followed by the administration of emetics (to induce vomiting so as to expel out poisons). Sometimes, some inorganic compounds are ingested which help in precipitating the poisons so as to prevent them from absorption. In case, where the poison is totally absorbed in the body, some organic antidotes are used for systemic effect against such poisons. Example : The inorganic antidotes are Activated Charcoal, Light Kaolin, Copper Sulphate, Magnesium Sulphate, Sodium Phosphate, etc. and the organic antidotes are DPenicillamine, Deferoxamine, Dimercaprol, Succimer, Calcium disodium edetate, etc. Activated Charcoal : It is commercially prepared as a residue during destructive distillation of various organic matters or from burning of organic materials in a special manner. It is a fine black, odourless, tasteless powder and free from gritty particles. Insoluble in all the solvents. Light Kaolin : It is chemically hydrated aluminium silicate which is prepared from natural clay by powdering and separating the particles by electrical sedimentation and made free from gritty particles and other impurities. It is light, white powder, odourless, tasteless and very fine to touch.

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Dr.D.Panda – Inorganic Pharm.Chem. – Poisons and Antidots

Copper Sulphate (CuSO4.5H2O Mol. Wt. – 249.7) : It is prepared by treating granulated copper with sulphuric acid in the presence of air. The solution is filtered and evaporated to crystallize and separate out the copper sulphate crystals. 2Cu + 2H2SO4 + O2

2CuSO4 + 2H2O

It exists in the form of blue crystalline granules of powder , soluble in water, very soluble in boiling water, slowly soluble in glycerol and almost insoluble in alcohol. At higher temperature (more than 200 o C) , it decomposes into SO2, Oxygen and black cupric oxide. 2CuSO4

CuO + 2SO2 + O2

Assay – Accurately weighed qty. of CuSO4 is dissolved in water. To this solution, a slightly excess of KI is added followed acetic acid. The liberated iodine is titrated with std. Sodium thiosulphate solution using starch as indicator. The titration is continued until a faint blue colour persists. 2CuSO4 + 4KI 2CuI2 (cupric iodide) + 2K2SO4. Then 2gm of potassium thiocyanate (KCNS) is added and the titration is continued until the blue colour disappears. I2 + 2Na2S2O3 Na2S4O6 + 2NaI Cu2I2 + KCNS 2CuCNS + 2KI 1ml of 0.1N Na2S2O3 is equivalent to 0.02497gm of CuSO4.5H2O Magnesium Sulphate (MgSO4.7H2O Mol. Wt. – 246.5) : It is prepared by the action of sulphuric acid on magnesium carbonate. MgCO3 + H2SO4 MgSO4 + H2O + CO2 . . The solution is filtered and the filtrate is evaporated to crystallization. MgSO4 occurs as colourless crystals having a cool, saline bitter taste. Soluble in water but sparingly soluble in alcohol. Assay : 0.3gm of sample dissolved in 50ml of water + 10ml of strong ammonium chloride solution titrated with 0.05M disodium ethylene diamine tetraacetate solution using 0.1gm of Mordant Black II mixture as indicator until the pink colour gets discharged from the blue. Each ml of 0.05M Disodium ethylene diamine tetraacetate is equivalent to 0.00602gm of MgSO4. Sodium Phosphate (Disodium hydrogen phosphate) (Na2HPO4 . 12H2O Mol.Wt. 358.14) It is prepared by adding sodium carbonate to a hot solution of phosphoric acid. H3PO4 + Na2CO3 Na2HPO4 + H2O + CO2 The solution is neutralised, concentrated and the crystals are separated out by centrifuging, washed and dried. The compound occurs as colourless transparent crystals, having a saline taste, odourless. It is soluble in water but insoluble in alcohol. On more heating ( above 300 o C ) the compound is converted to sodium pyrophosphate. 2Na2HPO4 Na4P2O7 + H2O

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Dr.D.Panda – Inorganic Pharm.Chem. – Poisons and Antidots

Cyanide Poisoning It normally takes place due to either accidental or intentional intake of cyanides. The ingested cyanide combines with the ferric ion of cytochrome oxidase ( the enzyme present in our body which is responsible for electron transfer reactions ) and inhibits / blocks the cellular respiration and metabolic reactions. Cyanide poisoning is usually fatal if it is not instantly treated. Cyanide poisoning is treated with the both two inorganic antidotes, namely; Sodium nitrite and Sodium thiosulphate. While ingesting both the antidotes, sodium nitrite converts the haemoglobin to methemoglobin which binds the cyanide ions whereas, sodium thiosulphate converts the cyanide ions into non-toxic thiocyanate ions which are excreted out by the kidney.

Sodium Nitrite – NaNO2 - Mol. Wt. – 68.99 It is prepared by passing Nitrogen oxide gas (NO) and Oxygen in Sodium carbonate (Na2CO3) solution. The resultant solution is then concentrated to crystallize out Sodium nitrite (NaNO2). 2Na2CO3 + 4NO + O2

4NaNO2 + 2CO2

Sod. Nitrite occurs as white granular powder or as white crystal having saline taste. Soluble in water, sparingly soluble in alcohol. It is easily decomposed on acidification with dil.H2SO4. 2NaNO2 + H2SO4

Na2SO4 + 2HNO2

When a cooled solution of NaNO2 is acidified with dil.HCl, free nitrous acid is produced. NaNO2 + H3O + Cl

-

HNO2 + H2O + NaCl

Assay : The method is based upon the oxidation of nitrite to nitrate. 1gm of sample is dissolved in 100ml of water. 10ml of this solution is slowly added to 50ml of 0.1N potassium permanganate solution, 100ml of water and 5ml of sulphuric acid. In contact with the acid, 3

Dr.D.Panda – Inorganic Pharm.Chem. – Poisons and Antidots

nitrous acid (HNO2) is formed which immediately gets oxidised to nitric acid (HNO3) by potassium permanganate. Then a standard solution of 25ml of oxalic acid is added to it and the solution is back titrated with standard potassium permanganate solution to neutralise the excess oxalic acid added to the solution. Each ml of 0.1N KMnO4 is equivalent to 0.00345gm of NaNO2. Use : Nitrites easily form methaemoglobin which in turn reacts with cyanide ion and forms cyanmethaemoglobin and so, sodium nitrite is used as an antidote in cyanide poisoning.

Sodium Thiosulphate - Na2S2O3.5H2O

- Mol. Wt. – 248.2

It is prepared from Sodium carbonate (soda ash) , Sulphur dioxide and Sulphur. Sodium carbonate is first made to dissolve in hot water and then, sulphur dioxide gas is passed through the solution. The resulting bisulphate solution is again treated with a further quantity of soda ash and then the solution is made to heat with sulphur. The final solution is then concentrated to get the crystallized mass of sodium thiosulphate. Na2CO3

+ H2O + 2SO2

2NaHSO3 + CO2

2NaHSO3 + Na2CO3

2Na2SO3 + H2O + CO2

Na2SO3 + S

Na2S2O3

It is found as large colourless crystals or as coarse crystalline powder, odourless and alkaline taste. When it is treated with HCl, decomposed to liberate sulphur, sulphur dioxide and water. Na2S2O3 H2S2O3

H2S2O3 S

+ 2NaCl

+ H2O + SO2

It reduces the ferric salts to their corresponding ferrous salts. 2FeCl3 + 2No2S2O3

2FeCl2 + 2NaCl + Na2S4O6

Assay : 1gm of Na2S2O3 is dissolved in 20ml of water and titrated with 0.1N iodine solution using starch as indicator. 2 Na2S2O3 + I2 Na2S4O6 + 2NaI Each ml of 0.1N iodine is equivalent to 0.02482g of Na2S2O3 . 5H2O Use : It is used as an antidote in cyanide poisoning by intravenous injection followed by the injection of sodium nitrite, also used in parasitic skin diseases (ring worm, athlete’s foot, etc.). ++++++++++++++++++++/////////////////////////////////////////////++++++++++++++++++++ 4