Iodine value

it deals with iodine value as per IP

1. Iodine value

2. Iodine value The iodine value is the number which expresses in grams the quantity of halogen, calculated as iodine which is absorbed by 100 g of substance under the described condition. It may be determined by any of the following methods. It also known as   iodine adsorption value  or  iodine number  or  iodine index Saturated fatty acids will not give the halogenation reaction Oil /fat sample+ ICl or I 2 in ethanol and in presence of mercuric chloride

3. Significance The iodine value is a measure of the degree of unsaturation in an oil. It is constant for a particular oil or fat. Iodine value is a useful parameter in studying oxidative rancidity of oils since higher the unsaturation the greater the possibility of the oils to go rancid. Iodine numbers are often used to determine the amount of unsaturation in fatty acids. This unsaturation is in the form of double bonds, which react with iodine compounds.

4. Significance The higher the iodine number, the more C=C bonds are present in the fat If the iodine number is between 0-70, it will be  a fat and if the value exceeds 70  it is an oil. Starch is used as the indicator for this reaction so that the liberated iodine will react with starch to give purple coloured product and thus the endpoint can be observed.

5. Method Iodine monochloride method or Wijis method Iodine monobromide method or Hanus method Pyridine bromide method

6. Method A- iodine mono chloride method Principle The oil/fat sample taken in carbon tetrachloride is reacted with an excess of iodine monochloride solution ( Wjis solution). Unsaturated fatty acids undergo halogenation reaction resulting in the addition of an iodine atom to one carbon of the double bond. On completion of the reaction, the remaining iodine monochloride reacts with potassium iodide leading to the formation of molecular iodine. The liberated iodine is then evaluated by titration with a standard solution of sodium thiosulphate using starch as indicator. Mercuric ions are added to fasten the reaction

7. Method A- iodine mono chloride method

8. Wijis reagent Iodine monochloride is produced simply by combining the halogens in a 1:1 molar ratio, according to the equation I 2  + Cl 2  → 2 ICl When   chlorine gas is passed through iodine crystals, one observes the brown vapour of iodine mono chloride . Dark brown iodine mono chloride liquid is collected. Excess chlorine converts iodine monochloride into iodine trichloride  in a reversible reaction: ICl + Cl 2  ⇌ ICl 3

9. IP procedure Place an accurately weighed quantity of the substance (100 g)under examination in a dry 500ml iodine flask, add 10ml of carbontetrachloride and dissolve. Add 20ml of iodine monochloride solution , insert the stopper and allow to stand in the dark at a temperature between 15°C and 25°C for 30 minutes. Place 15ml of potassium iodide solution in the cup top , carefully remove the stopper , rinse the stopper and the sides of the flask with 100ml of water, shake and titrate with 0.1M sodium thiosulphate using starch solution , added towards the end of the titration , as indicator .

10. IP procedure Note the number of ml of 0.1M sodium thiosulphate (a). Repeat the operation without the substance under examination and note the number of ml required(b). (BLANK) SPECIAL SAFETY NOTE Carbon tetrachloride is a carcinogen in laboratory animals. Avoid breathing vapors or skin contact. Work in a well ventilated hood but avoid dispersing to atmosphere

11. Calculation Calculate the iodine value from the expression Iodine value = 1.269 (b-a) / w Where w= weight in grams od the substance a = the number of ml of 0.1M sodium thiosulphate b = the number of ml of 0.1M sodium thiosulphate with out substance w =weight of the substance in gram 1.269 is atomic mass of iodine

12. Iodine monobromide method or Hanus method Some of the IBr reacts with the double bonds in the unsaturated lipids, while the rest remains: R-CH=CH-R + IBr (excess) → R-CHI- CHBr -R + IBr (remaining ) The amount of IBr remaining is determined by adding excess potassium iodide to the solution to liberate iodine, and then titrating with a sodium thiosulfate (Na 2 S 2 O 3 ) solution in the presence of starch to determine the concentration of iodine released:

13. IBr (remaining) + 2KI → KBr + KI + I I 2 + starch + 2Na 2 S 2 O 3 (blue) 2NaI + starch + Na 2 S 4 O 6

14. Haus solution   Hanus solution (for iodine number). Dissolve 13.2 g of resublimed iodine in 1 L of glacial acetic acid which will pass the dichromate test for reducible matter. Add sufficient bromine to double the halogen content, determined by titration (3 mL is about the proper amount). The iodine may be dissolved by the aid of heat, but the solution should be cold when the bromine is added . Store the hanus solution in a amber bottle and away from light. The Hanus solution can be used for a year . Extremely hazardous in case of eye contact (corrosive ) and Causes severe eye burns. Extremely hazardous in case of skin contact (corrosive).

15. Procedure Unless otherwise specified, weigh accurately the quantity of substance under examination, stated in the table , place it in a dry 300ml iodine flask or which has been rinsed with glacial acetic acid unless otherwise specified in the monograph. Add 15ml of chloroform and dissolve Presumed iodine value Quantity of the substance Less than 20 1.0 20 to 60 0.25 to 0.5 61 to 100 0.15 to 0.25 More than 100 0.10 t o 0.15

16. Procedure Add slowly from a burette 25.0 ml of iodine monobromide solution , insert the stopper allow to stand the dark for 30minutes , unless otherwise specified in the monograph, shaking frequently. Add 10ml of potassium iodide solution and 100 ml of water and titrate with 0.1M sodium thiosulphate using stach solution , added towards the end od the titration, as indicator, note the number of ml required (a). Repeat the operation without the substance under examination and note the number of ml required(b). Calculate the iodine value from the expression given under method A

17. Calculation Calculate the iodine value from the expression Iodine value = 1.269 (b-a) / w Where w= weight in grams od the substance a = the number of ml of 0.1M sodium thiosulphate b = the number of ml of 0.1M sodium thiosulphate with out substance w =weight of the substance in gram 1.269 is atomic mass of iodine

18. Pyridine bromide method Place an accurately weighed quantity of the substance under examination in a dry iodine flask, add 10ml of carbon tetrachloride and dissolve. Add 25ml of pyridine bromide solution, allow to stand for 10minutes in the dark and complete the determination described under method A beginning at the words “place 15ml of….”

19. The approximate weight in gram of the substance to be taken may be calculated by dividing 12.5 by the highest expected iodine value. If more than half the available halogen is absorbed, the test must be repeated with a smaller quantity of the substance.