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 I2 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
1. Iodine monochloride method or Wijis
method
2. Iodine monobromide method or Hanus
method
3. 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
I2 + Cl2 → 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 + Cl2 ⇌ ICl3

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 (Na2S2O3) solution in the presence of
starch to determine the concentration of iodine
released:

13. IBr(remaining) + 2KI → KBr + KI + I
I2 + starch + 2Na2S2O3 (blue)
2NaI + starch + Na2S4O6

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 to 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.