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== | The '''iodine value''' (or "iodine adsorption value" or "iodine number" or "iodine index") in [[chemistry]] is the mass of [[iodine]] in grams that is consumed by 100 grams of a [[chemical substance]]. Iodine numbers are often used to determine the amount of unsaturation in [[fatty acid]]s. This unsaturation is in the form of double bonds, which react with iodine compounds. The higher the iodine number, the more C=C bonds are present in the fat.<ref name=Ullmann>{{cite encyclopedia |first=Alfred |last=Thomas |title=Fats and Fatty Oils|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry |publisher=Wiley-VCH |place=Weinheim |year=2002 |doi=10.1002/14356007.a10_173}}</ref> It can be seen from the table that [[coconut oil]] is very saturated, which means it is good for making [[soap]]. On the other hand, linseed oil is [[unsaturated fatty acid|highly unsaturated]], which makes it a [[drying oil]], well suited for making [[oil paint]]s. | ||
==Table of iodine values== | |||
{| class="wikitable sortable" | |||
!Fat | |||
!Iodine number<ref name=Ullmann/> | |||
|- | |||
| [[Tung oil]] | |||
|align="right"| {{Nts|163}} – 173 | |||
|- | |||
| [[Grape Seed oil]] | |||
|align="right"| {{Nts|124}} – 143 | |||
|- | |||
| [[Palm oil]] | |||
|align="right"| {{Nts|44}} – 51 | |||
|- | |||
| [[Olive oil]] | |||
|align="right"| {{Nts|80}} – 88 | |||
|- | |||
| [[Coconut oil]] | |||
|align="right"| {{Nts|7}} – 10 | |||
|- | |||
| [[Palm Kernel oil]] | |||
|align="right"| {{Nts|16}} – 19 | |||
|- | |||
| [[Cocoa butter]] | |||
|align="right"| {{Nts|35}} – 40 | |||
|- | |||
| [[Jojoba oil]] | |||
|align="right"| ~{{Nts|80}} | |||
|- | |||
| [[Cottonseed oil]] | |||
|align="right"| {{Nts|100}} – 117 | |||
|- | |||
| [[Corn oil]] | |||
|align="right"| {{Nts|109}} – 133 | |||
|- | |||
| [[Wheat Germ Oil]]<ref>http://online.personalcarecouncil.org/ctfa-static/online/lists/cir-pdfs/pr248.pdf</ref> | |||
|align="right"| {{Nts|115}} – 134 | |||
|- | |||
| [[Sunflower oil]] | |||
|align="right"| {{Nts|125}} – 144 | |||
|- | |||
| [[Linseed oil]] | |||
|align="right"| {{Nts|136}} – 178 | |||
|- | |||
| [[Soybean oil]] | |||
|align="right"| {{Nts|120}} – 136 | |||
|- | |||
| [[Peanut oil]] | |||
|align="right"| {{Nts|84}} – 105 | |||
|- | |||
| [[Ricebran oil]] | |||
|align="right"| {{Nts|99}} – 108 | |||
|} | |||
== | ==Methodology== | ||
This particular analysis is an example of [[iodometry]]. A solution of iodine ions is yellow/brown in color. When added to a complex solution however, any chemical group (usually C=C double bonds) in solution that react with iodine effectively reduce the strength, or magnitude of the colour (by taking iodine ions out of solution). Thus the amount of iodine required to make a solution retain the characteristic yellow/brown colour can effectively be used to determine the amount of iodine sensitive groups present in the solution. | |||
In a typical procedure, the fatty acid is treated with an excess of the Hanuš or [[Wijs solution]]s, which are, respectively, solutions of [[iodine monobromide]] (IBr) and [[iodine monochloride]] (ICl) in glacial acetic acid. Unreacted iodine monobromide (or monochloride) is then allowed to react with [[potassium iodide]], converting it to iodine, whose concentration can be determined by titration with [[sodium thiosulfate]].<ref name="pmid8012219">{{cite journal |author=Firestone D |title=Determination of the iodine value of oils and fats: summary of collaborative study |journal=J AOAC Int. |date=May–Jun 1994 |volume=77 |issue=3 |pages=674–6 |pmid=8012219}}</ref> | |||
= | The chemical reaction associated with this method of analysis involves formation of the diiodo alkane (R and R' symbolize alkyl or other organic groups): | ||
:<math>\mathrm{R{-}CH{=}CH{-}R' + I_2 \longrightarrow R{-}CHI{-}CHI{-}R'}</math> | |||
The precursor alkene (RCH=CHR') is colourless and so is the organoidine product (RCHI-CHIR'). | |||
== | <!-- | ||
==Methods for the Determination of iodine value== | |||
===Huebl's iodine=== | |||
Introduced the iodine value was Hübl which titrated fats in the presence of mercuric chloride with iodine, but with the actual reagent (probably iodine chloride) is formed in situ from mercuric chloride and iodine. Pure iodine accumulates concerned not to alkenes, which is why the still valid definition of iodine is only a formal one. | |||
=== Wijs iodine value after=== | |||
Addition of [[iodine chloride]] and back-titration with [[sodium]] by [[German Institute for Standardization | DIN]] 53241-1:1995-05. | |||
== | ===Iodine by H. P. Kaufmann=== | ||
([[Bromination]] of the double bonds in the dark, reducing the excess bromine with [[iodide]], [[backtitration]] of [[iodine]]s of [[thiosulfate]]) | |||
The fat is mixed with an excess of bromine. This bromine is added to the double bonds in the unsaturated fats. This reaction must be carried out in the dark, since the formation of bromine radicals is suppressed by light. This would lead to undesirable side reactions, and thus falsifying a result consumption of bromine. | |||
:<math>\mathrm{Br_2 + \ R_1{-}CH{=}CH{-}R_2 \longrightarrow R_1{-}CHBr{-}CHBr{-}R_2}</math> | |||
Then the unused bromine is reduced to iodide with bromide. | |||
:<math>\mathrm{Br_2 + 2 \ I^- \longrightarrow I_2 + 2 \ Br^-}</math> | |||
Now, the amount of iodine formed is determined by titration with sodium thiosulfate solution. | |||
:<math>\mathrm{I_2 + 2 \ S_2O_3^{2-} \longrightarrow 2 \ I^- + \ S_4O_6^{2-}}</math> | |||
--> | |||
==Related methods of analysis== | |||
* [[Saponification value]] | |||
* [[Acid number]] | |||
* [[Bromine number]] | |||
* [[Hydroxyl value]] | |||
==References== | |||
{{Reflist}} | |||
{{DEFAULTSORT:Iodine Value}} | |||
[[Category:Analytical chemistry]] | |||
[[Category:Dimensionless numbers of chemistry]] | |||
[[Category:Iodine|Number]] | |||
Revision as of 00:58, 8 October 2013
The iodine value (or "iodine adsorption value" or "iodine number" or "iodine index") in chemistry is the mass of iodine in grams that is consumed by 100 grams of a chemical substance. 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. The higher the iodine number, the more C=C bonds are present in the fat.[1] It can be seen from the table that coconut oil is very saturated, which means it is good for making soap. On the other hand, linseed oil is highly unsaturated, which makes it a drying oil, well suited for making oil paints.
Table of iodine values
| Fat | Iodine number[1] |
|---|---|
| Tung oil | Template:Nts – 173 |
| Grape Seed oil | Template:Nts – 143 |
| Palm oil | Template:Nts – 51 |
| Olive oil | Template:Nts – 88 |
| Coconut oil | Template:Nts – 10 |
| Palm Kernel oil | Template:Nts – 19 |
| Cocoa butter | Template:Nts – 40 |
| Jojoba oil | ~Template:Nts |
| Cottonseed oil | Template:Nts – 117 |
| Corn oil | Template:Nts – 133 |
| Wheat Germ Oil[2] | Template:Nts – 134 |
| Sunflower oil | Template:Nts – 144 |
| Linseed oil | Template:Nts – 178 |
| Soybean oil | Template:Nts – 136 |
| Peanut oil | Template:Nts – 105 |
| Ricebran oil | Template:Nts – 108 |
Methodology
This particular analysis is an example of iodometry. A solution of iodine ions is yellow/brown in color. When added to a complex solution however, any chemical group (usually C=C double bonds) in solution that react with iodine effectively reduce the strength, or magnitude of the colour (by taking iodine ions out of solution). Thus the amount of iodine required to make a solution retain the characteristic yellow/brown colour can effectively be used to determine the amount of iodine sensitive groups present in the solution.
In a typical procedure, the fatty acid is treated with an excess of the Hanuš or Wijs solutions, which are, respectively, solutions of iodine monobromide (IBr) and iodine monochloride (ICl) in glacial acetic acid. Unreacted iodine monobromide (or monochloride) is then allowed to react with potassium iodide, converting it to iodine, whose concentration can be determined by titration with sodium thiosulfate.[3]
The chemical reaction associated with this method of analysis involves formation of the diiodo alkane (R and R' symbolize alkyl or other organic groups):
The precursor alkene (RCH=CHR') is colourless and so is the organoidine product (RCHI-CHIR').
Related methods of analysis
References
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