Iodine [Monograph #5034, Merck Index, Ed. 12.1]

CAS Registry number:

[7553-56-2]

Literature references:

I; at. wt 126.9045; at. no. 53; valences 1 to 7 (usually monovalent); elemental state: I₂. A halogen. Abundance in igneous rocks: 3x10^-5% by wt; in seawater 5x10^-8% by wt. Natural isotope: 127 (100%); isotopes range in mass number from 117 to 139; radioactive tracer elements: 124, 125, 128, 131, 132. Discovered in 1811 by Courtois. Classed among the rarer elements. Extracted from Chilean nitrate-bearing earth (caliche) and from seaweed. Prepn of ultra-pure iodine for research purposes according to the equation 2KI + CuSO₄·5H₂O → CuI + K₂SO₄ + ½ I₂ + 5H₂O: Schmeisser in Handbook of Preparative Inorganic Chemistry, Vol. 1, G. Brauer, Ed. (Academic Press, New York, 2nd ed., 1963) p 275. Reviews: MTP Int. Rev. Sci.: Inorg. Chem., Ser. One, Vol. 3, V. Gutmann, Ed. (Butterworths, London, 1972); Downs, Adams, "Chlorine, Bromine, Iodine and Astatine" in Comprehensive Inorganic Chemistry vol. 2, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) p 1107-1594; C. J. Mazac in Kirk-Othmer Encyclopedia of Chemical Technology vol. 13 (Wiley-Interscience, New York, 3rd ed., 1981) pp 649-677.

Properties:

Bluish-black scales or plates; diatomic; metallic luster; characteristic odor; sharp, acrid taste; violet corrosive vapor.

Vapor pressure (solid):

0.030 mm (0°C); 0.305 mm (25°C); 2.154 mm (50°C); 26.78 mm (90°C).

Heat capacity at constant pressure (25°C)

13.011 cal/mole/°C: Shirley, Giauque, J. Am. Chem. Soc. 81, 4778 (1959).

Total soly in water (25°C):

0.0013 moles/l with negligible formation of HOI (6.4x10^-6 moles/l); freely sol in aq solns of HI or iodides.

Soly in organic solvents (g I₂/100 g soln, 25°C):

benzene 14.09; CS₂ 16.47; ethanol 21.43; ethyl ether 25.20; cyclohexane 2.719; CCl₄ (35°C) 2.603: Hildebrand, Jenks, J. Am. Chem Soc. 42, 2180 (1920); Hildebrand et al., ibid. 72, 1017 (1950); sol in chloroform, glacial acetic acid, glycerol oils.

Miscellaneous:

Solutions of iodine in aq solns of inorganic iodides are brown or deep brown, depending on the concentration of the iodine. Solvents contg nitrogen atoms, such as pyridine, amines, or quinoline dissolve iodine to form brown solns. Chloroform, carbon tetrachloride, carbon disulfide, and especially phosphorus trichloride give violet solns. The violet color is also given by fluorinated amines. The soly in water is also increased by alkali bromides, but decreased by sulfates and nitrates. Less reactive than bromine; E°_(aq) ½ I₂/I^- 0.535 V dissociation energy (25°C): 36.115 kcal. Iodine stains may be removed with sodium thiosulfate soln or ammoniated alc. Incompat: alkaloids, starch, tannins.

Melting point:

113.60°C

Boiling point:

185.24°C

Density:

4.93 (solid, 25°C)

Caution:

Potential symptoms of overexposure are irritation of eyes and nose; lacrimation; headache; tight chest; skin burns, rash; cutaneous hypersensitivity. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 90-117, 1990) p 128. Ingestion of large quantities causes abdominal pain, vomiting and diarrhea due to the highly corrosive action of iodine on the GI tract. See Clinical Toxicology of Commercial Products, R. E. Gosselin et al., Eds. (Williams Wilkins, Baltimore, 5th ed., 1984) Sect. III, pp 213-214.

Iodine liberation from KI with ultrasound

Radical Reactions - Hetrolytic Fission

In classical organic chemistry covalent bonds can be broken to form radicals useing heat or light. Hetrolytic fission can also be acheived through sonochemistry and such reactions are typified by the sonochemical degradation of hydrocarbons. [...]

The sonochemical reaction most frequently quoted for radical production is the sonolysis of water in the cavitation bubble a simplified scheme for which is shown below. The intial homolytic fission of the H-O bond is followed by a whole series of other radical reactions.

• H-O-H → H· + HO·
• H· + O₂→ HOO·
• HOO· + HOO·→ H₂O₂ + O₂
• HO· + HO·→ H₂O₂

[...] A whole range of reations can take place subsequently one of which is the production of H₂O₂, hydrogen peroxide a common oxidant. It is the decomposition of water from which are derived the most frequently used forms of chemical dosimetry for sonochemistry. These are (a) the oxidation of iodide ion to iodine and (b) methods based on the trapping of the free radical species HO· as they emerge from the bubble. [...]

Iodine dosimetry is based upon the oxidation of iodide ion by the hydrogen peroxide generated by sonolysis of water (Eq. 3).

The yield of iodine is usually quite small when the reaction is carried out useing pure aqueous potassium iodide solution. In order to increase the iodine yield, i.e. the sensitivity of the reaction, a saturated aqueous solution of carbon tetrachloride is sometimes used in place of water as the solvent (Weissker's solution). When this solution is sonicated the normal oxidation process occurs together with generation of chlorine from the hetrolytic breakdown of CCl₄ in the bubble (Eq. 4). The chlorine itself then acts as an oxidizing agent for the iodide ion (Eq. 5).

There is also a possiblity of using CHCl₃ (Chloroform) which might not have as perfect result but the liberation iodine will still be there.

Ref: L. J. Mason, J. L. Reisse, and K. S. Suslick (Ed.), Sonochemistry and Sonoluminescence, p. 276 (1999)

Iodine from Iodine Tincture (Written by Seelight)

Materials:

• 5% Tincture: 5% I₂, 5% KI, IPA, H₂O
• 97% H₂SO₄ or whatever you have
• Bleach (unscented)
• Gravity filtration, a buttload of coffee filters
• 2L pyrex or glass bowl
• 500 ml mason jar

Procedure:

1. 4x25ml (100ml total) of 5% tincture was added to the mason jar. 100 ml of dH₂O was added to the tincture. If your anal like I am you can use this water to wash out the remaining tincture in the bottles.
2. To the tincture/H₂O mix there was added slowly 5 ml of 97% H₂SO₄ with stirring. If you dont have 97% just convert the volume added based on the percentage you do have. Fumes were emitted and the solution heated slightly. Let cool back to room temp. The acid functions to convert KI into HI facilitating the oxidation of iodide to iodine.
3. Fill the 2L pyrex or glass bowl with 1L of dH₂O, set aside.
4. Add slowly and with good stirring 12 ml of bleach to the tincture/dH₂O. Use your good observation skills at this point. You are waiting to see a colour change of the solution from a deep red to a even more deep red/black colour and for the emergence of I₂ precipitate. When I₂ precipitates, some of it rises to the surface and gives a noticeable "metallic" appearance to the surface.
5. Add another 12 ml of bleach like you did before all the while, looking for signs of precipitation. Once you see those signs, immediately (oh, the drama) dump the tincture/dH₂O/I₂ into that 1L of dH₂O you set aside.
6. Sit back and watch the I₂ completely fall out of solution. Let it sit for 20 min. Feel free examine it an ponder about the wonders of the world.
7. Set up gravity filtration with 2 coffee filters. Filter out the I₂. Rinse the bowl with dH₂O, add rinse to I₂ in filter. Rinse I₂ with 500 ml dH₂O. This gets rid of any salts. Try to coax the I₂ to the center of the filter.
8. Time to dry out the I₂. Put some gloves on (if you haven't already) and gather the edges of the filter and twist them down to wring out the moisture. Keep adding fresh filters on the outside and keep wringing until no more moisture surfaces to the new filters.
9. Take that wad and squish the hell out of it on a hard surface. Unwrap the wad and transfer I₂ to a container. Dessicate under vaccumm. Or just put the container in a bigger one with drying agent and seal shut. Store out of light.
10. Seelight got 8.2 g of I₂ out of 100 ml of 5% tincture. From what info has been gathered on de Hive, this seem suitable for I₂/RP of pseudo.

Note: I₂ from I₂ stained filters penetrate plastic bags so wrap it up good prior to chucking it.

Povidone Iodine Recovery via Sublimation (Written by LabTop)

Procedure

Make or buy a coldfinger (see below), boil your fluid to absolute dryness, without burning the dry restant, then hang your coldfinger in an appropriate Erlenmeyer, and heat gently the now dry restant. Make your coldfinger fat-free with acetone first (on the outside where the I₂ will condense). The I₂ will sublimate from the solid form into the gas form, without getting a fluid first (that's sublimation), and the gaseous I₂ will resublime from the gaseous form into the solid form against the cold wall from the coldfinger. A little bit will of course also resublime against the upper part of the Erlenmeyer, but that you can also scrape off later, when all your 10% I₂ hangs on the cold glass walls.

Coldfinger

The coldfinger can just be a reflux condenser with cold water running through it. The I₂ will condense on the walls of the condenser. It can then be scraped out when it begins to build up.

If you don't have a reflux condenser at hand, you could improvise a so-called coldfinger, by making a big enough hole in a cork or rubber stop, and in that big hole you press a big glass-reagens-tube all the way down, wherein you fit another 2-hole stopper, which you fit with a long L-shaped glass pipe and a short L-shaped glass pipe. Fit plastictubing to both L-shaped glaspipes, and one tube to an aquarium submersible pump, which you place in a bucket with Icecubes/water. The other tube just returns the water to the bucket. Make a tiny little extra hole in the big stopper with a S-shaped glass pipe or plastic tubing, the bend of the S filled with a tiny bit of MeOH to compensate for overpressure, which will nearly not appear, if you keep the bucket full of ice cubes. If suck-back appears, only MeOH will drop in your system, no harm done.

Now you have a perfect condenser for less then 20 US$.

For the more daring ones, you can use a short fat glaspipe, a bit widened at one end, and fix a rubber balloon over that end, and strap that balloon with one of those nylon straps they use to keep bundles of cables together in automobiles. Now you can frott the empty balloon through your 3 or 5 liter Erlenmeyer mouth opening, fix the rubber stopper, and fill your balloon with ice water from the bucket with that little aquarium pump. Your cooling area is much bigger this way, only test in advance if the rubber will not get attacked by one of your solvents when you use it in another setup then MM's. Acetone is not good for a rubber balloon, more so when it is hot, then you must fall back to the glass test tube. But if you look for those wide-mouth glass vessels in household stores, you could even use a 250 ml round-bottom flask as your coldfinger to fit in a big cork. Use candle wax then to fix the big stopper. Can be easily broken loose after completion of the reaction.