------------------------------------------------------------------------------- Iodine liberation from KI with ultrasound ------------------------------------------------------------------------------- From "Sonochemistry and Sonoluminescence", Edited by Lawerence J. Mason, Jacques L. Reisse, and Kenneth S. Suslick (1999), Library of Congress # QD 801 S66 1999 Page 276 "5.2 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 --> HO2* HO2* + HO2* --> 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 (Equation 3). H2O2 + 2 KI + 2 H(+) ---> I2 + 2 H2O Equation 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 (Equation 4). The chlorine itself then acts as an oxidizing agent for the iodide ion (Equation 5). CCl4 + H2O --> Cl2 + CO2 + 2 HCl Equation 4 2 I(-) + Cl2 --> I2 + 2 Cl(-) Equation 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. -------------------------------------------------------------------------------