Iodination by iodine

Grimison and Ridd225 also suggested the preformation of a positive iodinating species as a means of explaining the results obtained in the iodination by iodine in aqueous potassium iodide, of imidazole at 25 °C. The kinetics of this reaction follow equation (121)... 

A third method utilizes iodine titration. Both R salt and Schaeffer salt are iodinated by iodine, preferably in the presence of sodium bicarbonate. A sample is titrated with 0.1 IV iodine solution, adding an excess and back-titrating. A second sample is then separated into its constituents by alcohol, as described above, and a second determination is made. Some dye chemists believe that this is the best method, since the coupling methods give values which are too high this belief is probably correct. 

Although a stable dibromide cannot be isolated for a similar study of the bromination of benzene, the kinetics of the iodine catalyzed bromina-tion of benzene is identical with that of phenanthrene.26 Consequently it is very probable that the mechanism of the halogenation of benzene is the same as that proposed for phenanthrene. The kinetics of chlorination,27 bromination,28 and iodination by iodine chloride29 are also in agreement with this interpretation. The halogenation of phenols, however, appears to be a different, more complex process. 0... 

For direct introduction of iodine into the nucleus of aromatic hydrocarbons, usually only the most energetic of the methods mentioned on page 152 are useful. Iodination by iodine and HN03 (d 1.5)410 is strongly exothermic and useful for benzene and alkylbenzenes, but phenols and nitrocompounds are formed as by-products the phenols can be removed by shaking the crude product with 10% sodium hydroxide solution, and the nitro compounds by reduction of the crude product with iron filings and hydrochloric acid then the crude solution is made acid to Congo Red and the iodinated aromatic compound is distilled off in steam. 

Iodination by iodine and iodic acid or iodate420b is quite generally applicable.4166 A suitable solvent is glacial acetic acid, for it is indifferent to iodic acid up to 80° although it is attacked at 100° with generation of C02 nitrobenzene, which is itself iodinated only at 120°, can be added to increase the solubility to effect dissolution of the iodic acid, about 10 vol-% of water can be added. For each 2 moles of iodine 1.1-1.15 mole of iodic acid is used, i.e., a 10-15% excess the C6H5R is also used in slight excess. 

Iodination by iodine and HgO has been known for a long time and is discussed on page 198. Mercuric acetate in acetic acid may be used in place of HgO to trap the HI produced in this way, for example, 3,3 -dimethoxybenzyl affords 93% of its 6,6 -derivative (2,2 -diiodo-5,5/-dimethoxybibenzyl).494... 

The physiological action of pilocarpidine is qualitatively similar to, but much weaker than, that of pilocarpine (25, 26). Pilocarpidine is iodinated by iodine in potassium iodide solution, in the presence of potassium carbonate, to give 2-iodopilocarpidine (172), which, like... 

Andrews deration An important titration for the estimation of reducing agents. The reducing agent is dissolved In concentrated hydrochloric acid and titrated with potassium iodale(V) solution. A drop of carbon tetrachloride is added to the solution and the end point is indicated by the disappearance of the iodine colour from this layer. The reducing agent is oxidized and the iodate reduced to ICl, i.e. a 4-eiectron change. 

The most widely used reactions are those of electrophilic substitution, and under controlled conditions a maximum of three substituting groups, e.g. -NO2 (in the 1,3,5 positions) can be introduced by a nitric acid/sul-phuric acid mixture. Hot cone, sulphuric acid gives sulphonalion whilst halogens and a Lewis acid catalyst allow, e.g., chlorination or brom-ination. Other methods are required for introducing fluorine and iodine atoms. Benzene undergoes the Friedel-Crafts reaction. ... 

Trichloroethanoic acid, CCI3COOH. A crystalline solid which rapidly absorbs water vapour m.p. 58°C, b.p. 196-5" C. Manufactured by the action of chlorine on ethanoic acid at 160°C in the presence of red phosphorus, sulphur or iodine. It is decomposed into chloroform and carbon dioxide by boiling water. It is a much stronger acid than either the mono- or the dichloro-acids and has been used to extract alkaloids and ascorbic acid from plant and animal tissues. It is a precipitant for proteins and may be used to test for the presence of albumin in urine. The sodium salt is used as a selective weedkiller. 

The diazonium salts usually decompose when warmed with water to give a phenol and nitrogen. When treated with CuCl, CuBr, KI, the diazo group is replaced by chlorine, bromine or iodine respectively (Sandmeyer reaction). A diazonium sulphate and hydroxyl-amine give an azoimide. The diazonium salt of anthranilic acid (2-aminobenzoic acid) decomposes to give benzyne. ... 

McjC = CHCOCH3. Colourless liquid b.p. 129"C, with a strong peppermint-like odour. Prepared by distilling diacetone alcohol in the presence of a trace of iodine. Converted to phorone by heating in propanone with dehydrating agents such as sulphuric acid. It is a solvent For cellulose acetate and ethyl-cellulose and other polymers. 

M.p. 255-257 C. Prepared by the direct chlorination of phlhalic anhydride in 50-60% oleum in the presence of iodine, the temperature being raised from 50-200 C as the reaction proceeds. 

The sample is pyrolyzed in an 80/20 mixture of oxygen and nitrogen at from 1050 to 1100°C the combustion gases are analyzed by iodine titration or by UV fluorescence. Up to 20% of the sulfur can escape analysis, however. 

Figure Al.6.20. (Left) Level scheme and nomenclature used in (a) single time-delay CARS, (b) Two-time delay CARS ((TD) CARS). The wavepacket is excited by cOp, then transferred back to the ground state by with Raman shift oij. Its evolution is then monitored by tOp (after [44])- (Right) Relevant potential energy surfaces for the iodine molecule. The creation of the wavepacket in the excited state is done by oip. The transfer to the final state is shown by the dashed arrows according to the state one wants to populate (after [44]).

The analysis of recent measurements of the density dependence of has shown, however, that considering only the variation of solvent structure in the vicinity of the atom pair as a fiinction of density is entirely sufficient to understand tire observed changes in with pressure and also with size of the solvent molecules [38]. Assuming that iodine atoms colliding with a solvent molecule of the first solvation shell under an angle a less than (the value of is solvent dependent and has to be found by simulations) are reflected back onto each other in the solvent cage, is given by... 

Plenary 11. W Kiefer et al, e-mail address wolfgang.kiefer mail.imi-wue.de (TR CARS). Ultrafast impulsive preparation of ground state and excited state wavepackets by impulsive CARS with REMPI detection in potassium and iodine duners. 

This technique with very high frequency resolution was used to study the population of different hyperfme structure levels of the iodine atom produced by the IR-laser-flash photolysis of organic iodides tluough multiphoton excitation ... 

As an example, we mention the detection of iodine atoms in their P3/2 ground state with a 3 + 2 multiphoton ionization process at a laser wavelength of 474.3 run. Excited iodine atoms ( Pi/2) can also be detected selectively as the resonance condition is reached at a different laser wavelength of 477.7 run. As an example, figure B2.5.17 hows REMPI iodine atom detection after IR laser photolysis of CF I. This pump-probe experiment involves two, delayed, laser pulses, with a 200 ns IR photolysis pulse and a 10 ns probe pulse, which detects iodine atoms at different times during and after the photolysis pulse. This experiment illustrates a frindamental problem of product detection by multiphoton ionization with its high intensity, the short-wavelength probe laser radiation alone can photolyse the... 

He Y, Pochert J, Quack M, Ranz R and Seyfang G 1995 Dynamics of unimolecular reactions induced by monochromatic infrared radiation experiment and theory for C F XI—> C F X + I probed with hyperfine-, Doppler- and uncertainty limited time resolution of iodine atom infrared absorption J. Chem. Soc. Faraday Discuss. 102 275-300... 

A complete set of trihalides for arsenic, antimony and bismuth can be prepared by the direct combination of the elements although other methods of preparation can sometimes be used. The vigour of the direct combination reaction for a given metal decreases from fluorine to iodine (except in the case of bismuth which does not react readily with fluorine) and for a given halogen, from arsenic to bismuth. 

The large value for fluorine, and the marked decrease from fluorine to iodine, are points to be noted. The high value for fluorine means that the bond between an element M and fluorine is likely to be more ionic (more polar) than a bond formed by M with any other elements. The low value for iodine indicates the possibility that iodine may be electropositive in some of its compounds. 

Iodine is rarely prepared in the laboratory the method used is the oxidation of an iodide by manganese(IV) oxide and sulphuric acid, for example with sodium iodide ... 

The iodine distils off and can be collected on a cooled surface. It may be purified by sublimation in vacuo. 

Most iodine produced commercially comes from the sodium iodate(V) remaining after sodium nitrate has been crystallised from Chile saltpetre. The iodatefV) is first reduced to iodide by blowing sulphur dioxide into the solution (or by addition of sodium sulphite) ... 

The iodine is then liberated by heating the copper(I) iodide with sulphuric acid and iron(III) oxide ... 

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