Iodination, of alcohols

We have examined the applications of IBH2 and I2BH complexes for hydroboration of alkenes to obtain dialkyl and mono alkyl boranes. Unfortunately, these species disproportionate and hence the dialkyl and trialkyl boranes were not formed cleanly. Fortunately, however, the HBI2 and BI3 complexes are found to be useful for iodinations of alcohols, reductive iodinations of carbonyl compounds and hydroiodination of alkenes and alkynes. 

Iodine compounds are important in organic chemistry and very useful in medicine. Iodides, and thyroxine which contains iodine, are used internally in medicine, and as a solution of KI and iodine in alcohol is used for external wounds. Potassium iodide finds use in photography. The deep blue color with starch solution is characteristic of the free element. 

The aHphatic iodine derivatives are usually prepared by reaction of an alcohol with hydroiodic acid or phosphoms trHodide by reaction of iodine, an alcohol, and red phosphoms addition of iodine monochloride, monobromide, or iodine to an olefin replacement reaction by heating the chlorine or bromine compound with an alkaH iodide ia a suitable solvent and the reaction of triphenyl phosphite with methyl iodide and an alcohol. The aromatic iodine derivatives are prepared by reacting iodine and the aromatic system with oxidising agents such as nitric acid, filming sulfuric acid, or mercuric oxide. 

Iodoveratrole has been prepared by iodination of veratrole in the presence of mercuric oxide and by methylation of 4-iodoguaiacol with methyl iodide in alcoholic sodium ethoxide solution. ... 

Worenine. This alkaloid, also obtained by Kitasato from Coptis japonica was isolated as the tetrahydro-base, C,oHjg04N, which crystallises from alcohol in colourless prisms, m.p. 212-3°, and is oxidised by iodine in alcohol to worenine iodide, yellow crystals from which worenine chloride, thin orange-yellow prisms, m.p. 295° (dec.), can be obtained. Tetrahydro-worenine behaves as a tertiary base, contains methylenedioxy- but no methoxyl groups, and its absorption spectrum closely resembles that of tetrahydrocoptisine from which it differs in empirical composition by. CHj. Worenine is, therefore, represented by (XXX), the alternative position (a) for the methyl group being untenable, since a-methyltetra-hydrocoptisine obtained by Freund s method is not identical with... 

Reaction.—A delicate test for ethyl alcohol is the lodofornt reaction. Pour a few drops of alcohol into a test-tube and add about 5 c.c of a solution of iodine in potassium iodide, and then dilute caustic soda solution until the iodine colour vanishes. Shake up and narm very gently to about 6o°. If no turbidity 01 precipitate appears at once, set the test-tube aside for a time. Yellow crystals of iodoform will ultimately deposit, which have a peculiar odoui, and a characteiistic star shape nhen viewed under the microscope. The same reaction is given with... 

Isopropyl Iodide.—The replacement of hydroxyl by iodine in the action of phosphorus and iodine on alcohols has alieady been described (see Piep. 6, p. 68), but here the presence of an excess of hydriodic acid, which is due to the action of water on the phosphorus iodide,... 

Despite this qualitative similarity, the solubility of iodine in CC14 is very different from its solubility in alcohol. One liter of alcohol dissolves 0.84 mole of iodine, whereas one liter of CCli dissolves only 0.12 mole ... 

Expression (2) applies to a solubility equilibrium, provided we write the chemical reaction to show the important molecular species present. In Section 10-1 we considered the solubility of iodine in alcohol. Since iodine dissolves to give a solution containing molecules of iodine, the concentration of iodine itself fixed the solubility. The situation is quite different for substances that dissolve to form ions. When silver chloride dissolves in water, no molecules of silver chloride, AgCl, seem to be present. Instead, silver ions, Ag+, and chloride ions, Cl-, are found in the solution. The concentrations of these species, Ag+ and Cl-, are the ones which fix the equilibrium solubility. The counterpart of equation (7) will be... 

There is a risk of acute renal failure when iodi-nated contrast material that is used for radiological studies is administered with metformin. Metformin therapy is stopped for 48 hours before and after radiological studies using iodinated material. Alcohol, amiloride, digoxin, morphine, procainamide, quini-dine, quinine ranitidine, triamterene, trimethoprim, vancomycin, cimetidine, and furosemide all increase the risk of hypoglycemia. There is an increased risk of lactic acidosis when metformin is administered with the glucocorticoids. 

Last but not least HMDS 2 is, in the laboratory and in pilot plants, quite stable when stored in a normal closed vessel whereas trimethylchlorosilane (TCS) 14 should be stored in a hood, because it reacts with humidity to hexamethyldisilox-ane 7 and HCl. Because HMDS 2 is a very non-polar compound, the silylation of very polar compounds, e.g. purines or pteridines, with HMDS 2 wiU often proceed only on addition of a polar solvent such as pyridine which is, however, readily removed after silylation, with excess HMDS 2, on codistillation with abs. xylene. Interestingly, it was recently reported that addition of catalytic amounts of iodine dramatically accelerates the silylation of alcohols, in particular tertiary alcohols, with HMDS 2 in CH2CI2 at room temperature [63]. 

Finally, phthalocyanine iron catalysts were also used for the oxidation of alcohols to yield corresponding carbonyl compounds with nonbenign hypervalent iodine oxidants [147]. 

Several modifications of procedures based on halophosphonium ion have been developed. Triphenylphosphine and imidazole in combination with iodine or bromine gives good conversion of alcohols to iodides or bromides.22 An even more reactive system consists of chlorodiphenylphosphine, imidazole, and the halogen,23 and has the further advantage that the resulting phosphorus by-product diphenylphosphinic acid, can be extracted with base during product workup. 

Such reactions are also possible in vitro, as several mild oxidizing agents are at hand nowadays. Thus, the Dess-Martin periodinane (DMP) [50] has been proven to be a versatile and powerful reagent for the mild oxidation of alcohols to the corresponding carbonyl compounds. In this way, a series of new iodine(V)-mediated reactions has been developed which go far beyond simple alcohol oxidation [51], Ni-colaou and coworkers have developed an effective DM P-mediated domino polycy-clization reaction for converting simple aryl amides, urethanes and ureas to complex phenoxazine-containing polycycles. For example, reaction of the o-hydroxy anilide 7-101 with DMP (2 equiv.) in refluxing benzene under exposure to air led to polycycle 7-103 via 7-102 in a yield of 35 % (Scheme 7.28) [52]. 

The tetrahydrofuranylation of alcohols with hypervalent iodine compounds is described in [479]. 

Several organohypervalent iodine reagents have been used for the oxidation of alcohols and phenols such as iodoxybenzene, o-iodoxybenzoic acid (IBX), bis(trifluoroa-cetoxy)iodobenzene (BTI), and Dess-Martin periodinane etc. But the use of inexpensive iodobenzene diacetate (IBD) as an oxidant, however, has not been fully exploited. Most of these reactions are conducted in high boiling DMSO or toxic acetonitrile media that results in increased burden on the environment. 

Need 0.6 g of iodine, 20 g of boric acid, and 99.4 g of lactose. Place iodine in mortar, add a few drops of alcohol and reduce to a fine powder. Then add boric acid and talc. Mix thoroughly until alcohol evaporates. Dry and sieve to break the lumps. Fill in a wide mouth 4-oz bottle and label appropriately. 

The second reaction proceeds much more energetically than the first, especially if preformed phosphorus halide is used. This is, however, not always necessary, at least not in the case of replacements by bromine and iodine in many cases the procedure is rather to produce the halide only during the reaction, either by dropping bromine from a separating funnel into a mixture of alcohol and red phosphorus or, as above, by adding finely powdered iodine. Like the former, this reaction can also be applied to polyhydric and to substituted alcohols indeed, it is possible to replace all the OH groups by halogens, and in particular also by chlorine. 

Chlorine and bromine can be replaced by iodine by means of alkali iodide, and this is of importance in cases where direct treatment of alcohols with hydriodic acid gives a bad yield or none at all, e.g. in the preparation of ethylene iodohydrin ... 

Experiments—Dissolve 0-02 g. of cholic acid in 0-5 c.c. of alcohol and add to the solution 1 c.c. of 0-1 A-iodine solution. On cautious dilution with water the blue crystalline iodine compound of cholic acid, comparable to starch iodide, separates. 

Procedure Weigh accurately about 0.4 g and dissolve in a mixture of 40 ml of alcohol and 10 ml of 0.01 N hydrochloric acid. Titrate the resulting mixture with 0.1 N iodine solution till a yellow colour that... 

Preparation and phytochemical reduction of 2,2 -thenoin and 2,2 -thenil have been studied in the authors laboratory (20a). It has been shown that 2,2 -thenoin gives a color reaction similar to that shown by benzoin and other acyloin condensation products in- the presence of alcoholic alkali. The hydroxy ketone may be oxidized by iodine in the presence of sodium methoxide to give the diketone, 2,2 -thenil, in excellent yields. Phytochemical reduction was shown also to be applicable to both compounds. It is significant that thenoin differs from benzoin, since reduction products were not obtained enzymatically from the latter. 

---