Hypoiodite

The reactions involved are similar in both cases, and closely parallel to those which give rise to chloroform. The sodium hypochlorite probably first oxidises the potassium iodide to potassium hypoiodite, which then oxidises the ethanol to acetaldehyde and then iodinates the latter to tri-iodo ... 

Acetaldehyde reacts with phosphoms pentachloride to produce 1,1-dichloroethane [75-34-3] and with hypochlorite and hypoiodite to yield chloroform [67-66-3] and iodoform [75-47-8], respectively. Phosgene [75-44-5] is produced by the reaction of carbon tetrachloride with acetaldehyde in the presence of anhydrous aluminum chloride (75). Chloroform reacts with acetaldehyde in the presence of potassium hydroxide and sodium amide to form l,l,l-trichloro-2-propanol [7789-89-1] (76). 

Iodine dissolves without reaction in concentrated sulfuric acid and with concentrated nitric acid it reacts to form iodine pentoxide (47). Iodine reacts with alkah metal hydroxide solutions to form the corresponding hypoiodite and the rate of the reaction increases with the alkaU concentration and temperature. At 50°C, the reaction is almost instantaneous ... 

Subsequendy, the hypoiodite is oxidized to iodate, and this reaction is not induenced by the alkah concentration, temperature, or iodate concentration. 

Ha.logen Compounds. Fluorine is unreactive toward ozone at ordinary temperatures. Chlorine is oxidized to Cl20 and Cl20y, bromine to Br Og, and iodine to I2O2 and I4O2. Oxidation of haUde ions by ozone increases with the atomic number of haUde. Fluoride is unreactive chloride reacts slowly, ultimately forming chlorate and bromide is readily oxidized to hypobromite (38). Oxidation of iodide is extremely rapid, initially yielding hypoiodite the estimated rate constant is 2 x 10 (39). HypohaUte ions are oxidized to haUtes hypobromite reacts faster than hypochlorite (40). 

Hypochlorite, hypobromite, and hypoiodite are also strong enough to oxidize thiosulfate to sulfate ... 

Similarly, bromofomi [75-25-2] CHBr, and iodoform [75-47-8] CHI, are obtained from sodium hypobromite and hypoiodite, respectively. Ethyl alcohol is the only primary alcohol that undergoes this reaction. 

Although such alkoxides have never been isolated it is assumed that with bulky alcohols such as steroidal alcohols, the main contributing structure in such an equilibrium (especially when excess lead tetraacetate is present) is the one in which n = 1. An advantage of this procedure held in common with the hypoiodite reaction is the fact that the alcohol derivative is formed in situ. Intermolecular hydrogen abstraction e.g., reaction with solvent)... 

The homolysis of tertiary hypochlorites for the production of oxy radicals is well known." The ease with which secondary hypohalites decompose to ketones has hampered the application of hypohalites for transannular reactions. However the tendency for the base-catalyzed heterolytic decomposition decreases as one passes from hypochlorites to hypobromites tohypoidites. Therefore the suitability of hypohalites for functionalization at the angular positions in steroids should increase in the same order. Since hypoidites (or iodine) do not react readily with ketones or carbon-carbon double bonds under neutral conditions hypoiodite reactions are more generally applicable than hypochlorite or hypobromite decompositions. 

A considerable extension of the synthetic utility of the hypoiodite reaction is achieved if the steroid hypoiodite (2) is generated from the alcohol and acetyl hypoiodite and then decomposed in a nonpolar solvent. In this case ionic hydrogen iodide elimination in the 1,5-iodohydrin intermediate (3) is slow, thereby allowing (3) to be converted into an iodo hypoiodite (5). 

The efficiency with which hypoiodites are formed and/or homolytic-ally decomposed ... 

With 11/3-hydroxy steroids, 11/3, 19-ether formation competes with hemi-acetal formation.This is a consequence of steric hindrance of the 11/5-oxygen by the C-18 and C-19 iodomethyl groups which reduces the rate of hypoiodite formation [(3) (5)] even though the conformation of the... 

No systematic study of the minimal required amount of lead tetraacetate has been made. In cases where the product of the hypoiodite reaction is an iodo ether (20-hydroxy steroids) the reaction can be interrupted at the iodohydrin stage by reducing the amount of iodine to about 0.5 mole. For the oxidation of iodo ethers to lactones, chromium trioxide-sulfuric acid in acetone has been used. Silver chromate is often added to the reaction mixture but comparable yields are obtained without the addition of silver salt. 

The intramolecular formation of 18-cyano-20-ketones in 30-50% yield from 20-cyanohydrins in the hypoiodite reaction is particularly interesting. The reaction is considered to occur through the following steps ... 

K. Heusler, unpublished results. 62a. This statement does not apply to the reaction of 6/S-hydroxy steroids, as both the hypoiodite as well as the lead tetraacetate reactions furnish the same 6/S, 19-oxido compounds in high yields. 

Decomposition of hypoiodites, 247 Deformylation of steroid 19-aldehydes, 273 1-Dehydrotestosterone acetate, 320, 330, 333, 337... 

Lactone formation by hypoiodite functionalization, 251 Lead tetraacetate, 147, 150 Lead tetraacetate reactions, 207, 239, 240, 281... 

The most stable solid hypochlorites are those of Li, Ca, Sr and Ba (see below). NaOCl has only poor stability and cannot be isolated pure KOCl is known only in solution, Mg yields a basic hypochlorite and impure Ag and Zn hypochlorites have been reported. Hydrated salts are also known. Solid, yellow, hydrated hypobromites Na0Br.xH20 (x = 5, 7) and K0Br.3H20 can be crystallized from solutions obtained by adding Br2 to cold cone solutions of MOH but the compounds decompose above 0°C. No solid metal hypoiodites have yet been isolated. 

The normal reduction potential of the iodine-iodide system is independent of the pH of the solution so long as the latter is less than about 8 at higher values iodine reacts with hydroxide ions to form iodide and the extremely unstable hypoiodite, the latter being transformed rapidly into iodate and iodide by self-oxidation and reduction ... 

Discussion. Iodine (or tri-iodide ion Ij" = I2 +1-) is readily generated with 100 per cent efficiency by the oxidation of iodide ion at a platinum anode, and can be used for the coulometric titration of antimony (III). The optimum pH is between 7.5 and 8.5, and a complexing agent (e.g. tartrate ion) must be present to prevent hydrolysis and precipitation of the antimony. In solutions more alkaline than pH of about 8.5, disproportionation of iodine to iodide and iodate(I) (hypoiodite) occurs. The reversible character of the iodine-iodide complex renders equivalence point detection easy by both potentiometric and amperometric techniques for macro titrations, the usual visual detection of the end point with starch is possible. 

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