Hydriodic acid fuming

Properties—Hydrogen iodide is a colourless gas. It is very soluble in water and fumes in moist air (cf. hydrogen chloride), to give hydriodic acid. Its solution forms a constant boiling mixture (cf. hydrochloric and hydrobromic acids). Because it attacks mercury so readily, hydrogen iodide is difficult to study as a gas, but the dissociation equilibrium has been investigated. 

Like sulfonyl esters, sulfonamides can be reduced either to sulfinic acids, or to thiols. Heating of p-toluenesulfonamide with fuming hydriodic acid and phosphonium iodide at 100° afforded 85% of p-thiocresol [703]. 

The sp. gr. of soln. of hydrogen iodide sat. at atm. press, is 1-99 or 2 00, and it fumes in air. The sp. gr. of different concentrations between 12° and 14°, is indicated in Table VIII, where the numbers are referred to water at the same temp. The sp. gr. of hydrobromic or hydriodic acid does not increase proportionally with the cone. The numbers by different observers are not very concordant. 

The catalytic method6,7 for the preparation of hydrogen iodide with the subsequent absorption of the gas in water to form hydriodic acid has the advantage that a very pure product of any desired concentration up to that of the fuming acid may be prepared in a single operation. 

Hydrazine dihydrochloride, 92 Hydrazine residues, recovery of, 92 Hydrazine sulfate, 90, 92 Hydrazoic acid, 77, 78 Hydriodic acid, 157, 159 by action of iodine on hydrogen sulfide, 157 constant boiling, 158 fuming, 162 stabilization of, 159 Hydrobromic acid, 151, 152, 155 constant boiling, 155... 

Hydriodic acid, 1 157, 159 by action of iodine on hydrogen sulfide, 1 157 constant-boiling, 1 158 fuming, 1 162... 

Experiment 126. — Put three or four crystals of potassium iodide in a test tube and add a few drops of concentrated sulphuric acid. Fumes of hydriodic acid are formed among other products. Observe the most obvious properties of these fumes as in Exp. 120, and compare with the fumes of hydrochloric and hydrobromic acids. Are the acids similar ... 

The transformation of chloropurines to iodopurines with fuming hydriodic acid and phosphonium iodide is occasionally accompanied by the reduction of one of the chloro groups.Using cold 47% hydriodic acid, the transformation of 6-chloropurine to 6-iodo-purine (Ij can be successfully achieved. 

Caution. Hydriodic acid is toxic and corrosive all operations with it should be carried out in a well-ventilated fume hood. 

The gaseous hydriodic acid is an intensely fuming substance, which may be easily shown by removing the cork from the receiver containing the aqueous acid, for a moment. Hydriodic acid is absorbed by water with great aridity. The acid, boiling constantly at 1270, contains approximately 50% of anhydrous hydriodic acid. 

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