Hydriodic acid constant-boiling

Reduction of alkenylsilanes. Hydriodic acid (constant boiling) reacts with alkenylsilanes (1) with replacement of (CH3)3Si by H ... 

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. 

Principle. A definite amount of the substance ca. 25 mg.) is weighed out and transferred to the reaction bulb of the apparatus where it is decomposed by refluxing with constant-boiling hydriodic acid, the essential reaction being ... 

By the slow distillation of the alcohol with constant boiling point (57 per cent) hydriodic acid, for example ... 

Mix 30 g. (38 ml.) of iaopropyl alcohol with 450 g. (265 ml.) of constant boiling point hydriodic acid (57 per cent.) (Section 11,49,2) in a 500 ml. distilling flask, attach a condenser for downward distillation, and distil slowly (1-2 drops per second) from an air bath (compare Fig. II, 5, 3). When about half the liquid has passed over, stop the distillation. Separate the lower layer of crude iodide (80 g.). Redistil the aqueous layer and thus recover a further 5 g. of iodide from the flrst quarter of the distillate (1). Wash the combined iodides with an equal volume of concentrated hydrochloric acid, then, successively, with water, 5 per cent, sodium carbonate solution, and water. Dry with anhydrous calcium chloride and distil. The isopropyl iodide distils constantly at 89°. 

Cleavage of ethers with hydriodic acid. Aliphatic ethers suflFer fission when boiled with constant boiling point hydriodic acid ... 

Reflux 1 ml. of the ether with 5 ml. of freshly distilled, constant boiling point hydriodic acid (Section 11,49,2), b.p. 126-128°, for 2-3 hours. Add 10 ml. of water, distil and collect about 7 ml. of liquid. Decolourise the distillate by the addition of a httle sodium bisulphite, and separate the two layers by means of a dropper pipette (Fig. 11,27,1). Determine the b.p. of the resulting iodide by the Siwoloboff method (Section 11,12) and prepare a crystalline derivative (Section 111,42). 

Hydriodic Add.—Both the cone, acid and the acid of constant boiling point (D. 1 7, 57% HI (see p. 506)) are on the market. Usual impurity iodine. 

Alkyl iodides are the most easily formed of the alkyl halides and the slow distillation of the alcohol with constant boiling hydriodic acid is a general method of preparation (e.g. Expt 5.57). As with the corresponding chlorides and bromides (q.v.), the yields of the required alkyl iodides in this reaction may be diminished in the case of certain (tertiary and secondary) alcohols as a result of skeletal rearrangement. 

Hydriodic acid should be preserved in a well-stoppered dark bottle sealed with paraffin and if care is taken to displace the air above the surface of the liquid with an inert gas before sealing, the constant-boiling hydriodic acid can be preserved in a satisfactory condition for some... 

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... 

If the dicyanoguanidine is added to constant boiling hydriodic acid at 90-100°, the reductive cleavage of the iodo-group of 167 occurs and 168 is obtained, but the yields are poor. 

This is supplied as an azeotrope with water (constant boiling hydriodic add), b.p. 125.5-126.5 °C/760mmHg, d 1.70, which contains 55-57 per cent w/w HI (0.936 to 0.99 g HI per ml). Additional grades available contain 45 per cent w/w HI and 67 per cent w/w HI the latter is stabilised by the addition of 0.03 percent w/w of hypophosphorous acid. Once a bottle is opened the contents tend to deteriorate, becoming discoloured in a few days. This can be avoided by purging the container with nitrogen before resealing. 

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