Hydriodic acid, preparation properties

It is common practice to refer to the molecular species HX and also the pure (anhydrous) compounds as hydrogen halides, and to call their aqueous solutions hydrohalic acids. Both the anhydrous compounds and their aqueous solutions will be considered in this section. HCl and hydrochloric acid are major industrial chemicals and there is also a substantial production of HF and hydrofluoric acid. HBr and hydrobromic acid are made on a much smaller scale and there seems to be little industrial demand for HI and hydriodic acid. It will be convenient to discuss first the preparation and industrial uses of the compounds and then to consider their molecular and bulk physical properties. The chemical reactivity of the anhydrous compounds and their acidic aqueous solutions will then be reviewed, and the section concludes with a discussion of the anhydrous compounds as nonaqueous solvents. 

The preparation and properties of 2-substituted isoarsindolines (28) have been examined in some detail. They are prepared from o-xylylene dibromide (32) by the reactions shown in Scheme 8 (50JCS1917). Isoarsindolines have many of the properties of stable tertiary arsines and form arsine oxides, methopicrates and methiodides. With concentrated nitric acid the intermediate arsine oxide is polar enough to react further to give the water soluble hydroxynitrate (33). With boiling hydriodic acid, 2-iodoisoarsindoline (34) is formed. This... 

At this stage, the possible presence of a branched-chain saccharinic acid in Kiliani s preparation was supported only by (a) the properties of the barium salt of the hydroxyhexanoic acid obtained from it on reduction and (b) the reported oxidation of parasaccharinic acid with nitric acid to a tribasic acid. The latter evidence was retracted by Kiliani in his final report on the matter, when he stated that the previous identification of hydroxycitric acid was in error and that this tribasic acid is, in fact, ( — )-tartaric acid. In addition, he now observed that oxidation of parasaccharinic acid with nitric acid, followed by reduction with hydriodic acid and red phosphorus, gives a low yield of adipic acid. 

This phosphine is prepared in a similar manner to the phenyl compound and possesses similar properties to the latter. It melts at 4° C. and boils at 178° C. Its hydriodide, C7H7 PH2.HI, is a yellow powder crystallising from fuming hydriodic acid in glistening needles which may be sublimed. The product is deliquescent and decomposed by water. The phosphine forms a yellow platinichloride, (C7H7.PH2.HCl)2PtCl4. p-Ethylphenylphosphine, ... 

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