Potassium iodate, preparation

In the second method a solution of the approximate strength required is prepared, and this is standardised against some standard alkaline substance, such as sodium tetraborate or anhydrous sodium carbonate standard potassium iodate or pure silver may also be used (see Section 10.84). If a solution of an exact strength is required, a solution of an approximate strength somewhat greater than that desired is first prepared this is suitably diluted with water after standardisation (for a typical calculation, see Appendix 17). 

Preparation ofpure potassium hydrogeniodate. Dissolve 27 g of potassium iodate in 125 mL of boiling water, and add a solution of 22 g of iodic acid in 45 mL of warm water acidified with six drops of concentrated hydrochloric acid. Potassium hydrogeniodate separates on cooling. Filter on a sintered-glass funnel, and wash with cold water. Recrystallise three times from hot water use 3 parts of water for 1 part of the salt and stir continuously during each cooling. Dry the crystals at 100 °C for several hours. The purity exceeds 99.95 per cent. 

The standard solution is prepared by dissolving a weighed amount of pure potassium iodate in a solution containing a slight excess of pure potassium iodide, and diluting to a definite volume. This solution has two important uses. The first is as a source of a known quantity of iodine in titrations [compare Section 10.115(A)] it must be added to a solution containing strong acid it cannot be employed in a medium which is neutral or possesses a low acidity. 

For the preparation of standard iodine solutions, resublimed iodine and iodate-free potassium iodide should be employed. The solution may be standardised against pure arsenic(III) oxide or with a sodium thiosulphate solution which has been recently standardised against potassium iodate. 

The standardisation of thiosulphate solutions may be effected with potassium iodate, potassium dichromate, copper and iodine as primary standards, or with potassium permanganate or cerium)IV) sulphate as secondary standards. Owing to the volatility of iodine and the difficulty of preparation of perfectly pure iodine, this method is not a suitable one for beginners. If, however, a standard solution of iodine (see Sections 10.112 and 10.113) is available, this maybe used for the standardisation of thiosulphate solutions. 

Note. This is prepared by dissolving 5 g of potassium iodate in 167 mL of concentrated nitric acid, and diluting to 500 mL. 

Vicinal iodo carboxylates may also be prepared from the reaction of olefins either with iodine and potassium iodate in acetic acid/ or with N-iodosuccinimide and a carboxylic acid in chloroform. " A number of new procedures for effecting the hydroxylation or acyloxylation of olefins in a manner similar to the Prevost or Woodward-Prevost reactions include the following iodo acetoxylation with iodine and potassium chlorate in acetic acid followed by acetolysis with potassium acetate reaction with iV-bromoacetamide and silver acetate in acetic acid reaction with thallium(III) acetate in acetic acid and reaction with iodine tris(trifluoroacetate) in pentane. ... 

MRH Barium chlorate 5.06/83, calcium chlorate 5.61/77, potassium chlorate 6.07/76, sodium bromate 4.98/80, sodium chlorate 7.32/75, zinc chlorate 6.11/76 Dry finely divided mixtures of red (or white) phosphorus with chlorates, bromates or iodates of barium, calcium, magnesium, potassium, sodium or zinc will readily explode on initiation by friction, impact or heat. Fires have been caused by accidental contact in the pocket between the red phosphorus in the friction strip on safety-match boxes and potassium chlorate tablets. Addition of a little water to a mixture of white or red phosphorus and potassium iodate causes a violent or explosive reaction. Addition of a little of a solution of phosphorus in carbon disulfide to potassium chlorate causes an explosion when the solvent evaporates. The extreme danger of mixtures of red phosphorus (or sulfur) with chlorates was recognised in the UK some 50 years ago when unlicenced preparation of such mixtures was prohibited by Orders in Council. 

Fluorescein (147) is prepared by the same route as Pigment Red 90 (see p. 575). The compound is iodized with iodine and potassium iodate in an acidic medium. The iodic acid reoxidizes the resulting hydrogen iodide back to iodine ... 

Theory First of all the potassium iodate is dried to a constant weight at 110°C to make it completely free from moisture and then brought to room temperature in a desiccator. It is pertinent to mention here that KI03 is a very stable salt and may be obtained in a very pure form. Therefore, it is possible to prepare the standard solutions of KI03 by dissolving the calculated weight of the salt in water and diluting the same to an approximate volume. 

Potassium periodate can be prepared by oxidation of potassium iodate with a powerful oxidizing agent such as potassium permanganate, chlorine or bromine in basic solution ... 

Potassium Iodate ( ). A 0.1000 N solution was prepared by weighing 3.567 g and dissolving into a 1000-mL volumetric flask with distilled water. 

F. C. Mathers and C. G. Schluderberg 124 prepared indium iodate, In(I03)3, by mixing soln. of indium trichloride and potassium iodate. The precipitate is amorphous. The mixture was evaporated to dryness on a water-bath the residue extracted on a Gooch s crucible with warm water and dried in vacuo over sulphuric acid. The mass was dissolved in boiling nitric acid (1 10), and on evaporation white crystals of indium iodate were formed. 100 grms. of water at 20° dissolve 0 067 grm., and 100 grms. of nitric acid (1 5) at 80° dissolve 0 67 grm. of the salt. It also dissolves in dil. sulphuric or hydrochloric acid. The soln. in the last-named add decomposes with the liberation of chlorine. The crystals decompose with the evolution of iodine when heated by a free flame and explode if touched with a red-hot iron wire. 

It has not yet been possible to isolate noradrenolutin from the products of the direct rearrangement of noradrenochrome in solution. [Noradrenolutin should probably be formulated in the keto form (38) however, it is often represented in the trihydroxy form (39).] However, pure samples of this valuable compound have recently been obtained by the cautious hydrolysis of 3,5,6-triacetoxyindole (40),70,71 obtained by deiodination of 3,5,6-triacetoxy-7-iodoindole (41),70,71 which can readily be obtained by the action of acetic anhydride and pyridine on 7-iodonoradrenochrome (42).70,71,74 7-Iodonoradreno-chrome (42) has been prepared in pure crystalline form by the oxidation of noradrenaline (43) with potassium iodate.70,71... 

EXERCISE 88. PREPARATION OF POTASSIUM IODATE FROM POTASSIUM CHLORATE... 

An excellent way to prepare standard If is to add a weighed quantity of potassium iodate to a small excess of Kl.21 Then add excess strong acid (giving pH 1) to produce If by quantitative reverse disproportionation ... 

Free Acid. — Dissolve about 0.5 gm. of potassium iodate in about 20 cc. of boiled water, and add a small crystal of neutral potassium iodide and a few drops of freshly prepared starch solution. The liquid should not immediately acquire a blue color. 

A solution of sodium iodate, prepared from lOg of iodine according to (I), is diluted to 120ml with water and 4g of sodium hydroxide are added. Twenty-two grams of potassium persulfate are used as m (II) and then a second portion of 17g sodium hydroxide is added. The mixture is boiled for 15 minutes longer, then cooled to 40° C, and the liquid is decanted. The solid is broix it on to the filter with about 25ml of ice water, pressed dry, and then heated at 110°C for one or two hours. 

The corresponding potassium salt, which is considerably less stable, may be prepared by triturating 2g of potassium iodate in a mortar with the addition of 10ml of concentrated hydrochloric acid in drops from a burette. 

Iodine pentoxide is a white solid substance that, at ordinary temperatures, is entirely stable. It cannot be prepared by direct synthesis from iodine and oxygen, because when cold the elements combine too slowly, and when heated the compound is unstable. It may be readily prepared by the direct oxidation of iodine by means of strong oxidizing agents, such as concentrated nitric acid or chlorine. One method for the oxidation of iodine has already been illustrated under the preparation of potassium iodate, but... 

Iodate Dissolve 1.1 g of sample in sufficient ammonia- and carbon dioxide-free water to make 10 mL of solution, and transfer to a color-comparison tube. Add 1 mL of starch TS and 0.25 mL of 1 A sulfuric acid, mix, and compare the color with that of a control containing, in each 10 mL, 100 mg of Potassium Iodide, 1 mL of standard iodate solution (prepared by diluting 1 mL of a 1 2500 solution of potassium iodate to 100 mL with water), 1 mL of starch TS, and 0.25 mL of 1 N sulfuric acid. Any color in the sample solution does not exceed that in the control. 

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