Iodide-starch paper

Fluorine in the atmosphere can be detected by chemical methods involving the displacement of halogens from haUdes. Dilute fluorine leaks are easily detected by passing a damp piece of starch iodide paper around the suspected area. The paper should be held with metal tongs or forceps to avoid contact with the gas stream and immediately darkens when fluorine is present. 

By starch iodide paper (original colour white)... 

Jod-saure, /, iodic acid, -schwefel, m. sulfur iodide, -serum, n. iodized serum, -silber, n. silver iodide, -silizium, n. silicon iodide. -stSrke, /. starch iodide, iodized starch. -stSrkepapier, n. starch iodide paper, -stick-stoff, m. nitrogen iodide, -thymol, n.iPhaTm.) thymol iodide, -tinktur,/. tincture of iodine, -toluol, n. iodotoluene. -iibertrilger, m. iodine carrier. 

To detect nitrous acid, a drop of the mixture is diluted with water and tested with starch iodide paper. 

Forty-three grams (0.25 mole) of />-bromoaniline (Note 1) and 20 cc. of water are warmed in a 400-cc. beaker until the bromoaniline melts, and then 50 cc. of concentrated hydrochloric acid (sp. gr. 1.19) is added with mechanical stirring. The mixture is heated and stirred until solution is practically complete (Note 2). The beaker is then set in a dish of ice water and the solution is stirred as it cools in order to precipitate the />-bromoaniline hydrochloride in fine crystals. A few small pieces of ice are added and the cold (about 0-5 °) suspension is diazotized with a solution of 18 g. of sodium nitrite in 36 cc. of water to an end point with starch-iodide paper. 

A mixture of 280 g. (1.52 moles) of commercial benzidine and 880 cc. (10.23 moles) of concentrated hydrochloric acid (sp. gr. 1.182) is placed in a 5-I. round-bottomed flask and wanned on a steam bath for one to two hours, with occasional shaking, to form the dihydrochloride. The flask is then equipped with a mechanical stirrer and a dropping funnel, and cooled, with stirring, to — ro° in an ice-salt bath. When this temperature has been reached, the benzidine dihydrochloride is tetrazotized over a period of two hours with a solution of 232 g. (3.19 moles) of 95 per cent sodium nitrite in 800 cc. of water, until a faint test for nitrous acid with starch-iodide paper is obtained after twenty minutes. During this reaction, the temperature is kept below —5 °. 

B. 2H-Pyran-2-one. A mixture of 9.81 g. (0.100 mole) of 5,6-dihydro-2/I-pyran-2-one, 200 mg. of benzoyl peroxide, 18.6 g. (0.105 mole) of A-bromosuccinimide [2,5-Pyrrolidinedione, 1-bromo-] (Note 7), and 800 ml. of carbon tetrachloride is prepared in a 2-1., three-necked, round-bottomed flask equipped with a reflux condenser and a mechanical stirrer. The resulting suspension is stirred and heated to reflux. After 1.5 hours at reflux, most of the solid is dissolved, and the solution gives a negative test with starch-iodide paper. The reaction mixture is then allowed to cool, dining which time succinimide [2,5-Pyrrolidine-dione] crystallizes out. The precipitate is removed by filtration, and the filtrate is concentrated under reduced pressure to leave crude 5-bromo-5,6 -dihy dro 211 -pyran-2 one [ 211 Py ran - 2-one, 5-bromo-5,6-dihydro] as an oil. 

A. o-Bromobenzenediazonium hexafluorophosphate. A solution of 95 ml. of 12N hydrocMoric acid in 650 ml. of water is added with stirring to 60 g. of o-bromoaniline (0.35 mole Note 1) in a 2-1. three-necked flask equipped with stirrer and thermometer. Solution is effected by heating the mixture on a steam bath (Note 2). A solution of 29 g. (0.42 mole) of sodium nitrite in 75 ml. of water is added with stirring while the mixture is maintained at — 5° to —10° by means of a bath of ice and salt or of dry ice and acetone. At the end of the addition there is an excess of nitrous acid, which can be detected with starch iodide paper. Seventy-four milliliters (134 g., 0.60 mole) of 65% hexafluorophosphoric acid (Note 3) is added in one portion, with vigorous stirring, to the cold solution of the diazonium salt. Cooling and slow stirring are continued for an additional 30 minutes, and the precipitated diazonium hexafluorophosphate is then collected on a Bilchner funnel. The diazonium salt is washed on the funnel with 300 ml. of cold water and with a solution of 80 ml. of methanol in 320 ml. 

Bromine (Br2> displaces iodine from a solution of potassium iodide and, as a consequence, the iodine turns starch blue-black. (Starch-iodide paper may also be used.)... 

Test Place 0.05 ml of a 10% w/v solution on starch-iodide paper. 

The excess of bromine is removed by warming the acidic solution gently till the vapours show a negative test with starch-iodide paper. However, the residual traces of Br2 are reduced by treatment of the resulting solution with phenol to yield the corresponding 2,4,6-tribromophenol as shown below ... 

Materials Required Thyroid gland dried 1.0 g anhydrous potassium carbonate 17.0 g bromine solution (9.6 ml of Br2 and 30 g of KBr in 100 ml DW) 7.0 ml dilute phosphoric acid (10% w/v) 42.0 ml starch iodide paper phenol solution (saturated solution of phenol in water) 5.0 ml potassium iodide solution (10% w/v in water) 0.01 N sodium thiosulphate solution starch solution. 

In other words, the small excess of HN02 present at the end-point can be detected visually by employing either starch-iodide paper or paste as an external indicator. Thus, the liberated iodine reacts with starch to form a blue green colour which is a very sensitive reaction. Besides, the end-point may also be accomplished electrometrically by adopting the dead-stop end-point technique, using a pair of platinum electrodes immersed in the titration liquid. 

Materials Required Calcium aminosalicylate 0.5 g hydrochloric acid ( 11.5 N) 10.0 ml potassium bromide 1.0 g 0.1 M sodium nitrite starch-iodide paper. 

Procedure Weigh accurately about 0.5 g of phthalylsulphathiazole and heat on a water-bath for 2 hours after the addition of 10.0 ml of sodium hydroxide solution. Cool the contents of the flask to 15°C in an ice-bath, add to it 10.0 ml of water and 20.0 ml of hydrochloric acid and carry out the titration slowly with 0.1 M sodium nitrite solution. The contents of the flask are shaken thoroughly and continuously until a distinctly visible blue colour is obtained when a drop of the titrated solution is placed on a starch-iodide paper 5 minutes after the last addition of the 0.1 M NaN02 solution. Towards the approach of the endpoint the addition of NaN02 solution must be at the rate of 0.1 ml. Each ml of 0.1 M sodium nitrite is equivalent to 0.04034 g of C17H13N305S2. 

Dapsone 0.3 g Starch-iodide paper/paste Each ml of 0.1 M NaN02 = 0.01242 g of c12h12n2o2s... 

While the naphthol is dissolving, a solution of benzenedi-azonium chloride is prepared. In a 3-I. wide-mouth bottle are placed 128 g. of aniline and 1.5 kg. of cracked ice, and on to this mixture while it is stirred (by hand) is poured 410 cc. of concentrated hydrochloric acid (32 per cent sp. gr. 1.16). Some crystals of aniline hydrochloride separate at this point. A solution of 100 g. of sodium nitrite in 200 cc. of water is now run in slowly from a 500-cc. separatory funnel. The tip of the stem of the separatory funnel should dip well below the surface of the liquid. The mixture is stirred (by hand if desired) and a drop is tested from time to time with starch iodide paper. This is... 

Forty-seven grams (48 ml., 0.5 mole) of aniline is dissolved in 200 ml. of aqueous hydrochloric acid (prepared from equal volumes of concentrated acid and water) in a 2-1. beaker. The beaker is equipped with a mechanical stirrer and immersed in an ice-salt bath. After the solution has cooled to 5°, 36 g. (0.52 mole) of sodium nitrite dissolved in 1 1. of water is added slowly, with stirring, from a separatory funnel. The tip of the stem of the separatory funnel should dip well below the surface of the liquid. The rate of addition is adjusted to maintain the temperature below 10°. A drop of the reaction mixture is tested from time to time with starch-iodide paper (Note 2). The sodium nitrite solution is added until nitrous acid persists in the solution during a 5-minute interval. 

The test is made by diluting the test drop on a watch glass with about 1 ml. of water and then placing a drop of this solution on the starch-iodide paper. 

A positive test is the immediate formation of a dark violet or brown spot on starch-iodide paper moistened with 2N hydrochloric acid. A negative test may consist of a very faint beige color or complete absence of color. 

A solution of 320 g of sodium nitrite in 21. of water is added to a suspension of 1000 g of the sodium salt of picramic acid in 81. of water. Next, 61. of 5.5% hydrochloric acid is added dropwise for 2 hr, stirring continuously. The initial temperature of 20°C rises to 25°C. Completion of the reaction is determined by means of starch-iodide paper. The product is filtered off, washed with cold water and dried at 35-40°C. Its yield amounts to 80% of the theoretical. 

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