Starch, iodide

Starch Iodide coloration. To a small volume of starch solution ... 

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. 

Before coupling, excess nitrous acid must be destroyed. Nitrite can react with coupling components to form nitroso compounds causiag deHterious effects on the final dyestuff. The presence of nitrite can be detected by 4,4 -diamiQO-diphenyHnethane-2,2 -sulfone [10215-25-5] (Green reagent) or starch—iodide. Removal of nitrite is achieved by addition of sulfamic acid or urea [57-13-6], however, sulfamic acid [5329-14-6] has been more effective ia kinetic studies of nine nitrous acid scavangers (18). 

Determination. The most accurate (68) method for the deterrnination of copper in its compounds is by electrogravimetry from a sulfuric and nitric acid solution (45). Pure copper compounds can be readily titrated using ethylene diamine tetracetic acid (EDTA) to a SNAZOXS or Murexide endpoint. lodometric titration using sodium thiosulfate to a starch—iodide endpoint is one of the most common methods used industrially. This latter titration is quicker than electrolysis, almost as accurate, and much more tolerant of impurities than is the titration with EDTA. Gravimetry as the thiocyanate has also been used (68). 

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. 

Sodium -toluenesulfonate, 3, 37, 38 Splitting C C linkage, 4, 39 Splitting C Hg linkage, 7, 19 Stabilizer, 8, 56 Stannous chloride, 8, 96 Starch-iodide test 3, 7 79, 8, 42, 80 Steam distillation apparatus, 2, 0 Steam distillation, reduced pressure, 5, 80... 

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. 

Free nitrous acid causes an immediate blue color at the point of contact with starch-iodide test paper. A delayed color or a color around the periphery of the wetted area is of no significance. At all times there must be an excess of mineral acid (blue color on Congo paper). 

Ozonolysis. Ozonolysis of the methylhexadiene polymer was conducted (21)at room temperature on a solution of 1,03 g. polymer in 20 ml. tetrahydrofuran with the aid of the Wellsbach ozonizer. The end point for the ozonolysis was observed after about 15 min. by the reaction of excess ozone with starch-iodide solution. Triphenylphosphine was added to the reaction mixture and allowed to react at room temperature for 60 hr. The resulting product was analyzed by GLC (Hewlett Packard 5750, Porapak Q 10 ft. x 1/8 in. column at 110°C, helium pressure 60 psi, thermal conductivity detector at 190°C, injector 200°c). 

Larger scale operations may require th use of a pH meter or starch/iodide test paper to ensure that the scrubbing capacity is not being exceeded. 

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.)... 

It was Brown and Morris (15) in 1888 who employed Raoult s method. They reported a value of 30,000 for the molecular weight of amylodextrin, a degradation product of the hydrolysis of starch. Subsequently Lintner and Dull (16) also using cryoscopy reexamined amylodextrin, and reported the molecular weight as 17,500. In a third paper, Rodewald and Kattein (17) in 1900, measured the molecular weight of starch by osmotic pressure experiments carried out on aqueous solutions of starch iodide. They obtained somewhat higher molecular weights, 36,700 and 39,700. 

Experiments—Dissolve 0-02 g. of cholic acid in 0-5 c.c. of alcohol and add to the solution 1 c.c. of 0-1 A-iodine solution. On cautious dilution with water the blue crystalline iodine compound of cholic acid, comparable to starch iodide, separates. 

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. 

This excess HN02 may be detected by employing either starch iodide strip or paste and designated by the following equation ... 

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. 

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