Iodine alkaline solution

Iodine has the lowest standard electrode potential of any of the common halogens (E = +0.54 V) and is consequently the least powerful oxidising agent. Indeed, the iodide ion can be oxidised to iodine by many reagents including air which will oxidise an acidified solution of iodide ions. However, iodine will oxidise arsenate(lll) to arsenate(V) in alkaline solution (the presence of sodium carbonate makes the solution sufficiently alkaline) but the reaction is reversible, for example by removal of iodine. 

The dialkyl disulphides may be prepared by the oxidation of an alkaline solution of a mercaptan with iodine, for example ... 

Because of their use in the rubber industry various sulfenamido thiazoles (131) have been prepared. They are obtained in good yields through the oxidation of A-4-thiazoline-2-thiones (130) in aqueous alkaline solution in the presence of an amine or ammonia (Scheme 66) <123, 166, 255, 286, 308, 309). Other oxidizing agents have been proposed (54, 148. 310-313) such as iodine (152), chlorine, or hydrogen peroxide. Disulfides can also be used as starting materials (3141. 

In alkaline solutions, iodine can be oxidized to iodate by sodium hypochlorite or hypobromite, whereas chlorine passed into a solution of iodine and alkah oxidizes ah the way to periodate. 

Phosphonic acid and hydrogen phosphonates are used as strong but slow-acting reducing agents. They cause precipitation of heavy metals from solutions of their salts and reduce sulfur dioxide to sulfur, and iodine to iodide in neutral or alkaline solution. 

Sodium iodide [7681-82-5] Nal, occurs as colorless crystals or as a white crystalline solid. It has a salty and slightly bitter taste. In moist air, it gradually absorbs as much as 5% water, which causes caking or even Hquefaction (dehquescence). The soHd slowly becomes brown when exposed to air because some iodide is oxidized to iodine. Water solutions are neutral or slightly alkaline and gradually become brown for the same reason. Aqueous solutions are stabilized with respect to oxidation by raisiag the pH to 8—9.5 (see Iodine and iodine compounds). 

Wet-Chemical Determinations. Both water-soluble and prepared insoluble samples must be treated to ensure that all the chromium is present as Cr(VI). For water-soluble Cr(III) compounds, the oxidation is easily accompHshed using dilute sodium hydroxide, dilute hydrogen peroxide, and heat. Any excess peroxide can be destroyed by adding a catalyst and boiling the alkaline solution for a short time (101). Appropriate ahquot portions of the samples are acidified and chromium is found by titration either using a standard ferrous solution or a standard thiosulfate solution after addition of potassium iodide to generate an iodine equivalent. The ferrous endpoint is found either potentiometricaHy or by visual indicators, such as ferroin, a complex of iron(II) and o-phenanthroline, and the thiosulfate endpoint is ascertained using starch as an indicator. 

This is due partly to the great insolubility of TI2O3 (2.5 X 10- "g r at 25 ) and partly to the enhanced oxidizing power of iodine in alkaline solution as a result of the formation of hypoiodate ... 

Reaction of the potassium salt of salicylaldehyde with chlo-roacetone affords first the corresponding phenolic ether aldol cyclization of the aldehyde with the ketonic side chain affords the benzofuran (1). Reduction of the carbonyl group by means of the Wolf-Kischner reaction affords 2-ethyl-benzofuran. Friedel-Crafts acylation with anisoyl chloride proceeds on the remaining unsubstituted position on the furan ring (2). The methyl ether is then cleaved by means of pyridine hydrochloride (3). lodina-tion of the phenol is accomplished by means of an alkaline solution of iodine and potassium iodide. There is thus obtained benziodarone (4)... 

The alkaline solution of thymol is made up to 100 or 200 c.c. as the case may require, using a 5 per cent, soda solution. To 10 c.c. of this solution in a graduated 500 c.c. flask is added a normal iodine solution in shgbt excess, whereupon the thymol is precipitated as a dark reddish-brown iodine compound. In order to ascertain whether a sufficient quantity of iodine has been added, a few drops are transferred into a test tube and a few drops of dilute hydrochloric acid are added. When enou iodine is present, the brown colour of the solution indicates the presence of io ne, otherwise the liquid appears milky by the separation of thymol. If an excess of iodine is present, the solution is slightly acidified with dilute hydrochloric acid and diluted to 500 c.c. From this 100 c.c. are filtered,off, and the excess of iodine determined by titration with normal solution of sodium thiosulphate. For calculation, the number of cubic centimetres required is deducted from the number of cubic centimetres of normal iodine solution added and the resultant figure multiplied by 5, which gives the number of cubia centimetres of iodine required by the thymol. 

Every cubic centimetre of normal iodine solution equals G 003753 gram of thymol. Knowing the quantity of thymol in the alkaline solution, the percentage in the original oil is readily found. 

A similar procedure may also be used for the determination of antimony(V), whilst antimony (III) may be determined like arsenic(III) by direct titration with standard iodine solution (Section 10.113), but in the antimony titration it is necessary to include some tartaric acid in the solution this acts as complexing agent and prevents precipitation of antimony as hydroxide or as basic salt in alkaline solution. On the whole, however, the most satisfactory method for determining antimony is by titration with potassium bromate (Section 10.133). 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

Lugol solution chem A solution of 5 grams of iodine and 10 grams of potassium iodide per 100 milliliters of water used in medicine. Iu,g6l so lir-shon luminol orgchem CgffyNjOj Awhite, water-soluble, crystalline compound that melts at 320°C used in an alkaline solution for analytical testing in chemistry. Also known as 3-aminophthalic hydrazide. lu mo.nol )... 

Iodine behaves as a powerful oxidizing agent in strong alkaline solution due to the formation of hypoiodite ion ... 

When chlorine is passed through an alkaline solution of iodine, the latter is oxidized to periodate ... 

Various microchemical tests are available for the detection of minute quantities of sulphur, both free and combined. The substance under examination may be treated with a little sodium hydroxide solution, the extract evaporated just to dryness, a few drops of aqueous sodium cyanide (0-1 per cent.) added and the evaporation repeated. The residue, moistened with dilute sulphuric acid and a drop of ferric chloride, gives the characteristic ferric thiocyanate colour if sulphur is present.6 In the ease of minerals, traces of sulphur dioxide produced on heating may be detected 6 by the colour change of an alkaline solution of Bromocrcsol Green or by the deeolorisation of starch-iodine solution. 

If iodine solution is added to a neutral or alkaline solution of an arsenite, the former is decolorised and oxidation occurs ... 

A commun means of detecting hypochlorites is the production of u blue color (caused by free iodine) with starch iodide paper by hypochlorites in weakly alkaline solution. Silver nitrate also precipitates part of the hypochlorite in solutions as white silver chloride. 

VelumdncdUy.—Iodine in alkaline solution reacts with acetone to give iodoform, a reaction which is used in the estimation of the ketone. 

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