Starch-iodide test

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... 

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). 

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. 

Caution Peroxides may be present. The checkers observed a negative test for peroxides on the filtrate using acidified starch/iodide test paper prior to the final concentration and drying. The checkers recommend testing for peroxides prior to the final concentration and drying. 

This procedure may be used for the preparation of a variety of a-amino ketones as is indicated in Table I, which summarizes most of the submitters experience with this reaction. Principal deviations from the procedure wifi be in the time required for a negative starch-iodide test and the nature and amount of extraction and recrystallization solvent. It is strongly recommended that any one using the reaction for the first time carry out the preparation on a-phenylethylamine before attempting to use it on other more valuable amines. 

Time for negative starch-iodide test. 6 Usually with decomposition. 

Cyclododecanone (2.0 g, 11 mmol) is added to m-chloroperbenzoic acid (4.2 g, 21 mmol) in 25 ml of dry chloroform (CAUTION). The reaction mixture is heated at reflux for 48 hours after which time a starch-iodide test for peroxide is negative. After the mixture is cooled in ice-water, the precipitated m-chlorobenzoic acid is removed by filtration and the chloroform is evaporated to dryness. The residue is taken up in 60 ml of ether, washed three times with 20-ml portions of aqueous potassium carbonate, and once with brine. After drying and removal of solvent there remains crude dodecanolide (1.9 g,... 

The helical structure of amylose also serves as the basis for an interesting and useful reaction. The inside of the helix is just the right size and polarity to accept an iodine (I2) molecule. When iodine is lodged within this helix, a deep blue starch-iodine complex results (Figure 23-19). This is the basis of the starch-iodide test for oxidizers. The material to be tested is added to an aqueous solution of amylose and potassium iodide. If the material is an oxidizer, some of the iodide (I-) is oxidized to iodine (I2), which forms the blue complex with amylose. 

A solution of 28 grams (0.3 mole) of aniline in 350 cc. 2 N hydrochloric acid is externally cooled to about 20°C. and then to 0° by the addition of crushed ice. The solution is diazotized by the addition of a solution of 22 grams of technical sodium nitrite in 150 cc. ice water. The addition of the nitrite solution can be completed in less than 1 minute. The resulting diazo solution must be clear, any cloudiness indicating lack of sufficient acid. The diazotization is complete after about 10 minutes (Congo red and starch-iodide tests). 

If the starch-iodide test is still positive for the presence of peroxide, additional thiosulfate solution should be added until a negative starch-iodide test is obtained. 

Diphenyl disulfide. In a 100-mL, round-bottomed flask equipped with a magnetic stirrer are placed 11.0 g (10.25 ml, 0.1 mol) of benzenethiol and 50 mL of trifluoroethanol (Note 1). The mixture is stirred and cooled in an ice bath (Note 2) and 12.5 mL (3.73 g, 0.11 mol) of 30% aqueous hydrogen peroxide (Note 3) is added dropwise over a period of 15 min through an addition funnel. After completion of the addition, the ice bath is removed and the reaction mixture is allowed to stir at room temperature for 24 hr. Diphenyl disulfide is sparingly soluble in trifluoroethanol and precipitates out of solution. The solids are collected on a Buchner funnel and dried under vacuum to afford 10.6 g of diphenyl disulfide (97%) (Note 4). Sodium sulfite 2.52 g (0.02 mol) is added to the mother liquor to decompose the excess peroxide and the mixture is heated in a water bath at 50°C for 30 min. A starch iodide test is negative. The liquid is transferred to a 100-mL, round-bottomed flask, fitted with a distillation unit having a Vigreux column (5 cm). The flask is heated in an oil bath and the solvent is distilled to recover the trifluoroethanol (Note 5). 

Add a drop of the reaction mixture to a piece of starch-iodide paper. Any unreacted hypochlorite will cause the appearance of the blue starch-triiodide complex. Add 1-mL portions of saturated sodium bisulfite solution to the reaction mixture until the starch-iodide test is negative. 

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