Bromine color

The flask is then cooled in ice water, and the contents are filtered with as little suction as possible (Note 3). The filter cake is pressed dry and washed with three 15-ml. portions of tetrachloroethane first used to rinse out the flask. The combined filtrates are dried with a little calcium chloride. Sometimes the solution contains a little bromine it is removed by adding allyl alcohol dropwise until the bromine color is discharged (usually 0.5-1.0 ml. suffices). 

Note 2). Carbon dioxide is introduced at such a rate "that no bromine vapor is observed in the outlet tube (5-8 bubbles per second). The stream of carbon dioxide is continued for thirty minutes after all the bromine color has disappeared from the train. The reaction is complete in ten to thirteen hours, depending upon the rate at which the bromine has been introduced into the reaction mixture. 

A. a,a,ot, a -Tetrabromo-o-xylene. In a 2-1. three-necked flask equipped with an oil-lubricated Trubore stirrer, a dropping funnel, a thermometer extending nearly to the bottom of the flask, and a reflux condenser (Note 1) attached to a gas absorption trap 2 is placed 117 g. (1.1 moles) of dry o-xylene (Note 2). An ultraviolet lamp such as a General Electric R.S. Reflector Type 275-watt sun lamp is placed about 1 cm. from the flask so as to admit the maximum amount of light. The stirrer is started, and the o-xylene is heated to 120° with an electric heating mantle. A total of 700 g. (4.4 moles) of bromine (n.f. grade) is added in portions from the dropping funnel to the reaction flask at such a rate that the bromine color is removed as fast as it is added. 

A sample (approximately 0.2 g.) is weighed accurately and dissolved in 25 ml. of water then 25 ml. of 0.1 N hydrochloric acid and 0.2 g. of potassium bromide are added. The solution is titrated with 0.017 M potassium bromate until a permanent yellow color is produced. Potassium iodide (0.1 g.) is added, and the solution is backtitrated to a starch end point with 0.1 N sodium thiosulfate. The blue color returns in about a minute since the high acidity promotes air oxidation of excess iodide. The accuracy is only slightly less if the appearance of a faint yellow bromine color is taken as the end point. One mole of potassium bromate is equivalent to 3 of sodium /8-styrenesul-fonate. 

A solution of 2.45 gm (0.019 mole) of A-heptyl-4-hydroxylamine is prepared in 2 AT hydrochloric acid. To this solution is added, with vigorous stirring, bromine water until the bromine color just persists. During this addition a colorless precipitate of the product begins to form. After the addition has been completed, stirring is continued for a short time. Then the product is filtered off, washed with a small quantity of ice-cold water, and dried on an unglazed clay plate yield 1.93 gm (80%), m.p. 46°-48°C. The product may be recrystallized from acetone or distilled under reduced pressure (b.p. 90°-93°C, 0.4 mm Hg). The final melting point is reported as 49°-50°C. 

The intensity of the color in the reduced bromine solution depends somewhat on the quality of bromine used, and with the technical product special care is needed in noting the endpoint of the reduction i.e., the transition from the bromine color to a yellowish-brown color. 

To determine the purity of any sample of allyl alcohol, 1 cc. is run into 15 to 25 cc. of carbon tetrachloride and this solution is then treated in the cold with a carbon tetrachloride solution of bromine (standardized with potassium iodide and sodium thiosulfate) until a permanent bromine coloration is obtained. The amount of allyl alcohol present in any solution may also be determined roughly by conversion to allyl bromide. From several experiments it was found that the allyl bromide obtained was equivalent to the amount of allyl alcohol as determined by bromine titration. 

Exercise 17-10 When a small amount of bromine is added to a solution of cyclohexanone in carbon tetrachloride, the brown-red bromine color persists for quite some time. Subsequent additions of bromine result in more rapid reaction and finally the bromine is decolorized almost as rapidly as it can be poured in (until all of the ketone has reacted). Explain this sequence of events. 

Bromine test The compound to be tested is treated with a few drops of 1 to 5% Br2/CCl4 solution. A positive test is indicated by decolonization of the bromine color. 

In methylene chloride (3 L) was dissolved m-chloropropiophenone (698.0 g 4.15 mole). The solution was stirred with charcoal (Darco) and magnesium sulfate for 2 h and filtered. To it was added with stirring (662.0 g) of bromine in methylene chloride (1 L). When the bromine color had faded completely, the solvent was evaporated in vacuum and m-chloro-a-bromopropiophenone was obtained as oil. 

Dibromosiloxene is the first product which can be isolated. It is formed in the reaction between a carbon disulphide solution of bromine (about 10%) and a carbon disulphide suspension of siloxene the reagents are mixed while cooling with ice, as in a titration. When the bromine color remains, a dibromosilo-... 

The reaction with bromine is a classical test for the presence of double (or triple) bonds in an unknown compound. In the test, the unknown is added dropwise to a solution of bromine in a solvent such as CC14 or CH2C12. The bromine solution has a red-brown color. If the unknown contains carbon-carbon double or triple bonds, the addition reaction is nearly instantaneous. Because the addition products are colorless, the rapid disappearance of the bromine color constitutes a positive test for the presence of unsaturation. 

Bromine is added dropwise with stirring to 35 g. (0.118 mole) of methyl oleate (Note 1) in a 500-ml. round-bottomed flask. The mixture is kept below 50° throughout the addition, which is continued until a slight excess of bromine is present approximately the theoretical amount (18.9 g.) is decolorized. Methyl oleate (2 or 3 drops) is then added until the bromine color just disappears. w-Amyl alcohol (50 ml.) (Note 2) and potassium hydroxide pellets (40 g., 0.61 mole assuming 85% purity) are added to the flask, and the mixture is heated under reflux for 4 hours in an oil bath at 150°. Then approximately 50 ml. of the w-amyl alcohol is distilled at atmospheric pressure (Note 3). The residue on cooling solidifies into a tan-colored mass. Phe-... 

Tellurophene1 A 1 /, three-necked flask is fitted with a reflux condenser, a stirrer, an addition funnel, and a nitrogen inlet tube. 4.0 g (31 mmol) of tellurium, 28 g(200 mmol) of 85% sodium formaldehyde sulfoxylate, 17 g (425 mmol) of sodium hydroxide, and 150 ml of water are placed in the flask which is then purged with pure nitrogen. The stirred mixture is heated under reflux for 15 min and cooled to 20°. 8.2 g (42 mmol) of 1,4-bis[trimethylsilyl]-l,3-butadiyne dissolved in 100 m/ of ethanol are slowly added dropwise to the stirred sodium telluride solution, the mixture is heated under reflux for 15 min, then stirred at 20° for 3 h, extracted with diethyl ether, and the extract is dried with anhydrous sodium sulfate. The extract is filtered and 10 ml (200 mmol) of bromine are added dropwise to the filtrate until the bromine color persists. The solution is concentrated on a water bath at 40° under aspirator vacuum to a volume of 50 ml and the red precipitate of tellurophene. dibromide is collected yield 8.9 g (84%) m.p. 120° (dec.). 

When a solution of bromine (red-brown) is added to cyclohexene, the bromine color quickly disappears because bromine adds across the double bond. When bromine is added to cyclohexane (at right), the color persists because no reaction occurs. 

Addition of a catalyst such as ferric bromide to the mixture of bromine and benzene causes the bromine color to disappear slowly. HBr gas is evolved as a by-product, but the expected addition of Br2 does not take place. Instead, the organic product results from substitution of a bromine atom for a hydrogen, and all three double bonds are retained. 

When bromine is added to two beakers, one containing phenyl isopropyl ether and the other containing cyclohexene, the bromine color in both beakers disappears. What observation could you make while performing this test that would allow you to distinguish the alkene from the aryl ether ... 

Perbromic acid is a strong monobasic acid. Its aqueous solutions are stable up to about 6 M (55% HBr04), even at 100°. Fairly concentrated solutions may develop a yellow bromine color from the decomposition of traces of bromate ion and hypobromous acid. If a 6 M perbromic acid solution is allowed to stand for several months, the bromate and hypobromite will have all decomposed, and the resulting bromine can be flushed out with pure nitrogen, leaving a colorless solution. 

It was clear that if the formulation O2+ [PtF,]- were true, then platinum hexafluoride should oxidize molecular oxygen. A sample of platinum hexafluoride was therefore prepared, and since it has a vapor pressure of 80 mm. at room temperature, the interaction with molecular oxygen was followed tensimetrically. The deep red (bromine colored) platinum hexafluoride vapor reacted instantly with the oxygen in a 1 1 molar ratio to give the familiar red compound. Interestingly, the solid made by this method at low temperatures, is iso-morphous and almost isodimensional with rhombohedral potassium hexafluoroplatinate (V). At higher temperatures transition to the cubic phase occurs. 

A mixture of 23.5 g. (0.25 mole) of phenol and 70 g. of hydrobromic acid (sp. gr. 1.49) is warmed to melt the phenol and then cooled to —10° in a freezing mixture. There is added very slowly a solution of 80 g. (0.50 mole) of bromine in 40 g. of hydrobromic acid, and the temperature is held below 0° during this operation. Hood.) The mixture is allowed to stand for 1 hour at 0°, after the addition of the bromine. It is then warmed to 30° until the bromine color disappears, allowed to stand for 3 hours, and the supernatant liquid decanted. The remaining dibromophenol is washed several times with warm water and dried in a vacuum desiccator. The crude product weighs 55 g. (88%) and melts at 37--38°. One recrystallization from low-boiling petrolemn ether gives a product melting at 40°. 

A) Bromine in Nonaqueous Solution. Treat 1.0-mL samples of purified ligroin, unpurified ligroin, and cyclohexene with 5-6 drops of a 3% solution of bromine in dichloromethane. In case decolorization occurs, breathe across the mouth of the tube to see if hydrogen bromide can be detected. If the bromine color persists, illuminate the solution, and if a reaction occurs, test as before for hydrogen bromide. 

In a 1.5-I. round-bottomed Pyrex flask fltted with a dropping fuimel, an efficient mechanical stirrer, and a thermometer, is placed 176 g. (2 moles) of tert.-z.my alcohol (redistilled, b.p. range 0.5°). The flask is surrounded by a water bath, and the temr perature of the alcohol is held at 50-60° while 320 g. (103 cc., 2 moles) of bromine is slowly added with stirring during about two hours (Notes i and 2). The stirring is continued for a few minutes until the bromine color has disappeared. 

A SOLUTION of 50 g. (49 cc., 0.42 mole) of acetophenone in 50 cc. of pure anhydrous ether (Note 1) is placed in a dry threenecked flask fitted with a separatory funnel, mechanical stirrer, and reflux condenser (Note 2). The solution is cooled in an ice bath, o-s g. of anhydrous aluminum chloride is introduced (Note 3), and 67 g. (21.5 cc., 0.42 mole) of bromine is added gradually from the separatory fuimel, with stirring, at the rate of about I cc. per minute. The bromine color disappears rapidly although very little hydrogen bromide is evolved towards the end of the reaction the solution becomes pink in color. 

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