With bromine

The only halogenation reactions of the ring substituents of pyrazol-3-ones known are those with bromine, TV-bromosuccinimidc and hydrogen bromide. 

Selective bromination of the methyl group at position 5 of 4,4,5-trimethylpyrazol- 

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Aniline is readily halogenated, treatment with bromine water giving an instant precipitate of 2,4,6-tribromoaniline. 

CH3C(0)CH2Br. Colourless liquid which rapidly becomes violet in colour it is a powerful lachrymator b.p. 1367725 mm. Manufactured by treating aqueous propanone with bromine at 30-40 C it is usual to add sodium chlorate(V) to convert the hydro-bromic acid formed by the reaction back to bromine. It is not very stable and decomposes on standing. 

Bromine, like chlorine, also undergoes a photochemical chain reaction with hydrogen. The reaction with bromine, however, evolves less energy and is not explosive. 

Since, however, some compounds, such as aniline (p. 164), react very rapidly with bromine by substitution, the bromine test should whenever possible be confirmed by the alkaline permanganate test. 

Bromine. Slip the glass cover of a jar momentarily aside, add 2-3 ml. of bromine water, replace the cover and shake the contents of the jar vigorously. Note that the bromine is absorbed only very slowly, in marked contrast to the rapid absorption by ethylene. This slow reaction with bromine water is also in marked contrast to the action of chlorine water, which unites with acetylene with explosive violence. (Therefore do not attempt this test with chlorine or chlorine water.)... 

It should be noted that phenol also reacts very readily with bromine to give the corresponding 2.4,6-tribromophenol, C6H2(OH)Br,v... 

If cold benzene is treated with bromine in the absence of sunlight, very little reaction occurs if, however, a halogen carrier, such as iron, iodine, pyridine, etc., is also present, a rapid reaction by substitution occurs, forming first... 

Certain phenols give white bromo derivatives with bromine water. 

In the nineteenth century. Merling treated eyeloheptatriene with bromine and obtained a crystalline solid. Reasoning from some information gained in working Problem 15. what might this solid be ... 

Chakactkrisation of Unsaturatkd Aliphatic Hydrocarbons Unlike the saturated hydrocarbons, unsaturated aliphatic hydrocarbons are soluble in concentrated sulphuric acid and exhibit characteristic reactions with dUute potassium permanganate solution and with bromine. Nevertheless, no satisfactory derivatives have yet been developed for these hydrocarbons, and their characterisation must therefore be based upon a determination of their physical properties (boiling point, density and refractive index). The physical properties of a number of selected unsaturated hydrocarbons are collected in Table 111,11. 

The conversion of an aliphatic carboxylic acid into the a-bromo- (or a-chloro ) acid by treatment with bromine (or chlorine) in the presence of a catal3rtic amount of phosphorus tribromide (or trichloride) or of red phosphorus is known as the Hell-Volhard-Zelinsky reaction. The procedure probably involves the intermediate formation of the acyl halide, since it is known that halogens react more rapidly with acyl haUdes than with the acids themselves ... 

Undecylenic acid (or 10-undecenoic acid) (I), a comparatively inexpensive commercial product obtained from castor oil, reacts with bromine in dry carbon tetrachloride to give 10 11-dibromoundecoic acid (II), which upon heating with a concentrated solution of potassium hydroxide yields 10-niidecynoic acid (III) ... 

Condensed aromatic hydrocarbons may be brominated directly with bromine in the presence of a solvent, such as carbon tetrachloride ... 

Place 50 g. (57 ml.) of dry A.R. benzene and 0 5 ml. of dry p rridine (1) (dried over potassium hydroxide pellets) in a 500 ml. round-bottomed flask. Attach a reflux condenser to the flask and an inverted funnel (just dipping into some water in a beaker) to the top of the condenser (Fig. II, 13, 8, b). Partially immerse the flask in a bath of cold water, supported upon a tripod and gauze. Carefully pour 125 g, (40 ml.) of bromine (for precautions to be taken with bromine, see Section 111,35, Note 1) through a condenser and immediately insert the absorption device into the upper end of the condenser. A vigorous reaction soon occurs and hydrogen bromide is evolved which is absorbed by the water in the beaker when the reaction slackens, warm the bath to 25-30° for... 

Mono-substitution products of primary amines cannot easUy be prepared by direct action of the appropriate reagent for example, bromination of aniline yields largely the 2 4 6-tribomo derivative and nitration results in much oxidation. If, however, the amino group is protected as in acetanilide, smooth substitution occurs. Thus with bromine, />-bromoacetanilide is the main product the small quantity of the ortlio isomeride simultaneously formed can be easily eliminated by crystallisation. Hydrolysis of p-bromoacetanilide gives/ -bromoaniline ... 

Dissolve the solid in 700 ml. of water in a 1500 ml. round-bottomed flask, and add a solution of 88 ml. of concentrated sulphuric acid in about 200 ml. of water until the liquid has a distinct odour of sulphur dioxide sufficient heat will be liberated in the neutralisation to cause the solution to boil. Immediately steam distil the liquid (Fig. II, 40, 1 it is better to use the apparatus shown in Fig. II, 41, 3) until a sample of the distillate gives only a slight precipitate with bromine water. About 700 ml. of distillate should be collected. Saturate the steam distillate with salt, extract the dl with ether, dry the extract with a little anhydrous magnesium or calcium sulphate, distil oflF the ether (compare Fig. II, 13, 4, but with a 50 ml. Claisen flask replacing the distilling flask) and distil the residue under diminished pressure. Collect the p-cresol at 95-96°/15 mm. the colourless liquid solidifies to a white crystalline solid, m.p. 31°. The yield is 24 g. 

Nitrosomethylurea is conveniently prepared by treating acetamide (2 0 mols) with bromine (1 1 mols), followed by 10-25 per cent aqueous caustic alkali (2 0 mols) when acetylmethylurea is produced ... 

Bromination of quinaldine (I) (Section V,2) with bromine in glacial acetic acid in the presence of anhydrous sodium acetate aflFords dilute sulphuric acid gives quinaltiinic acid (III). 

Eosin (Tetrabromofluorescein). Place 16 5 g. of powdered fluorescein and 80 ml. of rectified (or methylated) spirit in a 250 ml. flask. Support a small dropping funnel, containing 36 g. (12 ml.) of bromine, above the flask make sure that the stopcock of the funnel is well lubricated before charging the latter with bromine. Add the bromine diopwise during about 20 minutes. When half the bromine has been introduced, and the fluorescein has been converted into dibromofluor-escein, all the solid material disappears temporarily since the dibromo derivative is soluble in alcohol with further addition of bromine the tetrabromofluorescein (sparingly soluble in alcohol) separates out. Allow the reaction mixture to stand for 2 hours, filter ofiF the eosin at the pump, wash it with alcohol, and dry at 100°. The yield of eosin (orange-coloured powder) is 25 g. 

It is worth noting here that the results of some other studies of aromatie substitutions, sueh as the Friedel-Crafts benzylation and iso-propylation of alkylbenzenes, and the bromination of alkylbenzenes with bromine, eatalysed by ferrie ehloride, are under suspicion as depending upon slow mixing. As regards halogenation eatalysed by Lewis aeids, positive evidenee to support this eritieism has been obtained. ... 

The problem really isn t the concentration of the HBr, but rather is the result of the HBr being in water. As long as there is a significant amount of water present in the reaction mix with safrole, that water is going to compete with bromine for that juicy beta carbon on safrole. And it s gonna win, too. The answer is to use non-aqueous HBr solutions. 

Furthermore, treatment of the aminopalladation product with bromine affords aziridines[176]. The aziridine 160 was obtained stereoselectively from methylamine and 1-decene in 43% yield. The aminopalladation of PdCl2 complexes of ethylene, propylene, and 1-butene with diethylamine affords the unstable ir-alkylpalladium complex 161, which is converted into the stable chelated acylpalladium complex 162 by treatment with CO[177],... 

The reaction of 2-amino-4(2-furyl)thiazole in acetic acid with bromine yields product 198 brominated on the furan ring (Scheme 126). The... 

The preparation and spectroscopic properties (infrared, ultraviolet, NMR) of iV-alkoxycarbonyl-N -(2-thiazolyl)thioureas (268) have been studied by the Nagano group (78, 264). These compounds react with bromine in acetic acid or chloroform to give 2--alkoxycarbonylimino-thiazolo[3,2-h]thiadiazolines (Scheme 162), whose structures were established by mass spectroscopy, infrared, NMR, and reactivity patterns (481). 

When unsubstituted, C-5 reacts with electrophilic reagents. Thus phosphorus pentachloride chlorinates the ring (36, 235). A hydroxy group in the 2-position activates the ring towards this reaction. 4-Methylthiazole does not react with bromine in chloroform (201, 236), whereas under the same conditions the 2-hydroxy analog reacts (55. 237-239. 557). Activation of C-5 works also for sulfonation (201. 236), nitration (201. 236. 237), Friede 1-Crafts reactions (201, 236, 237, 240-242), and acylation (243). However, iodination fails (201. 236). and the Gatterman or Reimer-Tieman reactions yield only small amounts of 4-methyl-5-carboxy-A-4-thiazoline-2-one. Recent kinetic investigations show that 2-thiazolones are nitrated via a free base mechanism. A 2-oxo substituent increases the rate of nitration at the 5-position by a factor of 9 log... 

Halogenation (e.g., bromination) takes place in chloroform for the 2,4-dialkylthiazoles, and the majority of studies have been of 2,4-dimethylthiazole (227, 228). In other cases and in acetic or stronger acids, substitution occurs at the 5-position and is promoted by electronreleasing groups in the 2-position. When the releasing group is in the 4-(or 5-)-position, steric hindrance may decrease the yield of substitution at the 5- (or 4-) position. Nevertheless, the thiazole nucleus is not very reactive since 4-methylthiazole and 2.5-dimethylthiazole are inert in dilute sulfuric acid with bromine (229-231). 

The carbon atom m bromomethane can accept an electron pair if its covalent bond with bromine breaks with both electrons m that bond becoming an unshared pair of bromide ion Thus bromomethane acts as a Lewis acid m this reaction... 

Many of the features of the generally accepted mechanism for the addition of halogens to alkenes can be introduced by referring to the reaction of ethylene with bromine... 

Relative Rates of Reaction of Some Representative Alkenes with Bromine... 

When treated with bromine or chlorine in aqueous solution alkenes are con verted to vicinal halohydrins A haloni um ion IS an intermediate The halogen adds to the carbon that has the greater number of hydrogens Addition is anti... 

The relative rates of reaction of ethane toluene and ethylbenzene with bromine atoms have been measured The most reactive hydrocarbon undergoes hydrogen atom abstraction a million times faster than does the least reactive one Arrange these hydrocarbons in order of decreasing reactivity... 

Iron(III) bromide is a weak Lewis acid It combines with bromine to form a Lewis acid Lewis base complex... 

Only small quantities of iron(III) bromide are required It is a catalyst for the brommation and as Figure 12 6 indicates is regenerated m the course of the reaction We 11 see later m this chapter that some aromatic substrates are much more reactive than benzene and react rapidly with bromine even m the absence of a catalyst... 

This method of a bromination of carboxylic acids is called the Hell-Volhard-Zelinsky reaction This reaction is sometimes carried out by using a small amount of phosphorus instead of phosphorus trichloride Phosphorus reacts with bromine to yield phosphorus tribromide as the active catalyst under these conditions... 

Treatment of 2 4 6 tn tert butylphenol with bromine in cold acetic acid gives the compound CigH29BrO in quantitative yield The infrared spectrum of this compound contains absorptions at 1630 and 1655 cm Its H NMR spectrum shows only three peaks (all singlets) at 8 1 2 13 and 6 9 in the ratio 9 18 2 What is a reasonable structure for the compound" ... 

Derivatives of aldoses in which the terminal aldehyde function is oxidized to a car boxylic acid are called aldonic acids Aldonic acids are named by replacing the ose ending of the aldose by omc acid Oxidation of aldoses with bromine is the most com monly used method for the preparation of aldonic acids and involves the furanose or pyranose form of the carbohydrate... 

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