Bromine dioxane

Treatment of 2,7-di-/ert-butylthiepin (1) either directly with bromine at — 78 °C, or with pyridinium bromide perbromide at room temperature, gives the thiophene compound 2. In contrast, bromination with bromine-1,4-dioxane complex or pyridinium bromide perbromide in the presence of acetic acid leads to the thiopyran derivative 3.87 To account for these results a homothiopyrylium ion has been proposed as a common intermediate, formed by electrophilic bromination at C4 in the first step. 

Hassel O, Hvoslef J (1954) The structure of bromine 1,4-dioxanate. Acta Chem Scand 8 873-873... 

Related Reagents. Bromine-r-Butylamine Bromine Chloride Bromine-l,4-Diazabicyclo[2.2.2]octane Bromine-1,4-Dioxane Bromine-Silver(I) Oxide Bromine-Triphenyl Phosphite iV-Bromosuccinimide A7-Bromosiiccinimide-Dimethylformamide 7V-Bromosuccinimide-Dimethyl Sulfide Al-Bromosuccinimide-Sodium Azide Copper(II) Bromide Hy-drobromic Acid Mercury(II) Oxide-Bromine Phosphoms(III) Bromide Pyridinium Hydrobromide Perbromide Sodium Bromide Thallium(III) Acetate-Bromine. 

Charge-transfer compounds can be isolated ia the crystalline state, although low temperatures are often required. The bromine—dioxane compound, for example, has a chain stmeture (42). 

Yakhontov et al. also brominated the 4-methyl-7-azaindoles, using bromine in chloroform or bromine-dioxan, obtaining high yields of the brominated 6-H (82%), 6-Cl (82%), and 6-MeO (71%) compounds. The ultraviolet spectra of these compounds agrees with the assignments of the bromine to the 3-position. 

Similarly, AT-allylthioamides derived from carboxylic acids cyclize to 2-thiazoline derivatives by the action of the bromine-dioxane complex <93PJCI043>. The Mitsunobu reaction can be eflSciently used for preparing 4-carboxy-2-thiazolines from -hydroxy-a-amino acids <92TL2807). Diethyl-... 

Chlorination of dioxan affords a series of definite products that vary according to the reaction conditions (for a comprehensive review see Stumpf52). For instance, at 90° in the presence of iodine it affords up to 94% of 2,3-dichloro-dioxan,522 which is an important intermediate, e.g., in the synthesis of glyoxal bisulfate 523 and 2,3-dibromodioxan is obtained by brominating dioxan in CC14 which is a poor solvent for the resulting HBr that hinders the direct bromination.524... 

Bromination was carried out using bromine in presence of catalytic amount of aluminum chloride or bromine-dioxane complex at 0-20 °C to form 3-bromoderivative 173 in high yield [63], Electrophilic carbenoid species, generated at elevated temperature, reacted with polyfluoroindole to form indolyl carboxylic esters 174 after treatment with formic acid [58c],... 

The next two bromination recipes use recyclable bromine donors that can be used over and over again. They are called dioxane and succinimide and are more common than you think. No, dioxane is not the same as the notorious dioxin but it is still pretty toxic. 

METHOD 2 [128, 129]--To make dibromodioxane one stirs 500g dioxane in a flask which is in an ice bath, all of which is in the hood. 990g of liquid Bra is rapidly added, causing the solution to get hot (one can also bubble in an approximate amount of bromine from a gas canister). The solution is dumped into a bucket containing 2L of ice water, causing the immediate formation of a large mass of orange dibromodioxane crystals which are separated by vacuum filtration and dried. 

Another method of aldehyde bromination, apart from Riehl s established method (432) from bromine at 20°C, is to use trimethylphenyl-ammonium bromide in tetrahydrofuran solution, prepared by Vorlander and Siebert s method (50). However, the yield of 5-phenylthiazole using this method with thioformamide dissolved in dioxane is only 8% (513). 

Syntheses of a,)3-dihalogenoethers can be achieved in various ways the classical method (37), wherein a current of dry gaseous hydrochloric acid, is made to react in an equimolar mixture of ethanol and aldehyde at 20°C first to form the monochloroether (50% yield) and then by the action of bromine, the dibromoether (80 to 90% yield) can be used. The second and simpler method is the direct bromination of ethylvinylether in a chloroformic or dioxane solution if the product is used directly without purification,... 

Furan reacts vigorously with chlorine and bromine at room temperature to give poly-halogenated products. Low temperature (-40 °C) reaction of furan with chlorine in dichloromethane yields mainly 2-chlorofuran and reaction of furan with dioxane dibromide at 0 °C affords 2-bromofuran in good yield. 2-Iodofuran is obtained by treatment of 2-furoic acid with iodine and potassium iodide in aqueous sodium hydroxide. 

Oxidations usually proceed in the dark at or below room temperature in a variety of solvents ranging from aqueous bicarbonate to anhydrous benzene-pyridine. Base is quite commonly used to consume the hydrogen halide produced in the reaction, as this prevents the formation of high concentrations of bromine (or chlorine) by a secondary process. The reaction time varies from a few minutes to 24 hours or more depending on the nature of the reagent and the substrate. Thus one finds that NBS or NBA when used in aqueous acetone or dioxane are very mild, selective reagents. The rate of these oxidations is noticeably enhanced when Fbutyl alcohol is used as a solvent. In general, saturated, primary alcohols are inert and methanol is often used as a solvent. 

A solution of 16jS-methyl-l la,17a,21-trihydroxy-5j5-pregnane-3,20-dione 21-acetate (52), 45 g, in dioxane (297 ml) is cooled to 15° and treated over a 5 min period with a solution of bromine (34.2 g) in dioxane (594 ml) precooled to 18°. After 2 min a solution of sodium acetate (60 g) in water (600 ml) is added and the mixture poured into ice water (8 liters). The precipitate is filtered off, washed to neutrality with water, and dried to give the crude dibromide (53), 55.7 g mp 125-126° (dec.) [aJu 58°. A mixture of dibromide (53), 55.5 g, lithium bromide (27.8 g), lithium carbonate (27.8 g) and DMF (1.11 liters) is refluxed under rapid stirring for 6 hr. The mixture is concentrated under vacuum to about 250 ml, poured into ice water (8 liters) containing hydrochloric acid (250 ml), and extracted with methylene dichloride. The extracts are washed to neutrality with water and evaporated to dryness. The residue is dissolved in acetone, evaporated to dryness under reduced pressure, redissolved in acetone and crystallized by the additon of hexane. This gives the dienone (54) 24.4 g, mp 236-239°. 

A French patent claims the successful use of methanol for the 21-bromination of 17a-hydroxy-20-ketopregnanes as well as 21-bromination of 17-desoxy-20-ketopregnanes. This solvent has been successfully employed with dioxane dibromide as the brominating agent. 

Bromination of monosubstituted benzenes by HOBr and HC1O4 in 50% dioxane 25 -5.78... 

Procedures have been worked out which increased the yield of 2-bromothiophene to 78% on direct bromination in acetic acid-ether mixtures and to 67% in carbon tetraehlorided With the mild brominating agent, dioxane dibromide, quantitative yields of 2-bromothiophene are obtained. A very convenient procedure for the iodination of thiophenes consists of the acid-catalyzed (HzSOi) reaction with iodine and HIO3, giving 2-iodothiophene in 75% yieldd In contrast to the HgO method, all the iodine is utilized. 

Aqueous dioxan (50%) has been used as a medium for bromination with acidified hypobromous acid and de la Mare and Harvey195 showed that, with perchloric acid as catalyst, the bromination of toluene followed the usual kinetic equation (89). At 25 °C, in ca. 0.0013 M hypobromous acid, the average value of fc2/[H+] for toluene (0.008-0.15 M) was 21.7 and for benzene (0.0011-0.016 M) was 0.60, so that ktoWtnc/kbtaztae was 36.2. The bromination of f-butylbenzene196 and biphenyl197 gave k2/[H+] = 7.25 and 7.52, and hence relative rates of 12.1,... 

De la Mare and Hilton198 measured the rates at 25 °C of bromination of benzene, benzoic acid, phthalic acid, 2-nitrobenzoic acid, trimethylanilinium perchlorate and nitrobenzene by hypobromous acid with sulphuric or perchloric acids as catalysts, in some cases in aqueous dioxan, in an attempt to discover if Br+ or H2OBr+ was the appropriate brominating species since the logarithm of the rates should then follow the acidity functions H0 or HR (J0) respectively. The results, however, were inconclusive and relative rates of bromination were determined (see Table 53). 

At 0.9 °C the rate of bromination of biphenyl relative to benzene was approximately 1,270, compared to 26.9 in the presence of mineral acid, and this latter value is fairly close to that obtained with 50 % aqueous dioxan. The possibility that the positive brominating species might be protonated bromine acetate, AcOHBr+, was considered a likely one since the reaction rate is faster in aqueous acetic acid than in water, but this latter effect might be an environmental one since bromination by acidified hypobromous acid is slower in 50 % aqueous dioxan than in... 

A kinetic isotope effect, kH/kD = 1.4, has been observed in the bromination of 3-bromo-l,2,4,5-tetramethylbenzene and its 6-deuterated isomer by bromine in nitromethane at 30 °C, and this has been attributed to steric hindrance to the electrophile causing kLx to become significant relative to k 2 (see p. 8)268. A more extensive subsequent investigation304 of the isotope effects obtained for reaction in acetic acid and in nitromethane (in parentheses) revealed the following values mesitylene, 1.1 pentamethylbenzene 1.2 3-methoxy-1,2,4,5-tetramethyl-benzene 1.5 5-t-butyl-1,2,3-trimethylbenzene 1.6 (2.7) 3-bromo-1,2,4,5-tetra-methylbenzene 1.4 and for 1,3,5-tri-f-butylbenzene in acetic acid-dioxan, with silver ion catalyst, kH/kD = 3.6. All of these isotope effects are obtained with hindered compounds, and the larger the steric hindrance, the greater the isotope... 

The kinetics of bromination with the complex formed between bromine and dioxan have been examined using benzene (which is unattacked) as solvent311, and it is probably appropriate to regard this as a catalysed bromination in view of the effect of dioxan upon the polarity of the bromine-bromine bond. With anisole, phenetole, and isopropoxybenzene, third-order kinetics are obtained, viz. 

The bromination of /-butylbenzene by acidified hypobromous acid in 50% aqueous dioxan at 25 °C follows the kinetic equation (89) (p. 84)196, and the kinetic form of bromodebutylation is assumed to be the same since only 1.9% of the total reaction (k3 = 7.25) is debutylation, leading to a partial rate factor of 1.4 the same conclusions apply as outlined above. 

D-lysergic acid propargylamide (0.016 mole) was dissolved in a mixture dichloro-methane/dioxane (85/15), 400 ml. Under vigorous stirring into this solution the polymer supported bromine (prepared acc. to ref. 29) containing 0.024... 

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