Carbon tetrabromide, reaction

Another halogenated photolysis (30), using carbon tetrabromide to produce hydrogen bromide and subsequent reaction with spiropyran (5), produces a highly colored spiropyrilium bromide salt. 

When treated with aluminum bromide at 100°C, carbon tetrachloride is converted to carbon tetrabromide [558-13-4], reaction with calcium iodide, Cal2, at 75°C gives carbon tetraiodide [507-25-5]. With concentrated hydroiodic acid at 130°C, iodoform [75-47-8], CHI, is produced. Carbon tetrachloride is unaffected by gaseous fluorine at ordinary temperatures. Replacement of its chlorine by fluorine is brought about by reaction with hydrogen fluoride at a... 

One of the older preparative free-radical reactions is the addition of polyhalomethanes to alkenes. Examples of addition of carbon tetrabromide, carbon tetrachloride, and bromoform have been recorded. The reactions are chain processes that depend on facile abstraction of halogen or hydrogen from the halomethane ... 

AP951). Alternatively, reduction of the ester in 586 gave the alcohol 587 that upon reaction with carbon tetrabromide/triphenylphosphine gave the respective bromide which was cyclized under the reaction condition to give 588 (92JMC1076) (Scheme 98). 

When carbon tetrabromide is used, the alkyl bromide is formed. Providing moisture is excluded from the reaction mixture (HX is formed otherwise), the reaction conditions are completely neutral, affording a convenient preparation of the halides of acid-sensitive substrates (for example, sugars). 

Bromocyclopropane has been prepared by the Hunsdiecker reaction by adding silver cyclopropanecarboxylate to bromine in dichlorodifluoromethane at —29° (53% yield) or in tetrachloro-ethane at —20° to —25° (15-20% yield).3 Decomposition of the peroxide of cyclopropanecarboxylic acid in the presence of carbon tetrabromide gave bromocyclopropane in 43% yield.4 An attempt to prepare the bromide via the von Braun reaction was unsuccessful.3... 

B. Nucleophilic Attack on Halogen.- (/ )-( +)-2,2-dimethylpropan( H)ol has been converted to the chloride with inversion of configuration using triphenylphosphine and carbon tetrachloride. The corresponding reaction using carbon tetrabromide gave the bromide with considerable racemiza-tion. ... 

For n = 1, this is the standard synthesis of [l.l.l]propellane 40a.20,21 Also for n = 3, this method makes [3.1.1]propellane 40c accessible with reasonable effort.22 Although [2.1.1]propellane 40b was detected by its IR spectrum at liquid nitrogen temperature,23 it could not be obtained as a stable compound via this route.22 The addition of halomethanes across the central bond by a radical chain mechanism is common to 40a and 40c. The addition of carbon tetrabromide to 40c afforded a 45% yield of 41.18 Likewise, a number of bicy-clo[l.l.l]pentane derivatives 42 were obtained by reaction of the corresponding halomethanes with 40a.17,24... 

The reaction of phosphines and alkyl halides presents an alternative way to generate phosphonium electrophiles (Scheme 3.8). In particular, the combination of a phosphine and carbon tetrabromide (the Appel reaction) allows for in situ formation of a phosphonium dibromide salt (48, X = Br). Treatment of a hemiacetal donor 1 with the phosphonium halide 48 initially provides the oxophosphonium intermediate 38 (X = Br). However, the oxophosphonium intermediate 38 can react with bromide ion to form the anomeric bromide intermediate 49 (X = Br) with concomitant generation of phosphine oxide. With the aid of bromide ion catalysis (i.e. reversible, catalytic formation of the more reactive P-anomeric bromide 50) [98], the nucleophile displaces the anomeric bromide to form the desired glycoside product 3. The hydrobromic add by-product is typically buffered by the presence of tetramethyl urea (TMU). 

Prior to starting the reaction, 1.5 equivalents (relative to the amount of alcohol 2 to be used) each of carbon tetrabromide and triphenylphosphine were weighed and set aside. An additional 0.5 equivalents of each was also weighed and set aside. Alcohol 2 (37.93 g, 0.118 mol) dissolved in 50 mL of THF was placed in a 250 mL round bottom flask containing a magnetic stirrer and the solution was stirred while carbon tetrabromide (1.5 equiv.) (58.91 g, 0.178 mol) was added. Once dissolution was complete, triphenylphosphine (1.5 equiv.) (42.95 g, 0.178 mol) was added quickly but portionwise (i.e. - a large, full spatula at a time) as the reaction is very exothermic. The solution turned to a yellowish color, which usually occurs when the reaction is near completion. Monitoring by TLC (1% methanol / dichloromethane) confirmed that the reaction was indeed complete. 

TLC analysis. After running TLC, wait several minutes to allow them to evaporate. Recheck TLC to observe the product or to determine if CBrJCHBr3 is present. The reaction was immediately quenched by the addition of water ( 50 mL). In the event that the reaction had not gone to completion, the additional 0.5 equiv. of carbon tetrabromide set aside earlier would have been added and the solution stirred until it had dissolved. The 0.5 equiv. of triphenylphosphine set aside earlier would then have been added immediately afterward. Stir the reaction and watch for a sudden change in color to a very deep, dark yellow color. Once this color change is seen, the reaction should immediately be quenched with water to limit side reactions. This also applies to the addition of the initial dose of PPh3 if the solution turns a deep, dark yellow, it should be immediately quenched with water. 

Triphosphine reacted with carbon tetrabromide to form an organic salt [13]. This reactive species then reacted with alcohol to form the corresponding bromide. Kinetics results showed that there is no significant difference in reaction rate when resin beads of different sizes were used. This demonstrated that the diffusion of the organic salt into bead was not rate hmiting compared with the reaction rate. 

Tribromoethanol derivatives are also obtained by the reaction of carbon tetrabromide with aldehydes in the presence of stannous fluoride. 2,3-Di-O-acetyl-D-erythronolactone 16 is synthesized as shown below (II). 

This reaction presumably proceeds via the acyl chloride, because it is known that triphenylphosphine and carbon tetrachloride convert acids to the corresponding acyl chloride.104 Similarly, carboxylic acids react with the triphenylphosphine-bromine adduct to give acyl bromides.105. Triphenylphosphine/lV-bromosuccinirnide also generates acyl bromides in situ 06 Alcohols can be esterified by heating in excess ethyl formate or ethyl acetate and triphenylphosphine in carbon tetrabromide.107 All these reactions are mechanistically analogous to the alcohol-to-halide conversions that were discussed in Section 3.1.2. 

Show by chemical equations the reactions involved in chain transfer by hexane, benzene, isopropylbenzene, propanol, butyl iodide, carbon tetrabromide, n-butyl... 

A Steady-State and Time-Resolved Fluorescence Study of Quenching Reactions of Anthracene and 1,2-Benzanthracene by Carbon Tetrabromide and Bromoethane in Supercritical Carbon Dioxide (Zhang et al., 1997)... 

Catalytic hydrogenation of (23-12) over palladium on charcoal results in the scission of the weak N—O bond and the formation of amino alcohol (24-1). This is converted to a pyrrolidine by an internal alkylation reaction. Thus, reaction of the intermediate with carbon tetrabromide and triphenyl phosphine presumably converts the alcohol to a bromide internal displacement by the primary amine forms the five-membered ring (24-2). Alkylation of that amine with the complex bromo amide (24-3) then affords the endothehn antagonist atrasentan (24-4) [25]. 

To a stirred reaction mixture consisting of 55.0 gm (0.50 mole) of c/s-cyclo-octene and 41.5 gm (0.125 mole) of carbon tetrabromide cooled to —65°C is added 74.0 ml (0.125 mole) of methyllithium in ether (Foote Mineral Co.) over a 45 min period. After stirring at -65° to -68°C for an additional hr, another 80.5 ml (0.135 mole) of methyllithium is added over a -hour period. The reaction mixture is stirred for another i hr at —68°C, warmed to 0°C, water added, the ether separated, washed with water until neutral, dried over sodium sulfate, and then fractionally distilled to afford 11.3 gm (74%), b.p. 62°-63°C (16 mm), d° 1.5060. 

At very short times, very little motion of reactants has occurred so that little, if any, reaction will have taken place. But the manner of creation of the mixture of A and B reactants should be considered. A very simple means of preparing a reaction mixture is by photolysis. For instance, consider a solution of anthracene and carbon tetrabromide. Photostimulation of anthracene with an extremely short duration light pulse produces excited singlet (and triplet) states. The carbon tetrabromide quenches the excited singlet state fluorescence very efficiently. Just before the photostimulation event, the quencher (i.e. B) is randomly distributed throughout the system volume and for a short time after photostimulation, it remains randomly distributed. With the exception of the location where the fluorophor A is, there is no preferred location of the quencher B. No... 

Many of the fast chemical reactions discussed in the preceding sections involve at least one reactant which is of low symmetry. The reactions of the solvated electron with nitrate, naphthalene or pyrene are instances where the oxidant has a mirror plane (in the molecular plane) in the accepting orbital. Hence, reaction of the solvated electron with such a scavenger when both are contained in this plane should be slower than in other configurations. Similarly, the contact quenching of fluorescence from naphthalene or 1,2-benzanthracene by carbon tetrabromide [7], or... 

Aluminum chloride induces polymerization of 1,1-dimethylsilacyclobutane but causes (66) to ring expand to th trisilacyclohexane and, remarkably, the tetrasilaadamantane (Scheme 115) (75IZV953). The polymerization of 1,3-disilacyclobutanes, variously substituted, both thermally and catalyzed has been widely studied by Russian workers. Di-/jl -chlorobis(cyclohexene)diplatinum(II) is most effective at catalyzing the polymerization of (66). The reaction is vigorous at 20-60 °C with small amounts of triethylsilane or carbon tetrabromide (Scheme 116) <66JCS(C)1137>. 

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