Aluminum tribromide catalyst

Very high yields of the dibromomaleic anhydride 70 (X = Br) have been obtained by Brown using liquid-phase bromination in the presence of aluminum tribromide catalyst. It is also possible to replace both hydrogens of MA for halogens by other means. Relies,during a study on maleimide chemistry, has shown that dichloromaleic anhydride 70 can be obtained in a 99% yield. Chlorination of MA was performed with thionylchloride/pyridine. 

Other Rea.ctions, The photolysis of ketenes results in carbenes. The polymeriza tion of ketenes has been reviewed (49). It can lead to polyesters and polyketones (50). The polymerization of higher ketenes results in polyacetals depending on catalysts and conditions. Catalysts such as sodium alkoxides (polyesters), aluminum tribromide (polyketones), and tertiary amines (polyacetals) are used. Polymers from R2C—C—O may be represented as foUows. 

We found highly active catalysts, which are shown in Table I (3). The main component is a stable carboxylate of uranium in the oxidation state of +4, in combination with a Lewis acid and an aluminum alkyl, e.g. uranium octoate, aluminum tribromide, and triisobutylaluminum in a molar ratio of 1 0.8 25. The catalyst is usually aged for at least 2 hours at room temperature. 

Aluminum trichloride is the most commonly used catalyst, although aluminum tribromide is more efficient.1 For the rearrangement of l-broino-2-chloro-1,L2-lrifluoroethane (3) to 2-bromo-2-chloro-l,l,l-trifhioroethane (4). none of the following Lewis acids are effective iron(III) chloride. iron(III) bromide, antimony(III) chloride, antimony(V) chloride. tin(IV) chloride, titanium(IV) chloride, zinc(II) chloride, and boron trifluoride-diethyl ether complex.1" ... 

Much work has been done to develop catalyst systems that optimize yield and reduce side reactions. The reaction has an induction period, which depends on the temperature and the amount of catalyst.8 An early patent from Bayer claims that a nearly quantitative yield can be achieved in the conversion of l,2-dibromo-1-chloro-l.2.2-trifluoroethane(5) into 1,1-di-bromo-l-chloro-2,2.2-trifluoroethane (6) when aluminum tribromide is used in 2-broino-2-chloro-1,1,1-trifluoroethane (4) as solvent.12 A Japanese patent26 describes the activation of aluminum trichloride or alumina by pretreatinent with l,L2-trichloro-l,2,2-trifluoroethane (1) (see discussion of compound 19, vide infra). A later patent claims that aluminum trichloride and tribromide can also be activated by complexing with 1,1-dichloro- (CF3CFC12) and 1,1-dibromo-1,2,2,2-tetrafluoroethane (CF3CFBr2), respectively 2 an example of the latter is shown in the formation of bromofluoroalkane 10. 

The catalysts used successfully in the liquid phase in the order of their efficiency are anti-niony(V) chloride, aluminum tribromide, aluminum trichloride, and iron(Ill) chloride. Zinc(ll) chloride, tin(ll) chloride, boron trifluoride diethyl ether complex, and aluminum trifluoridc do not catalyze the dismutation. 

In sharp contrast, benzene is unreactive with bromine tinder these same conditions. Under more vigorous reaction conditions (the presence of a Lewis acid catalyst, such as aluminum tribromide, and higher temperature), benzene does react with bromine However, the product results from a substitution of a Br for a H, rather than addition of Br2 to one of the double bonds. The product retains the benzene structure of three conjugated double bonds in a six-membered ring ... 

Hydrogen halides have been added to some vinylcyclopropanes to give the corresponding addition product in good yield.In order to speed up the reaction Lewis acids [aluminum tribromide, titanium(IV) chloride] have been used as catalysts.For example, formation of chloride 2. Formation of addition products may be hampered by ring opening of the cyclopropane. ... 

In the second step of the mechanism, the sigma complex is then deprotonated, thereby restoring aromaticity and regenerating the Lewis acid (FeBt3). Notice that the Lewis acid is ultimately not consumed by the reaction and is, therefore, a catalyst. Aluminum tribromide (AlBr3) is another common Lewis acid that can serve as a suitable alternative to FeBt3. 

Aluminum trialkyls, 315, 369 Aluminum tribromide, bromination catalyst, 61 Aluminum triisopropoxide, MA adduct, 235 Alusuisse/UCB process, MA production, 26 Amines... 

Boron tribromide [10294-33A], BBr, is used in the manufacture of diborane and in the production of ultra high purity boron (see Boron, ELEMENTAL BoRON COMPOUNDS). Anhydrous aluminum bromide [7727-15-3], AIBr., is used as an acid catalyst in organic syntheses where it is more reactive and more soluble in organic solvents than AlCl. Tballium bromide [7789AOA], TlBr, is claimed as a component in radiographic image conversion panels (39). 

Jensen et al.16 also studied the decomposition of 5-ethoxythiatriazole in dibutyl phthalate solution in the presence of trichloroacetic acid, tripentylamine, 4-benzylpyridine, anhydrous aluminum chloride, or trinitrobenzene, but practically no effect on the reaction rate was observed. However, later experiments have shown that the decomposition can indeed by enhanced catalytically by Lewis acids under conditions where the catalyst is not sequestered by complex formation with the solvent.19 Thus the addition of aluminum chloride to 5-phenylthiatriazole in benzene causes a brisk evolution of nitrogen at room temperature, and if instead boron tribromide is added, a rather violent reaction sets in. However, when esters or ethers are used as... 

Kobayashi et al. developed chiral Lewis acids derived from A -benzyldiphenylproli-nol and boron tribromide and used these successfully as catalysts in enantioselective Diels-Alder reactions [89]. The corresponding polymeric catalyst 71 was prepared and used for the Diels-Alder reaction of cyclopentadiene with methacrolein [90]. Different polymeric catalysts 72, 73, 74 were prepared from supported chiral amino alcohols and diols fimctionalized with boron, aluminum and titanium [88,90]. In these polymers copolymerization of styrene with a chiral auxiliary containing two polymerizable groups is a new approach to the preparation of crosslinked chiral polymeric ligands. This chiral monomer unit acts as chiral ligand and as a crosslink. 

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