Bromination of emodin

Using emodin as an example, it has been shown that in the bromination of hydroxyanthraquinones the qualitative composition and quantitative ratio of the reaction products depend on the nature of the brominating agent and the solvent, the ratio of the rea Lants, and the temperature regime. In order to obtain bromo-3-methyl-1,6,8-trihydroxyanthraquinone it is recommended to use dioxane dibromide in acid solution as the brominating agent, and to obtain 5-bromo-3-methyl-1,6,8-trihydroxyanthraquinone the same reagent in dioxane solution. The optimum conditions for obtaining 3-bromomethyl-1,6,8-trihydroxyanthraquinone by the methods of initiated bromination and photobromination have been selected. S. M. Kirov Kazakh State University, Alma-Ata. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 618–621, September–October, 1990.     

Bromination of 1-alkyl-2-pyridones

The corresponding monobromides were obtained in the bromination of 1-alkyl-2-pyridones with bonded bromine (with N-bromosuccinimide and dioxane dibromide). The conditions under which the yields of the mixtures of isomers were 60–80%, and almost no dibromides were obtained, were found. It was established that the ratios of the 3- and 5-bromo isomers depend on the character of the brominating agent.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1662–1664, December, 1982.     

Synthesis of 2-carbethoxy-3-methyl-4-hydroxybenzofuran derivatives

A number of 2-.carbethoxy-3-methylbenzofuran derivatives were synthesized. A 5,5-gem-dibromo derivative was obtained in the bromination of 2-carbethoxy-3-methyl-4-oxo-4, 5,6,7,tetrahydrobenzofuran. Dehydrobromination of this, dibromo derivative gave 2-carbethoxy-3-methyl-4-hydroxy-5-bromobenzofuran. Depending on the structure of the starting compound and the brominating agent, the bromine in the bromination of 2-carbethoxy-3-methyl-4-hydroxy- and 4-acetoxybenzofurans with bromine and N-bromosuccinimide is incorporated either in the methyl group or in 5 and 7 positions of the benzofuran ring. The nitration of 2-carbethoxy-3-methyl-4-hydroxybenzofuran and its bromo derivative leads to 5-nitro- and 5,7-dinitrobenzofuran derivatives. The structures of the synthesized benzofuran derivatives were established by means of the PMR spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 27–29, January, 1980.     

Formation of furo- and difuro-1,4-dihydropyridines in the bromination 0f 2,6-dimethyl-3,5-dimethoxycarbonyl-4-(o-nitrophenyl)-1,4-dihydropyridine

Furo- and difuro-1,4-dihydropyridines were obtained by bromination of 2,6-dimethyl-3,5-dimethoxycarbonyl-4-(o-nitrophenyl)-1,4-dihydropyridine with mild brominating agents (pyridinium bromide perbromide, N-bromosuccinimide, and dioxane dibromide).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1227–1232, September, 1987.     

Bromination of 4-(2-thienyl)thiazoles and 2-(2-thienyl)quinoline

Depending on the substituent, the bromination of 4-(2-thienyl)thiazoles and 2-(2-thienyl)quinoline takes place in the 5 position of the thiophene or thiazole ring. When an amino group is present in the 2 position of the thiazole ring, bromination takes place in the 5 position of the thiazole ring. When excess brominating agent is present, a second bromine atom enters the 5 position of the free ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 35–38, January, 1982.     

Bromination of 8R-4-phenyl-2,3-dihydro-1H-1,5-benzodiazepinones-2

The influence of the nature of the substituents and the brominating agent on the direction of the bromination of 8R-4-phenyl-2,3-dihydro-1H-1,5-benzodiazepinones-2 containing various substituents in the annelated benzene ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1133–1135, August, 1984.     

Synthesis and structure of bromonitro-6(5H)-phenanthridinones

Treatment of 2-bromo-6(5H)-phenanthridone with nitrating mixture or fuming nitric acid results in nitration, debromination, and bromination in the 10-position. The brominating agent is apparently Br⁺, formed in the reaction mixture following replacement of the bromine in the 2-position by a nitro-group. Monocrystals of 2-bromo-1,4,8-trinitro-6(5H)-phenanthridinone and 10-bromo-2,4,8-trinitro-6(5H)-phenanthridinone have been subjected to x-ray diffraction examination. PMR has been used for structural identification.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 789–795, June, 1990.We thank A. N. Sobolev for assistance in calculating the structure of (III).     

Synthesis and properties of brominated poly(1-trimethylsilyl-1-propyne)

Russian Chemical Bulletin - A procedure of selective bromination of poly(1-trimethylsilyl-1-propyne) using N-bromosuccinimide as the brominating agent was developed. This method allows to obtain...     

Reaction of isocyanates with pyrazol-5-ones

Treatment of mono- and diisocyanates with 3-methyl-4-alkyl(aryl)pyrazol-5-ones by heating in absolute dioxane gives the corresponding 1-carbamoylpyrazol-5-ones. Using PMR spectroscopy it has been shown that they exist in the 5-hydroxypyrazole form in DMSO, dimethylacetamide, chloroform, or acetone solutions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1058–1060, August, 1990.     

Liquid phase bromination of aromatics over zeolite H-beta catalyst

The liquid phase bromination of chlorobenzene, toluene and xylenes (o-, m-, p-) is catalyzed using zeolite as catalyst and N-bromosuccinimide (NBS) as the brominating agent. In addition, the bromination of toluene has been investigated over various zeolites using both NBS and liquid Br₂ as brominating agents. A comparison under similar reaction conditions with H₂SO₄, in the absence of catalyst and FeCl₃ (in the case of toluene) is also investigated for each reaction. Zeolite H-beta is found to be selective compared to the conventional catalysts and other zeolites in the bromination of chlorobenzene and toluene whereas selectivity for 4-bromo-o-xylene (4-BOX/3-BOX) over H-beta and H₂SO₄ was found nearly comparable in the bromination of o-xylene. In the bromination of toluene, acidic H-beta favours the formation of nuclear products whereas in the absence of any catalyst, in the presence of weakly acidic H–Y and potassium exchanged zeolites K-beta and K–L, the concentration of side-chain product, œ-bromotoluene, is enhanced. The conversion of NBS, rate of NBS conversion (mmol g⁻¹ h⁻¹) and selectivity for products are strongly influenced by the reaction parameters. As the reaction time, catalyst amount, reaction temperature and molar ratios of NBS/toluene are increased, an increase in the conversion of NBS is noticed. Presumably, the catalytic bromination of aromatics proceeds by an electrophile (Br⁺) which is generated by the heterolytic cleavage of NBS/Br₂ by an acidic zeolite. Thus, the generated Br⁺ attacks the aromatic ring resulting in the formation of brominated nuclear products.     

Pyridinium bromochromate: a new and efficient reagent for bromination of hydroxy aromatics

Pyridinium bromochromate (PBC) has been used as an efficient and selective nuclear brominating agent for bromination of various substituted hydroxy-acetophenones, aldehydes and phenols.     

Electrophilic Bromination of Nitrobenzene Using Barium Tetrafluorobromate (III)

It has been shown that Ba (BrF₄)₂ acted as a highly-active brominating agent. In case of interaction with nitrobenzene, the pure 3-bromo-nitrotoluene is formed. It has been shown that typical electrophilic bromination of the aromatic compound with electron-donating and electron-accepting substituents occurred without any catalysts or hard conditions.     

高立体选择性地合成薄荷基溴和新薄荷基溴

薄荷基溴和新薄荷基溴是一类非常有用的不对称合成中间体。以L-薄荷醇为原料,通过与不同的溴化剂反应高立体选择性地得到薄荷基溴和和新薄荷基溴。当L-薄荷醇与盐酸和无水溴化锌反应时高立体选择性地得到薄荷基溴,当L-薄荷醇与三溴化磷反应时高立体选择性地得到新薄荷基溴.     

Synthesis of biologically active bromine derivatives of quercetin

The synthesis of a series of bromine derivatives of quercetin differing by the number of bromine atoms introduced is described. It has been shown that in the dynamics of the bromination process the deciding factors affecting the qualitative and quantitative compositions of the reaction products are the temperature regime and the ratio of the reactants. Thus, the use of equimolar amounts of the reactants in dioxane in the temperature interval from 20 to 25° C gives a monobromo derivative, while all other conditions give mixtures of bromo derivatives. The antiviral and antitumoral activities of the mono- and dibromo derivatives of quercetin have been studied.Al-Farabi Kazakh State National University, Almaty, fax (3272) 47 26 09. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 709–711, September–October, 1996. Original article submitted February 27, 1995.     

Phosphorylation of emodin

A convenient method has been developed for the interaction of dialkyl phosphites with 1,6,8-trihydroxy-3-methylanthraquinone (emodin) under the conditions of the Todd—Atherton reaction. It has been shown that the -hydroxy groups of emodin are not phosphorylated at an equimolar ratio of emodin and dialkyl phosphite. The phosphorylation of 7-bromo-1,6,8-trihydroxy-3-methylanthraquinone with potassium dialkyl phosphorothioates has been studied. The reaction takes place at the sulfur atom, with the formation of of the product of S-alkylation.Al-Farabi Kazakh State National University, Almaty. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 212–216, March–April, 1994.     

Conversions of methyl esters of (6-methyl-2-methylthio-4-pyrimidinyloxy)- and (3,4-dihydro-6-methyl-2-methylthio-4-oxo-3-pyrimidinyl)acetic acids

A study has been made of nucleophilic reactions (hydrolysis, hydrazinolysis, ammonolysis, reduction) and electrophilic reactions (bromination, nitration) of isomeric methyl esters of (6-methyl-2-methylthio-4-pyrimidinyloxy) acetic acid and (3,4-dihydro-6-methyl-2-methylthio-4-oxo-3-pyrimidinyl)acetic acid. Carboxyl-group derivatives and also derivatives with substituents in position 5 of the pyrimidine ring have been synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1655–1659, December 1992.     

Spectrophotometric determination of dopamine in pharmaceutical formulations

A new spectrophotometric method was developed for the estimation of dopamine. The method is based on the bromination of the dopamine with a solution of excess brominating mixture. After bromination, the excess brominating mixture is treated with potassium iodide to produce a yellow solution. The absorbance of yellow solution was measured at 350 nm on a Spectronic 1001 spectrophotometer against distilled water as a blank.From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 2842285.Original English Text Copyright © 2005 by Rami Reddy, Sreedevi, Prabhavathi, Chakravarthy.This article was submitted by the authors in English.     

Carbon Tetrabromide-A New Brominating Agent for Alkanes and Arylalkanes

Quantitative catalytic bromination of alkanes, cycloalkanes, and arylalkanes with carbon tetrabromide as brominating agent was accomplished for the first time.     

One‐Pot Synthesis of 2,5‐Furandicarboxylic Acid from 2‐Furoic Acid by a Pd‐catalyzed Bromination–Hydroxycarbonylation Tandem Reaction in Acetate Buffer

The one‐pot synthesis of 2,5‐furandicarboxylic acid from 2‐furoic acid with a yield of 57 % was achieved for the first time using a Pd‐catalyzed bromination‐hydroxycarbonylation tandem reaction in HOAc‐NaOAc buffer. This synthetic protocol shows major improvements compared to previously reported methods, such as using biomass‐based 2‐furoic acid as low‐cost raw material, one‐pot synthesis without isolation of intermediate products, and no need for an acidification procedure. Experiments indicate that the involved Xantphos‐modified Pd‐catalyst and the buffer solution play significant promoting roles for each individual reaction whereas Br₂ (as the brominating reagent) had a negative effect on the second hydroxycarbonylation step, while CO was deleterious for the first bromination step. Hence, in this practical one‐pot synthesis, Br₂ should be consumed in the first bromination step as fully as possible, and CO is introduced after the first bromination step has been completed.     

Zur Chemie der Bromisocyanursäuren: Eigenschaften und Reaktionen der Dibromisocyanursäure

Of the bromo derivatives of isocyanuric acid, unknown until 1967, dibromoisocyanuric acid (DBI) has proved to be a particularly powerful brominating agent, which can be easily handled in the laboratory.The chemistry ofDBI has been studied in depth by determination of the hydrolysis and dissociation constants, the redox potential in aqueous solution, and by investigation of its thermal behaviour, reaction with alkali ions (salt formation) and tertiary nitrogen compounds (formation of complexes). Its superiority as a brominating agent to other N-bromo compounds derives from the highly positive character of the bromine. The differences between the chloro-, bromo- and iodoisocyanuric acids are discussed, and related to the respective N-halogene and C–N bonding strengths.

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