Efficient conversion of substituted aryl thioureas to 2-aminobenzothiazoles using benzyltrimethylammonium tribromide

The reaction of molecular bromine (Br2) with arylthioureas is known to produce 2-aminobenzothiazoles (Hugerschoff reaction). We show here that benzyltrimethylammonium tribromide (1, PhCH2NMe3Br3), a stable, crystalline organic ammonium tribromide (OATB), can be readily utilized as an alternative electrophilic bromine source. It is easier to control the stoichiometry of addition with an OATB, which minimizes aromatic bromination caused by excess reagent. We have developed a direct procedure from isothiocyanates and amines using tetrabutylammonium thiocyanate (Bu4NSCN) and PhCH2NMe3Br3 to afford functionalized 2-aminobenzothiazoles.     

Synthesis and characterization of bromine source supported on magnetic Fe3O4 nanoparticles: A new,versatile and efficient magnetically separable catalyst for organic synthesis

Tribenzylammonium tribromide supported onto magnetic nanoparticles (Br₃‐TBA‐Fe₃O₄) as a bromine source was successfully synthesized and characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and vibrating sample magnetometry. The synthesized catalyst is shown to be a versatile and highly efficient heterogeneous catalyst for the Knoevenagel condensation and synthesis of 2,3‐dihydroquinazolin‐4(1H )‐one and polyhydroquinoline derivatives. To the best of the authors' knowledge, this is the first report of the use of a bromine source immobilized on Fe₃O₄ nanoparticles as a magnetically separable catalyst for these reactions. The nanosolid catalyst can be magnetically recovered and reused readily several times without significant loss in catalytic efficiency.     

A Raman and resonance Raman study of polybromide anions and a study of the temperature dependence of the Raman-active phonons of tetrabutylaminonium tribromide

Raman and resonance spectroscopy are shown to be capable of characterizing the tribromide and pentabromide anions and interstitial dibromine. The anions have Raman-active phonons which display a broad maximum in their excitation profiles at 600 nm, whereas interstitial bromine has a maximum in its excitation profile shifted towards the blue.Large shifts in band wavenumber are observed for the symmetric and asymmetric bromine stretching vibrations in tribromide salts with different cations. The bromine stretch force constants for the tribromide anions, for dibromine and for the recently reported decabromide dianion, have been shown to obey the relationship, k=0.01r^−6.7.The Raman-active phonons of tetrabutylammonium tribromide have been studied as a function of temperature, from 10 to 300 K. No first order phase changes were observed and remarkably small coefficients (∂ν/∂T)_P, were measured for both the internal and the external modes.     

Bromination of alkylbenzenes in 1-butyl-3-methylimidazolium bromide and its dibromide complex

Alkylbenzenes were subjected to bromination with molecular bromine using 1-butyl-3-methylimidazolium bromide as solvent. A complex of 1-butyl-3-methylimidazolium bromide with bromine was synthesized. It ensured bromination of alkylbenzenes with no bromine and solvent. The results of bromination in binary solvents and ionic liquids, 1-butyl-3-methylimidazolium bromide and tribromide were compared. The bromination of ethylbenzene with 1-butyl-3-methylimidazolium tribromide was accompanied by formation of a considerable amount of α-bromoethylbenzene, which is not typical of electrophilic aromatic substitution process.     

Benzylic Bromination of Toluene Derivatives with Boron Tribromide

A facile method for the benzylic bromination of toluene derivatives was developed. Various substituted toluenes were brominated with boron tribromide as bromine source in carbon tetrachloride at room temperature, affording their corresponding benzyl bromides in good yields.     

Reaction of N,N-Dialkylcarboxamides with Halogens

N,N-Dialkylcarboxamides react with halogens in the absence of water to form complexes which are likely to have an ionic structure with the Hlg⁺ ion coordinated at the carbonyl oxygen atom. These products can be isolated as individual compounds. Complexes with bromine undergo further transformations to afford bis-dialkylamide hydrogen tribromide and the corresponding -bromo amide. When the reaction is carried out in the presence of water, the products are only bis-dialkylamide hydrogen tribromides; here, the N-alkyl groups act as a source of protons.     

In Process Citation

A new method of bromine number determination appropriate to heavy-ends petroleum is reported. This method, which uses an electrochemical titration and tetrabutylammonium tribromide as reagent, has been tested on Boscan atmospheric residues. The titration of the unreacted tribromide ions and of the bromide ions produced enables the proportion of the bromine addition to multiple bonds and the proportion of substitution reactions with aromatic compounds (phenols, amines, etc.) to be estimated. The sensitivity and reproducibility of this easy method are both good.     

Reactions of 4H-selenopyrans with halogens

The reactions of 2,4,4,6-tetraphenyl-4H-selenopyran with chlorine or bromine give the corresponding 1,1-dichloro- or 1,1-dibromo-4H-selenopyrans, whereas the reaction of 2,4,6-triphenyl-4H-selenopyran with bromine gives 2,4,6-triphenylselenopyrylium tribromide.     

Addition of bromine to 2-methyl-2-azabicyclo[2.2.1]hept-5-ene

Addition of bromine to 2-methyl-2-azabicyclo[2.2.1]hept-5-ene was studied. Unexpectedly, 3-bromo-1-methyl-1-azoniatricyclo[2.2.1.0^2,6]heptane tribromide was isolated rather than the product of bromine addition to the double bond. The former reacted with the starting alkene in a polar solvent to form the corresponding monobromide.     

Addition of Bromine to trans-Stilbene: Reversal of Stereoselectivity upon Cyclodextrin Complexation

In contrast to the formation of meso-stilbene dibromide as the major productin the electrophilic addition of bromine to trans-stilbene in nonpolar solvents,stereoselectivity decreases in cyclodextrin cavities and a significant yield ofdl-stilbene dibromide is also obtained. This reversal of stereoselectivity isattributed to the polar environment provided by the secondary hydroxyl groupsof cyclodextrins which stabilises the acylic -halocarbonium ion intermediateand also hinders the approach of the incoming tribromide ion.     

A new recyclable ditribromide reagent for efficient bromination under solvent free condition

1,2-Dipyridiniumditribromide-ethane (DPTBE) has been synthesized and explored as a new efficient brominating agent. The crystalline ditribromide reagent is stable for months and acts as a safe source of bromine requiring just 0.5 equiv for complete bromination. It has high active bromine content per molecule and shows a remarkable reactivity compared to other tribromide reagents toward various substrates by just grinding the reagent and substrates in a porcelain mortar at room temperature. No organic solvent has been used during any stage of the reaction for substrates giving product as solid. Product can easily be isolated by just washing the highly water soluble 1,2-dipyridiniumdibromide-ethane (DPDBE) from the brominated product. The spent reagent can be recovered, regenerated, and reused without any significant loss.     

Oxidation of Sulfides with Pyridinium Tribromide in the Presence of Hydrated Silica Gel

A variety of sulfides have been oxidized to sulfoxides utilizing pyridinium tribromide in the presence of hydrated silica gel in a non‐aqueous media. A combination of pyridinium tribromide and hydrated silica gel releases molecular bromine slowly in the reaction, affecting the oxidation. Hydrated silica gel also promotes decomposition of the bromosulfonium intermediate to the product. This procedure employs non‐aqueous media for the first time in such a reaction.     

The synthesis of a series of (α-amino)indol-3-yl ketones

A series of [(α-amino)indol-3-yl]-2-methyl-1-propanones and [(α-amino)indol-3-yl]cyclopentylmethanones has been synthesized by a variety of reductive reactions performed on the corresponding series of (α-azido)-indol-3-yl ketones. One of the more interesting reductive procedures involved the palladium-catalyzed decomposition of formic acid with the formation of hydrogen in situ. The (α-azido)ketones were prepared in excellent yield by the displacement of the tertiary bromine atom from the (α-bromo)ketones using sodium azide in N,N-dimethylformamide. Bromination was accomplished by using either cupric bromide in ethyl acetate/chloroform or phenyltrimethylammonium tribromide in tetrahydrofuran.     

Synthesis and reactivity of bis(cycloamidinium-2-yl)alkane bromide tribromides, brominating agents and tectons for molecular engineering

Bis(cycloamidine-2-yl)alkanes easily form bromide tribromide salts in the reduction-oxidation processes with bromine. Bis(tetrahydroimidazolium-2-yl)ethane and bis(hexahydropyrimidinium-2-yl)-ethane bromide tribromides are such new convenient brominating agents for aromatic amides in chemo- and regioselective electrophilic substitutions and α-bromination reactions.     

Preparation of acid bromides of tri- and pentavalent phosphorus acids

Conclusions It was shown that the acid bromides of phosphorus acids can be obtained via the exchange of chlorine by bromine in the corresponding acid chlorides under the influence of phosphorus tribromide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1193–1194, May, 1972.     

On bromination of 2,4-pentanedionato-copper(II)

Treatment of bis-2,4-pentanedionato-copper(II), with liquid bromine, at room temperature, gave a low melting dark green reaction product containing weakly coordinated tribromide ion. Characterization of this product using elemental analysis, conductivity, electronic, IR and ESR-spectra was carried out and suggested that the composition of the product was [Cu(HacacBr)Br(Br₃)].     

A computational approach to understanding the mechanism of aromatic bromination using quaternary ammonium tribromides

Quaternary ammonium tribromides (QATBs) have garnered interest for nearly a century now. Various types of tribromides have been synthesized over the years and their diverse applications have been extensively reported. However, despite the fact that these reagents are touted as safer alternatives to the very poisonous bromine, there is insufficient information on the structure of Br₃^? in QATB systems and there is still no clear explanation for how the tribromide ion (Br₃^?) participates in bromination reactions. This paper reports a through structural assessment of Br₃^?, followed by an attempt was made to fully understand the mechanistic behaviour of tribromide during bromination of aromatic compounds.     

α-Fe_2O_3 immobilized benzimidazolium tribromide as novel magnetically retrievable catalyst for one-pot synthesis of highly functionalized piperidines

Nanostructured α-Fe_2O_3 were prepared by precipitation followed by calcination method.Cetyltrimethylammonium bromide(CTAB) was used as surfactant.The nano α-Fe_2O_3 was then silanized with(3-chloropropyl)-triethoxysilane(CPTES) by room temperature mixing of α-Fe_2O_3 and CPTES to produce silane coated α-Fe_2O_3(ClPr-Si@Fe_2O_3).As-synthesized ClPr-Si@Fe_2O_3 was functionalized via covalent grafting of benzimidazole to produce 3-(l-benzimidazole)Pr-Si@Fe_2O_3.This was further reacted with bromine to afford α-Fe_2O_3 immobilized benzimidazolium tribromide(α-Fe_2O_3-BIM tribromide).This ionic liquid(IL)α-Fe_2O_3 BIM tribromide was characterized by FT-IR,XRD,TEM,SEM,TGA,VSM,EDX and BET analysis.The as-synthesized IL tribromide was used as catalyst for one-pot synthesis of highly substituted piperidines.The method is greener in terms of solvent selection,recovery of the catalyst and efficiency.     

Preparation of new nitrogen-bridged heterocycles. 55. Reinvestigation of the bromination/dehydrobromination of ethyl 3-[2-(methylthio)indolizin-3-yl]acrylate derivatives

The bromination/dehydrobromination reactions of ethyl 3-[1-alkoxycarbonyl-2-(methylthio)indolizin-3-yl]acrylates were reinvestigated. Reactions of the title compounds with two equivalents of bromine, followed by heating of the resulting reaction mixture and then treatment with a base gave the unexpected dialkyl 7-bromothieno[2,3-b]indolizine-2,9-dicarboxylates, while similar reactions using benzyltrimethylammonium tribromide as a brominating agent afforded only non-brominated thieno[2,3-b]indolizine derivatives, which were converted to the corresponding 7-bromo derivatives upon further treatment with bromine.     

{[K.18-Crown-6]Br3}n: a unique tribromide-type and columnar nanotube-like structure for the oxidative coupling of thiols and bromination of some aromatic compounds

Reaction of 18-crown-6 with KBr and then with bromine (Br₂) afforded a unique tribromide salt with a nanotube-like structure ({[K.18-crown-6]Br₃}_n). Oxidative coupling of thiols and bromination of some aromatic compounds is the first report on the chemistry of this reagent.