Iodine Monobromide Research Articles

Observations on the activation of methyl thioglycosides by iodine and its interhalogen compounds 1,2

Treatment of ‘armed’ methyl thiogalactosides with iodine in the absence of an acceptor alcohol results in thioglycoside epimerisation, whereas there is no effect on the corresponding ‘disarmed’ methyl thioglycosides. In contrast, iodine–hexamethyldisilane (which generates iodotrimethylsilane in situ) brings about epimerisation of ‘disarmed’ thioglycosides, ultimately giving rise to the corresponding α-glycosyl iodides on extended exposure. Cross-over experiments show the former iodine-promoted epimerisation process to be intermolecular, whereas the latter iodine–hexamethyldisilane-promoted epimerisation is intramolecular. Treatment of the same methyl thiogalactosides with iodine monobromide gives rise to the thermodynamically favoured α-glycosyl bromides, whereas reaction with iodine monochloride initially gives the kinetic β-glycosyl chlorides, which slowly epimerise to the thermodynamic α-linked products. Differences in the outcome of thioglycoside activation by I–I, I–Br and I–Cl suggest there may be scope for influencing the stereochemical course of thioglycoside-based glycosylation reactions through careful choice of promoter.

Further structural motifs from the reactions of thioamides with diiodine and the interhalogens iodine monobromide and iodine monochloride: an FT-Raman and crystallographic study †

The reactions of the thioamides thiourea, tu, 1-ethyl-2-thiourea, etu, 1,3-dimethyl-2-thiourea, dmtu, 1,3-diethyl-2-thiourea, detu, 3-methylbenzothiazole-2-thione, mbtt and 3-methylrhodanine, mrh, with one equivalent of diiodine have been studied; attempts have been made to characterise the resultant 1∶1 addition products using FT-Raman spectroscopy. It has been shown that these materials lie on a CT–ionic borderline. The crystal structure of dmtu·I2 has been determined and is shown to be ionic and of the form [(dmtu)2I]+I3−, an arrangement previously only rarely found in crystallographic reports. The reactions of etu and dmtu with iodine monobromide and iodine monochloride and of mbtt with iodine monobromide give 1∶1 interhalogen addition products; initial FT-Raman investigations point to these adopting a CT ‘spoke’ structure. The reaction of tu with two equivalents of diiodine to give a bulk material of stoichiometry tu·I4 has been studied in detail and shown to lead to a variety of novel polyiodide arrangements, the crystal structures of two of which are reported, (tu)2(I2)3 and (tu)3(I2)5, and compared to each other, the previously reported (tu)2I2 and to tu itself. These two structures represent further, previously unreported, structural motifs available for these highly complicated systems.

ChemInform Abstract: Iodine and Its Interhalogen Compounds: Versatile Reagents in Carbohydrate Chemistry. Part 9. A Mild and Selective Deprotection of tert‐Butyldimethylsilyl (TBDMS) Ethers in the Presence of Various Protecting Groups Using Iodine Monobromide.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Iodine and its Interhalogen Compounds: Versatile Reagents in Carbohydrate Chemistry IX. A Mild and Selective Deprotection of tert-Butyldimethylsilyl (TBDMS) Ethers in the Presence of Various Protecting Groups Using Iodine Monobromide

Iodine and its Interhalogen Compounds: Versatile Reagents in Carbohydrate Chemistry IX. A Mild and Selective Deprotection of <i>tert</i>-Butyldimethylsilyl (TBDMS) Ethers in the Presence of Various Protecting Groups Using Iodine Monobromide

Synthesis and polymerisation of fluorinated monomers bearing a reactive lateral group. Part 5 – Radical addition of iodine monobromide to chlorotrifluoroethylene to form a useful intermediate in the synthesis of 4,5,5-trifluoro-4-ene-pentanol

The synthesis of the new halogenated alcohol BrCF 2CFClCH 2CHICH 2OH as a precursor of 4,5,5 trifluoro-4-ene pentanol F 2CCFC 3H 6OH is based on a two-step process. First, the radical addition of iodine monobromide to chlorotrifluoroethylene (CTFE) led to the expected BrCF 2CFClI (I) and ICF 2CFClBr (II), but also to BrCF 2CFClBr (III) and ICF 2CFClI (IV), the amount of which determined by 19 F NMR depended on the reaction conditions: by feeding CTFE into IBr continuously or in batches; photochemical or thermal initiations, and with various initial [IBr] 0/[CTFE] 0 molar ratios. In most cases, isomer (I) was mainly produced. The second step concerned the addition of such a mixture to allyl alcohol yielding the polyhalogenoalcohol with a quantitative conversion of (I). The reactivity of different halogeno end-groups of these isomers toward the allyl alcohol was discussed. Reduction of the iodine atom into hydrogen and the halogenated alcohol was accompanied by that of the bromine atom leading to BrCF 2CFClC 3H 6OH and HCF 2CFClC 3H 6OH (V). Dehalogenation of the former alcohol in the presence of zinc led to F 2CCFC 3H 6OH while dehydrochlorination of (V) into trifluorovinyl hydroxy monomers was achieved in the presence of potassium hydroxide but in poor yields. Strategies starting from the radical additions of iodine monochloride and of iodine monobromide were compared showing that the former led to better overall yields of trifluorovinyl alcohol than the latter.

Reaction of thiones with dihalogens; comparison of the solid state structures of 4,5-bis(methylsulfanyl)-1,3-dithiole-2-thione–diiodine, –dibromine and –iodine monobromide

Reaction of 4,5-bis(methylsulfanyl)-1,3-dithiole-2-thione 1 with diiodine or iodine monobromide in CH2Cl2 resulted in the formation of molecular charge-transfer complexes 1·I2 and 1·IBr respectively. Both complexes have been characterised crystallographically and contain a linear S–I–X (X = I or Br) moiety with the sulfur adopting a tetrahedral geometry taking into account the stereochemically active lone pairs. The S–I [2.716(3)] and I–I [2.808(3) Å] bond lengths in 1·I2 are similar to those reported for diiodine complexes of related thione donors. The adduct 1·IBr is the first crystallographically characterised thione–iodine monobromide charge-transfer complex. The S–I distance [2.589(2) Å] is shorter than that in 1·I2, consistent with IBr being a stronger acceptor than I2. The I–Br distance [2.7138(11) Å] is lengthened with respect to that in unco-ordinated IBr, but within bonding distance when compared to the sum of the van der Waals radii for iodine and bromine (3.75 Å). Treatment of 1 with dibromine under identical conditions resulted in the formation of the adduct 1·Br2 and the dithiolylium salt [C5H6S4Br][Br3]·½Br2 2. Treatment of 1 with Br2 in toluene led to the isolation of 1·Br2 only. The crystal structure of 1·Br2 shows the compound to contain a linear Br–S–Br moiety with the sulfur in a T-shaped or Ψ-trigonal bipyramidal environment (taking into account the stereochemically active lone pairs). The structure of 2 reveals a three component system consisting of the [C5H6S4Br]+ cation, the [Br3]– anion and a molecule of Br2 in a 2∶2∶1 ratio. These components are held in the lattice by a series of weak intermolecular interactions which link the tribromide ions and dibromine molecules into zigzag chains.

The reaction of N-methylbenzothiazole-2-selone with the interhalogens iodine monobromide and iodine monochloride

Two 1∶1 interhalogen adducts of N-methylbenzothiazole-2-selone (mbts) have been prepared and crystallographically characterised: mbts·IBr (1) and mbts·ICl (2). Both exhibit the charge transfer ‘spoke’ structure consisting of a linear Se–I–X arrangement (X = Br or Cl) where d(C–Se) increases from that seen for mbts by 0.058(5) and 0.062(8) A (1 and 2 respectively); d(C–N) decreases by 0.019(4) and 0.019(9) A. This indicates electron density moves towards the Se–I–X moiety upon co-ordination, causing a partial positive charge to reside on the nitrogen atom. The I–X bond lengthens with respect to the unco-ordinated species for both molecules. The addition of two equivalents of ICl to mbts gave a dark purple material of stoichiometry C8H7Cl2.9I1.1NSSe 3; the fractional stoichiometry for iodine and chlorine may be indicative of ‘halogen scrambling’. An additional product from this reaction was examined crystallographically and found to consist of the ion pair [C8H7NSCl]+[ICl2]–4, i.e. the C–Se double bond has been completely cleaved and replaced by a C–Cl single bond. The positive charge is again supported mostly by the nitrogen atom; d(C–N) decreases to 1.294(10) A indicating a double bond.

Adsorption dynamics of monoenergetic iodine monobromide (IBr) on the Si(111)-7×7 surface

The adsorption of monoenergetic IBr molecules on the Si(111)-7×7 surface has been studied using scanning tunneling microscopy, mass spectrometry, Auger electron spectroscopy, and supersonic molecular beam techniques. The adsorption proceeds predominantly via the direct abstractive adsorption mechanism and preferentially occurs at the center Si adatoms. The IBr abstraction probabilities at the incident energies of 0.15 and 0.82 eV have been determined to be 0.90±0.03 and 0.77±0.03, respectively. The minor dissociative adsorption channel of IBr can be enhanced at the expense of the abstractive adsorption channels by raising the incident energy. Most importantly, no atomic selectivity for iodine or bromine was observed. A reaction mechanism involving two types of transition states, Si⋯I⋯Br(s) and Si⋯Br⋯I(s), has been proposed to interpret the experimental observations. The attractive interaction between the nearly symmetric highest occupied molecular orbitals (HOMO, π* antibond) of IBr and the partially-filled Si adatom dangling bonds governs the surface site selectivity and the atomic selectivity of IBr adsorption on Si(111). Comparison with the adsorption of ICl on the surface has also been made to clarify the role of the asymmetric molecular bonding in adsorption dynamics.

Effect of intercalation in graphite epoxy composites on the shielding of high energy radiation

The half-thickness and mass absorption coefficient of 13.0 keV x-rays, 46.5 keV γ-rays, and 1.16 MeV βƟ particles have been measured for pristine, bromine intercalated, and iodine monobromide intercalated pitch-based graphite fiber composites. Since these materials have been proposed to replace aluminum structures in spacecraft, the results were compared to aluminum. Pristine graphite epoxy composites were found to have about 4.0 times the half-thickness, and 40% of the mass absorption of aluminum for ionizing radiation. Bromine intercalation improved performance to 90% of the half-thickness, and 1.7 times the mass absorption coefficient of aluminum. Iodine monobromide extended the performance to 70% of the half-thickness and 3.0 times the mass absorption of aluminum. Thus, intercalation not only makes up the deficiency conventional composites have in shielding components from ionizing radiation, but actually confers advantages in mass and thickness over aluminum. The βƟ particle shielding of all the materials tested was found to be very effective. The shielding of all of the materials was found to have nearly the same mass absorption coefficient of 17.8 ± 0.9 cm2/g. Inelastic scattering processes were found to be important in βƟ particle shielding; however, the extent of inelastic scattering and thus the distribution of energies of the transmitted electrons did not vary with material.

Characterization of a Br( 2 P 1/2 )-CO 2 (10 0 1-10 0 0) transfer laser driven by photolysis of iodine monobromide

laser operating on the 1001-1000 transition at λ=4.3 μm and pumped by E –V energy transfer from Br(2P1/2) has been demonstrated. The dynamics and performance of this device were characterized by observing the time-resolved stimulated emission and the steady-state spontaneous side fluorescence after photolysis of IBr or Br2 by a frequency-doubled Nd:YAG laser or Ar+ laser, respectively. Although the E –V excitation kinetics are favorable, rapid vibrational relaxation limits laser action to CO2 pressures of less than 1 Torr. Numerical modeling of laser pulse shapes and the dependence on IBr and CO2 pressure and photolysis energy establish a relatively high gain of 0.33%/cm, a CO2-pressure-dependent optical loss of 0.04–0.06%/cm, and an efficiency of 2×10-5 4.3-μm-laser photons per incident photolysis photon. The CO2 fluorescence after photolysis of a fixed Br2/CO2 gas mixture decreases as a function of photolysis time by about 30%/h, indicating the photolytic production of an important quencher.

ChemInform Abstract: Iodine and Its Interhalogen Compounds: Versatile Reagents in Carbohydrate Chemistry. Part 6. Glycosylation Chemistry Promoted by Iodine Monobromide: Efficient Synthesis of Glycosyl Bromides from Thioglycosides and O‐Glycosides from ′Disarmed′ Thioglycosides and Glycosyl Bromides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Glycosylation chemistry promoted by iodine monobromide: Efficient synthesis of glycosyl bromides from thioglycosides, and O-glycosides from ‘disarmed’ thioglycosides and glycosyl bromides

Iodine monobromide has been found to be an efficient reagent for the conversion of both ‘armed’ and ‘disarmed’ thioglycosides (SMe, SPr i , SPh) into glycosyl bromides. This reagent is compatible with most common protecting groups, and O-glycosidic linkages. The additional potency of IBr, compared to iodine, as an iodonium ion source also permits the glycosylation of sugar alcohols by ‘disarmed’ glycosyl bromides and thioglycosides.

Dynamics of a Br(4 2 P 1/2 →4 2 P 3/2 ) pulsed laser and a Br( 2 P 1/2 )-NO(v=2→v=1) transfer laser driven by photolysis of iodine monobromide

P1/2 – 42P3/2 transition at λ=2.71 μm and pumped by photolysis of IBr with a frequency-doubled Nd:YAG laser has been demonstrated. The dynamics and performance of this device were characterized by observing the temporal dependence of the stimulated emission for various laser photolysis energies (20–125 mJ/pulse) and IBr pressures (0.7–6.7 torr). The gain is directly proportional to the number of absorbed photolysis photons, with a value of 0.9 %/cm over 41 cm at an IBr pressure of 5 torr. The inversion is quenched rather slowly, with a pulse duration of greater than 2 μs, after short-pulse (10 ns) excitation. The laser energy is maximized at 2.5 torr of iodine monobromide in a photolysis cell of 90 cm. A numerical solution to the rate equations for the laser pulse shapes provides a threshold inversion of Δth=2.9×1013 atoms/cm3. The energy efficiency of this device is limited principally by the low quantum efficiency, poorly matched pump and cavity mode volumes, and the photolysis yield of a single isotope hyperfine component of Br(2P1/2). A nitric oxide, NO(v=2→v=1), laser at λ=5.4 μm pumped by electronic-to-vibrational energy transfer from the photolytically produced Br(2P1/2) has also been demonstrated. The output energy and gain of this NO laser is adversely affected by rapid V-V relaxation.

Titration of Mercaptans and Some Mercaptan-Based Drugs with Iodine Monobromide in Non-Aqueous Dimethyl Sulfoxide

Mercaptans undergo smooth and quantitative oxidation to the corresponding disulfides with iodine monobromide in non-aqueous (dimethyl sulfoxide) medium, which has been made the basis of a simple, rapid and rugged method for the determination of mercaptan-based drugs viz. mercaptopurine and dimercaprol. The method has been thoroughly tested with a number of mercaptans before applying it to drugs. The salient features of the method are discussed.

Structural characterisation of the diorganoselenium interhalogen compounds R2SeIBr (R = Ph or Me) and the ionic compound [Me3Se][IBr2

The reaction of R2Se (R = Ph or Me) with iodine monobromide in diethyl ether solution produced the charge-transfer complexes R2SeI–Br. In the case of Ph2Se, Ph2SeIBr was produced quantitatively. However, for Me2Se, both Me2SeIBr and the ionic product [Me3Se][IBr2] were produced indicating ease of methyl migration for Me2SeIBr and that it lies close to the ionic/covalent structural borderline. The other product from this autoionisation is believed to be Me2Se2I2, although this was not extensively characterised. The compounds Ph2SeIBr and Me2SeIBr show markedly different d(I–Br) 2.640(2) and 2.797(5) Å, respectively, illustrating how the R groups on the selenium affect its donor power towards iodine monobromide. The three compounds Ph2SeIBr, Me2SeIBr and [Me3Se][IBr2] have been characterised by single-crystal X-ray diffraction.

Microwave Induced Selective Bromination of 1,4-Quinones and Coumarins

Abstract Microwave irradiation accelerates the bromination of 1, 4-quinones and coumarins with (i) bromine adsorbed on neutral alumina in “dry media” and (ii) with iodine monobromide in acetic acid as compared to the reactions run at room temperature. Bromination takes place selectively at active quinonoid position in 1,4-quinones and at α, β-double bond in coumarins.

Thermochemistry of Molecular Complexes of Iodine Monochloride, Iodine Monobromide, and Bromine with Benzene and Benzene Derivatives

Thermochemistry of Molecular Complexes of Iodine Monochloride, Iodine Monobromide, and Bromine with Benzene and Benzene Derivatives

Kinetics and Mechanism of the Complex Bromate−Iodine Reaction

The mechanism of the reaction between bromate and iodine in an acidic medium (HClO4), in a closed system, has been investigated by both experimental and computer simulation techniques. The stoichiometry of the reaction is 2BrO3- + I2 → 2IO3- + Br2. The reaction is preceded by an induction period whose length is inversely proportional to the concentration of bromate and the square of the acid concentration. The induction period increases upon the addition of iodide and bromide ions, with the effect of bromide ions being less marked. These ions consume HOI and HOBr molecules, which are precursors to the oxidation of iodine. At the end of the induction period iodine is suddenly depleted while simultaneously a transient interhalogen, iodine bromide, IBr, is formed and consumed rapidly. As soon as the IBr concentration reaches its maximum value, i.e., [IBr]max = 2[I2]0, it is rapidly consumed at an exponential rate given by −d[IBr]/dt = k1[IBr]. When all the IBr has been depleted, molecular bromine is formed at the rate d[Br2]/dt = k2[H+][BrO3-][I2]. Values of k1 and k2 were evaluated as 0.47 ± 0.10 s-1 and 0.26 ± 0.02 M-2 s-1, respectively. A 17-step mechanism which encompasses the mechanisms of the bromate−iodine and bromate−iodide reactions gives good agreement between experimental data and computer simulation. An extensive set of experimental data is presented that supports a molecular mechanism over a radical-dominated one.

NMR investigation on IBr-doped C 60, where IBr is iodine monobromide

It was found by 13C-NMR that the doping of iodine monobromide (IBr) into C 60 solid changes significantly the electronic states of C 60, indicating chemical reaction between C 60 and halogen atoms, such as charge transfer and bonding. On the other hand, no significant change in 13C-NMR characteristics was observed in C 60 solids doped by iodine (I 2) and iodine tricloride (ICl 3). A possibility of metallic states at C 60 sites was suggested by spin-lattice relaxation time measurement in IBr-doped C 60.

Peroxidation of egg yolk phosphatidylcholine liposomes by hypochlorous acid

The powerful neutrophil-derived oxidant hypochlorous acid HOCl/OCl − is assumed to contribute to tissue injury m a number of pathological states accompanied by massive accumulation of neutrophils. The production of malondialdehyde to indicate lipid peroxidation was studied in egg yolk phosphatidylcholine liposomes upon treatment with NaOCl as a source for hypochlorous acid. Its accumulation was inhibited by a-tocopherol and butylated hydroxytoluene. Singlet oxygen, hydroxyl radicals or Superoxide anion radicals derived from direct reactions of hypochlorous acid seem not to be involved in initiation of lipid peroxidation because the malondialdehyde accumulation was unaffected by hydrogen peroxide, catalase, Superoxide dismutase, ferrous sulphate or ferric chloride. Double bonds of fatty acid residues seem to be the primary target for NaOCl. Their number is continuously diminished in liposomes (2 mg lipids/ml) after incubation with increasing amounts of NaOCl at 37°C for 40 min as detected by two independent methods (iodine bromide reduction and 1H-NMR spectroscopy). A 1:1 molar ratio between the loss of double bonds and NaOCl added was found only at low NaOCl concentrations. Then double bonds are decreased with a lower efficiency. A continuous increase of lipid peroxidation products was only observed up to 0.5–0.7 mmol/1 NaOCl. The yield of lipid hydroperoxides kept constant at higher NaOCl concentrations. However, diene conjugates and malondialdehyde exhibit a maximum at 0.7–1 mmol/1 or 0.5 mmol/1 NaOCl, respectively, while the concentration of these products decreases at higher doses of NaOCl. The decrease of malondialdehyde was more pronounced than for diene conjugates. These results were discussed from the background that at minimum two (diene conjugates) or three (malondialdehyde) double bonds in a fatty acid residue are necessary for formation of lipid peroxidation products.