Dibromomethane Research Articles

Model analysis of the anisotropic angular motion in liquid methylene bromide

Carbon-13 spin-lattice relaxation times and nuclear Overhauser enhancements were measured in neat dibromomethane as a function of temperature. Derived C-H correlation times were observed to increase with decreasing temperature. Various theoretical models were utilized to predict the temperature dependence of the correlation times. It was found that the extended diffusion model of inertially controlled reorientation was superior in predicting the temperature behavior of the reorientating vector. Bromine relaxation times were also calculated and were found to be consistent with accepted values.

ChemInform Abstract: Ambident Nucleophilicity of Silver Hyponitrite Toward Organic Halides.

AbstractIn contrast to the known reaction of bromo(diphenyl)methane (I) with silver hyponitrite (II) in methylene chloride, yielding bis(diphenylmethyl) hyponitrite (III), the chloro analogue (IV) of (I) is treated with (II) in a benzene/hexanes mixture to give the diazene N‐oxide (V).

Reaction of 3,3,3-trifluoropropene-1 with bromoform and methylene bromide

The radical telomerization of 3,3,3-trifluoropropene with bromoform and methylens bromide has been studied. The nature of the products with bromoform depends substantially on the method of initiation. In the presence of Fe(CO)5 + DMF, telomers of CHBr2(CH52CHCF3)nBr are formed, while with initiation with benzoyl peroxide other compounds are also formed that contain two, three, or four bromine atoms per molecule. To elucidate the formation of these products a reaction scheme is proposed that involves rearrangement of CHBr2CH2CH(CF3)CH3CHCF3 radicals to CBr2CH2CH(CF3)CH2CH2CF3 radicals.

Crystal structures of methylene bromide and methylene iodide

The crystal structures of the three solid phases of methylene iodide and the stable phase of deuterated methylene bromide have been determined using the neutron powder profile structure refinement technique. For CH2I2, both phase I at 50K and phase III at 16K, and for CD2Br2, the stable phase at 15K, have eight molecules per unit cell on general sites of the monoclinic space group C2/c. The structure of CH2I2, phase II, has been determined at 16K, 30K, 50K and 255K. This phase is face centred orthorhombic, space group Fmm2, with four molecules per unit cell on sites with C 2v symmetry. Molecular bond lengths and angles are given for all structures. The lattice energy of each structure has been calculated using an empirical potential. Phase II is found to be the most stable phase for CH2I2, but the energy differences between all three phases are small.

Reaction of 2.6-diphenyl-4-pentafluorophenylverdazyl with disubstituted mono- and dibromomethanes

Dicyano- and dicyanoethoxycarbonylbromomethane cause fragmentation of 2,6-diphenyl-4-pentafluorophenylverdazyl to 1,3,5-trisubstituted 1,2,4-triazoles. Trifluoro-methylsulfonylcyano- and trifluoromethylethoxycarbonyldibromomethane acylate the dazyl radical to give 1-R-2,6-diphenyl-4-pentafluorophenyl-1,2,3,4-tetrahydro-symtetrazines.

Zur direkten Synthese von Organobromgermanen aus Methylenbromid und Germanium/Kupfer-Gemischen/Direct Synthesis of Organobromogermanes from Methylenebromide and Germanium/Copper Mixtures

Abstract A lkylbrom ogerm anes, Synthesis, C V D Feeding G as, G erm anium /Copper Mixtures From the copper-catalyzed reaction o f germanium powder with dibrom om ethane at 310 °C a mixture o f alkylbrom ogermanes is obtained. The major products are CH 3G eB r3, Br3G eC H 2Br

Solvent Diffusion in Selected Polyimide Films

AbstractThe absorption of several solvents including methylene chloride (MC), methyl chloroform (MCF), gamma-butyrolactone (BLO), dibromomethane (DBRO), 1,2-dichloroethane (DCE), and 1,2-dichloropropane (DCP) in Kapton H*, Upilex S**, and Upilex R** polyimide film was measured gravimetrically. A significant difference in the rate and amount of absorption of these chemicals by the various films was observed. Complimentary Rutherford Backscattering Spectrometry (RBS) measurements provided additional information regarding the amount of solvent absorbed and mode of transport.

Empirical correlations of partial molar volumes at infinite dilution of organic solutes and transition states for S N 2 hydrolysis and ethanolysis of n-alkyl bromides

Pseudo-first-order rate constants under pressures ⩽98.1 MPa have been measured for the hydrolysis of ethyl, n-propyl, and n-butyl bromides in water at 298.15 K and for the ethanolysis of methyl, n-propyl, and n-butyl bromides in ethanol at 333.15 K. Activation volumes (cm3 mol–1) were ca. –11 for the hydrolysis and about –25 for the ethanolysis. Partial molar volumes at infinite dilution were measured for n-butyl bromide in water at 298.15 K and for 66 organic solutes in ethanol at 333.15 K. Partial molar volumes of the transition states are shown to be adaptable to volumetric behaviour for, common solutes, in which the partial molar volume of each solute is compared with that of the n-alkane having the same van der Waals volume.

Rapid Determination of Fumigant and Industrial Chemical Residues in Food

A gas chromatographic (GC) method is described for the determination of 22 fumigant and industrial chemical residues in a variety of foods. The fumigants and industrial chemicals determined are methyl bromide, methylene chloride, carbon disulfide, chloroform, 1,1-dichloroethane, ethylene dichloride, methyl chloroform, carbon tetrachloride, methylene bromide, propylene dichloride, 2,3-dichloropropene, trichloroethylene, 1,3-dichloropropylene, 1,1,2-trichloroethane, chloropicrin, ethylene dibromide, tetrachloroethylene, propylene dibromide, 1,1,2,2-tetrachloroethane, p-dichlorobenzene, o-dichlorobenzene, and 1,2-dibromo-3-chloropropane. Except for the latter three, the fumigants are determined at 90 degrees C on 3.6 m 20% loaded OV-101 columns with electron-capture and Hall-electroconductivity detectors. The other 3 compounds (o-dichlorobenzene, p-dichlorobenzene, and 1,2-dibromo-3-chloropropane), which elute beyond 30 min on the above columns, are determined at 90 degrees C on 1.8 m 5% loaded OV-101 columns with the same detectors. The ng/g-level fortifications have an overall mean analyte recovery of 70% and a coefficient of variation of 40%. The variety of foods examined includes both fatty and nonfatty food types (e.g., off-the-shelf cooked and uncooked grain-based items, dairy products, fresh and canned fruits and vegetables, and meats). Samples are extracted and cleaned up according to fat content and food type. Samples containing less than 71% fat are extracted by using an aqueous: nonaqueous shakeout (20% acetone solution under isooctane). Most extracts (isooctanes) are analyzed directly. Extracts from samples containing from 21 to 70% fat (e.g., ground beef, pecans, and corn chips) are cleaned up further on micro-Florisil columns to remove excess fat. A few other samples containing more than 71% fat or oil (e.g., butter, salad dressing, and vegetable oil) are diluted directly in isooctane and, depending on the degree of dilution, can be cleaned up further on micro-Florisil columns. Also, clear beverages (e.g., soda and tea) are extracted directly with isooctane. These extraction and cleanup techniques were tested on 231 different table-ready foods. Three-hundred incurred residues of 10 different fumigants were found in 138 items examined; 93 items had no detectable residues. The main advantage of the method is rapid semiquantitative determination of multiple fumigants from all food types.

A Convenient Preparation of Bistrimethylsilylmethane

Abstract Bistrimethylsilylmethane has been prepared from chlorotrimethylsilane, dibromomethane and lithium with a 55% yield, based on chlorotrimethylsilane.

Properties of the liquid crystals of some biopolymers.

Nematic liquid-crystalline solutions of polypeptides such as PBLG and PELG orient in the direction of a very low static electric field as if the polypeptide molecules were a collection of rod-like molecular clusters having a huge, permanent electric dipole moment. This dipole moment originates from fluctuation of the distribution of polymer helices in both directions of the rod-like molecular cluster with roughly equal likelihood. The molecular cluster of PBLG is estimated to be composed of some 5 x 10(5) molecules and has dimensions of a few to several micrometers x 0.1 microns phi in methylene bromide when the degree of polymerization (mean) is 650. The nematic solutions also orient in the direction of a static magnetic field. The peptide groups of the polypeptide form planes which are parallel to the polymer helix and the magnetic-field orientation is due to the demagnetizing field produced in the peptide groups perpendicular to their planes by the ring current of the pi electrons. The formation of rod-like molecular clusters is absolutely necessary to invite the magnetic-field orientation as in the electric-field orientation. The anisotropy of the magnetic susceptibility has been estimated to be on the order of 10(-8) emu/g, and the twist elastic constant of the cholesteric structure on the order of 10(-7) dyn/cm. Derivatives of PBLG with long alkyl chains as pendant groups assume thermotropic liquid crystals, in which melted alkyl chains behave as a solvent in a similar manner as in lyotropic liquid crystals of the parent PBLG. An analogy of thermotropic liquid crystals of the modified polypeptides with those of discotic liquid crystals in the columnar phase has been suggested. Concentrated solutions of a double-stranded helix of poly(A).poly(U) and a triple-stranded helix of poly(A).2poly(U) form liquid crystals both of the nematic and the cholesteric types. The nematic solutions of these polyribonucleotide complexes orient perpendicular to the direction of a static magnetic field owing to the diamagnetic dipole moments induced in the purine or pyrimidine bases of the polyribonucleotides perpendicular to their planes, which are roughly perpendicular to the polymer helices. Any rod-like polymer has a good chance to form liquid crystals in which the occurrence of forces acting among the molecules is not necessary. The PLGA-Na in a neutral aqueous solution undergoes a "coil-to-alpha helix transition" when the polymer concentration is increased.(ABSTRACT TRUNCATED AT 400 WORDS)

The synthesis of cyclic methylene dicarboxylates from caesium dicarboxylates and dibromomethane

The synthesis of cyclic methylene dicarboxylates from caesium dicarboxylates and dibromomethane

Raman and far‐infrared spectra of crystalline methylene bromide

AbstractLattice vibrations of polycrystalline CH2Br2 and CD2Br2, obtained by Raman and far‐infrared spectroscopy, are reported. The observed peaks are compared with the predictions of a group theoretical analysis based on the known structure of the stable phase. Assignments are proposed on the basis of isotopic shifts and intensities. Evidence of a metastable phase is presented, but attempts to isolate this phase at low temperatures were unsuccessful.

Aliphatic and aromatic halocarbons as potential mutagens in drinking water part I. halogenated methanes

Members of the group of halogenated methanes can either be formed during chlorination of drinking water or are of commercial importance and therefore produced in considerable amounts. Out of this group, Dichloromethane (DCM), Bromodichloromethane (BDM), Bromochloromethane (BCM), Bromotrichloromethane (BTM) and Dibromomethane (DBM) have been tested for their mutagenic activity. The Ames‐test and in vitro cell cultures were used. All substances were positive in the Ames‐test. In the in vitro test with FAF‐cells of Chinese hamsters only BCM produced an increase of the SCE‐frequency. All tested substances induced an increase in the aberration ratio/cell. The highest ratios were induced by DCM, DBM and BCM.

A physiological pharmacokinetic model for dermal absorption of vapors in the rat

Absorption of chemical vapors through the skin is a passive process that is not easily quantitated, but may be important in the assessment of health hazards in some occupational circumstances. Physiological modeling is a quantitative technique which may provide insight into the system being modeled and can be used for interspecies extrapolation. We developed a physiological model for the penetration of organic vapors through skin in vivo which allows the prediction of blood concentrations, after dermal vapor exposures in the rat, when chemical distribution coefficients, physiological and metabolic parameters, and skin permeability constants are known. We used the model in two distinct ways. First, permeability constants for dibromomethane (DBM), bromochloromethane (BCM), and methylene chloride (DCM) were calculated by using a physiologically based pharmacokinetic model for dihalomethanes to relate blood concentrations during dermal vapor exposures to the total amount of chemical which was absorbed through the skin. Second, a skin compartment was added to the model which had input based on the permeability-area-concentration product. This predictive model adequately described blood concentrations after DBM, BCM, and DCM dermal vapor exposures over a wide range of concentrations. This model could easily be modified for use with other organic vapors, and could be used to extrapolate to human vapor exposure conditions by substituting human physiological parameters for the animal values, providing permeability constants are known or can be determined.

Topological studies of the molecular species that characterize lower alkanol + methylene bromide mixtures: molar excess volumes and molar excess enthalpies

Molar excess volumes, V E, and molar excess enthalpies, H E, have been determined at 298.15 and 308.15 K for the binary mixtures of methanol (A) or ethanol (A) with methylene bromide (B). The V E data for these mixtures have been analysed in terms of an approach that employs the graph theoretical connectivity parameters of the third degrees of the A and the B molecular entities to show, for the first time, that (i) in the pure states while methanol exists mainly as cyclic dimers (with perhaps open chain dimers and trimers), ethanol exists mainly as open chain trimers, and that (ii) in the (A+B) mixtures A (= a n ( n = 1 and/or 2))B molecular species characterize these mixtures. The H E data of these (A+B) mixtures have been utilized to understand the energetics of the various interactions that characterize these binary mixtures. These conclusions have further been substantiated with an analysis of the V E- and the H E data of ROH (A) (R = -CH 3 or -C 2H 5)+CHX 3 (B) (X = Cl or Br) mixtures.

Semi-empirical molecular orbital calculations of the infrared band intensities of some simple polyatomic molecules—II. Brominated methanes and silanes, difluorosilane and dichlorosilane

The i.r. band intensities and equilibrium dipole moments and molecular geometries of methyl and silyl bromides, dibromomethane, bromoform and tribromositane have been determined by means of a series of semi-empirical molecular orbital calculations. The intensities of difluoro- and dichlorosilane have also been calculated from previously determined dipole moment derivatives and recently published force fields. In the case of the brominated methanes, the calculated intensities have been compared with some experimental values, and reasons for the discrepancies between theory and experiment discussed.

Molecular interactions in binary mixtures of non-electrolytes: Molar excess enthalpies

Molar excess enthalpies, H E, for pyridine ( i) + α-picoline ( j), + β-picoline ( j), + γ-picoline ( j); pyridine ( i) + cyclohexane ( j); β-picoline ( i) + cyclohexane ( j); methylenebromide ( i) + pyridine ( j), + β-picoline ( j) mixtures have been measured calorimetrically as a function of temperature and composition. The H E data at 298.15 and 308.15 K have been analysed in terms of the Sanchez and Lacombe theory and the “graph theoretical approach”. The graph theoretical approach describes the H E data well for all these mixtures. This approach has been critically examined and it is found to provide an insight into the nature of molecular interactions between the components of these mixtures. NMR studies on methylene bromide ( i) + β-picoline ( j) andβ-picoline ( i) + pyridine ( j) further support these conclusions.

Dermal absorption of dihalomethane vapors

The dermal absorption of dibromomethane (DBM) and bromochloromethane (BCM) vapors was studied in rats placed in a specially designed chamber incorporating individual respiratory protection to avoid pulmonary uptake. Exposures (DBM: 500 to 10,000 ppm; BCM: 2500 to 40,000 ppm) lasted 4 hr during which time five blood samples were drawn from jugular cannulae for analysis of the parent dihalomethane by gas chromatography. Estimates of the amounts of chemicals stored in tissues and exhaled were based on concentrations in the blood and tissue partition coefficients, tissue volumes, and ventilation rate. Total metabolism was estimated from the amount of bromide released during the 4-hr exposure. The total amount of vapor absorbed through the skin was calculated from the estimates of the amount of parent chemical in blood and tissues, and the amounts exhaled and metabolized. The dermal flux for each concentration (DBM: 0.004 to 0.078 mg/cm 2/hr; BCM: 0.011 to 0.164 mg/cm 2/hr) was calculated by dividing the amount absorbed by exposed surface area and duration of exposure. Flux was divided by exposure concentration to calculate a permeability constant. With each dihalomethane the permeability constants (DBM: ⋍1.12 cm/hr; BCM: ⋍0.79 cm/hr) were essentially independent of exposure concentration. This study shows that a whole-body dermal vapor exposure in rodents is technically possible, and quantitation of penetration can be accomplished using calculations based on achieved blood concentrations and some measure of metabolism.

Pressure-tuning resonance between the vibron and the libron in molecular solid dibromomethane

Pressure-tuning resonance between the vibron and the libron in molecular solid dibromomethane