Presence Of Hydrogen Bromide Research Articles

The ion pair mechanism in the thermal deamination of primary amines catalyzed by HBr in the gas phase: DFT and AIM analysis

The possible reaction mechanisms for the gas-phase thermal deamination of isopropylamine, tert-butylamine, and dextroamphetamine in the presence of hydrogen bromide are investigated by DFT calculations with several functionals. In each case, QTAIM analysis supports the formation of an ion-pair complex, which subsequently decays through a six-membered cyclic transition state (TS). NBO charges and interatomic lengths suggest the polarization of the N1δ−···δ+C2 bond in the TS is rate determining.

Hydrolysis of 6,6-dimethyl-4,8-dioxo-5,7-dioxaspiro[2.5]octane-1,1,2,2-tetracarbonitrile

Hydrolysis of 6,6-dimethyl-4,8-dioxo-5,7-dioxaspiro[2.5]octane-1,1,2,2-tetracarbonitrile in aqueous dioxane in the presence of hydrogen bromide gave a mixture of 2,2,3,3-tetracyanocyclopropane-1-carboxylic acid and ammonium 3-cyano-4-dicyanomethylidene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate. Hydrolysis of the same compound in the presence of sulfuric acid was accompanied by nitrogen migration and led to the formation of (1R*,2S*,3S*)-1,3-dicyanocyclopropane-1,2-dicarboxamide whose structure was proved by X-ray analysis.

Molecular Rectangle Formed by Head-to-tail Self-Assembly of 1-(Dipyrrin-2-yl)-1-(dipyrrin-3-yl)methane

1-(Dipyrrin-2-yl)-1′-(dipyrrin-3-yl)methane, the N-confused analog of biladiene-ac, is prepared by condensation of 2,3′-dipyrromethane with two molecules of 2-formylpyrrole in dichloromethane in the presence of hydrogen bromide. Self-assembly of the ligand with Zn(II) in dichloromethane and methanol offers a dinuclear dimeric complex with a ligand:metal ratio of 2:2. X-Ray crystal structure analysis reveals two ligands bound through a head-to-tail pattern to two zinc centers to form a severely distorted helical conformation, which has the shape of a rectangle.

Materials selection for HBr service

This study was undertaken to determine the compatibility of hydrogen bromide (HBr) with common materials of construction used for specialty gas delivery systems. Reactions between reactive gases and materials of construction can result in the formation of particles and volatile metal complexes as well as the creation of corrosion products that can retain water. We found that when moisture is below 1 ppm v (designated as anhydrous), bromine from HBr is not incorporated beyond the native oxide of electropolished 316L stainless steel (EP316L) and no macroscopic degradation of the metal occurs. Also, if adequate purging and evacuation procedures are followed to remove the HBr, this material can be exposed to moist air without diminishing the initial surface quality. However, if adequate precautions are not followed to eliminate water in the presence of HBr, iron-and bromine-rich crystalline deposits form on the surface. Purge and evacuation procedures are inadequate for removal of the reactive species on this surface and corrosion proceeds upon subsequent exposure to air. EP316L exposed to HBr containing 1700 ppm v H 2O appears visually unaltered, but close inspection by SEM reveals the onset of corrosion. Of the materials examined in this study, Nickel-200 and Hastelloy C-22 are more resistant to HBr corrosive environments. In contrast, deleterious reactions occur between anhydrous HBr and elemental iron and the iron-rich surface of oxygen-passivated 316L.

First syntheses of natural products with the 2,7‐dihydroxy‐2H‐1,4‐benzoxazin‐3(4H)‐one skeleton

Abstract2,7‐Dihydroxy‐2H‐1,4‐benzoxazin‐3(4H)‐one 11 (DHBOA) and 2,4,7‐trihydroxy‐2H‐1,4‐benzoxazin‐3(4H)‐one 14 (TRIBOA) representing aglucones of naturally occurring acetal glucoside type allelo chemicals found in Gramineae have been for the first time synthesized by two pathways both involving selective reductive cyclizations of appropriate 7‐benzyloxy‐2‐nitrophenol derivatives as precursors. TRIBOA 14 and its bioactive naturally occurring 7‐methyl ether DIMBOA have been found to undergo a hitherto unknown transformation to the corresponding 2,6‐dibromo substituted lactam forms 20 and 21 in the presence of hydrogen bromide in acetic acid, which is of value in a better understanding of the possible mode of bioactivity.

Opp-dibenzoporphyrins from benzopyrromethene derivatives

Condensation of 1-formyl-3-haloisoindoles with α-free pyrroles in the presence of hydrogen bromide gives the corresponding benzopyrromethene hydrobromides: heating α-halo-α′-methylbenzopyrromethene hydrobromides in o-dichlorobenzene in air provides an economical synthesis of the opp-dibenzoporphyrin system in acceptable yields.

Oxo-phospholes from the alkoxyphosphonium ylides formed in the reaction of trialkyl phosphites or dialkyl phosphonites with dimethyl acetylenedicarboxylate

The cyclic ylides (3), formed by the reaction of trialkyl phosphites or dialkyl phosphonites with 2 mol equiv. of dimethyl acetylenedicarboxylate, undergo protonation and dealkylation in the presence of hydrogen bromide to give the 1-substituted 2,5-dihydrophosphole 1-oxides (4). The phospholes (4) undergo ready elimination of a molecule of alcohol on being heated to give the phosphole 1-oxides (5).

Reactions of 4-fluoren-9-ylidene-2-methylpent-2-ene and 2-fluoren-9-yl-2- methylpentan-4-one

The photochromic title hydrocarbon undergoes a photochemical 1,5-H shift to 4-fluoren-9-yl-2-methylpenta-1,3-diene and photocyclisation to red 3,3a-dihydro-1,3,3-trimethylfluoranthene; the latter undergoes a thermal 1,9-H shift in toluene and a photochemical 1,7-H shift in ethanol. The title ketone (17) cyclises in the presence of hydrogen bromide in acetic acid to yield 1,10b-dihydro-1,1,3-trimethylfluoranthene which, on catalytic hydrogenation, yields the same tetrahydrofluoranthene derivative as is obtained when 2-fluoren-9-yl-2-methylpentan-4-ol (20) is cyclised with sulphuric acid. On treatment with PCl5, the ketone (17) yields 4-chloro-2-fluoren-9-yl-2-methylpent-4-ene, which reacts with sodium in xylene to give trans-2-fluoren-9-yl-2-methylpent-3-ene, obtained also when the alcohol (20) is heated at 180 °C with KHSO4.

Solutions of carbonyl compounds in dibromodifluoromethane in the presence of hydrogen bromide: protonation of ketones and formation of 1 -bromo-alcohols from aldehydes

HBr in CBr2F2 is capable of protonating a variety of ketones, and at low temperatures separate 1H n.m.r. signals can be seen for the acid and protonated base. Line shape analysis of the signals enables rates of protonation to be calculated. Aldehydes in HBr–CBr2F2 give n.m.r. spectra that are consistent with the formation of 1-bromoalcohols.

The hydrogen bromide catalysed decomposition of 3-methylbutan-2-ol

In the presence of hydrogen bromide at 372-446�C 3-methylbutan-2-ol decomposes into methylbutenes and water with rate K2=1013.02exp(-150000/8.314T) ml mol-1s-1 The effects of substitution at the β-carbon atom (C3) are summarized and compared with those at the α-carbon atom (C2). A polar transition state involving mainly the α-carbon atom site is proposed.

Kinetics of Hydrogen Oxidation—Part 4. Inhibition and Catalysis at High Degrees of Conversion

Abstract The mechanisms of inhibition and catalysis at high degrees of conversion are analysed. A complete set of isothermal kinetic equations for inhibited hydrogen oxidation is computed. The inhibition efficiency is considered as a function of pressure, temperature, initial composition, and degree of conversion. The regions of no inhibition or of catalysis of hydrogen oxidation in the presence of hydrogen bromide are found. The contributions from regeneration of initial HBr and of the secondary inhibitor Br2 are discussed. The parametric dependences of inhibited hydrogen oxidation rates are investigated for a number of elementary rate constants. The potential efficiency of inhibition with bromine compounds is evaluated.

N‐alkoxydipyrrylmethenes

Abstract2‐Cyano‐N‐hydroxypyrroles are O‐alkylated and the nitrile function reduced to the corresponding aldehyde with diisobutylaluminum hydride. Condensation with pyrroles in the presence of hydrogen bromide gives the difficultly purified N‐alkoxydipyrrylmethanes.

Studies on Xanthenyl and Thioxanthenyl Derivatives. Reactions of Xanthenyl and Thioxanthenyl Halides with Substituted-Ethylenes

Abstract Xanthenyl and thioxanthenyl chlorides (1) were added to 1,1-bis-(p-alkoxyphenyl)-2-substituted-ethylenes (2) to give 1,1-bis-(p-alkoxyphenyl)-2-substituted-2-[xanthen(or thioxanthen)-9-yl]ethylenes (3). The 2-nitroderivatives (3) were converted in boiling methanolic potassium hydroxide into the allenes, 1,1-bis-(p-alkoxyphenyl)-2-[xanthen(or thioxanthen)-9-ylidene]ethylenes (4). The 2-methyl(or chloro)-derivatives (3) reacted with bromine in the presence of hydrogen bromide, to yield xanthylium or thioxanthylium tribromide (5) and the corresponding 2,2-disubstituted-ethylene (6). The tribromides (5) reacted with the ethylene (2, Z=H to give, after spontaneous dehydrobromination, the corresponding 2-bromo-derivatives (3, Z=Br).

Reactions of 1,5-diphenyl-2,4-dimethyl-1,5-pentanedione with hydrogen sulfide

1,5-Diphenyl-2,4-dimethyl-1,5-pentanedione reacts with hydrogen sulfide in the presence of boron trifluoride etherate or 70% perchloric acid to give the corresponding thiapyrylium salts and 2,6-diphenyl-3,5-dimethyldihydrothiopyran; complete disproportionation to give 2,6-diphenyl-3,5-dimethylthiacyclohexane and 2,6-diphenyl-3,5-dimethylthiapyrylium bromide occurs in the presence of hydrogen bromide. The possibility of catalytic hydrogenation in the presence of 10% Pd/C of compounds with a thiopyran ring was established.

Hydrocarbon cool flames and the influence of hydrogen bromide

Small amounts of hydrogen bromide added ton-pentane + 1.33 O2mixtures lower both the limiting pressure for the onset of two-stage ignition and also, to a smaller extent, that for the appearance of cool flames. The induction period preceding the first cool flame, ז1, is shown to be related to the initial pressure,P0, by a relation of the form ז1=kP-n0+c, wherek,nandcare constants for a given set of initial conditions. The results show that c ≠ 0 and that the addition of hydrogen bromide reduces both ז1andc. However, since ז1≽candcis always finite, it is clear that, even at temperatures above the ignition profiles, ignition continues to take place as a two-stage process. Plots of lg ז1against reciprocal temper­ature are invariably characterized by a well-defined change in slope and the temperature at which this occurs decreases with increasing concentration of hydrogen bromide, eventually reaching a limiting value ofca. 270 °C. Above this temperature the slopes of the plots are more or less independent of hydrogen bromide and correspond to an overall activation energy of 82 kJ mol-1. Below this temperature the apparent energy of activation decreases from 206 to 113 kJ mol-1as the concentration of hydrogen bromide is increased. Similarly there is a limiting concentration of the additive above which the pressure change accompanying the first cool flame is not appreciably increased except at low temperatures. In systems which exhibit multiple cool flames, the second and fourth cool flames are generally too indistinct for their characteristics to be measured with any accuracy. However, the third cool flame appears as a well-defined but relatively weak pressure pulse. In striking contrast to the behaviour of the first cool flame, neither the third cool flame nor the induction period preceding it is appreciably affected by the presence of hydrogen bromide. It thus appears that, although the halogen compound is pre­sumably involved in the chemical reactions leading to the first cool flame, the third cool flame is propagated by intermediates whose mode of forma­tion is independent of the additive.

Synthesis of bilenes-b. Some side reactions

Condensation of a 5-ethoxycarbonyl-5′-formyl-2,2′-dipyrromethane with a fully alkyl-substituted 5-carboxy-2,2′-dipyrromethane in the presence of hydrogen bromide yielded a tripyrrene salt rather than a bilene-b salt. In the presence of trifluoroacetic acid with subsequent addition of hydrogen bromide, the bilene-b salt obtained from the foregoing components was derived from the self-condensation of two molecules of the formyl component with elimination of one formyl group. The expected bilene-b salts were obtained from the above dipyrromethanes when the carboxy-component contained an electronegative substitutent, such as acetyl or ethoxycarbonyl, on the noncarboxy-substituted ring.

Free radical substitution in aliphatic compounds. Part XXVI. The gas-phase bromination of halogenocycloalkanes

The gas-phase bromination of halogenocyclohexanes gave the expected isomeric bromohalogenocyclohexanes, together with cyclohexene, bromocyclohexane, and traces of trans-1,2-dibromocyclohexane. These latter products were formed as a result of elimination of hydrogen halide from the starting material. The initial halogenocyclohexanes were shown to undergo elimination of hydrogen halide in the presence of hydrogen bromide. Variation of the surface: volume ratio had a pronounced effect on the elimination which suggested that this reaction had a large heterogeneous component. Bromination of chloro- and fluoro-cyclopentane also produced elimination products which were formed as a result of the reaction of hydrogen bromide with the halogenocyclopentane.

The Bromination of 13α-Androstan-15-one

In order to examine the behaviors toward bromination 3β-acetoxy-5α, 13α-androstan-15-one (X) was prepared from the 17-keto steroid (I) according to the method worked out by Djerassi, et al. with the C/D-trans steroid (see Chart 1). On treatment with bromine in acetic acid in the presence of hydrogen bromide, bromination occurred exclusively at C-16 yielding a mixture of 16β-bromo and 16, 16-dibromo derivatives (XI and XII), which could be separated readily by preparative thin-layer chromatography.

The gas-phase reaction of acetic acid with hydrogen bromide. The effect of isobutene

Addition of isobutene to reaction mixtures of acetic acid and hydrogen bromide brings about a lowering in the initial rate of pressure change. The lowering is proportional to the pressure of isobutene and is explained in terms of a molecular reaction producing mesityl oxide. Mesityl oxide is formed steadily throughout the course of the reaction in quantities proportional to the pressure of isobutene. The quantities of mesityl oxide detected are less than those required to account quantitatively for the lowering of dp/dt, but the presence of the products of the thermal reactions of mesityl oxide, and the minima observed in the pressure-time curves at 407� show that the discrepancies can be accounted for in terms of the polymerization undergone by mesityl oxide in the presence of hydrogen bromide. The reaction appears analogous to the formation of mesityl oxide by the acetylation of isobutene in solution.

Catalysis by hydrogen halides in the gas phase. XVI. Methyl trimethylacetate, isopropanol, and hydrogen bromide

In the presence of hydrogen bromide at 407�, methyl trimethylacetate decomposes to isobutene, carbon monoxide, and methanol. Isopropanol reacts with an intermediate to form isopropyl trimethylacetate, which decomposes quickly to propene. Methanol competes effectively with isopropanol. Some ratios of individual rate constants are obtained from the rate reductions in the competition reactions.