- Compounds and methods for the reduction of halogenated hydrocarbons
-
The present application relates to methods for the reduction of halogenated hydrocarbons using compounds of Formula (I): wherein the reduction of the halogenated compounds is carried out, for example, under ambient conditions without the need for a transition metal containing co-factor. The present application also relates to methods of recovering precious metals using compounds of Formula (I) that are absorbed onto a support material.
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Page/Page column 21-22
(2017/12/27)
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- One-Pot Conversion of Methane to Light Olefins or Higher Hydrocarbons through H-SAPO-34-Catalyzed in Situ Halogenation
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Methane was converted to light olefins (ethene and propene) or higher hydrocarbons in a continuous flow reactor below 375 °C over H-SAPO-34 catalyst via an in situ halogenation (chlorination/bromination) protocol. The reaction conditions can be efficiently tuned toward selective monohalogenation of methane to methyl halides or their in situ oligomerization to higher hydrocarbons. The presence of C5+ hydrocarbons in the reaction products clearly indicates that by using a properly engineered catalyst under optimized reaction conditions, hydrocarbons in the gasoline range can be produced. This approach has significant potential for feasible application in natural gas refining to gasoline and materials under moderate operational conditions.
- Batamack, Patrice T. D.,Mathew, Thomas,Prakash, G. K. Surya
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p. 18078 - 18083
(2017/12/26)
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- The selective high-yield conversion of methane using iodine-catalyzed methane bromination
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Methyl bromide is used as feed in a process that converts it to gasoline. It is prepared by the gas-phase reaction of CH4 with Br2, a reaction that produces, besides the desired CH3Br, large amounts of CH2Br2. The latter cokes the catalyst used for gasoline production. The separation of CH2Br2 by distillation makes gasoline production too expensive. It is therefore important to increase the selectivity of the bromination reaction. We show that a small amount of I 2 catalyzes the reaction CH2Br2 + CH 4 → 2CH3Br, which leads to higher CH4 conversion and higher selectivity to CH3Br. These findings are promising for developing a low-cost integrated bromine-iodine based dual-halogen pathway to convert stranded natural gas into fuels and chemicals.
- Ding, Kunlun,Metiu, Horia,Stucky, Galen D.
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p. 474 - 477
(2013/08/25)
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- Bromination of hydrocarbons with CBr4, initiated by light-emitting diode irradiation
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The bromination of hydrocarbons with CBr4 as a bromine source, induced by light-emitting diode (LED) irradiation, has been developed. Monobromides were synthesized with high efficiency without the need for any additives, catalysts, heating, or inert conditions. Action and absorption spectra suggest that CBr4 absorbs light to give active species for the bromination. The generation of CHBr3 was confirmed by NMR spectroscopy and GC-MS spectrometry analysis, indicating that the present bromination involves the homolytic cleavage of a C-Br bond in CBr4 followed by radical abstraction of a hydrogen atom from a hydrocarbon.
- Nishina, Yuta,Ohtani, Bunsho,Kikushima, Kotaro
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p. 1663 - 1667
(2013/10/22)
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- Effects of silyl substituents on the palladium-catalyzed asymmetric synthesis of axially chiral (allenylmethyl)silanes and their S E2′ chirality transfer reactions
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A series of axially chiral 4-substituted-1-silyl-2,3-butadienes [(allenylmethyl)silanes] were synthesized from 3-bromo-5-silylpenta-1,3-dienes by a Pd-catalyzed asymmetric reaction with a soft nucleophile. The optically active (allenylmethyl)silanes react with an acetal in the presence of TiCl 4 to give the enantiomerically enriched 1,3-diene derivatives through an SE2′ pathway. Effects of the silyl groups on the enantioselectivity of the asymmetric allene synthesis and the subsequent S E2′ chirality transfer reaction were studied. It was found that as the steric bulk of the silyl groups in the 3-bromo-5-silylpenta-1,3-dienes was increased from -SiMe3 to -SiiPr3, the enantioselectivity of the two enantioselective processes also improved.
- Ogasawara, Masamichi,Ge, Yonghui,Okada, Atsushi,Takahashi, Tamotsu
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experimental part
p. 1656 - 1663
(2012/04/23)
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- PROCESS FOR THE PREPARATION OF 3-HYDROXY-3-METHYLBUTYRIC ACID OR ITS CALCIUM SALTS
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A new process for preparing calcium salts of 3-hydroxy-3-methylbutyric acid is described. Lactones obtained from ketene and acetone are hydrolyzed in selective and scalable manners. The 3-hydroxy-3-methylbutyric acid or its calcium salts are useful in preparations for inhibiting protein depletion or as immuno-stimulating feedstuff additives for mammals.
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Page/Page column 29
(2012/11/06)
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- AN INTEGRATED PROCESS TO COPRODUCE AROMATIC HYDROCARBONS AND ETHYLENE AND PROPYLENE
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An integrated process for producing aromatic hydrocarbons and ethylene and/or propylene and optionally other lower olefins from low molecular weight hydrocarbons, preferably methane, which comprises: (a) contacting at least one low molecular weight alkane, preferably methane, with a halogen, preferably bromine. under process conditions sufficient to produce a monohaloalkane, preferably monobromomethane, (b) reacting the monohaloalkane in the presence of a coupling catalyst to produce aromatic hydrocarbons and C2+ alkanes, (c) separating the aromatic hydrocarbons from the product mixture of step (b) to produce aromatic hydrocarbons, and (d) cracking at least part of the C2+ alkanes in an alkane cracking system to produce ethylene and/or propylene and optionally other lower olefins.
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Page/Page column 20
(2010/04/28)
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- INTEGRATED PROCESS TO COPRODUCE AROMATIC HYDROCARBONS AND ETHYLENE AND PROPYLENE
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An integrated process for producing aromatic hydrocarbons and ethylene and/or propylene and optionally other lower olefins from low molecular weight hydrocarbons, preferably methane, which comprises: (a) contacting one or more low molecular weight alkanes, preferably methane, with a halogen, preferably bromine, under process conditions sufficient to produce a monohaloalkane, preferably monobromomethane, (b) reacting a first portion of the monohaloalkane in the presence of a coupling catalyst under process conditions sufficient to produce aromatic hydrocarbons and C2-5 alkanes, (c) separating the aromatic hydrocarbons from the product mixture of step (b) to produce aromatic hydrocarbons, (d) reacting a second portion of the monohaloalkane in the presence of a coupling catalyst under process conditions sufficient to produce ethylene and/or propylene.
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Page/Page column 8
(2010/09/18)
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- Effects of bromide on the formation of THMs and HAAs
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The role of bromide in the formation and speciation of disinfection by-products (DBPs) during chlorination was investigated. The molar ratio of applied chlorine to bromide is an important factor in the formation and speciation of trihalomethanes (THMs) and halogenacetic acids (HAAs). A good relationship exists between the molar fractions of THMs and the bromide incorporation factor. The halogen substitution ability of HOBr and HOCl during the formation of THMs and HAAs can be determined based on probability theory. The formation of HAAs, and their respective concentrations, can also be estimated through use of the developed model.
- Chang,Lin,Chiang
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p. 1029 - 1034
(2007/10/03)
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- Brominated-trihalomethane formation from phenolic derivatives as a model of humic materials by the reaction with hypochlorite and hypobromite ions
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Among the 21 phenolic derivatives tested for the model system of the disinfection process in the natural water containing humic acid, 2-hydroxytoluene and 2,6-dihydroxybenzoic acid produced high yields of CHBr3 under the co-existence of NaOCl and NaOBr. In the study of distribution of THMs produced, the amount of CHBr3 increased with the relative concentration of NaOCl added to NaOBr. These results were similar to the case of halogenation of the humic acid under the co-existence of NaOCl and NaOBr.
- Ichihashi, Keiko,Teranishi, Kiyoshi,Ichimura, Akio
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p. 957 - 958
(2007/10/03)
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- Occurrence of bromoperoxidase in the marine green macro-alga, ulvella lens, and emission of volatile brominated methane by the enzyme
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Bromoperoxidase activity was detected in the marine green macro-alga, Ulvella lens, which is used to induce the larval metamorphosis of sea urchin in aquaculture in Japan. The enzyme activity was enhanced 8.5- and 2.2-fold by the addition of cobalt and vanadium ions to the reaction mixture, respectively. The volatile halogenated compounds dibromomethane and tribromomethane were formed in the reaction mixture when the enzyme was incubated with oxaloacetate, hydrogen peroxide and potassium bromide. These results suggest that dibromomethane, which was reported to be released by U. lens and play an important role as the inducer of larval settlement and metamorphosis, is produced by bromoperoxidase in the alga.
- Ohshiro, Takashi,Nakano, Satoru,Takahashi, Yoshinori,Suzuki, Minoru,Izumi, Yoshikazu
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p. 1211 - 1215
(2007/10/03)
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- Brominated trihalomethane formation in halogenation of humic acid in the coexistence of hypochlorite and hypobromite ions
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Brominated trihalomethanes (Br-THMs) such as CHCl2Br, CHClBr2, and CHBr3 are produced by the reaction of hypobromite with humic acid in the presence of hypochlorite. In the presence of excess NaOCl, addition of NaOBr enhanced the formation of Br-THMs but reduced the formation of CHCl3. The product distribution of THMs was affected by the ratio of [NaOBr]/[NaOCl] and was independent of pH and reaction time. In the presence of excess NaOBr, the yield of CHBr3 only increased linearly with the NaOCl concentration added. However, the other three THMs were hardly produced even though NaOCl concentration was increased up to 0.5 of the [NaOCl]/[NaOBr] molar ratio. Our results suggest that in the process of THM formation, hypochlorite ion reacts effectively with humic acid in the oxidation reaction and hypobromous acid plays a predominant role in the electrophilic substitution when both of hypohalites are present. Brominated trihalomethanes (Br-THMs) such as CHCl2Br, CHClBr2, and CHBr3 are produced by the reaction of hypobromite with humic acid in the presence of hypochlorite. In the presence of excess NaOCl, addition of NaOBr enhanced the formation of Br-THMs but reduced the formation of CHCl3. The product distribution of THMs was affected by the ratio of [NaOBr]/[NaOCl] and was independent of pH and reaction time. In the presence of excess NaOBr, the yield of CHBr3 only increased linearly with the NaOCl concentration added. However, the other three THMs were hardly-produced even though NaOCl concentration was increased up to 0.5 of the [NaOCl]/[NaOBr] molar ratio. Our results suggest that in the process of THM formation, hypochlorite ion reacts effectively with humic acid in the oxidation reaction and hypobromous acid plays a predominant role in the electrophilic substitution when both of hypohalites are present.
- Ichihashi, Keiko,Teranishi, Kiyoshi,Ichimura, Akio
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p. 477 - 483
(2007/10/03)
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- Reactions of carbonyl compounds in basic solutions. Part 33. 1 Effect of 2-trichloro-and tribromoacetyl substituents on the alkaline hydrolysis of methyl benzoate, as well as the hydrolysis of the corresponding benzoate anions and ionisation/ring-chain tautomerism of the corresponding acids
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Rate coefficients have been measured for the alkaline hydrolysis of methyl 2-trichloro-and tribromoacetylbenzoate, as well as the alkaline hydrolysis of the corresponding 2-trichloro-and tribromobenzoate anions, in 30% (v/v) dioxane-water at several temperatures. The relative rates of hydrolysis and activation parameters demonstrate relatively rapid hydrolysis via neighbouring group participation by the acyl-carbonyl group in the ester hydrolysis and slower hydrolysis via intramolecular fission of the adducts in the benzoate anion hydrolysis. The pKa values of the corresponding benzoic acids have been measured in water and their ring-chain tautomeric equilibrium constants determined.
- Bowden, Keith,Raja, Sivani
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-
- Modelling the formation of brominated trihalomethanes in chlorinated drinking waters
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The chlorination of water containing bromide and natural organic matter (NOM) leads to the formation of brominated trihalomethanes (THMs). The extent of brominated THM formation depends, inter alia, on the bromide:chlorine concentration ratio ([Br-]:[chlorine]). A reaction scheme is proposed from which a simple kinetic model is developed that mathematically relates the extent of bromination, and the relative abundances of the four THMs, to the [Br-]:[chlorine] ratio. In the scheme, the trihalogenated precursors to THMs are formed by three steps each of which substitutes either bromine or chlorine into an activated carbon site in the NOM. This leads to six pairs of competing bromination:chlorination reactions, whose rate constant ratios (k(b):k(c)) have been estimated by using the model to fit THM data obtained from the chlorination of 17 waters from New Zealand. The individual k(b):k(c) ratios range from 4 to 15. From a plot of the ratio of total bromine to total chlorine present in the THMs as a function of the [Br-]:[chlorine] ratio, an apparent overall k(b):k(c) ratio of 9.1 is obtained. Using USEPA cancer potency factors, the model is used to predict the relative cancer risk associated with THMs as a function of the [Br-]:[chlorine] ratio. This risk increases steeply to a peak at a [Br-]:[chlorine] ratio of approximately 0.15, then gradually decreases to the value associated with bromoform alone. The risk associated with THMs may vary considerably through changes in the [Br-]:[chlorine] ratio as the result of natural variation in the [Br-], or through poor control of chlorine dosing.
- Nokes,Fenton,Randall
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p. 3557 - 3568
(2007/10/03)
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- Chemistry of the biosynthesis of halogenated methanes: C1-organohalogens as pre-industrial chemical stressors in the environment?
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We have chemical evidence that in the biosynthesis of the halomethanes C1H(4-n),X(n) (n = 1-4) three different pathways of biogenic formation have to be distinguished. The formation of methyl chloride, methyl bromide, and methyl iodide, respectively, has to be considered as a methylation of the respective halide ions. The dihalo- and trihalomethanes are formed via the haloform and/or via the sulfo-haloform reaction. The possible formation of tetrahalomethanes may involve a radical mechanism. Methionine methyl sulfonium chloride used as substrate in the incubation together with chloroperoxidase (CPO) and H2O2 gave high yields of monohalomethanes only. We were able to show that next to the CPO/H2O2 driven haloform reaction of carbonyl activated methyl groups also methyl-sulphur compounds - e.g. dimethylsulfoxide, dimethylsulfone, and the sulphur amino acid methionine - can act as precursors for the biosynthesis of di- and trihalogenated methanes. Moreover, there is some but not yet very conclusive evidence for an enzymatic production of tetrahalogenated methanes. In our experiments with chloroperoxidase involving amino acids and complex natural peptide based substrates, dihalogenated acetonitriles and several other volatile halogenated but yet unidentified compounds were formed. On the basis of these experiments we like to suggest that biosynthesis of halogenated nitriles occurs in general and therefore a natural atmospheric background should exist for halogenated acetonitriles and halogenated acetaldehydes, respectively.
- Urhahn, Thorsten,Ballschmiter, Karlheinz
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p. 1017 - 1032
(2007/10/03)
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- Substituted phenoxymethylphenyl derivatives, their preparation and their use for controlling pests and fungi
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Substituted phenoxymethylphenyl derivatives I STR1 X is =CH--OCH3, =C--CH3 or =N--OCH3 ; R1 is, inter alia, R2 and R3 are, inter alia, H, halogen, CN, NO2, C1 -C4 -alkyl, C1 -C2 -haloalkyl, C1 -C4 -alkoxy or C1 --C2 -haloalkoxy; R4 is, inter alia, CN, Cl, Dr, C1 -C6 -alkoxy, C1 -C6 -alkylthio or C1 -C4 -haloalkoxy; R5 is, inter alia, NO2, CN, halogen, C1 -C4 -alkyl, C1 -C4 -haloalkyl, C1 -C4 -alkoxy or C1 -C4 -haloalkoxy; n is 0-4; Y is --O--, --NH--, --N(CH3)--; R6 is H, C1 -C4 -alkyl. The compounds are useful for controlling pests and fungi.
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-
- Fluoride anion catalyzed halogen dance in polyhalomethanes
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Tetrabutylammonium fluoride catalyzes the exchange of halogens between tetrahalomethanes.The presence of small amounts of haloform is suspected to be a necessary co-catalyst.Key Words: tetrabutyl ammonium fluoride; tetrahalomethanes; halogen exchange in.
- Sasson, Y.,Kitson, F.,Webster, O, W.
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p. 599 - 600
(2007/10/02)
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- Electrochemical oxidation of ketones in methanol in the presence of alkali metal bromides
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Electrochemical oxidation of methyl ketones in methanoi in the presence of alkali metal bromides affords methyl carboxylates. Benzyl alkyl ketones are transformed under similar conditions into methyl 3-phenylalkanoates, while ketones lacking σ-benzyl or σ-methyl group are oxidized into σ-hydroxyketals.
- Nikishin, Gennady I.,Elinson, Michail N.,Makhova, Irina V.
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p. 895 - 905
(2007/10/02)
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- Process for the preparation of dibromomethane
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A process for the preparation of dibromomethane is described, in which gaseous methyl bromide and bromide are reacted as temperatures of 300° C. or higher. The reaction is highly selective to DBM and almost quantitative Br2 conversion is obtained in the absence of catalysts.
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- Kinetic Isotope Effects for Proton Abstraction from Methanol by Polyhalogenomethyl Carbanions. Cleavage of Me3SiCHX2 and Me3SiCX3 by Base in Methanol.
-
The carbanions XxH(3-x)C- (X=Cl or Br; x=2 or 3) generated by base cleavage of Me3SiCH(3-x)Xx (or some related compounds) in MeOH, show a kinetic isotope kH/kD of ca. 1.1 in proton abstraction from methanol, as given by the product ratio XxH(3-x)CH/XxH(3-x)CD observed for reaction in MeOH-MeOD (1:1) at ca. 21 deg C.The low value of the isotope effect is attributed to the fact that the free electron pair in the carbanion is localized on the carbon centre; carbanions derived from acids of acidities comparable with those of X3CH and X2CH2 but in which the electron pair is conjugatively delocalized, show much larger isotope effects.
- Eaborn, Colin,Stanczyk, Wlodzimierz A.
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p. 471 - 473
(2007/10/02)
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- Alkaline cleavage of trihaloacetophenones
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Rate constants for haloform cleavage of trifluoro-, trichloro-, and tribromoacetophenone have been measured in aqueous solution; apparent second-order rate constants for reaction by the monoanion are in the ratio 1:5.3x1010:2.2x1013.
- Guthrie, J. Peter,Cossar, John
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p. 1640 - 1642
(2007/10/02)
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- A convenient preparation of mono- or gem-di-halogenoalkanes from α-sulfonyl carbanions and halogenolithiocarbenoids.
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Various α-sulfonyl carbanions have been shown to react at low temperature with di- or tri-halogenolithiocarbenoids, to give 1-mono- or 1,1-di-halogenoalkanes.Bromocarbenoids gave better results than their chloro-analogues.Reaction of dibromolithiomethane with α-lithiated sulfones gives a high yield of vinylic bromides, the stereochemistry of which is cleanly E.Evidence is presented that the carbenoid itself is responsible for the reaction, and is not first converted into the corresponding carbene.
- Charreau, Philippe,Julia, Marc,Verpeaux, Jean-Noel
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p. 201 - 210
(2007/10/02)
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- Electron Transfer Reactions in Organic Chemistry XVI. The Reduction of Carbon Tetrabromide and some other Polyhaloalkanes by N,N,N',N'-Tetramethyl-p-phenylenediamine
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The reaction between CBr4 and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPDA) has been studied in acetonitrile at 20 and 50 deg C.The formation of TMPDA(+*) was found to be first order in both and , while its disappearance was first order in but zeroth order in .The rate constants at 50 deg C were 6.5E-4 l mol-1 s-1 and 5E-5 s-1, respectively.The only products detected were carbon monoxide, bromide ion and acid.The following mechanism is proposed: TMPDA reduces CBr4 in an initial electron-transfer step to form TMPDA(+*), Br3C(*) and Br(-).The radical couples with oxygen to form the tribromomethylperoxyl radical, which is further reduced to the anion by another molecule of TMPDA.CBr3OO(-) then forms CO, Br(-) and H(+), probably by hydrolysis.CBrCl3 and CBr2Cl2 are proposed to react with TMPDA by the same mechanism, while (CBrCl2)2 reacts by another mechanism.The reaction rates with CHBr3 and C2Cl6 were too slow to be measurable.The order of reactivity is CBr4 > CBr2Cl2 > CBrCl3 >> (C2Cl6 and CHBr3).
- Eberson, Lennart,Ekstroem, Mikael
-
-
- Electron Transfer Reactions in Organic Chemistry. XIII. The Reaction between Carbon Teterabromide and the Heteropoly Blues Co(II)W12O407- and Co(II)W12O408-. A Kinetic and Product Study
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The reaction between carbon tetrabromide and Co(II)W12O407- was investigated at 20 deg C in CH3CN/H2O (64/36 v/v) buffered at pH ca.7.It was found to be first-order in both substrate and reagent, the rate determining step being an outer-sphere electron transfer reaction.The rate constant was determined to be 1.1 +/- 0.3 M-1 s-1.The only products found were CHBr3 (77percent) and C2Br6(1percent).Product studies in CH3CN/D2O showed that almost all of the tribromomethyl radical formed in the first step was further reduced to the corresponding anion.The rate constant for this reaction was estimated to be 106 M-1 s-1.The effect of inert salts on the overall reaction rate was also investigated.Tetraalkylammonium salts were found to augment the rate while alkali metal ions lowered it, which is the opposite of results with heteropoly ions as oxidants.The reaction between CBr4 and Co(II)W12O408- was first order in heteropoly blue and if it was assumed it was first-order in CBr4 also, the rate constant could be calculated to be 4.3 M-1 s-1.
- Eberson, Lennart,Ekstroem, Mikael
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p. 101 - 112
(2007/10/02)
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- Electron Transfer Reactions in Organic Chemistry. XI. The Reaction between Carbon Tetrabromide and the Cage Complex 2+. A Kinetic and Product Study
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A kinetic and product study of the reaction between CBr4 and the cage complex 2+ in CH3CN/H2O at 20 deg C has been performed.The reaction was found to be first order in both CBr4 and 2+, the only products found being CHBr3 and C2Br6.The mechanism is discussed and suggested to be an outer-sphere electron transfer mechanism, with a rate constant for the rate determining electron transfer step kET = 0.020 M-1 s-1 (CH3CN/H2O ; 36 mM, 3.6 mM and 9.1 mM).The possibility that the complexation c hemistry of CBr4 might influence the reaction is critically considered.
- Eberson, Lennart,Ekstroem, Mikael
-
-
- Syntheses og Stilbenes with a C2-Sidechain in o-Position and of their Deuteriated Analogues
-
Syntheses of o-(β-aminoethyl)-stilbene-urethanes (types 1, 2 and 3) and o-(β-phenethyl)-stilbenes 4 are described.The urethanes are obtained by degradation of 1-benzyl-1,2,3,4-tetrahydroisoquinolines with ethylchloroformate; 4 is synthesized by reduction of desoxybenzoines, followed by o-formylation and Wittig-reaction.The deuteriated isotopomers were obtained via the corresponding deuteriated precursors. - Keywords: Stilbenes, o-substituted; Deuteriated compounds
- Mayer, Klaus K.,Prior, Silvia,Wiegrebe, Wolfgang
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p. 511 - 532
(2007/10/02)
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- Effects of Solvent and Additives on the Rearrangement Pathway of the Seyferth Reaction
-
The Seyferth reagent has dual reactivity with electron-deficient alkenes. trans-1,2-Dichloroethene reacts both with the free carbene to give cyclopropane stereospecifically and with a complex between carbene and a second molecule of Seyferth reagent (homogeneous catalysis) to give a rearranged propene.The addition of other materials to the reaction mixture can have a profound effect on the ratio of the two pathways.Good ? donors such as p-xylene decrease the pathway to rearranged propene via the complexed carbene.Such materials thus serve as inhibitors to the process of homogeneous catalysis by forming a competing complex that does not go on to propene but instead reverts to free carbene.The existence of the inhibitor-carbene complex is supported by concentration studies.The presence of insoluble materials such as zinc chloride, on the other hand , serves to decrease the pathway that leads through free carbene to the cyclopropane.Free carbene may react with the surface of the additive and be removed as a reactive species.This latter process would have no effect on carbene previously complexed with the homogeneous catalyst, the Seyferth reagent , which could still proceed to rearranged propene.
- Lambert, Joseph B.,Boch, Richard J.,Larson, Eric G.
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p. 3054 - 3059
(2007/10/02)
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- KINETICS OF THE DECOMPOSITION OF 1-ARYL-2,2,2-TRIHALOGENOETHANOLS IN AQUEOUS BASE
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The decomposition of several 1-aryl-2,2,2-trichloro- and 1-aryl-2,2,2-tribromo-ethanols in aqueous base is studied.The title compounds yield the corresponding benzaldehydes and the halogenoform with base.The kinetics are compatible with an (E1cB)R mechanism.Values for the rates of collapse of the intermediate alkoxides and for the pKa values of all ethanols are estimated.Electron-donating substituents on the ring facilitate decomposition and decrease the acidity of the ethanols.Solvent isotope effects, kH2O/kD2O, for the reactions are small.The absence of mandelic acid derivatives among the products, in apperent disagreetment with other related studies, is discussed and justified in the light of a scheme which reconciles previous conflicting observations found in the literature.
- Lins, Hilvania Silva e,Nome, Faruk,Rezende, Marcos Caroli,Sousa, Iolanda de
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p. 1521 - 1526
(2007/10/02)
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- Halogenation of Acetone. A Method for Determining pKas of Ketones in Aqueous Solution, with an Examination of the Thermodynamics and Kinetics of Alkaline Halogenation and a Discussion of the Best Value for the Rate Constant for a "Diffusion-Controlled Reaction". Energetic ...
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The pKa of a simple ketone can be determined by analysis of the kinetics of halogenation in alkaline solution (J.Am.Chem.Soc. 1982, 104, 895).Details of the determination of the pKa of acetone are reported.The stoichiometry of chlorination of acetone is 2.15 hypohalites per acetone; bromination consumes 2.83 hypobromites.The major product from chlorination is lactate and not acetate; lactate is a minor product from bromination of acetone.The kinetic significance of the possible side reactions is discussed.The determination of the pKa requires knowledge of the rate constant for a diffusion-controlled reactionof nonspherically symmetrical molecules in water; the state of our knowledge of this rate constant is reviewed critically.It is shown that for reactions involving diffusion together of reactants which then undergo direct heavy-atom bond making it is very unusual for the diffusion limit to be reached, although the observed rate constant may become insensitive to the thermodynamic rectivity of the reactants.
- Guthrie, J. Peter,Cossar, John,Klym, Alex
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p. 1351 - 1360
(2007/10/02)
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- REARRANGEMENT AND CATALYSIS IN THE SEYFERTH REACTION.
-
The Seyferth reagent PhHgCBr//3 reacts with trans-1,2-dichloroethene to give two major products, trans-1,1-dibromo-2,3-dichlorocyclopropane (C) and 1,1-dibromo-3,3-dichloropropene (P). The stereospecifically formed cyclopropane is consonant with a singlet carbene mechanism, but the rearranged propene requires a second intermediate. Observation that the concentration ratio left bracket P right bracket / left bracket C right bracket is inversely proportional to the concentration of the alkene demonstrates that there are two intermediates, that the cyclopropane comes from the first-formed intermediate, and that the propene comes from the second-formed intermediate.
- Lambert,Bosch,Mueller,Kobayashi
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p. 3584 - 3589
(2007/10/02)
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- Applications of Phase Transfer Catalysis, 23. Note on Bromoiodocarbene and on Pertinent Halogen Exchange Processes
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A rapid halogen exchange between HCBr3, HCBr2I, HCBrI2, and HCI3 occurred in the presence of conc. sodium hydroxide and a quaternary ammonium salt.Trapping experiments with various alkenes gave cyclopropane derivatives only in 3 cases.Depending on the nucleophilicity of the alkene and the haloform, different proportions of CBr2, CBrI, and CI2 adducts were obtained.The most nucleophilic acceptor trapped those carbenes preferentially that were formed by elimination of iodide.
- Dehmlow, Eckehard V.,Broda, Witold
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p. 3894 - 3897
(2007/10/02)
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- REACTIONS OF STERICALLY HINDERED PHOSPHINES WITH CARBON TETRAHALIDES: P-HALOGENYLIDS
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1.A study has been made of the effects of steric factors on the reactions of tertiary phosphines with carbon tetrahalides.It is found that in the interaction of sterically hindered phosphine with carbon tetrabromide one gets the formation of bromophosphonium tribromomethylid, which exists at a low temperature, this being in an ionic pair containing the anion CBr3-.A sterically hindered phosphine having hydrogen at the α carbon atom forms P-halogenylids on reaction with carbon tetrahalides. 2.Unstabilized P-halogenylids with unsubstituted methylene and alkylidene gr oups have been synthesized, and also P-halogenylids with trimethylsilyl, methyl sulfide, phosphine, acyl, and aromatic groups on the ylid carbon atom. 3.A study has been made of the reactions of P-chlorylids with chlorine-bearing electrophilic reagents , which give rise to new P-halogenylids.
- Kolodyazhnyi, O. I.
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p. 2125 - 2137
(2007/10/02)
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