- Formation of iodo-trihalomethanes during disinfection and oxidation of iodide-containing waters
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The formation of iodo-trihalomethanes (I-THMs) such as iodoform (CHI3) during oxidative treatment of iodide-containing drinking waters can be responsible for taste and odor problems. I-THMs are formed by reactions of hypoiodous acid (HOI) with natural organic matter. HOI is quickly formed from naturally occurring iodide (I-) by oxidation with ozone, chlorine, or chloramine. The kinetics of reactions of HOI with organic model compounds as well as the resulting CHI3 formation were measured. Substituted phenols, phenol, and, to a smaller extent, α-methyl carbonyl compounds were found to be reactive toward HOI and: also to yield CHI3. Resorcinol (m-hydroxyphenol) had the highest yield of CHI3. The kinetics of I-THM formation were also measured in natural waters which were oxidatively treated with ozone, chlorine, or chloramine. When ozone was used, no I-THMs were detected and ≥ 90% of I- was transformed to IO3-. Chlorine led to the formation of both IO3- and I-THMs. With increasing chlorine doses, the CHI3 formation decreased, whereas IO3- formation, as well as the formation of classical THMs such as chloroform, increased. In chloramination processes, I-THMs (especialliiy CHI3)were the main products. The CHI3 formation in the oxidation of natural waters increased in the order O3 2 2Cl. The formation of iodo-trihalomethanes (I-THMs) such as iodoform (CHI3) during oxidative treatment of iodide-containing drinking waters can be responsible for taste and odor problems. I-THMs are formed by reactions of hypoiodous acid (HOI) with natural organic matter. HOI is quickly formed from naturally occurring iodide (I-) by oxidation with ozone, chlorine, or chloramine. The kinetics of reactions of HOI with organic model compounds as well as the resulting CHI3 formation were measured. Substituted phenols, phenol, and, to a smaller extent, α-methyl carbonyl compounds were found to be reactive toward HOI and also to yield CHI3. Resorcinol (m-hydroxyphenol) had the highest yield of CHI3. The kinetics of I-THM formation were also measured in natural waters which were oxidatively treated with ozone, chlorine, or chloramine. When ozone was used, no I-THMs were detected and ≥90% of I- was transformed to IO3-. Chlorine led to the formation of both IO3- and I-THMs. With increasing chlorine doses, the CHI3 formation decreased, whereas IO3- formation, as well as the formation of classical THMs such as chloroform, increased. In chloramination processes, I-THMs (especially CHI3) were the main products. The CHI3 formation in the oxidation of natural waters increased in the order O3 2 2Cl.
- Bichsel, Yves,Von Gunten, Urs
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- Base-Catalyzed Halogenation of Acetone
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The kinetics of iodination and bromination of acetone were measured in basic aqueous solutions, buffered with trifluoroethanol, under conditions in which halogenation of the enolate ion is the rate-determining step.With the assumption of diffusion-controlled halogenation of the enolate ion by I2 and HOBr with k = 5 * 109 M-1 s-1, rate constants for other halogenating agents (M-1 s-1) are BrO-, 8 * 107; IO-, 108; IOH, 2.5 * 108; and I3-, 3.6 * 108; the pKa of acetone is 18.9 +/- 0.3 at 25 deg C, ionic strength 1.0 M (KCl) or 1.0 M (KNO3).Iodoform was identified spectrofotometrically as the product of iodination.Values of pKaSH = 10.8 and 10.6 for the enol give pKE = 8.1 and 8.3, respectively, for formation of the enol from acetone.It is suggested that the reactions of IO- and BrO- may proceed through the formation of a complex with the enolate, followed by protonation and halogenation, and that I3- may serve as an iodine donor through a preassociation mechanism.The observed dependence of the absorbance of I3- on buffer concentration and pH indicates the formation of a significant amount of a species with the composition ROIOH- at high concentrations of trifluoroethoxide and hydroxide ions.
- Tapuhi, Eliana,Jencks, William P.
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- The synergistic effect of copper chromite spinel nanoparticles (CuCr2O4) and basic ionic liquid on the synthesis of cyclopropanecarboxylic acids
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Abstract: An efficient synthesis of cyclopropanecarboxylic acids using copper chromite spinel nanoparticles and basic ionic liquid is described. In this study, a relatively simple method starting with trans-cinnamic acid for the synthesis of (±)-trans-2-phenylcyclopropanecarboxylic acid, a key intermediate in the synthesis of tranylcypromine sulfate as an active pharmaceutical ingredient, was employed. Using a combination of basic ionic liquid [Bmim]OH and copper chromite spinel nanoparticles as a catalytic system, the best results were obtained in THF as a polar solvent. This method is a useful alternative to other approaches described in the literature. The use of commercially available chemicals, decreased environmental hazards, with no need for the separation of stereoisomers, and consequently a reduced number of overall steps, are the advantages of this approach that make it an appropriate choice at an increased scale. Graphical Abstract: [Figure not available: see fulltext.]
- Ghasemi, Mohammad Hadi,Kowsari, Elaheh
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p. 7963 - 7975
(2016/11/25)
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- Metal free amide synthesis via carbon-carbon bond cleavage
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A metal-free oxidative coupling of methyl ketones and primary amines to amides has been developed. The reaction tolerates a variety of functional groups, and is operationally simple. The reaction is proposed to go through a radical pathway to form the triiodomethyl ketone intermediate and the amide is formed by the nucleophilic attack of amine on triiodomethyl ketone carbonyl.
- Zhu, Chunyin,Wei, Wei,Du, Peng,Wan, Xiaobing
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p. 9615 - 9620
(2015/01/09)
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- Photoproduct Characterization and Dynamics in the 248 nm Photlysis of CH3I Thin Films on Ag(111)
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The 248 nm photochemistry of methyl iodide thin films was studied using reflection absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), and time-of-flight quadrupole mass spectrometry (TOF-QMS).The formation of predominantly CH2I2 and CH4 and some C2H6, CH3CH2I, CHI3 and I2 photoproducts retained in the film was characterized by RAIRS and TPD.The integrated areas of the IR absorption bands for the two major photoproducts, CH2I2 and CH4, increase to a maximum and then decrease as photolysis of the film proceeds.A cross section for the loss of CH3I by 248 nm photolysis of the film was measured to be (1.0+/-0.1)E-19 cm2, approximately 1 order of magnitude lower than the gas-phase cross section.At all laser fluences used in this study, CH3, I, and CH3I were ejected into the gas phase.The CH3 TOF distribution showed the signature of the gas-phase CH3I photodissociation dynamics-two sharp peaks corresponding to the production of iodine atoms in the I(2P3/2) and I*(2P1/2) states.The TOF distributions of I and CH3I were fit by Maxwell-Boltzmann distributions corresponding to temperatures of 1400 and 1170 K, respectively.Three other species-CH4, I2 and CH2I2-were observed in TOF-QMS, but only at higher laser fluences.It was determined that the I2 and CH2I2 species are most likely fragments of a larger molecule, perhaps a cluster species, that photodesorbs as the film becomes enriched with photoproducts.The mechanism for CH4 photoejection appears to be of a different nature.The photochemistry of methyl iodide thin films can be understood in terms of a combination of photoproceses occuring in the film and at the film surface.
- Coon, S. R.,Myli, K. B.,Grassian, V. H.
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p. 16416 - 16424
(2007/10/02)
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- Formation of Radical Cations of Polyiodomethanes: A Pulse Radiolysis Study
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The transient optical absorption band (λmax = 380nm, t1/2 = 23μs and ε = 2010dm3 mol-1 cm-1) produced on pulse radiolysis of N2O-saturated aqueous solution of CH2I2 (pH 6.0) has been assigned to the OH adduct radical, CH2I2*OH.In acidic aqueous solutions, CH2I2+ (λmax = 380 and 570nm, t1/2 = 3μs and ε570 = 2150dm3 mol-1 cm-1) has been identified as the intermediate.The rate constants for the reaction of OH radicals with CH2I2 to form CH2I2*OH and CH2I2+ have been determined to be 2.1*109 and 6.0*109 dm3 mol-1 s-1 respectively.Cl2- has been found to oxidize CH2I2 to CH2I2+ with a bimolecular rate constant of 1.7*108 dm3 mol-1 s-1.CH2I2+ is a good oxidant and oxidizes I-, Br-, and methyl disulphide with high rate constants close to the diffusion limit.I2 is the main stable end product formed on γ-radiolysis and its yield is equal to 1/2G(-CH2I2).The transient optical absorption bands observed on pulse radiolysis of CH2I2 and CHI3 in 1,2-dichloroethane have been assigned to CH2I2+ (λmax = 380 and 590nm) and CHI3+ (λmax = 400 and 610nm).
- Mohan, Hari,Moorthy, Pervaje N.
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p. 277 - 282
(2007/10/02)
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- Intraoral medicament delivery and procedure
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A method for cushioning dental appliance in the mouth using a visible light cured polymeric material which can also be used in a method for intraoral medicament delivery in the mouth is provided. When used with an orthodontic bracket, for example, the light cured polymeric material is dispensed on the orthodontic bracket after the bracket is in place and the material is light cured on the bracket. When used in a method of intraoral delivery of a medicament, a medicament is added to the polymeric material and the polymeric material is applied in the same manner as described for cushioning an orthodontic bracket.
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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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- BIOSYNTHESIS OF PODOPHYLLUM LIGNANS - I. CINNAMIC ACID PRECURSORS OF PODOPHYLLOTOXIN IN PODOPHYLLUM HEXANDRUM
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Feeding experiments in Podophyllum hexandrum plants have established that phenylalanine, cinnamic acid and ferulic acid are good precursors of the two major aryltetralin lignans podophyllotoxin and 4'-demethylpodophyllotoxin.Sinapic and 3,4,5-trimethoxycinnamic acids were poorly utilized, showing that the substitution pattern of the pendent aryl ring is built up after coupling of the two phenylpropane units.Degradation studies on podophyllotoxin derived from ferulic acid show that the two halves of the lignan molecule are equally labelled supporting a biosynthetic sequence involving oxidative coupling of two similar phenylpropane precursors having the substitution pattern of ferulic acid.Although 3,4-methylenedioxycinnamic acid was readily incorporated, degradative studies prove that this compound is not incorporated intact, but via a metabolic sequence in which the methylenedioxy carbon atom enters the C1-pool and then labels the methylenedioxy and methoxyl substituents of podophyllotoxin.The rest of the skeleton is incorporated via ferulic acid, presumably by way of caffeic acid.Key Word Index - Podophyllum hexandrum; Podophyllaceae; aryltetralin; lignans; biosynthesis; podophyllotoxin.
- Jackson, David E.,Dewick, Paul M.
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p. 1029 - 1036
(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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