Identification and Persistence of 5,6-Dihydro-2H-pyran-3-carboxaldehyde in Aged Aqueous Acrolein Media.

Acrolein hydrolysis byproducts are a part of good industrial stewardship practice. Aqueous acrolein is used worldwide as an industrial raw material, an herbicide, an oilfield biocide, a hydrogen sulfide scavenger, and a molluscicide. Industrial acrolein is obtained by the catalytic oxidation of propylene followed by aqueous absorption and then by distillations. Generally, the fate of aqueous acrolein is described as occurring by hydrolysis, evaporation, absorption into the ground, and its consumption by the intended application purposes and conditions. Measurements of acrolein in water are normally confined to its loss. However, its byproducts are rarely discussed. In this study, an aged acrolein solution has been found to contain byproduct aldehydes, including the major soluble 5,6-dihydro-2H-pyran-3-carboxaldehyde. Despite acrolein's facile hydrolysis degradation, this byproduct is surprisingly stable in aqueous media for at least 25 years at ambient temperatures. The presence of this byproduct has been established by 1H and 13C NMR, using DEPT, COSY, and HMBC, and UV spectroscopy at λmax 229 nm in natural water systems.

Kinetic studies on the reaction of chlorosulfonyl isocyanate with monofluoroalkenes: experimental evidence for both stepwise and concerted mechanisms and a pre-equilibrium complex on the reaction pathway.

Chlorosulfonyl isocyanate (CSI) is reported to react with hydrocarbon alkenes by a stepwise dipolar pathway to give N-chlorosulfonyl-ß-lactams that are readily reduced to ß-lactams. Substitution of a vinyl hydrogen for a vinyl fluorine changes the dynamics for reaction with CSI so that a concerted pathway is favored. Rate constants were measured for reactions of CSI with monofluoroalkenes and some hydrocarbon alkenes. Activation parameters for two hydrocarbon alkenes and two monofluoroalkenes support this change in mechanism. A plot generated from the natural log of rate constants vs ionization potentials (IP) indicates that fluoroalkenes with IP values >8.9 eV react by a concerted process. Electron-rich monofluoroalkenes with IP values <8.5 eV were found to react by a single-electron transfer (SET) pathway. Hydrocarbon alkenes were also found to react by this dipolar stepwise SET intermediate rather than the previously accepted stepwise dipolar pathway. Data support a pre-equilibrium complex on the reaction pathway just before the rate-determining step of the concerted pathway and a SET intermediate for the stepwise reactions. When the reactions are carried out at lower temperatures, the equilibrium shifts toward the complex or SET intermediate enhancing the synthetic utility of these reactions. Kinetic data also support formation of a planar transition state rather than the orthogonal geometry as reported for ketene [2 + 2] cycloadditions.

Reaction of chlorosulfonyl isocyanate with fluorosubstituted alkenes: evidence of a concerted pathway.

Concerted reactions are indicated for the electrophilic addition of chlorosulfonyl isocyanate with monofluoroalkenes. A vinyl fluorine atom on an alkene raises the energy of a stepwise transition state more than the energy of the competing concerted pathway. This energy shift induces CSI to react with monofluoroalkenes by a one-step process. The low reactivity of CSI with monofluoroalkenes, stereospecific reactions, the absence of 2:1 uracil products with neat fluoroalkenes, and quantum chemical calculations support a concerted pathway.

Rearrangement of 3-membered 1,1,2-trifluorobromonium and iodonium ions and comparison of trifluorochloronium to fluorocarbenium ions.

Reactions of chlorine (Cl(2)) with 4-halo-1,1,2-trifluorobut-1-enes (1, 2, or 3) give open-ion intermediates A and E that are in equilibrium. The open-chloronium ions (E) rearrange to a five-membered-ring halonium ion during ionic chlorination of 3 when the number-4 halo-substituent is iodine. Three-membered-ring bromonium and iodonium ions from alkenes 1, 2, or 3 are rather symmetrical and similar in structure. Quantum chemical calculations show that five-membered-ring halonium ion intermediates are 11 to 27 kcal/mol more stable than the three-membered-ring halonium ions or the open-ions A and E. The five-membered-ring intermediates lead to rearranged products. Rearranged products increase as the number-4 halogen (Z) becomes more nucleophilic (Z: Cl < Br < I). Open chloronium ions from ionic chlorination of terminal fluorovinyl alkenes are compared to the open ions generated by protons to similar alkenes.

Investigations of the reactions of monochloramine and dichloramine with selected phenols: examination of humic acid models and water contaminants.

Our paper reports on the reactivities and orientations of two common phenols, phenol (2) and m-cresol (3), and some of their chlorinated intermediates with aqueous monochloramine, NH2Cl, and dichloramine, NHCl2. We also examined the further reactivity of 2,4,6-trichlorophenol (4) with the chloramines. The phenols are an important area of investigation because they are substituents in the humic acids and are common contaminants in water. m-Cresol (3) was found to be more reactive than phenol (2)with both chlorinating agents. Both NH2Cl and NHCl2were sufficiently reactive to chlorinate all positions ortho and para to the hydroxyl groups. Mono- and dichloramine showed the same orientation with 2 but different orientations in their reactions with the substituent phenols. Indophenol (as its salt) was formed to a minor extent at high pH but not at pH 9. Both NH2Cl and NHCl2 rapidly replaced the parachlorine in 2,4,6-trichlorophenol (4) to give a mixture of 2,6-dichloro-1,4-benzoquinone-4-(N-chloro) imine (5) and 2,6-dichloro-1,4-benzoquinone (18). Similar reactions occurwith 2,4,6-trichloro-m-cresol (17) and 2,4,6-trichloro-3-methoxyphenol (29). The products for 17 were confirmed by mass spectrometry (El and Cl), 1H NMR, 13C NMR, and IR; the products for 29 were confirmed by mass spectrometry (El and Cl) and IR. An ion radical mechanism is suggested to account for the chlorine replacement by the chloramines. [No side chain oxidation of the methyl group in 17 in H20 or ether occurred, with or without ultraviolet radiation.] Both 5 and 18 underwent further chlorination with NH2Cl or NHCl2. Imine 5 did not function as a chlorinated agent.

Ionic reaction of halogens with terminal alkenes: the effect of electron-withdrawing fluorine substituents on the bonding of halonium ions.

Ionic reactions of terminal alkenes with chlorine (Cl(2)), bromine (Br(2)), and iodine monochloride (ICl) are sensitive to the alkyl substituents, and the positions and number of vinyl fluorine atoms. These perturbations influence the symmetry of the halonium ion intermediates, which can be determined by the distribution of the Markovnikov to anti-Markovnikov products. A vinyl fluorine on the number-2 carbon favors an unsymmetrical intermediate with greater charge on the number-2 carbon unless the alkyl group is electron withdrawing. A vinyl fluorine on the terminal number-1 carbon favors positive charge development on that carbon unless a resonance stabilizing group is on the number-2 carbon. The symmetry of halonium ions with vinyl fluorines on both carbons-1 and -2 depends primarily on the characteristics of the alkyl substituent. Intermediates range from open-ions with the positive charge on carbon-2, to various bridged species, to open-ions on the terminal carbon.

Formation of dimer-type ketals in the reaction of 2,4,6-trichlorophenol and 2,4,6-trichloro-m-cresol with calcium hypochlorite in methanol: conversion to quinones and other compounds.

2,4,6-Trichlorophenol (2) and 2,4,6-trichloro-m-cresol (5) react with calcium hypochlorite (Ca(OCl)(2)) in MeOH to give respectively dimer-type ketals 2-(2',4',6'-trichlorophenoxy)-4,4-dimethoxy-6-chlorocyclohexadien-2,5-one (6) and 2-(3'-methyl-2',4',6'-trichlorophenoxy)-4,4-dimethoxy-5-methyl-6-chlorocyclohexadien-2,5-one (7). Ketal 6, which was too unstable to be isolated, and 7 hydrolyzed in H(2)O/HCl to 2-(2',4',6'-trichlorophenoxy)-6-chloro-1,4-benzoquinone (8) and 2-(3'-methyl-2',4',6'-trichlorophenoxy)-5-methyl-6-chloro-1,4-benzoquinone (9), respectively. Ketal 6 and quinone 8 were also produced when 2 and Ca(OCl)(2) reacted in DMF, followed by addition of MeOH and H(2)O, respectively. The mechanisms of these reactions are examined. Conversion of the ketals and quinones to other products is described.

Addition of bromine chloride and iodine monochloride to carbonyl-conjugated, acetylenic ketones: synthesis and mechanisms.

The reactions of 3-butyn-2-one (1), 3-hexyn-2-one (2), and 4-phenyl-3-butyn-2-one (3) with bromine chloride (BrCl) and iodine monochloride (ICl) in CH(2)Cl(2), CH(2)Cl(2)/pyridine, and MeOH are described. The data show that the major products in CH(2)Cl(2) are (Z)-AM (anti-Markovnikov) regioisomers. With the exception of 3 and ICl, the (E)-AM regioisomers predominate when pyridine was added as an acid scavenger. Minor amounts of the M regioisomers were formed with 1 and 2 and BrCl. The percentage of M regioisomer increased significantly with 1 and BrCl in MeOH, but MeOH had little affect on the other reactions. Isolation and stability of the products are discussed. Detailed evidence for the structures of the products, involving a combination of MS, (1)H and (13)C NMR, and IR, is presented; HRMS analyses are provided as proofs for all of the products. The acid-catalyzed mechanism and the halonium ion mechanism are considered as possible pathways in the formation of the products.