Rate constants for the gas‐phase reaction of CF3CF2CF2CF2CF2CHF2 with OH radicals at 250–430 K

The rate constants k₁ for the reaction of CF₃CF₂CF₂CF₂CF₂CHF₂ with OH radicals were determined by using both absolute and relative rate methods. The absolute rate constants were measured at 250–430 K using the flash photolysis–laser‐induced fluorescence (FP‐LIF) technique and the laser photolysis–laser‐induced fluorescence (LP‐LIF) technique to monitor the OH radical concentration. The relative rate constants were measured at 253–328 K in an 11.5‐dm³ reaction chamber with either CHF₂Cl or CH₂FCF₃ as a reference compound. OH radicals were produced by UV photolysis of an O₃–H₂O–He mixture at an initial pressure of 200 Torr. Ozone was continuously introduced into the reaction chamber during the UV irradiation. The k₁ (298 K) values determined by the absolute method were (1.69 ± 0.07) × 10^?15 cm³ molecule^?1 s^?1 (FP‐LIF method) and (1.72 ± 0.07) × 10^?15 cm³ molecule^?1 s^?1 (LP‐LIF method), whereas the K₁ (298 K) values determined by the relative method were (1.87 ± 0.11) × 10^?15 cm³ molecule^?1 s^?1 (CHF₂Cl reference) and (2.12 ± 0.11) × 10^?15 cm³ molecule^?1 s^?1 (CH₂FCF₃ reference). These data are in agreement with each other within the estimated experimental uncertainties. The Arrhenius rate constant determined from the kinetic data was K₁ = (4.71 ± 0.94) × 10^?13 exp[?(1630 ± 80)/T] cm³ molecule^?1 s^?1. Using kinetic data for the reaction of tropospheric CH₃CCl₃ with OH radicals [k₁ (272 K) = 6.0 × 10^?15 cm³ molecule^?1 s^?1, tropospheric lifetime of CH₃CCl₃ = 6.0 years], we estimated the tropospheric lifetime of CF₃CF₂CF₂CF₂CF₂CHF₂ through reaction with OH radicals to be 31 years. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 26–33, 2004     

Radiation-induced heterogeneous polymerization of acrylamide in acetone and acetone–water mixtures

The effects of temperature, dose rate, and monomer concentration on the heterogeneous polymerization of acrylamide in acetone–water mixtures have been studied. Heterogeneous polymerization takes place in mixtures containing less than 60 vol-% water. The polymerization is steady in acetone and nonsteady in acetone an nonsteady in mixtures containing 10–50 vol-% water. The average rate of polymerization is highest in mixtures with about 20 vol-% water. Polymer molecular weight increases with the increasing water content in range 0–10 vol-% and does not change in the range of 30–70 vol-% water. For the polymerization in acetone and an acetone–water 60/40 mixture the activation energies are 2.3 and ?1.8 kcal/mole, the dose rate exponents of rate are 0.78 and 0.52, and the monomer concentration exponents of rate are 0.5 and 1.6, respectively. The polymer molecular weight increases with decreasing dose rate, decreasing temperature, and increasing monomer concentration. These results are discussed in connection with the mechanism of heterogeneous polymerization and the solvent effect.     

Preparation of 1,1,1,3,3-pentafluoropropane (HFC-245fa) by using a SbF5-attached catalyst

In this report, a simple process for preparing HFC-245fa through the reaction of 1,1,1,3,3-pentachloropropane (PCP) and anhydrous HF via two-step vapor-phase catalytic fluorination is described. The antimony pentafluoride catalyst was supported on inert porous materials to improve the catalytic activity. The resulting process catalyst not only exhibited high catalytic activity and excellent thermo-stability, but also improved the performance of SbF₅, in terms of hygroscopicity and corrosion.     

Theoretical study of the electronic structure of the lower states of the [Cr2Cl9]3- and [Mo2Cl9]3- ions

The electronic structure of the lower states of a trigonal Cr3+ pair and Mo3+ pair, which occur in the Cs3M2Cl9 crystal (M=Cr,Mo), were studied by theoretical calculations carried out according to several methods: multireference singly and doubly excited configuration interaction, second-order configuration interaction, and multireference coupled-pair approximation. We employed a model of a [M2Cl9]3- anion embedded in a cage of point charges, which were arranged so as to simulate the anion in the crystal. The model core potential was utilized, where the relativistic effect was included for Mo. Results of the Cr complex showed that there were no direct bonds between the Cr metals. The lower electronic spectra of the [Cr2Cl9]3- ion were interpreted in terms of the electronic spectra of [CrCl6]3-. The lowest state of simultaneous excitation in both metals was considered. The [Mo2Cl9]3- ion exhibited a single direct bond between the metals. Reflecting this single bond, the observed singlet-triplet splitting was much larger than that in the case of Cr and the calculated splitting was in good agreement with the observed one. We account for the electronic spectra of the [Mo2Cl9]3- complex, which exhibited quite different features in the electronic excitation spectra in comparison with those of the Cr complex.     

Thermal rearrangements of allyl 2,2-dichlorovinyl and 1,2,2-trichlorovinyl sulfides

Unique rearrangements of allyl 2,2-dichlorovinyl and 1,2,2-trichlorovinyl sulfides have been found. On heating the former gave 1,2-dichloro-l,4-pentadienes and the latter 2,3-dichloro-5-chloromethyl-4,5-dihydrothiophenes and 3,5,6-trichloro-3,4-dihydro-2H-thiopyranes .     

SbF5/PAF—a novel fluorinating reagent in preparing fluorine compounds

A novel fluorination reagent and catalyst, SbF₅/PAF (porous aluminum fluoride), was prepared by impregnating SbCl₅ into PAF and then treating with anhydrous hydrogen fluoride. The prepared reagent had an excellent catalytic activity in halogen-exchange, and also improved the properties of SbF₅, such as hydroscopicity, corrosion, and toxicity. SbF₅/PAF was successfully used in organic synthesis as a fluorinating reagent, and a fixed bed catalyst for F/Cl exchange.     

Synthesis of Telechelic Polystyrene by Radical Polymerization Using 1,4-Bis(p-tert-Butylphenylseleno-Methyl)benzene as a Photoiniferter

Abstract

1,4-Bis(p-tert-butylphenylselenomethyl) benzene was synthesized, and used as a bifunctional photoiniferter for the polymerization of styrene. Both the polymer yields and the number average of molecular weights (_n) of polymers increased with the polymerization. The polymerization of styrene by this iniferter permitted telechelic polystyrene containing arylseleno groups at both chain ends, and the degree of functionality was 1.9. The seleno groups of both chain ends of polystyrene were reduced quantitatively by tri-n-butyltin hydride. These seleno groups in polystyrene were also eliminated by treatment with hydrogen peroxide to give telechelic polystyrene with carbon-carbon double bond at both chain ends. Further, polystyrene with double bonds was converted to telechelic polystyrene carrying terminal functional groups as epoxy, hydroxy, and iodide group, respectively.

     

Invited Lecture. Ferroelectric liquid crystalline polymers and related model compounds with a low–moderate degree of polymerization

Abstract

Ferroelectric liquid crystalline polymers (FLCPs) with a low-moderate degree of polymerization were synthesized. These had a comb structure; the main chain was polyacrylate and the side chain consisted of a flexible spacer, a core and an optically active chiral end group. They exhibited electro-optic switching times ranging from a few milliseconds to a few seconds in the S*_c phase. As the molecular weight M _n increased, the range of the S*_c shifted to higher temperatures. At a given temperature, the switching time increased with M _n .

Spontaneous polarizations P _s , apparent cone angles 2θ, electro-optic switching times τ and rotational viscosities η of some polyoxyethylene FLCPs and corresponding low molecular weight ferroelectric liquid crystal materials (FLCs) were also measured. This is the first report of polyoxyethylene FLCPs. There was no significant difference in P _s and 2θ, which shows that the arrangement of the side chains in the FLCP is similar to that of the molecules in ordinary FLC. On the contrary, τ and η for the FLCPs were 10²–10³ times as large as those for FLCs. The rotational viscosity of the FLCP was mainly dependent on the side chain structure rather than on the spacer. Therefore collisions between adjacent side chains cause large η values in FLCPs rather than hindrance to side chain gyration due to the spacer group. By combining FLCPs with ITO-coated plastic substrates, a large area matrix driven display has been made. Although an improvement in switching time is still needed, a flexible and lightweight display like a sheet of paper will be available in the near future.     

Calix[4]arene-Based Triple-Stranded Metallohelicate in Water

The title complex is a triple-stranded metallohelicate organized by the self-assembly of 5,17-difunctionalized calix[4]arenes and metal cations with octahedral coordination geometry. Due to hydrophilic triethylene glycol chains on the lower rim of the calix[4]arene, the metallohelicate can encapsulate cationic guests in water. NMR and UV-vis titration experiments reveal that the metallohelicate captures a pyridinium guest with an alanine derivative to form a host-guest complex with a host-guest ratio of 1 : 1. CD spectroscopy confirms the bias of the P- and M-helical sense of the metallohelicate by the captured guest. The metallohelicate captures two molecules of dicationic N,N’-dimethyl-DABCO and monocationic N-methyl quinuclidine, exhibiting a positive allosteric effect. ¹H NMR titration experiments indicate that the bound guests are in close proximately to the aromatic rings of the ligands. Molecular mechanics calculations based on the UV-vis and NMR observations suggest that the first guest preorganizes the conformation of the metallohelicate to facilitate access of the second guest to the cavity.