Synthesis and characterization of poly(ethylene oxide-co-ethylene sulfone)s and their precursors: Poly(ethylene oxide-co-ethylene sulfide)s

Three poly(ethylene oxide-co-ethylene sulfide)s with oxygen to sulfur ratios of 2/1, 2/2, and 1/2 were prepared by phase-transfer catalyzed polycondensations of (1) sodium sulfide and 1,2-bis (2-chloroethoxy)ethane, (2) 1,2-ethanedithiol and 1,2-bis(2-chloroethoxy)ethane, and (3) 1,2-ethanedithiol and 2-chloroethyl ether, respectively. A buffered solution with pH between the pK_a of the monothiol (RSH) and the pK_a2 of the dithiol (HS–R–SH), or H₂S, was needed to obtain high molecular weight polymers, which suggests that nucleophiles transfer and react as monoanions rather than dianions. These poly(ethylene oxide-co-ethylene sulfide)s were oxidized completely to poly(ethylene oxide-co-ethylene sulfone)s using 3-chloroperoxybenzoic acid as oxidant. Both the final polymers and the precursors have regular sequenced structures and are semicrystalline. As expected, their glass transition temperatures and melting points increase and solubilities decrease with the decrease of ether oxygen to sulfur ratio. © 1994 John Wiley & Sons, Inc.     

Synthesis of (pyridinyl)-1,2,4-triazolo[4,3-a]pyridines

Methods for the synthesis of (pyridinyl)-1,2,4-triazolo[4,3-a]pyridines were developed. The principal route to the required intermediate 2-chloropyridines was based on rearrangements of mono N-oxides of 2,2′-bipyridine, 2,3′-bipyridine, 3,3′-bipyridine, 2,4′-bipyridine and 4,4′-bipyridine with phosphorus oxychloride. Reaction of 3,3′-bipyridine 1-oxide or 2,2′-bipyridine 1-oxide with phosphorus oxychloride gave mixtures of chloro isomers. Reaction with acetic anhydride, 3,3′-bipyridine 1-oxide and 2,2′-bipyridine 1-oxide gave exclusively [3,3′-bipyridine]-2(1H)-one and [2,2′-bipyridine]-6(1H)-one, respectively. 1,2,4-Triazolo[4,3-a]pyridines with pyridinyl groups at the 5,6,7 and 8 positions were synthesized.     

Preparation of poly(methyl methacrylate) and copolymers having enhanced thermal stabilities using sucrose-based comonomers and additives

A series of methyl methacrylate polymers have been prepared containing sucrose-based crosslinkers and additives. Thermogravimetry and long-term aging studies at 200°C show that sucrose-based alkyl and allyl ethers provide unprecedented thermal stability to linear, as well as crosslinked, poly (methyl methacrylate) or PMMA. Linear PMMA and PMMA crosslinked with trimethylolpropane trimethacrylate (TMPTMA) both degrade at 284°C. PMMA containing octa-O-crotylsucrose (1 mol %) degraded at 322°C. Depending on concentration, PMMA containing octa-O-allylsucrose (0.1-1.0 mol % and higher) degraded between 334 and 354°C, and PMMA containing 1′,6,6′-trimethacryloyl-2,3,3′,4,4′-penta-O-methylsucrose (0.1-1.0 mol %) degraded between 309 and 320°C. PMMA containing (1 mol % each) sucrose-based esters, ester-ether derivatives, all degraded at or below the degradation temperature of pure PMMA. Long-term air aging studies revealed that PMMA containing penta-O-methylsucrose trimethacrylate, octa-O-allylsucrose, and octa-O-crotylsucrose did not flow or sag after heating for 24 h at 200°C, but the polymers did show yellowing. While linear and crosslinked samples of PMMA containing compounds other than sucrose ethers lost more than 50% of their original weight within 15 h at 200°C, PMMA containing sucrose-based ethers lost about 8 and 20% of their original weight after 1 and 8.5 days, respectively. Herein we propose a unique mechanism by which saccharide ethers may be imparting this unprecedented thermal stabilization to PMMA. While tertiary hydrogens alpha to oxygens in saccharide ethers are stable to chain transfer during normal polymerization temperatures, they readily chain transfer at 200°C where PMMA is unstable. Chain transfer of these hydrogens is followed by fragmentation to produce alkyl, allyl or crotyl radicals, which combine with the macroradicals and terminate depropagation. © 1995 John Wiley & Sons, Inc.     

The kinetics of styrene emulsion polymerization

A study has been carried out on the kinetics of persulfate-initiated emulsion polymerization of styrene in the presence of an anionic (oleate) or mixed anionic-nonionic emulsifier. In both cases it appears that Smith-Ewart kinetics are obeyed, i.e., there is a constant-rate period up to 40–50% conversion, during which there is a concomitant constant molecular weight development. The sharp increases in molecular weight with conversion reported by Grancio and Williams appear to be an artifact resulting from the use of an impure emulsifier (Triton X-100), which acts as a chain transfer agent to reduce the molecular weight by approximately an order of magnitude. Hence there does not appear to be any kinetic justification for assuming an inhomogeneous swollen latex particle (“core-shell” morphology), and normal thermodynamic considerations should still apply to this swelling phenomemon.     

Intramolecular fluorine migration via four-member cyclic transition states

Gaseous CF(3)(+) interchanges F(+) for O with simple carbonyl compounds. CF(3)(+) reacts with propionaldehyde in the gas phase to produce (CH(3))(2)CF(+) via two competing pathways. Starting with 1-(13)C-propionaldehyde, the major pathway (80%) produces (CH(3))(2)CF(+) with the carbon label in one of the methyl groups. The minor pathway (20%) produces (CH(3))(2)CF(+) with the carbon label in the central position. The relative proportions of these two pathways are measured by (19)F NMR analysis of the neutral CH(3)CF=CH(2) produced by deprotonation of (CH(3))(2)CF(+) at <10(-)(3) Torr in an electron bombardment flow (EBFlow) reactor. Formation of alkene in which carbon is directly bonded to fluorine means that (in the minor product, at least) an F(+) for O transposition occurs via adduct formation followed by 1,3-atom transfer and then isomerization of CH(3)CH(2)CHF(+) to the more stable (CH(3))(2)CF(+). Use of CF(4) as a chemical ionization (CI) reagent gas leads to CF(3)(+) adduct ions for a variety of ketones, in addition to isoelectronic transposition of F(+) for O. Metastable ion decompositions of the adduct ions yield the metathesis products. Decompositions of fluorocycloalkyl cations formed in this manner give evidence for the same kinds of rearrangements as take place in CH(3)CH(2)CHF(+). Density functional calculations confirm that F(+) for O metathesis takes place via addition of CF(3)(+) to the carbonyl oxygen followed by transposition via a four-member cyclic transition state. A computational survey of the effects of different substituents in a series of aldehydes and acyclic ketones reveals no systematic variation of the energy of the transition state as a function of thermochemistry, but the Hammond postulate does appear to be obeyed in terms of progress along the reaction coordinate. Bond lengths corresponding to the central barrier correlate with overall thermochemistry of the F(+) for O interchange, but in a sense opposite to what might have been expected: the transition state becomes more product-like as the metathesis becomes increasingly exothermic. This reversal of the naive interpretation of the Hammond postulate is accounted for by the relative positions of the potential energy wells that precede and follow the central barrier.     

Determination of phosphorus:glycerol:acyl ratios in phospholipids

Phospholipids (1–5 mg) are mixed with methyl heptadecanoate as an internal standard. One part of the sample is reduced with Vitride in tetrahydrofuran in a sealed tube at 50 2C for 1 hr. The reaction products are acetylated in the same tube by treatment with acetic acid-acetic anhydride at 140 °C. After 1 hr total O-acyl and after 16 additional hours glycerol are determined as the fully acetylated compounds by gas-liquid chromatography.Another part of the sample is subjected to acidic hydrolysis and total O-acyl and N-acyl groups are determined by GLC as fatty-acid methyl esters. The aqueous phase is heated to 100 °C with 6 N HCl for 72 hr and phosphorus is measured colorimetrically.     

1,4-Difluoro-2,5-dimethoxybenzene as a precursor for iterative double benzyne-furan Diels-Alder reactions

[reaction: see text] The use of 1,4-difluoro-2,5-dimethoxybenzene as a novel precursor for iterative two-directional benzyne-furan Diels-Alder reactions, using a range of 2- and 3-substituted furans, is reported. Substituted oxabenzonorbornadienes were synthesized following the initial Diels-Alder reaction, which upon ring opening under acidic conditions gave substituted naphthol derivatives. Highly substituted anthracenols were generated in the second benzyne-furan Diels-Alder reaction following acid-catalyzed isomerization of the cycloadducts.     

Lateral Metallation and Redistribution Reactions of Sodium Ferrates Containing Bulky 2,6-Diisopropyl-N-(trimethylsilyl)anilide Ligands

Alkali-metal ferrates containing amide groups have emerged as regioselective bases capable of promoting Fe−H exchanges of aromatic substrates. Advancing this area of heterobimetallic chemistry, a new series of sodium ferrates is introduced incorporating the bulky arylsilyl amido ligand N(SiMe₃)(Dipp) (Dipp=2,6-iPr₂-C₆H₃). Influenced by the large steric demands imposed by this amide, transamination of [NaFe(HMDS)₃] (HMDS=N(SiMe₃)₂) with an excess of HN(SiMe₃)(Dipp) led to the isolation of heteroleptic [Na(HMDS)₂Fe{N(SiMe₃)Dipp}]_∞ ( 1 ) resulting from the exchange of just one HMDS group. An alternative co-complexation approach, combining the homometallic metal amides [NaN(SiMe₃)Dipp] and [Fe{N(SiMe₃)Dipp}₂] induces lateral metallation of one Me arm from the SiMe₃ group in the iron amide furnishing tetrameric [NaFe{N(SiCH₂Me₂)Dipp}{N(SiMe₃)Dipp}]₄ ( 2 ). Reactivity studies support that this deprotonation is driven by the steric incompatibility of the single metal amides rather than the basic capability of the sodium reagent. Displaying synergistic reactivity, heteroleptic sodium ferrate 1 can selectively promote ferration of pentafluorobenzene using one of its HMDS arms to give heterotrileptic [Na{N(SiMe₃)Dipp}(HMDS)Fe(C₆F₅)]_∞ ( 4 ). Attempts to deprotonate less activated pyridine led to the isolation of NaHMDS and heteroleptic Fe(II) amide [(py)Fe{N(SiMe₃)Dipp}(HMDS)] ( 5 ), resulting from an alternative redistribution process which is favoured by the Lewis donor ability of this substrate.