Methylene chloride terminal

CeUulose triacetate is insoluble in acetone, and other solvent systems are used for dry extmsion, such as chlorinated hydrocarbons (eg, methylene chloride), methyl acetate, acetic acid, dimethylformamide, and dimethyl sulfoxide. Methylene chloride containing 5—15% methanol or ethanol is most often employed. Concerns with the oral toxicity of methylene chloride have led to the recent termination of the only triacetate fiber preparation faciHty in the United States, although manufacture stiH exists elsewhere in the world (49). 

The terminal R groups can be aromatic or aliphatic. Typically, they are derivatives of monohydric phenoHc compounds including phenol and alkylated phenols, eg, /-butylphenol. In iaterfacial polymerization, bisphenol A and a monofunctional terminator are dissolved in aqueous caustic. Methylene chloride containing a phase-transfer catalyst is added. The two-phase system is stirred and phosgene is added. The bisphenol A salt reacts with the phosgene at the interface of the two solutions and the polymer "grows" into the methylene chloride. The sodium chloride by-product enters the aqueous phase. Chain length is controlled by the amount of monohydric terminator. The methylene chloride—polymer solution is separated from the aqueous brine-laden by-products. The facile separation of a pure polymer solution is the key to the interfacial process. The methylene chloride solvent is removed, and the polymer is isolated in the form of pellets, powder, or slurries. 

A number of reaction variables or parameters have been examined. Catalyst solutions should not be prepared and stored since the resting catalyst is not stable to long term storage. However, the catalyst solution must be aged prior to the addition of allylic alcohol or TBHP. Diethyl tartrate and diisopropyl tartrate are the ligands of choice for most allylic alcohols. TBHP and cumene hydroperoxide are the most commonly used terminal oxidant and are both extremely effective. Methylene chloride is the solvent of choice and Ti(i-OPr)4 is the titanium precatalyst of choice. Titanium (IV) t-butoxide is recommended for those reactions in which the product epoxide is particularly sensitive to ring opening from alkoxide nucleophiles. ... 

Two-dimensional thin-layer chromatography. This method is used to verify the presence of terminal 5-sultones, terminal unsaturated y-sultone, and terminal 2-chloro-y-sultone, if they are detected in the gas chromatographic determination. After extraction of the neutral oil from the AOS sample, the neutral oil is made up volumetrically to at least a 10% solution in hexane. Of this solution 3 pi is spotted onto a silica gel TLC plate together with standard sultones. It is twice developed with 2-propyl ether and then after turning the plate 90° twice developed with 60/40 n-butyl chloride/methylene chloride. The... 

Preparation of siloxane-carbonate segmented copolymers by interfacial polymerization involves the reaction of carboxypropyl-terminated siloxane oligomers with bisphenol-A and phosgene, in the presence of a strong base and a phase transfer catalyst, in water/methylene chloride solvent system l50 192), as shown in Reaction Scheme XIV. 

Where B = pyridine, piperidine or 1-methylimidazole, in methylene chloride solution, but under normal conditions rapid irreversible autoxidation takes place 232) leading to the formation of the well characterised 247, 248) fi-oxo product, (TPP)Fe(IlI)—0—Fe(III) (TPP) and since the rate of oxidation decreases 249, 250) with increasing excess of axial base, B, it follows 232, 251) that a five co-ordinate species, Fe(II) (Base)TPP, is probably involved as an intermediate which can then undergo a bimolecular termination reaction with Fe(II) (Base)02TPP, followed by autoxidation. Firstly 251),... 

A conveniently prepared amorphous silica-supported titanium catalyst exhibits activity similar to that of Ti-substituted zeolites in the epoxidation of terminal linear and bulky alkenes such as cyclohexene (22) <00CC855>. An unusual example of copper-catalyzed epoxidation has also been reported, in which olefins are treated with substoichiometric amounts of soluble Cu(II) compounds in methylene chloride, using MCPBA as a terminal oxidant. Yields are variable, but can be quite high. For example, cis-stilbene 24 was epoxidized in 90% yield. In this case, a mixture of cis- and /rans-epoxides was obtained, suggesting a step-wise radical mechanism <00TL1013>. 

Hydroxy-terminated polybutadiene (8) (HTPB) has been treated with dinitrogen pentoxide in methylene chloride. The product (9) is an energetic oligomer but is unlikely to find application because of the inherent instability of /3-nitronitrates." Initial peroxyacid epoxidation of some of the double bonds of HTPB followed by reaction with dinitrogen pentoxide yields a product containing vtc-dinitrate ester groups and this product (NHTPB) is of much more interest as an energetic binder (see Section 3.10)." ... 

In an analogous late-stage arylation approach, terminal alkyne 31 was envisioned as a versatile intermediate. Slow addition of 4-pentynoyl chloride to imine 3 and (n-Bu)3N at reflux (efficient condenser, 100°C, 12 h, 1 1 toluene heptane) afforded only trace amounts of 31. Reaction of 4-pentynoyl chloride with triethylamine in methylene chloride under preformed ketene conditions ( 78°C, 1 h), followed by addition of 3 and warming to — 10°C over 4 h, afforded a complex mixture of products. Since high-yield preparation of 31 remained elusive, access to internal alkynyl analogs (type 33) was accomplished by preassembly of the appropriate arylalkynyl acid substrate for the ketene-imine cycloaddition reaction (Scheme 13.9). 

To a heavy-walled flask equipped with a nitrogen inlet side arm was added resin-bound terminal acetylene (684.4 mg resin, 0.274 mmol, 0.448 mequiv/g resin) and aryl iodide (120.6 mg, 0.3011 mmol) (Scheme 11). The flask was evacuated and back-filled with nitrogen a minimum of three times. The supernatant of a separate 0.2 M catalyst cocktail solution (previously prepared) was added via cannula (5 mL, 3.0 mmol) to the reaction flask. The flask was kept sealed at 65°C for 12 h and agitated periodically to remix polymer beads stuck on flask walls. The beads were then transferred to a fritted filter using methylene chloride and washed with methylene chloride (21 mL). Excess aryl iodide can be recovered from the first methylene chloride wash. All further washes were carried out in the ratio of 30 mL/g resin. The resin was washed sequentially with DMF, 0.05 M solution of sodium diethyl dithiocarbamate in 99 1 DMF-diisopropylethylamine,... 

For N-vinylcarbazole in methylene chloride solutions cycloheptatrienyl ion has been shown to be a very efficient initiator, reacting by a rapid and direct addition to the olefin (82). A mechanistic scheme involving virtually instantaneous and quantitative initiation, rapid propagation (and transfer) and no true termination appears to operate, enabling rate constants for propagation kp, to be determined very simply from initial slopes of conversion/time curves. Under the experimental conditions used the initiators were almost totally dissociated and there seems every reason to suppose that the propagating cations are similarly dissociated (Section II.C.2). The derived rate constants therefore refer to the reactivity of free poly-(N-vinylcarbazole) cation, kp, and relevant data are summarised in Table 7. 

IODO-GEN (l,3,4,6-tetrachloro-3-6-diphenylglycouril) is a better reagent for the lodination of proteins than chloramine-T, is less damaging, and has fewer side reactions than the latter. The insolubility of IODO-GEN in water means that tubes can be precoated with the reagent dissolved in methylene chloride or chloroform. Then the tubes are stored in the dark until required. The reaction is started by adding the protein and radioiodide, and terminated by removing the sample from the reaction vessel. 

The allenes bearing four tert-butyl or four trimethylsilyl groups at the terminal carbons react in methylene chloride with antimony pentachloride. The cation radicals formed contain an unpaired electron delocalized along the neighbouring -rr-bonds. The conclusion is based on the analysis of 1H, 13C, and 29Si ESR spectra (Bolze et al. 1982) as well as on photoelectron spectra (Elsevier et al. 1985 Kamphius et al. 1986). These data have found corroboration in a recent study (Werst Trifunac 1991). The tetramethylallene cation radical spectrum was observed by fluorescent-detected magnetic resonance. The well-resolved multiplet due to this cation radical consists of a binomial 13-line pattern owing to 12 equivalent methyl protons. This is in full accord with Scheme 3-60. 

Denmark has developed a practical dioxirane-mediated protocol for the catalytic epoxidation of alkenes, which uses Oxone as a terminal oxidant. The olefins studied were epoxidized in 83-96% yield. Of the many reaction parameters examined in this biphasic system, the most influential were found to be the reaction pH, the lipophilicity of the phase-transfer catalyst, and the counterion present. In general, optimal conditions feature 10 mol% of the catalyst l-dodecyl-l-methyl-4-oxopiperidinium triflate (30) and a pH 7.5-8.0 aqueous-methylene chloride biphasic solvent system [95JOC1391]. 

The introduction of acetylene, terminal alkynes or internal alkynes into methylene chloride solutions of iodosylbenzene and triflic acid [1 1, in situ generation of PhI(OH)OTf] results in the production of [j3-(trifluoromethanesulfonyloxy)vinyl]iodonium triflates (equation 172)78,133. Since the -configuration has been determined for selected members of this series (R1, R2 = n-Pr, H n-Bu, H), these reactions appear to proceed via stereoselective anti-additions of PhI(OH)OTf to the alkynes. 

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