Antimony pentachloride, initiation

With gallium chloride, ferric chloride and antimony pentachloride the rate coefficients were dependent upon the concentration of chlorobenzene and the square of the concentration of the catalyst, but the third-order coefficients varied with the initial concentration of the catalyst (Table 103)394. The overall kinetic equation was, therefore,... 

The polymerization of 1,3,3-trimethyl-2,7-dioxabicyclo[2.2.1 Jheptane 35 was carried out in methylene chloride, toluene, and 1-nitropropane at temperatures between —78 and 0 °C32l Boron trifluoride etherate, triethyloxonium tetrafluoro-borate, antimony pentachloride, and iodine were used as initiators. Irrespective of the solvents and initiators employed, the products obtained at 0 °C were white powders with melting points of 50—55 °C, while those obtained at tower temperatures were sirups. The number average molecular weight of the unfractionated products ranged from 400 to 600. The molecular weight distribution of the oligomers prepared at 0 °C was broad, in contrast to the relatively narrow distribution of those obtained at -40 °C. 

Hydrocarbons undergo related reaction.s in the super-acid media, such as fluorosuiphuric acid and antimony pentachloride. It has been suggested that the initial one-electron processes during the electrochemical oxidation of alkanes in fluorosuiphuric acid involve a protonated carbon-hydrogen bond with formation of a carbon radical and release of two protons [15]. 

THF can be polymerized only with cationic initiators, for example, boron trifluoride or antimony pentachloride. The initial step consists of the formation of a cyclic oxonium ion one of two activated methylene groups in the a-position to the oxonium ion is then attacked by a monomer molecule in an S 2-reaction, resulting in the opening of the ring. Further chain growth proceeds again via tertiary oxonium ions and not, as formerly assumed, via free carbonium ions ... 

Several catalysts and initiator systems have been tested for the polymerization of GlcAnBzl3, including the following Lewis acids boron trifluoride and its etherate, phosphorus pentafluoride, titanium tetrachloride, and antimony pentachloride and pentafluoride. Several cationic initiators have also been used, including (triphenylmethyl) antimony hexachloride, 2,3,4,6-tetra-O-acetyl-D-glucopyranosyl hexa-fluorophosphate, acetyl hexafluorophosphate, pentamethylbenzyl hexa-fluorophosphate (most of which were generated in situ), and triethyl-... 

Lyudvig, Rozenberg et al. (41) have also considered the kinetics of polymerization of THF initiated by antimony pentachloride. Their rate curves are clearly S-shaped (Fig. 17). This is similar to the results obtained in the triethyl aluminum system (Fig. 13) and in the PF5 case (Fig. 16). 

The initiation of tetrahydrofuran polymerization by direct addition of oxonium salts is of interest because it reveals a good deal about the mechanism, but for practical purposes the salts may be formed in the reaction mixture. The obvious method is, of course, to add a little epichlorohydrin to the mixture of monomer and Friedel Crafts reagent for only antimony pentachloride is sufficiently active to start the reaction with monomer alone, but other reactions which accomplish the same purpose are ... 

The chlorination of adamantane by either antimony pentachloride or ferric chloride in carbon tetrachloride gives low (approximately 4) initial tertiary secondary product ratios. Attention was called to the similarity of these ratios to those of known radical processes 36°). 

Compared with 49, 2,5-dioxabicyclo[2.2.2]octan-3-one (54) prepared from sodium 3,4-dihydro-2//-pyran-2-carboxylate has a much low polymerization reactivity [54] Lewis acids such as antimony pentachloride, phosphorus pentafluoride, and boron trifluoride etherate were not effective at all to initiate the polymerization of 54. Trifluoromethanesulfonic acid induced the polymerization of 54, but the yield and molecular weight of the polymer were low. Bicyclic lactone 54 was allowed to polymerize with anionic and coordination initiators such as butyl-lithium, lithiumbenzophenone ketyl, and tetraisopropyl titanate. However, the... 

Colour Tests. Antimony Pentachloride—brown Liebermann s Test-—black Naphthol-Sulphuric Acid—green, yellow dichroism/orange Sulphuric Acid—no initial colour (yellow-green fluorescence under ultraviolet light). 

As we have already mentioned, it was Kennedy who proposed that monomers possessing an allylic hydrogen can be converted into the corresponding allylic cart nium ions through a hydride-ion abstraction promoted by Levns acids. This reaction would not require a cocatalyst and could therefore explain in principle the occurrence of direct initiation. A similar mechanism had previously been claimed by Holmes and Pettit to rationalise the formation of carbenium ions from certain hydrocarbons and antimony pentachloride, e.g. ... 

Two further tests for heptachlor involve addition to the sterically hindered double bond. Normally, chlorine does not add to heptachlor unless an initiator, such as antimony pentachloride, is present. Heptachlor is resistant to epoxidation by peracids but both addition and epoxidation can readily be achieved chemically by tert-BuOCl/HOAc and CrOa oxidation, respectively (Table II). For the addition of teri-BuOCl to pro-... 

Initiation of polyalkene cyclization by an acid chloride and termination by an alkenylsilane have been combined in a synthesis of an octahydronaphthalene as part of studies towaids the synthesis of dihydro-compactin, where the silane can be viewed as controlling the Friedel-Crafts acylation of the disubstituted double bond (equation 10). In this case, antimony pentachloride gave superior yields compared to a wide variety of commonly used Lewis acid catalysts. 

The way in which Lewis acids oxidize aromatic compounds is not known clearly. Aromatics which are not easily oxidized, such as benzene, alkylbenzenes, naphthalene, and which give colored solutions as noted above, undoubtedly form charge-transfer complexes with the Lewis acid (see p. 175). Aromatics which are oxidized easily undergo complete electron transfer and form the cation radical, but the final state of the electron acceptor is not too-well known. A Lewis-acid anion radical has never been detected in these systems. Although the initial reaction in oxidations by antimony pentachloride has been represented as in eqn (12), it is not... 

On treatment in carbon tetrachloride with antimony pentachloride, tri-0-acetyl-/3-D-xylopyranosyl chloride (69), tetra-0-acetyl-/3-D-xylo-pyranose (70), and tri-O-acetyl-a-D-xylopyranosyl chloride (71) give an acetoxonium salt that precipitates directly from the solution. This salt consists of a mixture of the D-xylo, B-lyxo, and D-arabino derivatives (72, 73, and 74, respectively). None of these three compounds crystallize out preferentially. Evidently, the D-xylo derivative 72 is formed initially, and is then transformed by reversible acyloxonium rearrangements into 73 and 74. Salts are not isolated when the reaction is conducted in dichloromethane, because of their high solubility in this solvent. 

The effect of solvent on monomer reactivity ratios cannot be considered independent of the counterion employed. Again, the situation is difficult to predict with some comonomer systems showing altered r values for different initiators and others showing no effects. Thus the isobutylene-p-chlorostyrene system (Table 6-10) shows different ri and r-i for AlBrs and SnCU. The interdependence of the effects of solvent and counterion are shown in Table 6-11 for the copolymerization of styrene and p-methylstyrene. The initiators are listed in order of their strength as measured by their effectiveness in homopolymeiization studies. Antimony pentachloride is the strongest initiator and iodine the weakest. The order is that based on the relative concentrations of different types of propagating centers. 

The polymerization of propiolactone in methylene chloride with an antimony pentachloride-dieth te catalyst was investigated. The results show that the concentration of the active centers is dependent upon catalyst concentration and upon the initial concentration of the monomer. They also support the concept that opening of the lactone rings includes initial formation of oxonium ions ... 

Pyrimidine bases can be less reactive than purines in these processes, but the tri-O-acetyl-D-galactal-derived compounds 51 have been obtained (a, 40% (3, 24%) by use of bis-0-(trimethylsilyl)uracil in ethyl acetate with antimony pentachloride as catalyst, the -anomer being required for the synthesis of an antibiotic [83]. Although trace proportions of 3-substituted glycals are present in the products of this reaction, their formation from the initial 2,3-unsaturated compounds is apparently less easy than is the case with the purine analogues. 

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