3238-38-8Relevant academic research and scientific papers
Hyperbranched copolymers versus linear copolymers: A comparative study of thermal properties
Behera, Girish Ch.,Saha, Animesh,Ramakrishnan
, p. 7695 - 7701 (2008/02/02)
Copolymerization of two AB2-type monomers that incorporate spacer segments of similar lengths but different flexibility permitted, for the first time, the preparation of a range of hyperbranched copolymers, wherein the backbone rigidity was varied while maintaining similar branching densities. The copolymers were prepared via a recently developed melt transetherification methodology to yield moderately high molecular weight polymers, with molecular weights ranging from 20 000 to 50 000. 1H NMR spectroscopic studies revealed that the composition of the copolymers varied linearly with monomer composition, confirming the formation of truly random copolymers. Analogous linear copolymers based on suitably designed AB-type monomers, containing the same two spacers, were also prepared for comparison. Thermal analysis of these copolymers using DSC indicated that the Tg's of both linear copolymers and hyperbranched copolymers varied with composition in a manner that was in complete accordance with the Fox equation, although all the linear copolymers exhibited significantly higher Tg values than their hyperbranched counterparts. It is interesting that, despite their very different topology and the presence of large number of chain ends, hyperbranched copolymers exhibit a similar Tg variation as their linear analogues. The generality of this observation in the broader context of hyperbranched copolymers, such as those possessing different branching densities and terminal functionalities, remains to be tested.
Orthoalkylation catalyst for phenol and process for producing orthoalkylated phenol with use thereof
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Page/Page column 7-10, (2008/06/13)
The orthoalkylation catalyst for phenols of the invention is one produced by calcining a catalyst precursor comprising basic magnesium carbonate (a) and magnesium oxide (b) optionally together with manganese oxalate (c), the basic magnesium carbonate (a) and magnesium oxide (b) being mixed together at a weight ratio ((a)/(b)) of 20/80 to 80/20. The process for producing an orthoalkylated phenol according to the invention comprises performing a vapor phase reaction of a phenol with an alkyl alcohol in the presence of the above orthoalkylation catalyst so that an orthoalkylated phenol is obtained.The invention enables obtaining an orthoalkylation catalyst for phenols which has high activity and high selectivity, has long catalytic life and exhibits more stable catalytic life than those of conventional orthoalkylation catalysts for phenols. Moreover, by virtue of the use of the catalyst capable of exerting these effects, there can be obtained a process for producing an orthoalkylated phenol which ensures prolonged and constant catalyst regeneration cycle.
Ortho-alkylation of phenol with methanol using Pb-Cr promoted magnesium oxide catalysts
Ke, Jyh-Harng,Zena, Jyh-Myng,Wang, Fey-Long
, p. 1407 - 1410 (2007/10/03)
In this study, Pb-Cr promoted magnesium oxide catalysts were used to catalyze the ortho-alkylation of phenol in the presence of excess methanol. The Cr/MgO catalyst exhibited a high conversion of phenol and a relatively high selectivity for the ortho-alkylation of phenol. The catalytic activity and the stability of Cr/MgO were improved by the addition of a fairly small amount of Pb. The Pb-Cr/MgO catalyst showed specificity for the ortho-alkylation of phenol, which was proved by a series of phenol derivative reactions with methanol.
Synthesis of polyalkylphenyl prop-2-ynoates and their flash vacuum pyrolysis to polyalkylcyclohepta[b]furan-2(2H)-ones
Nagel, Matthias,Hansen, Hans-Juergen
, p. 1022 - 1048 (2007/10/03)
A new method for the smooth and highly efficient preparation of polyalkylated aryl propiolates has been developed. It is based on the formation of the corresponding aryl carbonochloridates (cf Scheme 1 and Table 1) that react with sodium (or lithium) propiolate in THF at 25-65°, with intermediate generation of the mixed anhydrides of the arylcarbonic acids and prop-2-ynoic acid, which then decompose almost quantitatively into CO2 and the aryl propiolates (cf. Scheme 11). This procedure is superior to the transformation of propynoic acid into its difficult-to-handle acid chloride, which is then reacted with sodium (or lithium) arenolates. A number of the polyalkylated aryl propiolates were subjected to flash vacuum pyrolysis (FVP) at 600-650°and 10-2 Torr which led to the formation of the corresponding cyclohepta[b]furan-2(2H)-ones in average yields of 25-45% (cf. Scheme 14). It has further been found in pilot experiments that the polyalkylated cyclohepta[b]furan-2(2H)-ones react with 1-(pyrrolidin-1-yl)cyclohexene in toluene at 120-130°to yield the corresponding 1,2,3,4- tetrahydrobenz[a]azulenes, which become, with the growing number of Me groups at the seven-membered ring, more and more sensitive to oxidative destruction by air (cf. Scheme 15).
The Baeyer-Villiger Oxidation of Aromatic Aldehydes and Ketones with Hydrogen Peroxide Catalyzed by Selenium Compounds
Syper, Ludwik
, p. 167 - 172 (2007/10/02)
A series of organoselenium compounds was investigated as activators of hydrogen peroxide in the Baeyer-Villiger oxidation.As a result, a convenient and cheap method for transformation of aromatic aldehydes, having polycondensed ring systems or electron-donating substituents, and polymethoxy derivatives of acetophenone, into phenols was elaborated.This method utilizes hydrogen peroxide activated by areneseleninic acids, as oxidizing agent.
Thermal isomerizations of protonated bicyclohexenones
Childs, Ronald F.,George, Baha E.
, p. 1350 - 1354 (2007/10/02)
The thermal isomerizations of a wide range of protonated methyl substituted bicyclohex-3-en-2-ones to protonated phenols has been examined using triflic acid as a strong acid solvent.The rate constants and activation energies of these isomerization has been determined.The barriers to the isomerizations were shown to be dependent on the number and position of the methyl substituents.The results show that three different mechanisms are needed to account for these isomerizations, two of which involve a preliminary circumambulatory rearrangement prior to ring opening and the other process involving a direct ring opening of the initial protonated bicyclohexenone to give an intermediate meta-protonated phenol.
A quantitative examination of the photoisomerization of some protonated phenols
Childs, Ronald F.,George, Baha E.
, p. 1343 - 1349 (2007/10/02)
The photoisomerization of a series of protonated, methyl substituted phenols to protonated bicyclohexenones has been examined.These reactions, which were carried out in CF3SO3H as a strong acid solvent at ambient temperatures, provide a convenient route to a variety of bicyclohexenones.The quantum yields for these photoisomerizations vary from 0.018 for protonated 3,5-dimethylphenol to 0.65 for protonated 2,6-dimethylphenol.This variation in efficiency can be understood in terms of a competition between ring opening, to regenerate the starting phenol, or cyclopropyl migration, to give product, of aninitially formed intermediate.
The use of homogeneous and heterogeneous Lewis acids to catalyse the photoisomerizations of phenols
Chadda, Satish K.,Childs, Ronald F.
, p. 3449 - 3455 (2007/10/02)
The reaction of methyl substituted phenols with CH2Cl2 solutions of Al2Br6 leads to the formation of two types of complexes.In both of these the aluminum is bound to the oxygen atom of the phenol but they differ in that the OH proton can either remain on oxygen, oxonium complex, or migrate to one, usually the para, ring carbon, keto complex.The equilibrium position between the two types of complex depends on the position of the methyl groups.Irradiation of a complex of the keto type leads initially to the formation of a complexed bicyclohexenone and subsequently to the formation of an isomeric complexed phenol.Only in the case of the tetramethylphenols is the yield of the bicyclic ketone high enough to warrant the use of this photoisomerization as a preparative procedure, although the technique can be used to isomerize a range of phenols to their 4-substituted isomers.The photoisomerizations are not restricted to the use of a homogeneus Lewis acid such as Al2Br6 but heterogeneus aluminosilicates can also be used.The adsorption of 2,3,5,6-tetramethylphenol, 1h, on an aluminosilicate was monitored quantitatively and it was shown that a monolayer was formed in which the phenol was at least partially present in the keto form.Irradiation of 1h in the presence of stirred slurries of the aluminosilicate led to the formation of 2,3,4,6-tetramethylphenol.No bicyclic ketones were present in the contacting solution but traces were detected on the catalyst when the irradiations were carried out on adsorbed material in the absence of a solvent.In the case of heterogeneous acids, the selectivity in the adsorption of the starting phenol and the photoproducts is important in determining the composition of the final mixture.
Photochemical Transformationos of Protonated Phenols. A One-Step Synthesis of Umbellulone from Thymol
Baeckstroem, Peter,Jacobsson, Ulla,Koutek, Bohumir,Norin, Torbjoern
, p. 3728 - 3732 (2007/10/02)
UV irradiation of thymol (7) at 254 or 300 nm in trifluoromethanesulfonic acid affords ten products, eight of which have been isolated and characterized.Four competitive processes are suggested to be operating in the formation of the photoproducts: (i) regioselective type A rearrangement leading to umbellulone (8, about 10percent, (ii) formal C2->C3 migration by type A rearrangement and ring opening which affords the principal products, 3-isopropyl-5-methylphenol (12, 17percent), (iii) intermolecular transalkylation leading to diisopropylphenols 13-15 (17percent), and (iv) formation ofpiperitenone (10, 5percent) initiated by hydrogen abstraction.A mechanism for the formation of 10 is proposed.Both para- and ortho-protonated 7 are suggested to be involved in product formation.
QUANTITATIVE DESCRIPTION OF REACTIONS OF AROMATIC COMPOUNDS WITH ELECTROPHILIC AGENTS. I. ELECTROPHILIC HYDROXYLATION OF METHYLBENZENES
Koptyug, V. A.,Rogozhnikova, O. Yu.,Detsina, A. N.
, p. 1193 - 1203 (2007/10/02)
A scheme is proposed by means of which it is possible to assess the role of various reaction paths and the composition of the reaction products in terms of the theory of electrophilic hydroxylation of methylbenzenes by the initial addition of the electrophile at a ring carbon-carbon ? bond, controlled by charge and orbital factors, and the subsequent formation of isomeric ? complexes in ratios determined by their thermodynamic stability.
