The fractal dimension of a macromolecular coil is used for the characterization of a polymeric melt structure. It is shown that the kinetics of oxygen consumption is defined by both the chemical constitution of a polymer and its structure. The quantitative analysis of the kinetical curves of the oxygen consumption in the thermooxidative degradation process was carried out in the framework of the fractal approach. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2378–2381, 2003

At T ≥ 200 • C, in the presence of K 2 CO 3 as a catalyst, an original etherification procedure of non-toxic acetals such as glycerol formal (GlyF) and solketal has been investigated by using dialkyl carbonates as safe alkylating agents. The effects of parameters including the temperature, the reaction time, and the loading of both the catalyst and the dialkyl carbonate have been detailed for the model case of dimethyl carbonate (DMC). Both GlyF and solketal were efficiently alkylated by DMC to produce the corresponding O-methyl ethers with selectivity up to 99% and excellent yields (86-99%, by GC). The high selectivity could be accounted for by a mechanistic study involving a combined sequence of methylation, carboxymethylation, decarboxylation and hydrolysis processes. The O-methylation of GlyF and solketal could be successfully scaled up for multigram synthesis even operating with a moderate excess (5 molar equiv.) of DMC and in the absence of additional solvent. Notwithstanding the advantageous reduction of the process mass index, scale up experiments provided evidence that prolonged reaction times may induce the decomposition of DMC mainly by the loss of CO 2 . The K 2 CO 3 -catalyzed etherification of solketal with other carbonates such as dibenzyl and diethyl carbonate (DBnC and DEC, respectively), proceeded with the same good selectivity observed for DMC. However, at 220 • C, the solketal conversion did not exceed 81% since both DBnC and DEC were extensively consumed in competitive decarboxylation and hydrolysis reactions.

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At T≥ 140 °C, different primary aromatic amines (pX-C(6)H(4)NH(2); X = H, OCH(3), CH(3), Cl) react with both ethylene- and propylene-carbonates to yield a chemoselective N-alkylation process: bis-N-(2-hydroxyalkyl)anilines [pX-C(6)H(4)N(CH(2)CH(R)OH)(2); R = H, CH(3)] are the major products and the competitive formation of carbamates is substantially ruled out. At 140 °C, under solventless conditions, the model reaction of aniline with ethylene carbonate goes to completion by simply mixing stoichiometric amounts of the reagents. However, a class of phosphonium ionic liquids (PILs) such as tetraalkylphosphonium halides and tosylates turn out to be active organocatalysts for both aniline and other primary aromatic amines. A kinetic analysis monitored by (13)C NMR spectroscopy, shows that bromide exchanged PILs are the most efficient systems, able to impart a more than 8-fold acceleration to the reaction. The reactions of propylene carbonate take place at a higher temperature than those of ethylene carbonate, and only in the presence of PIL catalysts. A mechanism based on the Lewis acidity of tetraalkylphosphonium cations and the nucleophilicity of halide anions has been proposed to account for both the reaction chemoselectivity and the function of the catalysts.

At 165-200 uC, in the presence of sodium-exchanged faujasites (NaX or NaY) as catalysts, the reaction of dimethyl carbonate with benzyl-, o-and p-methoxybenzyl-, p-hydroxybenzyl-, diphenylmethyl-, and triphenylmethyl-alcohols (1a, 2a,b, 3a, 4a, and 4c, respectively), produces the corresponding methyl ethers in up to 98% yields. A peculiar chemoselectivity is observed for hydroxybenzyl alcohols (compounds 3a and 3b, para-and ortho-isomers) whose etherification takes place without affecting the OH aromatic groups. Acid-base interactions of alcohols and DMC over the faujasite surface offer a plausible explanation for the catalytic effect of zeolites NaY and NaX, as well as for the trend of reactivity shown by the different alcohols (primary . secondary . tertiary). However, in the case of substrates with mobile protons in the b-position (i.e. 1-phenylethanol and 1,1-diphenylethanol), the dehydration reaction to olefins is the major, if not the exclusive, process.

At 140• C, in the presence of alkali metal exchanged faujasites, preferably NaY, as catalysts, glycerine carbonate (GlyC) is an efficient and green alkylating agent of primary aromatic amines (p-XC 6 H 4 NH 2 , X = H, OMe, OH, Cl): the reaction takes place with a high conversion (~90%) and a good selectivity (80-90%) for the formation of N- (2,3-dihydroxy)propyl anilines (p-XC 6 H 4 NHCH 2 CH(OH)CH 2 OH). The alkylation process does not proceed through an exclusive nucleophilic substitution of anilines at the C5 position of GlyC. Evidence proves that a dehydrative condensation of anilines with GlyC produces intermediate species, and both transesterification and hydrolysis reactions are involved to obtain the final N-alkyl derivatives. A mechanism is proposed accordingly. Experiments show that faujasites are recyclable catalysts on condition that they are exposed to a mild thermal activation (70 • C, 18 mbar) prior to their re-use.Otherwise, if zeolites are calcined (400 • C, air), both the catalyst activity and the reaction selectivity drop. Isolated yields (60-65%) of N- (2,3-dihydroxy)propyl anilines are somewhat limited by the difficult separation of the unreacted GlyC and of the by-product glycerine. Nonetheless, the overall efficiency of the method is comparable to that of alternative routes based on highly toxic reagents (glycidol and aryl halides).

The anionic and the cationic partners of ionic liquids may act cooperatively and independently as nucleophilic and electrophilic catalysts. This ambiphilic propensity was demonstrated by kinetically discriminating the contributions of the anion (nucleophilic catalyst) and of the cation (electrophilic catalyst) to the solvent-free Baylis-Hillman dimerization of cyclohexenone catalysed by ionic liquids.

Anilines (R¢C 6 H 4 NH 2 : R¢ = H, p- MeO, ) react with a mixture of ethylene carbonate and methanol at 180• C in the presence of alkali metal exchanged faujasites-preferably of the X-type-to give the corresponding N,N-dimethyl derivatives (R¢C 6 H 4 NMe 2 ) in isolated yields up to 98%. Evidence proves that methanol is not the methylating agent. The reaction instead takes place through two sequential transformations, both catalyzed by faujasites: first transesterification of ethylene carbonate with MeOH to yield dimethyl carbonate, followed by the selective N-methylation of anilines by dimethyl carbonate. Propylene carbonate, is less reactive than ethylene carbonate, but it can be used under the same conditions. The overall process is highly chemoselective since the competitive reactions between the anilines and the cyclic carbonates is efficiently ruled out. Ethanol and propanol form the corresponding diethyl-and dipropyl-carbonates in the first step, but these compounds are not successful for the domino alkylation of anilines.