Reaction profiles and substituent effects for the reduction of carbonyl compounds with monomer and dimer simple metal hydride reagents

Reaction profiles and energetics for the reactions of substituted benzaldehydes with a series of different simple metal hydrides (BH(3), BMeH(2), BMe(2)H, AlH(3), and AlMe(2)H) are examined computationally. B3LYP/6-31G optimizations and MP2/6-311G single point energy calculations revealed that the Al reagents are more reactive than B reagents. Replacement of H with Me on BH(3) or AlH(3) makes the reduction transition state (TS) less stable. Accordingly the overall reactivity is in the order AlH(3) > AlMe(2)H > BH(3) > BMe(2)H. The Hammett rho value for substituted benzaldehydes (BAs) is negative for the initial complex formation and positive for the hydride-transfer step. The size and the sign of the apparent rho value depend on the relative stabilities of the separated reactants and the complex. The TS structures vary according to the Hammond postulate for substituted BAs and the variation is reflected in carbonyl-carbon and aldehyde-deuterium isotope effects. Comparison of the reaction profiles of the monomer and dimer reagents reveals that the real reacting species is the monomer in the gas phase for BH(3) but the dimer for BMe(2)H.     

Preparation of copolyesters from diols and bisphenols by the solution polycondensation with TsCl/DMF/Py as a condensing agent

A novel synthetic method for the preparation of copolyesters comprised of diols and bisphenols using tosyl chloride (TsCl)/DMF/pyridine (Py) as a condensing agent has been developed. A variety of combinations of monomers could produce relatively high molecular weight copolymers, and better results were obtained by initial oligomerization of diols followed by bisphenols. In order to demonstrate usefulness of this method, copolymers comprised of IPA/TPA (50/50), bis(2‐hydroxyethyl)terephthalate (BHET),and several bisphenols were prepared and compared to the poly(ethylene terephthalate) (PET) modified by TPA and 2,2‐bis(4‐hydroxyphenyl)propane (BPA) diacetate in terms of their thermal properties. The length of mesogenic unit segments in the thermotropic IPA/TPA (50/50)‐BHET/ 4,4′‐dihydroxybenzophenone (4,4′‐DHBP) (50/50) copolymer was changed by initial reaction of BHET followed by dropwise addition of 4,4′‐DHBP in the two‐stage polycondensation and also by varying the amounts of BHET used at the initial and final stages in the three‐stage copolycondensation, and the results were studied by NMR and their thermal properties. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1270–1276, 2000     

Direct polyesterification with thionyl chloride in pyridine improved by a modification of monomer sequences in copolymers

The direct polyesterification with thionyl chloride (SOCl₂) in pyridine was further investigated. Copolycondensations of dicarboxylic acids, bisphenols, and hydroxybenzoic acids were significantly affected by the reaction temperatures and combinations of monomers which could change relative rates of alcoholyses of the activated dicarboxylic acids and the hydroxyacids consequently to vary monomer sequences in the copolymers resulted. The sequences were tried to be varied more directly by stepwise reactions of monomers in copolycondensations of dicarboxylic acids, bisphenols, and p-hydroxybenzoic acid (PHB), as well as PHB and m-hydroxybenzoic acid (MHB). The reactions proceeded smoothly and satisfactorily when carried out by initial reaction of dicarboxylic acids and PHB followed by bisphenols likely to favor sequential to random distributions of monomers. Reverse addition of PHB and bisphenols, and then dicarboxylic acids resulted in rapid precipitation due to some oligomerization of PHB at an earlier stage of reaction, and largely retarded the reaction. This was also the case for the copolycondensation of PHB and MHB. Copolymers of high inherent viscosities with up to 65 mol% PHB could be obtained by initial reaction of MHB followed by PHB.     

Polyamide synthesis by the direct polycondensation with phenylphosphonic dichloride in pyridine

The direct polycondensation of isophthalic acid (IPA) and aromatic diamines with a new phosphorus compound, phenylphosphonic dichloride (PPDC), was studied. PPDC could actually react with nearly a two molar amount of carboxyl groups, but more than 75 mol % PPDC with respect to the carboxyl groups of IPA were satisfactorily used in the polycondensation. The initial reaction of IPA with PPDC in pyridine at room temperature and then at 120°C was needed to complete the activation, and the subsequent aminolysis at 120°C for 3 h was most effective. The polyamides of high inherent viscosity were obtained even from weakly basic aromatic diamines, and their values were more than those obtained by the conventional method. In their thermal properties determined by the DTA, they showed T_gs and T_ms higher than those reported before.     

Propagation in the two-step solution copolycondensation with p-xylyleneglycol and bisphenols with the TsCl/DMF/Py condensing agent

A two-stage solution copolycondensation of IPA/TPA (50/50), ineffective aliphatic p-xylyleneglycol (PXG), and effective bisphenols (BPs) using tosyl chloride/dimethylformamide/pyridine condensing agent was studied by examining factors, such as, kinds of BPs, reaction temperature, and the order of addition of PXG and BPs. Better results were obtained by initial reaction of PXG followed by BPs at a lower temperature (80 °C). BPs, when reacted randomly with the preformed oligomers from PXG, gave better results. These results were discussed in terms of the reaction of the preformed oligomers with PXG or BPs by measuring the distributions of growing oligomers by GPC and of PXG or BPs in the copolymers by 1H NMR.     

Effect of association of dicarboxylic acids activated by TsCl/DMF/pyridine upon the copolycondensation with bisphenols

When a mixture of terephthalic acid (TPA) and various dicarboxylic acids was activated by tosyl chloride (TsCl)/dimethyl‐ formamide (DMF)/pyridine (Py), the resulting mixture became dissolved in Py, although the activated TPA was insoluble even at 120 °C. The temperature at which the mixture became soluble was varied with their compositions and the structure of diacids. Mixing the separately activated TPA and isophthalic acid (IPA) also improved the solubility of the activated TPA to some extent. The interesting phenomena were attributed to associations of the activated diacids through the dipole–dipole interactions between the carbonyl groups. The structures of associates were estimated in terms of transition temperatures of the thermotropic IPA/TPA‐methylhydroquinone and IPA/TPA‐chlorohydroquinone copolymers. The transition temperatures were significantly affected by the temperature of polycondensation, the preparative procedures of a mixture of the activated diacids, and several additives. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 196–201, 2001     

Promoted random orientation of the phenyl substituent of phenylhydroquinone–terephthalic acid polyesters prepared with a diphenyl chlorophosphate/pyridine condensing agent

The reaction of sterically hindered hydroxyl groups at the 2-position of methylhydroquinone and phenylhydroquinone (PhHQ) to form esters was largely promoted by their slow addition to benzoic acid activated by diphenyl chlorophosphate in pyridine. A modification of this reaction was applied to the preparation of thermotropic terephthalic acid/PhHQ and 2,5-dichloroterephthalic acid/PhHQ polymers with randomly oriented phenyl substituents, and the properties of the polymers were studied in terms of their transition temperatures, which were determined by differential scanning calorimetry and microscopic observation. The melting points were lowered by about 30–50 °C by the dropwise addition of PhHQ over 10–30 min. The molecular structures of the 2,5-dichloroterephthalic acid/PhHQ polymers were studied by ¹³C NMR. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1726–1732, 2001     

ESR study of radiation-induced polymerization of methyl methacrylate on solid surfaces

ESR spectra of methyl methacrylate (MMA) adsorbed on solid surfaces such as silica, alumina, and CPG-10 show a seven-line absorption due to monomer radicals when γ-irradiated at ?196°C. These spectra turn into conventional nine-line spectra by annealing at ?86°C as a result of polymerization. The intensity ratio of the four-line component to the five-line component changes with further polymerization. The ratio depends on the kind of solid and the smallest value is obtained in the spectra of alumina-MMA. The temperature of irradiation strongly affects the value in alumina-MMA. These results suggest that MMA is strongly adsorbed and deformed the conformation on alumina surface.