First-order solvolysis rate constants are reported for solvolyses of acetyl chloride in methanol and MeOD, and in binary aqueous mixtures with acetone, acetonitrile, ethanol, methanol, and trifluoroethanol at 0 degrees C. Product selectivities (S = [MeCOOR]/[MeCOOH] x [water]/[alcohol]) are reported for solvolyses in ethanol/ and methanol/water at 0 degrees C. Solvolyses of acetyl chloride show a high sensitivity to changes in solvent ionizing power, consistent with C-Cl bond cleavage. As the solvent is varied from pure ethanol (or methanol) to water, S values and rate-rate profiles show no evidence for the change in reaction channel observed for solvolyses of benzoyl and trimethylacetyl chlorides. However, using rate ratios in 40% ethanol/water and 97% trifluoroethanol/water (solvents of similar ionizing power but different nucleophilicities) to compare sensitivities to nucleophilic attack, solvolyses of acetyl chloride are over 20-fold more sensitive to nucleophilic attack than benzoyl chloride. The solvent isotope effect of 1.29 (MeOH/MeOD) for acetyl chloride is similar to that for p-methoxybenzoyl chloride (1.22) and is lower than for benzoyl chloride (1.55). Second-order rate constants for aminolyses of acetyl chloride with m-nitroaniline in methanol at 0 degrees C show that acetyl chloride behaves similarly to p-methoxybenzoyl chloride, whereas benzoyl chloride is 40-fold more sensitive to the added amine. The results indicate mechanistic differences between solvolyses of acetyl and benzoyl chlorides, and an S(N)2 mechanism is proposed for solvolyses and aminolyses by m-nitroaniline of acetyl chloride (i.e. these reactions are probably not carbonyl additions, but a strong sensitivity to nucleophilic attack accounts for their high rates).
Poly(p-phenylene-cis-benzobisoxazole) (cis-PBO) articles such as fibers possess exceptional mechanical strengths and moduli as well as high thermal performance and chemical resistance. These properties are assumed to be the result of the "rodlike" shape of this polymer. The intrinsic viscosity dependence on molecular weight (Mark-Houwink relationship) and the dependence of radius of gyration Rg with the degree of polymerization in methanesulfonic acid (MSA) solutions, however, suggest considerable deviations from rodlike behavior. This behavior might be attributed either to aggregation or to a semistiff backbone. A polyelectrolyte semistiff chain model was in excellent agreement with the light scattering and viscometric experimental results. The apparent chain flexibility of cis-PBO in solution was attributed to a significant "kidney-bean" shape of the heterocycles induced by the protonation of the N-atoms. The uncharged chain on the other hand, appears to conform more closely than the chain in solution to the ideal rodlike model.
Methanesulfonic acid (MSA) is often employed as a solvent for high-performance polymers such as poly-(p-phenylene-cis-benzobisoxazole) or PBO, aramides, and conducting polymers. Since MSA is highly hygroscopic, and water has very strong effects on the physicochemical properties of the acid, it is important to develop methods to control and assess its composition. An approach involving the use of methanesulfonic anhydride (MSAA) is presented. The properties and compositions of MSAA solutions in MSA were investigated by combining NMR, conductimetry, viscometry, and differential refractometry. The results showed that previous studies involving MSA polymer solutions, and reported physical properties of MSA, were affected by water contamination. New values for the refractive index, viscosity, and specific conductivity of water-free MSA are presented.
A comparative study of the conductivity behavior of methane‐sulfonic acid solutions of poly(p‐phenylene‐cis‐benzobisoxazole) or cis‐PBO and other compounds, including CH3SO3Na (NaMSA), a cis‐PBO model compound, and 6,7‐dimethyl‐2,3‐di(2‐pyridyl) quinoxaline, a molecule containing four protonating sites, was carried out to determine the degree of protonation of PBO and its model compound. The conductivity dependence with increasing cis‐PBO concentration indicates that only two sites per repeat unit are protonated. © 1994 John Wiley & Sons, Inc.
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