Kinetics and mechanism of the reactions of polyallylamine with aryl acetates and aryl methyl carbonates

Abstract

The reactions of polyallylamine (PAA) with 4-nitrophenyl acetate (NPA), 2,4-dinitrophenyl acetate (DNPA), 2,4,6-trinitrophenyl acetate (TNPA), 4-nitrophenyl methyl carbonate (NPC), 2,4-dinitrophenyl methyl carbonate (DNPC) and 2,4,6-trinitrophenyl methyl carbonate (TNPC) at pH 7.0-11.5 were subjected to a kinetic investigation in aqueous solution at 25.0 C and an ionic strength of 0.1 M (KCl). Potentiometric titration curves were obtained at different polymer concentrations under the same conditions as for the kinetic measurements. The degree of dissociation () and pK app values for PAA at each pH were found from the titration curves. The shape of these curves shows a conformational change of the polymer at > 0.7. Similar behavior was observed through the dependence of logk N on either pH or , where k N is the second-order rate constant for the title reactions. The k N value is influenced by the electrostatic interactions in the polymer chain and the conformational changes that PAA undergoes in solution. The Brønsted-type plots (logk N vs pK app ) are linear with slopes ( values) of 0.5, 0.4, 0.5, 0.7, 0.6 and 0.7 for the reactions of PAA with NPA, DNPA, TNPA, NPC, DNPC and TNPC, respectively. These data are consistent with concerted mechanisms. The k N values increase in the sequence TNPA > DNPA > NPA and TNPC > DNPC > NPC. These results are in accordance with those found for the reactions with monomeric amines, which are due to the increasing nucleofugality of the leaving groups, and also the increasing electrophilic character of the carbonyl carbon, as more nitro groups are added to the substrate. Acetates are more reactive than the corresponding methyl carbonates, which can be explained by the larger electron-releasing effect exerted by MeO relative to Me. PAA destabilizes the putative tetrahedral intermediate relative to the monomeric amines and the stability of tetrahedral intermediates would decrease in the sequence pyridines > anilines > secondary alicyclic amines > quinuclidines > PAA. a In aqueous solution at 25 C, ionic strength 0.1 M (KCl). b Concentration of total amino groups (free base plus protonated forms). c 0.01 M phosphate buffer. d 0.01 M borate buffer. e 0.01 M carbonate buffer.

A non-damaging chemical amination protocol for poly(ethylene terephthalate) – application to the design of functionalized compliant vascular grafts

“…Such a drastic modication of the aminolysis reaction rate was already observed in solution. 44 The authors hypothesized a conformational change of the polyelectrolyte when the intramolecular electrostatic repulsions lessened. More signicantly, intermolecular repulsions between graed and free PVAm chains could have prevented the latter from reacting with the PET mat due to its surface charge.…”

Self-Healing Mussel-Inspired Multi-pH-Responsive Hydrogels

“…It is immediately clear from the data that their nanostructures, as probed by SAXS, are drastically different. The polyallylamine data could be described by a relatively simple worm-like-chain (WLC) model. − Above the pI value, polyallylamine undergoes a structural transition, which is also clearly seen in the data (see the Supporting Information for a detailed discussion (Figure S4)). The DOPA-functionalized polyallylamine, on the contrary, displayed a more complex behavior at all pH values that could not be described by a simple polymer model but (for pH below 9) by a polymer model with a large length scale fluctuation term added (see Supporting Information) as one has for polymer gels. , The SAXS curves change systematically from low to high pH with a clear change in the curve shape around the p K a value of polyallylamine with a further increase in intensity at low q due to an increase in large length scale fluctuations.…”

Enthalpy–Entropy Correlations in Reactions of Aryl Benzoates with Potassium Aryloxides in Dimethylformamide

“…One of the most common and important reactions in organic chemistry is that of aryl esters with nucleophiles. Acyl group transfer reactions have been studied by several groups, and there is now considerable data on the kinetics and mechanisms of those processes . Two distinct reaction mechanisms, concerted A N D N and stepwise addition‐elimination A N + D N , have been suggested.…”

“…Two distinct reaction mechanisms, concerted A N D N and stepwise addition‐elimination A N + D N , have been suggested. As a rule, the aminolysis reactions of aryl esters proceed through the addition‐elimination mechanism, in which the rate‐determining step (RDS) is dependent on the basicity of the entering amine and the leaving group . The evidence provided is a nonlinear Brønsted‐type plot that has often been observed for the reactions of esters with a good leaving group .…”