Premium
Kinetic and spectroscopic studies of the hydrolysis of bis (2,4‐dinitrophenyl ether)s of poly (ethylene glycol)
Author(s) -
Dust Julian M.,
Secord Mary D.
Publication year - 1995
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610081208
Subject(s) - chemistry , ethylene glycol , hydrolysis , ether , hydroxide , polymer chemistry , alkaline hydrolysis , context (archaeology) , alkoxide , aqueous solution , aryl , alkyl , organic chemistry , paleontology , biology , catalysis
Bis(2,4‐dinitrophenyl ether)s of the water‐soluble polymer poly(ethylene glycol) (PEG) are low‐loading models for time‐release herbicide systems and may potentially hydrolyse in basic aqueous media according to a mechanistic menu that includes elimination, aliphatic and/or aromatic displacement, as well as anchimerically assisted displacement involving O‐6 of the plyether backbone. This paper study reports kinetic (second‐order rate constnts, k 2 , and activation parameters) and 1 H (400 MHz) NMR results (monitoring of the reaction in DMSO‐ d 6 and D 2 O) for the alkaline hydrolysis of a series of these ethers (DNPEGs). DNPEGs with varying average molecular weights (MW) of the polymer backbone (DNPEG‐59, ‐1900 and ‐3200, where the numbers refer to the PEG MW) were studied, as were DNPEGs that differed only in the degree of end‐group substitution, namely DNPEG‐1900‐59 and ‐81 (where the final numbers refer to the percentage substitution). The 1 H NMR studies show significant aryl ring hydrogen–deuterium exchange in the hydroxide–DMSO‐ d 6 and hydroxide–D 2 O systems examined, as well as a poly(ethylene glycol) alkoxide (PEG‐O − ) C‐1 adduct in DMSO‐ d 6 ; the PEG‐O − is displaced in an S N Ar fashion from DNPEG as a result of initial hydroxide attack at C‐1 of DNPEG. The kinetic and spectroscopic results are discussed in the context of previous kinetic studies of alkaline hydrolysis of alkyl 2,4‐dinitrophenyl ethers, recent 1 H NMR spectroscopic studies of electron‐deficient aryl ethers and the mechanism of hydrolysis in the DNPEG systems. The possible significance of these results for the development of time‐release herbicide systems is cosidered briefly.