ISSN:
0894-3230
Keywords:
Organic Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
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, k2, and activation parameters) and 1H (400 MHz) NMR results (monitoring of the reaction in DMSO-d6 and D2O) 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 1H NMR studies show significant aryl ring hydrogen-deuterium exchange in the hydroxide-DMSO-d6 and hydroxide-D2O systems examined, as well as a poly(ethylene glycol) alkoxide (PEG-O-) C-1 adduct in DMSO-d6; the PEG-O- is displaced in an SNAr 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 1H 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.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/poc.610081208
