ACCELERATION OF O-IODOSOBENZOATE-CATALYZED HYDROLYSIS OF P-NITROPHENYL DIPHENYL PHOSPHATE BY CATIONIC POLYMER COLLOIDS

Authors
Citation
Jj. Lee et Wt. Ford, ACCELERATION OF O-IODOSOBENZOATE-CATALYZED HYDROLYSIS OF P-NITROPHENYL DIPHENYL PHOSPHATE BY CATIONIC POLYMER COLLOIDS, Journal of the American Chemical Society, 116(9), 1994, pp. 3753-3759
Citations number
60
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry
ISSN journal
0002-7863
Volume
116
Issue
9
Year of publication
1994
Pages
3753 - 3759
Database
ISI
SICI code
0002-7863(1994)116:9<3753:AOOHOP>2.0.ZU;2-O
Abstract
Cross-linked polystyrene latexes containing (styrylmethyl)trialkylammo nium chloride repeat units greatly accelerate the o-iodosobenzoate (IB A) catalyzed hydrolysis of p-nitrophenyl diphenyl phosphate (PNPDPP). The half-life of PNPDPP is as short as 3 s with 0.10 mg mL(-1) of part icles containing 24 mol % of (styrylmethyl)tributylammonium chloride r epeat units (TBAQ24) and 4 x 10(-5) M IBA in TAPS buffer at pH 9.1 and 25.0 degrees C, and the apparent second-order rate constant (k(IBA)) exceeds that in the absence of latexes by 6300 times, the largest rate enhancement reported for IBA-catalyzed hydrolysis of PNPDPP in any co lloidal or polymeric medium. The k(IBA) value increases with increasin g radius of the quaternary ammonium ion (trimethyl < triethyl < tripro pyl < tributyl) and with decreasing mole % of (styrylmethyl)trimethyla mmonium chloride (TMAQ) repeat units in the latexes. The amounts of IB A and chloride ions bound to latexes were measured directly by UV spec trophotometry and chloride-selective electrode analysis of ultrafiltra tes from dispersions, and ion exchange selectivity coefficients for IB A and TAPS anions relative to chloride were calculated. The sizes of w ater-swollen particles were measured by dynamic and static light scatt ering. Using an ion-exchange model, the second-order rate constants k( 2L) in the latex phase were estimated from observed rate constants, th e percent of IBA bound, and the particle volumes. The 6300 times rate enhancement in the TBAQ24 dispersion is due ten times to a higher intr aparticle rate constant and 630 times to higher local concentrations o f IBA and PNPDPP in the latex phase. With the most hydrophilic TMAQ la tex particles, the rate enhancements are due entirely to higher reacta nt concentrations in the particles. The intraparticle rate constants a t pH 9.1 and the ion exchange selectivity coefficients can be used to predict rate constants as functions of pH, amount of latex particles, and amount of added NaCl.