Kinetics and Mechanism of Styrene Epoxidation by Chlorite: Role of Chlorine Dioxide

An investigation of the kinetics and mechanism for epoxidation of styrene and <i>para-</i>substituted styrenes by chlorite at 25 °C in the pH range of 5–6 is described. The proposed mechanism in water and water/acetonitrile includes seven oxidation states of chlorine (−I, 0, I, II, III, IV, and V) to account for the observed kinetics and product distributions. The model provides an unusually detailed quantitative mechanism for the complex reactions that occur in mixtures of chlorine species and organic substrates, particularly when the strong oxidant chlorite is employed. Kinetic control of the reaction is achieved by the addition of chlorine dioxide to the reaction mixture, thereby eliminating a substantial induction period observed when chlorite is used alone. The epoxidation agent is identified as chlorine dioxide, which is continually formed by the reaction of chlorite with hypochlorous acid that results from ClO produced by the epoxidation reaction. The overall stoichiometry is the result of two competing chain reactions in which the reactive intermediate ClO reacts with either chlorine dioxide or chlorite ion to produce hypochlorous acid and chlorate or chloride, respectively. At high chlorite ion concentrations, HOCl is rapidly eliminated by reaction with chlorite, minimizing side reactions between HOCl and Cl₂ with the starting material. Epoxide selectivity (>90% under optimal conditions) is accurately predicted by the kinetic model. The model rate constant for direct reaction of styrene with ClO₂(aq) to produce epoxide is (1.16 ± 0.07) × 10^–2 M^–1 s^–1 for 60:40 water/acetonitrile with 0.20 M acetate buffer. Rate constants for <i>para</i> substituted styrenes (R = −SO₃^–, −OMe, −Me, −Cl, −H, and −NO₂) with ClO₂ were determined. The results support the radical addition/elimination mechanism originally proposed by Kolar and Lindgren to account for the formation of styrene oxide in the reaction of styrene with chlorine dioxide

Percent frequency of occurrence of directional shifts in distribution among larval taxa by seasonal occurrence in the Northeast U.S. Shelf Ecosystem.

<p>Occurrence of each type of distributional shift for larvae were grouped by season to examine patterns in relation to seasonal occurrence.</p

Change in distribution of larval <i>Gadus morhua</i> (Atlantic Cod) in the Northeast U.S. Shelf Ecosystem.

<p>Locations of strata with significant differences in annual relative proportions of larval <i>Gadus morhua</i> between 1977–1987 and 1999–2008 in January—February (A), March—April (B), and May—June (C), were used to examine directional shifts. Linear regressions of the Kruskal-Wallis chi-square (Chi H) for each stratum were tested for each direction: along-shelf (C), cross-shelf (D), and depth (E) to determine if slopes were significantly different than zero, and classify the significant directional shifts. Larval <i>Gadus morhua</i> shifted significantly northward and deeper.</p

Relationship between directional shifts in distribution of larvae and adults in the Northeast U.S. Shelf Ecosystem.

<p>Slopes of the linear regressions of the Kruskal-Wallis H values were used for each the 27 taxa where both life stages were examined in the along-shelf (A), cross-shelf (B), and depth (C) directions. Adults from the spring and fall trawl surveys were compared separately to larvae, and the slope of each regression line was tested to determine whether it was significantly different from zero, indicating the metrics of larval change and adult change were significantly related. * 0.025 < p ≤ 0.05, ** 0.001 < p ≤ 0.025, *** p ≤ 0.001.</p

<i>A priori</i> expectations and results for change in spatial distribution and seasonal occurrence of larval fish in the Northeast U.S. Shelf Ecosystem.

<p>Based on recent meta-analyses [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137382#pone.0137382.ref034" target="_blank">34</a>], studies from other regions [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137382#pone.0137382.ref021" target="_blank">21</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137382#pone.0137382.ref022" target="_blank">22</a>] and studies in the Northeast U.S. Shelf Ecosystem [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137382#pone.0137382.ref004" target="_blank">4</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137382#pone.0137382.ref032" target="_blank">32</a>], we developed several <i>a priori</i> expectations.</p

Long-Term Changes in the Distributions of Larval and Adult Fish in the Northeast U.S. Shelf Ecosystem

<div><p>Many studies have documented long-term changes in adult marine fish distributions and linked these changes to climate change and multi-decadal climate variability. Most marine fish, however, have complex life histories with morphologically distinct stages, which use different habitats. Shifts in distribution of one stage may affect the connectivity between life stages and thereby impact population processes including spawning and recruitment. Specifically, many marine fish species have a planktonic larval stage, which lasts from weeks to months. We compared the spatial distribution and seasonal occurrence of larval fish in the Northeast U.S. Shelf Ecosystem to test whether spatial and temporal distributions changed between two decades. Two large-scale ichthyoplankton programs sampled using similar methods and spatial domain each decade. Adult distributions from a long-term bottom trawl survey over the same time period and spatial area were also analyzed using the same analytical framework to compare changes in larval and adult distributions between the two decades. Changes in spatial distribution of larvae occurred for 43% of taxa, with shifts predominately northward (i.e., along-shelf). Timing of larval occurrence shifted for 49% of the larval taxa, with shifts evenly split between occurring earlier and later in the season. Where both larvae and adults of the same species were analyzed, 48% exhibited different shifts between larval and adult stages. Overall, these results demonstrate that larval fish distributions are changing in the ecosystem. The spatial changes are largely consistent with expectations from a changing climate. The temporal changes are more complex, indicating we need a better understanding of reproductive timing of fishes in the ecosystem. These changes may impact population productivity through changes in life history connectivity and recruitment, and add to the accumulating evidence for changes in the Northeast U.S. Shelf Ecosystem with potential to impact fisheries and other ecosystem services.</p></div

Correlation results among methods used to examine change in distribution of adult fish in the Northeast U.S. Shelf Ecosystem.

<p>Methods used to examine change in along-shelf distribution of mature adult fishes were correlated for spring to fall as measured in this study (A), spring from this study to Nye et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137382#pone.0137382.ref004" target="_blank">4</a>] (B), spring from this study to Pinsky and Fogarty [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137382#pone.0137382.ref049" target="_blank">49</a>] (C), and fall from this study to Pinsky and Fogarty [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137382#pone.0137382.ref049" target="_blank">49</a>] (D). Our analyses produced a linear slope based on a spatially explicit change statistic. Nye et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137382#pone.0137382.ref004" target="_blank">4</a>] calculated a linear slope from the annual change in the center of biomass in an along-shelf direction for the spring survey. Pinsky and Fogarty [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137382#pone.0137382.ref049" target="_blank">49</a>] calculated a linear slope for the annual change in the center of biomass in a north-south direction averaged across the spring and fall surveys.</p

Percent frequency of occurrence of directional shifts in distribution among taxa by life-stage and habitat type in the Northeast U.S. Shelf Ecosystem.

<p>Occurrence of each type of distributional shift among taxa of larvae (A) and spring- (B) and fall-collected adults (C) were grouped based on adult use of the demersal and pelagic habitat to examine patterns in relation to habitat type.</p

Change in spatial distribution and seasonal occurrence of larval fish in the Northeast U.S. Shelf Ecosystem.

<p>Distribution in the annual relative proportions among strata between 1977–1987 and 1999–2008 and among bimonthly season of larval fish was tested using Kruskal-Wallis chi-square. By examining changes in slopes using linear analyses, distributional changes were analyzed in: the along-shelf, the cross-shelf, and the depth directions. Distributional shifts were then classified into the categories: no significant change (blank), southward shift (South), northward shift (North), inshore shift (In), offshore shift (Off), shallower (Shallow), and deeper (Deep). Seasonal changes were examined for the three highest ranked bi-monthly seasons based on annual relative proportion. The resulting change was classified as no significant change (blank), earlier (E), or later (L). Spatial and seasonal shifts were examined relative to regional occurrence (M—GB = Mid-Atlantic Bight to Georges Bank, S—GOM = Southern New England to Gulf of Maine, and GB—GOM = Georges Bank to Gulf of Maine), timing of larval occurrence (W = winter, Sp = spring, Su = summer, and F = fall), management status (M = managed, N = not managed), and habitat type (D = demersal, P = pelagic).</p

Percent frequency of occurrence of directional shifts in distribution among taxa by life-stage and management status in the Northeast U.S. Shelf Ecosystem.

<p>Occurrence of each type of distributional shift among taxa of larvae (A) and spring- (B) and fall-collected adults (C) were grouped as managed and not managed to examine patterns in relation to management status.</p