CEE 697K ENVIRONMENTAL REACTION KINETICS Lecture #2. Reactions with Chlorine

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1 9/4/3 Updated: 4 September 3 Print version CEE 697K ENVIRONMENTAL REACTION KINETICS Lecture # Rate Expressions: omide + Chlorine case study & lab project Kumar & Margerum paper Introduction Reactions with Chlorine The THMs C H The Precursors! HO + natural organics (NOM) C H C H Oxidized NOM and inorganic chloride Aldehydes Chlorinated Organics TOX THMs HAAs C H Chloroform omodichloromethane Chlorodibromomethane omoform

COOH H C COOH H C COOH Dichloroacetic omochloroacetic Dibromoacetic Acid Acid Acid

2 9/4/3 The Haloacetic Acids 3 C COOH C COOH C COOH C COOH Trichloroacetic omodichloroacetic Chlorodibromoacetic Tribromoacetic Acid Acid Acid Acid (TCAA) H C COOH H C COOH H C COOH Dichloroacetic omochloroacetic Dibromoacetic Acid Acid Acid (DCAA) Distribution: Variability within a single system 4 Example: New Haven Service Area DS model

7 MG Millroc Basins Maltby Tan 3 MG Lae Gaillard WTP Lae

3 9/4/3 New Haven Distribution System 5 Sept, 997 : chlorine 3,4 pipes,5 junctions West River WTP 8.7 MG Millroc Basins Maltby Tan 3 MG Lae Gaillard WTP Lae Saltonstall WTP. mg/l DOC (Treated) ph 7.8 mg/l chlorine dose 6 Sept, 997 : TTHM 3

9/4/3 7 Sept, 997 : HAA6 Genotoxicity 8 DBP Chemical ass Other DBPs Haloacetamides Haloacetonitriles Halonitromethanes Halo Acids Haloacetic Acids IAA BAA DBNM Dibromoacetonitrile Iodoacetamide

4 9/4/3 7 Sept, 997 : HAA6 Genotoxicity 8 DBP Chemical ass Other DBPs Haloacetamides Haloacetonitriles Halonitromethanes Halo Acids Haloacetic Acids IAA BAA DBNM Dibromoacetonitrile Iodoacetamide Iodoacetonitrile omoacetonitrile omoacetamide BDCNM TBNM 3,3-Dibromo-4-oxopentanoic Acid TCNM Wor of Michael Plewa BNM DBCNM BCNM Univ. of Illinois MX Tribromopyrrole omochloroacetonitrile 3,3-omochloro-4-oxopentanoic Acid DCNM CAA Chloroacetonitrile Dibromoacetamide Trichloroacetonitrile Chloroacetamide CNM Dichloroacetonitrile DBAA DIAA TBAA BIAA BCAA EMS +Control Trihloroacetamide omate -omobutenedioic Acid -Iodo-3-bromopropenoic Acid,3-Dibromopropenoic Acid CDBAA Single Cell Gel Electrophoresis Genotoxicity Potency Log Molar Concentration (4 h Exposure) Not Genotoxic: DCAA, TCAA, BDCAA, Dichloroacetamide, 3,3-Dibromopropenoic Acid, 3-Iodo-3-bromopropenoic Acid,,3,3,Tribromopropenoic Acid July 6 4

5 9/4/3 omide: THM Formation 9 8 CH 3 Data from: Minear & Bird, hours, ph 7. 5 mg/l Chlorine Dose mg/l Humic Acid Percent of TTHM 6 4 CH CH CH omide Concentration (mg/l) Impact of omide on DHAA Formation Concentration (g/l as - ) CH COOH CHCOOH ph 7, 5 o C, 7 days 5 mg/l chlorine dose.9 mg/l TOC CH COOH omide Concentration (mg/l) From Pourmoghaddas, 99 5

6 9/4/3 Formation of ominated THMs H HO HO HO A B C C D HO E HO H C H F HO C HO CEE 697K Lecture HO # H C omo speciation. Full-scale data (small symbols) from Weinberg et al., (All plants) THM Mole Fraction (THM4 only) Lab data (large symbols) from Hua & Rechow, 4 Lines are geometric model CH3 CH CH CH3 CH3 Lab tests CH Lab tests CH Lab tests CH3 Lab tests THM /(+) 6

7 9/4/3 Case study: chlorine + bromide 3 Observed reaction HO Nucleophilic attac of bromide on oxygen in hypochlorous acid =.95 x 3 M - s - at 5ºC Note that HO deprotonates at elevated phs From Faras et al., 949 Transfer of + to form intermediate () HA HO 3 A H O From Kumar & Margerum, 987 fast HO fast 3 Bacground 4 Absorbance for monitoring reaction Known equilibria 7

nm pea for hypochlorite (O - ) Followed for 4 half-lives Complete from:.

8 9/4/3 Alaline Experiments 5 Pseudo- st order omide in great excess Slow reactions Could be monitored directly by conventional UV spectrophotometer 9 nm pea for hypochlorite (O - ) Followed for 4 half-lives Complete from:. sec 4 hr Plot ln(a t -A ) vs time Slope is obs K obs is a linear function of omide 6 8

9 9/4/3 ph dependency 7 Overall ph dependence 8 How to explain ph effect on nd order rate constant? See also, ezoni, pg 3; figure 4-9

10 9/4/3 Buffer Tests 9 Low ph High ph Buffer Effect Proposed dependence on HA obs [ H C [ H ] [ H [ ] H C [ H ] C K [ H T T K T a [ H ] a HA ] HA 8.9.3M s HPO 4 - HCO 3 - ] ] obs [ [ H H HA [ buffer] Ka [ H T ] HA (.5.5) x M s

11 9/4/3 High ph only obs [ H ] [ H [ ] H HA d[ O dt More generally d[ ( I)] dt ] [ O ] [ HO] [ H[ O ] [ ] [ H ] [ H [ O ][ ] H HO HA HA Acidic Experiments Pseudo- st order omide in great excess Fast reactions Required high-speed setup Stopped-flow spectrophotometer Could monitor º product 66 nm pea for tribromide ( 3- ) Followed for 4 half-lives Complete from.4-. sec Plot ln(a t -A ) vs time Slope is obs

12 9/4/3 Stopped-flow 3 Principle Commercial instruments Limitations obs obs For Durrum instrument: m = 7 s - obs m Correct for slow mixing speed ( m ) K obs is still linear with - 4 No difference in mechanism?

13 9/4/3 Acidic data: impact of acids 5 General and specific acid Overall ph dependence 6 Three effective zones See also, ezoni, pg 3; figure 4- H + + HO HO O - 3

9/4/3 Catalysis: comparison with pka 7 onsted catalysis G HA A K a CH HPO - COOH 4 H CH H 3 O + O 3 COOH HCO - 3.75.

14 9/4/3 Catalysis: comparison with pka 7 onsted catalysis G HA A K a CH HPO - COOH 4 H CH H 3 O + O 3 COOH HCO Indicates that HA engages in greater donation of proton to O - than to HO Mechanisms 8 Proposed mechanism Alternative Less liely 4

9/4/3 Temperature: Arrhenius Equation 9 Arrhenius Equation Where R is the universal gas constant Transforms to: E Ln( ) ( ) a T Ln A R T Ae E / RT a Tb J R 8.

15 9/4/3 Temperature: Arrhenius Equation 9 Arrhenius Equation Where R is the universal gas constant Transforms to: E Ln( ) ( ) a T Ln A R T Ae E / RT a Tb J R o M K Or: e Ta Ea R Tb Ta Ln() /T Pizza Kinetics 3 Leenson, 999 What are the inetics of pizza spoilage? Do they conform to Arrhenius? J. Chem Ed., 76:4:

16 9/4/3 Pizza II 3 Arrhenius plot t~ Lab Project Example Data #I 3. M NaOH.35.3 What is the Abs inf? Absorbance at 9 nm (cm - ) Time (min) 6

17 9/4/3 Lab Project Example Data #II 33. M NaOH - - Set Abs inf =.85 Ln (A 9 -A 9inf ) b[] b[] Time (min) Lab Project Example Data #III 34.5 M NaOH.35.3 Set Abs inf =? Absorbance at 9 nm (cm - ) time vs ln(a-ainf) Plot Regr Time (min) 7

18 9/4/3 Lab Project Example Data #IV 35.5 M NaOH - Ln (A 9 -A 9inf ) b[] b[] Set Abs inf =.94 Maybe too high? Downward curvature Time (min) Lab Project Example Data #V 36.5 M NaOH - - Set Abs inf =.9 Ln (A 9 -A 9inf ) time vs ln(a-ainf) Plot Regr b[] b[] Loos better, except for final data where relative error is high, Use only earlier data? Time (min) 8

9/4/3 Lab Project Example Data #VI 37.5 M NaOH -. -.5 -. b[] -.54659344 b[] -.744464 Set Abs inf =.9 Ln (A 9 -A 9inf ) -.5-3. -3.

19 9/4/3 Lab Project Example Data #VI 37.5 M NaOH b[] b[] Set Abs inf =.9 Ln (A 9 -A 9inf ) Using only earlier data where relative error is low, Better linearity and estimate of obs? Time (min) Related systems 38 9

20 9/4/3 Updated: 4 September 3 39 Print version CEE 697K ENVIRONMENTAL REACTION KINETICS Lecture #b Introduction: Simple Rate Laws ezoni, pp.3-39 Introduction Variable Kinetic Order 4 Any reaction order, except n= dc dt c n n c n c n t n o n c c o n n n c t n o

21 9/4/3 Half-lives 4 Time required for initial concentration to drop to half, i.e.., c=.5c o For a zero order reaction: cco t.5co co t c For a first order reaction: c e o t.5c o c o e t t t.5c o ln().693 Example: Benzyl Chloride 4 Use: Manufacture of benzyl compounds, perfumes, pharmaceuticals, dyes, resins, floor tiles Toxicity Intensely irritating to sin, eyes, large doses can cause CNS depression Emission 45, lb/yr Fate Benzyl chloride undergoes slow degradation in water to benzyl alcohol

22 9/4/3 Benzyl chloride II Sources: Schwarzenbach et al., 993, Env. Organic Chemistry 97, J. Chem.Soc. Chem. Comm , Acta Chem. Scand. : , J. Chem. Soc Benzyl chloride to benzyl alcohol H CH O CH OH 5ºC Nucleophilic substitution S N or S N? H How to distinguish? Salt effects d[ [ dt Temperature.ºC 5ºC K.4x -5 s -.38x -5 s - T / 9. d.58 d Mixed Second Order A B products 44 Two different reactants d d[ rate V dt dt A dx dt [ B] [ x[ B] x Initial Concentrations are different; [ [B] The integrated form is: Which can be expressed as: [ B] [ ln t [ B] [ B] log.43 [ B] [ B] t [ B] log log [ B ] log [ B ] t

9/4/3 Mixed Second Order A B products 45 Initial Concentrations are the same; [ =[B] dx dt [ [ x[ x The integrated form is: [ B] x [ B] d[ dt A x t Which can be integrated: t [ A ] t Pseudo first

23 9/4/3 Mixed Second Order A B products 45 Initial Concentrations are the same; [ =[B] dx dt [ [ x[ x The integrated form is: [ B] x [ B] d[ dt A x t Which can be integrated: t [ A ] t Pseudo first order A B products 46 For most reactions, n= for each of two different reactants, thus a second-order overall reaction 3.9x 5 c B Lmg min Many of these will have one reactant in great excess (e.g., B) These become pseudo- st order in the limiting reactant, as the reactant in excess really doesn t change in concentration c A dc dt c A c B 3

24 9/4/3 47 Concentration Pseudo- st order (cont.) c A c obs Ao c e B obs.3 min Time (min) t 3.9x 5 (8) dc dt c A c B Since C changes little from its initial 8 mg/l, it is more interesting to focus on C A C A exhibits simple st order decay, called pseudo- st order The pseudo- st order rate constant is just the observed rate or obs Example: O 3 & Naphthalene 48 How long will it tae for ozone (4.8 mg/l dose) to reduce the concentration of naphthalene by 99%? Used in moth balls and as a chemical intermediate nd order reaction; = 3 M - s - Table in Hoigne & Bader, 983 [Wat. Res. 7::73] Industrial WW with.mm naphthalene Both reactants are at same (.mm) concentration Therefore, this reduces to a simple nd order reaction [ A ] 6 4 3t 99, t 33sec 5.5 min t 3t 4

25 9/4/3 O 3 & Naphthalene (cont.) 49 Contaminated river water (. mm) Now ozone is in great molar excess, so this is a pseudo- st order reaction [ B] t [ A e ] ln [ [ ] [ ] B t A t ln t t 5.4sec Molecularity of three: 3 rd order inetics 5 Quite improbably, but sometimes happens Three different reactants dx dt Complicated integrated form exists Two different reactants A dx dt B C products 3 [ B] 3[ x [ B] x Integrated form: [ [ [ B] [ [ B] [ ln [ B] [ A 3t [ B] ] A 3 [ x[ B] x[ C x 3 [ B][ C] 3 ] 3 B products 5

26 9/4/3 3 rd Order (cont.) 3A 3 products 5 dx dt Only one reactant or Initial Concentrations are the same [ [ 3 3 [ x[ x[ x The integrated form is: d[ 3 dt A 3 A3t 3t 6 Which can be integrated: 6 3t [ A ] t 3 rd Order (cont.) 5 Pseudo- nd order reactions When one of the reactants has a fixed concentration E.g., present in excess or buffered, or acts catalytically Lie a regular nd order reaction with two reactants but observed constant is fundamental rate constant times concentration of the 3 rd reactant. The integrated form: [ B] [ ln 3[ C] t [ B] [ B] obs 6

27 9/4/3 Example: chlorate formation 53 Formation of chlorate in concentrated hypochlorite solutions Concern: chlorate is toxic MCLG=. mg/l Stoichiometry Is this 3 rd order? Be septical! Observed inetics So, why is it nd order? 3O O3 d O dt O [ ] 3 obs Chlorate example (cont.) H 54 Answer: this is a reaction pathway composed of two elementary reactions slow Step # O O fast Step # O O O3 In multi-step reactions such as these, we say that the overall rate is determined by the slowest step Called the rate-limiting step or RLS Rate law is written based on the RLS Subsequent steps are ignored Prior steps are incorporated as they determine the concentrations of the RLS reactants Homewor # is based on this reaction 7

28 9/4/3 Reversible reaction inetics 55 For a general reversible reaction: aa+ bb pp + qq And the rate law must consider both forward and reverse reactions: rate C C f a A b B r p P q Q where, f = forward rate constant, [units depend on a and b] b or r = bacward rate constant, [units depend on a and b] C P = concentration of product species P, [moles/liter] C Q = concentration of product species Q, [moles/liter] p = stoichiometric coefficient of species P q = stoichiometric coefficient of species Q C C f r 56 Reversible st order reactions Kinetic law db dt [ B] Eventually the reaction slows and, Reactant concentrations approach the equilibrium values Stumm & Morgan Fig.. Pg. 69 db [ [ B] dt [ B] K eq 8

29 9/4/3 57 Reversible st order (cont.) Solution to non-equilibrium reaction period See ezoni, pg for details [ A * ] e r f * t A P f r Where * = f + r And: [ ] [ equ e [ equ Where: f [ P] Kequ A * t r equ equ Linearized version 58 To next lecture 9

CEE 697K ENVIRONMENTAL REACTION KINETICS Lecture #2

CEE 697K ENVIRONMENTAL REACTION KINETICS Lecture #2 Updated: 4 September 13 1 Print version CEE 697K ENVIRONMENTL RECTION KINETICS Lecture # Rate Expressions: Bromide + Chlorine case study & lab project Kumar & Margerum paper Introduction Reactions with