4/12/2008 Updated: 12 April 2008 CEE690K Lecture #17 1 Print version CEE 690K ENVIRONMENTAL REACTION KINETICS Lecture #17 Case Study: DCAN & DCAD research Primary Literature as noted Introduction David A. Reckhow H DCAN Cl C C N DHAN OCl Cl OH k 4 H k 2 N k 1 H H 2 O Cl C C N OCl Cl C C fast Cl OH H H Cl fast NH NCl � Key intermediate K i di Cl C C Cl C C H 2 O OH OH O N-Cl-DCAD Cl Cl � Concentrations are anion fast well known pKa = 3.7 N-Cl-DCAD DCAD H H NH 2 NHCl Cl(+II) Cl C C Cl C C S (+IV) O O Cl Cl k 1-2 k 1-1 OH HOCl H H NH 2 NHCl Cl C C OH Cl C C OCl O Cl fast OH Cl fast NH 3 H O NHCl 2 Cl C C CEE690K Lecture #17 2 David A. Reckhow OH Cl DCAA 1
4/12/2008 Proposed Rate Law for DCAN 3 � Hydrolysis and oxidation � Hydrolysis and oxidation dC − = − + + + { k k OH [ ] k Cl [ ( I )]} C 1 2 3 dt k1 = 1.78 x10-7 ±0.35 x10-7 (s-1) k2 = 3.42 ±0.31 (M-1s-1) k3 = 1.30 x 10-1 ±0.08 x 10-1 (M-1s-1) CEE690K Lecture #17 David A. Reckhow DCAN half-life based on pH & HOCl 4 100 At 20 C � 1 Hour 1 Hour 8 Hours From Reckhow, � 10 Minutes Platt, MacNeill & rine Residual (mg/L) 1 Day McClellan, 2001 10 OCl- � Aqua 50:1:1-13 3 Days Degradation in DS � observed to increase with 1 Week increasing pH 1 � ICR data: Chlor Obolensky & Frey, 2002 OH- H2O 0.1 3 Weeks 6 7 8 9 10 11 CEE690K Lecture #17 David A. Reckhow pH 2
4/12/2008 Halamides 5 � Compounds � Compounds � Monohaloacetamides � Chloroacetamide, Bromoacetamide � Dihaloacetamides � Dichloroacetamide (DCAD) � Bromochloracetamide (BCAD) � Dibromoacetamide (DBAD) � T ih l � Trihaloacetamides t id � trichloroacetamide & analogues � Chlorination byproducts � Probably a bit less prevalent with chloramines � Pre-oxidation will probably reduce subsequent formation CEE690K Lecture #17 David A. Reckhow DCAD degradation � In presence of chlorine residual � Rate limiting step is hypochlorous acid attack in N- chloro-DCAD [ ] [ ][ ] d DCAD = − − − t k HOCl N Cl DCAD − 2 1 dt � But since we usually measure DCAD t , then DCAD , then [ ] ⎛ + ⎞ [ ] [ ] d DCAD [ H ] ⎜ ⎟ = − t k HOCl ⎜ ⎟ DCAD − − + + 1 2 t 3 . 7 ⎝ ⎠ dt 10 [ H ] � Where, k 1-2 ~ 800 M -1 s -1 3
4/12/2008 DCAD Halflife 100 DCAD Stability 10 Minutes 1 Hour 7 ual (mg/L) 8 Hours 10 Chlorine Residu 1 Day 1 Day 3 Days 1 HOCl 1 Week 3 Weeks 0.1 6 7 8 9 10 11 pH 6 7 8 9 10 11 3 Days 1 Hour OH- Reducing 1 Week 8 Hours Conditions CEE690K Lecture #17 1 Day David A. Reckhow 3 Weeks Amino Acids and Proteins 8 � Simple Amino Acids � some form THMs and HANs f M d AN NH 2 Alanine Alanine � Highest reactivity for activated AAs H 2 C C COOH � Tyrosine & Tryptophan: activated aromatic H � Cysteine: sulfhydryl group � Proteins NH 2 � many linked AAs; relatively HO C C COOH unreactive polypeptide bonds H 2 H � Reactions with proteins occurs Tyrosine Tyrosine most readily on AA side chains CEE690K Lecture #17 David A. Reckhow 4
4/12/2008 Degradation pathways R 1 =H 9 X R 4 R 1 R 4 R 1 R 4 X + X + N C N C N C Nu Nu X R 3 X R 3 H R 3 R 2 R 2 R 2 II I R 2 =H or COOH R 2 =H or COOH HX (CO 2 ) HX (CO 2 ) R 1 =H R 1 R 4 X R 4 X + � General scheme for carbonyl N C N C Nu R 3 R 3 and cyano formation from IV III R 4 =H chlorination of amines and amino acids amino acids NH 2 X NH 2 X HX (adapted from Nweke and � Scully, 1989, and Armesto et R 4 al., 1998). R 1 NH 2 O C N C R 3 VI V R 3 CEE690K Lecture #17 David A. Reckhow Monohalamine Dihalamine Pathway Pathway Isoleucine Isoleucine HOCl & AAs � Pathways y � Rapid formation of nitriles and aldehydes from chlorine, slower and more complex behavior with chloramines Froese, Kenneth L., Wolanski, Alina, and Hrudey, Steve E. “Factors Governing Odorous Aldehyde Formation as Disinfection By-Products in Drinking Water”. Water Research 33[6], 1355-1364. 1999. Nitrile Nitrile Aldehyde Aldehyde 5
4/12/2008 � Formation of aldehydes Froese, Kenneth L., Wolanski, Alina, and Hrudey, Steve E. “Factors Governing Odorous Aldehyde Formation as Disinfection By-Products in Drinking Water”. Water Research 33[6], 1355-1364. 1999. 12 � To next lecture CEE690K Lecture #17 David A. Reckhow 6
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