CEE 670 Fall 2010

# Kinetics Homework #2

1.      The data below are for the decomposition of Dichloroacetonitrile (DCAN) at pH 7, and 20 C.  One column is for and ionic strength of 0.01 M (mostly NaCl), and the other for 0.03 M.  Analyze these data and make any conclusions you can regarding the nature of the hydrolysis reaction of DCAN.

 DCAN Concentration (µg/L) Time (hours) I = 0.01 M I = 0.03 M 0.00 44.49 44.74 0.75 41.10 42.29 1.50 43.73 41.64 2.50 38.84 37.87 3.50 38.27 38.45 6.50 29.22 31.97 9.50 26.94 29.17 19.50 16.25 19.31 24.50 12.66 16.44 29.50 9.52 13.49 41.50 5.42 10.06 69.50 1.55 3.83 116.50 2.05

2.      Prepare a Hammett Plot for the chlorination of phenol at high pH (i.e., phenate ions).  Use all of the rate constants in Figure 13 from Deborde & von Gunten, 2008 [Water Research 42:13-51].  To help you with this you should number each carbon and treat the attack on different carbon atoms separately even if they result in the same product.  Use the Hammett substituent constants in the attached table.  Compare your results with those obtained by Deborde & von Gunten in their Figure 15.

3.      Use the Hammett Plot prepared for #2, and predict the rate constant for the reaction of chlorine with the phenate ion of 2-amino-4-nitro-5-methyl phenol.  Assume that the two unsubsituted carbons (C3 and C6) are the only sites of attack.  Estimate the relative rate of attack on these two carbons.

Assigned: 1 Dec10

Due: 10 Dec 10

Hammett Substituent Constants

 Substituent σp σm σo σp+ σ+m σ* R F -N(CH3)2 -0.83 -0.16 -0.36 -1.70 -0.98 0.15 -O- -0.81 -0.47 -1.10 -NH2 -0.66 -0.15 0.03 0.10 -0.74 0.08 -OH -0.35 0.08 0.04 0.25 -0.70 0.33 -OCH3 -0.26 0.08 0.00 -0.76 0.05 0.25 -0.56 0.29 -C(CH3)3 -0.20 -0.10 -0.52 -0.26 -0.18 -0.02 -CH3 -0.16 -0.07 -0.13 -0.31 -0.06 -0.05 -0.18 0.01 -CH(CH3)2 -0.15 -0.04 -0.23 -0.28 -0.19 0.04 -CH2C6H5 -0.09 -0.08 -0.28 -0.05 -0.04 -CH=CHC6H5 -0.07 0.03 -1.00 -0.17 0.10 -CH=CH2 -0.04 0.06 -0.16 -0.17 0.13 -OC6H5 -0.03 0.25 -0.50 -0.40 0.37 -C6H5 -0.01 0.06 0.00 -0.18 0.11 0.10 -0.13 0.12 -H 0 0 0 0 0 0 0 0 -NHCOCH3 0.00 0.21 -0.60 -0.31 0.31 -CH2OH 0.01 0.01 0.04 -F 0.08 0.35 0.54 -0.07 0.35 0.52 -0.39 0.45 -Cl 0.23 0.37 0.68 0.11 0.40 0.47 -0.19 0.42 -Br 0.23 0.39 0.70 0.15 0.41 0.45 -0.22 0.45 -I 0.28 0.35 0.63 0.14 0.36 0.39 -0.24 0.42 -CONH2 0.36 0.28 0.72 0.10 0.26 -CHO 0.42 0.35 0.75 0.73 0.09 0.33 -COC6H5 0.43 0.34 0.51 0.12 0.31 -COOCH3 0.45 0.36 0.49 0.11 0.34 -COCH3 0.50 0.38 0.17 0.33 -CN 0.68 0.62 1.32 0.66 0.56 0.58 0.15 0.51 -CH3SO2 0.71 0.65 0.59 -NO2 0.79 0.71 1.40 0.79 0.67 0.63 0.13 0.65

Note that σo values are estimated for phenols; source: Appendix A5 in Perrin, Dempsey & Serjeant, 1981, pKa Prediction for Organic Acids and Bases, Chapman & Hall.