KiaL = Cia/CiLOctanol-waterKiow = Cio/CiwSolid-waterChapter 7 organic solvent-water partitioningthe solvent - water partitioning constant Near the end of the 19thcentury people interested in pharmaceuticals discovered that organic drugs accumulated in organisms in waythat was proportional to their partitioning in octanol.More recently environmental chemist have found similar correlations with partitioning to solid humus and other naturally occurring organic phases.by analogy to the dimentionless Henry’s law constant, Kiaw = Cia/Ciwwe could define partitioning between and organic phase (solvent) and the water phase as:Kisw = Cis / CiwWater is somewhat soluble in the octanol phase, such that 1 out of every 4 molecules 1in the organic phase or octanol phase will be water.In the aqueous phase the octanol activity coef. is iw = 3.7x1031/iw = xiw = 2.7x10-4only 27 molecules out of 100,000 will be solublein the water phase.first, we must be concerned about the effects of intermolecular interactions of solute molecules with solvent moleculessecond, we must be aware that the high amount of water in the octanol phase can influence the molar volume of the octanol phasepure n-octanol oV_ = 0.16L/mol (at 25oC)Water saturated octanolVs =(0.79)(0.16) + (0.21)(0.018) = 0.12 L mol-12What about the molar vol. of water saturatedwith octanol?What if we used hexane?What happens when we add a high water. organic to an octanol-water system?3From the thermodynamics of Chapter 3,at equilibriumisxis = iw xiwgoing to molar concentrations Ci = Xi / Vmixis Cis Vs = iw Ciw Vwsolving for Cis/Ciw and defining a partitioning coefficient KiswKisw = Cis/Ciw givessiswiwiwisiswVVCCKln Kisw = ln iw - ln is + ln swVVIf our solvent is octanolAn octanol-water partitioning coef. is defined; when is it hexane, a hexane-water Ksw is definedKisw = Cis/CiwComparing partitioning in Octanol-water and hexane water; octanol is an amphiphilic solvent, e.g., it has both a non polar and polar group. 4KiowKihwN hexane 13000 52,000Benzene 130 170Toluene 490 569Chlorobenzene 830 810Naphthalene 2300 2400Benzaldehyde 30 13Nitrobenzene 68 291-hexanol 34 2.8aniline 7.9 0.8phenol 28 0.1water 0.04 5e-55For weakly apolar or polar compounds Kiow and Kios are relatedLog Kihw = 1.21 log Kiow -0.43Figure 7.1 new book6Basic assumptions of partitioning into an organic and an aqueous phase1. the activity coefficient of compound i in water is independent of its amount in the aqueous phase; ie. even at saturation the probability of two solute molecules “seeing”one another is small…This is especially true for compounds with low solubilities and large wsat.2. The organic phase molecules in the water phase (ie. octanol in water) do not affect the wsat of compound i.This may not actually be the case for some for some very hydrophobic molecules.Ignoring this possibility, for a dilute compound i, we can sayiw Vw = iwsat Vwandiwsat Vw = 1/Ciwsat Thus in siswiwiwisiswVVCCK7Kisw= 1/( Ciwsat is Vs) log Kiow= -log Ciwsat -log io - log VO8new book Fig 7.2 , plots Kiow vs. iw before we said ln Kisw = ln iw - ln is + ln Vw /Vs9Going back toln Kiow= ln iw - ln iO + ln Vw /VOKiow is related to the activity coef. of a compound in both the water and octanol phasesWe might expect that the activity coef. iO of organics in octanol is reasonably constant for a given compound class such as PAHs or alkanes.Vw /Vo is also constant andiw is proportional to 1/ Ciw(sat) so ln Kiow= -a ln Ciw(sat) + bIf we have a number of compounds from given classes of compounds with known Kiow and Csatiw values we can generate regression coefficients for a and b  ln Kow= -a ln Cw(sat) + b known Kiow known Ciw(sat) PAH1PAH210PAH3PAH4============================================= log Kiow= -a ln Csatiw + b’ a b’ r2Alkanes 0.85 0.62 0.98PAHs 0.75 1.17 0.99 alkylbenzenes 0.94 0.60 0.99 chlorobenzens 0.90 0.62 0.99PCBs 0.85 0.78 0.92phthalates 1.09 -0.26 1.00Alcohols 0.94 0.88 0.98If you have the Csatiw for anthracene, could you calculate its Kiow?11Remember in Chapter 5 we estimated Csatiw from molar volumes ln Csatiw = -a (size) +b12From combinatorial methods you can also estimate a Kiow for many compoundslog Kiow =  nk fk + nj cj+0.23where n is the frequency of a fragment type (fk) and specific interaction (cj) for adjacent functional groups. 131415If we have a Kiow we can add or subtract functional units to get another Kiow for a similar compound. Say we have the Kiow for DDT and want to estimate the Kiow for methoxychlor.161718To ReviewWe have estimation techniques for relationships for Csatiw Csatiw = -a (size) +b19from the boiling point you can estimate its vapor pressurefrom Henry’s law structural units you can estimate a Kiaw Kiaw x RT = P*i(L) / Csatiw Csatiw can then be used in ln Kiow = -a ln Csatiw + b’------------------------------------------------Kiow from Chromatographic data20HPLCPAH 2&3 ringsTotalPAHs>3 ringsTotalTotal-PAHsuv orfluorescencedetectorHPLCPAH 2&3 ringsTotalPAHs>3 ringsTotalTotal-PAHsuv orfluorescencedetectorThe column in many HPLC systems is reverse phase, (column is non-polar and mobile phase is polar, often ACN-water or MeOH-H2OPartitioning of a hydrophobic organic may be view as sorbing into the non-polar C18 alkanes on the LC packing and then back into the mobile polar phase. Generally non-polar Kiow and Ki hex-w correlate well21MeOH-H2OSince the time that a partitioning compound spends in the mobile phase will depend on the partitioning coefficient (Kiow or Kism) log Kiow = a log t +b; where t is the retention time of the non-polar compoundlog Kiow = a log (t-to )/to +bwhere to is the r.t. of some non-retained species22Bioaccumulation and octanol water, KiowIt has long been recognized that non-polar organic compounds accumulate in organisms in a way that is directly related toinsolubility in water (iw). Kiow is related to related to Ciwsat, and bioaccumulation in lipids is related to Kiow. Hence, Veinth et al (Water Res, 13, 43-47, 1979) have related bioaccumulation factors (BCF) to Kiow.)(.log.}//{log aKmlwatermolfishwetgmolBCFiowii700850  n = 59, r2 = 0.90--------------------Chou et al (ES&T , 19, 57-62, 1985) does it for fish lipids)(.log.}//{log