Congener-Specific Partition Properties of Chlorinated Paraffins Evaluated with COSMOtherm and Gas Chromatographic Retention Indices

Abstract

<p>Chlorinated Paraffins (CPs) are high volume production chemicals and have been found in various organisms including humans and in environmental samples from remote regions. It is thus of great importance to understand the physical-chemical properties of CPs. In this study, gas chromatographic (GC) retention indexes (RIs) of 26 CP congeners were measured on various polar and nonpolar columns to investigate the relationships between the molecular structure and the partition properties. Retention measurements show that analytical standards of individual CPs often contain several stereoisomers. RI values show that chlorination pattern have a large influence on the polarity of CPs. Single Cl substitutions (-CHCl-, -CH<sub>2</sub>Cl) generally increase polarity of CPs. However, many consecutive -CHCl- units (e.g., 1,2,3,4,5,6-C<sub>11</sub>Cl<sub>6</sub>) increase polarity less than expected from the total number of -CHCl- units. Polyparameter linear free energy relationship descriptors show that polarity difference between CP congeners can be explained by the H-bond donating properties of CPs. RI values of CP congeners were predicted using the quantum chemically based prediction tool COSMO<i>thermX</i>. Predicted RI values correlate well with the experimental data (R<sup>2</sup>, 0.975–0.995), indicating that COSMO<i>thermX</i> can be used to accurately predict the retention of CP congeners on GC columns. </p>

Predicting Partition Coefficients of Short-Chain Chlorinated Paraffin Congeners by COSMO-RS-Trained Fragment Contribution Models

“…Indeed, our training set contained only two congeners with a −CH 2 –CH 2 –CH 2 –CH 2 – fragment and none with a longer CH 2 chain. That said, the experimental K aw value for 1,2,9,10-C 10 Cl 4 could also be somewhat too high, as log K aw of -2 in combination with log K ow of 5 would result in log K oa of 7 (via K oa = K ow / K aw ), and this is even smaller than an experimentally measured log hexadecane–air partition coefficient ( L ) of 8.4 for 1,2,9,10-C 10 Cl 4 …”

“…A recent study suggested that the first, second, and third carbons from an end of the chain and central carbons all have differing likelihood of chlorination . Also, it is known that chlorination occurs less likely to the neighbors of the carbon that is already chlorinated due to a steric effect, , which is also inferred by GC retention measurements for CP mixtures. , Nevertheless, in highly chlorinated CP mixtures, dichloro-substituted carbons and trichloromethyl groups have also been identified. , Since general rules for positions of Cl in CPs of different lengths and chlorination degrees are still under investigation, we opted for the “fully random” and “one Cl per C” rules to generate congener sets for this work.…”

Predicting Partition Coefficients of Short-Chain Chlorinated Paraffin Congeners by COSMO-RS-Trained Fragment Contribution Models

“…21 Also, it has been known that chlorination occurs less likely to the neighbors of the carbon that is already chlorinated due to a steric effect, 22,23 which is also inferred by GC retention measurements for CP mixtures. 4,24 Nevertheless, in highly chlorinated CP mixtures, dichloro-substituted carbons and trichloromethyl groups have also been identified. 21,25 Since general rules for positions of Cl for CPs of different lengths and chlorination degree are still under investigation, we opted for the "fully random" and "one Cl per C" rules to generate congener sets for this work.…”

“…As (via Koa = Kow/Kaw) and this is even smaller than an experimentally measured log hexadecane-air partition coefficient (L) of 8.4 for 1,2,9,10-C10Cl4. 24 Koa ≳ L is generally expected because CPs interact with octanol via additional polar interactions that do not occur with apolar hexadecane. COSMOfrag.…”

“…(A) Extension to M/LCCPs, (B) further experimental validation, and (C) use of more realistic CP compositions. (A) is currently undertaken, and (B) will be possible in the future, as availability of isomer-specific CP standards is being improved and more data are expected (e.g., ref 24). (C) also has a good hope, as more and more knowledge regarding Cl substitution patterns in the bulk CP mixtures is becoming available, 21,25,33 and congener compositions used for the prediction of partition coefficients could be elaborated further.…”