Volatile Methylsiloxanes Research Articles

An experimental approach for the development of direct-absorption sampling method for determination of trimethylsilanol and volatile methylsiloxanes by the GC-MS technique in landfill gas

This paper reports on an absorption method used for the determination of six target volatile methylsiloxanes and trimethylsilanol existing in raw biogas samples by means of a special and portable sampling train system. After biogas sampling (no accurate pump needed), the samples obtained were analysed by gas chromatography-mass spectrometry (GC-MS). The optimisation of the used solvent was carried out, and acetone was selected as the preferred liquid medium for trapping the siloxanes. The results clearly showed that using pure acetone and a mixture of acetone and water (97/3% = v/v) ensures very good solvation of silicon-contained molecules; thus the sampling procedure was more accurate. Replicate samples showed that the relative standard deviation of the method was less than 5.7% and 6.3% for methylsiloxanes as well as less than 2.1% and 2.4% for trimethylsilanol analysed 24 and 72 hours after sampling, respectively. Furthermore, limits of detection were determined theoretically and experimentally. The limits of detection for siloxanes and trimethylsilanol were in the range 0.04–0.11 mg/Nm3 and 0.08–0.12 mg/Nm3, respectively. The limit of quantification for trimethylsilanol was 0.1 mg/Nm3, whereas the limit for siloxanes ranged from 0.1 to 0.13 mg/Nm3. Finally, raw biogas samples were successfully analysed by the developed method. Trimethylsilanol and methylsiloxanes were found in the concentrations of 34.5 mg/Nm3 and 1.7–20 mg/Nm3 in the analysed raw biogas, respectively.

Rate Constants and Activation Energies for Gas-Phase Reactions of Three Cyclic Volatile Methyl Siloxanes with the Hydroxyl Radical.

ABSTRACTReaction with hydroxyl radicals (OH) is the major pathway for removal of cyclic volatile methyl siloxanes (cVMS) from air. We present new measurements of second‐order rate constants for reactions of the cVMS octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) with OH determined at temperatures between 313 and 353 K. Our measurements were made using the method of relative rates with cyclohexane as a reference substance and were conducted in a 140‐mL gas‐phase reaction chamber with online mass spectrometry analysis. When extrapolated to 298 K, our measured reaction rate constants of D4 and D5 with the OH radical are 1.9 × 10−12 (95% confidence interval (CI): (1.7–2.2) × 10−12) and 2.6 × 10−12 (CI: (2.3–2.9) × 10−12) cm3 molecule−1 s−1, respectively, which are 1.9× and 1.7× faster than previous measurements. Our measured rate constant for D6 is 2.8 × 10−12 (CI: (2.5–3.2) × 10−12) cm3 molecule−1 s−1 and to our knowledge there are no comparable laboratory measurements in the literature. Reaction rates for D5 were 33% higher than for D4 (CI: 30–37%), whereas the rates for D6 were only 8% higher than for D5 (CI: 5–10%). The activation energies of the reactions of D4, D5, and D6 with OH were not statistically different and had a value of 4300 ± 2800 J/mol.

Unexpected occurrence of volatile dimethylsiloxanes in Antarctic soils, vegetation, phytoplankton, and krill.

Volatile methyl siloxanes (VMS) are high-production synthetic compounds, ubiquitously found in the environment of source regions. Here, we show for the first time the occurrence of VMS in soils, vegetation, phytoplankton, and krill samples from the Antarctic Peninsula region, which questions previous claims that these compounds are "flyers" and do not significantly reach remote ecosystems. Cyclic VMS are the predominant compounds, with concentrations ranging from the limits of detection to 110 ng/g in soils. Concentrations of cyclic VMS in phytoplankton are negatively correlated with sea surface salinity, indicating a source from ice and snow melting and consistent with snow depositional inputs. After the summer snow melting, VMS accumulate in the Southern Ocean and Antarctic biota. Therefore, once introduced into the marine environment, VMS are eventually trapped by the biological pump and, thus, behave as "single hoppers". Conversely, VMS in soils and vegetation behave as "multiple hoppers" due to their high volatility.

Development of a method for determination of VOCs (including methylsiloxanes) in biogas by TD-GC/MS analysis using Supel™ Inert Film bags and multisorbent bed tubes

An analytical method based on TD-GC/MS was developed and validated for the determination of volatile organic compounds (VOCs), including linear and cyclic volatile methylsiloxanes (VMSs), in biogas. Biogas was first sampled in Supel™ Inert Film bags and subsequently dynamically sampled onto multisorbent bed tubes (Carbotrap, Carbopack X and Carboxen 569) using portable pump equipment. Two sample volumes, 100 and 250 ml, were evaluated. Desorption efficiency values for both volumes are in the range of 99–100% for almost all studied compounds while breakthrough values (%VOC on sample tube back section) are below 1% for most evaluated VOCs. However, acetaldehyde, carbon disulphide, ethanol and 1,3-butadiene have breakthrough values higher than 5%. Method detection limits were in the range of 0.01–0.8 ng per sample. The most abundant VOCs in biogas were terpenes with concentrations between 500 and 700 mg m−3. Other important families were ketones, aromatic hydrocarbons and alkanes, with concentrations in the range of 36–46 , 20–35 and 14–16 mg m−3, respectively. VMSs presented average concentrations of 4.9 ± 0.4 mg m−3. Additionally, the Supel™ Inert Film bags were evaluated for stability for 4 days at room temperature. Although several VOC families’ concentrations in the bag increased or decreased significantly (t-test; p ≤ 0.01, n = 5) 2 days after collection, recoveries were around 70–130% for most studied VOCs. The results shown demonstrate that the presented methodology is reliable and satisfactory for the evaluation of VOCs in biogas and presents an alternative to the currently existing biogas analytical techniques.

Modeling and monitoring cyclic and linear volatile methylsiloxanes in a wastewater treatment plant using constant water level sequencing batch reactors

The fate of cyclic and linear volatile methylsiloxanes (VMSs) was evaluated in a wastewater treatment plant (WWTP) using constant water level sequencing batch reactors from Dalian, China. Influent, effluent, and sewage sludge samples were collected for seven consecutive days. The mean concentrations of cyclic VMSs (cVMSs) in influent and effluent samples are 1.05μgL−1 and 0.343μgL−1; the total removal efficiency of VMSs is >60%. Linear VMS (lVMS) concentration is under the quantification limitation in aquatic samples but is found in sludge samples with a value of 90μgkg−1. High solid-water partition coefficients result in high VMS concentrations in sludge with the mean value of 5030μgkg−1. No significant differences of the daily mass flows are found when comparing the concentration during the weekend and during working days. The estimated mass load of total cVMSs is 194mgd−11000inhabitants−1 derived for the population. A mass balance model of the WWTP was developed and derived to simulate the fate of cVMSs. The removal by sorption on sludge increases, and the volatilization decreases with increasing hydrophobicity and decreasing volatility for cVMSs. Sensitivity analysis shows that the total suspended solid concentration in the effluent, mixed liquor suspended solid concentration, the sewage sludge flow rate, and the influent flow rate are the most influential parameters on the mass distribution of cVMSs in this WWTP.

Volatile Methyl Siloxanes as Potential Hazardous Air Pollutants

Volatile Methyl Siloxanes as Potential Hazardous Air Pollutants

Contribution of siloxanes to COD loading at wastewater treatment plants: Phase transfer, removal, and fate at different treatment units

Cyclic volatile methylsiloxanes (cVMSs) are entering to waste stream in increasing quantities due to their increasing use in personal care products (i.e., shampoos, creams). The cVMSs have high vapor pressures and low solubilities and are mostly transferred into the gaseous phase via volatilization; however, some are sorbed onto biosolids. The purpose of this study was to track and estimate the phase transfer (water, solids, gas), fate, and contribution to COD loading of selected siloxanes (D4, D5 and D6) which are the most commonly found cVMSs in the wastewater systems. Removal efficiencies of the wastewater treatment units were evaluated based on the partitioning characteristics of the cVMSs in gas, liquid, and biosolids phases. The contributions of the siloxanes present in the influent and effluent were estimated in terms of COD levels based on the theoretical oxygen demand (ThOD) of the siloxanes. Siloxanes constitute approximately 39 and 0.001mgL−1 of the COD in the influents and effluent. Oxidation systems showed higher removal efficiencies based COD loading in comparison to the removal efficiencies achieved aeration tanks and filtration systems. Treatment systems effectively remove the siloxanes from the aqueous phase with over 94% efficiency. About 50% of the siloxanes entering to the wastewater treatment plant accumulate in biosolids.

Measurement of cyclic volatile methylsiloxanes in the aquatic environment using low-density polyethylene passive sampling devices using an in-field calibration study – Challenges and guidance

Cyclic volatile methylsiloxanes (cVMS) are used in personal care products and are hydrophobic, volatile and persistent. Their environmental water concentrations are low and are difficult to detect using conventional sampling methods. This study shows the potential of passive sampling for cVMS. We used low-density polyethylene (LDPE) samplers and in-field calibration methods for octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5). 13C-D4 and 13C-D5, methyltris(trimethylsiloxy)silane (MT), tetrakis(trimethylsiloxy)silane (TK), and five deuterated polycyclic aromatic hydrocarbons (PAHs) were used as performance reference compounds (PRCs). Samplers were calibrated (7-d) using effluent at a treatment plant, with uptake of cVMS and losses of the PRCs measured at 12 time-points. Concentrations of D4 (53ngL−1) and D5 (1838ngL−1) were stable in the effluent. Uptake of D4 and loss of 13C-D4 were isotropic and equilibrium was approached by 7-d. Two estimates of sampler uptake rate (Rs) were 2.1Ld−1 and 2.5Ld−1. The estimated log LDPE/water partition coefficient was 4.4. The uptake of D5 was slower (Rs=0.32Ld−1) and equilibrium was not reached. Offloading of 13C-D5, MT and TK were slow, and isotropic behaviour was not demonstrated for D5. Offloading of PAHs followed the predicted pattern for LDPE. Uptake of cVMS appeared to be under membrane control, due to low diffusion coefficients in LDPE. Samplers can monitor time-weighted average concentrations of D4 for less than a week, and D5 for longer periods. LDPE samplers allow cVMS to be determined at lower concentrations than by spot sampling methods.

Evaluation of the three‐phase equilibrium method for measuring temperature dependence of internally consistent partition coefficients (KOW, KOA, and KAW) for volatile methylsiloxanes and trimethylsilanol

Partitioning equilibria and their temperature dependence of chemicals between different environmental media are important in determining the fate, transport, and distribution of contaminants. Unfortunately, internally consistent air/water (KAW), 1-octanol/air (KOA), and 1-octanol/water (KOW) partition coefficients, as well as information on their temperature dependence, are scarce for organosilicon compounds because of the reactivity of these compounds in water and octanol and their extreme partition coefficients. A newly published 3-phase equilibrium method was evaluated for simultaneous determination of the temperature dependence of KAW, KOA, and KOW of 5 volatile methylsiloxanes (VMS) and trimethylsilanol (TMS) in a temperature range from 4 °C to 35 °C. The measured partition coefficients at the different temperatures for any given compound, and the enthalpy and entropy changes for the corresponding partition processes, were all internally consistent, suggesting that the 3-phase equilibrium method is suitable for this type of measurement. Compared with common environmental contaminants reported in the literature, VMS have enthalpy and entropy relationships similar to those of alkanes for air/water partitioning and similar to those of polyfluorinated compounds for octanol/air partitioning, but more like those for benzoates and phenolic compounds for octanol/water partitioning. The temperature dependence of the partition coefficients of TMS is different from those of VMS and is more like that of alcohols, phenols, and sulfonamides. Environ Toxicol Chem 2014;33:2702–2710. © 2014 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc.

Fate of anthropogenic cyclic volatile methylsiloxanes in a wastewater treatment plant

The fate of cyclic volatile methylsiloxanes (cVMS) – octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) – was evaluated in a typical secondary activated sludge wastewater treatment plant (WWTP). Water samples (influent, primary effluent, and final effluent) and sludge (primary sludge and waste activated sludge) samples were collected at overnight low, morning high, afternoon low, and evening high flows. Concentrations of cVMS in influents fluctuated with the influent flows, ranging from 0.166 to 1.13 μg L−1, 3.47–19.3 μg L−1, and 0.446–3.87 μg L−1 for D4, D5, and D6, respectively. Mass balance analysis of cVMS showed the average mass of D4, D5, and D6 entering and exiting the plant in influent and effluent, respectively, were 109 g d−1, 2050 g d−1, 280 g d−1, and 1.41 g d−1, 27.0 g d−1, 1.90 g d−1. The total removal efficiency of cVMS was >96%. To elucidate their detailed removal mechanisms, Mackay's fugacity-based treatment plant model was used to simulate the fate of cVMS through the WWTP. Due to the unusual combination of high hydrophobicity and volatility of cVMS, volatilization in the aeration tank and adsorption to sludge were the two main pathways of cVMS removal from water in this WWTP based on the experimental and modeled results. The morning and evening high influent mass flows contributed almost equally at approximately 40% of the total daily cVMS mass, with D5 accounting for the majority of this daily loading.

Critical review and interpretation of environmental data for volatile methylsiloxanes: partition properties.

Volatile methylsiloxanes (VMS) enter the environment through industrial activities and the use of various consumer products. Reliable measurements of environmental partition properties for these compounds are critical for accurate prediction of their environmental fate, distribution, transport, exposure and potential effects. In this study, the measured partition properties including air/water (K(AW)), octanol/water (K(OW)), and octanol/air partitioning coefficients (K(OA)), soil organic carbon/water distribution coefficient (K(OC)), and biological medium/fluid partition coefficients, and their temperature dependence were critically reviewed. Based on these results, organosilicon compounds such as methylsiloxanes are expected to behave differently in the environment compared to conventional hydrophobic environmental contaminants, as a result of their inherent characteristics related to molecular size and capacity for different types of molecular interactions that control partitioning. The differences are critical and need to be taken into consideration in environmental exposure and risk analyses of these compounds.

Differences in volatile methyl siloxane (VMS) profiles in biogas from landfills and anaerobic digesters and energetics of VMS transformations

The objectives of this study were to compare the types and levels of volatile methyl siloxanes (VMS) present in biogas generated in the anaerobic digesters and landfills, evaluate the energetics of siloxane transformations under anaerobic conditions, compare the conditions in anaerobic digesters and municipal solid waste (MSW) landfills which result in differences in siloxane compositions. Biogas samples were collected at the South District Wastewater Treatment Plant and South Dade Landfill in Miami, Florida. In the digester gas, D4 and D5 comprised the bulk of total siloxanes (62% and 27%, respectively) whereas in the landfill gas, the bulk of siloxanes were trimethylsilanol (TMSOH) (58%) followed by D4 (17%). Presence of high levels of TMSOH in the landfill gas indicates that methane utilization may be a possible reaction mechanism for TMSOH formation. The free energy change for transformation of D5 and D4 to TMSOH either by hydrogen or methane utilization are thermodynamically favorable. Either hydrogen or methane should be present at relatively high concentrations for TMSOH formation which explains the high levels present in the landfill gas. The high bond energy and bond distance of the Si–O bond, in view of the atomic sizes of Si and O atoms, indicate that Si atoms can provide a barrier, making it difficult to break the Si–O bonds especially for molecules with specific geometric configurations such as D4 and D5 where oxygen atoms are positioned inside the frame formed by the large Si atoms which are surrounded by the methyl groups.

Temporal variations of cyclic and linear volatile methylsiloxanes in the atmosphere using passive samplers and high-volume air samplers.

Cyclic and linear volatile methylsiloxanes (cVMSs and lVMSs, respectively) were measured in ambient air over a period of over one year in Toronto, Canada. Air samples were collected using passive air samplers (PAS) consisting of sorbent-impregnated polyurethane foam (SIP) disks in parallel with high volume active air samplers (HV-AAS). The average difference between the SIP-PAS derived concentrations in air for the individual VMSs and those measured using HV-AAS was within a factor of 2. The air concentrations (HV-AAS) ranged 22-351 ng m(-3) and 1.3-15 ng m(-3) for ΣcVMSs (D3, D4, D5, D6) and ΣlVMSs (L3, L4, L5), respectively, with decamethylcyclopentasiloxane (D5) as the dominant compound (∼75% of the ΣVMSs). Air masses arriving from north to northwest (i.e., less populated areas) were significantly less contaminated with VMSs compared to air arriving from the south that are impacted by major urban and industrial areas in Canada and the U.S. (p < 0.05). In addition, air concentrations of ΣcVMSs were lower during major snowfall events (on average, 73 ng m(-3)) in comparison to the other sampling periods (121 ng m(-3)). Ambient temperature had a small influence on the seasonal trend of VMS concentrations in air, except for dodecamethylcyclohexasiloxane (D6), which was positively correlated with the ambient temperature (p < 0.001).

Determination of soil-water sorption coefficients of volatile methylsiloxanes.

The sorption behaviors of 4 cyclic and linear volatile methyl siloxane (VMS) compounds between water and organic matter in 3 United Kingdom soils were studied by a batch equilibrium method using13C-enriched sorbates. Sorption and desorption kinetics and isotherms were determined for octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), octamethyltrisiloxane (L3), and decamethyltetrasiloxane (L4). Concentrations of [13C]-VMS in the soil and aqueous phases were measured directly by extraction and gas chromatography–mass spectrometry techniques. All VMS compounds were sorbed rapidly, reaching constant distributions in all soils by 24 h. Desorption kinetics were very rapid, with reattainment of equilibrium within 1 h. In the main, linear isotherms were observed for aqueous concentrations at or below 4% of the solubility limits. The average sorption organic carbon partition coefficient (log KOC) values across soils were 4.23 for D4, 5.17 for D5, 4.32 for L3, and 5.13 for L4, with standard deviations of 0.09 to 0.34. Desorption KOC values were systematically greater by 0.1 log units to 0.3 log units. The linear isotherms and low variation in KOC values across soils suggested partitioning-dominated sorption of the VMS. Compared with traditional hydrophobic organic compounds, KOC values for the VMS compounds were significantly lower than expected on the basis of their octanol–water partition coefficients. A linear free energy relationship analysis showed that these differences could be rationalized quantitatively in terms of the inherent characteristics of the VMS compounds, combined with the differences in solvation properties of organic matter and octanol. Environ Toxicol Chem 2014; 33:1937–1945.

Siloxanes removal from biogas by a lab-scale biotrickling filter inoculated with Pseudomonas aeruginosa S240

Removing volatile methyl siloxanes (VMSs) from biogas remains a longstanding challenge in the field of biological process due to their low bioavailability and biodegradation. To address this issue, a lab-scale aerobic biotrickling filter, packed with porous lava and inoculated with an effective strain of Pseudomonas aeruginosa, was developed and its performance for octamethylcyclotetrasiloxane (D4, selected as a model VMS) removal from an aerobic synthetic gas was monitored. The biotrickling filter exhibited a relatively high removal efficiency over 74% at empty bed residence time of 13.2min. Rhamnolipids, biosurfactants produced by P. aeruginosa, were identified in the liquid phase of the biotrickling filter by HPLC–MS and ATR-FTIR, and they were found to be the main factor of improving D4 removal. Moreover, dimethylsilanediol, methanol, silicic acid in the liquid phase and carbon dioxide in the gas phase, as the biodegradation products of D4, were determined by GC–MS, silicic acid analysis and non-dispersive infrared analysis. To our knowledge, it is the first time to report the existence of methanol in the D4 degradation products. Finally, a metabolic pathway for D4 degradation by P. aeruginosa was proposed based on our results.

Allometric relationships to liver tissue concentrations of cyclic volatile methyl siloxanes in Atlantic cod

Spatial distribution and relationship of allometric measurements (length, weight and age) to liver concentrations of cyclic volatile methyl siloxanes (cVMS) including octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclosiloxane (D6) in Atlantic cod (Gadus morhua) collected near the community of Tromsø in Northern Norway were assessed. These congeners were benchmarked against known persistent polychlorinated biphenyls (PCBs 153 and 180) to assess accumulation behavior of cVMS. D5 was the dominate cVMS detected in all fish livers with lipid normalized concentrations up to 10 times or greater than those observed for PCB 153 and 180. D4 and D6 concentration were negatively correlated with fish length and weight, indicating a greater elimination capacity compared to uptake processes with increasing fish size for these chemicals. These results indicate relationships between allometric measurements and cVMS concentrations may account for concentration variations observed within fish and should be assessed in future studies evaluating cVMS bioaccumulation potential.

Photocatalytic oxidation of octamethylcyclotetrasiloxane (D4): Towards a better understanding of the impact of volatile methyl siloxanes on photocatalytic systems

Photocatalytic treatment of air, using TiO2 as the catalyst, is developing more and more because of increasing air pollution which is becoming a serious problem that needs to be addressed immediately. Furthermore Volatile Methyl Siloxanes (VMS) are becoming more and more abundant indoors and in ambient air owing to their increased use in different domain such as cosmetic and personnel care products. Once VMS are present in air, rapid catalyst deactivation can be observed and this reduces the efficiency of the photocatalytic system. In this study octamethylcyclotetrasiloxane D4 was chosen as the VMS model, and its photocatalytic oxidation was investigated. Experiments were performed at various D4 concentrations in synthetic air under 40% relative humidity and D4 conversion was measured using TD-GC-MS analysis, while the TiO2 surface was analyzed by X-ray photoelectron spectroscopy (XPS). Under these conditions at 250ppbv of D4, the photocatalytic activity as measured by D4 conversion decreased from 98% to 30% after 3 days of irradiation, thus revealing the deactivation of TiO2, and total deactivation was observed after three days of irradiation at 500ppbv of D4. The photocatalysis of toluene was studied under the same conditions over a period of three days and a conversion close to 100% was found without any deactivation, hence leading to the confirmation that only D4 contributes to the deactivation of TiO2. Additional experiments on a binary mixture of D4 and toluene allowed us to gain a better understanding of the impact of VMS on photocatalytic systems.For the photocatalytic oxidation of D4, three photoproducts were identified, viz. heptamethylhydroxycyclotetrasiloxane, heptamethyl(hydroxymethyl)cyclotetrasiloxane and hexamethylcyclotrisiloxane. XPS analyses of the media show an increase in Si/Ti ratio and the appearance of a SiOH component, which allows us to better understand the nature of the deposit responsible for the deactivation of TiO2.

Development of chromatographic methods by using direct-sampling procedure for the quantification of cyclic and linear volatile methylsiloxanes in biogas as perspective for application in online systems.

By empirically examining the persistent theme, we hope to produce a more complete understanding of methods for determination of volatile methylsiloxanes in biogas stream. Therefore, we made an attempt to investigate a rapid and sensitive method for simultaneous analysis of linear and cyclic volatile methylsiloxanes in sewage biogas in the context of the perspective for application in online systems. The gas chromatographic (GC) parameters were optimised, and sampling of volatile methylsiloxanes from biogas was performed using novel direct sampling procedure with applying of three kinds of liquid-media. Through application of well-established gas chromatography technique coupled with two types of detector – flamed ionisation detector and mass spectrometer detector – we developed the characterisation of the presented methods. Moreover, during the samples preparation the extraction procedure was consistently excluded, as well as the time of analysis was significantly reduced. The analyses were carried out by applying special constructed sampling train where the absorbed VMSs were trapped and analysed directly by GC technique, afterwards. The instrumental analytical protocol was found to yield a linear calibration in the range 0.1–55.13 (µg g−1) with R2 values 0.996 and in the range from 0.1 to 65.17 µg g−1) with R2 values > 0.99 for GC-FID and GC-MS method respectively. In all analysed samples linear and cyclic VMSs were found in sewage gas with quantities exceeding 4.6 mg Nm−3 and 19.9 mg Nm−3, respectively Furthermore, estimation of VMSs solvent absorption efficiency was tested and the highest absorption efficiency was obtained when acetone was used as a primary solvent. High range of linearity (0.1–65.17 µg/g), and low values of limit of detection (0.01 µg/g), limit of quantification (0.04 µg/g) clearly indicate that the analysis can be successfully repeated in other independent laboratory. The proposed method creates the real perspective for analyis of VMSs in on-line system.

Predicting Partition Coefficients of Polyfluorinated and Organosilicon Compounds using Polyparameter Linear Free Energy Relationships (PP-LFERs)

The environmental behavior, fate, and effects of polyfluorinated compounds (PFCs) and organosilicon compounds (OSCs) have received increasing attention in recent years. In this study, polyparameter linear free energy relationships (PP-LFERs) were evaluated for predicting partition coefficients of neutral PFCs and OSCs, using experimental data for fluorotelomer alcohols (FTOHs) and cyclic volatile methylsiloxanes (cVMS) reported in the literature and measured newly for this work. It was found that the recently proposed PP-LFER model that uses the McGowan characteristic volume (V), the logarithmic hexadecane-air partition coefficient (L), and three polar interaction descriptors can accurately describe partition coefficients of PFCs and OSCs. The prediction errors were <1 log unit when literature descriptors were used, and the errors were reduced to <0.2 log units on average by further optimization of the descriptors. Surprisingly, the conventional forms of PP-LFERs that include the excess molar refraction (E) sometimes led to substantial errors (>1 log unit) even with optimized parameters. The system parameters for octanol-water, air-water, octanol-air, oil-water, liposome-water, and organic carbon-water partition coefficients as well as the solute descriptors for FTOHs and cVMS were recalibrated in this work, which should provide even more reliable predictions of partition coefficients. The results also confirm the consistency of the published experimental partition coefficients for FTOHs and cVMS.

The potential of methylsiloxanes as solvents for synthetic chemistry applications

The potential use of volatile methylsiloxanes (VMSs) as solvents for chemicals synthesis has been explored. Assessment of the environmental impact of these VMS solvents is made and found to be significantly lower than those of the non-polar organic solvents that they have the potential to replace. The polarities of the VMSs, as expressed by empirical polarity measurements, and miscibilities with other liquids are found to be similar to those of alkane solvents. Finally, some uses of VMSs as solvents for both organic and inorganic transformations are described. The VMSs provide environmentally more sustainable (greener) alternatives to the nonpolar solvents that they have the potential to replace.