Stereochemical study on polymers with stereogenic silicon atoms

Phenylmethylsiloxanes in indoor dust from residential area of China: Source, occurrence, bioavailability and exposure assessment

Phenylmethylsiloxanes, as modified products of dimethylsiloxanes, have been used in personal care products (PCPs) and household appliances, with indoor dust serving as one potential reservoir due to their particle-binding properties. This study measured six isomers of two phenylmethylsiloxanes (P3 and P4) in PCPs (99 %) intakes of phenylmethylsiloxanes for adults, while dust ingestion/adsorption (0.19 ng/d) may play important roles for toddlers/infants with little usage of phenylmethylsiloxanes-containing PCPs. Additionally, total daily intakes of PhMeSi(OH)2 (0.30-0.84 ng/d) via ingestion and dermal absorption of dust were higher than P3 (0.06-0.31 ng/d) and P4 (0.02-0.09 ng/d), suggesting exposure risk of degradation product of phenylmethylsiloxanes deserving attention.

Stereospecific synthesis of silicon-stereogenic optically active silylboranes and general synthesis of chiral silyl Anions

Silicon-stereogenic optically active silylboranes could potentially allow the formation of chiral silyl nucleophiles as well as the synthesis of various chiral silicon compounds. However, the synthesis of such silicon-stereogenic silylboranes has not been achieved so far. Here, we report the synthesis of silicon-stereogenic optically active silylboranes via a stereospecific Pt(PPh3)4-catalyzed Si-H borylation of chiral hydrosilanes, which are synthesized by stoichiometric and catalytic asymmetric synthesis, in high yield and very high or perfect enantiospecificity (99% es in one case, and >99% es in the others) with retention of the configuration. Furthermore, we report a practical approach to generate silicon-stereogenic silyl nucleophiles with high enantiopurity and configurational stability using MeLi activation. This protocol is suitable for the stereospecific and general synthesis of silicon-stereogenic trialkyl-, dialkylbenzyl-, dialkylaryl-, diarylalkyl-, and alkylary benzyloxy-substituted silylboranes and their corresponding silyl nucleophiles with excellent enantiospecificity (>99% es except one case of 99% es). Transition-metal-catalyzed C-Si bond-forming cross-coupling reactions and conjugate-addition reactions are also demonstrated. The mechanisms underlying the stability and reactivity of such chiral silyl anion were investigated by combining NMR spectroscopy and DFT calculations.

Review of recent findings on occurrence and fates of siloxanes in environmental compartments

In view of their vast global usage in both consumer products and industrial processes, environmental emission and fates of siloxanes have become concerned issue. This review summarized the research progress, especially in the last decade, on production/consumption data, toxicities, analysis methods, environmental distribution, migration and degradation/transformation of both dimethylsiloxanes and modified siloxanes in atmospheric, aquatic and terrestrial compartments from various areas (especially in China). In spite of their fast degradation (hydrolysis and hydroxylation, etc) in various matrices (except sediment), dimethylsiloxane oligomers have been found in various environmental matrices from many countries due to their constant usage and emission. Moreover, recent literatures have paid attention to behaviors of dimethylsiloxanes in industrial areas, e.g., their higher residual levels compared with residential areas and unique transformed products (such as halogenated products) arose from special industrial production scenarios. Meanwhile, although most prior studies focused on dimethylsiloxanes, identification of modified-siloxanes with other functional groups in environment have been beginning to attract the attention of scientists. Furthermore, related literatures indicated that compared with dimethylsiloxanes, both halogenated-dimethylsiloxanes and modified methylsiloxanes (phenylsiloxanes and trifluoropropylsiloxanes) could have stronger persistence due to their weaker volatilization and degradation, especially in terrestrial matrices.

Phenylmethylsiloxanes and trifluoropropylmethylsiloxanes in municipal sludges from wastewater treatment plants in China: Their distribution, degradation and risk assessment

Based on wastewater and raw/digested sludge samples from 29 wastewater treatment plants in 25 Chinese cities, the nationwide profiles of cis- and trans- isomers of phenylmethylsiloxanes (P3 and P4) and trifluoropropylmethylsiloxanes (D3F and D4F) were investigated. Calculated with paired influents/sludges positive for these compounds, majority (93% at mean) of them were found accumulating in raw sludges [<LOQ-188 ng/g dw (dry weight), df (detection frequency) = 0-96.6%, n = 58] during wastewater treatment. Overall, trifluoropropylmethylsiloxanes were merely found in 6 cities, while phenylmethylsiloxanes were found in all cities distributed over seven geographic regions of China. Sludge emissions of phenylmethylsiloxanes in each region correlated with their reported consumption volume (R² = 0.81, except for the Southwest China), per capita gross domestic products (R² = 0.20), and annual average temperature (R² = 0.63). Although not found in wastewater biological treatment processes, degradation of phenylmethylsiloxanes and trifluoropropylmethylsiloxanes was apparent (3.0-25.9%) during sludge-digestion processes. In digestion experiments, detection of silanediols and silanetriols indicated possible biodegradation pathway, i.e., hydrolysis of Si-O and Si-C bones, with half-lives ranging from 33.7-57.7 d The calculated hazard quotients of these compounds in soils undergoing one year sludge-fertilization were less than 0.01, but their ecological risks should be further studied in view of their potential accumulation in soils.