TY - JOUR

T1 - Are Si–C bonds formed in the environment and/or in technical microbiological systems?

AU - Rücker, Christoph

AU - Winkelmann, Magnus

AU - Kümmerer, Klaus

N1 - Open Access funding enabled and organized by Projekt DEAL Publisher Copyright: © 2023, The Author(s).

PY - 2023/8

Y1 - 2023/8

N2 - Organosiloxanes are industrially produced worldwide in millions of tons per annum and are widely used by industry, professionals, and consumers. Some of these compounds are PBT (persistent, biaccumulative and toxic) or vPvB (very persistent and very bioaccumulative). If organosiloxanes react at all in the environment, Si–O bonds are hydrolyzed or Si–C bonds are oxidatively cleaved, to result finally in silica and carbon dioxide. In strong contrast and very unexpectedly, recently formation of new Si–CH3 bonds from siloxanes and methane by the action of microorganisms under mild ambient conditions was proposed (in landfills or digesters) and even reported (in a biotrickling filter, 30 °C). This is very surprising in view of the harsh conditions required in industrial Si–CH3 synthesis. Here, we scrutinized the pertinent papers, with the result that evidence put forward for Si–C bond formation from siloxanes and methane in technical microbiological systems is invalid, suggesting such reactions will not occur in the environment where they are even less favored by conditions. The claim of such reactions followed from erroneous calculations and misinterpretation of experimental results. We propose an alternative explanation of the experimental observations, i.e., the putative observation of such reactions was presumably due to confusion of two compounds, hexamethyldisiloxane and dimethylsilanediol, that elute at similar retention times from standard GC columns.

AB - Organosiloxanes are industrially produced worldwide in millions of tons per annum and are widely used by industry, professionals, and consumers. Some of these compounds are PBT (persistent, biaccumulative and toxic) or vPvB (very persistent and very bioaccumulative). If organosiloxanes react at all in the environment, Si–O bonds are hydrolyzed or Si–C bonds are oxidatively cleaved, to result finally in silica and carbon dioxide. In strong contrast and very unexpectedly, recently formation of new Si–CH3 bonds from siloxanes and methane by the action of microorganisms under mild ambient conditions was proposed (in landfills or digesters) and even reported (in a biotrickling filter, 30 °C). This is very surprising in view of the harsh conditions required in industrial Si–CH3 synthesis. Here, we scrutinized the pertinent papers, with the result that evidence put forward for Si–C bond formation from siloxanes and methane in technical microbiological systems is invalid, suggesting such reactions will not occur in the environment where they are even less favored by conditions. The claim of such reactions followed from erroneous calculations and misinterpretation of experimental results. We propose an alternative explanation of the experimental observations, i.e., the putative observation of such reactions was presumably due to confusion of two compounds, hexamethyldisiloxane and dimethylsilanediol, that elute at similar retention times from standard GC columns.

KW - Biotrickling filter

KW - Bond enthalpy

KW - Decamethylcyclopentasiloxane

KW - Dimethylsilanediol

KW - GC retention time

KW - Hexamethyldisiloxane

KW - Octamethylcyclotetrasiloxane

KW - Chemistry

UR - http://www.scopus.com/inward/record.url?scp=85165454766&partnerID=8YFLogxK

U2 - 10.1007/s11356-023-28528-3

DO - 10.1007/s11356-023-28528-3

M3 - Journal articles

C2 - 37486465

AN - SCOPUS:85165454766

VL - 30

SP - 91492

EP - 91500

JO - Environmental Science and Pollution Research

JF - Environmental Science and Pollution Research

SN - 0944-1344

IS - 39

ER -