Degradation of Monophenylheptamethylcyclotetrasiloxane and 2,6-cis-Diphenylhexamethylcycloterasiloxane in Londo Soil

• Published in: Journal of polymers and the environment Vol. 10; no. 4; pp. 119 - 131
• Main Authors: Varaprath, Sudarsanan, Larson, Paul S
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01-10-2002
• Subjects: Degradation; Degradation products; Drying; Gas chromatography; Ionization; Liquid chromatography; Mass spectrometry; Phenols; siloxanes; Soil (material); Soils; Spectrometry; Spectroscopy; Transformations
• ISSN: 1566-2543; 1572-8919; 1572-8900
• DOI: 10.1023/A:1021146419479

The natural degradation of monophenylheptamethylcyclotetrasiloxane and 2,6-cis-diphenylhexamethylcyclotetrasiloxane in soil was evaluated under laboratory conditions. Both monophenyl and 2,6-cis underwent rapid degradation in dry soil generating the same products in varying proportions. During the first 24 hr, approximately 99% of the two materials underwent significant chemical transformations forming silanols of various structures, dimethyl cyclic siloxanes of the structure (Me^sub 2^SiO)x, and rearrangement products (geometrical isomers) of diphenylhexamethylcyclotetrasiloxane. Among the silanols, the following were identified as trimethylsilyl derivatives: HOSiMe^sub 2^OH, HOSiMePhOH, HOSiMe^sub 2^OSiMe^sub 2^OH, HOSiMePhOSiMe^sub 2^OH, HOSiMePhOSiMePhOH, HOSiMe^sub 2^OSiMe^sub 2^OSiMe^sub 2^OH, HOSiMePhOSiMe^sub 2^OSiMe^sub 2^OH, HOSiMe^sub 2^OSiMePhOSiMe^sub 2^OH, HOSiMePhSiMe^sub 2^OSiMePhOH, HOSiMePhOSiMePhOSiMe^sub 2^OH, HOSiMePhOSiMe^sub 2^OSiMe^sub 2^OSiMe^sub 2^OH, HOSiMe^sub 2^OSiMePhOSiMe^sub 2^OSiMe^sub 2^OH, HOSiMePhOSiMe^sub 2^OSiMePhOSiMe^sub 2^OH, HOSiMePhOSiMePhOSiMe^sub 2^OSiMe^sub 2^OH, HOSiMePhOSiMe^sub 2^OSiMe^sub 2^OSiMePhOH, HOSiMe^sub 2^OSiMePh-OSiMePhOSiMe^sub 2^OH. Derivatization was carried out using bis(trimethylsilyl)trifluoroacetamide. Gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry (atmospheric pressure chemical ionization) analyses were used to derive structures. Structures were confirmed by gas chromatography-mass spectrometry comparisons of synthetic standards. Degradation was slower in wet soil. Nevertheless, in 14 days, the chemical transformation was essentially found to be complete as soil was allowed to dry. Detection of phenol as one of the degradation products revealed the occurrence of carbon-silicon bond cleavage promoted by soil.[PUBLICATION ABSTRACT]