3 Siloxane


Siloxane

The siloxane unit

A siloxane is any chemical compound composed of units of the form R2SiO, where R is a hydrogen atom or a hydrocarbon group. They belong to the wider class of organosilicon compounds.

Siloxanes can have branched or unbranched backbones consisting of alternating silicon and oxygen atoms -Si-O-Si-O- (connected by a σ-bond with a length of 1,64 ± 0,03 Å[1]), with side chains R attached to the silicon atoms.[2] More complicated structures are also known, for example eight silicon atoms at the corners of a cube, connected by 12 oxygen atoms as the cube edges.[3]

The word siloxane is derived from the words silicon, oxygen, and alkane.

Polymerized siloxanes with organic side chains (R ≠ H) are commonly known as silicones or as polysiloxanes. Representative examples are [SiO(CH3)2]n (polydimethylsiloxane) and [SiO(C6H5)2]n (polydiphenylsiloxane). These compounds can be viewed as a hybrid of both organic and inorganic compounds. The organic side chains confer hydrophobic properties while the -Si-O-Si-O- backbone is purely inorganic. Also halogens, mainly chlorine, are possible as side compound R.[4]

Contents

Naming

Decamethylcyclopentasiloxane, a cyclic siloxane

M-units: (CH3)3SiO½, D-units: (CH3)2SiO, T-units: (CH3)SiO2

Cyclic siloxanes Linear siloxanes
D3: hexamethylcyclotrisiloxane MM: hexamethyldisiloxane
D4: octamethylcyclotetrasiloxane MDM: octamethyltrisiloxane
D5: decamethylcyclopentasiloxane MD2M: decamethyltetrasiloxane
D6: dodecamethylcyclohexasiloxane MDnM: polydimethylsiloxane

Production

Industrially, siloxanes are fabricated [5]

Applications

Siloxanes can be found in products such as cosmetics, deodorant, defoamers, water repelling windshield coating, lubricants, molded lenses for high-powered LED's[6],food additives and some soaps. They occur in landfill gas and are being evaluated as alternatives to perchloroethylene for drycleaning. Perchloroethylene is widely considered environmentally undesirable.

Siloxanes in biogas

A boron-including siloxane

In internal combustion engines, siloxanes are oxidized to silicon dioxide which then forms deposits on pistons and cylinder heads which are extremely abrasive and cause damage to the internal components of the engine. Engines can require a complete overhaul at 5,000 h or less of operation.[7][8] Deposits on the turbine of the turbocharger will eventually reduce the components efficiency.[citation needed]

Siloxanes for the membrane technology

Siloxanes can be a serious issue for some materials, used in the membrane technology, like polyvinylidene fluoride e.g.. Due to their hydrophobe behaviour and their large molecular weight, an accumulation of siloxanes on the membrane surface is possible, resulting in fouling.

References

  1. ^ VORONKOV, M. G.; MILESHKEVICH, V. P.; YUZHELEVSKII, Yu. A.: The Siloxane Bond, Physical Properties and Chemical Transformations, Studies in Soviet Science, New York - London, (1978), Page 9, 11, ISBN 10 0306109409.
  2. ^ Siloxanes, IUPAC Gold Book
  3. ^ Stephen D. Kinrade, Jeffrey C. H. Donovan, Andrew S. Schach and Christopher T. G. Knight (2002), Two substituted cubic octameric silicate cages in aqueous solution. J. Chem. Soc., Dalton Trans., 1250 - 1252. DOI: 10.1039/b107758a
  4. ^ RATUSCHEK, H.; GÜHNE, R.; SCHICKMANN, H.: Catalyst for the preparation of organosiloxanes and polyorganosiloxanes, patent application DE000004344664A1, (1995), page 3.
  5. ^ KAISER, W.; RIEDLE, R.: Silikone, In: Winnacker-Küchler: Chemische Technologie, Organische Technologie I, 4th ed, vol 6, Carl Hanser , Munich, (1982), page 830-834.
  6. ^ Cree® XLamp® LEDs Chemical Compatibility
  7. ^ Presentation - Siloxanes in landfill gas
  8. ^ Paper - Siloxanes in landfill and digester gas

External links


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Look at other dictionaries:

  • Siloxane — Disiloxan Hexamethyldisiloxan, ein di Siloxan …   Deutsch Wikipedia

  • Siloxane —   [Kurzwort], Siliciumverbindungen …   Universal-Lexikon

  • siloxane — [si läk′sān] n. [ SIL(ICON) + OX(YGEN) + ANE] any of a class of compounds, varying from liquids to hard resins, whose molecules are composed of chains of alternate silicon and oxygen atoms, usually with hydrogen or hydrocarbon groups attached to… …   English World dictionary

  • Siloxane — Decamethylcyclopentasiloxane, un siloxane cyclique. Les Siloxanes sont une classe de composés du silicium dont la formule empirique est R2SiO, où R est un groupe radical qui peut être organique. Des exemples représentatifs sont [SiO(CH3)2]n… …   Wikipédia en Français

  • siloxane — noun Etymology: silicon + oxygen + methane Date: 1917 any of various compounds containing alternate silicon and oxygen atoms in either a linear or cyclic arrangement usually with one or two organic groups attached to each silicon atom …   New Collegiate Dictionary

  • siloxane — /si lok sayn/, n. Chem. any of the class of compounds containing the structural unit R2SiO, where R is an organic group or hydrogen. [1920 25; SIL(ICON) + OX(YGEN) + ANE] * * * …   Universalium

  • siloxane — noun any of a class of compound having a short repeating unit of silicon and oxygen atoms (either in a chain or a ring) with organic side chains …   Wiktionary

  • siloxane — si·lox·ane (si lokґsān) any of various compounds based on a substituted backbone of alternating silica and oxygen molecules; in polymeric form they are also called polysiloxanes, and those in which the side chain substituents are organic… …   Medical dictionary

  • Siloxane — Si|lo|xa|ne die (Plur.) Kunstw. aus ↑Silicium, ↑Oxygen(ium) u. ↑...an> Verbindungen des Siliciums mit Sauerstoff u. Wasserstoff (Chem.) …   Das große Fremdwörterbuch

  • siloxane — si·lox·ane …   English syllables

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