Hexamethyldisiloxane

Hexamethyldisiloxane
Names
Preferred IUPAC name
Hexamethyldisiloxane
Other names
Bis(trimethylsilyl) ether
Bis(trimethylsilyl) oxide
Identifiers
Abbreviations HMDSO, (TMS)2O
1736258
107-46-0 Yes
ChEBI CHEBI:78002 
ChemSpider 23150 Yes
EC number 203-492-7
Jmol-3D images Image
MeSH Hexamethyldisiloxane
PubChem 24764
RTECS number JM9237000
UNII D7M4659BPU Yes
UN number 1993
Properties
Molecular formula
 C6H18OSi2
Molar mass 162.38 g·mol−1
Appearance Colourless liquid
Density 0.764 g cm−3
Melting point −59 °C (−74 °F; 214 K)
Boiling point 100 °C (212 °F; 373 K)
930.7±33.7 ppb (23 °C) [1]
Vapor pressure 43 hPa (20 °C) [2]
1.377
Hazards
Main hazards Highly flammable liquid and vapour

Causes serious eye irritation

EU classification F
R-phrases R11
S-phrases S16
NFPA 704
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g., propane Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
4
1
0
Flash point -1(1) °C
Related compounds
Related compounds
 Disiloxane

Tetramethylsilane
Dimethyl ether
Bis(trimethylsilyl)amine

Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Hexamethyldisiloxane (HMDSO) is an organosilicon compound with the formula O[Si(CH3)3]2. This volatile colourless liquid is used as a solvent and as a reagent in organic synthesis. It is prepared by the hydrolysis of trimethylsilyl chloride. The molecule is the protypical disiloxane and resembles a subunit of polydimethylsiloxane.

Synthesis and uses

Hexamethyldisiloxane can be produced by hydrolysis of trimethylsilyl chloride:

2 Me3SiCl + H2O → 2 HCl + O[Si(CH3)3]2

It also results from the hydrolysis of silylethers and other silyl-protected functional groups. HMDSO can be converted back to the chloride by reaction with Me2SiCl2.[3] The relevant reactions are (Me = CH3):

Hexamethyldisiloxane is mainly used as source of the trimethylsilyl functional group (-Si(CH3)3) in organic synthesis. For example, in the presence of acid catalyst, it converts alcohols and carboxylic acids into the silyl ethers and silyl esters, respectively.[4]

Niche uses

HMDSO is used as an internal standard for calibrating chemical shift in1H NMR spectroscopy. It is more easily handled since it is less volatile than the usual standard tetramethylsilane but still displays only a singlet near 0 ppm.

HMDSO has even poorer solvating power than alkanes. It is therefore sometimes employed to crystallize highly lipophilic compounds.

It is used in liquid bandages (spray on plasters) such as cavilon spray, to protect damaged skin from irritation from other bodily fluids. It is also used to soften and remove adhesive residues left by medical tape and bandages, without causing further skin irritation.

HMDSO is being studied for making low-k dielectric materials for the semi-conductor industries by PECVD (plasma-enhanced chemical vapor deposition).

HMDSO has recently been used as a reporter molecule to measure tissue oxygen tension (pO2). HMDSO is highly hydrophobic and exhibits high gas solubility, and hence strong nuclear magnetic resonance spin lattice relaxation rate (R1) response to changes in pO2. Molecular symmetry provides a single NMR signal. Following direct injection into tissues it has been used to generate maps of tumor and muscle oxygenation dynamics with respect to hyperoxic gas breathing challenge.[5]

References

  1. ↑ Sudarsanan Varaprath, Cecil L. Frye, Jerry Hamelink (1996). "Aqueous solubility of permethylsiloxanes (silicones)". Environmental Toxicology and Chemistry 15 (8): 1263–1265. doi:10.1002/etc.5620150803.
  2. ↑ Record of CAS RN 107-46-0 in the GESTIS Substance Database of the IFA, accessed on March 11, 2015.
  3. ↑ Röshe, L.; John, P.; Reitmeier, R. “Organic Silicon Compounds” Ullmann’s Encyclopedia of Industrial Chemistry. John Wiley and Sons: San Francisco, 2003. doi:10.1002/14356007.a24_021.
  4. ↑ Pfeifer, J. "Hexamethyldisiloxane" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289.
  5. ↑ Kodibagkar VD, Cui W, Merritt ME, Mason RP. A novel 1H NMR approach to quantitative tissue oximetry using hexamethyldisiloxane. Magn Reson Med 2006;55:743–748 and Kodibagkar VD, Wang X, Pacheco-Torres J, Gulaka P, Mason RP. Proton Imaging of Siloxanes to map Tissue Oxygenation Levels (PISTOL): a tool for quantitative tissue oximetry. NMRBiomed 2008;21:899-907.