Hexamethyldisiloxane
| Hexamethyldisiloxane | |
|---|---|
 | |
| Hexamethyldisiloxane | |
| Other names Bis(trimethylsilyl) ether | |
| Identifiers | |
| Abbreviations | HMDSO, (TMS)2O |
| CAS number | 107-46-0  |
| PubChem | 24764 |
| ChemSpider | 23150 |
| UNII | D7M4659BPU |
| EC number | 203-492-7 |
| UN number | 1993 |
| MeSH | Hexamethyldisiloxane |
| RTECS number | JM9237000 |
| Beilstein Reference | 1736258 |
| Jmol-3D images | {{#if:O([Si](C)(C)C)[Si](C)(C)C|Image 1 |
| |
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| 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 to 101 °C; 212 to 214 °F; 373 to 374 K |
| Refractive index (nD) | 1.377 |
| Hazards | |
| EU classification |  F |
| R-phrases | R11 |
| S-phrases | S16 |
| Main hazards | Highly flammable liquid and vapour Causes serious eye irritation |
| NFPA 704 |
 4
1
0
|
| Flash point | -1(1) °C |
| Related compounds | |
| Related compounds | Disiloxane |
(verify) (what is: / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa) | |
| 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 also 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.[1] 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.[2]
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 also used in liquid bandages (spray on plasters) such as cavilon spray, to protect damaged skin from irritation from other bodily fluids.
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.[3]
References
- ↑ 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.
- ↑ Pfeifer, J. "Hexamethyldisiloxane" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289.
- ↑ 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.