Hexamethyldisiloxane can be produced by the addition of trimethylsilyl chloride to purified water:
2 Me3SiCl + H2O → 2 HCl + O[Si(CH3)3]2
It also results from the hydrolysis of silyl ethers and other silyl-protected functional groups. HMDSO can be converted back to the chloride by reaction with Me2SiCl2.[3]
Hexamethyldisiloxane is mainly used as source of the trimethylsilylfunctional 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]
It reacts with rhenium(VII) oxide to give a siloxide:[5]
Re2O7 + O[Si(CH3)3]2 → 2 O3ReOSi(CH3)3
Niche uses
HMDSO is used as an internal standard for calibrating chemical shift in1HNMR spectroscopy. It is more easily handled since it is less volatile than the usual standard tetramethylsilane but still displays only a singlet near 0ppm.
HMDSO has even poorer solvating power than alkanes. It is therefore sometimes employed to crystallise 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 has 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 tumour and muscle oxygenation dynamics with respect to hyperoxic gas breathing challenge.[6]
^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:10.1002/047084289X.
^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.
