2-Methyl-2,4-pentanediol (MPD) is an organic compound with the formula (CH3)2C(OH)CH2CH(OH)CH3. This colourless liquid is a chiral diol. It is produced industrially from diacetone alcohol by hydrogenation.[4] Total European and USA production was 15000 tonnes in 2000.[5]
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| Names | |
|---|---|
| Preferred IUPAC name 2-Methylpentane-2,4-diol | |
| Other names 2-Methyl-2,4-pentanediol Hexylene glycol Diolane 1,1,3-Trimethyltrimethylenediol 2,4-Dihydroxy-2-methylpentane Isol | |
| Identifiers | |
| |
3D model (JSmol) | |
| Abbreviations | MPD |
| 1098298 | |
| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.003.173 |
| EC Number |
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PubChem CID | |
| RTECS number |
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| UNII | |
| UN number | 1993 |
CompTox Dashboard (EPA) | |
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| Properties | |
| C6H14O2 | |
| Molar mass | 118.176 g·mol−1 |
| Appearance | colourless liquid |
| Odor | mild, sweetish[1] |
| Density | 0.92 g/mL |
| Melting point | −40 °C (−40 °F; 233 K) |
| Boiling point | 197 °C (387 °F; 470 K) |
| miscible[1] | |
| Vapor pressure | 0.05 mmHg (20°C)[1] |
| Hazards | |
| GHS labelling:[3] | |
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| Warning | |
| H315, H319 | |
| P264, P264+P265, P280, P302+P352, P305+P351+P338, P321, P332+P317, P337+P317, P362+P364 | |
| Flash point | 98.3 °C (208.9 °F; 371.4 K)[2] |
| Explosive limits | 1.3%-7.4%[1] |
| NIOSH (US health exposure limits): | |
PEL (Permissible) | none[1] |
REL (Recommended) | C 25 ppm (125 mg/m3)[1] |
IDLH (Immediate danger) | N.D.[1] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
2-Methyl-2,4-pentanediol exists as two enantiomers, (4R)-(−) and (4S)-(+). In the Protein Data Bank, the 3-letter code "MPD" refers to the (S)-(−) enantiomer, while "MRD" is used to refer to the (R)-(+) version. Commercial products labeled "MPD" are usually the racemate,[6] also sold as and referred to as "hexylene glycol".[7][8]
Uses
2-Methyl-2,4-pentanediol exhibits both surfactant and emulsion-stabilizing properties. Its relatively high viscosity and low volatility are advantageous in coatings, cleansers, cosmetics, solvents, lubricants, and hydraulic fluids.[9] Although it is an irritant at higher concentrations, it is sometimes used in skin care, hair care, soap, and eye cosmetic products at concentrations ranging from 0.1% - 25%.[10][11]
It is biodegradable and unlikely to accumulate in the environment.[12]
Laboratory uses
In the laboratory it is a common precipitant and cryoprotectant in protein crystallography.[13] Since hexylene glycol is compatible with polar and nonpolar molecules, it competes with the solvent in a crystallography experiment causing the protein to precipitate.[14] Hexylene glycol is so effective in protein crystallography because its amphiphilic nature and small, flexible structure allows it to bind to many different locations on a protein secondary structure including alpha helices and beta sheets.[15] When hexylene glycol binds to these different locations, water is removed and the protein crystals anneal, which prevents ice formation during cryocrystallography techniques.[16] Incorporation of hexylene glycol into solution has been known to improve the resolution of X-ray diffraction making protein structures easily identifiable.[17] Additionally hexylene glycol is not a strong denaturing agent and thus does not significantly alter the structure of a protein during the crystallography procedure.[15]
Hexylene glycol is also used as a lubricant for polishing specimens in metallography.[18]
Like related diols, it forms borate esters.