2-Methyl-2,4-pentanediol

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.[3] Total European and USA production was 15000 tonnes in 2000.[4]

2-Methyl-2,4-pentanediol
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
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.003.173
UNII
  • InChI=1S/C6H14O2/c1-5(7)4-6(2,3)8/h5,7-8H,4H2,1-3H3 ☒N
    Key: SVTBMSDMJJWYQN-UHFFFAOYSA-N ☒N
  • CC(CC(C)(C)O)O
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
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).
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Infobox references

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,[5] also sold as and referred to as "hexylene glycol".[6][7]

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.[8] 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%.[9][10]

It is biodegradable and unlikely to accumulate in the environment.[11]

Laboratory uses

In the laboratory it is a common precipitant and cryoprotectant in protein crystallography.[12] Since hexylene glycol is compatible with polar and nonpolar molecules, it competes with the solvent in a crystallography experiment causing the protein to precipitate.[13] 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.[14] When hexylene glycol binds to these different locations, water is removed and the protein crystals anneal, which prevents ice formation during cryocrystallography techniques.[15] Incorporation of hexylene glycol into solution has been known to improve the resolution of X-ray diffraction making protein structures easily identifiable.[16] Additionally hexylene glycol is not a strong denaturing agent and thus does not significantly alter the structure of a protein during the crystallography procedure.[14]

Hexylene glycol is also used as a lubricant for polishing specimens in metallography.[17]

Like related diols, it forms borate esters.

References
  1. NIOSH Pocket Guide to Chemical Hazards. "#0328". National Institute for Occupational Safety and Health (NIOSH).
  2. CDC - NIOSH Pocket Guide to Chemical Hazards
  3. Stylianos Sifniades, Alan B. Levy, "Acetone" in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi:10.1002/14356007.a01_079.pub3
  4. SIDS Initial Assessment Report for SIAM 13: Hexylene Glycol
  5. MPD at Hampton Research , MPD Product Page
  6. Hexylene Glycol at Sigma Aldrich , Hexylene Glycol Product Page
  7. Hexylene Glycol at Jena Bioscience, Hexylene Glycol Product Page
  8. Chemicalland21.com Hexylene glycol
  9. Kinnunen, T. (1991). "Antibacterial and antifungal properties of propylene glycol, and 1,3-butylene glycol in vitro". Acta Dermato-Venereologica.
  10. R. Rietschel; J. Fowler; A. Fisher Hexylene Glycol. In Fisher's Contact Dermatitis; Holmes, M., Ed.; BC Decker Inc.: Hamilton,Ontario, 2008; pp 290
  11. Rhodia Hexylene glycol GPS Safety Summary. 2012.
  12. Crystallization Techniques: Additives, Enrico Stura, University of Glasgow
  13. Dumetz, A. (2009). "Comparative Effects of Salt, Organic and Polymer Precipitants on Protein Phase Behavior and Implications for Vapor Diffusion". J. Cryst. Growth. 9 (2): 682–691. doi:10.1021/cg700956b.
  14. Anand, K (2002). "An overview on 2-methyl-2,4-pentanediol in crystallization and in crystals of biological macromolecules". Acta Crystallogr. 58 (10): 1722–1728. doi:10.1107/s0907444902014610. PMC 7161645. PMID 12351894.
  15. Viatcheslav, Berejnov (2006). "Thornea Effects of cryoprotectant concentration and cooling rate on vitrification of aqueous solutions". J. Appl. Crystallogr.
  16. Vera, L (2006). "Strategies for Protein Crystallography". Cryst. Growth Des.
  17. "GreenLube". Allied High Tech. Retrieved 2023-09-23. GreenLube is a medium viscosity hexylene glycol based lubricant used for general metallographic preparation
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