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Chemical Sampling Information (CSI)
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General Description

Synonyms: DMH

OSHA IMIS Code Number: D625

Chemical Abstracts Service (CAS) Registry Number: 28777-67-5 (mixed isomers)

Other Chemical Abstracts Service (CAS) Registry Numbers: 563-16-6 (3,3-dimethylhexane); 583-48-2 (3,4-dimethylhexane); 584-94-1 (2,3-dimethylhexane); 589-43-5 (2,4-dimethylhexane); 590-73-8 (2,2-dimethylhexane); 592-13-2 (2,5-dimethylhexane); 8002-05-9 (Petroleum distillate)

Chemical Description and Physical Properties:

liquid, gasoline component
molecular formula: C8H18

Incompatibilities: Vary; Mixture of dimethylhexane isomers

Health Factors

Potential Symptoms: No human data was found. For petroleum distillates: Irritation of eyes, nose, throat; dizziness, drowsiness, headache, nausea; dry cracked skin; chemical pneumonitis (aspiration liquid). In animals: Narcosis (in mice at 70-80 mg/L); kidney damage (in rats given 0.8 g/kg/48 hr orally for two weeks)

Health Effects: Irritation-Eyes, Nose, Throat, Skin---Mild (HE16); Potential narcosis (HE8); Flammable (HE18)

Affected Organs: Eyes, skin, respiratory system, CNS, (kidneys)


  1. 2,5-Dimethylhexane is found in fuel oils (e.g., JP-4 jet fuel), gasoline combustion exhaust (smog) and tobacco fumes. It may be formed in structural fires and as a byproduct of the extrusion of polyvinyl chloride. It has been found among VOCs that migrated into a building's indoor air from an underground source.
  2. 2,5-Dimethylhexane is metabolized in rats to hexanoic acid and hexanediol derivatives, which are excreted in the urine as conjugates; the major conjugate is that of 2,5-dimethyl-2,5-hexanediol.
  3. Among 14 hexane and octane derivatives tested for inhibition of a cytochrome P450 activity in rat lung, 2,5-dimethylhexane was the most potent inhibitor and the only one tested to have a submicromolar IC50.
  4. Kidney damage in male rats by 2,5-dimethylhexane might not be relevant to human toxicity.
  5. Incubation of 3,4-dimethylhexane with rat liver microsomes caused adduct formation, possibly via the γ-diketone metabolite, 3,4-dimethyl-2,5-hexanedione. The latter has been shown to cause covalent crosslinking of neurofilaments in vitro and was found to be 20-30 times as potent for causing neurotoxicity in rats as the neurotoxic metabolite of n-hexane, 2,5-hexanedione.
  6. The amount of 3,4-dimethylhexane in regular gasoline (0.14-0.16 %) is one-third or less than the relative amounts of 2,3-, 2,4-, or 2,5-dimethylhexane. Relative amounts of the latter three are much greater in aviation gasoline (3.0-4.5 %) than in regular 87-octane gasoline (0.42-0.70 %).

Literature Basis:

  • NIOSH Pocket Guide to Chemical Hazards: Petroleum distillates (naphtha).
  • Anthony, D.C., Boekelheide, K. and Graham, D.G.: The effect of 3,4-dimethyl substitution on the neurotoxicity of 2,5-hexanedione. I. Accelerated clinical neuropathy is accompanied by more proximal axonal swellings. Toxicol. Appl. Pharmacol. 71(3): 362-371, 1983.
  • Graham, D.G., Szakál-Quin, G., Priest, J.W. and Anthony, D.C.: In vitro evidence that covalent crosslinking of neurofilaments occurs in γ-diketone neuropathy. Proc. Natl. Acad. Sci. 81(15): 4979-4982, 1984.
  • Lazarew, N.W.: [On the toxicity of various hydrocarbon vapors.] Arch. Exp. Pathol. Pharmakol. 143: 223-233, 1929 (German).
  • Rabovsky, J. and Judy, D.J.: The in vitro effects of alkanes, alcohols, and ketones on rat lung cytochrome P450-dependent alkoxyphenoxazone dealkylase activities. Arch. Toxicol. 63(1): 13-17, 1989.
  • Sanz, P., Flores, I.C., Soriano, T., Repetto, G. and Repetto, M.: In vitro quantitative structure-activity relationship assessment of pyrrole adducts production by gamma-diketone-forming neurotoxic solvents. Toxicol. In Vitro 9(5): 783-787, 1995.
  • Servé, M.P., Bombick, D.D., Roberts, J., McDonald, G.A., Mattie, D.R. and Yu, K.O.: The metabolism of 2,5-dimethylhexane in male Fischer 344 rats. Chemosphere 22(1-2): 77-84, 1991.
  • No author: Identifying hydrocarbons. In, Forensics Primer: An Introduction to Environmental Forensic Geochemistry. ZymaX Forensics, Division of ZymaX™ Envirotechnology, Inc.

Date Last Revised: 03/15/2005

Monitoring Methods used by OSHA

Primary Laboratory Sampling/Analytical Method (SLC1):

  • sampling media: Charcoal Tube (100/50 mg sections, 20/40 mesh)
    analytical solvent: (99:1) Carbon Disulfide:Dimethylformamide
    maximum volume: 4 Liters
    maximum flow rate: 0.2 L/min
    current analytical method: Gas Chromatography; GC/FID
    method reference: NIOSH Analytical Method (NIOSH 1500 [127 KB PDF, 8 pages])
    method classification: Partially Validated

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