4-Methylcyclohexanemethanol

4-Methylcyclohexanemethanol (MCHM, systematic name 4-methylcyclohexylmethanol) is an organic compound with the formula CH3C6H10CH2OH. Classified as a saturated higher alicyclic primary alcohol. Both cis and trans isomers exist, depending on the relative positions of the methyl (CH3) and hydroxymethyl (CH2OH) groups on the cyclohexane ring. Commercial samples of MCHM consists of a mixture of these isomers as well as other components that vary with the supplier. It is a colourless oil with a faint mint-like alcohol odor. The trans isomer has a particularly low odor threshold (~7 ppb in water) and a more licorice-like quality which is not associated with the less detectable cis isomer. Like other 8-carbon alcohols, such as 1-octanol, this compound is only slightly soluble in water but highly soluble in many organic solvents. The solubility of 1-octanol in water is 2.3 grams per liter. It was first prepared in 1908 by Bouveault–Blanc reduction of a methylcyclohexanecarboxylate ester. It is also produced as a byproduct (ca. 1%) in the production of cyclohexanedimethanol, a commodity chemical, during hydrogenation of dimethyl terephthalate. It has been patented for use in air fresheners. U.S. Patent 4915825 describes a froth flotation process for cleaning coal where a mixture of 95% MCHM, 4% water, and 0.1% 4-methylcyclohexanemethanol monoether (such as 4-(methoxymethyl)cyclohexanemethanol) is used as a frothing agent, and finely divided coal particles adhere to air bubbles induced into the agent which rise to the surface. Other cyclohexane-based alcohols can also be used. MCHM has the advantage of being less toxic than previous frothing agents containing 2-ethylhexanol. The original patent owners let the patent expire after eight years for failure to pay maintenance fees. Reliable information on health and safety of this compound is limited. The ChemSpider entry for MCHM indicates that it has been evaluated for ligand activity via SimBioSys's LASSO analysis, which predicted low to no activity on 40 biologically significant receptors, indicating a low likelihood for significant biological activity on them. Eastman Chemical Company's MSDS for 'crude' (unpurified) MCHM, as supplied by NPR, reports an oral LD-50 of 825 mg/kg and a dermal LD-50 greater than 2,000 mg/kg, both in rats. Further data from Eastman's internal studies was released after the Elk River, West Virginia (2014) spill, including the studies upon which the LD-50 estimate was based and one 28-day study of oral toxicity of pure MCHM which concluded that 400 mg/kg doses were associated with erythropoietic, liver, and kidney effects, though these were not considered more than 'minor toxicity' and the 'no observed effect' level was considered to be 100 mg/kg/day. A World Health Organization study of the toxicity of alicyclic primary alcohols and related alicyclic carbohydrates (of which MCHM is one type) found that LD-50 values for substances in this class generally 'ranged from 890 to 5700 mg/kg bw for rats and > 1000 to 4000 mg/kg bw for mice, demonstrating that the oral acute toxicity of alicyclic primary alcohols, aldehydes, acids and related esters is low'. The same study indicated that these alcohols are metabolized primarily to corresponding carboxylic acids, which in the case of MCHM is 4-methylcyclohexanecarboxylic acid (CAS 13064-83-0), a naphthenic acid. The toxicity and environmental properties of these naphthenic acids have been well studied recently due to their occurrence as a major contaminant in water used for extraction of oil from tar sands. Naphthenic acids have both acute and chronic toxicity to fish and other organisms. The methyl ester of this acid is also listed as one of the major impurities in the 'crude MCHM' as supplied by Eastman.