Methylcyclohexane (MCH) CAS 108-87-2: Properties, Solvent and Hydrogen Carrier Uses

What Is Methylcyclohexane (MCH)?

Methylcyclohexane, abbreviated MCH, is a saturated cyclic hydrocarbon with the formula C7H14 and CAS number 108-87-2. It belongs to the cycloalkane family and consists of a cyclohexane ring carrying one methyl group. The compound is a colourless liquid with a faint, mild odour, practically insoluble in water and miscible with most organic solvents.

Because the molecule is fully saturated, it is chemically more stable and markedly less toxic than aromatic solvents of comparable solvency, such as toluene or xylene. That profile makes MCH attractive for coatings, cleaning and process applications where aromatics are being restricted or where odour and toxicity must be reduced.

Physical and Chemical Properties

The low flash point means the liquid must be treated as a flammable solvent from the moment it is decanted. Its moderate evaporation rate, between that of hexane and that of xylene, gives formulators useful control over drying and film formation.

Solvent Applications

MCH dissolves fats, oils, waxes, resins and rubber, so it is used in paint and varnish removers, industrial cleaning and degreasing solutions, adhesive formulations and printing inks. Coating producers employ it in paints and lacquers where its balanced evaporation rate helps the film level out and dry without orange peel or solvent popping.

In agrochemical and rubber processing, MCH serves as a carrier and diluent that replaces heavier aromatic fractions, reducing odour and improving workplace air quality. It is also found in specialty correction fluids and in metal cleaning blends where a saturated hydrocarbon backbone avoids attack on elastomeric seals.

Chemical Intermediate and Fuel Applications

Methylcyclohexane is a chemical intermediate as well as a solvent. Dehydrogenation of MCH over platinum or platinum-rhenium catalysts produces toluene, a reaction used in catalytic reforming to raise the octane number of gasoline, and the reverse hydrogenation is equally well established. MCH also appears as a component of reference fuels and in research on combustion behaviour of naphthenic hydrocarbons.

In refining terms the MCH-toluene pair is fully reversible, which is the property that makes it interesting both for octane upgrading and for energy storage, discussed below.

Liquid Organic Hydrogen Carrier Role

Because the dehydrogenation is reversible, the MCH-toluene couple is one of the most studied liquid organic hydrogen carrier systems. MCH releases three moles of hydrogen per mole when converted to toluene, corresponding to about 6.2 mass percent hydrogen and roughly 47 grams of hydrogen per litre, and the spent toluene can be re-hydrogenated at elevated pressure.

The carrier is stored and transported as a normal organic liquid at ambient conditions, which suits long-distance hydrogen delivery, seasonal storage and hydrogen refuelling concepts where compressed or liquefied hydrogen logistics are unattractive. The technical challenges are the heat duty of dehydrogenation and the purity limits that the fuel-cell grade hydrogen must meet.

Laboratory and Chromatography Use

In the laboratory, MCH is a useful non-polar mobile phase and diluent for chromatography and for reactions where aromatic solvents would interfere with spectra or unwanted side reactions. It has been applied in reversed-phase and normal-phase separations and in extraction work, and it functions as a substitute for hexane or toluene where a higher flash point is not required but lower toxicity relative to aromatics is preferred.

Storage, Handling and Safety

MCH is a flammable liquid with a closed-cup flash point near -4 C, so vapour can ignite far below room temperature. Storage areas require ventilation, grounding and bonding of drums and transfer equipment, and separation from ignition sources and strong oxidisers. The liquid is stable under normal conditions and does not require a polymerisation inhibitor.

Prolonged skin contact defats and dries the skin, and high vapour concentrations irritate the respiratory tract and central nervous system, causing dizziness. Workers should use gloves, goggles and, in poorly ventilated spaces, respiratory protection, and spills should be absorbed with inert material and handled as hazardous waste.

Frequently Asked Questions

Q: What is methylcyclohexane used for?
MCH is used as a solvent for paints, inks, adhesives, cleaning products and rubber processing, as a chemical intermediate for toluene production, as a liquid organic hydrogen carrier and as a laboratory solvent.

Q: Is methylcyclohexane the same as cyclohexane?
No. Methylcyclohexane carries a methyl group on the ring and has the formula C7H14, while cyclohexane has the formula C6H12.

Q: Is methylcyclohexane toxic?
It is less toxic than aromatic solvents such as toluene, but repeated exposure can defat the skin and high vapour levels cause irritation and central nervous system effects, so ventilation and protective equipment are recommended.

Q: Is methylcyclohexane soluble in water?
No. It is practically insoluble in water but dissolves well in most organic solvents, and its density of about 0.77 g/cm3 means it floats on water.

Q: Why is methylcyclohexane converted to toluene?
Dehydrogenation raises the octane number of refinery streams, and the same reversible reaction is studied as a way to store and release hydrogen in liquid form.

Q: What is the flash point of methylcyclohexane?
About -4 C in a closed cup, so it is a flammable liquid that must be stored and transferred with grounding, bonding and strict ignition control.