Methanol

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Methanol
Methanol bottle and sample.jpg
Methanol sample and its original bottle.
Methanol structure.png
Structure of methanol
Names
IUPAC name
Methanol
Systematic IUPAC name
Methanol
Other names
Carbinol, Columbian spirits, Hydroxymethane, Methyl alcohol, Methyl hydrate, Methyl hydroxide, Methylic alcohol, Methylol, Pyroligneous spirit, Wood alcohol, Wood naphtha, Wood spirit
Identifiers
Jmol-3D images Image
Properties
CH4O
CH3OH
Molar mass 32.04 g/mol
Appearance Colorless volatile liquid
Odor Alcoholic
Density 0.810 g/cm3 (0 °C)
0.792 g/cm3 (20 °C)
0.7866 g/cm3 (25 °C)
Melting point −97.6 °C (−143.7 °F; 175.6 K)
Boiling point 64.7 °C (148.5 °F; 337.8 K)
Miscible
Solubility Reacts with acetyl chloride, formic acid, thionyl chloride
Miscible with benzene, diethyl ether, ethanol, glycerol, pentane, pyridine, toluene, xylene
Vapor pressure 13.02 kPa (at 20 °C)
Acidity (pKa) 15.5
Hazards
Safety data sheet ScienceLab
Flash point 11 to 12 °C
Lethal dose or concentration (LD, LC):
5628 mg/kg (rat, oral)
7300 mg/kg (mouse, oral)
12880 mg/kg (rat, oral)
14200 mg/kg (rabbit, oral)
64,000 ppm (rat, 4 hr)
Related compounds
Related compounds
Ethanol
Propanol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Methanol, or methyl alcohol is the simplest alcohol, with the formula CH3OH, also abbreviated as MeOH. It is a light, colorless, volatile, flammable liquid. It is an important chemical as a solvent and feedstock organic compound.[1]

Properties

Chemical

Methanol is a starting point for many organic compounds, such as formaldehyde, which is produced by oxidation of methanol.

CH3OH + [O] → CH2O + H2O

Methanol burns when ignited in air to give carbon dioxide and water vapors. Minute traces of formaldehyde are produced as side product if there isn't an excess of oxygen during burning.

2 CH3OH + 3 O2 → 2 CO2 + 4 H2O

Reaction of methanol with a haloacid, such as hydroiodic acid will give methyl iodide.

CH3OH + HI → CH3I + H2O

Unlike ethanol, the addition of hypochlorite anion to methanol will not give chloroform, but rather methyl hypochlorite, a very dangerous and unstable compound that decomposes violently and can even explode at high concentrations.

CH3OH + 2 NaClO → CH3ClO + NaCl + NaOH

Methanol vapors in air will decompose over the course of several days to form carbon dioxide and water vapor.[2] Methanol is used in the production of biodiesel.

Physical

Methanol is a colorless, volatile, flammable liquid, with an alcoholic odor. It has a molecular weight of 32.04, a boiling point of 65°C and a density of 0.7914 g/cm3.[3] Methanol is miscible with a variety of organic and inorganic solvents, though not as many as ethanol. Methanol/water mixtures can be separated into two layers by salting-out with potassium carbonate.

Availability

Methanol is available cheaply from most chemical suppliers.

Heet.png

A type of antifreeze and automotive cleaner known as Heet can be found in most gas stations in the United States and is 99% or higher methanol. Some alternative fuels are entirely or mostly made of methanol, and due to the large quantities typically sold this can be a very efficient way to purchase it.

Methanol is sometimes sold at paint supply stores as wood alcohol, or methyl alcohol.[4] It can also be bought from scientific suppliers in higher grades. Hardware supplies sometimes sell methanol as "methyl hydrate". Finally, some home fireplaces use methanol as fuel, so it can be found in this manner as well. Some window cleaning solutions contain 50-90% methanol, along with traces of water and dye, as well traces of ethanol and or isopropanol.

In some countries the sale of "clean" (high purity) methanol may be regulated, being classified poison or due to its use in counterfeit alcohol. Since May 2018, the sale of window washers containing more than 0.6% methanol is restricted in the EU countries, though the ban seems to be largely ignored in many places.[5]

Preparation

Industrially, methanol is produced by the reaction of carbon monoxide and hydrogen over a catalyst (typically a mixture of copper and zinc oxides) at high temperatures and pressures. This route is not practical on a lab scale.

Impure methanol can be obtained via destructive distillation of wood. The process is not economically viable on a small scale, and produces many side products/contaminants, acetic acid, acetone, and tars among them. It is still an interesting process though, and could be attempted solely for educational value.[6]

Another possible preparation route involves the hydrolysis of methyl esters, like methyl benzoate.[7] This route produces much purer methanol.

Projects

Handling

Safety

Methanol is significantly more toxic than other common alcohols such as ethanol or isopropanol, as it is metabolized to formic acid in the body, causing blindness and death at high doses. Inhalation of the vapors and skin contact are best avoided where possible.

Accidentally ingesting large amounts of methanol will lead to blindness and doses higher than 10 ml may prove fatal. If methanol is accidentally consumed, the first aid is giving the patient ethanol, orally, vodka or other food-grade ethanol drink and then immediately call the ambulance. Ethanol does not neutralize the effect of methanol but competes with it and prevents its immediate metabolism, giving the doctors more time to save the patient.

Methanol flames tend to have extremely low visibility, particularly in the daytime or well-lit environments, making burning methanol difficult to detect and posing a great risk. If it is being used in instances where burning is likely, the addition of a small amount of boric acid colors the flame green and allows it to be seen.

Identifying methanol

Given that methanol is very similar to ethanol in properties (the smell is practically identical, their densities are also very similar), it's important to have a good method of differentiating between methanol and ethanol.

Since even the smallest amount of impurities in methanol will color the flame, burning alcohol is not the best way to tell if it's methanol you have there.

A crude way to detect methanol involves inserting a red-hot piece of copper wire into the alcohol. If vapors have a stinging smell like "morgue" (the odor of formaldehyde), then the alcohol may contain methanol. However, this method is not very reliable, as many other compounds may give a similar smell, and not every person perceives the smell of formaldehyde the same, usually due to genetics or other biological factors.

The best way to verify if your alcohol contains or it's methanol, is to add a small amount of your alcohol to a light alkane, like pentane, hexane or heptane to the alcohol, as alkanes are miscible with ethanol, while methanol is immiscible. If your alcohol forms a separate layer, that is not water, then that is methanol. This works best with nearly anhydrous alcohol, but is not suitable for food-grade alcohol, which usually has water or some other organic compounds that will interfere with the test.

Storage

Methanol is best kept in glass or plastic bottles, away from any open flames, as it is highly volatile and flammable. Make sure you clearly label the bottle, to distinguish it from the less toxic and similar ethanol.

Disposal

Burning methanol is a good way to destroy it. Do this outside or in a fume hood. Since methanol burns with an almost invisible flame, which can be a serious risk, it is a good idea to make the flame visible by mixing the methanol with another solvent, like ethanol or acetone. Try not to burn too much at once, to prevent its vaporization in the air or inhalation of partial oxidation products such as formaldehyde, formic acid, or carbon monoxide.

References

  1. http://en.wikipedia.org/wiki/Methanol
  2. http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=887&loc=ec_rcs#itabs-2d
  3. CRC Handbook of Chemistry and Physics 66th Edition, 1985
  4. http://en.wikipedia.org/wiki/List_of_commonly_available_chemicals#L.E2.80.93N
  5. https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32018R0589
  6. http://www.sciencemadness.org/talk/viewthread.php?tid=2652
  7. https://www.youtube.com/watch?v=GJMGzIQE4RM

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