Methanol

Methanol, also known as methyl alcohol among others, is a chemical with the formula CH3OH (a methyl group linked to a hydroxyl group, often abbreviated MeOH). Methanol acquired the name wood alcohol because it was once produced chiefly by the destructive distillation of wood. Today, methanol is mainly produced industrially by hydrogenation of carbon monoxide. Methanol is the simplest alcohol, consisting of a methyl group linked to a hydroxyl group. It is a light, volatile, colorless, flammable liquid with a distinctive odor similar to that of ethanol (drinking alcohol). Methanol is however far more toxic than ethanol. At room temperature, it is a polar liquid. With more than 20 million tons produced annually, it is used as a precursor to other commodity chemicals, including formaldehyde, acetic acid, methyl tert-butyl ether, as well as a host of more specialized chemicals. Small amounts of methanol are present in normal, healthy human individuals. One study found a mean of 4.5 ppm in the exhaled breath of test subjects. The mean endogenous methanol in humans of 0.45 g/d may be metabolized from pectin found in fruit; one kilogram of apple produces up to 1.4 g methanol. Methanol is produced naturally in the anaerobic metabolism of many varieties of bacteria and is commonly present in small amounts in the environment. As a result, the atmosphere contains a small amount of methanol vapor. Atmospheric methanol is oxidized by air in sunlight to carbon dioxide and water over the course of days. Methanol is also found in abundant quantities in star-forming regions of space and is used in astronomy as a marker for such regions. It is detected through its spectral emission lines. In 2006, astronomers using the MERLIN array of radio telescopes at Jodrell Bank Observatory discovered a large cloud of methanol in space, 288 million miles (463 million km) across. In 2016, astronomers detected methanol in a planet-forming disc around the young star TW Hydrae using ALMA radio telescope. Methanol has low acute toxicity in humans but is dangerous because, together with ethanol, it is occasionally ingested in large volumes. As little as 10 mL (0.34 US fl oz) of pure methanol can cause permanent blindness by destruction of the optic nerve. 30 mL (1.0 US fl oz) is potentially fatal. The median lethal dose is 100 mL (3.4 US fl oz) (i.e. 1–2 mL/kg body weight of pure methanol). The reference dose for methanol is 0.5 mg/kg in a day. Toxic effects begin hours after ingestion, and antidotes can often prevent permanent damage. Because of its similarities in both appearance and odor to ethanol (the alcohol in beverages), it is difficult to differentiate between the two (such is also the case with denatured alcohol, adulterated liquors or very low quality alcoholic beverages). However, cases exist of methanol resistance, such as that of Mike Malloy who was the victim of a failed murder attempt by methanol in the early 1930s. Methanol is toxic by two mechanisms. First, methanol can be fatal due to effects on the central nervous system, acting as a CNS depressant in the same manner as ethanol poisoning. Second, in a process of toxication, it is metabolized to formic acid (which is present as the formate ion) via formaldehyde in a process initiated by the enzyme alcohol dehydrogenase in the liver. Methanol is converted to formaldehyde via alcohol dehydrogenase (ADH) and formaldehyde is converted to formic acid (formate) via aldehyde dehydrogenase (ALDH). The conversion to formate via ALDH proceeds completely, with no detectable formaldehyde remaining. Formate is toxic because it inhibits mitochondrial cytochrome c oxidase, causing hypoxia at the cellular level, and metabolic acidosis, among a variety of other metabolic disturbances.