Denatured alcohol, also known asmethylated spirits,metho, ormeths in Australia, Ireland, New Zealand, South Africa, and the United Kingdom, and asdenatured rectified spirit, isethanol that has additives to make itpoisonous, bad-tasting, foul-smelling, ornauseating to discourage itsrecreational consumption. It is sometimes dyed so that it can be identified visually.Pyridine andmethanol,[1] each and together, make denatured alcohol poisonous;denatonium makes it bitter.
Denatured alcohol is used as asolvent and as fuel foralcohol burners andcamping stoves. Because of the diversity of industrial uses for denatured alcohol, hundreds of additives and denaturing methods have been used. The main additive usually is 10% methanol (methyl alcohol), hence the namemethylated spirits. Other common additives includeisopropyl alcohol,acetone,methyl ethyl ketone, andmethyl isobutyl ketone.[1]
Denaturing alcohol does not alter the ethanol molecule (chemically or structurally), unlikedenaturation in biochemistry. Rather, the ethanol ismixed with other chemicals to form a foul-tasting, often toxic, solution. For many of these solutions, it is intentionally difficult to separate the components.
In many countries denaturated alcohol is traditionally dyed withmethyl violet or similar hue (crystal violet,methylene blue) dye for safety reasons. InCentral and Eastern Europe (what are now) Czech Republic, Slovakia, Poland and others, this was mandatory during thecommunist era.
In many countries, sales of alcoholic beverages are heavilytaxed for revenue and public health policy purposes (seePigovian tax). In order to avoid requiring beverage taxes on alcohol that is not meant to be consumed, the alcohol is usually "denatured", or treated with added chemicals to make it unpalatable. Its composition is tightly defined by government regulations in countries that tax alcoholic beverages. Denatured alcohol is used identically to ethanol itself but only for applications that involve fuel, surgical and laboratory stock. Pure ethanol is required for food and beverage applications and certain chemical reactions where the denaturant would interfere. Inmolecular biology, denatured ethanol should not be used for theprecipitation ofnucleic acids, since the additives may interfere with downstream applications.[2]
Denatured alcohol has no advantages for any purpose over normal ethanol; it is a public policy compromise. As denatured alcohol is sold without the often heavy taxes onalcohol suitable for consumption, it is a cheaper solution for most uses that do not involve drinking. If pure ethanol were made cheaply available for fuel, solvents, or medicinal purposes, it could be used as a beverage without payment of alcohol tax.[3]
Despite its poisonous content, denatured alcohol is sometimes consumed as asurrogate alcohol. This can result in blindness or death if it contains methanol. For instance, during the thirteen-yearprohibition of alcohol in the US, federal law required methanol be added to domestically manufactured industrial alcohols. From 25 to 27 December 1926, which was roughly at the midpoint of nationwide alcohol prohibition, 31 people in New York City alone died of methanol poisoning.[4] To help prevent this,denatonium is often added to give the substance an extremely bitter flavour. Substances such aspyridine are added to give the mixture anunpleasant odour, and agents such assyrup of ipecac may also be included to induce vomiting.
New Zealand has removed methanol from its government-approved "methylated spirits" formulation.[5][6]
In theUSSR, denatured alcohol was used as drinking alcohol surrogate, along with many other technical ethanol-containing products. This was especially common during variousanti-alcohol campaigns initiated by the Soviet government. There is much evidence to that in both popular folklore and in literature and music. The word "denaturat" (Russian: денатурат) even gained a special symbolic meaning. Its consumption is mentioned in songs ofVladimir Vysotsky, as well as written works ofVenedikt Yerofeev,Yuz Aleshkovsky, andVyacheslav Shishkov.[7]
Diverse additives are used to make it difficult to usedistillation or other simple processes to reverse the denaturation. Methanol is commonly used both because its boiling point is close to that of ethanol and because it is toxic. Another typical denaturant is pyridine. Often the denatured alcohol is dyed withmethyl violet.[8]
There are several grades of denatured alcohol, but in general the denaturants used are similar. As an example, the formulation forcompletely denatured alcohol, according to 2005 British regulations was as follows:[9]
Completely denatured alcohol must be made in accordance with the following formulation: with every 90 parts by volume of alcohol mix 9.5 parts by volume of wood naphtha [i.e., methanol] or a substitute and 0.5 parts by volume of crude pyridine, and to the resulting mixture add mineral naphtha (petroleum oil) in the proportion of 3.75 litres to every 1000 litres of the mixture and synthetic organic dyestuff (methyl violet) in the proportion of 1.5 grams to every 1000 litres of the mixture.
The European Union agreed in February 2013 to the following mutual procedures for the complete denaturing of alcohol:[10]
Per hectolitre (100 L) of absolute ethanol: 3 litres of isopropyl alcohol, 3 litres of methyl ethyl ketone (Butanone) and 1 gramdenatonium benzoate.
Aspecially denatured alcohol (SDA) is one of many types of denatured alcohol specified under the United StatesTitle 27 of the Code of Federal Regulations Section 21.151.[11] A specially denatured alcohol is a combination of ethanol and another chemical substance, e.g.,ethyl acetate in SDA 29, 35, and35A, added to render the mixture unsuitable for drinking.[12] SDAs are often used in cosmetic products, and can also be used in chemical manufacturing, pharmaceuticals, and solvents.[13] Another example isSDA 40-B, which containstert-butyl alcohol and denatonium benzoate, N.F. In the United States and other countries, the use of denatured alcohol unsuitable for beverages avoidsexcise taxes on alcohol.[14]
