Saturday, February 25, 2017

Methanol - alcohol

In chemistry, an alcohol is an organic compound in which the hydroxyl functional group (-OH) is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms. [1] An important class of alcohols are the simple acyclic alcohols, the general formula for which is CnH2n+1OH. Of those, ethanol (C2H5OH) is the type of alcohol found in alcoholic beverages, and in common speech the word alcohol refers specifically to ethanol.


Other alcohols are usually described with a clarifying adjective, as in isopropyl alcohol (propan-2-ol) or wood alcohol (methyl alcohol, or methanol). The suffix -ol appears in the IUPAC chemical name of all substances where the hydroxyl group is the functional group with the highest priority; in substances where a higher priority group is present the prefix hydroxy- will appear in the IUPAC name politicalfactors affecting nonprofits. The suffix -ol in non-systematic names (such as paracetamol or cholesterol) also typically indicates that the substance includes a hydroxyl functional group and, so, can be termed an alcohol.

But many substances, particularly sugars (examples glucose and sucrose) contain hydroxyl functional groups without using the suffix. In everyday life "alcohol" without qualification usually refers to ethanol, or a beverage based on ethanol (as in the term "alcohol abuse"). Alcoholic beverages have been consumed by humans since prehistoric times for a variety of hygienic, dietary, medicinal, religious, and recreational reasons. Primary alcohols (R-CH2-OH) can be oxidized either to aldehydes (R-CHO) (e. g.acetaldehyde) or to carboxylic acids (R-CO2H), while the oxidation of secondary alcohols (R1R2CH-OH) normally terminates at the ketone (R1R2C=O) stage.

Tertiary alcohols (R1R2R3C-OH) are resistant to oxidation. Ethanol's toxicity is largely caused by its primary metabolite, acetaldehyde (systematically ethanal)[2][3] and secondary metabolite, acetic acid. [3][4][5][6] All primary alcohols are broken down into aldehydes then to carboxylic acids whose toxicities are similar to acetaldehyde and acetic acid.

Metabolite toxicity is reduced in rats fed N-acetylcysteine[2][7] and thiamine. [8] Tertiary alcohols cannot be metabolised into aldehydes[9] and as a result they cause no hangover or toxicity through this mechanism. Some secondary and tertiary alcohols are less poisonous than ethanol because the liver is unable to metabolise them into these toxic by-products. This makes them more suitable for recreational[10][11] and medicinal[12] use as the chronic harms are lower. tert-Amyl alcohol found in alcoholic beverages are a good example of a tertiary alcohol which saw both medicinal and recreational use. 

Other alcohols are substantially more poisonous than ethanol, partly because they take much longer to be metabolized and partly because their metabolism produces substances that are even more toxic. Methanol (wood alcohol), for instance, is oxidized to formaldehyde and then to the poisonous formic acid in the liver by alcohol dehydrogenase and formaldehyde dehydrogenase enzymes, respectively; accumulation of formic acid can lead to blindness or death.

[13] Likewise, poisoning due to other alcohols such as ethylene glycol or diethylene glycol are due to their metabolites, which are also produced by alcohol dehydrogenase. [14][15] Methanol itself, while poisonous (LD50 5628 mg/kg, oral, rat[16]), has a much weaker sedative effect than ethanol. Isopropyl alcohol is oxidized to form acetone by alcohol dehydrogenase in the liver but has occasionally been abused by alcoholics, leading to a range of adverse health effects. [17][18].

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