
In
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, propertie ...
, an alcohol is a type of
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...
that carries at least one
hydroxyl
In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydro ...
()
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...
bound to a
saturated carbon atom. The term ''alcohol'' originally referred to the primary alcohol
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
(ethyl alcohol), which is
used as a drug and is the main alcohol present in
alcoholic drink
An alcoholic beverage (also called an alcoholic drink, adult beverage, or a drink) is a drink that contains ethanol, a type of alcohol that acts as a drug and is produced by fermentation of grains, fruits, or other sources of sugar. The con ...
s. An important class of alcohols, of which
methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a l ...
and ethanol are the simplest examples, includes all compounds which conform to the general formula . Simple monoalcohols that are the subject of this article include primary (), secondary () and tertiary () alcohols.
The suffix ''-ol'' appears in the
IUPAC chemical name of all substances where the hydroxyl group is the functional group with the highest priority. When a higher priority group is present in the compound, the prefix ''hydroxy-'' is used in its
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
name. The suffix ''-ol'' in non-IUPAC names (such as
paracetamol
Paracetamol, also known as acetaminophen, is a medication used to treat fever and mild to moderate pain. Common brand names include Tylenol and Panadol.
At a standard dose, paracetamol only slightly decreases body temperature; it is inferior ...
or
cholesterol
Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell mem ...
) also typically indicates that the substance is an alcohol. However, some compounds that contain hydroxyl functional groups have ''trivial names'' which do not include the suffix ''-ol'' or the prefix ''hydroxy-'', e.g. the sugars
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
and
sucrose
Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula .
For human consumption, sucrose is extracted and refined ...
.
History
The inflammable nature of the exhalations of wine was already known to ancient natural philosophers such as
Aristotle
Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ph ...
(384–322 BCE),
Theophrastus
Theophrastus (; grc-gre, Θεόφραστος ; c. 371c. 287 BC), a Greek philosopher and the successor to Aristotle in the Peripatetic school. He was a native of Eresos in Lesbos.Gavin Hardy and Laurence Totelin, ''Ancient Botany'', Routledg ...
(–287 BCE), and
Pliny the Elder
Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, naturalist and natural philosopher, and naval and army commander of the early Roman Empire, and a friend of the emperor Vespasian. He wrote the encyclopedic ' ...
(23/24–79 CE). However, this did not immediately lead to the isolation of alcohol, even despite the development of more advanced distillation techniques in second- and third-century
Roman Egypt
, conventional_long_name = Roman Egypt
, common_name = Egypt
, subdivision = Province
, nation = the Roman Empire
, era = Late antiquity
, capital = Alexandria
, title_leader = Praefectus Augustalis
, image_map = Roman ...
. An important recognition, first found in one of the writings attributed to
Jābir ibn Ḥayyān (ninth century CE), was that by
adding salt to boiling wine, which increases the wine's
relative volatility, the flammability of the resulting vapors may be enhanced. The distillation of wine is attested in Arabic works attributed to
al-Kindī (–873 CE) and to
al-Fārābī (–950), and in the 28th book of
al-Zahrāwī's (Latin: Abulcasis, 936–1013) ''Kitāb al-Taṣrīf'' (later translated into Latin as ''Liber servatoris''). In the twelfth century, recipes for the production of ''aqua ardens'' ("burning water", i.e., alcohol) by distilling wine with salt started to appear in a number of Latin works, and by the end of the thirteenth century it had become a widely known substance among Western European chemists.
The works of
Taddeo Alderotti
Taddeo Alderotti (Latin: Thaddaeus Alderottus, French : Thaddée de Florence), born in Florence between 1206 and 1215, died in 1295, was an Italian doctor and professor of medicine at the University of Bologna, who made important contributions t ...
(1223–1296) describe a method for concentrating alcohol involving repeated
fractional distillation
Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation to ...
through a water-cooled still, by which an alcohol purity of 90% could be obtained. The medicinal properties of ethanol were studied by
Arnald of Villanova
Arnaldus de Villa Nova (also called Arnau de Vilanova in Catalan, his language, Arnaldus Villanovanus, Arnaud de Ville-Neuve or Arnaldo de Villanueva, c. 1240–1311) was a physician and a religious reformer. He was also thought to be an alche ...
(1240–1311 CE) and
John of Rupescissa
:''Johannes de Rupescissa may also refer to Cardinal Jean de La Rochetaillée''
Jean de Roquetaillade, also known as John of Rupescissa, (ca. 1310 – between 1366 and 1370) was a French Franciscan alchemist and eschatologist.
Biography
Af ...
(–1366), the latter of whom regarded it as a life-preserving substance able to prevent all diseases (the ''
aqua vitae
''Aqua vitae'' (Latin for "water of life") or aqua vita is an archaic name for a concentrated aqueous solution of ethanol. These terms could also be applied to weak ethanol without rectification. Usage was widespread during the Middle Ages an ...
'' or "water of life", also called by John the ''
quintessence'' of wine).
Nomenclature
Etymology
The word "alcohol" derives from the Arabic ''
kohl'' ( ar, الكحل, al-kuḥl), a powder used as an eyeliner. The first part of the word () is the Arabic
definite article
An article is any member of a class of dedicated words that are used with noun phrases to mark the identifiability of the referents of the noun phrases. The category of articles constitutes a part of speech.
In English, both "the" and "a(n)" ar ...
, equivalent to ''the'' in English. The second part of the word () has several antecedents in
Semitic languages
The Semitic languages are a branch of the Afroasiatic language family. They are spoken by more than 330 million people across much of West Asia, the Horn of Africa, and latterly North Africa, Malta, West Africa, Chad, and in large immigrant and ...
, ultimately deriving from the
Akkadian 𒎎𒋆𒁉𒍣𒁕 (guḫlum), meaning stibnite or
antimony
Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient times ...
.
Like its antecedents in Arabic and older languages, the term ''alcohol'' was originally used for the very fine powder produced by the
sublimation of the natural mineral
stibnite to form
antimony trisulfide . It was considered to be the essence or "spirit" of this mineral. It was used as an
antiseptic
An antiseptic (from Greek ἀντί ''anti'', "against" and σηπτικός ''sēptikos'', "putrefactive") is an antimicrobial substance or compound that is applied to living tissue/skin to reduce the possibility of infection, sepsis, or putre ...
, eyeliner, and
cosmetic. Later the meaning of alcohol was extended to distilled substances in general, and then narrowed again to ethanol, when "spirits" was a synonym for
hard liquor.
Bartholomew Traheron, in his 1543 translation of
John of Vigo, introduces the word as a term used by "barbarous" authors for "fine powder." Vigo wrote: "the barbarous auctours use alcohol, or (as I fynde it sometymes wryten) alcofoll, for moost fine poudre."
The 1657 ''Lexicon Chymicum'', by William Johnson glosses the word as "antimonium sive stibium." By extension, the word came to refer to any fluid obtained by distillation, including "alcohol of wine," the distilled essence of wine.
Libavius in ''Alchymia'' (1594) refers to "vini alcohol vel vinum alcalisatum". Johnson (1657) glosses ''alcohol vini'' as "quando omnis superfluitas vini a vino separatur, ita ut accensum ardeat donec totum consumatur, nihilque fæcum aut phlegmatis in fundo remaneat." The word's meaning became restricted to "spirit of wine" (the chemical known today as
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
) in the 18th century and was extended to the class of substances so-called as "alcohols" in modern chemistry after 1850.
The term ''ethanol'' was invented in 1892,
blending "
ethane
Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petr ...
" with the "-ol" ending of "alcohol", which was generalized as a
libfix
In linguistics, a libfix is a productive bound morpheme affix created by rebracketing and back-formation, often a generalization of a component of a blended or portmanteau word. For example, ''walkathon'' was coined in 1932 as a blend of ''walk ...
.
Systematic names
IUPAC nomenclature
A chemical nomenclature is a set of rules to generate systematic names for chemical compounds. The nomenclature used most frequently worldwide is the one created and developed by the International Union of Pure and Applied Chemistry (IUPAC).
The ...
is used in scientific publications and where precise identification of the substance is important. In naming simple alcohols, the name of the alkane chain loses the terminal ''e'' and adds the suffix ''-ol'', ''e.g.'', as in "ethanol" from the alkane chain name "ethane".
When necessary, the position of the hydroxyl group is indicated by a number between the alkane name and the ''-ol'':
propan-1-ol for ,
propan-2-ol
Isopropyl alcohol (IUPAC name propan-2-ol and also called isopropanol or 2-propanol) is a colorless, flammable organic compound with a pungent alcoholic odor. As an isopropyl group linked to a hydroxyl group (chemical formula ) it is the simple ...
for . If a higher priority group is present (such as an
aldehyde
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl group ...
,
ketone
In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bon ...
, or
carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...
), then the prefix ''hydroxy-''is used,
[ e.g., as in 1-hydroxy-2-propanone (). Compounds having more than one hydroxy group are called ]polyol
In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups (). The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, thre ...
s. They are named using suffixes -diol, -triol, etc., following a list of the position numbers of the hydroxyl groups, as in propane-1,2-diol for CH3CH(OH)CH2OH (propylene glycol).
In cases where the hydroxy group is bonded to an sp2 carbon on an aromatic ring, the molecule is classified separately as a phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it re ...
and is named using the IUPAC rules for naming phenols. Phenols have distinct properties and are not classified as alcohols.
Common names
In other less formal contexts, an alcohol is often called with the name of the corresponding alkyl group followed by the word "alcohol", e.g., methyl
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in man ...
alcohol, ethyl alcohol. Propyl
In organic chemistry, propyl is a three-carbon alkyl substituent with chemical formula for the linear form. This substituent form is obtained by removing one hydrogen atom attached to the terminal carbon of propane. A propyl substituent is often ...
alcohol may be ''n''-propyl alcohol or isopropyl alcohol
Isopropyl alcohol (IUPAC name propan-2-ol and also called isopropanol or 2-propanol) is a colorless, flammable organic compound with a pungent alcoholic odor. As an isopropyl group linked to a hydroxyl group (chemical formula ) it is the simpl ...
, depending on whether the hydroxyl group is bonded to the end or middle carbon on the straight propane
Propane () is a three- carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used ...
chain. As described under systematic naming, if another group on the molecule takes priority, the alcohol moiety is often indicated using the "hydroxy-" prefix.
In archaic nomenclature, alcohols can be named as derivatives of methanol using "-carbinol" as the ending. For instance, can be named trimethylcarbinol.
Primary, secondary, and tertiary
Alcohols are then classified into primary, secondary (''sec-'', ''s-''), and tertiary (''tert-'', ''t-''), based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl
In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydro ...
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...
. (The respective numeric shorthands 1°, 2°, and 3° are sometimes used in informal settings.) The primary alcohols have general formulas . The simplest primary alcohol is methanol (), for which R=H, and the next is ethanol, for which , the methyl group
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in ...
. Secondary alcohols are those of the form RR'CHOH, the simplest of which is 2-propanol (). For the tertiary alcohols the general form is RR'R"COH. The simplest example is tert-butanol (2-methylpropan-2-ol), for which each of R, R', and R" is . In these shorthands, R, R', and R" represent substituents
A substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms ''substituent'' and ''functional group'', as well as ''side ...
, alkyl or other attached, generally organic groups.
Examples
Applications
Alcohols have a long history of myriad uses. For simple mono-alcohols, which is the focus on this article, the following are most important industrial alcohols:[.]
*methanol, mainly for the production of formaldehyde
Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section Fo ...
and as a fuel additive
Petrol additives increase petrol's octane rating or act as corrosion inhibitors or lubricants, thus allowing the use of higher compression ratios for greater efficiency and power. Types of additives include metal deactivators, corrosion inhibitors ...
*ethanol, mainly for alcoholic beverages, fuel additive, solvent
*1-propanol, 1-butanol, and isobutyl alcohol for use as a solvent and precursor to solvents
*C6–C11 alcohols used for plasticizer
A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture.
Plasticiz ...
s, e.g. in polyvinylchloride
*fatty alcohol (C12–C18), precursors to detergent
A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are mor ...
s
Methanol is the most common industrial alcohol, with about 12 million tons/y produced in 1980. The combined capacity of the other alcohols is about the same, distributed roughly equally.
Toxicity
With respect to acute toxicity, simple alcohols have low acute toxic
Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...
ities. Doses of several milliliters are tolerated. For pentanols, hexanols, octanol
Octanols are alcohols with the formula C8H17OH. A simple and important member is 1-octanol, with an unbranched chain of carbons. Other commercially important octanols are 2-octanol and 2-ethylhexanol.
There are 89 possible isomers
In ch ...
s and longer alcohols, LD50
In toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is the ...
range from 2–5 g/kg (rats, oral). Ethanol is less acutely toxic. All alcohols are mild skin irritants.
The metabolism of methanol (and ethylene glycol
Ethylene glycol ( IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...
) is affected by the presence of ethanol, which has a higher affinity for liver alcohol dehydrogenase. In this way methanol will be excreted intact in urine.
Physical properties
In general, the hydroxyl group makes alcohols polar. Those groups can form hydrogen bond
In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing ...
s to one another and to most other compounds. Owing to the presence of the polar OH alcohols are more water-soluble than simple hydrocarbons. Methanol, ethanol, and propanol are miscible
Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also applies ...
in water. Butanol, with a four-carbon chain, is moderately soluble.
Because of hydrogen bonding, alcohols tend to have higher boiling points than comparable hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak o ...
s and ether
In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again b ...
s. The boiling point of the alcohol ethanol is 78.29 °C, compared to 69 °C for the hydrocarbon hexane
Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14.
It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relatively ...
, and 34.6 °C for diethyl ether
Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable li ...
.
Occurrence in nature
Simple alcohols are found widely in nature. Ethanol is the most prominent because it is the product of fermentation, a major energy-producing pathway. Other simple alcohols, chiefly fusel alcohols, are formed in only trace amounts. More complex alcohols however are pervasive, as manifested in sugars, some amino acids, and fatty acids.
Production
Ziegler and oxo processes
In the Ziegler process, linear alcohols are produced from ethylene and triethylaluminium
Triethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name it has the formula Al2( C2H5)6 (abbreviated as Al2Et6 or TEA), as it exists as a dimer. This colorless liquid is pyrophoric. It is an industriall ...
followed by oxidation and hydrolysis. An idealized synthesis of 1-octanol
1-Octanol, also known as octan-1-ol, is the organic compound with the molecular formula CH3(CH2)7OH. It is a fatty alcohol. Many other isomers are also known generically as octanols. 1-Octanol is manufactured for the synthesis of esters for use ...
is shown:
:Al(C2H5)3 + 9 C2H4 -> Al(C8H17)3
:Al(C8H17)3 + 3O + 3 H2O -> 3 HOC8H17 + Al(OH)3
The process generates a range of alcohols that are separated by distillation
Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heati ...
.
Many higher alcohols are produced by hydroformylation of alkenes followed by hydrogenation. When applied to a terminal alkene, as is common, one typically obtains a linear alcohol:
:RCH=CH2 + H2 + CO -> RCH2CH2CHO
:RCH2CH2CHO + 3 H2 -> RCH2CH2CH2OH
Such processes give fatty alcohol
Fatty alcohols (or long-chain alcohols) are usually high-molecular-weight, straight-chain primary alcohols, but can also range from as few as 4–6 carbons to as many as 22–26, derived from natural fats and oils. The precise chain length varies ...
s, which are useful for detergents.
Hydration reactions
Some low molecular weight alcohols of industrial importance are produced by the addition of water to alkenes. Ethanol, isopropanol, 2-butanol, and tert-butanol are produced by this general method. Two implementations are employed, the direct and indirect methods. The direct method avoids the formation of stable intermediates, typically using acid catalysts. In the indirect method, the alkene is converted to the sulfate ester, which is subsequently hydrolyzed. The direct hydration using ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds).
Ethylene i ...
( ethylene hydration) or other alkenes from cracking of fractions of distilled crude oil
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
.
Hydration is also used industrially to produce the diol ethylene glycol
Ethylene glycol ( IUPAC name: ethane-1,2-diol) is an organic compound (a vicinal diol) with the formula . It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odo ...
from ethylene oxide
Ethylene oxide is an organic compound with the formula . It is a cyclic ether and the simplest epoxide: a three-membered ring consisting of one oxygen atom and two carbon atoms. Ethylene oxide is a colorless and flammable gas with a faintly s ...
.
Biological routes
Ethanol is obtained by fermentation
Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
using glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
produced from sugar from the hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolys ...
of starch
Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diet ...
, in the presence of yeast and temperature of less than 37 °C to produce ethanol. For instance, such a process might proceed by the conversion of sucrose
Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula .
For human consumption, sucrose is extracted and refined ...
by the enzyme invertase into glucose and fructose
Fructose, or fruit sugar, is a ketonic simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbe ...
, then the conversion of glucose by the enzyme complex zymase into ethanol and carbon dioxide.
Several species of the benign bacteria in the intestine use fermentation
Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
as a form of anaerobic metabolism. This metabolic
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
reaction produces ethanol as a waste product. Thus, human bodies contain some quantity of alcohol endogenously produced by these bacteria. In rare cases, this can be sufficient to cause " auto-brewery syndrome" in which intoxicating quantities of alcohol are produced.
Like ethanol, butanol can be produced by fermentation processes. ''Saccharomyces'' yeast are known to produce these higher alcohols at temperatures above . The bacterium '' Clostridium acetobutylicum'' can feed on cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...
to produce butanol on an industrial scale.
Substitution
Primary alkyl halide
The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely us ...
s react with aqueous NaOH
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkal ...
or KOH mainly to primary alcohols in nucleophilic aliphatic substitution. (Secondary and especially tertiary alkyl halides will give the elimination (alkene) product instead). Grignard reagent
A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide ...
s react with carbonyl
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a ...
groups to secondary and tertiary alcohols. Related reactions are the Barbier reaction and the Nozaki-Hiyama reaction.
Reduction
Aldehydes
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl gr ...
or ketone
In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bon ...
s are reduced with sodium borohydride or lithium aluminium hydride (after an acidic workup). Another reduction by aluminiumisopropylates is the Meerwein-Ponndorf-Verley reduction. Noyori asymmetric hydrogenation is the asymmetric reduction of β-keto-esters.
Hydrolysis
Alkenes
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
engage in an acid catalysed hydration reaction using concentrated sulfuric acid as a catalyst that gives usually secondary or tertiary alcohols. Formation of a secondary alcohol via alkene reduction and hydration is shown on the right:
:
The hydroboration-oxidation and oxymercuration-reduction of alkenes are more reliable in organic synthesis. Alkenes react with N-bromosuccinimide
''N''-Bromosuccinimide or NBS is a chemical reagent used in radical substitution, electrophilic addition, and electrophilic substitution reactions in organic chemistry. NBS can be a convenient source of Br•, the bromine radical.
Preparati ...
and water in halohydrin formation reaction. Amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent su ...
s can be converted to diazonium salts, which are then hydrolyzed.
Reactions
Deprotonation
With aqueous p''K''a values of around 16–19, they are, in general, slightly weaker acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a se ...
s than water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
. With strong bases such as sodium hydride
Sodium hydride is the chemical compound with the empirical formula Na H. This alkali metal hydride is primarily used as a strong yet combustible base in organic synthesis. NaH is a saline (salt-like) hydride, composed of Na+ and H− ions, in c ...
or sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable is ...
they form salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
s called ''alkoxide
In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organic substituent. Alkoxides are strong bases and, when ...
s'', with the general formula (where R is an alkyl
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloal ...
and M is a metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typical ...
).
: 2 R-OH + 2 NaH -> 2 R-O-Na+ + 2 H2
: 2 R-OH + 2 Na -> 2 R-O-Na+ + H2
The acidity of alcohols is strongly affected by solvation
Solvation (or dissolution) describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the ...
. In the gas phase, alcohols are more acidic than in water. In DMSO, alcohols (and water) have a p''K''a of around 29–32. As a consequence, alkoxides (and hydroxide) are powerful bases and nucleophiles (e.g., for the Williamson ether synthesis
The Williamson ether synthesis is an organic reaction, forming an ether from an organohalide and a deprotonated alcohol (alkoxide). This reaction was developed by Alexander Williamson in 1850. Typically it involves the reaction of an alkoxide io ...
) in this solvent. In particular, or in DMSO can be used to generate significant equilibrium concentrations of acetylide ions through the deprotonation of alkynes (see Favorskii reaction).
Nucleophilic substitution
The OH group is not a good leaving group in nucleophilic substitution
In chemistry, a nucleophilic substitution is a class of chemical reactions in which an electron-rich chemical species (known as a nucleophile) replaces a functional group within another electron-deficient molecule (known as the electrophile). The ...
reactions, so neutral alcohols do not react in such reactions. However, if the oxygen is first protonated to give , the leaving group (water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
) is much more stable, and the nucleophilic substitution can take place. For instance, tertiary alcohols react with hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digesti ...
to produce tertiary alkyl halide
The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely us ...
s, where the hydroxyl group is replaced by a chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is ...
atom by unimolecular nucleophilic substitution. If primary or secondary alcohols are to be reacted with hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digesti ...
, an activator such as zinc chloride is needed. In alternative fashion, the conversion may be performed directly using thionyl chloride
Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year bein ...
.
Alcohols may, likewise, be converted to alkyl bromides using hydrobromic acid or phosphorus tribromide, for example:
: 3 R-OH + PBr3 -> 3 RBr + H3PO3
In the Barton-McCombie deoxygenation an alcohol is deoxygenated to an alkane
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in whi ...
with tributyltin hydride or a trimethylborane-water complex in a radical substitution reaction.
Dehydration
Meanwhile, the oxygen atom has lone pair
In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC '' Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lon ...
s of nonbonded electrons that render it weakly basic
BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth Colleg ...
in the presence of strong acids such as sulfuric acid
Sulfuric acid ( American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
. For example, with methanol:
Upon treatment with strong acids, alcohols undergo the E1 elimination reaction
An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one- or two-step mechanism. The one-step mechanism is known as the E2 reaction, and the two-step mechanism is known as the E1 r ...
to produce alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s. The reaction, in general, obeys Zaitsev's Rule, which states that the most stable (usually the most substituted) alkene is formed. Tertiary alcohols eliminate easily at just above room temperature, but primary alcohols require a higher temperature.
This is a diagram of acid catalysed dehydration of ethanol to produce ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds).
Ethylene i ...
:
A more controlled elimination reaction requires the formation of the xanthate ester.
Protonolysis
Tertiary alcohols react with strong acids to generate carbocations. The reaction is related to their dehydration, e.g. isobutylene from tert-butyl alcohol. A special kind of dehydration reaction involves triphenylmethanol and especially its amine-substituted derivatives. When treated with acid, these alcohols lose water to give stable carbocations, which are commercial dyes.
322px, Preparation of by protonolysis of the tertiary alcohol.">crystal violet by protonolysis of the tertiary alcohol.
Esterification
Alcohol and carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...
s react in the so-called Fischer esterification. The reaction usually requires a catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
, such as concentrated sulfuric acid:
: R-OH + R'-CO2H -> R'-CO2R + H2O
Other types of ester are prepared in a similar manner for example, tosyl (tosylate) esters are made by reaction of the alcohol with p- toluenesulfonyl chloride in pyridine.
Oxidation
Primary alcohols () can be oxidized either to aldehyde
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl group ...
s () or to carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...
s (). The oxidation of secondary alcohols () normally terminates at the ketone
In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bon ...
() stage. Tertiary alcohols () are resistant to oxidation.
The direct oxidation of primary alcohols to carboxylic acids normally proceeds via the corresponding aldehyde, which is transformed via an ''aldehyde hydrate'' () by reaction with water before it can be further oxidized to the carboxylic acid.
Reagents useful for the transformation of primary alcohols to aldehydes are normally also suitable for the oxidation of secondary alcohols to ketones. These include Collins reagent and Dess-Martin periodinane. The direct oxidation of primary alcohols to carboxylic acids can be carried out using potassium permanganate
Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, that dissolves in water as K+ and , an intensely pink to purple solution.
Potassium permanganate is widely used in the ...
or the Jones reagent.
See also
* Enol
In organic chemistry, alkenols (shortened to enols) are a type of reactive structure or intermediate in organic chemistry that is represented as an alkene ( olefin) with a hydroxyl group attached to one end of the alkene double bond (). The ...
* Ethanol fuel
* Fatty alcohol
Fatty alcohols (or long-chain alcohols) are usually high-molecular-weight, straight-chain primary alcohols, but can also range from as few as 4–6 carbons to as many as 22–26, derived from natural fats and oils. The precise chain length varies ...
* Index of alcohol-related articles
* List of alcohols
* Lucas test
* Polyol
In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups (). The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, thre ...
* Rubbing alcohol
* Sugar alcohol
Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compounds, typically derived from sugars, containing one hydroxyl group (–OH) attached to each carbon atom. They are white, water-soluble solid ...
* Transesterification
In organic chemistry, transesterification is the process of exchanging the organic group R″ of an ester with the organic group R' of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst. The reaction ca ...
Notes
Citations
General references
*
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