Alcohol (chemistry)

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This article is about the class of chemical compounds. For the alcohol found in alcoholic drinks, see Alcohol (drug). For other uses, see Alcohol (disambiguation).

Ball-and-stick model of an alcohol molecule (R3COH). The red and white balls represent the hydroxyl group (−OH). The three "R"s stand for carbon substituents or hydrogen atoms.[1]
The bond angle between a hydroxyl group (−OH) and a chain of carbon atoms (R) with two lone pairs on oxygen atom

In

hydroxyl (−OH) functional group bound to a saturated carbon atom.[2][3] Alcohols range from the simple, like methanol and ethanol, to complex, like sugar alcohols and cholesterol
. The presence of an OH group strongly modifies the properties of hydrocarbons, conferring hydrophilic (water-loving) properties. The OH group provides a site at which many reactions can occur.

History

The flammable nature of the exhalations of wine was already known to ancient natural philosophers such as Aristotle (384–322 BCE), Theophrastus (c. 371–287 BCE), and Pliny the Elder (23/24–79 CE).[4] 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.[5] 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.[6] The distillation of wine is attested in Arabic works attributed to al-Kindī (c. 801–873 CE) and to al-Fārābī (c. 872–950), and in the 28th book of al-Zahrāwī's (Latin: Abulcasis, 936–1013) Kitāb al-Taṣrīf (later translated into Latin as Liber servatoris).[7] 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.[8]

The works of

John of Rupescissa (c. 1310–1366), the latter of whom regarded it as a life-preserving substance able to prevent all diseases (the aqua vitae or "water of life", also called by John the quintessence of wine).[10]

Nomenclature

Etymology

The word "alcohol" derives from the Arabic

al-) is the Arabic definite article, equivalent to the in English. The second part of the word (kuḥl) has several antecedents in Semitic languages, ultimately deriving from the Akkadian 𒎎𒋆𒁉𒍣𒁕 (guḫlum), meaning stibnite or antimony.[12]

Like its antecedents in Arabic and older languages, the term alcohol was originally used for the very fine powder produced by the

hard liquor.[13]

Libavius both used the term alcohol to denote a fine powder, the latter speaking of an alcohol derived from antimony. At the same time Paracelsus uses the word for a volatile liquid; alcool or alcool vini occurs often in his writings.[14]

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."[15]

The 1657 Lexicon Chymicum, by William Johnson glosses the word as "antimonium sive stibium."

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) in the 18th century and was extended to the class of substances so-called as "alcohols" in modern chemistry after 1850.[15]

The term ethanol was invented in 1892, blending "ethane" with the "-ol" ending of "alcohol", which was generalized as a libfix.[17]

The term alcohol originally referred to the primary alcohol

alcoholic drinks
.

The suffix -ol appears in the International Union of Pure and Applied Chemistry (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 name. The suffix -ol in non-IUPAC names (such as paracetamol or cholesterol) also typically indicates that the substance is an alcohol. However, some compounds that contain hydroxyl functional groups have trivial names that do not include the suffix -ol or the prefix hydroxy-, e.g. the sugars glucose and sucrose.

Systematic names

propan-1-ol for CH3CH2CH2OH, propan-2-ol for CH3CH(OH)CH3. If a higher priority group is present (such as an aldehyde, ketone, or carboxylic acid), then the prefix hydroxy-is used,[18] e.g., as in 1-hydroxy-2-propanone (CH3C(O)CH2OH).[19] Compounds having more than one hydroxy group are called polyols. 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).

Example alcohols and representations
Structural formula Skeletal formula Preferred IUPAC name Other systematic names Common names Degree
CH3−CH2−CH2−OH
propan-1-ol
 1-propanol;
n-propyl alcohol 		propanol primary
propan-2-ol
 2-propanol isopropyl alcohol;
isopropanol 		secondary
cyclohexanol     secondary
2-methylpropan-1-ol
 2-methyl-1-propanol isobutyl alcohol;
isobutanol 		primary
tert-amyl alcohol 2-methylbutan-2-ol;
2-methyl-2-butanol 		TAA tertiary

In cases where the hydroxy group is bonded to an sp2 carbon on an aromatic ring, the molecule is classified separately as a phenol and is named using the IUPAC rules for naming phenols.[20] 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.,

Propyl alcohol may be n-propyl alcohol or isopropyl alcohol, depending on whether the hydroxyl group is bonded to the end or middle carbon on the straight propane chain. As described under systematic naming, if another group on the molecule takes priority, the alcohol moiety is often indicated using the "hydroxy-" prefix.[21]

In archaic nomenclature, alcohols can be named as derivatives of methanol using "-carbinol" as the ending. For instance, (CH3)3COH 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

substituents
, alkyl or other attached, generally organic groups.

Examples

Type Formula
IUPAC
Name 		Common name
Monohydric
alcohols 		CH3OH Methanol Wood alcohol
C2H5OH Ethanol Alcohol
C3H7OH
Propan-2-ol
 Isopropyl alcohol,
Rubbing alcohol
C4H9OH
Butan-1-ol
 Butanol,
Butyl alcohol
C5H11OH
Pentan-1-ol
 Pentanol,
Amyl alcohol
C16H33OH Hexadecan-1-ol Cetyl alcohol
Polyhydric
alcohols
(sugar
alcohols) 		C2H4(OH)2 Ethane-1,2-diol Ethylene glycol
C3H6(OH)2 Propane-1,2-diol Propylene glycol
C3H5(OH)3 Propane-1,2,3-triol Glycerol
C4H6(OH)4 Butane-1,2,3,4-tetraol Erythritol,
Threitol
C5H7(OH)5 Pentane-1,2,3,4,5-pentol Xylitol
C6H8(OH)6 hexane-1,2,3,4,5,6-hexol Mannitol,
Sorbitol
C7H9(OH)7 Heptane-1,2,3,4,5,6,7-heptol Volemitol
Unsaturated
aliphatic
alcohols 		C3H5OH Prop-2-ene-1-ol Allyl alcohol
C10H17OH 3,7-Dimethylocta-2,6-dien-1-ol Geraniol
C3H3OH Prop-2-yn-1-ol Propargyl alcohol
Alicyclic
alcohols 		C6H6(OH)6 Cyclohexane-1,2,3,4,5,6-hexol Inositol
C10H19OH 5-Methyl-2-(propan-2-yl)cyclohexan-1-ol Menthol

Applications

alcohol per capita consumption (15+), in litres of pure ethanol[23]

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:[24]

  • methanol, mainly for the production of
    fuel additive
  • 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
    polyvinylchloride
  • fatty alcohol (C12–C18), precursors to detergents

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.[24]

Toxicity

Main articles: Ethanol and Methanol

With respect to acute toxicity, simple alcohols have low acute

LD50 range from 2–5 g/kg (rats, oral). Ethanol is less acutely toxic.[25] All alcohols are mild skin irritants.[24]

The metabolism of methanol (and

liver alcohol dehydrogenase. In this way, methanol will be excreted intact in urine.[26][27][28]

Physical properties

In general, the

Butanol
, with a four-carbon chain, is moderately soluble.

Because of

hydrogen bonding, alcohols tend to have higher boiling points than comparable hydrocarbons and ethers. The boiling point of the alcohol ethanol is 78.29 °C, compared to 69 °C for the hydrocarbon hexane, and 34.6 °C for diethyl ether
.

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

Hydroxylation

Many alcohols are produced by

hydroxylases and oxidases
facilitate these conversions.

Many industrial alcohols, such as cyclohexanol for the production of nylon, are produced by hydroxylation.

Ziegler and oxo processes

In the

1-octanol
is shown:

The process generates a range of alcohols that are separated by distillation.

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:[24]

Such processes give fatty alcohols, 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

crude oil
.

Hydration is also used industrially to produce the diol ethylene glycol from ethylene oxide.

Fermentation

Ethanol is obtained by

butanol can be produced by fermentation processes. Saccharomyces yeast are known to produce these higher alcohols at temperatures above 75 °F (24 °C). The bacterium Clostridium acetobutylicum can feed on cellulose (also an alcohol) to produce butanol on an industrial scale.[30]

Substitution

Primary

Nozaki-Hiyama reaction
.

Reduction

Noyori asymmetric hydrogenation
is the asymmetric reduction of β-keto-esters.

Hydrolysis

Alkenes engage in an acid catalyzed 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:

Preparation of a secondary alcohol

The

diazonium salts
, which are then hydrolyzed.

Reactions

Deprotonation

With aqueous

alkyl and M is a metal
).

The acidity of alcohols is strongly affected by solvation. In the gas phase, alcohols are more acidic than in water.[31] In DMSO, alcohols (and water) have a pKa of around 29–32. As a consequence, alkoxides (and hydroxide) are powerful bases and nucleophiles (e.g., for the Williamson ether synthesis) in this solvent. In particular, RO− or HO− in DMSO can be used to generate significant equilibrium concentrations of acetylide ions through the deprotonation of alkynes (see Favorskii reaction).[32][33]

Nucleophilic substitution

Tertiary alcohols react with

alkyl chloride. Primary and secondary alcohols are converted to the corresponding chlorides using thionyl chloride and various phosphorus chloride reagents.[34]Some simple conversions of alcohols to alkyl chlorides

Primary and secondary alcohols, likewise, convert to alkyl bromides phosphorus tribromide, for example:

In the

trimethylborane-water complex in a radical substitution
reaction.

Dehydration

Meanwhile, the oxygen atom has lone pairs of nonbonded electrons that render it weakly basic in the presence of strong acids such as sulfuric acid. For example, with methanol:

Acidity & basicity of methanol

Upon treatment with strong acids, alcohols undergo the E1

Zaitsev's Rule
, which states that the most stable (usually the most substituted) alkene is formed. Tertiary alcohols are eliminated easily at just above room temperature, but primary alcohols require a higher temperature.

This is a diagram of acid catalyzed dehydration of ethanol to produce ethylene:

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.[35]

Preparation of crystal violet by protonolysis of the tertiary alcohol.

Esterification

Alcohol and

catalyst
, such as concentrated sulfuric acid:

Other types of ester are prepared in a similar manner – for example,

toluenesulfonyl
chloride in pyridine.

Oxidation

Main article: Alcohol oxidation

Primary alcohols (R−CH2OH) can be oxidized either to aldehydes (R−CHO) or to carboxylic acids (R−CO2H). The oxidation of secondary alcohols (R1R2CH−OH) normally terminates at the ketone (R1R2C=O) stage. Tertiary alcohols (R1R2R3C−OH) 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 (R−CH(OH)2) by reaction with water before it can be further oxidized to the carboxylic acid.

Mechanism of oxidation of primary alcohols to carboxylic acids via aldehydes and aldehyde hydrates

Reagents useful for the transformation of primary alcohols to aldehydes are normally also suitable for the oxidation of secondary alcohols to ketones. These include

Jones reagent
.

See also

Notes

  1. ^ Although commonly described as "salts", alkali metal alkoxides are actually better described structurally as oligomeric clusters or polymeric chains. For instance, potassium tert-butoxide consists of a cubane-like tetramer, [t-BuOK]4, that persists even in polar solvents like THF.

Citations

  1. doi:10.1351/goldbook.A00204
    . Retrieved 16 December 2013.
  2. doi:10.1351/goldbook.A00204
  3. ISBN 978-0-470-77125-9
    .
  4. ^ Berthelot M, Houdas OV (1893). La Chimie au Moyen Âge. Vol. I–III. Paris: Imprimerie nationale. vol. I, p. 137.
  5. ^ Berthelot & Houdas 1893, vol. I, pp. 138–139.
  6. ^ al-Hassan AY (2009). "Alcohol and the Distillation of Wine in Arabic Sources from the 8th Century". Studies in al-Kimya': Critical Issues in Latin and Arabic Alchemy and Chemistry. Hildesheim: Georg Olms Verlag. pp. 283–298. (same content also available on the author's website).
  7. ^ al-Hassan 2009 (same content also available on the author's website); cf. Berthelot & Houdas 1893, vol. I, pp. 141, 143. Sometimes, sulfur was also added to the wine (see Berthelot & Houdas 1893, vol. I, p. 143).
  8. ISBN 978-2-88124-594-7
    . pp. 204–206.
  9. ISBN 978-0-486-26298-7
    . pp. 51–52.
  10. ISBN 978-0-226-10379-2
    . pp. 69–71.
  11. Etymonline
    . MaoningTech. Retrieved 17 May 2018.
  12. ^ Zimmern, Heinrich (1915) Akkadische Fremdwörter als Beweis für babylonischen Kultureinfluss (in German), Leipzig: A. Edelmann, page 61
  13. ^ Lohninger H (21 December 2004). "Etymology of the Word "Alcohol"". VIAS Encyclopedia. Retrieved 17 May 2018.
  14. ^ Chisholm H, ed. (1911). "Alcohol" . Encyclopædia Britannica. Vol. 1 (11th ed.). Cambridge University Press. p. 525.
  15. ^
    OED Online. Oxford University Press
    . 15 November 2016.
  16. ^ Johnson W (1652). Lexicon Chymicum.
  17. doi:10.1039/PL8920800127
    . As ol is indicative of an OH derivative, there seems no reason why the simple word acid should not connote carboxyl, and why al should not connote COH; the names ethanol ethanal and ethanoic acid or simply ethane acid would then stand for the OH, COH and COOH derivatives of ethane.
  18. ^ a b William Reusch. "Alcohols". VirtualText of Organic Chemistry. Archived from the original on 19 September 2007. Retrieved 14 September 2007.
  19. ^ Organic chemistry IUPAC nomenclature. Alcohols Rule C-201.
  20. ^ Organic Chemistry Nomenclature Rule C-203: Phenols
  21. ^ "How to name organic compounds using the IUPAC rules". www.chem.uiuc.edu. THE DEPARTMENT OF CHEMISTRY AT THE UNIVERSITY OF ILLINOIS. Retrieved 14 November 2016.
  22. ^ Reusch W (2 October 2013). "Nomenclature of Alcohols". chemwiki.ucdavis.edu/. Retrieved 17 March 2015.
  23. ^ "Global Status Report on Alcohol 2004" (PDF). Archived (PDF) from the original on 9 October 2022. Retrieved 28 November 2010.
  24. ^
    ISBN 978-3527306732
    ..
  25. ^ Ethanol toxicity
  26. S2CID 6367081
    .
  27. PMID 10097201
    .
  28. PMID 11878258
    .
  29. ISBN 978-0-471-52677-3
    .
  30. S2CID 24074264
    .
  31. ISBN 978-0-471-72091-1
    .
  32. S2CID 204974842
    .
  33. ^ WO1994012457A1, Babler, James H., "Process for preparing tertiary alkynols", issued 1994-06-09 
  34. ISBN 978-0-470-77125-9
    .
  35. ISBN 978-3527306732
    .

General references
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