Ciudad de Londres de Croydon

See also: Alcohol

This article describes the chemical family of alcohols . For the other significances of the word, to see the page of homonymy Alcohol

In Organic chemistry, a alcohol is a Composé organics of which one of the Carbone S is related to a Groupement hydroxyl (- OH). The ethanol (or ethanol) entering the composition of the alcoholic drinks is a particular case of alcohol, but all alcohols are not specific to consumption. In particular, the Méthanol is toxic and mortal with high amount.

Use

Alcohols are used in chemical industry like:

  • Solvent S: the ethanol, not very toxic, are used in the Parfum S and the Médicament S

  • Combustible S: methanol and the ethanol can replace the gasoline and the Fioul because their combustion does not produce toxic smoke

  • Reactive S: the urethans, the Ester S or the Alcène S can be synthesized starting from alcohols

of them

Production

Alcohols can be produced by alcoholic fermentation, in particular methanol starting from wood and the ethanol starting from the fruits and of cereals. Industry has there recourse only in the case of ethanol to produce fuel and drinks. In the other cases, alcohols are synthesized starting from the organic compounds drawn from the Natural gas or the Pétrole.

Classification of alcohols

In a generic way, an alcohol thus contains the sequence
R - OH
where R is a variable radical, often an alkane of which one of the Hydrogène S.A. replaced by the grouping hydroxyl.

According to the nature of carbon carrying the grouping alcohol, one distinguishes:

  • the primary education alcohols , whose carbon comprising the grouping hydroxyl is related to two atoms of Hydrogène and an organic radical R:

  • the secondary alcohols , whose carbon comprising the grouping hydroxyl is related to an atom of organic Hydrogène and two radicals R and R':

  • the tertiary alcohols , whose carbon comprising the grouping hydroxyl is related to three organic radicals R, R' and R" :

  • the phenol S , are particular alcohols whose grouping hydroxyl is related to a carbon of a benzene Cycle

  • There exists also a particular group of alcohols called énol S . It is about a having alcohol moreover one function olefinic hydrocarbon. It is acted in fact of a tautomeric form of a Aldéhyde or a Cétone (the phenol is in addition a énol). The majority form is the aldehyde or the ketone, but not the énol.

Nomenclature

When alcohol is the principal function, it is enough to add the suffix - ol in the name of alkane corresponding and to indicate the number of the atom where the hydroxyl group is fixed, although sometimes when it is not necessary to description, this last information is omitted. If it is not the principal function, it is necessary to add the prefix hydroxy- preceded by the number of the atom or the group is fixed. For the combined base of alcohol, the ion alcoholate (see paragraph acidity), it is enough to add the suffix - oate with corresponding alkane.

Examples:

  • ethanol:
  • butan-2-ol:
  • acid 3-hydroxy-propanoïque:

Physicochemical properties

Aspect

Low-weight alcohols molecular are presented to room temperature like colorless liquids; heavier alcohols like solids blanchâtres.

Polarity and presence of hydrogen bonds

The hydroxyl group generally makes the alcohol molecule polar. That is with its geometry (trihedral, free doublets localized on oxygen), and with respective electronegativities of carbon, oxygen and hydrogen (Xsi (O) >Xsi (C)>Xsi (H). These groups can form hydrogen bonds between them or with others made up (what explains their solubility in water and other alcohols).

Not boiling

The point of boiling is high at alcohols

  • because of the grouping hydroxyl which allows the hydrogen bonds
  • because of the carbonaceous chain which undergoes forces of van der Waals.

Also, the point of boiling of alcohols is it all the more high as

  • the number of functions alcohol is large: a diol has a boiling point higher than that of the equivalent simple alcohol, which itself has a boiling point higher than corresponding hydrocarbon. For example, among alcohols derived from the isopropane, the Glycerol (propan-1,2,3-triol) end with 290 °C, the Propylene glycol (propan-1,2-diol) with 187 °C and the propan-1-ol with 97 °C.
  • the carbonaceous chain is long: among linear alcohols, methanol boils with 65 °C, the ethanol with 78 °C, the propan-1-ol with 97 °C, the butan-1-ol with 118 °C, the pentan-1-ol with 138 °C and the hexan-1-ol with 157 °C.
  • the carbonaceous chain is linear, by maximization of the surface of the molecule likely to undergo the forces of van der Waals. For example, among pentanols, the pentan-1-ol end with 138 °C, 2-methyl-butan-1-ol with 131 °C and thedimethylone with 102 °C.

Solubility

The solubility in water of alcohols depends on the two same factors as previously, but which are antagonistic here:

  • the chain carbonaceous, hydrophobic, tends to make the molecule nonsoluble.
  • the grouping hydroxyl, absorbent (thanks to its hydrogen bonds) tends to make the molecule soluble

Thus, alcohols are thus all the more water soluble:

  • the carbonaceous chain is small: methanol, the ethanol and the propan-1-ol are soluble in all proportions in water, the butan-1-ol in proportion of 79 g/l, the pentan-1-ol of 23 g/L, the hexan-1-ol of 6 g/l, the heptan-1-ol of 2 g/l and heavier alcohols are practically insoluble.
  • the number of function alcohols is high. For example, the butanediols are soluble in all proportions while butanol is it only in proportion of 79 g/l.
  • the carbonaceous chain is nonlinear: among pentanols, thedimethylone is soluble in a proportion of 102 g/l, the 2-methyl-butan-1-ol of 100 g/l and the pentan-1-ol of 23 g/l.

Low-weight alcohols molecular are generally soluble in organic solvents like the Acétone, or the ether.

Reactivity

Acidity

Had with connection O-H

The strong polarization of connection O-H gives the possibility of an ionic rupture: alcohols thus constitute Acide S weak, and same very weak (pKA lain in general between 16 and 18,10 for phenols, in water) by release of a H+ proton of the hydroxyl group. They are thus much weaker than water (except for methanol) and express their acid character only in nonaqueous solutions, while reacting for example with the bases NaNH2 in a solution of Ammoniac. One calls the combined base of an alcohol a ion alcoholate (or alkoxyde ).

Had with the free doublets of oxygen

One of the free doublets of oxygen is able to capture a proton: alcohol is thus a bases of Brönsted, indifferent (pKA (ROH2+/ROH) from approximately -2), its acid combined, the ion alkyoxonium, being a strong acid, being able to be present only in very minor amount (except in the presence of an important concentration in strong acid).

Thanks to the reactivity as of these doublets, alcohol is also a Base of Lewis

Nucleophilicity

Alcohols are very the good nucleophilic ones, property always due to the reactivity of the free doublets of oxygen, reaction in addition fast.

Nucleofugacity

  • the connection CO being polarized, there is possibility of rupture ionic: R-OH - > R+ +- OH. This rupture however remains very difficult, making group Hydroxyle a bad nucléofuge (group therefore).

  • However, in its protonic form, the ion alkyloxonium, the rupture is much easier.
This property in particular enables him, as we will see it thereafter, to take part in reactions of nucleophilic substitutions and reactions of eliminations.

Reactions

Nucleophilic reaction of substitution

Alcohols can undergo a nucleophilic Substitution in which the hydroxyl group is replaced by another radical Nucléophile.

Transformation into ethyl oxide

Synthesis of Williamson

Passage de l' alcohol with the halogénoalcanes

Starting from a hydracid

  • Reaction:

reaction with a hydracid, chloride, bromide or iodide of hydrogen to form a halogénoalcane (Halide of alkyl or halogenous derivative):

R- (OH) + HX - > X-ray + H2O, X representing the halogen Cl, Br or I (F is not used, the reaction is beacup too slow).

It is about the opposite reaction of the reaction of hydrolysis of the halogenous derivatives.

  • Properties:

    • slow Reaction.
    • reversible Réaction
    • It is favoured in the direct direction if hydracid is concentrated and in excess, in the other direction in the event of water excess, and in basic medium.
    • stereochemistry: on the class of alcohol (see mechanisms)
    • According to the class of alcohol depends, and of the nature of hydracid, the reaction more or less slow and is more or less limited (that is also due to the mechanisms).
One can thus carry out a classification: RIOH < RIIOH < RIIIOH (" <" = " reacts less quickly and in more limited way que") and HF<

  • Mechanisms: According to the class of alcohol, limiting mechanisms are possible.

    • a primary education alcohol (thus little encumbered stériquement) will react according to the one mechanism of the type SN2. All the properties are thus those of SN2 (inversion of relative configuration, enantierospecificity,…)
    • a tertiary alcohol follows a mechanism of the type SN1: indeed, the tertiary carbocation formed is relatively stable. The properties are thus those of SN1 (not stereoselectivity, Racémisation if carbon carrying the hydroxyl group is asymmetrical,…)
    • a secondary alcohol can follow a mechanism of the SN1 type, even a mechanism intermédiare between SN1 and SN2.

    • Note:

      • These reactions passing by an intermediary carbocationic can cause rearrangements.
      • these reactions can be catalyzed by an acid of Lewis like zinc chloride. It is then formed a adduit, which leads to the formation (HOZNCl2 is better group therefore than H2d' a carbocation, thus facilitating the addition of the halogen.
      • This reaction can be wide with other acids, like the acids phosphoric, sulphuric…

    From derivatives acid inorganic
    Various compounds can be employed to allow a halogenation of alcohols.
    • For chlorination, the most current reagents are phosgene (COCl2), the Chlorure of thionyl (SOCl2), the phosphorus oxychloride (POCl3), and the phosphorus chlorides (PCl3) and (PCl5).
    • For a bromination, (PBr3) and couples it CBr4/triphénylephosphine.
    • the iodides are generally synthesized by displacement of a chloride by NaI in the acetone (NaI is soluble there, contrary to NaCl, whose precipitation is the driving force of the reaction).

    Reaction of elimination

    Alcohols can undergo a Réaction of elimination at high temperature and produce olefinic hydrocarbons:

    CH3-CH2 (OH) - > CH2=CH2 + H2O
    This reaction can be reversed to synthesize alcohols starting from olefinic hydrocarbons and of water, but remains not very reliable because it produces mixtures of alcohols.

    Esterification

    In react with a Carboxylic acid , alcohol forms a Ester (for more precise details, to see the article concerned).

    Oxidation of alcohols

    See also: Oxidation of an alcohol

    Current alcohols

    Toxicity

    The ethanol is a substance toxic Psychotrope even mortal in great quantity, even in quantity moderated in the event of regular consumption (see Alcoolisme).

    Other alcohols are generally much more toxic because

    • their elimination is longer;
    • their elimination leads to renal damage ;
    • their elimination produces toxic substances (for example, the Foie degrades the Méthanol in Formaldéhyde which causes blindness or death).
    Their ingestion must be regarded as a medical emergency.

    See too

    Be-X-old: Сьпірт Simple: Alcohol

    Random links:Data-processing peripheral | Sabor | Moussac (Gard) | Putsch of Kapp | Automobile Grand Prix of Germany 1998 | Seattle University