Alcohols Or Alkanols And Phenol

Alcohols Or Alkanols And Phenol

Introduction
Aliphatic Monohydric Alcohols are monohydroxyl derivatives of alkanes and have a general formula

Alcohols Or Alkanols And Phenol
Aliphatic monools may be classified as 1,2 or 3 degrees according to the nature of the carbon atom to which
the hydroxyl group is attached i.e.
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Aromatic Alcohols have aryl group attached to aliphatic portion of the alcohol separated by at least a methylene group. E.g

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Alcohols containing two hydroxyl groups are described as dihydric alcohols or diols and those with three hydroxyl groups are triols while those containing many hydroxyl groups are polyols. E.g.

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NOMENCLATURE OF ALCOHOLS

The IUPAC Names are obtained by dropping the ending “–e “of alkane and replacing it with suffix “-ol”. The position of the hydroxyl group is indicated by inserting an appropriate number between the stem name and ol.
Example
Name the following compounds using the IUPAC System
Alcohols Or Alkanols And Phenol

Solution
(a) Methanol (b) Ethanol (c) Propan-1-ol (d) 2,2-dimethylpropan-1-ol
(e) 1-bromopropan-2-ol (f) 2-methylbutan-1-ol (g) Cyclohexanol (h) Cyclopropanol

ISOMERISM

Aliphatic monools have structural isomers .i.e. Chain, functional and Positional Isomers. Ethers are functional isomers of monools.
Example:
A compound X has molecular formula C3H8O. Write down the structural formulae and names of the possible isomers of X.
Solution:

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SYNTHETIC PREPARATION OF ALCOHOLS

  1. From Alkenes
Alcohols Or Alkanols And Phenol

From Alkyl halides

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  1. From Carbonyl compounds
    Reduction of carbonyl compounds generates alcohol. Aldehydes are reduced to Primary Alcohol while Ketones to Secondary Alcohol.
    The reducing agents commonly used are Na/ethanol, LiAlH4 in dry ether, NaBH4 and water, amalgamated Zinc and concentrated Hydrochloric acid, finely divided Ni or Pt with hydrogen gas.
    Lithium Aluminium hydride does reduce a double bond if it is present in the carbonyl compound.
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  1. Grignard Reagent Synthesis
    See Reactions of Haloalkanes.
  2. Reduction Of Carboxylic acids
    Carboxylic acids are reduced to Primary Alcohols using LiAlH4 in dry ether.
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  1. From Esters
    Esters are hydrolysed by aqueous sodium hydroxide solution to generate an alcohol. However this is not usually done since esters are obtained from alcohols.
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  1. Cannizzaro Reaction
    Aromatic Aldehydes without @-hydrogen atoms undergo self-reduction and oxidation in sodium hydroxide solution.
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DOMESTIC PRODUCTION OF ETHANOL

Ethanol is mainly prepared by fermentation process. Fermentation is a process where starch or sugar is converted to ethanol by yeast enzymes.

The main sources of the starch materials include maize, millet, cassava, sorghum, potatoes, banana, rice,
molasses, etc. The enzymes that participate in the fermentation process and their stages include:

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Qn:
a) Describe the processes involved in the production of ethanol from a named material domestically
b) State briefly how the purification of the ethanol produced can be done
c) State four uses of ethanol
d) State two effects of over consumption of ethanol on the human body.

Physical Properties of Alcohols

a) Solubility
Lower members of the series are soluble however, solubility decreases as the hydrocarbon portion increases. The miscibility of alcohols is due to ability of the formation of hydrogen bond with water molecule.

b) Boiling Points
Alcohols boil at higher temperatures expected because the molecules associate through hydrogen
bonding which requires an extra energy to break. Within the series, boiling points increase with molecular mass.

c) Density
Density increases with increasing molecular mass although branching reduces the factor. Aliphatic alcohols are less dense than water while Aromatic alcohols tend to be slightly denser than water.

REACTIONS OF ALCOHOLS

  1. With Electropositive Metals
    Although Alcohols are neutral to neutralization indicators, the hydroxyl group can be replaced by metals of Group I and II of the periodic table. The products are hydrogen gas and metal Alkoxide.
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  1. Halogenation
    This can be done by:
    a) Using Hydrogen Halide
    They react with hydrogen halides to form alkyl halides. The order of reactivity for alcohols is 3>2>1 degree
    while for hydrogen halides is HI>HBr>HCl.
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1degree Alcohols undergo bromination with hydrogen bromide which is generated from sodium bromide and
concentrated sulphuric acid.
In case of hydrogen chloride, the reaction is carried by using anhydrous Zinc chloride and concentrated
hydrochloric acid. (Luca’s Reagent)
The reagent is used to distinguish the classes of monools i.e.
– 3 degree Alcohol forms a cloudy solution immediately
– 2 degree Alcohols forms cloudiness between 5-10minutes
– 1 degree Alcohol no observable change.
Mechanism

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b) Using Phosphorous Halides

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c) Using Thionyl chloride
Thionyl Chloride and Phosphorous pentachloride generate alkyl chloride.

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  1. Concentrated Sulphuric acid
    The products of the reaction depend on the conditions of the reaction under which it is carried out.
    a) At lower temperatures (below 140 degrees C), alkyl hydrogen sulphate is obtained
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Mechanism

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b) At about 140 degrees (c) when excess alcohol, ether is obtained.

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Mechanism
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c) When the reaction is carried out at about 180oC, an alkene is obtained. Aluminium Oxide at 350 degrees C or concentrated orthophosphoric acid can be used.

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  1. Oxidation reaction
    The product oxidation depends on the type of alcohol and partly the power of oxidizing agent.

Primary Alcohols are oxidized to Aldehydes and the reaction proceeds to carboxylic acid while Secondary Alcohols are oxidized to Ketones.
Tertiary Alcohols are resistant to oxidation.
The oxidizing agents commonly used are acidified potassium dichromate or acidified chromium (VI) oxide

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  1. Esterification reaction
    The process whereby a primary alcohol reacts with a monocarboxylic acid is known as esterification.
    The reaction usually takes place in presence of concentrated sulphuric acid and it is reversible reaction.
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Mechanism:
This was determined using radioactive Oxygen (18). The primary alcohol containing oxygen-18 is reacted with monocarboxylic acid. The mass spectrometer is used to analyse the ester and water formed. The oxygen-18 is found in the ester only and not water indicating that carbonoxygen single bond in the acid and oxygen-hydrogen bond in the alcohol are bonded.

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Iodoform reaction

Alcohols of the form react with iodine in presence of sodium hydroxide solution to form a yellow solid.
Iodine is an oxidizing agent and can oxidize alcohols to Aldehydes or Ketones.

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IEthanol
is the only primary alcohol which gives a positive.
Note. Chlorine forms chloroform which is colourless liquid, Bromine forms bromoform which is reddish-brown.

PHENOL

Introduction. These are compounds containing a hydroxyl group attached directly to aromatic nucleus (Benzene) and
have a general formula ArOH.
Like alcohols they may be monools or polyols depending on the number of the hydroxyl groups they
contain.

Examples include:

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Physical Properties

Phenol is colourless crystalline solid although often found red tint due to presence of oxidation products. It is slightly soluble but very soluble in organic solvents.
Note. The introduction of the hydroxyl group into an already substituted aromatic ring especially in position-4 produces a marked increase in the boiling point. E.g. the greater volatility of 2-nitrophenol is attributed to intramolecular hydrogen bonding while the higher boiling points of 3- and 4- isomers are direct result of intermolecular hydrogen bonding.

Preparation of Phenol
a) From Benzene sulphonic acid

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b) From Benzene Diazonium salt.

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c) Cumene process

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Reactions of Phenol
Phenol undergoes two distinct reactions i.e.
a) Side-chain substitution reactions which generally involves replacement of the acidic proton
b) Electrophilic substitution in the ring.

Phenol as an acid
Phenol is a stronger acid than alcohols but weaker acid compared to carboxylic acid.
Question: Explain briefly why phenol is more acidic compared to Ethanol
Solution: In phenol, the lone pair of electrons on the oxygen atom interacts with delocalized electrons of
the benzene ring. This strengthens the carbon-hydrogen bond while weakening the oxygenhydrogen bond consequently; phenol loses a proton easily making it acidic.

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In ethanol, the oxygen-hydrogen bond is not weakened and the proton is not easily lost. This is because there are no delocalized electrons to interact with lone pairs of electrons on the electrons.

Note: Due to the above reason, phenol differs from alcohols in that it does not react with halogen
acids or Phosphorus halides and does not undergo elimination reaction
a) Side-chain reactions include:
1) Esterification reaction
Phenol reacts with acid chlorides and acid anhydrides to form esters

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2) Ether Formation
Sodium phenate (Sodium phenoxide) reacts with alkyl halides to form ethers