Alchohols,phenols,and ethers

• Acylation :
• Alcohols, phenols and ethers are compounds containing a C-O single bond.
• The functional group present in alcohols and phenols is -OH (hydroxyl) group and that present in ethers is -O- group (oxy group).
• In alcohols, the -OH group is bonded to an alkyl group, hence the general formula of alcohols is R - OH.
• In phenols, the -OH group is bonded to an aryl group, hence the general formula of phenols is Ar - OH.
• Alcohols are classified based on the number of -OH groups as monohydric (contain only one -OH group), dihydric (contain two -OH groups), trihydric (contain three -OH groups) and polyhydric (contain more than two -OH groups).
• Examples for monohydric alcohols are methanol (CH3 - OH), ethanol (CH3 - CH2 - OH) etc.
• Examples for dihydric alcohol are ethylene glycol (HO - CH2 - CH2 - OH) and trihydric alcohol is glycerol (HOCH2 - CHOH - CH2 OH).
• Monohydric alcohols may be further classified according to the hybridisation of the carbon atom to which the hydroxyl group is attached.
• Alcohols are soluble in water due to their ability to form hydrogen bonds with water molecules.
• The –OH group in alcohols and phenols is involved in intermolecular hydrogen bonding.
• The acid strength of alcohols decreases in the order: Primary alcohols > Secondary alcohols > Tertiary alcohols.
• In the resonating structures (II), (III) and (IV), there is a positive charge on the electronegative oxygen atom and hence it attracts the bond pair of electrons in O-H bond.
• The boiling points of alcohols and phenols increase with increase in the number of carbon atoms due to the increase in van der Waals forces of attraction.
• It is easy to remove the hydrogen atom as H+ ion and thus phenol is acidic in nature.
• The solubility of alcohols decreases with increase in size of alkyl/aryl groups.
• Alcohols and phenols react with active metals such as sodium, potassium and aluminium to yield corresponding alkoxides/phenoxides and hydrogen.
• Due to the greater electronegativity of sp2 hybridized carbon (due to greater s-character), the benzene ring acts as an electron withdrawing group.
• The lone pair electrons present in oxygen atom of –OH group enter in the benzene ring and the following resonating structures are obtained: (I) (II) (III) (IV) ( V )
• In phenols, the –OH group is directly bonded to an sp2 hybridized carbon atom of the benzene ring.
• Alcohols are weaker acids than water.
• Phenol is more acidic than alcohol due to the following reasons:
• Alcohols are acidic in nature due to the polar nature of O-H bond.
• Compounds containing sp3 C-O bond have the -OH group attached to an sp3 hybridised carbon atom of an alkyl group.
• These alcohols are further classified as primary, secondary and tertiary alcohols.
• Allylic alcohols have the -OH group attached to an sp3 hybridised carbon next to the carbon-carbon double bond.
• Ethers can be prepared by dehydration of alcohols.
• Both the enzymes invertase and zymase are produced by yeast.
• Ethanol can also be manufactured by hydration of ethene.
• Ethanol can be further concentrated to 100% by distilling with a small amount of benzene.
• Alcohols undergo dehydration in the presence of protic acids like H 2 SO 4 or H 3 PO 4 to give ethers based on the reaction conditions.
• This method is suitable for the preparation of ethers having primary alkyl groups only.
• Fermentation takes place in anaerobic conditions, i.e., in the absence of air.
• The commercial alcohol is made unfit for drinking by mixing in it some copper sulphate (to give it a colour) and pyridine (a foul smelling liquid), and it is known as denaturation of alcohol.
• If both the alkyl groups on both sides of the – O - group are identical, it is called symmetric ether and if they are different, it is called asymmetric ether.
• If methanol is used for denaturation, it is called methylated spirit.
• The ethanol solution can be concentrated upto 95.6% by fractional distillation, and the resulting 95.6% alcohol is called Rectified spirit.
• Invertase catalyzes the conversion of sucrose into glucose and fructose.
• If air gets into fermentation mixture, the oxygen of air oxidizes ethanol to ethanoic acid (acetic acid), which destroys the taste of alcohol.
• The ethanol solution obtained by fermentation contains only 8 - 10% ethanol and it is called wash.