Tamilnadu Samacheer Kalvi 12th Chemistry Notes Chapter 11 Hydroxy Compounds and Ethers Notes
Alcohols: An organic compounds containing hydroxyl (- OH) group is called alcohols.
Hydroboration:
Diborane reacts with an alkene to form trialkyl borane which on treatment with H2O2 in presence of NaOH gives an alcohol.
Baeyer’s reagent: Cold alkaline solution of potassium permanganate is called Baeyer’s reagent.
Saponification : The alkaline hydrolysis of these fats gives glycerol and the reaction is known as saponification.
Lucas test: When alcohols are treated with Lucas agent (a mixture of con. HC1 and anhydrous ‘ ZnCl2) they produce alkyl chloride.
Victor Meyer’s test: This test is based on the behaviour of the different nitro alkanes formed by the three types of alcohols with nitrous acid and it consists of the following steps.
- Alcohols are converted into alkyl iodide by treating it with I2 /P.
- Alkyl iodide so formed is then treated with AgNO2 to form nitro alkanes.
- Nitro alkanes are finally treated with HNO2 (mixture of NaNO2 / HCl) and the resultant solution is made alkaline with KOH.
Result:
- Primary alcohol gives red colour
- Secondary alcohol gives blue colour.
- No colouration will be observed in case of tertiary alcohol.
Elimination reactions: When alcohols are heated with a suitable dehydrating agents like sulphuric acid, the H and OH present in the adjacent carbons of alcohols are lost and it results in the formation of a carbon – carbon double bond.
Order of reactivity: The relative reactivities of alcohols in the dehydration reaction follows the order
primary < secondary < tertiary
Saytzeff’s rule: During intramolecular dehydration, if there is a possibility to form a carbon – carbon double bond at different locations, the preferred location is the one that gives the more substituted alkene (stable alkene).
Swern oxidation: In this method, dimethyl sulfoxide (DMSO) is used as the oxidising agent, which converts alcohols to ketones / aldehydes.
Biological oxidation: The fermentation of the food consumed by an animal produces alcohol. To detoxify the alcohol, the liver produces an enzyme called alcohol dehydrogenase (ADH). Nicotinamide adenine dinucleotide (NAD) present in the animals acts as a oxidising agent and ADH catalyses the oxidation of toxic alcohols into non-toxic aldehyde.
Uses of methanol:
- Methanol is used as a solvent for paints, varnishes, shellac, gums, cement, etc.
- In the manufacture of dyes, drugs, perfumes and formaldehyde.
Uses of ethanol:
- Ethanol is used as an important beverage.
- It is also used in the preparation of
- a. Paints and varnishes.
b. Organic compounds like ether, chloroform, iodoform, etc.,
c. Dyes, transparent soaps. - As a substitute for petrol under the name power alcohol used as fuel for aeroplane
- It is used as a preservative for biological specimens.
Uses of ethylene glycol:
- Ethylene glycol is used as an antifreeze in automobile radiator.
- Its dinitrate is used as an explosive with DNG.
Uses of glycerol:
- Glycerol is used as a sweetening agent in confectionery and beverages.
- It is used in the manufacture of cosmetics and transparent soaps.
- It is used in making printing inks and stamp pad ink and lubricant for watches and clocks.
- It is used in the manufacture of explosive like dynamite and cordite by mixing it with chaina clay.
Phenols: They are organic compounds in which a – OH group is directly attached to a benzene ring. The carbon bearing the – OH group is sp2 hybridized.
Dows process: When Chlorobenzene is hydrolysed with 6 – 8% NaOH at 300 bar and 633K in a closed vessel,sodium phenoxide is formed which on treatment with dilute HC1 gives phenol.
Kolbe’s Schmitt reaction: In this reaction, phenol is first converted into sodium phenoxide which is more reactive than phenol towards electrophilic substitution reaction with CO2. Treatment of sodium phenoxide with CO2 at 400K, 4-7 bar pressure followed by acid hydrolysis gives salicylic acid.
Riemer Tiemann Reaction: On treating phenol with CHCl3 / NaOH, a – CHO group is introduced at ortho position.
Phthalein reaction: On heating phenol with phthalic anhydride in presence of con.H2SO4, phenolphthalein is obtained.
Coupling reaction: Phenol couples With benzene diazonium chloride in an alkaline solution to form p-hydroxy azobenzene (a red orange dye).
Test to differentiate alcohol and phenols:
- Phenol react with benzene diazonium chloride to form a red orange dye, but ethanol has no reaction with it.
- Phenol gives purple colouration with neutral ferric chloride solution, alcohols do not give such coloration with FeCl3.
- Phenol reacts with NaOH to give sodium phenoxide. Ethyl alcohol does not react with NaOH.
Uses of phenol:
- About half of world production of phenol is used for making phenol formaldehyde resin. (Bakelite).
- Phenol is a starting material for the preparation of
a. drugs such as phenacetin, Salol, aspirin, etc.
b. phenolphthalein indicator.
c. explosive like picric acid. - It is used as an antiseptic-carbolic lotion and carbolic soaps.
Ethers: Ethers are a class of organic compound in which an oxygen atom is connected to two alkyl / aryl groups (R – O – R’). The general formula of aliphatic ether is CnH2n + 2O
Simple ethers: Both alkyl or aryl groups attached to oxygen atom are same. (R = R’)
Mixed ethers: Both alkyl or aryl groups attached to oxygen atom are different. (R ≠ R’)
Williamsons synthesis: When an alkyl halide is heated with an alcoholic solution of sodium alkoxide, the corresponding ethers are obtained. The reaction involves SN2 mechanism.
Uses of Diethyl ether:
- Diethyl ether is used as a surgical anesthetic agent in surgery.
- It is a good solvent for organic reactions and extraction.
- It is used as a volatile starting fluid for diesel and gasoline engine.
- It is used as a refrigerant.
Uses of anisole:
- Anisole is a precursor to the synthesis of perfumes and insecticide pheromones,
- It is used as a pharmaceutical agent
pKa Values of some alcohols and phenols:
|
S.No. |
Compound |
pKa Value |
| 1. | methonal | 15.5 |
| 2. | ethanol | 15.9 |
| 3. | propan – 2 – ol | 16.5 |
| 4. | 2 – methyl propan 2 – ol | 18.0 |
| 5. | Cyclohexanol | 18.0 |
| 6. | Phenol | 10.0 |
| 7. | o – nitrophenol | 7.2 |
| 8. | p – nitrophenol | 7.1 |
| 9. | m – nitrophenol | 8.3 |
| 10. | o – cresol | 10.2 |
| 11. | m – cresol | 10.1 |
| 12. | p – cresol | 10.2 |