Chemical property of Alcohol

Chemical property of Alcohol

A. Reaction involving cleavage of O-H bonds

B. A reaction involving cleavage of C-OH bond.

C. Other reactions.

A.A reaction involving cleavage of O-H bonds

1. Reaction with metals.acidic nature.

Alcohol reacts with active metals like sodium to evolve Hydrogen gas. This shows that alcohols are acidic in nature.

$$\underbrace{R-OH}_{Alcohol}+Na→\underbrace{RONa}_{Sodium\,alkoxide}+\frac{1}{2}H_2$$

The presence of electrons donating group (+I groups) decreases the acidic strength of alcohol. Therefore, alcohols are less acidic than water.

$$\underbrace{H-O-H}_{water}$$

$$\underbrace{R-O-H}_{Alcohol}$$

Similarly, acidic strength decreases gradually on moving from primary to secondary to tertiary alcohol.

$$R-CH_2-OH>R_2CH-OH>R_3-C-OH$$

2. Reaction with carboxylic acids.

Esterification Alcohols react with carboxylic acids in presence of small amount of conc. H₂SO₄ to produce sweet smelling compound called esters. Thereaction is known as esterification.

$$\underbrace{R-COOH}_{Carboxylic\,acid}+\underbrace{R-OH}_{alcohol}\xrightarrow{Conc.H_2SO_4}\underbrace{R-COOR}_{Ester}+H_2O$$

$$\underbrace{CH_3-COOH}_{Ethanoic\,acid\,or\,Acetic\,acid}+\underbrace{C_2-H_5-OH}_{Ethanol}\xrightarrow{Conc.H_2SO_4}\underbrace{CH_3-COOC_2H_5}_{Ethyl\,ethonate\,orEthyl\,acetate}+H_2O$$

3. Reaction with acid chlorides and anhydride.

Acylation when alcohols are treated with acid chlorides and anhydride seperately in presence of pyridine,ester are formed. This reaction is known as acylatuion.

$$\underbrace{R-OH}_{Alcohol}+\underbrace{R-COCl}_{Acid\,chloriode} \xrightarrow{Pyridene}R-COOR+HCl$$

Example.

$$\underbrace{CH_3COCl}_{Ethanoyl\,chloride\,or\,(Acetyl\,chloride}+\underbrace{C_2H_5OH}_{Ethanol}\xrightarrow{Pyridene}\underbrace{CH_3COOC_2H_5}_{Ethyl\,ethonate}+HCl$$

$$\underbrace{R-OH}_{Alcohol}+\underbrace{RCOOCOR}_{Acid\,anhydride}\xrightarrow{Pyridene}\underbrace{R-COO-R}_{Ester}+\underbrace{R-COO-H}_{Carboxylic\,acid}$$

Example.

$$\underbrace{CH_3-COO-CO-CH_3}_{Ethanoic\,ahhydride\,or\,(Acetic\,anhydride)}\underbrace{C_2H_5OH}_{Ethanol}\xrightarrow{Pyridene}\underbrace{CH_3-COO-C_2H_5}_{Ethyl\,ethonate}+\underbrace{CH_3COOH}_{Ethoic\,acid}$$

4. Reaction with Grignards reagent.

Alcohols from alkenes by reacting with Grignard reagent in which alkanes contain carbon atom corresponding to Grignard reagent.

$$\underbrace{R-OH}_{Alcohol}+\underbrace{R'-Mg-X}_{Grignards\,Reagent}→\underbrace{R'-H}_{Alkane}+ROMgX$$

Example.

$$\underbrace{CH_3-CH_2-OH}_{Ethanol}+\underbrace{CH_3MgBr}_{Methyl\,Magnesium\,bromide}+\underbrace{CH_4}_{Methane}+CH_3CH_2OMgBr$$

B. The reaction involving cleavage of C-OH Bonds.

1. Reaction with halogen acid (HX).

Haloalkanes is obtained when alcohol is treated with halogen acid.

$$\underbrace{R-OH}_{Alcohol}\xrightarrow{HBr.Conc.H_2SO_4}\underbrace{R-Br}_{Bromo\,alkane}+H_2O$$

$$\underbrace{R-OH}_{Alcohol}\xrightarrow{HI\,AlCl_3\,(Anhy)}\underbrace{R-I}_{IOdoalkane}+H_2O$$

$$\underbrace{R-OH}_{Alcohol}\xrightarrow{Conc.HCL\,Anhy.ZnCl_2}\underbrace{R-Cl}_{Chloro\,alkane}+H_2O$$

2. Reaction with phosphorous halide (PCl₃ orPCl₅).

When alcohols are refluxed with phosphorous halides, haloalkane is obtained.

$$\underbrace{CH_3-CH_2OH}_{Ethanol}+PCl_3\xrightarrow{Δ}\underbrace{CH_3-CH_2-Cl}_{Chloro\,ethane}+H_3PO_3$$

$$\underbrace{CH_3-CHOH-CH_3}_{2-Propanol}+PCl_5\xrightarrow{Δ}\underbrace{CH_3-CHCl-CH_3}_{2-Chloro\,propane}+POCl_3+HCl$$

3. Reaction with thionyl chloride (SOCl₂).

Alcohols reacts with thionyl chloride in presence of pyridine to form chloroalkane.

$$\underbrace{CH_3-CH_2-CH_2OH}_{1-Propanol}+SoCl_2\xrightarrow{Pyridine\,heat}\underbrace{CH_3-CH_2-CH_2-Cl}_{1-Chloropropane}+SO_2(gas)+HCl(Gas)$$

4. Reaction with ammonia (NH₃).

$$\underbrace{C_2H_5-OH}_{Ethanol}+H-NH_2\xrightarrow{Al_2O_3\,360^0}\underbrace{C_2H_5-NH_2}_{Ethanamine}+H_2O$$

When vapour of alcohol are past over heated at 36⁰0, amine are obtained.

$$\underbrace{C_2H_5NH_2}_{Ethyl\,amine\,(1^0)}\xrightarrow{C_2H_5OH\,Al_2O_3\,360^0C}\underbrace{(C_2H_5)_2NH}_{Diethyl\,amine(2^0)}\xrightarrow{C_2H_5OH\,Al_2O_3\,360^0C}\underbrace{(C_2H_5)N+H_2O}_{Triethyl\,amine\,(3^0)}$$

Reference.

Bahl, B S, Bahl, and Arun. Advanced Organic chemistry. S. Chand and company Ltd., n.d.

Sthapit, M K, R R Pradhananga, and K B Bajracharya. Foundations of chemistry. Taleju Prakashan, n.d.

Tewari, K S, S N Mehrotra, and N K Vishnoi. A textbook of organic chemistry. Vikash publishing House Pvt. ltd., n.d.

Verma, N K and S K Khanna. Compressive chemistry. 8th edition. Laxmi publications P. Ltd., 1999.