Chemical property of Alcohol

Subject: Chemistry

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Overview

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. $$R-CH_2-OH>R_2CH-OH>R_3-C-OH$$ 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. $$\underbrace{R-COOH}_{Carboxylic\,acid}+\underbrace{R-OH}_{alcohol}\xrightarrow{Conc.H_2SO_4}\underbrace{R-COOR}_{Ester}+H_2O$$
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.

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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.

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

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

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

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

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