Methanol

Methanol, CH3OH, (i.e. methyl alcohol) is the simplest aliphatic alcohol, and is the first member of the homologous series.

Methanol is a colourless liquid, completely miscible with water and organic solvents and is very hydroscopic.

Methanol has an agreeable odour, and a burning taste.

Methanol is a potent nerve poison.

Methanol has the physical properties

Manufacture of Methanol

Methanol is made by a method different from that used in the preparation of the other alcohol. The naphtha fraction from the distillation of crude petroleum, is used as a raw material for the manufacture of methanol. When naphtha is reacted with a high steam ratio, under pressure and at high temperature, synthesis gas of low methane content is obtained. Most of the carbon from the naphtha is converted to carbon monoxide and carbon dioxide which can be removed from the gaseous mixture to leave hydrogen of high purity.


		            1000 degC       
	C    +    H2O           ==>             CO      +       H2      
			                     Carbon          Hydrogen        
		                            Monoxide        

When a mixture of hydrogen and carbon monoxide in the ratio 2:1 is passed over a catalyst (e.g. a mixture of zinc oxide and chromium oxide) under high pressure and at high temperature, methanol is formed.


			             400 degC        
	CO      +       2H2             ==>             CH3OH   
              				                Methanol 

Chemical Properties of Methanol

Combustion of Methanol
Methanol burns with a pale-blue, non-luminous flame to form carbon dioxide and steam.


	2CH3OH  +  302  ==>     2CO2   +  4H2O  

Oxidation of Methanol
Methanol is oxidised to form formaldehyde.


		 [O]    
         CH3OH   ==>             H.CHO   +       H2O     
        Methanol              Formaldehyde    

If the oxidising agent is in excess, the formaldehyde is further oxidised to formic acid and then to carbon dioxide and water.


		[O]             [O]     
	H.CHO   ==>     H.COOH  ==>     CO2 +  H2O      
    Formaldehyde        Formic  
		        Acid    

Catalytic Oxidation of Methanol
The catalytic oxidation of methanol using platinum wire is of interest as it is used in model aircraft engines to replace the sparking plug arrangement of the conventional petrol engine. The heat of reaction is sufficient to spark the engine.
Dehydrogenation of Methanol
Methanol can also be oxidised to formaldehyde by passing its vapour over copper heated to 300 degC. Two atoms of hydrogen are eliminated from each molecule to form hydrogen gas and hence this process is termed dehydrogenation.


			Cu              
		     300 degC        
		CH3OH   ==>    H.CHO + H2      
		Methanol    Formaldehyde    

Dehydration of Methanol
Methanol does not undergo dehydration reactions. Instead, in reaction with sulphuric acid the ester, dimethyl sulphate is formed.


	       concentrated    
		  H2SO4           
	2 CH3OH    ==>     (CH3)2SO4       +       H2O     
	Methanol            Dimethyl              Water   
		           Sulphate        

Esterification of Methanol
Methanol reacts with organic acids to form esters.


			      H(+)    
	CH3OH  +        H.COOH  ==>     H.COO.CH3 + H2O  
	Methanol        Formic            Methyl     Water   
		        Acid              Formate 

Substitution of Methanol with Sodium
Methanol reacts with sodium at room temperature to liberate hydrogen. This reaction is similar to the reaction of sodium with ethanol.


		2 CH3OH +       2 Na    ==>     2CH3ONa  +  H2 
		Methanol        Sodium          Sodium      Hydrogen      
	                 		       Methoxide       

Substitution of Methanol with Phosphorus Pentachloride
Methanol reacts with phosphorus pentachloride at room temperature to form hydrogen chloride, methyl chloride, (i.e. chloroethane) and phosphoryl chloride.


CH3OH   +   PCl5       ==>     HCl   +   CH3Cl   +  POCl3      
Methanol  Phosphorus         Hydrogen    Methyl     Phosphoryl
 	  Pentachloride      Chloride    Chloride   Chloride  

Substitution of Methanol with Hydrogen Chloride
Methanol reacts with hydrogen chloride to form methyl chloride (i.e. chloromethane) and water. A dehydrating agent (e.g. zinc chloride) is used.


	                  ZnCl2   
  CH3OH   +       HCl     ==>     CH3Cl   +    H2O        
 Ethanol                          Methyl  
		                Chloride 

Uses of Methanol

Methanol is an important industrial material and it is used
  1. in the manufacture of formaldehyde,
  2. as a solvent in the paint and varnish industry, and
  3. as an anti-Freeze in car radiators.

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