52 ORGANIC AGRICULTURAL CHEMISTRY 



Oxalic Acid 



Oxalic acid occurs free in certain plants such as sorrel and in 

 combination as calcium salts in the leaves and roots or tubers 

 of others (such as jack-in-the-pulpit, elephant ears, etc.) and in 

 animal urine. 



Oxalic acid is the dicarhoxy derivative of ethane, correspond- 

 ing to acetic acid, the monocarhoxy acid derived from ethane. 



CH3 - CH3 ^ CH3 - COOH -> COOH - COOH 



Ethane Acetic acid Oxalic acid 



Oxalic acid is, therefore, simply dicarboxyl, and is the simplest 

 representative of the polybasic acids. When oxalic acid is 

 heated, it reacts as acetic acid does, it loses CO2. Acetic acid 

 by such loss of CO2 yields methane while by loss of CO2 oxalic 

 acid yields formic acid, our simplest monobasic acid. 



CH3 - COOH -> CH3 - H + CO2 



Acetic acid Methane 



COOH - COOH -> H - COOH + CO2 



Oxalic acid Formic acid 



Now formic acid when heated with dehydrating agents yields 

 CO + H2O 



H - COOH -^ H2O + CO 



Formic acid 



Therefore the decomposition of oxalic acid when similarly 

 heated may be represented by the double reaction : 



-CO2 

 COOH - COOH -^ H - COOH -> CO + H2O 



Oxalic acid Formic acid Carbon monoxide 



Oxalic acid is a poison and it is possible that this action is 

 due to decomposition in the body similar to this decomposition 

 by heat, thus forming carbon monoxide, which is a poison. 



