Selenous acid can also be made directly by oxidizing elemental selenium with nitric acid:

  
    
      
        
          3
          
          Se
          +
          4
          
          
            HNO
            
              3
            
            
              
            
          
          +
          
            H
            
              2
            
            
              
            
          
          O
          ⟶
          3
          
          
            H
            
              2
            
            
              
            
          
          
            SeO
            
              3
            
            
              
            
          
          +
          4
          
          NO
        
      
    
    {\displaystyle {\ce {3 Se + 4 HNO3 + H2O -> 3 H2SeO3 + 4 NO}}}
  Unlike sulfur, which forms a stable trioxide, selenium trioxide is thermodynamically unstable and decomposes to the dioxide above 185 °C:

  
    
      
        
          2
          
          
            SeO
            
              3
            
            
              
            
          
          ⟶
          2
          
          
            SeO
            
              2
            
            
              
            
          
          +
          
            O
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {2 SeO3 -> 2 SeO2 + O2}}}
   (ΔH = −54 kJ/mol)Selenium trioxide is produced in the laboratory by the reaction of anhydrous potassium selenate (K2SeO4) and sulfur trioxide (SO3).Salts of selenous acid are called selenites.
Such measurements can be useful to avoid central nervous system toxicity in any person receiving large doses of the drug on a chronic basis, but they are especially relevant to patients with kidney failure, who may accumulate the drug due to reduced urinary excretion rates. Manufacture
The production of benzylpenicillin involves fermentation, recovery and purification of the penicillin.The fermentation process of the production of benzylpenicillin creates the product. The presence of the product in solution inhibits the reaction and reduces the product rate and yield. Thus, in order to obtain the most product and increase the rate of reaction, it is continuously extracted. This is done by mixing the mold with either glucose, sucrose, lactose, starch, or dextrin, nitrate, ammonium salt, corn steep liquor, peptone, meat or yeast extract, and small amounts of inorganic salts.The recovery of the benzylpenicillin is the most important part of the production process because it affects the later purification steps if done incorrectly. There are several types of techniques used to recover benzyl penicillin: aqueous two-phase extraction, liquid membrane extraction, microfiltration, and solvent extraction. Extraction is more commonly used in the recovery process.In the purification step, the benzylpencillin is separated from the extraction solution. This is normally done by using a separation column. Synonyms
Penicillin II (old UK nomenclature for naming penicillins)

References
External links
"Benzylpenicillin". Drug Information Portal. U.S. National Library of Medicine.