Preparation of organophosphorus pesticides

Organophosphorus pesticides are specific efficient contact and systemic (acting inside a plant) insecticides and acaricides. Among them are 0,0-dimethyl-(l -hydroxy-2,2,2-trichloroethyl)phosphonate (trichlorfon, or 

Trichlorfon can be synthesised in three stages the preparation of trichloroacetic aldehyde (chloral) the production of 0,0-dimethyl ether of phosphorous acid (dimethylphosphite) the synthesis of 0,0-dimethyl(l-hydroxy-2,2,2-trichloroethyl)phosphonate (trichlorfon). 

Chloral is obtained by direct chlorination of 96% ethyl alcohol with gaseous chlorine  

In fact, the process is much more complicated and is accompanied by secondary reactions. Thus, raw chloral usually contains various impurities. To obtain the pure product, raw chloral should be distilled over concentrated (approximately 92%) sulfuric acid. 

The distillation allows to separate two fractions. The first fraction, which is distilled below 92 °C in vapours, is a mixture of chloral, products of incomplete chlorination and hydrogen chloride (the latter in large quantities) this fraction is returned to repeated distillation. The second fraction, which is distilled in the 92-110 °C temperature range, contains mostly chloral (the boiling point is 97 °C) it is sent to the production of trichlor-fon. 

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