N-Alkylcarbamic acid esters

Of the N-alkylcarbamates only the aryl esters of N-alkylcarbamic acid possess herbicidal activity. The herbicidal activity of N-alkylcarbamic acid alkylesters and of the heterocyclic derivatives of N-alkylcarbamic add is mentioned only in the patents literature, but these latter derivatives have not found agricultural application. Examples are the N-dimethylcarbamic acid enol esters proposed by Whetstone and Kuddema (1959) and the N-methylcarbamic add pyridine esters proposed by Johnston (1964). 

The growth-modifying and herbicidal properties of N-methylcarbamic acid phenylesters and N-methylcarbamic add naphthylesters were recognised by Gysin and Knusli (1953), but these compounds did not gain ground in agriculture. 

Eleven years later Haubein (1964) applied for a patent for the N-methylcar-bamate group of 2,4-6-trisubstituted phenols as selective herbicides. 2,6-Di-/-butyl- 

4-methylphenyI N-methylcarbamate (terbutol, terbucarb, 1) was introduced in 1964 (Haubein and Hansen, 1965). 

Terbutol is prepared from 2,6-di-/-butyl-4-methylphenol and methyl isocyanate in an apolar solvent in the presence of a tertiary amine as catalyst (Haubein, 1972). 

---

In the case of N-phenylcarbamic acid esters containing a substituted phenyl group, changing the alcohol component produces similar changes in activity as with N-alkylcarbamic acid esters (see Table 6.6) (Shaw and Swanson, 1953). 

---