The herbicidal properties of 3-alkylthio-4-amino-6-alkyl-1,2,4-triazine-5-ones are disclosed in U.S. Pat. No. 4,346,220. Among these compounds is metribuzin, 3-methylthio-4-amino-6-t-butyl-1,2,4-triazine-5-one. These compounds, however, even with their relatively low water solubility, are subject to leaching in the soil and run-off during rainstorms. The N-methylol derivatives of these compounds, which regenerate the parent compounds slowly upon exposure to water, are less soluble. These derivatives provide a slow or controlled release version of the herbicidal compounds themselves. They are, therefore, useful forms of the herbicide in that they resist leaching and run-off and, among other benefits, provide greater residual activity.
The preparation of aldehyde derivatives is shown in U.S. Pat. No. 3,671,523, and the preparation in particular of N-methylol metribuzin is disclosed in "Symposium on Controlled Release of Bioactive Materials, III", pages 7-11, A. B. Peppermen, Jr. and K. E. Savage (1979). The methods disclosed in the references involve the use of organic solvents, which are inflammable and relatively expensive. These methods also present economic disadvantages based on the need to recover and recycle the solvent in a commercial process. Other methods of N-methylolation of amino compounds with aqueous formaldehyde require complete dissolution of the compounds. This also can lead to an economic penalty because of large volumes that must be handled in the manufacturing operation.