Methylamines are used to make intermediates for a wide range of agricultural chemicals, including herbicides, fungicides, insecticides, biocides, and miticides. Agricultural chemicals are one of the widest uses for methylamines.
One use for monomethylamine is to produce metam-sodium (n-methyldithiocarbamate), which is a soil fumigant and sterilant. It is made from the reaction of MMA, carbon disulfide, and caustic. Its applications are increasing, and it is currently used for potatoes, tomatoes, and home and garden applications. It is replacing methyl bromide as a soil fumigant, due to concerns of methyl bromide being a possible ozone depleter.
MMA is also phosgenated to make methyl isocyanate, which is used to make carbaryl, aldicarb, and trimethocarb. The insecticides carbofuran and carbosulfan are produced from these. Monomethylformamide (MMF), made from MMA and carbon monoxide, is being used to make methyl isocyanate in situ, due to concerns of storing and transporting this highly toxic material. MMF, sold by DuPont, can also be used as a solvent for other applications.
Dimethylamine is used to produce the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid). Its DMA salt improves the water solubility of pesticide formulations. Related agricultural products include the ferric reaction with N,N-dimethyl dithiocarbamate to make ferbam, a fungicide for apples and tobacco; the zinc reaction to make ziram, a fungicide for vegetables; and thiram (tetramethylthiuram disulfide), a disinfectant for grains, bulbs, tubers, and corn.
Other products from DMA include the herbicides diuron, linuron, hexazinone, and fluometuron. Quaternary biocides are produced from alkyldimethylamine (from DMA) and dialkylmethylamine (from MMA). Salts of DMA reacted with substituted naphthaquinones are used to make miticides and aphicides. DMA is also used to produce systemic insecticides such as octamethylpyrophosphoramide (OMPA) (schradan) that are absorbed into the plant rendering it toxic to sapsucking insects. Trimethylamine reacted with sulfur dioxide has been used to produce a volatile insecticide.