Synthesized dimers increased herbicidal activity with lowered volatility

Auxinic herbicides are widely used to control broadleaf weeds in cereal crop fields due to their excellent herbicidal activities. However, volatile drifting caused by their high vapor pressures is a great threat to neighbouring susceptible crops and environment and severely limits auxinic herbicide applications. In this study, a series of auxinic herbicide dimers were synthesized using 2,4-D, dicamba and MCPA as monomers to reduce their vapor pressures. The results showed that all of the dimers significantly reduced volatilities due to larger molecular weight. The dimers linked with two ester bonds had 2-fold higher herbicidal efficacies than their corresponding monomers in filed experiments. The dimers linked with amide bonds appeared to function as contact action and systemic action herbicides. The dimers, 3a-2(ethane-1,2-diylbis (2-(2,4-dichlorophenoxy)acetate)), 3a-4(2-((2-(2,4-dichlorophenoxy)acetyl)thio)ethyl 2-(2,4-dichlorophenoxy)acetate), 3b-2(ethane-1,2-diylbis(2-(4-chloro-2-methylphenoxy)acetate)) and 3c-2(ethane-1,2-diylbis(3,6-dichloro-2-methoxybenzoate)) significantly increased the efficacies and reduced volatilities, thus could be developed as potential novel postemergence herbicides.