A clean method for the rapid and solventless preparation of herbicides based on 2,4-dichlorophenoxyacetic acid (2,4-D esters) is reported. Micro-particulate inorganic materials such as silica, clays and zeolites are able to act as supports for the 2,4-D esterification reactions under mild conditions in the absence of organic solvents. The synthesis takes place with elevated yield and the conversion rate of the process is strongly enhanced when the reaction is microwave-assisted. Not only can well-defined supports be used but soil can also be used for this synthesis, except when iron oxides are present which lead to extensive oxidation under microwave irradiation. The 2,4-D ester remains adsorbed on the solid support as a bioactive product. Therefore the resulting powder is a partially formulated compound that can be directly applied in the field avoiding the use of solvents and with minimal hazardous and pollutant effects.