Characterization of Dialkyldithiophosphates as Slow Hydrogen Sulfide Releasing Chemicals and Their Effect on the Growth of Maize

Hydrogen sulfide is a key gasotransmitter for plants and has been shown to greatly increase their growth and survival in the presence of environmental stressors. Current methods for slowly releasing hydrogen sulfide use chemicals, such as GYY-4137, but these result in the release of chemicals not found in the environment, and chemicals used may lack structures that can be readily tuned to affect the rate of release of hydrogen sulfide. In this article, we describe the synthesis and slow release of hydrogen sulfide from dialkyldithiophosphates, which are a new set of hydrogen sulfide releasing chemicals that can be used in agriculture. The rates of hydrolysis of dibutyldithiophosphate and GYY-4137 were measured in water at 85 °C and compared with each other to investigate their differences. GYY-4137 is widely used as a chemical that slowly releases H₂S, but its rate of release was not previously quantified. The release of hydrogen sulfide in water at room temperature was measured for a series of dialkyldithiophosphates using a hydrogen sulfide electrode. It was shown that the structure of the dialkyldithiophosphate affected the amount of hydrogen sulfide released. The final degradation products of dibutyldithiophosphate were shown to be phosphoric acid and butanol, which are chemicals found in the environment. This result was notable because it demonstrated that dialkyldithiophosphates degrade to safe, natural chemicals that will not pollute the environment. To demonstrate that dialkyldithiophosphates have potential applications in agriculture, maize was grown for 4.5 weeks after exposure to 1–200 mg of dibutyldithiophosphate, and the weight of corn plants increased by up to 39% at low loadings of dibutyldithiophosphate.