Synthesis, Stability, and Kinetics of Hydrogen Sulfide Release of Dithiophosphates

The development of chemicals to slowly release hydrogen sulfide would aid the survival of plants under environmental stressors as well as increase harvest yields. We report a series of dialkyldithiophosphates and disulfidedithiophosphates that slowly degrade to release hydrogen sulfide in the presence of water. Kinetics of the degradation of these chemicals were obtained at 85 °C and room temperature, and it was shown that the identity of the alkyl or sulfide group had a large impact on the rate of hydrolysis, and the rate constant varied by more than 10⁴×. For example, using tert-butanol as the nucleophile yielded a dithiophosphate (8) that hydrolyzed 13,750× faster than the dithiophosphate synthesized from n-butanol (1), indicating that the rate of hydrolysis is structure-dependent. The rates of hydrolysis at 85 °C varied from a low value of 6.9 × 10^-4 h^-1 to a high value of 14.1 h^-1. Hydrogen sulfide release in water was also quantified using a hydrogen sulfide-sensitive electrode. Corn was grown on an industrial scale and dosed with dibutyldithiophosphate to show that these dithiophosphates have potential applications in agriculture. At a loading of 2 kg per acre, a 6.4% increase in the harvest yield of corn was observed.