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

Abstract

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 10 4 ×. 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.

Sustained Release of Hydrogen Sulfide from Di(t-butanol)dithiophosphate Phenethylamine Salt Encapsulated into Poly(lactic acid) Microparticles to Enhance the Growth of Radish Plants

“…Dithiophosphates are a new example of these chemicals and have been shown to increase the biomass of corn plants after 4.5 weeks of growth and to increase the harvest yield of corn by 4% after administration of a dithiophosphate once at planting of the seeds. In studies with dithiophosphates and other chemicals that slowly release H 2 S, chemicals are typically placed on seeds or in soil immediately adjacent to seeds . A challenge of chemicals used to deliver H 2 S is they are typically water-soluble and will diffuse away from plants when watered; this problem may be particularly acute after heavy rainfall.…”

“…In a prior publication in 2021, the rates of hydrolysis of dithiophosphates synthesized from alcohols (primary, secondary, and tertiary), thiols, dithiols, and diols were investigated, and the two chemicals in Figure 2a had rates of hydrolysis that were >50× faster than the others. 44 The dithiophosphate synthesized from mercaptoethanol was not selected for this project because mercaptoethanol is toxic, and it rapidly cleaves disulfides that are present in proteins within plant cells. Dithiophosphates with tertiary alcohols were selected for this project due to the safety of t-butanol in the environment, the range of tertiary alcohols available, and the lack of odor of these alcohols.…”

“…Although the application of H 2 S is an exciting new frontier in agriculture, it is challenging to deliver at known doses over specified periods of time, which are two important parameters for fundamental studies of the effect of H 2 S on plants and for eventual commercial applications . Chemicals such as GYY-4137 address some of these challenges, but the rate of release of H 2 S is not easily varied from chemicals with its general structure, and it hydrolyzes to release unsafe chemicals such as morpholine that have unknown effects on plants. , Furthermore, small chemicals such as GYY-4137 and dithiophosphates are water-soluble and can wash away from the roots of plants. What is needed in this field is a method to apply chemicals that slowly release H 2 S over well-defined time periods, release biocompatible and safe chemicals in addition to H 2 S, and will not diffuse away from the roots of plants.…”

“…In our prior work, we synthesized dithiophosphates from reactions between alcohols or thiols with P 4 S 10 and demonstrated that these chemicals hydrolyze in water at rates that varied by a factor of over 10 4 . Dithiophosphates hydrolyzed in water to release H 2 S as well as phosphoric acid and the alcohols or thiols used in their synthesis.…”

“…56−66 In our prior work, we synthesized dithiophosphates from reactions between alcohols or thiols with P 4 S 10 and demonstrated that these chemicals hydrolyze in water at rates that varied by a factor of over 10 4 . 44 Dithiophosphates hydrolyzed in water to release H 2 S as well as phosphoric acid and the alcohols or thiols used in their synthesis. By selection of biocompatible alcohols or thiols, the hydrolysis products of dithiophosphates were safe for the environment and unlikely to have a strong effect on plants which allows the response of plants to H 2 S to be measured.…”