nitrapyrin

Nitrapyrin is an organic compound with the formula ClC₅H₃NCCl₃, and is described as a white crystalline solid with a sweet odor.It is used as a nitrification inhibitor and bactericide, which is applied to soils for the growing of agricultural crops since 1974. Nitrapyrin was put up for review by the EPA and deemed safe for use in 2005. Nitrapyrin is an effective nitrification inhibitor to the bacteria ''Nitrosomonas'' and has been shown to drastically the reduce the amount of N₂O emissions from the soil.

Synthesis

Nitrapyrin is commonly produced by the photochlorination of 2-methylpyridine:
:CH₃-C₅H₄N + 4Cl₂ → CCl₃-ClC₅H₃N + 4 HCl

Function

Nitrapyrin affects the ammonia monooxygenase (AMO) pathway, which is important for NH₃ oxidation in nitrification; it also functions as an inhibitor of the urease enzyme in the nitrifying bacteria Nitrosomonas, preventing hydrolytic action on urea.JHG Slangen, P. Kerkhoff; Nitrification Inhibitors in Agriculture and Horticulture: A Literature Review It is applied to the region of soil and inhibits nitrification for 8–10 weeks. Urease Inhibition specifically prevents the following reaction:

(NH₂)₂CO + H₂O → CO₂ + 2NH₃

Without this capability Nitrosomonas cannot produce nitrite thus inhibiting nitrification:

2NH₄⁺ + 3O₂ → 2NO₂⁻ + 2 H₂O + 4H⁺

Degradation/Decomposition

Nitrapyrin decomposes both in soil and in plants. The compound itself tends not to persist in nature. The primary decomposition is the hydrolysis of the trichloromethyl functional group, resulting primarily in 6-chloro-picolinic acidJohn H. Montgomery Agrochemicals Desk Reference 2nd ed.; Boca Raton: CRC Press, 1997 which is the only detected residue in plant metabolisms.

Effects in Agriculture

In an agricultural setting, nitrapyrin is seen to increase nitrogen retention and decrease nitrogen leaching in root zone. Nitrapyrin also has the effect of increasing crop yield and decreasing emissions of N₂O gas.{{Cite journal , last1=Dawar , first1=Khadim , last2=Khan , first2=Aamir , last3=Sardar , first3=Kamil , last4=Fahad , first4=Shah , last5=Saud , first5=Shah , last6=Datta , first6=Rahul , last7=Danish , first7=Subhan , date=February 2021 , title=Effects of the nitrification inhibitor nitrapyrin and mulch on N2O emission and fertilizer use efficiency using 15N tracing techniques , url=http://dx.doi.org/10.1016/j.scitotenv.2020.143739 , journal=Science of the Total Environment , volume=757 , pages=143739 , doi=10.1016/j.scitotenv.2020.143739 , pmid=33229088 , bibcode=2021ScTEn.757n3739D , issn=0048-9697Nitrapyrin isn't the only product applied to soils for the growing of crops, when combined with urea and mulch, wheat biomass increased by 33% and overall yield increased by 23%. Total N₂O emissions reduced by 66-75% when compared to urea only experiments, suggesting that nitrapyrin affects the ability of ammonia-oxidizing bacteria to engage in nitrification and produce N₂O gas.

References

Chloropyridines
Trichloromethyl compounds
Sweet-smelling chemicals