Nitrapyrin

Nitrapyrin is an organic compound with the formula ClC5H3NCCl3. It is a widely used nitrification[2] inhibitor in agriculture [3] as well as a soil bactericide and has been in use since 1974. Nitrapyrin was put up for review by the EPA and deemed safe for use in 2005. Since nitrapyrin is an effective nitrification inhibitor to the bacteria Nitrosomonas it has been shown to drastically the reduce NO2 emissions of soil.[3] Nitrapyrin is a white crystalline solid with a sweet odor and is often mixed with anhydrous ammonia for application.

Nitrapyrin
Names
IUPAC name
2-Chloro-6-(trichloromethyl)pyridine
Other names
N-serve, 2,2,2,6-Tetrachloro-2-picoline
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.016.076
UNII
Properties
C6H3Cl4N
Molar mass 230.907
Appearance colorless/white crystalline solid[1]
Odor Sweet[1]
Melting point 63 °C; 145 °F; 336 K [1]
insoluble[1]
Vapor pressure 0.003 mmHg (22.8°C)
Hazards
Main hazards explosive[1]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp)[1]
REL (Recommended)
 TWA 10 mg/m3 (total) ST 20 mg/m3 (total) TWA 5 mg/m3 (resp)[1]
IDLH (Immediate danger)
 N.D.[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Synthesis

Nitrapyrin is commonly produced by the photochlorination of 2-methylpyridine:[4]

CH3-C5H4N + 4Cl2 → CCl3-ClC5H3N + 4 HCl

Produced by DOW Chemical, the product is marketed under the trade name N-Serve and contains small amounts (less than 5% wt) of the non-active ingredient 4,6-dichloro-2-trichloromethylpyridine.

Function

Nitrapyrin functions as an inhibitor of the urease enzyme in the nitrifying bacteria Nitrosomonas,[5] preventing hydrolytic action on urea.[6][7] 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 acid[7][8] which is the only detected residue in plant metabolisms.

References
  1. NIOSH Pocket Guide to Chemical Hazards. "#0136". National Institute for Occupational Safety and Health (NIOSH).
  2. Meta-analysis of Enhanced Efficiency Fertilizers in Corn, wheat, and sorghum in the Midwest http://research.ipni.net/page/RNAP-6379
  3. Heinrich Dittmar, Manfred Drach, Ralf Vosskamp, Martin E. Trenkel, Reinhold Gutser, Günter Steffens "Fertilizers, 2. Types" In: Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, 2009, doi:10.1002/14356007.n10_n01
  4. Powell, Steven J.; Prosser, James I. (1986). "Inhibition of ammonium oxidation by nitrapyrin in soil and liquid culture". Applied and Environmental Microbiology. 52 (4): 782–787. PMC 239114. PMID 16347171.
  5. Z. Amtul, Atta-ur-Rahman, R. A. Siddiqui, M. I. Choudhary; "Chemistry and Mechanism of Urease Inhibition" Curr Med Chem. 2002 Jul;9(14):1323-48.
  6. M.E. Trenkel Slow- and Controlled-Release and Stabilizing Fertilizers An Option for Enhancing Nutrient Use Efficiency in Agriculture, 2nd ed.; IFA: Paris, 2010 ISBN 978-2-9523139-7-1
  7. JHG Slangen, P. Kerkhoff; Nitrification Inhibitors in Agriculture and Horticulture: A Literature Review
  8. John H. Montgomery Agrochemicals Desk Reference 2nd ed.; Boca Raton: CRC Press, 1997 ISBN 1-56670-167-8
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