2,6-Lutidine

2,6-Lutidine is a natural heterocyclic aromatic organic compound with the formula (CH3)2C5H3N. It is one of several dimethyl-substituted derivative of pyridine, all of which are referred to as lutidines It is a colorless liquid with mildly basic properties and a pungent, noxious odor.

2,6-Lutidine[1]
Names
Preferred IUPAC name
2,6-Dimethylpyridine
Other names
Lutidine
Identifiers
3D model (JSmol)
105690
ChEBI
ChemSpider
ECHA InfoCard 100.003.262
EC Number
  • 203-587-3
2863
UNII
UN number 2734
Properties
C7H9N
Molar mass 107.153 g/mol
Appearance colorless oily liquid
Density 0.9252
Melting point −5.8 °C (21.6 °F; 267.3 K)
Boiling point 144 °C (291 °F; 417 K)
27.2% at 45.3 °C
Acidity (pKa) 6.72[2]
-71.72·10−6 cm3/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Occurrence and production

It was first isolated from the basic fraction of coal tar and from bone oil.[1]

A laboratory route involves condensation of ethyl acetoacetate, formaldehyde, and an ammonia source to give a bis(carboxy ester) of a 2,6-dimethyl-1,4-dihydropyridine, which, after hydrolysis, undergoes decarboxylation.[3]

It is produced industrially by the reaction of formaldehyde, acetaldehyde, and ammonia.[2]

Uses

2,6-Lutidine has been evaluated for use as a food additive owing to its nutty aroma when present in solution at very low concentrations.

Due to the steric effects of the two methyl groups, 2,6-lutidine is less nucleophilic than pyridine. Protonation of lutidine gives lutidinium, [(CH3)2C5H3NH]+, salts of which are sometimes used as a weak acid because the conjugate base (2,6-lutidine) is so weakly coordinating. In a similar implementation, 2,6-lutidine is thus sometimes used in organic synthesis as a sterically hindered mild base.[4] Oxidation of 2,6-lutidine with air gives 2,6-diformylpyridine:

C5H3N(CH3)2 + 2 O2 → C5H3N(CHO)2 + 2 H2O

Biodegradation

The biodegradation of pyridines proceeds via multiple pathways.[5] Although pyridine is an excellent source of carbon, nitrogen, and energy for certain microorganisms, methylation significantly retards degradation of the pyridine ring. In soil, 2,6-lutidine is significantly more resistant to microbiological degradation than any of the picoline isomers or 2,4-lutidine.[6] Estimated time for complete degradation was >30 days.[7]

See also

References
  1. Merck Index, 11th Edition, 5485
  2. Shimizu, Shinkichi; Watanabe, Nanao; Kataoka, Toshiaki; Shoji, Takayuki; Abe, Nobuyuki; Morishita, Sinji; Ichimura, Hisao (2007). "Pyridine and Pyridine Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a22_399.
  3. Singer, Alvin; McElvain, S. M. (1934). "2,6-Dimethylpyridine". Org. Synth. 14: 30. doi:10.15227/orgsyn.014.0030.
  4. Prudhomme, Daniel R.; Park, Minnie; Wang, Zhiwei; Buck, Jason R.; Rizzo, Carmelo J. (2000). "Synthesis of 2'-Deoxyribonucleosides: Β-3',5'-Di-o-benzoylthymidine". Org. Synth. 77: 162. doi:10.15227/orgsyn.077.0162.
  5. Philipp, Bodo; Hoff, Malte; Germa, Florence; Schink, Bernhard; Beimborn, Dieter; Mersch-Sundermann, Volker (2007). "Biochemical Interpretation of Quantitative Structure-Activity Relationships (QSAR) for Biodegradation of N-Heterocycles: A Complementary Approach to Predict Biodegradability". Environmental Science & Technology. 41: 1390–1398. doi:10.1021/es061505d. PMID 17593747.
  6. Sims, G. K.; Sommers, L.E. (1985). "Degradation of pyridine derivatives in soil". Journal of Environmental Quality. 14 (4): 580–584. doi:10.2134/jeq1985.00472425001400040022x.
  7. Sims, G. K.; Sommers, L.E. (1986). "Biodegradation of Pyridine Derivatives in Soil Suspensions". Environmental Toxicology and Chemistry. 5 (6): 503–509. doi:10.1002/etc.5620050601.
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