Picoline

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In chemistry, the picolines or methylpyridines form a group of organic compounds that belong to the heterocycles (more precisely: heteroaromatics ). They consist of a pyridine ring that is substituted with a methyl group . Their different arrangement results in three constitutional isomers . Their properties are quite similar to pyridine and can easily replace it where the exact molecular structure is not important, e.g. B. as a solvent . Otherwise, they serve in a variety of ways as synthetic building blocks for pharmaceutical and agrochemical products and dye production .

Representative

Picoline
Surname 2-picoline 3-picoline 4-picoline
other names α-picoline,
2-methylpyridine		 β-picoline,
3-methylpyridine		 γ-picoline,
4-methylpyridine
Structural formula Structure of 2-picoline Structure of 3-picoline Structure of 4-picoline
CAS number 109-06-8 108-99-6 108-89-4
1333-41-1 (mixture of isomers)
PubChem 7975 7970 7963
Molecular formula C 6 H 7 N
Molar mass 93.13 g mol −1
Physical state liquid
Brief description colorless liquid
Melting point −70 ° C −18 ° C 3 ° C
boiling point 128 ° C 144 ° C 145 ° C
pK s value
(of the conjugate
acid BH + ) 		5.94 5.63 6.03
solubility completely miscible with water
GHS
labeling
02 - Highly / extremely flammable 06 - Toxic or very toxic
danger
02 - Highly / extremely flammable 06 - Toxic or very toxic
danger
02 - Highly / extremely flammable 06 - Toxic or very toxic
danger
H and P phrases 226-302-312-332-319-335 226-302 + 332-311-315-319-335 226-302-311-315-319-332-335
no EUH phrases no EUH phrases no EUH phrases
261-280-305 + 351 + 338-312 210-280-302 + 352-304 + 340
305 + 351 + 338-308 + 310 		201-280-302 + 352
305 + 351 + 338-309 + 310

history

The 2-picoline was first isolated from coal tar in 1846 by T. Anderson . The name Picoline is made up of the Latin pix (pitch) and oleum (oil).

presentation

At present, 2-picoline is mainly produced by two synthetic routes: by condensation of acetaldehyde , formaldehyde and ammonia, and by cyclization of nitriles and acetylene ( Bönnemann cyclization ). An example is the reaction of acetaldehyde and ammonia:

Synthesis of 2-picoline

Approx. 8000 t were produced worldwide in 1989.

3-methylpyridine is produced industrially by reacting acrolein with ammonia:

A more efficient way starts from acrolein, propionaldehyde and ammonia:

Approx. 9,000 t were produced worldwide in 1989.

properties

The picolines are colorless liquids with a pyridine-like odor. They are miscible with water, ethanol and diethyl ether . The 4-picoline, which has the highest symmetry, has the highest melting point.

Since the methyl groups in 2- and 4-picoline are arranged in direct conjugation to the electron-withdrawing nitrogen atom, the methyl groups in these two isomers can be relatively easily deprotonated by strong bases such as lithium diisopropylamide or butyllithium and then further derivatized.

use

Picolines are used as intermediates in the production of other chemical compounds. For example, 2-vinylpyridine and the agrochemical nitrapyrine can be produced from 2-picoline . For example, 3-picoline is used as a starting material for the synthesis of chlorpyrifos and niacin , 4-picoline for the manufacture of the anti- tuberculosis active ingredient isoniazid .

By oxidation, e.g. B. by means of potassium permanganate (KMnO 4 ), picolinic acid is formed from 2-picoline , nicotinic acid from 3-picoline and isonicotinic acid from 4-picoline .

Oxidation of 2-picoline to picolinic acid
Oxidation of 3-picoline to nicotinic acid

See also

Individual evidence

  1. ↑ a b c Entry on methylpyridines. In: Römpp Online . Georg Thieme Verlag, accessed on November 25, 2014.
  2. ↑ a b c Entry on 2-methylpyridine in the GESTIS substance database of the IFA , accessed on July 27, 2017(JavaScript required) .
  3. ↑ a b c Entry on 3-methylpyridine in the GESTIS substance database of the IFA , accessed on July 27, 2017(JavaScript required) .
  4. ↑ a b c Entry on 4-methylpyridine in the GESTIS substance database of the IFA , accessed on July 27, 2017(JavaScript required) .
  5. ↑ CRC Handbook of Tables for Organic Compound Identification , Third Edition, 1984, ISBN 0-8493-0303-6 .
  6. ↑ T. Anderson: On the constitution and properties of Picoline, a new organic base from Coal Tar . In: Edinburgh New Phil. J. , XLI , 1846. pp. 146–156 and 291–300 ( limited preview in Google book search).
  7. ↑ a b c d e f g Shinkichi Shimizu, Nanao Watanabe, Toshiaki Kataoka, Takayuki Shoji, Nobuyuki Abe, Sinji Morishita, Hisao Ichimura: Pyridine and Pyridine Derivatives . In: Ullmann's Encyclopedia of Industrial Chemistry , 2002. doi : 10.1002 / 14356007.a22_399 .
  8. ↑ A. Behr: Applied homogeneous catalysis , Wiley-VCH, Weinheim 2008, ISBN 3-527-31666-3 , p. 722.
  9. ↑ Eric FV Scriven, Ramiah Murugan: Pyridine and Pyridine Derivatives . In: Kirk-Othmer Encyclopedia of Chemical Technology , 2005; XLI . doi : 10.1002 / 0471238961.1625180919031809.a01.pub2 .
  10. ↑ M. Sainsbury, M. Berry, JD Hepworth, C. Drayton, EW Abel, D Phillips, JD Woollins, AG Davies: Heterocyclic Chemistry , 1st Edition, Royal Society of Chemistry, 2009, ISBN 0-85404-652-6 , P. 30.
  11. ↑ Harold Hart (author), Leslie E. Craine (author), David J. Hart (author), Christopher M. Hadad (author); Nicole Kindler (translator): Organic Chemistry , 3rd edition, Wiley-VCH, Weinheim 2007, ISBN 978-3-527-31801-8 , p. 494.

Web links

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