Pyridine-''N''-oxide is the

heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...

C₅H₅NO. This colourless, hygroscopic solid is the product of the oxidation of

pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a d ...

. It was originally prepared using

peroxyacid A peroxy acid (often spelled as one word, peroxyacid, and sometimes called peracid) is an acid which contains an acidic –OOH group. The two main classes are those derived from conventional mineral acids, especially sulfuric acid, and the perox ...

s as the oxidising agent. The compound is used infrequently as an oxidizing

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

Structure

The structure of pyridine-N-oxide is very similar to that of pyridine with respect to the parameters for the ring. The molecule is planar. The N-O distance is 1.34Å. The C-N-C angle is 124°, 7° wider than in pyridine.

Synthesis

The oxidation of pyridine can be achieved with a number of

peracid A peroxy acid (often spelled as one word, peroxyacid, and sometimes called peracid) is an acid which contains an acidic –OOH group. The two main classes are those derived from conventional mineral acids, especially sulfuric acid, and the peroxy ...

s including

peracetic acid Peracetic acid (also known as peroxyacetic acid, or PAA) is an organic compound with the formula CH3CO3H. This peroxy acid is a colorless liquid with a characteristic acrid odor reminiscent of acetic acid. It can be highly corrosive. Peracetic a ...

and

perbenzoic acid Peroxybenzoic acid is an organic compound with the formula C6H5CO3H. It is the simplest aryl peroxy acid. It may be synthesized from benzoic acid and hydrogen peroxide, or by the treatment of benzoyl peroxide with sodium methoxide, followed by ...

. Oxidation can also be effected by a modified

Dakin reaction The Dakin oxidation (or Dakin reaction) is an organic redox reaction in which an '' ortho''- or ''para''-hydroxylated phenyl aldehyde (2-hydroxybenzaldehyde or 4-hydroxybenzaldehyde) or ketone reacts with hydrogen peroxide in base to form a ...

using a

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important r ...

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

complex, and

sodium perborate Sodium perborate is chemical compound whose chemical formula may be written , , or, more properly, ·. Its name is sometimes abbreviated as PBS (not to be confused with phosphate-buffered saline). The compound is commonly encountered in anhydro ...

or, using

methylrhenium trioxide Methylrhenium trioxide, also known as methyltrioxorhenium(VII), is an organometallic compound with the formula CH3ReO3. It is a volatile, colourless solid that has been used as a catalyst in some laboratory experiments. In this compound, rhenium h ...

() as catalyst, with

sodium percarbonate Sodium percarbonate is a chemical substance with formula . It is an adduct of sodium carbonate ("soda ash" or "washing soda") and hydrogen peroxide (that is, a perhydrate) whose formula is more properly written as 2 · 3 . I ...

Reactions

Pyridine ''N''-oxide is five

orders of magnitude An order of magnitude is an approximation of the logarithm of a value relative to some contextually understood reference value, usually 10, interpreted as the base of the logarithm and the representative of values of magnitude one. Logarithmic dis ...

less basic than pyridine, but it is isolable as a hydrochloride salt, ₅H₅NOHl. Further demonstrating its (feeble) basicity, pyridine-N-oxide also serves as a

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

coordination chemistry A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

. Treatment of the pyridine-''N''-oxide with

phosphorus oxychloride Phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula . It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. It is manufactured industrially on a large scale from phosp ...

gives 4- and 2-chloropyridines.

Related pyridine-N-oxides

The N-oxides of various pyridines are precursors to useful drugs: *

Nicotinic acid N-oxide Nicotinic acid ''N''-oxide is an organic compound with the formula (HO2C)C5H4NO. It is the ''N''-oxide of nicotinic acid ((HO2C)C5H4N). It is prepared by oxidation of nicotinic acid or the hydrolysis of 3-cyanopyridine ''N''-oxide. The compou ...

, derived from

nicotinic acid Niacin, also known as nicotinic acid, is an organic compound and a form of vitamin B3, an essential human nutrient. It can be manufactured by plants and animals from the amino acid tryptophan. Niacin is obtained in the diet from a variet ...

is a precursor to

niflumic acid Niflumic acid is a drug used for joint and muscular pain. It is categorized as an inhibitor of cyclooxygenase-2. In experimental biology, it has been employed to inhibit chloride channel Chloride channels are a superfamily of poorly understood ...

and

pranoprofen Pranoprofen (INN) is a nonsteroidal anti-inflammatory drug (NSAID) used in ophthalmology Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physi ...

. *2,3,5-trimethylpyridine N-oxide is a precursor to the drug

omeprazole Omeprazole, sold under the brand names Prilosec and Losec, among others, is a medication used in the treatment of gastroesophageal reflux disease (GERD), peptic ulcer disease, and Zollinger–Ellison syndrome. It is also used to prevent upper g ...

*2-chloropyridine N-oxide is a precursor to the fungicide

zinc pyrithione Zinc pyrithione (or pyrithione zinc) is a coordination complex of zinc. It has fungistatic (inhibiting the division of fungal cells) and bacteriostatic (inhibiting bacterial cell division) properties and is used in the treatment of seborrhoeic d ...

Safety

The compound is a skin irritant.

References