Pyridine liquid is an organic compound, chemical formula C5H5N, which is a six membered heterocyclic compound containing a nitrogen heteroatom. It can be regarded as a compound in which one (CH) of benzene molecules is replaced by N, so it is also called nitrobenzene, a colorless or yellowish liquid with a foul smell. It is miscible with water, alcohol, ether, petroleum ether, benzene, oil and other solvents. Pyridine and its homologues exist in bone tar, coal tar, gas, shale oil and petroleum. In industry, pyridine can be used as denaturant, dye aid, and raw material for synthesis of a series of products (including drugs, disinfectants, dyes, etc.).

Product Information :

Usage :

Use 1. pyridine liquid is used as organic solvent, analytical reagent, organic synthesis industry, chromatographic analysis, etc.

Use 2. Pyridine is the raw material of herbicide, insecticide, medicine, rubber auxiliary and textile auxiliary.

Use 3. It is mainly used as raw material for pharmaceutical industry, as solvent and alcohol denaturant, and also used to produce rubber, paint, resin and corrosion inhibitor.

Use 4. Raw materials for extracting and separating pyridine and its homologues Use GB2760-1996 is a permitted food flavor.

Use 5. It can be used as solvent in the manufacture of vitamins, sulfa drugs, pesticides and plastics. In industry, pyridine can also be used as denaturant, dye aid, and the starting material for the synthesis of a series of products, including drugs, disinfectants, dyes, food seasonings, adhesives, explosives, etc.

Use 6. Solvent, organic synthesis.

Use 7. It is used as a detection reagent for metal ions. Verification and determination of antimony, arsenic, aluminum, bismuth, cadmium, cerium, chlorate, chromate, cyanate, chromium, cobalt, copper, cyanide, gold, dichromate, halogen, lanthanum, lead, lithium, manganese, mercury, germanium, nickel, perchlorate, persulfate, platinum, phosphorus, rhenium, praseodymium, silicon, silver, sulfur, thallium, tellurium, thiocyanate, thorium, thiosulfate, titanium, uranium, vanadium, zinc, zirconium.

Use 8. Moisture determination, strain mutagen. Solvent for acylation reaction. catalyzer.

Manufacturing :

Preparation of pyridine liquid:

1. It can be obtained from natural coal tar or acetaldehyde and ammonia. Pyridine and its derivatives can also be synthesized by a variety of methods, of which the most widely used method is the synthesis of Hanqi pyridine, which uses two molecules β- Carbonyl compounds, such as ethyl acetoacetate, are condensed with a molecule of acetaldehyde, the product is then condensed with a molecule of ethyl acetoacetate and ammonia to form dihydropyridine compounds, and then dehydrogenated with an oxidant (such as nitrous acid), and hydrolyzed to decarboxylation to obtain pyridine derivatives.

2. Acetylene, ammonia and methanol can also be prepared through catalyst at 500 ℃.

Quality & Analysis :

Chemical properties of pyridine liquid:

Pyridine and its derivatives are more stable than benzene, and their reactivity is similar to nitrobenzene. Typical aromatic electrophilic substitution reactions occur at positions 3 and 5, but the reactivity is lower than that of benzene, and it is not easy to occur nitration, halogenation, sulfonation and other reactions. Pyridine is a weak tertiary amine, which can form insoluble salts with various acids (picric acid or perchloric acid, etc.) in ethanol solution. The pyridine used in industry contains about 1% 2-methylpyridine, so it can be separated from its homologues by taking advantage of the difference in salt forming properties. Pyridine can also form crystalline complexes with various metal ions. Pyridine is easier to reduce than benzene, such as hexahydropyridine (or piperidine) under the action of metal sodium and ethanol. Pyridine reacts with hydrogen peroxide and is easily oxidized to pyridine N-oxide.

1. Electrophilic substitution reaction:

Pyridine is a “π deficient” heterocycle, and the electron cloud density on the ring is lower than that of benzene, so its electrophilic substitution reaction activity is also lower than that of benzene, which is equivalent to nitrobenzene. Due to the passivation of nitrogen atoms on the ring, the conditions for electrophilic substitution reaction are relatively harsh, and the yield is low. The substituents mainly enter 3（ β) Bit.

Compared with benzene, the electrophilic substitution reaction of pyridine ring becomes more difficult, and the substituent mainly enters 3（ β) This effect can be explained by the relative stability of the intermediate.

Because of the existence of the absorbing nitrogen atom, the positive ions of the intermediate are not as stable as the corresponding intermediate substituted by benzene, so the electrophilic substitution reaction of pyridine is more difficult than that of benzene. Comparing the position of electrophilic reagent attack, we can see that when attack 2（ α) Bits and 4（ γ) There is a resonance limit formula for the intermediate formed when the positive charge is on the nitrogen atom with greater electronegativity. This limit formula is extremely unstable, and 3（ β) There is no such extremely unstable limit formula for the intermediate substituted by position, and the intermediate is more stable than the intermediate attacking position 2 and 4. Therefore, substituents at position 3 are easy to form.

2. Nucleophilic substitution reaction:

Due to the electron absorption of nitrogen atoms on the pyridine ring, the electron cloud density of carbon atoms on the ring decreases, especially at position 2 and 4, so the nucleophilic substitution reaction on the ring is easy to occur, and the substitution reaction mainly occurs at position 2 and 4.

The reaction of pyridine with sodium amino to produce 2-aminopyridine is called azinibabine reaction. If the 2 position has been occupied, the reaction takes place in the 4 position to obtain 4-aminopyridine, but the yield is low. If the α Bit or γ The nucleophilic substitution reaction is easy to occur when there is a good leaving group (such as halogen, nitro) in the. For example, pyridine can undergo nucleophilic substitution reaction with ammonia (or amine), alkyl oxide, water and other weak nucleophilic reagents.

3. Redox reaction:

Because the electron cloud density on the pyridine ring is low, it is generally not easy to be oxidized. Especially under acidic conditions, pyridine has a positive charge on the nitrogen atom after salifying, and the induction effect of electron absorption is strengthened, which makes the electron cloud density on the ring lower, and increases the stability of the oxidant. When the pyridine ring has side chains, the oxidation of side chains occurs.

Pyridine can undergo oxidation reaction similar to tertiary amine under special oxidation conditions to form N-oxide. For example, pyridine N-oxide can be obtained when pyridine reacts with peroxy acid or hydrogen peroxide.

Pyridine N-oxide can be deoxidized by reduction. In pyridine N-oxide, the unconsumed electron pair on the oxygen atom can have the p-π conjugation with the aromatic large π bond, which makes the electron cloud density on the ring increase α Bitsum γ The electrophilic substitution reaction of pyridine ring is easy to occur due to the remarkable increase of position. After the formation of pyridine N-oxide, the nitrogen atom has a positive charge, and the induction effect of electron absorption increases, so that α The density of the electron cloud at position 4 decreases, so the electrophilic substitution reaction mainly occurs at 4（ γ) On. At the same time, pyridine N-oxides are also prone to nucleophilic substitution reactions.

Contrary to the oxidation reaction, pyridine ring is easier to undergo hydrogenation reduction than benzene ring, which can be reduced by catalytic hydrogenation and chemical reagents.

The reduction product of pyridine is hexahydropyridine (piperidine), which has the property of secondary amine, is more alkaline than pyridine (pKa=11.2), and the boiling point is 106 ℃. Many natural products have this ring system and are commonly used organic bases.