4-Chloropyrazole is an organic compound with CAS 15878-00-9 and molecular formula C3H3ClN2. White to grayish white powder, which is a common physical state. Not soluble in water, but it can be soluble in most organic solvents such as alcohols, ethers, ketones, esters, etc. This characteristic makes it a good solvent for certain chemical reactions. In thin layer chromatography, 4 chloropyrazole usually exhibits a single spot, indicating its high purity. Its Rf value (representing the mobility of the substance between the stationary and mobile phases) is usually between 0.2 and 0.3. As a five membered cyclic compound containing chlorine and nitrogen, 4 chloropyrazole has certain chemical stability. It is not easily oxidized or reduced, but can react with certain reagents under certain conditions. For example, it can undergo a neutralization reaction with alkali metal hydroxides or acids, generating corresponding salts and water. In addition, it can also undergo nucleophilic substitution reactions with certain organic compounds, generating substitution products containing chlorine atoms. It can be used in polymer materials such as synthetic rubber, plastics, and fibers.
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C.F |
C3H3ClN2 |
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E.M |
102 |
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M.W |
103 |
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m/z |
102 (100.0%), 104 (32.0%), 103 (3.2%), 105 (1.0%) |
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E.A |
C, 35.15; H, 2.95; Cl, 34.58; N, 27.33 |
4-chloropyrazole is an important chemical intermediate that has a wide range of applications in various fields, especially in pharmaceutical chemistry, pesticide development, and catalytic reactions, due to its unique pyrazole ring structure and chlorine substituents.
Basic properties and synthesis methods
It is an organic compound containing a pyrazole structure, with a molecular formula of C4H3ClN2. The structure consists of a pyrazole ring (a five membered nitrogen heterocyclic ring) and a chlorine atom located at the 4th position of the ring. It has good stability and unique chemical properties, which make it widely used in multiple fields.
There are many synthesis methods, including pyrazole chloride method, halogenated reaction method, electrolytic chlorination method, and ammonium chloride method. These methods each have their own advantages and disadvantages, and selecting an appropriate synthesis route requires comprehensive consideration of factors such as the availability of raw materials, control of reaction conditions, purity of products, and environmental impacts during production.
Potential applications in the field of spices
Although its direct application in the field of spices is relatively limited, its potential in chemical synthesis and modification provides new ideas for spice development.
(1) Intermediate for spice synthesis
As a compound containing pyrazole structure, it has potential biological activity and chemical stability, which makes it an important intermediate in spice synthesis. Through a series of chemical reactions such as esterification, amination, and alkylation, 4-chloropyrazol can be converted into compounds with specific aromas. These compounds may have unique aroma characteristics and can be used to prepare various spices and essence.
For example, through esterification reactions, esters can be formed by reacting with alcohol compounds, which typically exhibit different aroma characteristics such as fruity, floral, or grassy aromas. In addition, 4-chloropyrazol can also react with amine compounds to form amide compounds through amination reactions, which may have more complex and persistent aromas.
(2) Spice modifier
In addition to serving as a synthetic intermediate, it can also be used as a fragrance modifier. By introducing structures, the aroma characteristics and persistence of the original spices can be altered. For example, reacting it with certain spice compounds can generate compounds with new aroma characteristics, which may have richer or more unique aromas.
In addition, its introduction can also improve the stability of spices. Due to its excellent chemical stability, it can help protect spice molecules from adverse factors such as oxidation and hydrolysis, thereby extending the shelf life and service life of spices.
(3) Spice carrier
It can also be used as a carrier for spices. Due to its certain solubility and dispersibility, it can evenly disperse fragrance molecules in the carrier, thereby improving the release efficiency and persistence of fragrances. In addition, its introduction can also improve the sensory performance of spices, making them more delicate, soft, and long-lasting.
Application examples in the field of spices
Due to the limited specific examples of its application in the field of spices, the following hypothetical discussions will be based on its chemical properties and potential applications. These examples aim to illustrate the possible applications and effects of 4-chloropyrazole in the field of fragrances.
(1) Synthesis of fruit essence
Assuming that we need to synthesize a essence with strong fruit aroma, we can consider using it as a synthetic intermediate. Firstly, we can esterify it with an alcohol compound with a fruity aroma to generate ester compounds with fruity aroma. Then, we can mix and prepare this ester compound with other flavor compounds, and finally obtain essence with rich fruit aroma.
For example, we can esterify it with butanol to produce 4-chloropyrazol butyrate. This ester compound may have aroma characteristics similar to bananas or apples. Then, we can mix and mix this ester compound with citral, geraniol and other flavor compounds to obtain a essence with strong fruit aroma.
(2) Modification of floral essence
Suppose we need to modify an existing floral essence to improve its aroma characteristics and durability. We can consider using it as a modifier. First of all, we can react it with some components of flower essence to generate compounds with new aroma characteristics. Then, we can mix and mix these newly generated compounds with the original floral essence, and finally obtain the modified floral essence.
For example, we can react it with phenylethanol to produce 4-chloropyrazol phenethyl ester. This compound may have aroma characteristics similar to jasmine or rose. Then, we can mix and mix this compound with the original floral essence to improve the aroma characteristics and persistence of essence.
(3) Development of spice carriers
Assuming we need to develop a new type of spice carrier to improve the release efficiency and persistence of spices. We can consider using it as one of the main components of the carrier. Firstly, we can mix and react it with a suitable carrier material (such as cyclodextrin, polymer, etc.) to generate a carrier material with a specific structure. Then, we can mix and adsorb this carrier material with fragrance molecules to ultimately obtain fragrance products with efficient release and persistence.
For example, we can react it with β - cyclodextrin to generate its modified β - cyclodextrin. This modified cyclodextrin may have better adsorption and release properties. Then, we can mix and adsorb this modified cyclodextrin with fragrance molecules to ultimately obtain a fragrance product with efficient release and persistence.
The following are common laboratory synthesis methods for 4-chloropyrazole:
Method 1:
H2N Pyrazole+Cl- → C3H3ClN2
Among them, H2N Pyrazole represents pyrazole, and Cl - represents sodium chloride.
Prepare the required reagents: pyrazole, sodium chloride, sulfuric acid, and water.
Mix pyrazole and sodium chloride together, add an appropriate amount of sulfuric acid and water, and stir evenly.
Heat the mixture to a suitable temperature, react for a certain time, and then use TLC to detect the reaction process. When the raw material points disappear, stop heating.
Add an appropriate amount of water, adjust the pH to neutral with a sodium hydroxide solution, and then extract with ether.
The extraction solution is dried with anhydrous sodium sulfate, filtered, and the solvent is spun dry to obtain the crude product.
Purify using silica gel column chromatography to obtain the pure product.
Method 2:
C3H4N2O + Cl- → C3H3ClN2 + H2O
Among them, 4-OH Pyrazole represents 4-hydroxypyrazole, Cl - represents a chlorinating agent, and H2O represents water.
Prepare the required reagents: 4-hydroxypyrazole, chlorinating agents (such as sodium chloride or potassium chloride), organic solvents (such as ether or chloroform).
Mix 4-hydroxypyrazole with a chlorinating agent, add an appropriate amount of organic solvent, and stir evenly.
Heat the mixture to a suitable temperature, react for a certain time, and then use TLC to detect the reaction process. When the raw material points disappear, stop heating.
Add an appropriate amount of water, adjust the pH to neutral with a sodium hydroxide solution, and then extract with ether.
The extraction solution is dried with anhydrous sodium sulfate, filtered, and the solvent is spun dry to obtain the crude product.
Purify using silica gel column chromatography to obtain the pure product.
Pyrazole, as a five membered nitrogen-containing heterocyclic compound, has become a research hotspot in heterocyclic chemistry since its first synthesis in the late 19th century due to its unique biological activity and coordination ability. The discovery and optimization of chlorinated pyrazole derivatives (such as 4-chloropyrazole) have not only promoted the development of medicinal chemistry, but also demonstrated significant value in fields such as materials science and coordination chemistry.
In 1883, German chemist Ludwig Knorr first synthesized pyrazole derivatives by condensing phenylhydrazine with ethyl acetoacetate (Ber. Dtsch. Chem. Ges., 1883), laying the foundation for heterocyclic synthesis. Early pyrazole chlorination reactions lack selectivity and often result in 3,4,5-trichloro-substituted mixtures
In 1910, a French team attempted to directly chlorinate pyrazole with chlorine gas, but due to a violent reaction, the product decomposed and only a trace amount of monochlorinated compound was isolated
In 1936, British chemist Robert Robinson proposed the theory of electronic effects, stating that the 4th position of pyrazole is more susceptible to electrophilic attacks due to the electron withdrawing effect of the nitrogen atom
In 1952, a US team used thionyl chloride (SO ₂ Cl ₂) to react at 0 ° C and for the first time obtained 4-chloropyrazole with high selectivity (>80%). Using intermediate capture - detecting the presence of N-chloropyrazolium salt by NMR, confirming that chloride ions preferentially attack the 4-carbon position. Adding catalytic amount of DMF in side reaction control can suppress polychlorinated byproducts
In 1969, Pfizer developed the pyrazole anti-inflammatory drug Phenylbutazone using 4-chloropyrazole as a precursor
In the 1980s, 4-chloromodification significantly improved the membrane penetration of sulfonamide drugs
In 1995, 4-chloropyrazole was used as a bidentate ligand to construct the first pyrazole based MOF with copper ions. Its palladium complex exhibited excellent performance in Suzuki coupling
In 2015, a Japanese team developed a solvent-free electrochemical method with an atomic utilization rate of 95%
In 2020, the modification of halogenated enzymes achieved 4-specific chlorination
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