2-Chlorobenzaldehyde (2-chloro-benzaldehyd), CAS No. 89-98-5, is a typical aromatic halogenated aldehyde compound. Its molecular structure consists of a benzene ring bearing a chlorine atom and an aldehyde group at the ortho positions respectively. It has a molecular formula of C₇H₅ClO and a molecular weight of 140.57. At ambient temperature, it appears as a colorless to pale yellow transparent liquid with a characteristic pungent aromatic odor. It is slightly soluble in water and readily soluble in common organic solvents such as ethanol, diethyl ether and dichloromethane.
This substance contains two types of reactive functional groups: aryl chloride and aldehyde group, endowing it with diverse chemical reactivity. The aldehyde group undergoes canonical aldehyde transformations including condensation, oxidation, reduction and addition reactions. Subject to suitable catalytic conditions, the ortho chlorine atom can participate in nucleophilic aromatic substitution, rendering this compound a vital building block for the construction of complex organic molecules. From an industrial perspective, it serves as a key fine chemical intermediate and is widely utilized in the synthesis of pharmaceuticals, dyes and pesticides, enabling the manufacture of antibacterial agents, fluorescent dyes and plant growth regulators.
| Chemical Formula | C7H5ClO |
| Exact Mass | 140 |
| Molecular Weight | 141 |
| m/z | 140 (100.0%), 142 (32.0%), 141 (7.6%), 143 (2.4%) |
| Elemental Analysis | C, 59.81; H, 3.59; Cl, 25.22; O, 11.38 |
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2-Chlorobenzaldehyde is an important organic synthetic intermediate with wide applications in various fields such as pesticides, pharmaceuticals, dyes, fragrances, functional materials, and analytical chemistry.
In the field of dyes and pigments
As an important intermediate in dye synthesis
Disperse dyes are one of the most widely used types of dyes in synthetic fiber dyeing, especially suitable for hydrophobic fibers such as polyester and nylon. 2-chloro-benzaldehyd plays a crucial role in the synthesis of dispersed dyes, as it can undergo condensation, coupling, and other reactions with other intermediates to construct dispersed dye molecules with specific molecular structures and color systems. For example, in the synthesis of certain high-performance dispersed dyes, the introduction of 2-chloro-benzaldehyd can improve the dispersibility of the dyes.
Due to the electronic and steric hindrance effects of chlorine atoms and aldehyde groups in 2-chloro-benzaldehyd, the polarity and intermolecular forces of dye molecules can be adjusted, making it easier for the dye to form a uniform dispersion system in water or organic solvents, thereby improving the dye's dye uptake and dyeing uniformity on fibers. In addition, the participation of 2-chloro-benzaldehyd can enhance the wash fastness and light fastness of dispersed dyes. During the dyeing process, dye molecules containing 2-chloro-benzaldehyd structure can form more stable chemical bonds or physical adsorption with fibers, reducing the shedding and fading of dyes under washing and light conditions, and giving the dyed fabric a more durable color.
Application in the synthesis of reactive dyes
Reactive dyes have excellent color fastness due to their covalent bonding with fibers, and are widely used for dyeing natural fibers such as cotton, linen, and silk. 2-chloro-benzaldehyd can be used as a key raw material for constructing reactive groups or intermediates in the synthesis of reactive dyes, enhancing the reactivity between dyes and fibers. For example, in the synthesis of certain vinyl sulfone reactive dyes, 2-chloro-benzaldehyd can be converted into an intermediate containing vinyl sulfone groups through a series of reaction steps. Ethylene sulfone groups can undergo nucleophilic addition reactions with hydroxyl groups on fibers under alkaline conditions, forming stable covalent bonds.
The presence of 2-chloro-benzaldehyd helps optimize the formation conditions and reaction activity of vinyl sulfone groups, enabling reactive dyes to bind more efficiently to fibers and improve the dye fixation rate. When synthesizing certain reactive dyes containing sulfonic acid groups, 2-chloro-benzaldehyd can serve as a linking arm to connect the sulfonic acid group with the chromophore. The introduction of sulfonic acid groups increases the water solubility of dyes, while the structural characteristics of 2-chloro-benzaldehyd help maintain the stability of dye molecules, prevent adverse reactions such as hydrolysis and oxidation during storage and use, and extend the service life of dyes.
Application in the synthesis of other types of dyes
Acid dyes are mainly used for dyeing protein fibers such as wool and silk. 2-chloro-benzaldehyd can be synthesized as an acidic dye intermediate with specific color and dyeing properties by reacting with aromatic amine compounds. These intermediates further bind with acidic groups to form acidic dye molecules.
For example, in the synthesis of certain azo acid dyes, 2-chloro-benzaldehyd undergoes diazotization coupling reaction with aromatic amines, resulting in azo dye intermediates with good chromogenic properties. Then, by introducing acidic groups such as sulfonic acid groups, protein fibers can be stained in acidic media. The presence of 2-chloro-benzaldehyd helps to regulate the color brightness and dyeing affinity of dyes, and improve the dyeing effect of acidic dyes on protein fibers.
Fragrance and essence
Provide unique aroma characteristics
2-chloro-benzaldehyd has a special aldehyde aroma, which is usually described as slightly fruity, sweet, and accompanied by a certain degree of irritation. The presence of aldehyde group makes its aroma highly volatile and diffusive, which can rapidly release the aroma in essence formula and bring fresh and bright smell to essence products.
Compared with other simple aldehyde fragrances such as benzaldehyde, the chlorine atom in 2-chloro-benzaldehyd introduces additional electronic and steric hindrance effects, making its aroma characteristics more unique and complex. This unique aroma feature enables 2-chloro-benzaldehyd to add personalized aroma elements to the product in essence preparation, and meet the needs of consumers for different flavor types.
Provide unique aroma characteristics
In the essence formula, 2-chloro-benzaldehyd can cooperate with other flavor ingredients to build a rich and harmonious aroma system. For example, when it is used together with citrus spices (such as citral and nerolide), it can enhance the freshness and vitality of citrus aroma, making essence products more suitable for summer perfume, air freshener and other products.
When combined with floral fragrances (such as rose alcohol and jasmine ketone), 2-chloro-benzaldehyd can balance the sweetness of floral fragrance, increase the level and three-dimensional sense of fragrance, and provide elegant and lasting fragrance for high-end perfume, cosmetics essence, etc. In addition, its combination with woody spices (such as sandalwood alcohol and cedar alcohol) can also produce a unique effect, giving essence products warm and deep woody fragrance, which is suitable for the deployment of men's perfume, cologne and other products.
Used for blending specific fragrance types
In the formulation of fruity essence, 2-chloro-benzaldehyd can simulate the aroma characteristics of some fruits, such as peaches and apricots. Through the synergistic effect with other fruit flavors (such as benzyl acetate, ethyl butyrate), a realistic and attractive fruit flavor essence can be formulated, which is widely used in food essence (such as candy, drinks, ice cream, etc.), daily chemical essence (such as bath gel, shampoo, etc.), and tobacco essence.
Among the food essence, the fruity essence containing 2-chloro-benzaldehyd can enhance the flavor and attractiveness of food, so that consumers can get more pleasant sensory experience when tasting food. Among daily chemical essence, fruity essence can give products fresh and natural fragrance, and satisfy consumers' pursuit of natural and healthy products. In tobacco essence, appropriate amount of 2-chloro-benzaldehyd can improve the taste and aroma of tobacco, reduce the irritation of tobacco, and improve the quality of tobacco products.
Used for blending specific fragrance types
When preparing rose essence, adding a small amount of 2-chloro-benzaldehyd can enhance the freshness and modernity of rose fragrance, making essence more in line with the aesthetic needs of contemporary consumers. In the formulation of jasmine essence, 2-chloro-benzaldehyd can complement jasmine and other major floral components, making the aroma of essence more lasting and elegant. In addition, 2-chloro-benzaldehyd can also be used as an important auxiliary flavor to add unique flavor characteristics to some flower essence with unique style (such as narcissus essence, violet essence).
Custom Notebook Solutions
In addition to fruity and floral essence, 2-chloro-benzaldehyd can also be used to prepare some characteristic essence. For example, in the marine flavor type essence, it can be combined with marine spices (such as ambergris, sea breeze aldehyde) to create a fresh and cool marine flavor, which is suitable for perfume, air freshener and other products. Among oriental flavor essence, 2-chloro-benzaldehyd can be matched with herbs, amber and other spices to add warm and mysterious oriental flavor to essence, which is often used in the deployment of high-end perfume, incense candles and other products.
2-Chlorobenzaldehyde has the following synthetic methods.
1. Chlorination and hydrolysis of o-chlorotoluene:
It is obtained by chlorination and hydrolysis of o-chlorotoluene.
① Chlorination: heat o-chlorotoluene, phosphorus trichloride and sulfoxide chloride to 150 ℃, and pass chlorine gas to theoretical amount under ultraviolet irradiation to obtain o-chlorobenzylidene dichloride.
② Hydrolysis: heat the mixture of o-chlorobenzylidene dichloride and zinc chloride at 120~130 ℃, stir and add 1% ferric chloride aqueous solution. After the addition, heat the mixture and return with water. The oil layer is refined o-chlorobenzaldehyde.
In addition, hydrolysis can also be carried out in the presence of sulfuric acid. Stir o-chlorobenzylidene dichloride and industrial concentrated sulfuric acid together until the temperature automatically decreases and the hydrogen chloride escape slows down, and then slowly heat for 12h to keep the temperature at 30-40 ℃.
After the reaction, the finished product is obtained by layering with cold water, separating the oily substance, washing and steam distillation.
2. Chlorination and oxidation of o-chlorotoluene:
The methyl in o-chlorotoluene is chlorinated and then oxidized with nitric acid.
Add 380g (3.0mol) of o-chlorotoluene into the 600mL photoreactor with thermometer, stirrer, chlorine blowing tube, reflux condenser and high-pressure mercury lighting device, heat it to 130 ℃, blow 106g/h (1.5mol/h) of chlorine under light, and the injection time is 3.6h.
A total of 5.4mol of chlorine gas is introduced. After the reaction, dry nitrogen was added to the reaction liquid to drive out the hydrogen chloride and chlorine gas.
A total of 558g of reaction liquid was obtained, including 0.5% (mol) of o-chlorotoluene, 28% of o-chlorobenzyl chloride, 67% of o-chlorodichlorotoluene, 3% of o-chlorotrichlorotoluene, and the average chlorination degree of o-chlorochlorotoluene was 1.8.
Add 64.7g (0.343mol) of the chlorinated mixture of o-chlorotoluene, 1440g of 3% (mass fraction) nitric acid and 2.0g of vanadium pentoxide into a 2L three-port flask with a thermometer, stirrer and reflux condenser, and heat and reflux for 6h under stirring.
After the reaction is completed, cool it, add 200mL toluene, separate the oil phase, and add 100mL toluene to the aqueous solution layer for extraction twice.
Combine the oil phase and extraction liquid, evaporate toluene, distill the residue, collect the fraction at 107~110 ℃ (4.0kPa), and obtain 36g of product o-chlorobenzaldehyde, with the yield of 73.5% based on o-chlorotoluene.
Compared with traditional zinc brightener, water-soluble 2-chlorobenzaldehyde has the following advantages:
Water-soluble this compound dissolved in water can give full play to the polarizing effect of brightener, and the added amount is small. The reference amount is 0.3~1.0 g/L.
The traditional carrier brightener is a softener. In order to ensure the complete dissolution of this compound and benzidine acetone, a certain high cloud point is required, and its demand is generally large. After the water solubility of water-soluble this compound is improved, the required carrier brightness dose will be reduced, that is, the cost of brightener will also be reduced, and COD will be reduced, which is more environmentally friendly. If the carrier brightener after sulfonation is added, the effect will be better.
3. Foam volume decreases
After the amount of carrier brightener is reduced, the amount of foam will be reduced, which will be more convenient and environmentally friendly in actual electroplating production.
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