Product name: Benzoic acid
CAS number: 65-85-0
Molecular formula: C7H6O2
EINECS number: 200-618-2

Overview of Benzoic Acid

Benzoic acid is also called benzoic acid. Its molecular formula is C6H5COOH. It is the simplest aromatic acid in which the carboxyl group is directly connected to the carbon atom of the benzene ring. It is a compound formed by replacing a hydrogen on the benzene ring with a carboxyl group (-COOH). It is a colorless, odorless flaky crystal. Melting point 122.13℃, boiling point 249℃, relative density 1.2659 (15/4℃). It sublimates rapidly at 100℃. Its vapor is highly irritating and can easily cause coughing after inhalation. It is slightly soluble in water and easily soluble in organic solvents such as ethanol, ether, chloroform, benzene, toluene, carbon disulfide, carbon tetrachloride and turpentine. It is widely present in nature in the form of free acid, ester or its derivatives. For example, it exists in the form of free acid and benzyl ester in benzoin gum; it exists in the free form in the leaves and stems of some plants; it exists in the form of methyl ester or benzyl ester in essential oils; it exists in the form of its derivative hippuric acid in horse urine. Benzoic acid is a weak acid, stronger than fatty acids. They have similar chemical properties and can form salts, esters, acyl halides, amides, anhydrides, etc., and are not easily oxidized. Electrophilic substitution reactions can occur on the benzene ring of benzoic acid, mainly obtaining meta-substituted products.

Solubility

Solubility in 100g water: 4℃, 0.18g; 18℃, 0.27g; 20℃, 0.29g; 25℃, 0.34g; 30℃, 0.42g; Chemicalbook40℃, 0.6g; 50℃, 0.95g; 60℃, 1.2g; 75℃, 2.2g; 80℃, 2.75g; 90℃, 4.6g; 95℃, 6.8g.

Chemical properties

Flake or needle-shaped crystals. With the smell of benzene or formaldehyde. Slightly soluble in water, soluble in ethanol, methanol, ether, chloroform, benzene, toluene, carbon disulfide, carbon tetrachloride and turpentine.

Benzoic acid Chemical Properties

Uses

Benzoic acid is an important acidic food preservative. Under acidic conditions, it has an inhibitory effect on molds, yeasts and bacteria, but has a weaker effect on acid-producing bacteria. The optimum pH value for antibacterial activity is 2.5-4.0, and it is generally better to be lower than pH 4.5-5.0. The maximum usage amount of concentrated fruit and vegetable juice in plastic barrels for the food industry shall not exceed 2.0g/kg; the maximum usage amount in jams (excluding canned food), juice (flavored) beverages, soy sauce, and vinegar is 1.0g/kg; the maximum usage amount in soft candies, wines, and fruit wines is 0.8g/kg; the maximum usage amount in low-salt pickles, sauces, and preserves is 0.5g/kg; the maximum usage amount in carbonated beverages is 0.2g/kg. Since benzoic acid is slightly soluble in water, it can be dissolved with a small amount of ethanol when used.

Uses

Benzoic acid is an important acid-type feed preservative. Under acidic conditions, it has an inhibitory effect on molds, yeasts and bacteria, but has a weaker effect on acid-producing bacteria. The optimal pH for antibacterial effect is 2.5-4.0, and it is generally better to be lower than pH 4.5-5.0.

Uses

Benzoic acid is mainly used for antifungal and disinfection and preservation, and is also used as an antimicrobial agent. Due to its low solubility, benzoic acid must be fully stirred or dissolved in a small amount of hot water or ethanol when used. When used in concentrated fruit juice for refreshing drinks, benzoic acid is easily volatilized with water vapor, so its sodium salt is often used. 1g of sodium salt is equivalent to 0.847g of benzoic acid.

Uses

Usually used as a fixative or preservative. Also used as a flavoring agent for fruit juice drinks. Can be used as a paste incense in aromatherapy essences. Can also be used in edible flavors such as chocolate, lemon, orange, berry, nut, candied fruit, etc. It is also commonly used in tobacco flavors.

Uses

Benzoic acid and its sodium salt are important food preservatives. Under acidic conditions, the inhibitory effect on yeast and mold is strong at pH 3, while the effect on many molds is very poor at pH 6, so the optimal pH value for antibacterial is 2.5-4.0. Benzoic acid is mainly used in the production of sodium benzoate food preservatives, dye intermediates, pesticides, plasticizers, mordants, medicines, and spices. It can also be used as a modifier for alkyd resins and polyamide resins, terephthalic acid, a raw material for the production of polyester, and as a rust inhibitor for steel equipment.

Uses

Used in the production of medicines, dye carriers, plasticizers, spices and food preservatives, etc., and also used to improve the performance of alkyd resin coatings; used as an intermediate for pharmaceuticals and dyes, used to make plasticizers and spices, etc., and also as a rust inhibitor for steel equipment

Uses

Alkali quantitative standard. Iodine quantitative standard. Calorific value standard. Verification of aluminum, boron, cerium, copper, iron, lead, manganese, mercury, nickel, nitrate, nitrite, silver, titanium, tungsten and vanadium. Determination of aluminum, copper, iron, titanium and uranium. Organic microanalysis of carbon, hydrogen, oxygen and relative molecular mass standard. Also used for benzoylation in organic analysis.

Production method

It was originally produced by dry distillation of benzoin gum or hydrolysis with alkaline water, and can also be produced by hydrolysis of hippuric acid. There are three industrial production methods for benzoic acid: toluene liquid phase air oxidation method, benzyl trichloride hydrolysis method and phthalic anhydride decarboxylation method, and toluene liquid phase air oxidation method is the most common. Toluene and air are introduced into a reactor containing a cobalt naphthenate catalyst, and react under the conditions of a reaction temperature of 140-160℃ and an operating pressure of 0.2-0.3MPa to generate benzoic acid. Unreacted toluene is evaporated to obtain crude benzoic acid, which is then distilled under reduced pressure and recrystallized to obtain the finished product. The final product obtained by the phthalic anhydride decarboxylation method is not easy to purify, and the production cost is high. It is only used in the manufacturing process of small-volume pharmaceutical products. The product of the toluene chlorination method is not suitable for food. Benzoic acid has different specifications such as industrial, food, and pharmaceutical. Food grade should comply with GB1901-80, with a content of more than 99.5%, a melting point of 121-123℃, and regulations on quality indicators such as oxidizable substances, carbides, chlorine compounds, ignition residues, heavy metals, and arsenic content. Raw material consumption quota: toluene 1140kg/t, cobalt naphthenate 4kg/t. In addition, benzoic acid can be produced as a by-product when benzaldehyde is produced from toluene.

Production method

It is obtained by direct liquid phase oxidation of toluene. It is obtained by decarboxylation of phthalic acid using lead oxide, zinc oxide, etc. as catalysts. It is obtained by chlorinating toluene into trichlorotoluene and then hydrolyzing it with lime milk and iron powder.

Production method

Although benzoic acid can be produced by toluene chlorination and phthalic acid decarboxylation, the most commonly used industrial production method at home and abroad is the liquid-phase catalytic air oxidation method using toluene as raw material. Toluene and air dissolved with a catalyst (cobalt naphthenate, cobalt cyclohexane or cobalt acetate) are pumped continuously into the oxidation tower (or kettle) respectively, and oxidized at 140~165℃ and 0.3~0.4MPa to produce benzoic acid. The tail gas at the top of the tower is condensed and adsorbed on activated carbon to recover toluene and then discharged; the reaction liquid in the kettle is distilled at normal pressure to recover unreacted toluene, benzyl alcohol, benzaldehyde and other light components, and then distilled under reduced pressure to obtain benzoic acid; the recovered toluene is returned to the oxidation tower, and the single-pass conversion rate of toluene can be controlled at more than 35%. 2C6CH5CH3+3O2[cobalt salt]→2C6H5COOH

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