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Chemical Properties of Benzoic Acid – Breakdown

Benzoic acid chemical formula

Chemical properties of benzoic acid:

Benzoic acid is the simplest aromatic carboxylic acid. It is aromatic and has the properties of carboxylic acid. Therefore, two major types of chemical reactions can occur. One is the substitution reaction on the benzene ring, and the other is the reaction of the carboxyl group. Benzoic acid is a weak acid, stronger than fatty acids. They have similar chemical properties and can form salts, esters, acid halides, amides, acid anhydrides, etc., and are not easily oxidized. Electrophilic substitution reaction can occur on the benzene ring of benzoic acid, mainly obtaining meta-substitution products.

Reaction on carboxyl group

(1) Convert into salt

The ionization constant of benzoic acid in water is Ka=6.4×10-5 (25 ℃). The acidity of benzoic acid is slightly stronger than that of cyclohexanecarboxylic acid. This is because the sp2 hybridized carbon atom on the benzene ring has a large electronegativity and donates electrons. The effect is weak. Can react with bases or alkaline substances.

(2) Convert to ester

Benzoic acid reacts with alcohols (such as methanol, butanol, benzyl alcohol, etc.) to generate the corresponding esters.

(3) Convert to acid chloride

The hydroxyl group in benzoic acid is replaced by chlorine to form benzoyl chloride [98-88-4]. The chlorine-containing reagents used in this reaction include phosphorus pentachloride, phosphorus trichloride and thionyl chloride.

(4) Convert to acid anhydride

When benzoic acid and dehydrating agent are heated together, two molecules of benzoic acid remove one molecule of water to form benzoic anhydride [93-97-0]. Acetic anhydride is commonly used as dehydrating agent and phosphoric acid is used as catalyst.

(5) Convert to amide

Benzoic acid reacts with aniline at a temperature of 180~190°C to form benzoanilide (N-benzoylanilide). The yield of this reaction is about 84%.

(6) Oxidation reaction

Using the copper salt of benzoic acid as a catalyst, oxidizing benzoic acid with oxygen can produce phenol and carbon dioxide.

(7) Reduction reaction

Under the catalyst prepared by Al(NO3) and Mn(NO3)2, benzoic acid can be catalytically reduced with hydrogen to obtain benzaldehyde.

Substitution reaction on benzene ring:

Benzoic acid undergoes an electrophilic substitution reaction on the benzene ring. The hydrogen atoms on the benzene ring, like the hydrogen atoms of benzene, can be substituted by various atoms or atomic groups. However, the segment group on the benzene ring of benzoic acid is an electron-withdrawing group, which makes The benzene ring is a passivated meta-positioning group, so substitution reactions such as sulfonation, nitration and chlorination of benzoic acid are more difficult than the corresponding reactions of benzene. This passivation trend can be overcome by using a catalyst and increasing the reaction temperature.

Hydrogenation reaction on benzene ring:

In the case of metal platinum as a catalyst, benzoic acid is hydrogenated to generate hexahydrobenzoic acid, which is an intermediate in the production of caprolactam. Adding water can speed up the reduction, and the reaction temperature and pressure should be lower than those during carboxyl reduction.

Decarboxylation reaction:

Benzoic acid can remove its carboxyl group and generate carbon dioxide under heating conditions, which is a decarboxylation reaction (a substitution reaction). The reaction temperature is about 150~170°C.

Reactions with metal organic compounds:

Benzoic acid can react with metal-organic compounds such as Green’s reagent and methyllithium to generate corresponding metal-organic compounds. Among them, the reaction of benzoic acid and methyllithium is a general method for preparing ketones.


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