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Ethyl p-aminobenzoate is also known as benzocaine. Its chemical formula is C9H11NO2. It is an organic compound. It is colorless oblique crystal, and it is odorless and tasteless. It is soluble in alcohol, ether and trichloromethane, almond oil, olive oil and dilute acid, but it is insoluble in water. Clinically, it is used for analgesia and antipruritic of wound, ulcer surface, burn, skin scratch and hemorrhoids.

Chinese Name
Ethyl p-aminobenzoate

Foreign Name


Chemical Formula

Molecular Mass

Colorless oblique crystal



1.17 g/cm³

Melting Point
88 – 90 ℃

Boiling Point
310.7 ℃

Flash Point
164.2 ℃

Security Description

Hazard Symbol

Hazard Description

Essential Information

Chinese name: ethyl p-aminobenzoate
Chinese alias: benzocaine; ethyl 4-aminobenzoate
English name: benzocaine
CAS No:94-09-7
MDL No.: MFCD00007892
EINECS No.: 202-303-5
RTECS No.: DG2450000
BRN No.: 638434
PubChem No.: 24894416
Molecular formula:C9H11NO2
Molecular mass: 165.189
Precise mass: 165.07900

Physicochemical Properties

Melting point: 88-90℃
Boiling point: 310.7℃
Flash point: 164.2℃
Refraction index: 1.555
Appearance: white crystalline powder
Water solubility: soluble in alcohol, ether and trichloromethane, almond oil, olive oil and dilute acid, insoluble in water

Molecular Structure Data
Molar refractivity: 46.89
Molar volume (cm3/mol): 146.1
Isotonic volume (90.2K): 377.7
Surface tension (dyne/cm): 44.6
Polarizability (10-24cm3): 18.59

Security Information
Packing grade:III
Customs Code: 2922499990
WGK Germany:2
Hazard category code: R36/37/38; R43
Safety instructions: S22; S24/25; S26; S37/39
RTECS No.: DG2450000
Dangerous goods signs: Xi


1. UV absorber. It is mainly used for sunscreen and tanning cosmetics. It is chemically stable to light and air, safe to skin, and it can form a film on the skin. It can effectively absorb U.V.B area 280-320 μm ultraviolet in the medium wave light area. The addition amount is usually about 4%.
2. Local anesthetics. It is used to relieve itching and pain on traumatic surface, ulcer and hemorrhoids. The use concentration is 5% ~ 20%. It is also used as intermediate in drug synthesis and organic synthesis.

Hazard Description

Hazard Overview
Health hazards: the product is a local anesthetic. It is irritating to respiratory tract, and it can cause cough and shortness of breath after inhalation. In very few cases, oral administration can cause cyanosis. It is irritating to eyes and sensitizing to skin.
Environmental hazards: serious harm to the environment.
Fire and explosion hazard: the product is flammable and it has mild sensitization effect.


Synthesis of Benzocaine

Experimental Principle


Benzocaine is the general name of ethyl p-aminobenzoate and it can be used as a local anesthetic. Benzocaine can be synthesized from 4-nitrotoluene in three different ways. The chemical name of benzocaine isethyl p-aminobenzoate, and the chemical structure formula is: Benzocaine is a white crystalline powder with a slightly bitter taste; mp. 88~90℃;it is soluble in ethanol, very slightly soluble in water.

The following is the synthetic route:



Experimental Scheme and Safety Precautions
(1) Preparation of 4-nitrobenzoic acid
(2) Esterification and reduction of 4-nitrobenzoic acid


Steps: add 4g 4-nitrobenzoic acid, 20ml 95% ethanol and 1.5ml concentrated sulfuric acid in a 250ml round bottom flask, heat and reflux them for 1.5h. Evaporate some ethanol (about 9ml) with low fire, pour the residue into 50ml cold water while it is hot and stir it [1], filter and collect the precipitated white precipitate, wash it with a small amount of water, transfer the precipitate to the mortar [2], add 5ml 5% sodium carbonate, grind it to remove unesterified 4-nitrobenzoic acid, filter it, wash the filtered materials with a small amount of water and drain to obtain white granular crystals. If necessary, ethanol can be used for recrystallization.
Output: 2~3g. Pure ethyl 4-nitrobenzoate is colorless crystal, and its melting point is 57 ℃.

(1) It must be stirred at any time, so that the precipitated solid particles are relatively fine for later treatment.
(2) If the particles are very fine, they cannot be ground in the mortar, but they can be washed with 5% sodium carbonate solution in the beaker.


Reduction: in a 100ml three-neck flask, put 5.6g iron filings, 18ml water and 1ml acetic acid, stir and reflux it, boil it for 10 minutes to activate the iron filings, cool them, add 2g ethyl 4-nitrobenzoate and 18ml 95% ethanol, slowly stir and reflux it for 1.5 ~ 2 hours, slowly add 13ml warm 10% sodium carbonate solution to the hot reactant, stir it along with addition, quickly filter it, and add water to the filtrate until the crystalline product is completely precipitated, cool, filter and collect the product, and recrystallize it with 50% ethanol if necessary.

(1) 95% ethanol as solvent can dissolve ethyl 4-nitrobenzoate, so that the reduction reaction can be carried out easily, and also control the reactant below 80℃for stirring and reflux, so as to avoid the decomposition of the product in boiling water.
(2) when heating and reflux, reddish brown iron hydroxide is formed first, and finally the reactant is dark brown and black, which is caused by Fe3O4.
(3) A small amount of products may be mixed in the filtered Fe3O4 residue. During mass preparation, it can be washed once with hot water or dilute alcohol to reduce the loss.
(4) Water may not be added too much.

(Method II) Refining

Put the crude product into a 100ml round bottom bottle equipped with a spherical condenser, add 10 ~ 15 times (ml/g) 50% ethanol, and heat it in a water bath to dissolve it. Cool it slightly, add activated carbon for decolorization (the amount of activated carbon depends on the color of the crude product), heat and reflux it for 20 min, and filter it while it is hot (Buchner funnel and filter bottle shall be preheated). Transfer the filtrate to the beaker while it is hot, and cool it naturally. After the crystal is completely precipitated, filter it, wash it twice with a small amount of 50% ethanol, press it dry, measure the melting point and calculate the yield.

Structural Confirmation
1. Infrared absorption spectroscopy, standard TLC control method.
2. Nuclear magnetic resonance spectroscopy.

(1) Take about 0.1g of this product, add 5ml sodium hydroxide test solution, and boil it to produce ethanol; when the iodine test solution is heated, yellow precipitation will be generated and the odor of triiodomethane will be caused.
(2) the infrared light absorption spectrum of this product shall be consistent with the control spectrum (spectrum set 237).
(3) identification reaction of aromatic first amines (Appendix III).

Check Acidity
Take 1.0g of this product, add 10ml of neutral ethanol (show neutral to indicator solution) to dissolve it, add 2 drops of indicator solution and 0.10ml of sodium hydroxide titrant (0.1mol / L), which should show light red.

Clarity and Color of the Solution
Take 1.0g of this product and add 20ml of ethanol to dissolve it. The solution should be clear and colorless. Related substances: take this product and add absolute ethanol to make a solution containing 10mg per 1ml as the test solution; accurately measure an appropriate amount and dilute it with absolute ethanol to make a solution containing 0.01, 0.025, 0.05 and 0.1 mg per 1ml as the control solution. Do the test according to the thin layer chromatography (Appendix VB), absorb 20μl respectively of the above five solutions. Put them on the same silica gel GF254 thin-layer plate respectively, use absolute ethanol- trichloromethane (0.75 : 99.25) as the developing agent, develop it, dry it, and inspect it under ultraviolet lamp (254nm). If the test solution shows impurity spots (if impurity spots are observed at the origin, impurity spots shall be calculated), the total amount of impurities may not exceed 1.0% compared with the main spots of the control solution.

Take 0.2g of this product, dissolve it with 5ml ethanol, add 3 drops of dilute nitric acid and 3 drops of silver nitrate test solution, and turbidity may not occur immediately.

Loss on Drying
Take the product and dry it in a phosphorus pentoxide dryer to constant weight. The weight loss may not exceed 0.5% (Appendix VIII L).

Residue on Ignition
Take 1.0g of this product and check it according to procedures (Appendix Ⅷ N). The residue may not exceed 0.1%.

Heavy Metals
Take the residue left under the item of ignition residue and check it according to procedure (the second method in Appendix VIII H). The content of heavy metals may not exceed ten millionths.

Content Determination Method
Method name: benzocaine API – Determination of benzocaine – dead-stop titration
Application scope: titration is used to determine the content of benzocaine in benzocaine API. the method is applicable to benzocaine API.

Method principle: the test sample is titrated with sodium nitrite titrant according to the dead-stop titration method, and the content of benzocaine is calculated according to the amount of titrant used.

1. concentrated ammonia test solution
2. hydrochloric acid solution (1 → 2)
3.  sodium nitrite titrant (0.1mol/l)
4.  reference 4-aminobenzenesulfonic acid
Sample preparation:1. sodium nitrite titrant (0.1mol/l)
Preparation: take 7.2g sodium nitrite, add 0.10g anhydrous sodium carbonate, and add an appropriate amount of water to dissolve it into 1000ml.

Calibration: take about 0.5g of reference 4-aminobenzenesulfonic acid which is dried to constant weight at 120 ℃, accurately weigh it, add 30ml water and 3ml concentrated ammonia test solution, dissolve it, add 20ml hydrochloric acid (1 → 2), stir it, titrate quickly with this solution below 30 ℃, insert the tip of the burette into about 2/3 below the liquid level during titration, and stir it along with the drop; when reaching the end point, lift the tip of the burette out of the liquid level, wash the tip with a small amount of water, incorporate the washing solution into the solution, continue to titrate slowly, and indicate the end point with the dead-stop titration. Every 1ml of sodium nitrite titrant (0.1mol/L) is equivalent to 17.32mg of 4-aminobenzenesulfonic acid. The concentration of this solution is calculated according to the consumption of this solution and the dosage of 4-aminobenzenesulfonic acid.

Operation Steps: accurately weigh about 0.35g of the test sample and titrate with sodium nitrite titrant (0.1mol/L) according to the dead-stop titration. Every 1ml of sodium nitrite titrant (0.1mol / L) is equivalent to 16.52mg of C9H11NO2.

Note: “Precise weighing” means that the weight shall be accurate to one thousandth of the weighed weight. “Precision measurement” means that the accuracy of the measured volume shall meet the accuracy requirements for the pipette of this volume in the national standard.The main manufacturers of benzocaine in the world include TCI, Merck KGaA, Aceto Corporation, Alfa aesar, penta manufacturing company, etc. the top five manufacturers in the world account for more than 40% of the market share. North America is currently the largest benzocaine market in the world, with a market share of more than 35%, followed by China and Europe with a total share of more than 45%. In 2020, the global benzocaine market reached 850 million yuan and it is expected to reach 980 million yuan in 2026, with a compound annual growth rate (CAGR) of 2.1%.

Major Manufacturers Include:

Merck KGaA
Aceto Corporation
Alfa Aesar
Penta Manufacturing Company
Pure Chemistry Scientific
Oakwood Products
Indofine Chemical Company
Jiutai Pharmaceutial
Changzhou Sunlight Pharmaceutical
Energy Chemical
Jinan Subang
Changzhou Josen
Ho Tai
Eashu Pharmaceutical

According to different product purity, it includes the following categories:


The applications mainly include the following aspects:

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