acetic acid

[y ǐ su ā n]

An organic monoacid

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Acetic acid, also called acetic acid, is an organic compound, chemical formula CH three COOH, an organic monoacid, is the main component of vinegar. Pure anhydrous acetic acid (glacial acetic acid) is a colorless hygroscopic liquid with a freezing point of 16.6 ℃ (62 ℉). After solidification, it is a colorless crystal. Its aqueous solution is weak acidic and corrosive, strongly corrosive to metals, and steam is irritant to eyes and nose.

Acetic acid is widely distributed in nature. For example, in fruits or vegetable oils, acetic acid is mainly Esters exist in the form of. Acetic acid exists in the form of free acid in animal tissues, excreta and blood. Many microorganisms can transform different organics into acetic acid through fermentation.^[4]

Chinese name: acetic acid
Foreign name: Acetic Acid
Alias: acetic acid 、 Glacial acetic acid
chemical formula: CH three COOH
molecular weight: sixty point zero five two
CAS login number: 64-19-7
EINECS login number: 231-791-2
Melting point: 16.6 ℃

Boiling point: 117.9 ℃
Water solubility: soluble
Density: 1.05 g/cm ³
Appearance: Colorless transparent liquid with pungent smell
Flash point: 39 ℃ （CC）
Security description: S23； S24/25； S26； S36/37/39； S45
Hazard symbol: C
Hazard description: R10； R35

catalog

A brief history of research

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Acetic acid fermentation bacteria (Acetobacter) can be found in every corner of the world. When every nation brews wine, it is inevitable to find vinegar - it is the natural product of these alcoholic drinks exposed to the air. For example, there is a saying in China that Du Kang's son Heita got vinegar because he had been brewing wine for too long.

In ancient Rome, people boiled sour wine in lead containers to get a high sweet syrup called "sapa". "Sapa" is rich in a kind of sweet lead sugar, namely Lead acetate 。 In the 8th century AD, the Persian alchemist Jaber concentrated acetic acid in vinegar by distillation.

During the Renaissance, people prepared glacial acetic acid by dry distillation of metal acetate. In the 16th century, German alchemist Andreas Libafius compared the glacial acetic acid produced by this method with the acid extracted from vinegar. Because of the existence of water, the nature of acetic acid has changed so much that for centuries, chemists thought that it was two different substances. Until French chemist Pierre Adet proved that the main components of these two substances were the same.

1847, Germany scientist Adolf William Herman Colby synthesized acetic acid from inorganic materials for the first time. The reaction process is as follows: first carbon disulfide After chlorination, it is converted into carbon tetrachloride , followed by hydrolysis and chlorination of carbon tetrachloride after high-temperature decomposition, resulting in Trichloroacetic acid In the last step, acetic acid is produced by electrolytic reduction.

In 1910, most of the glacial acetic acid was extracted from dry distillation of wood coal tar 。 The process is first to treat coal tar with calcium hydroxide, and then acidifie the calcium acetate formed with sulfuric acid to obtain acetic acid.

In 1911, the world's first industrial plant for the oxidation of acetaldehyde to acetic acid was built in Germany, and then the method for the oxidation of low-carbon alkanes to produce acetic acid was developed.^[4]

In 1925, Celanese UK developed the first pilot plant for methyl carbonylation to acetic acid. However, the application of this method has been limited due to the lack of high pressure (200 atm or higher) and corrosion resistant containers.

In 1963, BASF Chemical Company of Germany developed the first process suitable for industrial production of acetic acid with cobalt as catalyst.

In 1968, the rhodium catalyst greatly reduced the difficulty of the reaction. Using the catalyst system composed of rhodium carbonyl compound and iodide, methanol and carbon monoxide can react in the medium of water acetic acid at 175 ℃ and under the pressure of less than 3 MPa to obtain acetic acid products. Due to the high activity and selectivity of the catalyst, there are few by-products of the reaction. The low-pressure carbonylation of methanol to acetic acid has the advantages of cheap raw materials, mild operating conditions, high acetic acid yield, good product quality and simple process flow. However, the reaction medium is severely corrosive, requiring the use of special corrosion-resistant materials.

In 1970, Monsanto Company of the United States built a device using this process, so rhodium catalyzed methyl carbonylation to acetic acid gradually became the dominant Monsanto method.

In the late 1990s, BP successfully Cativa catalytic method Commercially, this method uses iridium catalyst ([Ir (CO) ₂ I ₂]), which is greener and has higher efficiency than Monsanto method.

Material structure

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Acetic acid molecular ball stick model

The crystal structure of acetic acid shows that the dimer (also called dimer) is formed by intermolecular hydrogen bonding, and the dimer also exists in the vapor state at 120 ℃. Dimer has high stability. It has been proved that carboxylic acids with small molecular weight, such as formic acid and acetic acid, exist in the form of dimer in the solid and liquid state, even in the gaseous state, through the method of determining molecular weight by freezing point reduction and X-ray diffraction. When acetic acid is dissolved in water, the hydrogen bond between the dimer will break quickly. Other carboxylic acids have similar dimerization phenomenon.^[1]

Molecular structure data
Molar refractive index	twelve point eight seven
Molar volume (cm three /mol）	fifty-six point one
Isotonic specific volume (90.2 K)	one hundred and thirty-three point five
Surface tension (dyne/cm)	thirty-one point nine
Polarization (10 -24 cm three ）	five point one zero^[9]

physical property

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melting point	16.6℃
boiling point	117.9℃
density	1.05g/cm three
flash point	39℃（CC）
Refractive index	1.371（20℃）
Saturated vapor pressure	1.52kPa（20℃）
critical temperature	321.6℃
critical pressure	5.78MPa
Pilot temperature	426℃
Upper explosive limit（ V / V ）	16%
Lower explosive limit（ V / V ）	5.4%
appearance	Colorless Transparent Liquid
Solubility	Soluble in water, ethanol, ether, glycerin, insoluble in carbon disulfide^[9]

chemical property

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Acidity of acetic acid

The carboxyl hydrogen atom of acetic acid can be partially ionized into hydrogen ions (protons) and released, resulting in the acidity of carboxylic acid. Acetic acid in aqueous solution is Monobasic weak acid, acidity coefficient 4.8, pK a =4.75 (25 ℃), the pH of the acetic acid solution with the concentration of 1mol/L (similar to the concentration of domestic vinegar) is 2.4, that is, only 0.4% of acetic acid molecules are dissociated.^[6]

Reaction description

React with inorganic substances

1. Acetic acid can react with some salts to generate corresponding acetate.

reaction	Reaction formula
Acetic acid and sodium carbonate	2CH three COOH+Na two CO three = 2CH three COONa+CO two ↑+H two O
Acetic acid and calcium carbonate	2CH three COOH+CaCO three = (CH three COO) two Ca+CO two ↑+H two O
Acetic acid and sodium bicarbonate	NaHCO three +CH three COOH = CH three COONa+H two O+CO two ↑
Reaction of acetic acid with weak acid salt	2CH three COOH+CO three 2- = 2CH three COO - +H two O+CO two ↑^[2]

2. Due to the nature of weak acid, acetic acid is corrosive to many metals, such as iron, magnesium and zinc, which react to generate hydrogen and metal acetate. Although aluminum will form an aluminum oxide protective layer on its surface in the air, under the action of acetic acid, the oxide film will be destroyed, and the internal aluminum can directly react with the acid.

reaction	Reaction formula
Acetic acid reacts with iron	Fe+2CH three COOH = (CH three COO) two Fe+H two ↑
Acetic acid reacts with aluminum	2Al+6CH three COOH = 2(CH three COO) three Al+3H two ↑
Acetic acid reacts with zinc	Zn+2CH three COOH = (CH three COO) two Zn +H two ↑
Acetic acid reacts with magnesium	Mg+2CH three COOH = (CH three COO) two Mg+H two ↑

3. Metal acetate can also be prepared by the reaction of acetic acid and corresponding alkali, such as the reaction of sodium hydroxide and vinegar. Except for chromium acetate (II), almost all acetate salts are soluble in water.

Ionic formula	CH three COOH+OH - = CH three COO - +H two O
Reaction of acetic acid with sodium hydroxide	CH three COOH+NaOH = CH three COONa+H two O
Reaction of acetic acid with ammonia	CH three COOH+NH three ·H two O = CH three COONH four +H two O^[4]

Biochemical reaction

Acetyl in acetic acid is the basis of all life in biochemistry. When combined with coenzyme A, it becomes the center of carbohydrate and fat metabolism. However, the concentration of acetic acid in cells is strictly controlled within a very low range to avoid damaging changes in the pH of cytoplasm. Unlike other long-chain carboxylic acids, acetic acid is not present in triglycerides. However, the artificial glycerol triacetate containing acetic acid is also called glycerol acetate (glycerol triacetate)^[3] , is an important food additive, also used to manufacture cosmetics and topical drugs.

Acetic acid is produced or secreted by certain bacteria. It is worth noting that Clostridium acetobutylicum of the genus Clostridium acetobacter, which widely exists in food, water and soil all over the world. Acetic acid is also naturally produced when fruits or other foods are putrid. Acetic acid is also a component of vaginal lubricant of all primates, including humans, and is used as a mild antibacterial agent.

Decarboxylation reaction

Acetic acid is catalyzed by copper and heated to produce Decarboxylation reaction , generating carbon dioxide and methane:^[4]

Redox reaction

Reduction reaction

Acetic acid can be Lithium aluminum hydride Restore to acetaldehyde ：^[4]

oxidation reaction

The combustion reaction of acetic acid is generalized oxidation reaction , complete combustion of acetic acid will generate carbon dioxide and water vapor:

Substitution reaction

esterification

Acetic acid and ethanol can occur under the catalysis of concentrated sulfuric acid and heating esterification , generating ethyl acetate ：^[1]

α- H Halogenation reaction

stay phosphorus In the presence of, halogen Can occur with acetic acid α- H Halogenation reaction. For example, acetic acid reacts with chlorine under the action of red phosphorus Chloroacetic acid ：^[4]

Dehydration reaction

Acetic acid can generate intermolecular Dehydration reaction One acetic acid molecule will remove one OH group, while another acetic acid molecule will remove one H, and finally form acetic anhydride ：^[4]

Reaction with phosphorus trichloride

Acetic acid and Phosphorus trichloride Heating can produce substitution reaction, and the reaction can generate Acetyl chloride And phosphite:

Reaction with ammonia

Acetic acid in lipase Under the catalysis of Acetamide ：^[5]

Preparation method

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Acetic acid can be prepared by artificial synthesis and bacterial fermentation. Biosynthesis, that is, bacterial fermentation, only accounts for 10% of the world's production, but it is still the most important method for the production of acetic acid, especially vinegar, because the food safety regulations of many countries stipulate that vinegar in food must be prepared by biological method, and the fermentation method can be divided into aerobic fermentation method and anaerobic fermentation method.

Aerobic fermentation

Acetobacter bacteria can produce acetic acid from food containing alcohol when there is sufficient oxygen. Usually, cider or wine is mixed with grains, malt, rice or potatoes and mashed before fermentation. These substances can be fermented into acetic acid under the action of catalytic enzyme and oxygen.

The specific method is to inoculate the bacteria of the genus Acetobacter into the diluted alcohol solution and maintain a certain temperature, and place it in a ventilated place. It can be fermented in a few months and finally produce vinegar. The method of industrial production of vinegar accelerates the reaction process by providing sufficient oxygen. This method has been adopted in commercial production, also known as "fast method" or "German method". It was named because it was successfully applied in Germany for the first time in 1823. In this method, fermentation is carried out in a tower filled with sawdust or charcoal. Raw materials containing alcohol are dropped from the top of the tower, and fresh air enters naturally or is forced to convection from the bottom. The enhanced air volume enables this process to be completed in a few weeks, greatly reducing the time for vinegar production.

Otto Hromatka and Heinrich Ebner first proposed to prepare vinegar through liquid bacterial culture medium in 1949. In this method, alcohol is fermented into acetic acid in continuous agitation, and air is filled into the solution in the form of bubbles. With this method, vinegar containing 15% acetic acid can be prepared in two to three days.

Anaerobic fermentation

Some anaerobic bacteria, including some members of Clostridium, can directly convert sugars into acetic acid without using ethanol as intermediate 。 In the absence of oxygen, sucrose can be fermented into acetic acid.

In addition, many bacteria can produce acetic acid from compounds containing only one carbon, such as methanol, carbon monoxide or a mixture of carbon dioxide and hydrogen.

Clostridium has the ability to react to sugars, reducing the cost, which means that these bacteria have the potential to produce acetic acid more efficiently than Acetobacter by ethanol oxidation. However, Clostridium is less acid tolerant than Acetobacter. Clostridium bacteria with the highest acid resistance can only produce less than 10% acetic acid, while some acetic acid bacteria can produce 20% acetic acid. Using acetic acid bacteria to produce vinegar is still more economical than using Clostridium bacteria to concentrate after preparation. Therefore, although Clostridium bacteria have been discovered as early as 1940, its industrial application scope is relatively narrow.

In addition to the above biological methods, industrial acetic acid is mostly synthesized by the following methods:

Methanol carbonylation method

Most acetic acids are synthesized by methyl carbonylation. In this reaction, methanol reacts with carbon monoxide to produce acetic acid, and the equation is as follows

This process is based on Iodomethane It is an intermediate, which is completed in three steps and needs polymetallic composition catalyzer (In the second step)

Acetic anhydride can also be produced by the same reaction by controlling the reaction conditions. Because carbon monoxide and methanol are common chemical raw materials, the industry often uses this method to prepare acetic acid.

Acetaldehyde oxidation

Before the commercial production of Monsanto method, most acetic acid was produced by oxidation of acetaldehyde. Although not compatible with methyl Carbonylation In contrast, this method is still the second industrial method to produce acetic acid.

Alkane liquid oxidation method

use N-butane As raw material, acetic acid as solvent, at 170 ℃ - 180 ℃, 5.5 MPa and Cobalt acetate In the presence of catalyst, air is used as oxidant for oxidation. At the same time, liquefied petroleum gas or light oil can also be used as raw materials for this method. The raw material cost of this method is low, but the process flow is long, the corrosion is serious, and the acetic acid yield is not high. This method is only used in areas where cheap isobutane or LPG raw materials are easily available.

This reaction can be carried out at the highest temperature and pressure that can keep butane liquid, and the by-products include butanone, ethyl acetate ， formic acid and propionic acid 。 Because some by-products also have economic value, the reaction conditions can be adjusted to generate more by-products. However, separating acetic acid and by-products increases the cost of the reaction.

Under similar conditions, acetaldehyde can be oxidized to acetic acid by oxygen in the air using the above catalyst.

Acetaldehyde can also be oxidized by copper hydroxide.

Using the new catalyst, the yield of acetic acid can be more than 95%. The main by-products are ethyl acetate, formic acid and formaldehyde 。 Because the boiling points of by-products are lower than that of acetic acid, they can be easily removed by distillation.

Ethylene oxidation process

from ethylene On the catalyst (the catalyst used is Palladium chloride ：PdCl₂、 Cupric chloride : CuCl ₂ and manganese acetate: (CH ∨ COO) ₂ Mn) react with oxygen in the presence of. This reaction can be regarded as the oxidation of ethylene to acetaldehyde and then the acetaldehyde oxidation method.

Topsos method

Topsos method uses single natural gas or coal as raw material. Step 1: synthesis gas generates methanol and dimethyl ether ； Part II: Methanol and dimethyl ether (both need not be purified) and CO Carbonylation This method is also called two-step method to generate acetic acid.

Production process

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BP Cativa Process

BP is the world's largest acetic acid supplier, and 70% of the world's acetic acid production uses BP technology. BP launched the Cativa technology patent in 1996. Cativa process uses a new catalyst system based on iridium, and uses a variety of new additives, such as rhenium, ruthenium, osmium, etc. The iridium catalyst system is more active than the rhodium catalyst, with fewer by-products, and can be operated under the condition of low water concentration (less than 5%), which can greatly improve the traditional methanol carbonylation process and reduce production costs by up to 30%, Reduce 50% of expansion cost. In addition, due to the reduction of water concentration, CO utilization efficiency is improved and steam consumption is reduced.^[7]

Celanese AOPlus process

Celanese is also one of the world's largest producers of acetic acid. In 1978, Hearst Celanese (now Celanese) industrialized and put the Monsanto acetic acid plant into operation in Lake Clare, Texas, USA. In 1980, Celanese launched the technology patent of AOPlus method (acid optimization method), which greatly improved the Monsanto process.

AOPlus process improves the stability of rhodium catalyst by adding high concentration inorganic iodine (mainly lithium iodide). After adding lithium iodide and methyl iodide, the concentration of water in the reactor is reduced to 4%~5%, but the carbonylation reaction rate remains at a high level, thus greatly reducing the separation cost of the device. The change of catalyst composition enables the reactor to operate at low water concentration (4%~5%), which improves the yield of carbonylation reaction and separation and purification capacity.^[8]

application area

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Industrial use

1. Acetic acid is a bulk chemical product and one of the most important organic acids. It is mainly used to produce acetic anhydride, acetate, cellulose acetate, etc. Polyvinyl acetate can be made into films and adhesives, and is also the raw material of synthetic fiber vinylon. Cellulose acetate can be used to make rayon and film.

2. Acetates formed from lower alcohols are excellent solvents and are widely used in the paint industry. Because acetic acid dissolves most organic substances, acetic acid is also a commonly used organic solvent (for example, it is used to oxidize paraxylene to produce terephthalic acid).

3. Acetic acid can be used in some pickling and polishing solutions, as a buffer in weak acid solutions (such as zinc plating and electroless nickel plating), as an additive in semi bright nickel plating electrolyte, and in zinc and cadmium passivation solutions to improve the adhesion of the passive film, and is often used to adjust the pH of weak acid plating solutions.

4. It is used to produce acetate salts, such as manganese, sodium, lead, aluminum, zinc, cobalt and other metal salts, and is widely used as catalyst, auxiliary agent in fabric dyeing and leather tanning industry; Lead acetate is the lead white paint color; Lead tetraacetate is an organic synthetic reagent (for example, lead tetraacetate can be used as a strong oxidant, a source of acetoxyl, and the preparation of organic lead compounds).

5. Acetic acid can also be used as analytical reagent, organic synthesis, pigment and drug synthesis.

Food use

In the food industry, when acetic acid is used as acidifier, flavor enhancer and spice to manufacture synthetic vinegar, dilute acetic acid to 4-5% with water and add various flavoring agents. The flavor is similar to that of alcohol vinegar, with short manufacturing time and low price. As a sour agent, it can be used as a compound condiment to prepare vinegar, canned food, jelly and cheese. It can be used moderately according to production needs. It can also be used as an aroma enhancer of fragrant wine, with the dosage of 0.1~0.3 g/kg.

Calculate chemical data

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Drainage parameter calculation reference value (XlogP)	-0.2
Number of hydrogen bond donors	one
Number of hydrogen bond receptors	two
Number of rotatable chemical bonds	zero
Number of tautomers	zero
Topological molecular polar surface area	thirty-seven point three
Number of heavy atoms	four
surface charge	zero
Complexity	thirty-one
Number of isotope atoms	zero
Determine the number of atomic geometric centers	zero
Number of atomic geometric centers in uncertainty	zero
Determine the number of chemical bond stereocenters	zero
Number of uncertain chemical bond stereocenters	zero
Number of covalent bond units	one^[9]

Safety measures

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danger

Electrostatic effect: possible polymerization hazard

Hazard characteristics: It can react strongly with oxidants, and react violently with sodium hydroxide, potassium hydroxide, etc. It is corrosive to metal after dilution.

Acetic acid with high concentration is corrosive, which can cause skin burns, permanent blindness of eyes and inflammation of mucous membrane. Therefore, appropriate protection is required. The above burns or blisters may not occur immediately, but most of them occur several hours after exposure. Latex gloves can not protect you, so you should wear special gloves when handling acetic acid, such as nitrile rubber gloves. Concentrated acetic acid is difficult to burn in the laboratory, but when the ambient temperature reaches 39 ℃ (102 ℉), it will pose a flammable threat. Above this temperature, acetic acid can be mixed with air for explosion (explosion limit: 4%~17% volume concentration).

The harm of acetic acid is related to the concentration of acetic acid solution. The following table illustrates the EU classification of acetic acid solution:

Concentration (mass)	Molar concentration	classification	R-Phrases
10%–25%	1.67–4.16 mol/L	Stimulation (Xi)	R36/38
25%–90%	4.16–14.99 mol/L	Corrosion (C)	R34
>90%	>14.99 mol/L	Corrosion (C)	R10, R35

Because of the strong pungent smell and corrosive steam, the operation of acetic acid with a concentration of more than 25% should be carried out under an eye mask. Dilute acetic acid solutions, such as vinegar, are harmless. However, high concentration of acetic acid solution is harmful to human and animal health.

Leakage treatment

Pollution discharge category: Z

Leakage treatment: cut off the fire source, wear protective glasses, gas masks and acid resistant overalls, and flush the spill with a large amount of water to make it flow into the channel and be diluted quickly, thus reducing the harm to human body.

Fire extinguishing method

Use fog water, dry powder, alcohol resistant foam, carbon dioxide to extinguish the fire. Keep the containers in the fire site cool with water. Use foggy water to disperse the steam, drive away the leaked liquid, and dilute it into a non combustible mixture. And spray water to the leaking stoppers.

First aid measures

Skin contact: In case of skin contact, wash with water first, and then wash thoroughly with soap.

Eye contact: wash the eyes with water and wipe them with dry cloth if they are irritated, and send them to hospital for treatment if serious.

Inhalation: If the inhalation of vapor has to make the patient out of the contaminated area, place the patient for rest and keep warm.

Ingestion: Rinse the mouth immediately after taking it by mistake, give emetics to induce vomiting, and send it to the hospital for emergency treatment.

Protective measures

Respiratory system protection: wear gas mask when the depth concentration in the air exceeds the standard.

Eye protection: wear chemical safety goggles.

Hand protection: wear rubber gloves.

Others: After work, take a shower and change clothes. Do not bring work clothes into the living area.

toxicology data

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1. Acute toxicity

LD fifty : 3530mg/kg (rat by mouth); 1060mg/kg (rabbit percutaneous)

LC fifty ：13791mg/m three (Inhaled by mice, 1h)

2. Irritation

Rabbit percutaneous: 50mg (24h), mild irritation.

Rabbit eyes: 5mg (30s), slightly stimulated (washed with water).

3. Mutagenicity

Microbial mutagenicity: Escherichia coli 300ppm (3h).

Sister chromatid exchange: human lymphocytes 5mmol/L.

Cytogenetic analysis: hamster ovary 10mmol/L.

4. Others

The lowest oral toxic dose (TDLo) of rats: 700mg/kg (18d, postpartum), which has an impact on the behavior of newborn rats.

The lowest toxic dose (TDLo) in the testes of rats: 400mg/kg (1d, male), which has an impact on the male fertility index.

Ecological data

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1. Ecotoxicity

LC50: 92~106mg/L (48h), 79~88mg/L (96h) (black headed fish); 75mg/L (96h) (bluegill sunfish); 251mg/L (96h) (Mosquito fish)

EC50: 32mg/L (48h) (Daphnia)

IC50: 90mg/L (72h) (algae)

2. Biodegradability

MITI-I test showed that the initial concentration was 100ppm, the sludge concentration was 30ppm, and the degradation rate was 74% after 2 weeks.

3. Non biodegradable

In the air, when the concentration of hydroxyl radical is 5.00 × 10 five Pcs/cm three The half-life of degradation is 22d (theoretical).

Storage and transportation

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Precautions for storage: store in a cool and ventilated warehouse. Keep away from kindling and heat sources. In winter, the warehouse temperature should be kept above 16 ℃ to prevent solidification. Keep container sealed. It shall be stored separately from oxidants and alkalis, and mixed storage is strictly prohibited. Explosion proof lighting and ventilation facilities shall be adopted. It is prohibited to use mechanical equipment and tools that are easy to generate sparks. The storage area shall be equipped with leakage emergency treatment equipment and appropriate materials.

Transportation precautions: The railway transportation time limit of this product is to use the aluminum enterprise's own tank car for shipment, and it needs to be reported to the relevant department for approval before shipment. The railway non tank transportation shall be carried out in strict accordance with the dangerous goods loading table in the Dangerous Goods Transportation Rules of the Ministry of Railways. The package shall be complete and the loading shall be stable when the goods are shipped. During transportation, the container shall not leak, collapse, fall or be damaged. The tank (tank) car used for transportation shall be equipped with grounding chain, and the tank can be equipped with hole partition to reduce static electricity generated by vibration. It is strictly prohibited to mix with oxidants, alkalis, edible chemicals, etc. Road transportation shall be carried out according to the specified route, and do not stay in residential areas and densely populated areas.

Pharmacopoeia information

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essential information

This product contains C two H four O two Not less than 99.0% (g/g).

character

This product is colorless clear liquid or colorless crystal block, with strong odor.

This product can be mixed with water, ethanol, glycerin or most of the volatile oil and fatty oil at will.

Freezing point

The freezing point of the product (general rule 0613) is not lower than 14.8 ℃.

identify

1. Take 1mL of this product, add 1mL of water, neutralize it with sodium hydroxide test solution, add ferric chloride test solution, it will become dark red, boil it, it will generate reddish brown sediment, add hydrochloric acid, it will dissolve into yellow solution.

2. Take a little of this product, add sulfuric acid and a small amount of ethanol, and heat it to produce the aroma of ethyl acetate.

inspect

chloride

Take 10mL of this product, add 20mL of water, and check according to the law (general rule 0801). Compared with the control solution made of 4.0mL of standard sodium chloride solution, it should not be more concentrated (0.0004%).

sulfate

Take 20mL of this product, add 1mL of 1% anhydrous sodium carbonate solution, evaporate it on a water bath, and check according to the law (general rule 0802). Compared with the control solution made of 1.0mL of standard potassium sulfate solution, it should not be more concentrated (0.0005%).

Formic acid and easy oxide

Take 5mL of this product, add 10mL of water to dilute it, take 5mL of it, add 2.5mL of potassium chromate titrant (0.01667mol/L) and 6mL of sulfuric acid, place it for 1 minute, add 20mL of water, cool it to 15 ℃, add 1mL of potassium iodide test solution, it should be dark yellow or brown.

acetaldehyde

Determine according to the residual solvent determination method (General Rule 0861, the second method).

Test solution: Take 1.8mL of this product, precisely weigh it, place it in a 10mL measuring bottle, dilute it with water to the scale, shake it up, take 2.5mL of it, place it in an empty top bottle, add 2.5mL of 3.2mol/L sodium hydroxide solution, seal it immediately, shake it up.

Reference solution: Take an appropriate amount of ether reference, precisely weigh it, dilute it with 1.6mol/L sodium acetate solution to make a solution containing about 0.01mg per 1mL, precisely measure 5mL, place it in an empty top bottle, and seal it.

Chromatographic conditions: the capillary column with polyethylene glycol polysiloxane (or with similar polarity) as the fixed liquid is the chromatographic column, the initial temperature is 35 ℃, and the column is maintained for 5 minutes. The temperature is raised to 120 ℃ at the rate of 30 ° C per minute, and the column is maintained for 2 minutes. The detector temperature is 250 ℃, the sample inlet temperature is 200 ℃, the balance temperature of the headspace bottle is 80 ℃, and the balance time is 30 minutes.

Determination method: Take the test solution and the reference solution for headspace injection respectively, and record the chromatogram.

Limit: calculated by peak area according to external standard method, the acetaldehyde content shall not exceed 0.01%.

Potassium permanganate reducing substance

Take 2mL of this product, add 10mL of water and 0.10mL of potassium manganate titrant (0.02mol/L), shake well, and place for 30 minutes. The pink color should not disappear completely.

Nonvolatile matter

Take 20mL of this product, place it in an evaporating dish with constant weight at 105 ℃, evaporate it on a water bath and dry it at 105 ℃ to constant weight. The residual residue shall not exceed 1mg.

ferric salt

Take 2.0mL of this product, put it on a water bath, evaporate it to dryness, add 15mL of water, dissolve it at a slight temperature, add an appropriate amount of water to make it 25mL, check according to the law (general rule 0807), and compare it with the reference solution made of 1.0mL of standard iron solution, it should not be deeper (0.0005%).

heavy metal

Take 10mL of this product, put it in a water bath, evaporate it to dryness, add 2mL of acetate buffer (pH3.5) and 15mL of water to dissolve it at a slight temperature, add an appropriate amount of water to make it 25mL, and check according to the law (general rule 0821 method 1), the content of heavy metals should not exceed 2 parts per million.

Assay

Take about 2mL of this product, put it into a conical flask with a stopper and weigh it precisely. Add 40mL of newly boiled cold water and 3 drops of phenolphthalein indicator solution, and titrate it with sodium hydroxide titrant (1mol/L). Every 1mL of sodium hydroxide titrant (1mol/L) is equivalent to 60.05mg of C two H four O two 。