Oxalic acid is an organic substance, with the chemical formula of H ₂ C ₂ O ₄, which is a metabolite of organisms. It is a medium strong acid, widely distributed in plants, animals and fungi, and plays different functions in different organisms.It is found that more than 100 kinds of plants are rich in oxalic acid, especiallySpinach、three-colored amaranth、beet、purslane, taro, sweet potato, rhubarb and other plants have the highest content. Because oxalic acid can reduce the bioavailability of mineral elements, it is easy to form calcium oxalate with calcium ions in the human body to cause kidney stones, so oxalic acid is often considered as a mineral element absorption and utilizationAntagonist。hisAcid anhydridebyCarbon trioxide。
Chinese name
oxalate[3]
Foreign name
Oxalic acid;Ethanedioic acid[3]
Alias
Oxalic acid
chemical formula
H₂C₂O₄
molecular weight
ninety point zero three four nine
CAS login number
144-62-7[3]
EINECS login number
205-634-3[3]
Melting point
189.5 ℃[3]
Boiling point
365.10 ℃
Density
1.772 g/cm³
Appearance
Colorless monoclinic sheet
Flash point
188.79 ℃
Security description
S24/25；S23；S36/37/39；S27；S26[3]
Hazard symbol
R21/22[3]
Hazard description
Xn[3]
UN dangerous goods number
three thousand two hundred and sixty-one[3]
Solubility
Soluble in water and ethanol, insoluble in benzene and chloroform.
Colorless monoclinic lamellar or prismatic crystal or white powder,Oxidation methodOxalic acid is odorless,Synthetic methodOxalic acid has a taste.150~160 ℃ sublimation.It can be weathered in high heat and dry air.1 g is soluble in 7 mL water, 2 mL boiling water, 2.5 mL ethanol, 1.8 mL boiling ethanol, 100 mL ether, 5.5 mL glycerol, and insoluble in benzene, chloroform, and petroleum ether.The pH of 0.1 mol/L solution is 1.3.Relative density (water=1) 1.653.Melting point 189.5 ℃.[3]Low toxicity, LD50 (rabbit, percutaneous) 2000 mg/kg3
Character: colorless transparent crystal or powder. Its crystal structure has two forms, namely, alpha (diamond) and beta (monoclinic), odorless and sour
Melting point: α type, 189.5 ℃, β type: 182 ℃
Boiling point: boiling point 150 ℃ (sublimation)
Refractive index: 1.540
Stability: 189.5 ℃ decomposition
Dissolution: soluble in ethanol, soluble in water, slightly soluble in ether, insoluble in benzene and chloroform.
chemical property
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Oxalic acidOxalic acidColourless columnar crystals, soluble in water but insoluble in organic solvents such as ether, are widely found in plant derived foods.
Oxalate is another kind of metal chelating agent in vegetable food because of its strong coordination.When oxalic acid is combined with some alkaline earth metal elements, its solubility is greatly reduced, for example, calcium oxalate is almost insoluble in water.Therefore, the presence of oxalic acid has a great impact on the bioavailability of essential minerals;When oxalic acid is combined with some transitional metal elements, a soluble complex is formed due to the coordination of oxalic acid, and its solubility is greatly increased[2]。
Oxalic acid starts to sublimate at 100 ℃, rapidly sublimates at 125 ℃, and largely sublimates at 157 ℃, and starts to decompose.
It can react with alkali, esterification, acyl halogenation and amidation.Reduction reaction can also take place, which occurs when heatedDecarboxylationReaction.Anhydrous oxalic acid is hygroscopic.Oxalic acid can form water soluble complexes with many metals.
acidic
Oxalic acid is a medium strong acid.Its first ionization constant Ka1=5.9×10-2, second ionization constant Ka2=6.4×10-5。It has the commonness of acid.It can neutralize with alkali, change the color of indicator, and release carbon dioxide through interaction with carbonate.
Oxalate has strong reducibility and is easily oxidized to carbon dioxide and water when it acts with oxidants.
Acid potassium permanganate (KMnOfour）The solution fades and is reduced to 2 valent manganese ion.This reaction is used as a method to determine the concentration of potassium permanganate in quantitative analysis.
It can also react with sodium hypochlorite (NaClO), oxalic acid is oxidized to carbon dioxide and water, and hypochlorite is reduced to chloride ion and water.
HtwoCtwoOfour+NaClO=NaCl+2COtwo↑+HtwoO
Instability
Oxalic acid will decompose into carbon dioxide, carbon monoxide and water at 189.5 ℃ or in the presence of concentrated sulfuric acid.
HtwoCtwoOfour=COtwo↑+CO↑+HtwoO
The laboratory can use this reaction to produce carbon monoxide gas.
Ammonium hydrogen oxalate decomposes into carbon dioxide, carbon monoxide, ammonia and water at 200 ℃.
(NHfour)twoCtwoOfour→ 2NHthree↑+ COtwo↑+CO↑+HtwoO
toxicity
Oxalic acid is toxic and has irritating and corrosive effects on skin and mucosa. It is easily absorbed by epidermis and mucosa to cause poisoning.The maximum allowable concentration in the air is 1 mg/mthree。
esterification
The oxalic acid can react with alcohol to form ester, for example, the oxalic acid and ethanol can react with concentrated sulfuric acid as catalyst and under heating conditions to form diethyl acetate.
3. Corrosive, irritating to skin and mucous membrane. Inhalation of steam and dust may cause poisoning, and ingestion may cause gastroenteritis, vomiting, diarrhea and other symptoms.The minimum lethal dose for adults is 71 mg/kg.[1]
The product is strongly irritant and corrosive.Its dust or concentrated solution can cause serious damage to skin, eyes or mucous membrane.It is highly toxic and corrosive.The minimum lethal dose of oxalic acid to humans is 71 mg/kg, and the lethal dose to adults is 15-30 g.
If a person takes 5 g oxalic acid orally, symptoms such as gastrointestinal inflammation, collapse, convulsion, shock and even death will occur.Chronic poisoning caused by inhaling oxalic acid vapor has symptoms such as extreme weakness, nasal mucosa ulcer, cough, systemic pain, vomiting, weight loss, and protein in urine.[1]
Ecological data
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This substance may be harmful to the environment, and special attention should be paid to water bodies[1]。
quality index
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The People's Republic of ChinaGB/T 1626-2008
quality index
existence
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Oxalic acid is found all over the nature, often in the form of oxalate in the cell membrane of plants such as Sagittaria, Bauhinia, Oxalis and Rumex. Almost all plants contain calcium oxalate.Oxalic acid is a common component in plants, especially in herbs, which mostly exists in the form of potassium salt or calcium salt, while in Begonia and plantain, it exists in the form of free acid.
Molecular structure data
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1. Molar refractive index: 14.44[3]
2. Molar volume: 50.8[3]cmthree/mol
3. Isotonic specific volume (90.2 K): 155.3[3]
4. Surface tension: 87.3 dyne/cm[3]
5. Polarization rate: 5.72 × 10-24cmthree[3]
Calculate chemical data
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1. Reference value of drainage parameter calculation (XlogP): - 0.3[3]
1. Sodium formate method: after carbon monoxide purification, it reacts with sodium hydroxide under pressure to generate sodium formate, which is then dehydrogenated at high temperature to generate sodium oxalate. Sodium oxalate is then lead (or calcified), acidified, crystallized, dehydrated and dried to obtain finished oxalic acid.The synthesis pressure of carbon monoxide and sodium hydroxide is generally 1.8-2.0 MPa.Dehydrogenation temperature is 400 ℃.
Sodium formate method
2. Oxidation method: Oxalic acid is obtained by oxidizing starch or glucose mother liquor with nitric acid sulfuric acid in the presence of alum catalyst.The nitrogen oxide in the waste gas is sent to the absorption tower to generate dilute nitric acid.
Oxidation method
3. Carbonyl synthesis method: after carbon monoxide is purified to more than 90%, it undergoes carbonylation reaction with butanol in the presence of palladium catalyst to generate dibutyl oxalate, and then oxalic acid is obtained through hydrolysis. This method can be divided into liquid phase method and gas phase method. The gas phase method has low reaction conditions and reaction pressure of 300-400 kPa.The reaction pressure of liquid phase method is 13.0-15.0 MPa.
Carbonyl synthesis
4. Ethylene glycol oxidation method: ethylene glycol is oxidized with air in the presence of nitric acid and sulfuric acid.
5. Propylene oxidation method: the oxidation process is divided into two steps.The first step is oxidation with nitric acid to convert propylene into α - nitrolactic acid;Then further catalytic oxidation is carried out to obtain oxalic acid.In the second step, mixed acid can also be used as oxidant.The total yield of industrial oxalic acid dihydrate produced by propylene oxidation is more than 90% based on propylene.
Raw material consumption quota: coke (84%) 510 kg/t, sulfuric acid (100%) 950 kg/t, caustic soda (100%) 920 kg/t.
Oxalic acid usually exists in many plant cell membranes in the form of salt in nature.Previously, in industry, sawdust and strong alkali were co melted at 240~250 ℃ to produce oxalate, which was then acidified to obtain oxalic acid.Later, oxalic acid was produced by dehydrogenation of sodium formate.In industry, carbon monoxide (such as tail gas from yellow phosphorus production) is absorbed by caustic soda to produce sodium formate, which is dehydrogenated at 380 ℃ to produce sodium oxalate, and then treated with lime and sulfuric acid to produce oxalic acid.
test method
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PressGB1626-88Test of analytical method specified in.
Oxalic acid content (as HtwoCtwoOfour*2HtwoO meter) with phenolphthalein as indicator, titrate with sodium hydroxide standard solution.
Sulfate radical(with SOfour2-Add sodium carbonate into the sample to generate sulfate from sulfate radical in oxalic acid.In order to decompose oxalic acid and oxalate with heat, the residue solution is added with barium chloride solution to generate barium sulfate for turbidimetry.
ash contentThe test shall be carried out according to GB7531.
heavy metal(Pb) shall be measured according to GB7531.
iron(Calculated by FE) Determine according to GB3049.
chloride(Calculated by Cl) In nitric acid acid solution, chlorides and silver nitrate generate silver chloride, and then conduct turbidimetry.
Storage method
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1. Store in a dry and cool place.Strictly prevent moisture, water and sun.The storage temperature shall not exceed 40 ℃.
2. Keep away from oxides and alkaline substances.Packed with polypropylene woven bags lined with plastic bags.[1]
Specific use
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Oxalic acid can be used as reducing agent, bleaching agent, dyeing aid, regulator, additive, etc[1]。
1. Oxalic acid is mainly used to produce antibiotics, borneol and other drugs, as well as solvent for extracting rare metals, dye reducing agent, tanning agent, etc.In addition, oxalic acid can also be used to synthesize various oxalates, oxalates and oxalamides, among which diethyl oxalate, sodium oxalate and calcium oxalate are the largest.Oxalic acid can also be used in the production of cobalt molybdenum aluminum catalysts, cleaning of metals and marbles, and bleaching of textiles.Acidity regulator used for synthesis of urea formaldehyde resin, melamine formaldehyde resin and other adhesives.The pharmaceutical industry is used to manufacture oxytetracycline, chlortetracycline and other drugs.
2. It is mainly used as reducing agent and bleaching agent, mordant in printing and dyeing industry, as well as for refining rare metals and synthesizing various oxalates, oxalates and oxalamides.
3. It is used as an acidity regulator to synthesize urea formaldehyde resin, melamine formaldehyde resin and other adhesives.It can also be added into polyvinyl formal water-soluble adhesive to improve drying speed and bonding strength.It is an important raw material for organic synthesis, used to produce various oxalate, oxalate, oxalamide, hydroquinone, pentaerythrite, gallic acid and other products.The pharmaceutical industry is used to manufacture aureomycin, oxytetracycline, tetracycline, streptomycin, borneol, vitamin B12, phenobarbital and other drugs.The printing and dyeing industry is used as color developing aids and bleaching agents.The plastic industry is used to produce PVC, amino plastics, urea formaldehyde plastics.Metallurgical industry is used to produce high-purity nickel, carbon rod and precipitate rare earth metal.It is also used as metal washing agent, tanning agent, chelating agent, catalyst, anaerobic adhesive and polymerization inhibitor of acrylate fast curing adhesive, machining rust remover, electroplating complexing agent, wood bleaching, marble cleaning and oil refining.
4. It can be used as an additive in shampoo in cosmetics, mainly for the manufacture of chemical industrial products;The pharmaceutical industry is used to manufacture antibiotics and other drugs;The printing and dyeing industry and leather industry are widely used;It is used as refining agent of terpineol, glycerin and stearate in oil chemistry;In addition, it is used in aluminum products processing and hard alloy manufacturing.
toxicity
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Around us, oxalic acid is generally used as a rust remover or to remove ink stains on white clothes, but it is also a dangerous chemical that can kill people.We take oxalic acid every day through many different channels. Oxalic acid exists in a small amount in many foods, but is high in a few foods.Cocoa is one of the foods with the highest content. Every 100 g of cocoa contains 500 mg of oxalic acid;The content of oxalic acid in green vegetables is generally high, 600 mg per 100 g of spinach, 500 mg per 100 g of rhubarb, and more oxalic acid in beets, peanuts, and tea.On average, one person consumes about 150 mg oxalic acid a day, while the half lethal dose (LD) of pure oxalic acidfifty）In terms of the impact on rats, it is about 375 mg per kg of body weight, which needs about 25 g to convert to a person of about 65 kg.In addition, the lowest oral lethal dose (LDLo）About 600 mg/kg.
Oxalic acid interacts with some essential inorganic salts, such as iron ions, magnesium ions, especially calcium ions.In our daily nutritional diet, spinach is a vegetable rich in iron. Indeed, spinach contains more iron than most other vegetables. 100g spinach contains 4 mg of iron.However, the oxalic acid contained in it will make 95% of the iron element not have a beneficial impact on the human body, which means that people can only absorb 5% of the iron element.The famous cartoon character "Popeye" attributed his magic power to spinach. In fact, this is just a wrong idea.Some scientists believe that spinach can only be eaten as an ordinary vegetable, no matter what method is used. It is difficult to get any inorganic salt nutrition except a proper amount of plant protein and a little VC.Magnesium ion is the central metal ion of chlorophyll. If you cover the pot cover when cooking green vegetables, the combination of oxalic acid and magnesium ion will make the fried vegetables yellow, so open the pot cover when frying green vegetables, so that oxalic acid can be volatilized in time to maintain the color of vegetables.
The fatal aspect of oxalic acid is that it can reduce the calcium ion content in human blood to a critical level.Everyone knows that calcium plays a crucial role in maintaining stable acidity and viscosity of blood, and also plays a key role in the transport and coagulation of phosphate in the body.If oxalic acid is poisoned, how to detoxify may be your concern.From the perspective of chemical balance, we should timely supplement calcium ions in the blood, and calcium gluconate, once a hot spot in TV advertisements, is just the antidote for the right medicine.Even though the content of oxalic acid in the body is not enough to worry about life, its effect on calcium ions can not be ignored, because it can form insoluble calcium oxalate, and its crystals can grow into stones in bladder, kidney and other organs, making people very painful.Although we can avoid overeating the above foods, we cannot completely exclude oxalic acid from the body, because people can obtain it from other sources.For example, Bao Lin, a famous chemist, once advocated taking a large amount of VC to prevent colds. During the SARS period, health care experts also suggested using VC to enhance the body's resistance;But when things reach their limit, we cannot store excess VC in our bodies, and it can be converted into oxalic acid.Therefore, excessive intake of VC is likely to cause diarrhea and even kidney stones.If we usually take too little water, the above situation is likely to occur.
harm
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Hazards of oxalic acid and precautions in use:
Oxalic acid is not easy to be oxidized and decomposed in the human body. The products formed after metabolism are acidic substances, which can lead to the imbalance of pH in the human body. If you eat too much, you will be poisoned.
In addition, if oxalic acid encounters calcium and zinc in the human body, it will generate calcium oxalate and zinc oxalate, which are difficult to absorb and excreted out of the body, affecting the absorption of calcium and zinc.
Excessive intake of oxalic acid can also cause stones.
security information
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Dangerous goods sign
Xn: Harmful
Safety terminology
S24/25: Avoid contact with skin and eyes.
Risk terminology
R21/22: Harmful in contact with skin and if swallowed.
