Oxalic acid powder is colorless transparent crystal or powder, and its crystal structure has two forms, namely α Type (diamond) and β Type (monoclinic). It has no smell and sour taste. Oxalic acid produced by oxidation is odorless, while oxalic acid produced by synthesis is odorless. 150~160 ℃ sublimation. It can be weathered in hot dry air. 1g is soluble in 7mL of water, 2mL of boiling water, 2.5mL of ethanol, 1.8mL of boiling ethanol, 100mL of ether, 5.5mL of glycerol, and insoluble in benzene, chloroform and petroleum ether.
Use of oxalic acid powder:
1.As reducing agent:
In the organic synthesis industry, it is mainly used to produce hydroquinone, pentaerythritol, cobalt oxalate, nickel oxalate, gallic acid and other chemical products.
2.The plastic industry is used to produce PVC, amino plastics, urea-formaldehyde plastics, paint chips, etc.
3.Dye industry is used to produce salt base magenta, etc.
In the printing and dyeing industry, acetic acid can be used as a color developing aid and bleaching agent for pigment dyes.
The pharmaceutical industry is used to manufacture aureomycin, oxytetracycline, tetracycline, streptomycin and ephedrine.
4.In addition, oxalic acid can also be used to synthesize various oxalates, oxalates, oxalamides and other products, with the largest output of diethyl oxalate, sodium oxalate and calcium oxalate.
5.Antimony oxalate can be used as a mordant, and ammonium ferric oxalate is a reagent for printing blueprints.
6.Rust removal function.
Oxalic acid can be used to remove rust: buy a bottle of oxalic acid from the shop selling chemical reagents, take some of it, prepare a solution with warm water, and smear it on the rust stain. Then wipe with metallographic abrasive paper, and finally spray paint. Generally, oxalic acid stores also sell some medical instruments and glass instruments.
(Precautions: Be careful when using. Oxalic acid has strong corrosivity to stainless steel. Oxalic acid with high concentration is also easy to corrode hands. And the acid oxalate generated has a high solubility, but it has a certain toxicity. Do not eat it when using. After contact with oxalic acid, wash it with water in time.)
chemical property:
Oxalic acid, also known as oxalic acid, is widely found in vegetable foods. Oxalic acid is a colorless columnar crystal, which is easily soluble in water but not in organic solvents such as ether,
Oxalate has a strong coordination effect and is another kind of metal chelating agent in vegetable food. 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.
Oxalic acid begins to sublimate at 100 ℃, rapidly sublimates at 125 ℃, sublimates in large quantities at 157 ℃, and begins to decompose.
It can react with alkali and can undergo esterification, acyl halogenation and amidation. Reduction reaction and decarboxylation reaction can also occur when heated. Anhydrous oxalic acid is hygroscopic. Oxalic acid can form water-soluble complexes with many metals.
Acidic:
Oxalic acid is a weak acid. Its first-order ionization constant Ka1=5.9 × 10-2, secondary ionization constant Ka2=6.4 × 10-5. It has acid permeability. It can neutralize with alkali, discolor the indicator, and react with carbonate to release carbon dioxide.
For example:
H2C2O4+Na2CO3=Na2C2O4+CO2↑+H2O
H2C2O4+Zn=ZnC2O4+H2↑
Reductibility:
Oxalate has a strong oxidation-reduction property, and can be easily oxidized into carbon dioxide and water when interacting with oxidants. It can fade the acidic potassium permanganate (KMnO4) solution and reduce it to 2 valent manganese ion. This reaction is used as a method to determine the concentration of potassium permanganate in quantitative analysis. Oxalic acid can also wash away the ink stains on the cloth.
2KMnO4+5H2C2O4+3H2SO4=K2SO4+2MnSO4+10CO2↑+8H2O
H2C2O4+NaClO=NaCl+2CO2↑+H2O
Instability:
Oxalic acid will decompose into carbon dioxide, carbon monoxide and water at 189.5 ℃ or in the presence of concentrated sulfuric acid.
H2C2O4=CO2↑+CO↑+H2O
The laboratory can use this reaction to produce carbon monoxide gas.
Ammonium hydrogen oxalate is decomposed into carbon dioxide, carbon monoxide, ammonia and water at 200 ℃.
Toxicity:
Oxalic acid is toxic, has irritating and corrosive effects on skin and mucous membrane, and is easily absorbed by skin and mucous membrane to cause poisoning. The maximum allowable concentration in the air is 1mg/m3.
Esterification reaction:
Acetic acid can react with alcohol to form ester, for example, oxalic acid reacts with ethanol to form diethyl oxalate.
Synthesis method of oxalic acid powder:
1. Ethylene glycol oxidation method is obtained by using ethylene glycol as raw material and oxidizing with air in the presence of nitric acid and sulfuric acid.
2. The oxidation process of propylene oxidation is carried out in two steps. The first step is oxidation with nitric acid to convert propylene into α- Nitrolactic acid; Then, oxalic acid is obtained by further catalytic oxidation. 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%.
Raw material consumption quota: coke (84%) 510kg/t, sulfuric acid (100%) 950kg/t, caustic soda (100%) 920kg/t.
3. In nature, oxalic acid usually exists in many plant cell membranes in the form of salt. In the past, wood chips and strong alkali were used to co-melt at 240~250 ℃ in industry to first produce oxalate, and 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 obtain sodium oxalate, and then treated with lime and sulfuric acid to produce oxalic acid.