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Melamine was first synthesized by Justus von Liebig in 1834. In the early stage, dicyandiamide method was adopted: calcium carbide (CaC2) was hydrolyzed and dimerized to produce dicyandiamide, and then heated and decomposed to produce melamine, so as to prepare calcium cyanamide (CaCN2).
At present, due to the high cost of calcium carbide, dicyandiamide method has been eliminated. Industrial synthesis mainly uses urea as raw material. Under the conditions of heating and certain pressure:
6 (NH2)2CO → C3H6N6 + 6 NH3 + 3 CO2
According to different reaction conditions, the synthesis process of melamine can be divided into high-pressure method (7- 10MPa, 370-450℃, liquid phase), low-pressure method (0.5- 1MPa, 380-440℃, liquid phase) and atmospheric method (
physical features
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Melting point is 345℃ (decomposed), and density is 1.573g/cm3 (16℃). Slightly soluble in water and hot ethanol. In industry, melamine is made by the reaction of dicyandiamide with ammonia at high temperature, or directly with urea at high temperature and high pressure. The latter is widely used because of its low cost. Melamine formaldehyde resin can be prepared by condensation of melamine and formaldehyde. In addition, melamine is also used as an intermediate in the synthesis of drugs.
chemical constitution
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C3H6N6
Melamine is an important organic chemical intermediate product, which is mainly used to manufacture melamine resin. It has excellent water resistance, heat resistance, arc resistance and flame retardancy. Uses: It can be used to make decorative boards, used in aminoplastics, adhesives, coatings, paper reinforcers, textile auxiliaries, etc.
chemical property
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Melamine is weakly alkaline (pKb=8) and can react with various acids to form melamine salt. When hydrolyzed with strong acid or strong alkali aqueous solution, amino groups are gradually replaced by hydroxyl groups and become cyanuric acid diamide, which is further hydrolyzed to form cyanuric acid monoamide, and finally cyanuric acid is generated.
Main applications
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(1) Decorative board: it can be made into fire-proof, earthquake-resistant and heat-resistant laminated board, bright-colored, high-strength and heat-resistant decorative board, used as veneer for airplanes, ships and furniture, as well as fire-proof, earthquake-resistant and heat-resistant building decorative materials.
(2) Coatings: After etherification with butanol and methanol, it can be used as the base material of advanced thermosetting coatings and solid powder coatings, and can be used to make metal coatings and advanced amino resin decorative paints for automobiles and electrical appliances.
(3) Molding powder: Melamine plastic can be made by mixing, granulating and other processes. It is not over standard, resistant to contamination, and can still maintain good electrical properties when wet. It can be made into white, fall-proof household utensils, sanitary ware, porcelain-like tableware, electrical equipment and other advanced insulating materials.
(4) Paper: It can be used as a paper treatment agent after etherification with ether to produce high-grade paper such as anti-wrinkle, shrink-proof and non-perishable banknotes and military maps.
(5) Melamine formaldehyde resin mixed with other raw materials can also produce fabric finishing agent, leather tanning agent, polishing agent and waterproof agent, rubber adhesive, combustion improver, high-efficiency cement water reducer, steel desalter, etc.
Biological toxicity
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At present, melamine is considered to be slightly toxic, and the lethal dose to rats is above 3 g/kg body weight. According to an experimental report of 1945, rats, rabbits and dogs were fed with large doses of melamine, and no obvious poisoning phenomenon was found. Long-term intake of melamine in animals will cause damage to reproductive and urinary systems, bladder and kidney calculi, and further induce bladder cancer. However, the preliminary investigation of pet food pollution in the United States in 2007 showed that wheat protein powder mixed with melamine ≤6.6% was the cause of pet food poisoning, which put a question mark on the above conclusion of slight toxicity. However, for safety reasons, melamine tableware will be marked "Do not use in the microwave oven".
CASNo.: 108-78- 1
Pseudoprotein principle:
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The biggest feature of melamine is its high nitrogen content (66%). In addition, its production process is simple and its cost is very low, which gives great benefits to counterfeiters and counterfeiters. It is estimated that protein will increase by one percentage point in plant protein powder and feed, and the cost of using melamine is only 1/5 of that of real protein raw materials. Therefore, "increasing" the apparent protein content of the product is the main reason for adding melamine. Melamine, as a white crystalline powder, has no smell and taste, and it is not easy to be found after doping, which has also become an auxiliary reason for adulteration and counterfeiters to take chances.
1994 Volume III of the International Handbook of Chemical Safety and the International Chemical Safety Card jointly edited by the International Chemical Safety Agency and the European Commission only show that long-term or repeated intake of melamine may affect the kidneys and bladder, leading to stones.
Related pathogenic cases
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Xinhuanet Beijing September 2008 1 1 Sunday (Reporter Zhou, Zhang Honghe,,) On the evening of June 1 1 Sunday, the Ministry of Health of China pointed out that many cases of urinary calculi in infants and young children were reported in Gansu and other places recently. The survey found that most children have a history of eating Sanlu infant formula. After investigation by relevant departments, the Sanlu infant formula milk powder produced by Shijiazhuang Sanlu Group Co., Ltd. is highly suspicious.
Xinhuanet Beijing, September 1 1 Sunday (Reporter's Week) Shijiazhuang Sanlu Group Co., Ltd. issued a product recall statement on the evening of June 1 1 Sunday, claiming that some batches of Sanlu infant milk powder that were shipped before August 6, 2008 were contaminated by melamine, and there were about 700 tons on the market.
The Ministry of Health of China reminds the public to stop using this variety of milk powder immediately. Infants who have already eaten this milk powder should seek medical advice in time if they have abnormal symptoms such as dysuria.
In addition, medical institutions in Jiangsu, Shaanxi, Hubei and other places have also treated a number of infants with urinary calculi. All babies are breast-feeding and have taken or are still taking the same brand of milk powder. After careful treatment, most of the children have recovered and been discharged.
According to Huang Songming, vice president of Nanjing Children's Hospital, who once treated children, the hospital found that these children had been fed the same brand of milk powder more or less. Due to the cross phenomenon of milk powder brands fed by some children, the hospital can't draw the conclusion that this brand of milk powder is directly related to kidney calculi.
Professor Sun Xizhao, doctoral supervisor of urology in Nanjing University School of Medicine and Nanjing Gulou Hospital, has successively received 0/0 urolithiasis samples from Nanjing Children's Hospital/KLOC. After examination, it was found that the mixed components of this 10 stone had never been found in China before, and all the patients were breast-fed babies.
According to doctors, the incidence of urinary calculi in infants is very low, and it is very rare for so many infants to have double kidney calculi in a short time.
What tripped Sanlu this time was a term that everyone was not familiar with in the past: melamine. According to the professional website, it is an important nitrogen heterocyclic organic chemical raw material, mainly used to produce melamine-formaldehyde resin, widely used in wood processing, plastics, coatings, paper-making, textile, leather, electricity, medicine and other industries, and it is an important post-treatment product of urea at present. In addition, melamine can also be used as flame retardant, water reducer and formaldehyde cleaner. According to the Ministry of Health, Sanlu infant formula may be contaminated by melamine, which can lead to urinary calculi. It is speculated that this is probably caused by the pollution of the production environment, or the process control in production is wrong.