It is wrong to soak seafood with formaldehyde solution, because formaldehyde solution will react with protein in seafood, destroy the structure of protein, deteriorate it and endanger human health. But animal specimens can be made of formaldehyde solution, so that specimens can be preserved for a long time.
Basic introduction Chinese name: formaldehyde aqueous solution English name:? Formaldehyde alias: formalin, Formilin Chemical formula: CH2O CAS RegistrationNo.: 50-00-0 EINECS RegistrationNo.: 200-00 1-8 Appearance: colorless liquid, pungent odor application: leather industry, medicine, dyestuff, plastic industry, synthetic fiber, corrosion protection hazard symbol: R: R23/24/ Harm and its source, use of formaldehyde, harm to human health, influence on on-site disinfection, detection, universal detector, spectrophotometry Meth *** * Chemical formula: ch2oHCHO's brief structure: HCHO molecular weight: 30.03 CAS registration number: 50-00-0 EINECS registration number: 200-00 1-8 Formaldehyde is colorless. Soluble in water, alcohol and ether. Formaldehyde is gaseous at room temperature and usually exists in the form of aqueous solution. Soluble in water and ethanol, 35 ~ 40% formaldehyde aqueous solution is called formalin. Chemical Properties Formaldehyde has carbonyl oxygen atoms and α -hydrogen atoms in its molecular structure, and its chemical properties are very active. It can react with many compounds to produce many important industrial chemicals and chemical intermediates. Only some of the most important chemical reactions are introduced here. (1) Addition Reaction Formaldehyde reacts with sodium sulfite to produce sodium formaldehyde sulfoxylate HOCH 2 OSO 2 Na, which is then reduced by zinc powder in acetic acid distillation to produce sodium formaldehyde sulfoxylate, which is widely used as pad printing agent for textiles in industry. Ch _ 2O+Na _ 2SO _ 3+H _ 2O → Hoch _ 2O _ 2SO _ 2Na+NaOH is often used as an analytical method for quantitative analysis of formaldehyde content, because formaldehyde can generate equimolar NaOH in the above reaction. (2) Condensation reaction Formaldehyde itself can slowly undergo condensation reaction to generate hydroxyl compounds such as lower hydroxyaldehyde and hydroxyl ketone, but it can accelerate the reaction in the presence of alkali. Formaldehyde can undergo condensation reaction with various compounds, which is called Torres reaction. Hydroxymethylene derivative (-CH2 OH) is generated under alkaline conditions, and methylene derivative (=CHz) is generated under acidic conditions or in gas phase. An important reaction in industry is the condensation of formaldehyde and phenol to produce phenolic resin. (3) The special property of polymerized formaldehyde is that it is easy to self-polymerize, but the dried gaseous formaldehyde is quite stable and will slowly polymerize only when the temperature is lower than 100℃. When the newly generated aqueous formaldehyde solution is left standing, it will automatically generate low molecular weight polymers and form a mixture of polyoxymethylene alcohols, some of which will precipitate. Formaldehyde aqueous solution will rapidly polymerize and release heat (63kJ/mol or 15.05kcal/mol) when placed in a closed container at room temperature. At room temperature, gaseous formaldehyde and formaldehyde aqueous solution can self-polymerize during the concentration operation, resulting in white powdery polymer with linear structure. (4) The decomposition reaction of formaldehyde has unexpected stability, and the decomposition rate is very slow when there is no catalyst below 300℃. At 400℃, the deCOmposition rate of formaldehyde is about 0.44% per minute (decomposition pressure is 10 1.3kPa), and the main products of decomposition are co and H 2. The phenomenon that formaldehyde decomposes into CO and H _ 2 observed under industrial conditions should be attributed to the reactor wall effect or the action of catalyst, and it is by no means caused by the gas phase thermal decomposition of formaldehyde. (5) Redox reaction Many metals (such as platinum, chromium, copper, etc. ) can reduce formaldehyde to methanol, methyl formate and methane, or deeply oxidize formaldehyde to formic acid, CO 2 and H 2 O, and hydrobromic acid also has catalytic effect. Physical properties Formaldehyde is easily soluble in water, and the dissolution process is exothermic, and the heat release does not depend on the solution concentration. Formaldehyde aqueous solution is a colorless and transparent liquid with strong smell, and its boiling point basically does not change with the change of its solution concentration. At standard or local atmospheric pressure, the boiling point of aqueous formaldehyde solution is lower than 55% (by weight). ) between 99℃ and 100℃. The water solution of formaldehyde with boiling point of 25% (by weight) is 99.65438 0℃, while 35%(wt. ) Formaldehyde aqueous solution is 99.9℃. Harm and its source Formaldehyde is a colorless gas with strong smell, and its 35%~40% aqueous solution is commonly known as formalin. Formaldehyde is a poison of protoplasm, which can combine with protein. After inhaling high concentration formaldehyde, severe respiratory edema, eye tingling, headache and bronchial asthma may occur. Direct contact with formaldehyde can cause dermatitis, pigmentation and necrosis. Regular inhalation of a small amount of formaldehyde can cause chronic poisoning, such as mucosal congestion, dermatosis, allergic dermatitis, nail keratinization and brittleness, nail bed finger pain and so on. Systemic symptoms include headache, fatigue, loss of appetite, palpitation, insomnia, weight loss and autonomic nervous disorder. All kinds of wood-based panels (particleboard, fiberboard, plywood, etc. ) may contain formaldehyde because of the use of adhesives. Adhesives should be used in the production of new furniture and the decoration and laying of walls and floors. Where adhesives are used in large quantities, formaldehyde will always be released. Besides, some chemical fiber carpets and paints also contain a certain amount of formaldehyde. Formaldehyde may also come from cosmetics. Cosmetics, detergents, pesticides, disinfectants, preservatives, ink, paper, textile fibers and other chemical and light industrial products. The use of formaldehyde is a popular chemical product with a wide range of uses, simple production process and sufficient supply of raw materials. It is the backbone of the downstream product tree of methanol. The annual output of the world is about 25 million tons, and about 30% of methanol is used to produce formaldehyde. However, formaldehyde is a low-concentration aqueous solution, which is not convenient for long-distance transportation from an economic point of view. Therefore, factories are generally located near major consumer markets, and there is little import and export trade. In addition to being directly used as disinfection, sterilization and preservative, formaldehyde is mainly used in organic synthesis, synthetic materials, coatings, rubber, pesticides and other industries, and its derivatives mainly include paraformaldehyde, paraformaldehyde, phenolic resin, urea-formaldehyde resin, amino resin, urotropine and polyol. The wood-based panel industry is developed and there is a great demand for formaldehyde. Formaldehyde is widely used, including synthetic resin, surfactant, plastic, rubber, leather, paper, dye, pharmacy, pesticide, photographic film, explosives, building materials, disinfection, fumigation and anticorrosion. It can be said that formaldehyde is a generalist in the chemical industry, but the use of anything must have * * * and standards. Once used, it will exceed the standard and * * *. According to informed sources, the price of 1 ton of formaldehyde is around 1.600 yuan, and the main reason why formaldehyde is abused is its low price. In recent years, the output of formaldehyde in China has increased year by year, which is consistent with the development of China's textile industry and building materials industry, indicating that formaldehyde will be the darling of China's chemical industry for a long time to come. According to experts, China has successfully developed formaldehyde-free non-ironing finishing agent and formaldehyde-free environment-friendly urea-formaldehyde resin, but they have not been put into mass production so far, mainly because they are expensive, visible and cheap, which hinders the process of replacing formaldehyde. 1), the wood industry is used to produce urea-formaldehyde resin and phenolic resin, which are mixed by formaldehyde and urea according to a certain molar ratio. 2) The use of formaldehyde should be involved in the resin finishing process of textiles and garments. In the fabric production of clothing, in order to achieve the functions of wrinkle resistance, shrink resistance and flame retardant, or to maintain the durability of printing and dyeing, or to improve the hand feel, formaldehyde needs to be added to the auxiliary. Cotton textiles are more commonly used as formaldehyde auxiliaries for printing and dyeing, because cotton textiles are prone to wrinkling. The stiffness of cotton fabric can be improved by using formaldehyde additives. Textiles containing formaldehyde will gradually release free formaldehyde when people wear and use them, which will cause respiratory tract inflammation and skin inflammation through the contact between human respiratory tract and skin, and will also cause * * * feeling to eyes. Formaldehyde can cause allergies and cancer. Manufacturers use dyeing auxiliaries containing formaldehyde, especially some manufacturers use cheap auxiliaries with high formaldehyde content in order to reduce costs, which is very harmful to human body. 3) Formaldehyde, antiseptic solution, is a substance released by decomposition of formaldehyde sodium bisulfite at above 60℃. It is colorless, odorous and soluble in water. 35% ~ 40% formaldehyde aqueous solution, commonly known as formalin, has antiseptic and bactericidal properties and can be used to soak biological specimens and disinfect seeds. The main reason why formaldehyde has antiseptic and bactericidal properties is that amino groups on protein, which constitute organisms (including bacteria), can react with formaldehyde. 4) The food industry uses the antiseptic properties of formaldehyde to add it to foods that are difficult to preserve, such as aquatic products. The development of formaldehyde industry in China began in Shanghai Solvent Factory in 1950s. At that time, Soviet technology was adopted, pumice silver was used as catalyst, the system pressure was lower than normal pressure, and the oxidation temperature was 650-750℃. The formaldehyde is diluted with water and evaporated in an evaporator without adding steam. With the successful development of new synthetic rubber technology with polyoxymethylene resin and allyl aldehyde in China, the concentration of formaldehyde aqueous solution was put forward in the mid-1960s. Iron-molybdenum oxide catalyst was used in formaldehyde production, which was first used in Shijinggou United Chemical Plant in Jilin, No.2 Petrochemical Plant in Tianjin and Anyang Plastic Factory in Henan. 65438-0977 The Department of Chemistry of Fudan University and Shanghai Solvent Factory jointly developed and trial-produced a new generation of formaldehyde catalyst-electrolytic silver. The catalyst has the characteristics of high activity, good selectivity, low unit consumption, convenient preparation and no pollution, and its preparation process has been used so far. After entering 2 1 century, various formaldehyde production enterprises have improved the production capacity of oxidation reactors, breaking through the traditional design capacity, and put forward higher requirements for the life, activity and anti-poisoning performance of catalysts. Harm to human health The harm of formaldehyde to health mainly includes the following aspects: A. The main harm of formaldehyde is the * * * effect on skin and mucosa. Formaldehyde is a protoplasmic toxic substance, which can combine with protein. When inhaled in high concentration, it will cause severe respiratory tract edema, eyes and headache. B. Sensitization: Direct skin contact with formaldehyde can cause allergic dermatitis, pigmentation and necrosis, and inhalation of high concentration formaldehyde can induce bronchial asthma. C. Mutagenesis: High concentration formaldehyde is still a genotoxic substance. Experimental animals can cause nasopharyngeal tumors under the condition of high concentration inhalation in laboratory. Note: Generally, formaldehyde in newly renovated houses will exceed the standard. As long as one or two pots of chlorophytum are put in the new house, all formaldehyde will be absorbed. Limitation of textile printing and dyeing auxiliaries on formaldehyde: make the formaldehyde content of textiles in direct contact with the skin exceed 30ppm, and all other textile auxiliaries with formaldehyde content exceeding 300ppm, such as wool protectants, fixing agents, cross-linking agents and adhesives with excessive formaldehyde content, cannot be used. Limit the content of free and partially hydrolyzable formaldehyde in textile dyes, and ensure that the content of free and partially hydrolyzable formaldehyde on textiles that are in direct contact with skin cannot exceed 30ppm, and all other textiles cannot exceed 300ppm. In textiles, heavy metal salts (except iron) or formaldehyde cannot be used as decoloring agents or fading agents. Field disinfection: control index and application method of 40% aqueous solution: 1 Control melon anthracnose, eggplant brown spot, cucumber Fusarium wilt and Fusarium wilt. Soak the seeds in 40% formalin 100 times solution for 30 minutes. After soaking the seeds, wash them with clear water, remove the liquid medicine from the seeds, and accelerate germination or dry them in the sun for later use. 2. Use 40% formalin 1.5 hours to control bacterial angular leaf spot of cucumber, soak the seeds, wash them with clear water, dry them and sow them. 3. To prevent and control tomato bacterial wilt, when it happens sporadically in the field, immediately pull out the diseased plants, take them out, and irrigate the diseased points with 200 times of 40% formalin, with a liquid medicine of about 0.2 kg per point. 4. To prevent the broad bean from wilting, soak the seeds in 50- 100 times solution of 40% formalin for 40 minutes, then rinse with water, dry and sow. 5. After the typhoon and rainstorm, the soil moisture is high and contains many germs and eggs. After soil preparation, the soil can be disinfected with 40% formalin and 0.2% liquid medicine, which can effectively control and eliminate germs, insects and eggs in the soil. Use 0.2% 40% formalin solution to control common virus diseases of vegetables such as tomatoes and eggplant. Chemicals with high formaldehyde toxicity can only be purchased with the approval of relevant departments of * * *. However, the toxicity of 40% formaldehyde aqueous solution (that is, 40% formalin) is greatly reduced, and the purchase does not require approval. The detection of universal detection reagent is to use the color change of detection reagent itself in the reaction process of formaldehyde, benzene series, tvoc, etc., and distinguish the pollution degree and pollution by naked eyes. Its advantages are simple, convenient, safe and easy to use. Spectrophotometry Spectrophotometry is a qualitative and quantitative analysis method based on the selective absorption of electromagnetic radiation by substances with different molecular structures, and it is the most conventional method to detect formaldehyde in indoor, textile and food. There are acetylacetone method, phenol reagent method, AHMT method, magenta sulfurous acid method, chromotropic acid method, phloroglucinol method, catalytic spectrophotometry and so on. Each detection method focuses on different application fields and has its own advantages and limitations. Acetylacetone method Acetylacetone method refers to the reaction of formaldehyde and acetylacetone in water bath at 45 ~ 60℃ for 30min or at room temperature at 25℃ for 2.5h in the presence of excessive ammonium salt to generate yellow compounds, and then the formaldehyde content is quantitatively determined by colorimetry. The reaction between formaldehyde and acetylacetone has good specificity, few interference factors, no interference from phenols and other aldehydes, stable chromogenic reagent, detection limit of 0.25 me/L and wide linear range. It is suitable for the detection of high-content formaldehyde, and is mostly used for the determination of formaldehyde in indoor and water-based foods. However, in the detection of formaldehyde in water-based food, the formaldehyde in the sample needs to be extracted by heating distillation in phosphoric acid medium, absorbed by aqueous solution, and then detected after constant volume. The operation process is complicated, tedious and time-consuming. Phenol reagent method Phenol reagent method is MBTH method, that is, formaldehyde reacts with phenol reagent (3- methyl -2- benzothiazole hydrazone hydrochloride, ugrn) to generate azine, which is oxidized to blue by iron ions in acidic solution, and then colored with 15 rain at room temperature, and then quantified by colorimetry. Phenol reagent method is simple and sensitive, and the detection limit is 0.02mg/L, which is suitable for the determination of trace formaldehyde. However, aliphatic aldehydes have similar reactions, which will interfere with the determination, and sulfur dioxide will also interfere with the determination, making the results low. Therefore, we must be careful when applying this method to determine sodium formaldehyde sulfoxylate. The stability of phenol reagent is poor. MITIH can only be stored for 3 days in the refrigerator at 4℃, and the stability of absorbance after color development is not as good as that of acetylacetone method. Color development is limited by time and temperature. This method is mostly used to detect formaldehyde in the living room, and sometimes it is also used to detect formaldehyde in textiles and food. AHMT method AHMT method refers to the method that formaldehyde is condensed with AHMT(4- amino -3- hydrazine -5- mercapto-1, 2,4- triazene) under alkaline conditions, and then oxidized into purple compounds by potassium periodate, and then the formaldehyde content is quantitatively detected by colorimetry. This method has good specificity and selectivity, and does not interfere with the determination when a large number of aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde and phenylacetaldehyde exist. The detection limit is 0.04 mg/L. However, the color development of AHMT method gradually deepens with the passage of time, and the color development reaction time of standard solution and sample solution must be strictly unified, with poor reproducibility and difficult operation. It is mostly used for indoor formaldehyde detection.