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urea

[niào sù]
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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.
Urea, also known as urea and carbamide, chemical formula is CH four N two O or CO (NH two ) two [4] Is composed of carbon, nitrogen, oxygen and hydrogen Organic compound , is a kind of white crystal 。 The simplest Organic compound One is in mammals and some fish protein metabolism The main nitrogen-containing end products of decomposition.
As a neutral fertilizer, urea is suitable for various soils and plants. It is easy to preserve, easy to use, and has little damage to the soil. It is a chemical nitrogen fertilizer with a large amount of use and the highest nitrogen content nitrogenous fertilizer 。 Industrial use ammonia and carbon dioxide Urea is synthesized under certain conditions.
Chinese name
urea
Foreign name
Urea, Carbamide
Alias
Urea, carbamide
chemical formula
CH four N two O or CO (NH two ) two
molecular weight
sixty point zero six
CAS login number
57-13-6
EINECS login number
200-315-5
Melting point
132.7 ℃
Boiling point
196.6 ° C/standard atmospheric pressure
Water solubility
1080 g/L (20℃)。
Density
1.335 g/cm ³
Appearance
Colorless or white needle like or rod like crystals
Flash point
72.7 ℃
Application
chemical fertilizer
Security description
S24/25； S26； S36
Hazard symbol
Xn； Xi
Hazard description
R36/37/38； R40

catalog

  1. one Discovery history
  2. two Compound Introduction
  3. ▪ physical property
  4. ▪ chemical property
  5. ▪ Molecular structure data
  6. ▪ Calculate chemical data
  7. three Preparation method
  8. ▪ Method 1
  9. ▪ Method 2
  10. ▪ Method 3
  11. ▪ Industrial process
  1. four application
  2. ▪ Medical field
  3. ▪ Agriculture
  4. ▪ Industrial field
  5. ▪ Laboratory application
  6. five keep in storage
  7. six new product
  8. seven national standard
  9. eight Drug description
  10. ▪ classification
  11. ▪ pharmacological action
  1. ▪ Biological metabolism
  2. ▪ Pharmacokinetics
  3. ▪ indication
  4. ▪ contraindication
  5. ▪ matters needing attention
  6. ▪ Adverse reactions
  7. ▪ Usage and dosage
  8. nine poisoning
  9. ▪ clinical manifestation
  10. ▪ treatment
  11. ten Pharmacopoeia information
  12. ▪ essential information
  1. ▪ character
  2. ▪ identify
  3. ▪ inspect
  4. ▪ Assay
  5. ▪ category
  6. ▪ Storage
  7. ▪ preparation
  8. eleven security information
  9. ▪ Safety terminology
  10. ▪ Risk terminology

Discovery history

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In 1773, Hilaire Rouelle discovered urea. In 1828, German chemist Friedrich Wohler First use of inorganic substances Ammonium cyanate （NH four CNO, an inorganic compound, can be composed of ammonium chloride and Silver cyanate Urea was synthesized with ammonium sulfate. Originally, he intended to synthesize ammonium cyanate, but he got urea. The synthesis of urea has opened the prelude to the artificial synthesis of organic compounds. This proves that Vitality theory In fact, it opens up the way for organic chemistry (the vitality theory believes that inorganic substances are fundamentally different from organic substances, so inorganic substances cannot be turned into organic substances, and organic compounds can only be produced by biological cells under the action of a special force - vitality. Artificial synthesis is impossible. The urine of mammals, amphibians and some fish contains urea; Birds and reptiles emit uric acid because they use less water during nitrogen metabolism). [1]

Compound Introduction

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physical property

Urea is easily soluble in water, 105g can be dissolved in 100ml water at 20 ℃, and the aqueous solution shows neutral reaction. There are two kinds of urea products. Crystalline urea It is white acicular or prismatic crystal, with strong hygroscopicity. It agglomerates after hygroscopicity, and the hygroscopicity speed is 12 times faster than granular urea. [1] Granular urea is a semitransparent particle with a particle size of 1~2mm, which has a smooth appearance and significantly improved moisture absorption. Critical at 20 ℃ Hygroscopic point The relative humidity is 80%, but at 30 ℃, the critical moisture absorption point drops to 72.5%, so urea should not be stored in a humid climate in midsummer. When hydrophobic substances such as paraffin are added in urea production, its hygroscopicity is greatly reduced.

chemical property

Urea can react with acids to form salts. It has hydrolysis. Condensation reaction can be carried out at high temperature to generate Biuret , Triuret and Cyanuric acid 。 Heating to 160 ℃ for decomposition, producing ammonia Simultaneously become Isocyanate 。 Because it is contained in human urine, it is named urea. Urea contains 46% nitrogen (N), which is the highest nitrogen content in solid nitrogen fertilizer.
Urea can be hydrolyzed into ammonia and carbon dioxide 。
Unstable to heat, heat to 150~160 ℃ to deamination to biuret. Copper sulfate and Biuret reaction It is purple and can be used to identify urea. [1] If heated rapidly, the ammonia will be removed and the cyanuric acid will be trimerized into a six membered ring compound. [Mechanism: first Deamination Generate isocyanate (HN=C=O) and trimer it.]
And Acetyl chloride or acetic anhydride Action can generate Acetylurea And diacetylurea.
Under the action of sodium ethoxide Diethyl malonate The reaction produces malonylurea (also known as Barbituric acid , because it has certain acidity).
stay ammonia Isobasicity catalyzer Under action, energy and formaldehyde Reaction, condensation to Urea formaldehyde resin 。
And Hydrazine hydrate Action generation Semicarbazide 。

Molecular structure data

Molar refractive index
thirteen point seven eight
Molar volume (cm three /mol）
forty-nine point five
Isotonic specific volume (90.2K)
one hundred and thirty-five
Surface tension (dyne/cm)
fifty-five point three
Polarization (10 -24 cm three ）
five point four six
reference material [5]

Calculate chemical data

Drainage parameter calculation reference value (XlogP)
-1.4
Number of hydrogen bond donors
two
Number of hydrogen bond receptors
one
Number of rotatable chemical bonds
zero
Number of tautomers
two
Topological molecular polar surface area
sixty-nine point one
Number of heavy atoms
four
surface charge
zero
Complexity
twenty-nine
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
reference material [5]

Preparation method

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Method 1

Synthesis with carbon dioxide and ammonia under high temperature and pressure Ammonium carbamate , after decomposition, absorption and transformation, crystallization, separation and drying.

Method 2

The preparation method is to mix purified ammonia with carbon dioxide at a molar ratio of 2.8~4.5 into the synthesis tower. The pressure in the tower is 13.8~24.6 MPa, the temperature is 180~200 ℃, and the residence time of the reaction material is 25~40 min Ammonium carbamate Urea solution , the ammonia and Ammonium carbamate After that, the urea liquid evaporates to more than 99.5%, and then granulates in the prilling tower to obtain finished urea.

Method 3

Urea is found in mammals protein metabolism The final product of. In 1922, the industrial production of urea from ammonia and carbon dioxide was realized in Germany. Ammonia reacts with carbon dioxide to form carbamate, and then dehydrates to form urea.

Industrial process

Production method: industrial use liquid ammonia With carbon dioxide as raw material, urea is directly synthesized under high temperature and high pressure. The chemical reaction is as follows:
2NH three + CO two → NH two COONH four → CO(NH two ) two + H two O。 [2]

application

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Medical field

The dermatology department uses certain medicaments containing urea to increase the humidity of the skin. The sealing dressing used for non operative nail removal contains 40% urea.
test Helicobacter pylori The existing carbon-14 breath test uses urea containing carbon-14 or carbon-13 markers. Because the urease of Helicobacter pylori uses urea to produce ammonia to increase the pH value in the surrounding stomach. The same principle can also be used to test similar bacteria living in the stomach of animals.

Agriculture

Urea is a high concentration nitrogen fertilizer, which is a neutral quick acting fertilizer and can also be used to produce a variety of compound fertilizers. No harmful substances remain in the soil, and long-term application has no adverse effects. Animal husbandry can be used as feed for ruminants. However, a small amount of biuret, also called biuret, will be produced when the temperature is too high during granulation, which has inhibitory effect on crops. China stipulates that the biuret content of urea for fertilizer should be less than 0.5%. When the biuret content exceeds 1%, it cannot be used as seed fertilizer, seedling fertilizer and foliar fertilizer, and the urea content in other application periods should not be too much or too concentrated.
Urea is an organic nitrogen fertilizer, which is hydrolyzed into ammonium carbonate or Ammonium bicarbonate Only then can it be absorbed and utilized by crops. Therefore, urea should be applied 4 to 8 days before the crop's fertilizer demand period.
Urea is suitable for base fertilizer, topdressing and sometimes seed fertilizer. Urea is in molecular state before conversion and cannot be adsorbed by soil, so it should be prevented from loss with water; The ammonia formed after conversion is also volatile, so urea should also be deeply covered with soil. (A small part of the soil transformed into soil is dissolved in the soil solution in molecular state, and absorbed by the soil through hydrogen bonding. Most of the other parts are hydrolyzed into ammonium carbonate under the action of urease, and then produce carbonic acid and ammonium hydroxide. Then the ammonium ion can be absorbed by plants and adsorbed by soil glue, Bicarbonate Ions can also be absorbed by plants, so urea will not leave any harmful components after being applied to soil. In addition, biuret contained in urea can also be decomposed into ammonia and carbonic acid under the action of urease. The transformation of urea in soil is affected by soil PH value, temperature and water content. The reaction in soil is neutral. When water content is appropriate, the higher the soil temperature, the faster the transformation; When the soil temperature is 10 ℃, it takes 7-10 days for urea to completely convert into ammonium nitrogen, 4-5 days when the soil temperature is 20 ℃, and 2-3 days when the soil temperature is 30 ℃. Ammonium nitrogen is generated after hydrolysis of urea, and surface application will cause ammonia volatilization, especially on alkaline or alkaline soil. Therefore, when applying urea, soil covering should be applied deeply, and paddy field should be applied deeply to the reducing layer.)
Urea is applicable to all crops and all soils, and can be used as base fertilizer and topdressing. It can be applied to dry and paddy fields. As urea can accumulate a large amount of ammonium ions in the soil, which will lead to the increase of pH by 2-3 units. In addition, urea itself contains a certain amount of biuret, which will inhibit the young roots and buds of crops when its concentration is 500 ppm. Therefore, urea should not be used as seed fertilizer.
Urea (nitrogen fertilizer) can promote cell division and growth, and make branches and leaves flourish. [2]
According to《 Circular of the National Development and Reform Commission on the Implementation of Preferential Railway Freight Policy for Agricultural Fertilizers such as Slow release Fertilizers 》(FGJG [2021] No. 1285), urea is listed in the Catalogue of Agricultural Fertilizers with Preferential Railway Freight Rates, and preferential railway freight is implemented.
Adjust flower amount
In order to overcome the big and small year of apple field, during the small year, spray 0.5% urea aqueous solution on the leaf surface for two times after 5-6 weeks after flowering (the critical period of apple flower bud differentiation, the growth of new shoots is slow or stopped, and the nitrogen content of leaves shows a downward trend), which can increase the nitrogen content of leaves, accelerate the growth of new shoots and inhibit flower bud differentiation, so as to make the flower amount suitable for the big year.
Flower thinning and fruit thinning
The flower organs of peach trees are more sensitive to urea, but the reaction to urea is relatively slow. Therefore, foreign countries have conducted flower and fruit thinning tests on peach and nectarine with urea. The results show that the flower and fruit thinning of peach and nectarine requires a large concentration (7.4%) to show a good effect. The most suitable concentration is 8% - 12%. The purpose of flower and fruit thinning can be achieved within 1-2 weeks after spraying. However, under different land conditions, the response of different periods and varieties needs further tests.
Rice seed production
In the hybrid rice seed production technology, in order to improve the outcrossing rate of parents and increase the hybrid rice seed production or the reproduction of male sterile lines, the female parent is generally sprayed with gibberellin to reduce the degree of neck covering or make it completely extracted; Or spray the parents to regulate their growth and synchronize their florescence. Due to the high price of gibberellin, its seed production cost is high. People use urea instead of gibberellin to carry out experiments, and use 1.5% - 2% urea at the peak booting stage and the first heading stage (20% heading). Its seed reproduction effect is similar to gibberellin, and does not increase plant height.
Pest control
After mixing 4:1:400 portions of urea, washing powder and clean water evenly, it can prevent aphids, red spiders, cabbage caterpillars and other pests on fruit trees, vegetables and cotton, with the insecticidal effect of more than 90%.
Urea iron fertilizer
Urea in the form of complex with Fe 2+ Form chelated iron. The organic iron fertilizer has low cost and good effect on preventing iron deficiency and chlorosis. In addition, 0.3% spraying on the blade surface ferrous sulfate When 0.3% urea is added, the effect of prevention and control of green loss is better than that of single spraying 0.3% ferrous sulfate.
Urea is an excellent dye solvent/hygroscopic agent in the textile industry because of its excellent solubility of dyes, mild reduction/oxidation resistance and extremely excellent moisture absorption/ Viscose fibre Expanding agent, Resin finishing agent , has a wide range of uses.
Comparison of moisture absorption between urea and other hygroscopics in textile industry: weight ratio of urea to itself.
feed additive ：
The shortage of human food resources and protein has also caused a major problem in the feed industry. The industry actively seeks new sources of protein and expands to nitrogen sources other than protein, such as urea with high nitrogen content.
In 1897, Waesk et al. put forward the idea that ruminants can convert non protein nitrogen into bacterial protein. In 1949, C J. Watson et al. fed sheep containing N fifteen Labeled urea capsules were found to contain N in sheep blood, liver and kidney 4 days later fifteen Protein. This proves that ruminants can utilize non protein nitrogen. In the same year, J. K. Looli et al. fed sheep with urea as the only nitrogen source and found that sheep could Positive nitrogen balance The results showed that the microbes in sheep rumen could use urea to synthesize 10 essential amino acids for their growth. Since then, urea and urea compounds have become feed additives for ruminants.

Industrial field

It can be used as melamine 、 Urea formaldehyde resin 、 Hydrazine hydrate 、 tetracycline 、 Phenobarbital 、 caffeine 、 Restore brown BR , phthalocyanine B, phthalocyanine Bx, monosodium glutamate and other raw materials for production of various products.
It has brightening effect on chemical polishing of steel and stainless steel, and is used as corrosion inhibitor in metal pickling, as well as preparation of palladium activation solution.
In industry, it is also used as raw material for manufacturing urea formaldehyde resin, polyurethane and melamine formaldehyde resin. When the urea is heated to 200 ℃, it generates solid melamine (i.e. cyanuric acid). Derivatives of cyanuric acid Trichloroisocyanuric acid , sodium dichloroisocyanate, tri (2-hydroxyethyl) isocyanurate, tri (allyl) isocyanurate, tri (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanate, triglycidyl ether of isocyanate, and melamine complex of cyanuric acid have many important applications. The first two are new high-end disinfection and bleaching agents, and the total production capacity of trichloroisocyanuric acid in the world exceeds 80000 tons.
Selective reducing agent used for denitration of combustion waste gas, as well as vehicle urea, which consists of 32.5% high-purity urea and 67.5% Deionized water 。
Selective catalytic reduction (SCR) exhaust after treatment is to combine ammonia produced by urea pyrolysis reaction in combustion exhaust with nitrogen oxide (NOx) is a kind of technology for selective catalytic reduction reaction, which is to reduce the combustion of boiler and Diesel engine It is the key and mainstream technology of nox, a harmful substance in combustion exhaust gas. SCR system meets Hyundai Motor Strictly enforce the necessary system of emission laws and regulations such as Euro IV/Euro V/Euro VI (national IV/national V/national VI) regulations. Vehicle urea is called AdBlue in Europe and DEF in the United States.
Raw materials of special plastics, especially Urea formaldehyde resin Some rubber raw materials, fertilizer and feed ingredients, replacing antifreeze salt on the street (the advantage is that it does not corrode metal), enhancing the smell of cigarettes, giving the industrial production of pretzels brown, some shampoo, detergent ingredients, ingredients of first-aid refrigeration package (because urea reacts with water to absorb heat), automotive urea treatment diesel engine, engine The waste gas from thermal power plants can especially reduce the composition of nitrogen oxide and rain catalyst (mixed salt), which was used to separate paraffin wax (Because urea can form inclusion compounds), refractory materials, components of environmental engine fuel, components of tooth whitening products, chemical fertilizers, and important auxiliary agents for dyeing and printing.
Application in cosmetics
Urea is a very useful moisturizing ingredient, which exists in the cuticle of the skin and belongs to the skin Natural moisturizing factor The main components of NMF. For the skin, urea has the effect of moisturizing and softening the cutin, so it can also prevent the cuticle from blocking the pores, thereby improving the problem of acne. It is used to add moisturizing ingredients in facial mask, skin care lotion, cream, hand cream and other products. The addition ratio is 3-5%. [3]

Laboratory application

Urea can make Protein denaturation , especially can destroy Noncovalent bond Binding proteins. This feature can improve the solubility of some proteins, and the concentration can reach 10 mol/volume. Urea can also be used to make urea nitrate.

keep in storage

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1. If urea is not stored properly, it is easy to absorb moisture and agglomerate, which affects the original quality of urea and brings some economic losses to farmers. This requires farmers to store urea correctly. Before use, the urea packaging bag must be kept intact, handled with care during transportation, protected from rain, and stored in a dry, well ventilated place with a temperature below 20 ℃.
2. If a large number of keep in storage The lower part shall be padded with wooden square for about 20 cm, and the upper part and the roof shall be left with a gap of more than 50 cm to facilitate ventilation and moisture dissipation. A passage shall be left between stacks. To facilitate inspection and ventilation. If the urea that has been opened is not used up, the opening of the bag must be sealed in time for use next year.
3. Avoid contact with skin and eyes. [2]

new product

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Polyurethane urea
Poly (amino acid) urea refers to urea added with biosynthetic poly (glutamic acid) polymer (molecular weight between 800000 and 1300000). Poly (ammonia) can play the role of ion pump, improve the affinity between ionic nutrients and roots, and improve nutrient absorption and transport rate; It can increase crop yield by 7% - 30%; It can effectively improve the fertilizer nutrient utilization rate (N increased by 24% - 32%); It can reduce fertilizer input (reduce nitrogen input by 15% - 20%); The product is non-toxic to people, livestock and plants, and meets the requirements of green agricultural production. Compared with ordinary urea, polyurethane urea can really play a role of one jin for two jin. Polyurethane urea is a new generation of quick acting and efficient fertilizer. Compared with conventional compound fertilizers, the polyamine synergic compound fertilizers contain polyamine active substances, which are characterized by drought resistance, water retention and high nutrient utilization rate.
Polypeptide urea
Polypeptide urea is added to urine during urea formation Metalloproteinase , condensed and granulated by evaporator. Enzymes are indispensable catalysts for biological development and growth, because almost all chemical reactions of organism metabolism are carried out in Biocatalyst It is completed under the action of enzyme. polypeptide It involves various cell functions in the organism biological activity Substance. Peptide bond is the main connection mode of amino acids in protein molecules. Metalloproteinases formed by the combination of peptide bond metal ions have strong biological activity. Enzymes clearly reflect the biological recognition, catalysis, regulation and other functions, which can stimulate fertilizer and promote the activity of fertilizer molecules. Metalloproteinase can be directly absorbed by plants, so it can save the "physical energy" required by plants in transforming trace elements, and greatly promote plant growth and development. According to the test, the application of polypeptide urea can generally mature plants 5-15 days in advance (about 5 days in advance for corn, 7-10 days in advance for cotton, 10-15 days in advance for tomatoes), and can improve the utilization rate of fertilizer and crop quality. [2]

national standard

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Current national standards related to urea
GB 2440-2001 Urea 2002-01-01 Implemented instead of GB 2440-1991, GB/T 13257-1991
GB/T 2602-2002 Urea Determination Method for Middle Cresol Content of Phenol Products 2003-04-01 Implemented instead of GB/T 2602-1981
GB/T 2947-2002 Determination of Free Water Content in Urea and Ammonium Nitrate Karl Fischer Method 2003-04-01 Implemented instead of GB/T 2947-1982
GB/T 18204.29-2000 Determination of Urea in Swimming Water Implemented from January 1, 2001
GB 18560-2001 Occupational Exposure Limit for Urea in the Air of Workshops Implemented on May 1, 2002
GB/T 10476-2004 Technical Conditions for Urea High Pressure Condenser Implemented on December 01, 2004, replacing GB 10476-1989
GB/T 9843-2004 Technical Conditions for Urea High Pressure Scrubber Implemented on December 01, 2004, replacing GB 9843-1988
GB/T 9842-2004 Technical Conditions for Urea Synthesis Tower Implemented on December 01, 2004, replacing GB 9842-1988
GB/T 8622-2006 Determination of Urease Activity in Soybean Products for Feed Implemented on September 1, 2006, instead of GB/T 8622-1988
GB/T 696-2008 Chemical reagent Urea (urea) Implemented on November 1, 2008, replacing GB/T 696-1994
GB/T 2441.1-2008 Determination of Urea Part 1: Total Nitrogen Content 2008-09-01 Implemented instead of GB/T 2441.1-2001
GB/T 2441.2-2010 Determination of Urea Part 2: Diuret Content Spectrophotometry 2011-01-01 Implemented instead of GB/T 2441.2-2001
GB/T 2441.3-2010 Determination of Urea Part 3: Moisture Karl Fischer Method Implemented on January 1, 2011, replacing GB/T 2441.3-2001
GB/T 2441.4-2010 Determination of Urea Part 4: Iron Content Orthophenanthroline Spectrophotometry 2011-01-01 Implementation, replacing GB/T 2441.4-2001
GB/T 2441.5-2010 Determination of Urea Part 5: Alkalinity Volumetric Method Implemented on January 1, 2011, replacing GB/T 2441.5-2001
GB/T 2441.6-2010 Determination of Urea Part 6: Gravimetric Method for Water Insoluble Matter 2011-01-01 Implemented instead of GB/T 2441.6-2001
GB/T 2441.7-2010 Determination of Urea Part 7: Particle Size Sieving Method Implemented on January 1, 2011, replacing GB/T 2441.7-2001
GB/T 2441.8-2010 Determination of Urea Part 8: Sulfate Content Visual Turbidimetry 2011-01-01 Implemented instead of GB/T 2441.8-2001
GB/T 2441.9-2010 Determination of Urea Part 9: Methylene Diurea Content Spectrophotometry 2011-01-01 Implemented instead of GB/T 2441.9-2001
GB/T 25151.3-2010 Manufacturing and Inspection Methods of Urea High Pressure Equipment Part 3: Urea Grade Ultra Low Carbon Chromium Nickel Molybdenum austenitic stainless steel Intergranular corrosion tendency test Implemented on March 1, 2011
GB/T 25151.4-2010 Manufacturing and Inspection Methods for Urea High Pressure Equipment Part 4: Sample Preparation for Intergranular Corrosion Tendency Test of Urea Grade Ultra Low Carbon Chromium Nickel Molybdenum Austenitic Stainless Steel Implemented on March 1, 2011
GB/T 25151.1-2010 Urea High Pressure Equipment Manufacturing Inspection Method Part 1: Stainless steel belt Ultrasonic testing of extremely automatic surfacing layer Implemented on March 1, 2011
GB/T 25151.5-2010 Manufacturing and Inspection Methods for Urea High Pressure Equipment Part 5: Ammonia Leakage Test Method for Urea High Pressure Equipment Implemented on March 01, 2011
GB/T 25151.2-2010 Manufacturing and Inspection Methods for Urea High Pressure Equipment Part 2: Selective Corrosion Inspection and Metallographic Examination of Urea Grade Ultra Low Carbon Chromium Nickel Molybdenum Austenitic Stainless Steel Implemented on March 1, 2011

Drug description

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classification

Circulating system drugs>antihypertensive drugs>diuretic and antihypertensive drugs

pharmacological action

Urea has the same effect as sorbitol and is a osmotic diuretic. Since part of urea can enter brain tissue through the blood cerebrospinal fluid barrier, when urea in blood is eliminated by the kidney and its concentration drops rapidly, urea that has entered brain tissue cannot be removed in time, and water can re-enter brain tissue, causing increased intracranial pressure and even aggravation of brain edema, that is, "rebound" phenomenon, so it should be used alternately with other dehydration drugs. In addition to rapid and powerful dehydration, urea can also dissolve and denature proteins. High concentration urea can change the structure of amino acid side chains and polypeptide main chains of proteins, dissolve proteins, increase the moisture content of the stratum corneum, enhance the hydration of the stratum corneum, make skin soft, and have antibacterial (including fungi), antipruritic, and promote granulation growth.

Biological metabolism

Urea cycle is also called "ornithine cycle", H Crebs and K Henseleit proposed.
After being produced in the liver, urea is integrated into the blood (the concentration in the human body is between 2.5 and 7.5 mmol per liter), and finally discharged from the urine through the kidney. A small amount of urea is excreted by sweat.
The biology synthesizes urea with carbon dioxide, water, aspartic acid, ammonia and other chemicals. The metabolic pathway that promotes urea synthesis is an anabolism, called urea cycle. This process is energy consuming but necessary. Because ammonia is toxic and a common metabolite, it must be eliminated. The liver needs N-acetylglutamic acid as a regulator when synthesizing urea.
Nitrogenous wastes are toxic and are generated from the catabolism of proteins and amino acids (i.e. deamination, the process of deamination of amino acids, in which the nitrogenous compounds generated are converted into urea in the liver, and the non nitrogenous parts are converted into sugars or Fat And so on). Most organisms must be reprocessed. Marine organisms usually discharge directly into the sea water in the form of ammonia. Terrestrial organisms convert ammonia into urea or uric acid and then excrete it. Birds and reptiles usually excrete uric acid, while other animals (such as mammals) excrete urea. For example, the aquatic tadpoles excrete ammonia, but during their metamorphosis, they excrete urea; The Dalmatian dog mainly excretes uric acid, not urea, because the gene of a conversion enzyme in its urea cycle is broken.
In mammals, urea is produced by a circulating reaction in the liver. This cycle was first proposed in 1932, and its starting point is the decomposition of ammonia. Clarification in 1940s Citrulline and Argininosuccinic acid After the role of, it has been fully understood. In this cycle, from ammonia and L-aspartic acid The amino group of L-ornithine, citrulline L-Arginine -Succinic acid and L-Arginine 。
Urea cycle is the main way for mammals and amphibians to excrete nitrogen containing metabolic wastes. But the same is true of other creatures, such as birds invertebrate , insects, plants, yeast, fungi and microorganisms.
Urea is basically a waste to biology, but it still has positive value. For example, urea in the renal tubules is introduced into the renal cortex to increase its osmotic concentration and promote water to permeate from the renal tubules back to the body for reuse.

Pharmacokinetics

After intravenous drip, it is filtered by the glomerulus, about 50% is resorbed from the renal tubules, and the remaining 50% is discharged from the renal tubules. If given a larger dose, it can increase the plasma osmotic pressure, produce dehydration and diuresis. Its action is rapid and powerful. It takes effect 15~30min after administration, reaches the peak in 1~2h, and lasts for 3~6h.

indication

Clinical application: brain edema, intracranial hypertension syndrome（ Intracranial hypertension ）Glaucoma is also used for oliguria after burns, surgery and trauma, and can promote urination after prostatectomy. External use can treat some skin diseases, such as making ointment or cream, which can soften the skin, prevent chapped hands and feet, and also can be used to stop itching. 15%~20% ointment is suitable for ichthyosis Chapped hands and feet Etc. High concentration ointment and hard ointment can be used to treat onychomycosis. Mucosa should not be used.

contraindication

As urea can increase non protein nitrogen in blood Renal insufficiency Severe shock and obvious dehydration, active intracranial hemorrhage And patients with high blood urea nitrogen levels.

matters needing attention

1. The urea aqueous solution is unstable in nature. The injection must be dissolved in 10% glucose solution before use, and must be used up within 24 hours to prevent ammonia release due to decomposition and toxicity. It cannot be reused after 24h.
2. Urea alone has hemolytic effect. 5% or 10% glucose injection or 10% invert sugar solution must be added for dilution Sterilized water for injection Dilution.
3. Urea should not spill to subcutaneous tissue when dripping. 0.25% in case of overflow procaine The injection was partially sealed and treated with heating or 50% magnesium sulfate wet compress.
4. Urea has many disadvantages and is rarely used in clinic.

Adverse reactions

1. If urea is stored for too long or the temperature of liquid medicine is too low, it may cause flushing, mental excitement Fidgety And other symptoms.
2. Urea is highly irritating, and the injection site may cause vein spastic pain, phlebitis or venous thrombosis; Leakage under the skin can cause local redness, swelling, blistering, or even Tissue necrosis 。 Occasionally, mild local irritation occurs.

Usage and dosage

For adults, 0.5~1g/kg is given once, and the infusion is completed within 20~30min. After 12 hours, the drug can be administered repeatedly, 1-2 times a day, generally for 1-3 days. External use: 1-2 times a day, and the dosage shall be adjusted according to the area of the lesion as per the doctor's advice.

poisoning

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Urea is a diuretic and dehydrating drug, and its effect is similar to mannitol. It is mainly used to treat brain edema, glaucoma, etc. The common dosage of the drug for intravenous or rapid intravenous drip is 0.5~1g/kg each time, and the infusion is completed within 20~30min.

clinical manifestation

There are few adverse reactions. If the drug is stored for too long or the temperature of the solution is too low, the injection may cause facial flushing, mental excitement, restlessness, headache and digestive tract reactions. If the medicine liquid leaks out of the blood vessel, it may cause local redness, swelling and blister.

treatment

The key points for treatment of urea poisoning are:
1. The leaked part can be sealed with 0.25% procaine, hot compress, or Ruyi Golden Yellow Powder 50% magnesium sulfate was applied externally.
2. Treat symptomatically. [3]

Pharmacopoeia information

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essential information

This product contains CH four N two O shall not be less than 99.5%.

character

This product is colorless prismatic crystal or white crystalline powder, almost odorless, salty and cool in taste. After being placed for a long time, it gradually produces weak ammonia odor, and the aqueous solution shows neutral reaction.
This product is soluble in water or ethanol, but insoluble in ether or chloroform.
melting point
The melting point of this product (general rule 0612) is 132~135 ℃.

identify

1. Take 0.5g of this product, heat it in a test tube, liquefy and release ammonia gas, continue to heat it until the liquid appears turbid, cool it, add 10mL of water and 2mL of sodium hydroxide test solution to dissolve it, add 1 drop of copper sulfate test solution, and it will appear purplish red.
2. Take 0.1g of this product, add 1mL of water to dissolve it, and then add 1mL of nitric acid to generate white crystalline sediment.
3. The infrared absorption spectrum of this product should be consistent with the control spectrum (spectrum set 210 figure).

inspect

chloride
Take 1.0g of this product and check it according to the law (general rule 0801). Compared with the reference solution made of 7.0mL of standard sodium chloride solution, it should not be more concentrated (0.007%).
sulfate
Take 4.0g of this product and check it according to the law (general rule 0802). Compared with the control solution made of 4.0mL of standard potassium sulfate solution, it should not be more concentrated (0.010%).
Insolubles in ethanol
Take 5.0g of this product and heat 50mL of ethanol. If there is any insoluble matter, filter it with a vertical melting glass crucible with constant weight at 105 ℃. Wash the filter residue with 20mL of hot ethanol and dry it at 105 ℃ to constant weight. The residual residue shall not exceed 2mg.
Ignition residue
Not more than 0.1% (general rule 0841).
heavy metal
Take 1.0g of this product, add 20mL of water to dissolve it, add 5mL of 0.1mol/L hydrochloric acid solution, and check according to the law (General Rule 0821, Method 1). The content of heavy metals should not exceed 20 parts per million.

Assay

Take about 0.15g of this product, precisely weigh it, put it into a Kjeldahl flask, add 25mL of water, 2mL of 3% copper sulfate solution and 8mL of sulfuric acid, slowly heat it until the solution turns clear green, continue heating for 30 minutes, cool it, add 100mL of water, shake it up, slowly add 75mL of 20% sodium hydroxide solution along the bottle wall, form a liquid layer, add 0.2g of zinc particles, connect the Kjeldahl flask with the condenser tube with a nitrogen balloon, And put the end of the condenser tube under the liquid level of a 500mL conical flask containing 50mL of 4% boric acid solution, gently swing the Kjeldahl flask to mix the solution evenly, heat and steam it, stop the steam distillation after the ammonia is completely digested, add a few drops of methyl red indicator solution into the digested solution, titrate it with hydrochloric acid titrant (0.2mol/L), and correct the titration result with blank test. Every 1mL of hydrochloric acid titrant (0.2mol/L) Equivalent to 6.006mg CH four N two O。

category

Cuticle softening cream.

Storage

Sealed storage.

preparation

1. Urea ointment.
2. Urea cream. [6]

security information

Announce
edit

Safety terminology

S24/25：Avoid contact with skin and eyes.
Avoid skin and eye contact.
S26：In case of contact with eyes, rinse immediately with plenty of water and seek medical advice.
After eye contact, immediately flush with plenty of water and seek medical advice.
S36：Wear suitable protective clothing.
Wear appropriate protective clothing.

Risk terminology

R36/37/38：Irritating to eyes, respiratory system and skin.
Irritating to eyes, respiratory system and skin.
R40：Possible risks of irreversible effects.
There may be risk of irreversible effects.
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