Background and overview[1][2]
Ethylene phosphorus (chloroethylphosphonic acid) is a plant growth regulator that slowly releases ethylene when the pH value is greater than 3, and the residue is non-toxic and harmless phosphate. Ethylene is an excellent plant growth regulator. It plays an important role in growth processes such as seed germination, plant growth, flowering, fruit ripening, tissue senescence and shedding. In addition, when plants are exposed to harsh environmental stress, attack by pests and diseases, or mechanical damage, ethylene can respond quickly and enhance various plant resistances.
However, since ethylene is often a gaseous substance and cannot be used directly in the field or outdoors, the application of ethylene on plants is greatly limited. The synthesis of vinyl phosphorus provides the possibility for the application of ethylene on plants. The pH value of plant tissue cell fluid is generally greater than 4. Ethylene phosphorus sprayed on the plant surface enters the functional plant tissue through plant seeds, leaves or fruits, and then the ethylene released has the same effect as the endogenous ethylene hormone. Ethylene phosphorus’ ripening technology for bananas and other agricultural products has been used around the world for more than 100 years, and has been used in my country for nearly 50 years.
Vinyl phosphorus has been gradually popularized in my country for applications in rubber flow, fruit ripening, tobacco leaf yellowing, and grain production due to its ability to increase plant milk secretion, accelerate maturation, abscission, senescence, promote flowering, and control growth. Greening and increasing production of crops and melons, and increasing the sugar content of sugarcane. At present, there are more than 50 kinds of food and cash crops that use ethephon all year round around the world, and it has broad application prospects in agriculture and horticulture.
Physical and chemical properties[1]
Vinyl phosphorus is a plant growth regulator that promotes maturation and is widely used in cotton, rubber, bananas, tomatoes, tobacco leaves, rice and other plants. The chemical name of vinyl phosphorus is 2-chloroethylphosphonic acid. It has good water solubility and is used on crops, usually using aqueous agents. Currently, 40% vinyl phosphorus aqueous agents are widely used. In order to reduce the cost of packaging and transportation and improve the use effect, manufacturers try to increase the concentration of vinyl phosphorus aqueous agent. At present, the conventional vinyl phosphorus technical material is solid vinyl phosphorus with a content of 80%-90%.
The concentration range of the ethephon aqueous agent prepared from the above-mentioned raw materials is generally 65%-70%. If the concentration is above 70%, solid ethylene phosphorus will precipitate during the 0°C cold storage test, affecting storage and use. . It has been reported that 80%-90% ethylene phosphorus original drug is used, ammonia gas is introduced during the preparation process, or ammonium bicarbonate is added to change the freezing point of the ethylene phosphorus solution diethanolamine, and 70%-80% diethanolamine can be prepared. Liquid vinyl phosphorus. However, the above method adds ammonia or ammonium bicarbonate, which increases the cost of raw materials in the production process. The total production cost of the enterprise cannot be saved, and there is no advantage in market competition.
Preparation [2]
The synthesis of vinyl phosphorus was first reported by Kabachnik MI and Rossiiskaya PA in 1946, and was subsequently reported in many literatures. According to its reaction mechanism, it can be divided into two main types. One is through Michaelis-Arbuzon rearrangement reaction, which mainly includes the synthesis method using ethylene oxide as raw material and phosphoric acid or alkyl phosphonate as raw material; the other is through free radical reaction. The reaction can be a synthesis method of reacting phosphite diester with vinyl chloride or vinyl acetate.
my country’s industry currently uses the phosphorus trichloride-ethylene oxide method to produce ethylene phosphorus. The reactions in each step are as follows:
(l) Esterification reaction of phosphorus trichloride and ethylene oxide
(2) Rearrangement reaction of tris(2-chloroethyl)phosphite
Acidolysis of (3) 2-chloroethylphosphonate di(2-chloroethyl) ester
This method has the advantages of lower raw material cost and simpler process operation using the original dispersant imported from Germany, but it also has the disadvantages of low selectivity of each reaction step and more impurities. The main by-product in the esterification reaction is chloroethanol, which is produced due to the reaction between hydrogen chloride in phosphorus trichloride and ethylene oxide; the main by-product in the rearrangement reaction is chloroethanol, which is generated by dehydration of chloroethanol at high temperature. The dichloroethane and phosphonous acid, 2-chloroethylphosphonic acid diester produced by the reaction of ethyl chloride, chloroethanol and phosphorus trichloride remove one molecule of dichloroethane or one molecule of hydrogen chloride in the molecule, or the cyclic ester or Vinyl phosphonic acid diester; the main by-products in the acidolysis reaction are vinyl phosphoric acid produced by the reaction of vinyl phosphoric acid diester and hydrogen chloride, and hydroxyethyl produced by the reaction of 2-chloroethylphosphonic acid and a small amount of water in hydrogen chloride. During the acidolysis process of phosphonic acid and high temperature for a long time, part of the ethylene phosphorus undergoes intermolecular and intramolecular dehydration to form ethylene phosphoric anhydride; during the production process, the fluctuating process conditions corrode the equipment, causing the product to contain metal compounds.
Detection method
The current detection methods for ethylene phosphorus mainly include automatic potentiometric titration, headspace GC, capillary GC, ion chromatography, etc. The analysis methods of vinyl phosphorus aqueous agent in the national standard are acid-base titration volumetric method and diazomethane methyl ester derivatization-gas spectrometry method. Phosphoric acid, phosphorous acid and the product vinyl phosphorus are mostly used in industrial production.The acid-base titration method is used for detection. This detection method cannot effectively distinguish between acid anhydride and vinyl phosphorus, resulting in a large error between the detection results and the analysis results such as gas chromatography. In 2009, the country issued new vinyl phosphorus standards, requiring the purity of vinyl phosphorus to be no less than 89%, and it was implemented on July 1, 2010.
