Background and overview[1][2]
Phosphorous acid decomposes into phosphine and orthophosphoric acid at 200°C. It is extremely hygroscopic and easily soluble in water and ethanol. It can gradually be oxidized to orthophosphoric acid when exposed to air. Although there are three hydrogen atoms in the chemical formula of phosphorous acid, it can only dissociate into two hydrogen ions in water. It is a dibasic acid, and its strength is close to that of the second strong acid (K1=1.6×10-2, K2=7×10-7). It has two types of salts, acid salts (such as NaH[PHO3]) and normal salts (such as Na2[PHO3]), With the exception of alkali metal salts, most salts are poorly soluble in water.
Phosphorous acid has strong reducing properties and can reduce silver ions to elemental silver; it can reduce divalent mercury ions to monovalent mercury ions or mercury; it can reduce sulfurous acid to elemental sulfur, etc. Phosphorous acid is usually used as a chemical reagent, reducing agent, and for making phosphite. The oxidizing property of phosphorous acid is not obvious, but the following disproportionation reaction occurs at 200°C.
The synthesis route of phosphorous acid generally adopts: 1) hydrolysis method, that is, hydrolyzing phosphorus trichloride, purifying it with steam, and cooling and crystallizing it; 2) dissolving phosphorus trichloride into concentrated hydrochloric acid, and then evaporating the hydrochloric acid at low temperature Obtained; 3) It can also be generated by the slow interaction of phosphorus trioxide with water.
There are also studies using phosphorus trichloride, saturated solution of phosphorous acid, and water as raw materials, and using hydrolysis reaction kettles, concentrated crystallization kettles, and centrifugal dryers as equipment. Through the hydrolysis of phosphorus trichloride, the crystallization of crude phosphorous acid, Phosphorous acid is produced through centrifugal drying and other processes. The main advantages of this method for producing phosphorous acid are: the equipment used is general-purpose equipment, the production cycle is short, there is no emission of toxic and harmful gases and liquids, the by-product hydrogen chloride gas can be recycled into hydrochloric acid, and the obtained product is industrial grade phosphorous acid.
Apply[3][4]
Phosphorous acid is used as a reducing agent, pesticide intermediate, and nylon whitening agent; it is a raw material for manufacturing phosphite, plastic stabilizers and organophosphorus pesticides; phthalocyanine pigments are used for polycarbonate Stabilizer, it is also used as an antioxidant for nylon 1010; as a chemical reagent, it can also be used to produce aminotrimethylenephosphonic acid, a high-efficiency water treatment agent. Examples of its application are as follows:
1. Use phosphorous acid or phosphite to prepare lithium iron phosphate cathode material.
The preparation method is as follows: mix lithium compounds, ferrous salts, phosphates, phosphorous acid or phosphites, add carbon compounds, then add wet grinding media, ball mill and mix, then vacuum dry, and dry the The powder is sintered to prepare lithium iron phosphate cathode material.
The lithium compound is lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate, lithium nitrate, lithium fluoride or lithium phosphate or a mixture thereof; the ferrous salt is ferrous oxalate, ferrous acetate, ferrous chloride Iron, ferrous sulfate or ferrous carbonate or a mixture thereof; phosphate is ammonium phosphate, diammonium hydrogen phosphate or ammonium dihydrogen phosphate or a mixture thereof; the molecular formula of phosphite is AH2 PO3 or A2HPO3, EHPO3 or E(H2 PO3)2 and or G(H2PO3)3; carbon-containing compounds are polypropylene, polyacrylamide, polyvinyl alcohol , glucose, sucrose or starch or a mixture thereof. The preparation process of the invention is simple, less time consuming, and the material has good circulation properties under large current discharge conditions.
2. Prepare an organometallic phosphorous acid complex.
The traditional method is to simply compound metal soap and phosphite to obtain a heat stabilizer, which cannot maximize the synergistic effect between metal soap and phosphite. There is research on reacting organic acids, metal oxides or metal hydroxides with dispersants to obtain organic acid metal salts; then reacting phosphorous acid and phosphite, and removing alcohol and phenol under vacuum to obtain acid phosphite; then organic acid metal salts are obtained. The reaction of salt and acid phosphite gives organometallic phosphite complex.
The organometallic phosphite complex synthesized by the above method can well exert the synergistic effect between metal soap and phosphite, which can greatly improve the initial coloration and long-term stability of PVC products. At the same time, it can Slow down the occurrence of “zinc burning” phenomenon.
Preparation[1][5]
Method 1: Phosphorous acid can be hydrolyzed from phosphorus trichloride, and the resulting solution is prepared by evaporating the hydrochloric acid at low temperature, dehydrating and cooling:
Method 2: A method of producing phosphorous acid by utilizing high boiling by-products of dialkyl phosphite. The molecular structural formula of the dialkyl phosphite is (RO)2P(OH), where R is carbon Alkyl group with 1 to 3 atoms. Adding hydrohalic acid or passing hydrogen halide into the high boiling substance causes the alkyl phosphite and polymer in the high boiling substance to undergo an acidolysis reaction to generate phosphorous acid, and the alkoxy group on the phosphono group is acidolyzed to halogen. Substitute hydrocarbons, and the product is a phosphorous acid aqueous solution; the phosphorous acid aqueous solution is concentrated and crystallized to obtain phosphorous acid crystals, and the mother liquor can be recycled to the acidolysis reaction or crystallization.
The characteristic of this new treatment process is that it can not only obtain phosphorous acid of various specifications, but also obtain by-product halogenated hydrocarbons, improve the atom utilization rate in the production of dialkyl phosphite, and reduce environmental pollution.
Main reference materials
[1] Encyclopedia of Chinese Middle School Teaching·Chemistry Volume
[2]一Production method of phosphorous acid. CN201310168814.1, application date 20130509
[3] Tong Qingsong; Lu Yang; Shi Jicheng; Huang Weijing; Li Bianyun. A method of preparing lithium iron phosphate cathode material using phosphorous acid or phosphite. CN200810071496.6, application date 20080731
[4] Xu Huizhi; Ge Qinqin; Shen Wei; Tan Lili; Lai Lei; Hu Juan; Bao Jiejie. Synthesis method and application of organometallic phosphorous acid complex. CN201410265224.5, application date emulsifier 20140613
[5] Wang Wei; Zhou Shuguang; Zhong Lianfa; Wang Qunxiao; Zheng Hongchao; Jiang Dong; Yang Wancheng; Tu Minghai. Method for producing phosphorous acid by using high boiling by-products of dialkyl phosphite. CN200310109095.2, application Day 20031202
