Methyl orange itself is weakly alkaline, and the color change range is between pH 3.1~4.4.The color change range of methyl orange is red when pH ≤ 3.1 and orange when pH ≤ 3.1~4.4,It is yellow when pH ≥ 4.4.
Put p-aminobenzenesulfonic acid and 10mL 5% sodium hydroxide solution into the beaker, and heat to dissolve.Take another small test tube and dissolve 0.8g sodium nitrite in 6mL water.Then pour the sodium nitrite solution into the cooled p-aminobenzenesulfonic acid solution, and cool it to below 5 ° C with ice salt bath.
Add 3mLconcentrated sulfuric acid(orConcentrated hydrochloric acid）Dilute it with 10mL of water, slowly drip it into the above cooling mixture under constant stirring, keep the temperature below 5 ° C, and check the blue color with starch potassium iodide test paper after adding.In addition, if it does not appear blue, add sodium nitrite solution.[2]
2. Coupling reaction
Mix 1.3mL in a tubeN. N-dimethylanilineAnd 1mLGlacial acetic acidAnd slowly add it to the diazonium salt solution.After adding, continue mixing for 10min, and then slowly add 5%sodium hydroxideSolution (about 25mL) until the reactant turns orange.The crude methyl orange is precipitated in the form of fine particles.The reactant was heated in a boiling water bath for 5 min, cooled to room temperature, and then cooled in an ice water bath to completely separate methyl orange crystals.Filter, collect and crystallize, wash with a small amount of water, ethanol and ether in turn, and press dry.
Dissolve a little methyl orange in water, add a few drops of dilute hydrochloric acid, then neutralize it with dilute sodium hydroxide solution, and observe the color change.[2]
Industrial process
1. ByP-aminobenzenesulfonic acidAfter diazotization andN. N-dimethylanilineReaction.Will beSulfamic acidDissolve in 2.5% sodium carbonate solution, addSodium nitriteAfter complete dissolution, add crushed ice and hydrochloric acidDiazotization reaction, precipitation of diazonium salt crystals.Add N to the diazonium salt solution,N-dimethylaniline andGlacial acetic acidAfter stirring for 10min, slowly add 10% sodium hydroxide solution to alkalinity.Cooling crystallization, filtering, washing with saturated salt water, drying, recrystallization with water to obtain methyl orange.
2. In an enamel container containing 6L 2mol/L sodium hydroxide, add 2kg p-aminobenzenesulfonic acid, and heat it to completely dissolve it (the solution is alkaline to litmus test paper).Then add 800g sodium nitrite, stir and dissolve it, and cool it with ice to 5 ℃.The obtained solution is slowly added to the mixture of 5L 2mol/L hydrochloric acid and 10kg crushed ice under continuous stirring, cooled, and left for 15min.useStarch potassium iodide test paperDetermine the end point of diazotization reaction (the test paper turns blue).The prepared solution is added to the prepared 1200gN under stirring,In the cold solution of N-dimethylamine and 10L 1mol/L glacial acetic acid, mix evenly, stand for 10min, slowly add 20% sodium hydroxide solution to obvious alkalinity, and precipitate yellow scale like methyl orange crystals.After the crude product is heated to be completely dissolved, add 2kg of chemically pure salt, heat and stir until it is dissolved, cool and crystallize with water, filter by suction, then dissolve it with a small amount of hot distilled water (dissolve 1g of crystal per 20mL of hot water), filter it while hot, cool and crystallize the filtrate, suck it dry, wash it with a small amount of ethanol and ether in turn, and dry it to get the finished product.[1-2]
Main purpose
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Methyl orange is a commonly used acid-base titration indicator in analytical chemistry, which is not suitable for the titration of organic acid compounds.The pH of the aqueous solution with the concentration of 0.1% is 3.1 (red)~4.4 (yellow), which is suitable for the titration between strong acids, strong bases and weak bases.It is also used for spectrophotometric determination of chlorine, bromine and bromine ions, and for biological dyeing.
Methyl orange has been used in the laboratory and industrial and agricultural production as the pH control of chemical reactions, as well as the acid-base titration analysis of chemical products and intermediates.The disadvantage of methyl orange indicator is that the yellow red color is difficult to identify and has been replaced by a wide range of indicators.Methyl orange is also a kind ofazo dyeIt can be used for printing and dyeing textiles.
Properties and stability
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Use and store according to specifications, without decomposition, and avoiding contact with oxides
Storage method
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1. Store in a cool, dry and well ventilated warehouse.Keep away from kindling and heat sources.Protect from direct sunlight.
2. Packing and sealing.It shall be stored separately from acids and edible chemicals, and mixed storage is strictly prohibited.
3. The storage area shall be equipped with appropriate materials to contain leakage.[1]
toxicology data
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acute toxicity
Rat oral LDfifty: 60mg/kg, no detailed description except for lethal dose;
Mouse intraperitoneal LCfifty: 101mg/kg, no detailed description except for lethal dose.
Mutagenic data
Microbial organism TEST system mutation: bacteria Salmonella typhimurium: 500 μ g/plate;
