Dithizone Reagent, the lead reagent, is the most widely used organic chromogenic reagent in colorimetric analysis. It can be used to determine trace heavy metal ions, such as Pb, Hg, Zn, Cd, etc. The molecular formula is C6H5NHNHCSN=NC6H5. Appearance is a purple-black crystalline powder. Insoluble in water and inorganic acids. Soluble in chloroform and carbon tetrachloride, the solubility in chloroform is excellent, and the solution is green. Slightly soluble in hydrocarbon solvents. A metal replaces an active hydrogen atom in its molecule, and the nitrogen atom forms a coordination bond with the metal ion to form a chelate complex. The solution is orange or red, and the reaction is empathetic. It is easily oxidized by air and can be protected by adding sulfur dioxide aqueous solution.
Prepare as follows. 1. Preparation of phenylhydrazine dithiocarboxylate phenylhydrazine salt. 13g of phenylhydrazine was dissolved in 60ml of ether, and 5.2ml of carbon disulfide was added dropwise. The resulting white precipitate was filtered off and washed with ether to give about 15 g. 2—preparation of diphenyldithiosemicarbazide. The above product was placed in a beaker and heated in a water bath at 96-98°C. After the material was melted, hydrogen sulfide was released and turned into a light yellow jelly. If there is the evolution of ammonia gas, remove the hot bath and cool with water. Cool with ice again. Then cool with ice, add 15 ml of anhydrous ethanol, take out from the ice bath, and heat slightly with stirring. The colloidal substance becomes a crystalline product, suction filtration, and washed with ethanol to obtain about 7.5 g. 3. Preparation of it. The diphenyldithiosemicarbazide obtained above was added to an acidic potash solution (6g potassium hydroxide dissolved in 60ml anhydrous methanol), refluxed in boiling water 5min, taken out, and cooled in an ice bath. After filtration, the filtrate was acidified with sulfuric acid until the Congo red test paper changed color, and a dark blue precipitate was precipitated. The residue is treated with caustic potash solution and sulfuric acid again and washed with water after suction filtration until there is no sulfate radical. Dry at 40°C to obtain about 3 g of it.
2. Cool the mixture of phenylhydrazine and toluene to below 0°C, add carbon disulfide under stirring, and control the addition rate to maintain the reaction temperature at 60~70°C. Leave it for more than 10min, then heat up to 90~95°C, and the crystals dissolve. And start reacting. When a large number of crystals are precipitated, and the lead acetate reagent is slightly brown, the reaction is completed, filtered after cooling, and the crystals are washed with cold toluene and ethanol in turn, and the obtained white crystals are3. For the phenylthiocarbamide. Then, diphenylcarbazide was added to the methanol solution of potassium hydroxide, heated to reflux for 5~10min, cooled to about 30°C with ice water, filtered to remove insoluble matter, and 0.5mol/L sulfuric acid was added to the filtrate while stirring. Aqueous solution to solution to just the fruit red test paper is just acidic. The crystals obtained by filtration are washed with cold water, then dissolved in a 5% sodium hydroxide solution, and the insoluble are filtered off. The filtrate is cooled with ice water, and at the same time, it is acidified with cold 0.5mol/L sulfuric acid to Congo red. The test paper is just acidic. After the precipitation is complete, filter it. The purified crystals are thoroughly washed with ice water until the SO4 ion is qualified and then dried at 40 ° C to obtain the finished product, diphenylthiocarbazone.
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