Potassium azide

inorganic compound

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Potassium azide is a kind of inorganic compound , the chemical formula is KN three , it is a colorless crystal at normal temperature and pressure, soluble in water, Slightly soluble in ethanol^{[3 ]} , insoluble in Ether 。

Chinese name: Potassium azide
Foreign name: Potassium azide
Azide potassium salt^[2]
Alias: Potassium trinitride
chemical formula: KN three
molecular weight: eighty-one point one one eight four zero
CAS login number: 20762-60-1

EINECS login number: 244-013-1
Melting point: 350 ℃ (decomposition)
Water solubility: Easily soluble in water
Density: 2.04 g/cm³^[2]
Appearance: Colorless crystal
PSA: forty-nine point seven five zero zero zero
Precision quality: eighty point nine seven two nine zero

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Physical and chemical properties

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1. Character: colorless crystal

2. Relative density: 2.04

3. Melting point (℃): 343

4. Solubility: insoluble in ether^[1] ， The solubility in 100g water is 41.4g (0 ℃), 49.6g (17 ℃), 105.7g (100 ℃). The solubility in 100g ethanol is 0.137g (16 ℃).^{[3 ]}

5. Stability: metal Azide If the total process is exothermic, it usually causes explosion. However, since the product is a simple substance, the decomposition heat is equivalent to the standard of the compound Enthalpy of formation 。 Where, and Sodium azide Different, the enthalpy of formation of potassium azide is negative, indicating a certain stability. alkali metal Azide does not explode, but decomposes smoothly.^{[4 ]}

Preparation method

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1. With Hydrazine With nitrite and Potassium hydroxide The reaction can produce potassium azide. The reaction is carried out in two steps.

Step 1: Preparation Butyl nitrite 。

Put a 2L large beaker in the ice salt cold bath, install an agitator on it, add 60mL water into the beaker, and slowly pour 8.7mL (1.5mol) of concentrated H two SO four Add it to water, keep it at 0 ℃, and slowly add 274mL (222g, 3mol) n-butanol while stirring.

In another 1.5L beaker, add 900mL of water and dissolve 228g (3.3mol) Sodium nitrite This solution also needs to be cooled to 0 ℃. Then slowly add NaNO2 solution to the above mixed solution under continuous stirring, which takes about 1h. Generated Butyl nitrite Float on the surface to separate the upper oil. Add water to the solution at the lower layer to shake, and oil will be separated again. Repeat the operation until the oil is completely separated.

Mix 45g of sodium chloride with sodium bicarbonate 5g is dissolved in 180mL water, and butyl nitrite is washed with this solution three times, 60mL each time. Butyl ester in Anhydrous sodium sulfate The yield is about 87%~94%, about 270~290g.

Step 2: Prepare potassium azide

Apply 70g Potassium hydroxide Add 500mL Anhydrous ethanol Heat to dissolve it, settle, pour the upper clear liquid into a 1L ground flask, install a reflux condenser tube, add 10g 85% hydrazine hydrate (hydrazine) to the flask, put the flask on a steam bath and heat it slightly, and add 15g at the same time Butyl nitrite Make it react. Remove the steam bath, and add 110g butyl ester (125g, 1.2mol in total) to the solution under the control of temperature and reflux rate, which takes about 1h. Put the flask on the steam bath and heat it for 15min to ensure that the reaction is completed. If the reaction is further carried out, potassium azide will precipitate and be cooled, filtered and washed in an ice bath. 50mL cold absolute ethanol will be used for washing four times each time. Then use Anhydrous ether 125mL and 100mL were washed twice, and the product was dried in air at 55~60 ℃ with a yield of 78%~84% and about 63~69g. The purity of the product thus obtained is 98.9%. If higher purity products are needed, they can be recrystallized in ethanol water solution.

2、 Azide acid, potassium hydroxide or Potassium carbonate It is prepared by neutralization reaction of aqueous solution.^{[3 ]}

Azide acid NaN three It is made by mixing and distilling with 6% sulfuric acid. Azide acid treatment is troublesome, and this method is generally not used to prepare potassium azide.^[1]

application area

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find Thiourea 、 Sodium nitrite and hydroxylamine hinder catalase The function of catalase usually prevents seed germination. Dormant seeds germinate due to catalase inactivation. If the above compounds are used to force weed seeds to germinate before winter starts, the weed seedlings will freeze to death, thus playing a role in weed control. After applying a small amount of potassium azide (herbicide), the weed seeds germinate. Potassium azide can promote the development of crops or seeds that are difficult to germinate.^[1]