Industrial Acetic Anhydride (2)

4 Test method

The reagents and water used in this standard, unless other requirements are specified, all refer to the analytical reagents and the tertiary water specified in GB/T6682

4.

4.

Measure according to GB/T3143, the capacity of the colorimetric tube is 100mL

4.

Measure according to Appendix A (standard appendix)

4.

4.

4.

The sample is hydrolyzed with excess sodium hydroxide standard solution to generate acetic acid

Take the same amount of sample and react with aniline to generate acetic acid

Calculate the acetic anhydride content based on the difference between the amount of sodium hydroxide consumed by the acetic acid produced by the hydrolysis reaction and the amination reaction

(CH ₃ CO) ₂ O+2NaOH→2CH ₃ COONa+H ₂ O

(CH ₃ CO) ₂ O+C ₆ H ₅ NH ₂ →C ₆ H ₅ NHCOCH ₃ +CH ₃ COOH

4.

a) Aniline: freshly distilled anhydrous reagent;

b) Cyclohexane : freshly distilled anhydrous reagent;

c) Methanol ;

d) Sodium hydroxide standard solution: c(NaOH)=1mol/L;

e) Hydrochloric acid standard titration solution: c(HCl)=1mol/L;

f) Phenolphthalein indicator solution: 5g/L ethanol solution

4.

General laboratory equipment and

a) Infusion bottle;

b) Erlenmeyer flask: with a ground glass stopper, with a capacity of 500mL

4.
2.
1.
4 Analysis steps

a) The first titration

Use a drip flask to weigh about 2g sample, accurate to 0.
0002g, and place it in an Erlenmeyer flask containing 50mL sodium hydroxide standard solution.
Cover the stopper and let it stand for 1h.
Add 40mL cyclohexane , 10mL aniline and 100mL methanol.
, Add 0.
5mL phenolphthalein indicator solution, titrate the excess sodium hydroxide with a hydrochloric acid standard titration solution until the pink color just disappears
.

b) The second titration

Weigh about 2g of the sample with a dropper bottle, accurate to 0.
0002g, and place it in another conical flask containing 20 mL of cyclohexane.
Cover the stopper and place it in an ice bath
.
Add 10 mL of ice-cooled aniline and 20 mL of cyclohexane, cap the bottle, and let it stand in an ice bath for 1 hour
.
Add 100mL methanol and 50mL sodium hydroxide standard solution, add 0.
5mL phenolphthalein indicator solution, and titrate the excess sodium hydroxide with a standard titration bath of hydrochloric acid until the pink color just disappears
.
At the same time, a blank test is carried out
.

4.
2.
1.
5 Expression of analysis results

The content of acetic anhydride X ₁ expressed in mass percentage is calculated according to formula (1):

In the formula: V ₀ -the volume of the standard titration solution of hydrochloric acid consumed in the blank test, mL;

V ₁ —The volume of the hydrochloric acid standard titration solution consumed in the first titration, mL;

V ₂ —The volume of hydrochloric acid standard titration solution consumed in the second titration, mL;

m ₁ —The mass of the sample taken for the first time, g;

m ₂ —The mass of the sample taken for the second time, g;

c—The actual concentration of hydrochloric acid standard titration solution, mol/L;

0.
1021—The mass of acetic anhydride expressed in grams equivalent to 1.
00mL hydrochloric acid standard titration solution [c(HCl)=1.
000mol/L].
Take the arithmetic mean of the results of two parallel determinations as the determination result, one of the results of the two parallel determinations The difference is not more than 0.
30%
.

4.
2.
2 Gas chromatography

Measure according to Appendix B (standard appendix)
.

4.
3 Determination of evaporation residue

Measure according to GB/T5324.
2
.

Take the arithmetic mean of the two parallel determination results as the determination result, and the difference between the two parallel determination results shall not exceed 0.
0005%
.