Safety specifications for the preparation of anhydrous solvents (1)

Many reactions in the laboratory often use anhydrous solvents or absolutely anhydrous solvents

As to the concept of anhydrous and absolutely anhydrous, there is no clear boundary so far

To determine whether an anhydrous or absolutely anhydrous solvent meets the reaction requirements, it is necessary to determine the trace amount of water in it, which can be detected with anhydrous copper sulfate powder.

1.

The preparation of absolutely anhydrous organic solvents generally requires a gradient operation process: from industrial grade with higher water content, through pretreatment to chemical purity (CP) or analytical purity (AR), then to anhydrous grade, and the final step is absolutely anhydrous Level

The physical method is through fractionation purification and 3A type molecular sieve (pore size 3A) or 4A type molecular sieve (pore size 4A) to remove water

The chemical method is generally to use CaO, CaH ₂ , Na, Mg and other desiccants to react with water to remove water:

CaO-H ₂ O=Ca(OH) ₂

CaH ₂ +2H ₂ O=Ca(OH) ₂ +2H ₂ ↑

2Na+2H ₂ O=2NaOH+H ₂ ↑

Mg+H ₂ O=MgO-H ₂ ↑

(1) Preparation of absolutely absolute ethanol

The first physical method: because 95.

The second chemical method: add calcium oxide (quicklime) and heat it to reflux, so that the water in the ethanol reacts with the quicklime to generate calcium hydroxide , and then the anhydrous ethanol is evaporated

The third step of the chemical method: processing with metallic magnesium or metallic sodium to prepare absolutely absolute ethanol (purity greater than 99.

1.

(1) Confirm that the heating devices such as electric heating mantle, round bottom flask, Soxhlet extractor (Figure 23-11 or Figure 23-12) are in good condition, the condensed reflux water is normal, the rubber tube is not aging or broken, and the nitrogen protection device is normal

(2) Confirm that the distillation unit is fully assembled

(3) Anhydrous ethanol , metal magnesium chips, and iodine with a water content of less than 0.

(4) Add 80g of magnesium metal chips to a 10L three-necked flask, and then add 500mL of absolute ethanol .

Figure 23-11 Soxhlet extractor

Figure 23-12 Improved Suotian Extractor

(5) Confirm that the condensate is turned on and maintain the proper flow rate, turn on the power switch, and adjust the transformer to the proper position

(6) Under the protection of nitrogen (or attach an anhydrous calcium chloride drying tube to the condenser), heat the anhydrous ethanol , add 5-6 iodine particles, and continue to heat the mixture to reflux all the magnesium Disappear
.
If the reaction has not started after adding iodine, you can add a few more iodine particles.
If the water content of the ethanol exceeds 0.
5%, it will be difficult to initiate
.

(7) After it is slightly cooled, 8L of absolute ethanol is added , and then the solution is heated to reflux
.

(8) After more than 3 hours of reflux, start to collect
.

(9) Transfer the collected solvent into a dry solvent bottle, fill it with nitrogen, screw the bottle cap tightly and seal it with a parafilm
.

(10) After processing about 20L of absolute ethanol , add water to the three-necked bottle to dispose of the residue.

2.
Specific operating procedures for the production of absolute absolute ethanol from metallic sodium

The equipment and operation are the same as above, and sodium metal is used instead of magnesium metal
.
Sodium metal should be taken in advance with a special sodium wire extrusion mechanism, or cut into small pellets to increase the specific surface area of ​​sodium
.
Be sure to add zeolite before heating.
If you forget to add it, you must cool it down to room temperature before adding it.
Otherwise, bump boiling will occur and cause a fire
.
Add 1g of benzophenone indicator to detect moisture
.
After the above was refluxed for 4h, was added 20mL gentle boiling at slightly cooler where diethyl phthalate or diethyl oxalate to remove the sodium hydroxide generated
.
Start collecting after being qualified
.
The residue (remaining sodium wire) can be treated with more than 95% ethanol
.

After using the sodium wire squeezing mechanism to take or cut, some sodium scraps may be produced, which must be picked up carefully and collected thoroughly to avoid future problems
.
The concentrated sodium shavings should be carefully put into petroleum ether, and then treated with ethanol to completely dissolve
.
Do not pour ethanol directly on the sodium crumbs, nor pour petroleum ether or ethanol containing sodium crumbs into the water (the resulting fire burned the hands and feet of an employee), and another R&D staff mistakenly set the water content The higher ethanol is petroleum ether .
When the sodium wire of the sodium wire extruder is squeezed into the ethanol with higher water content, it reacts violently and catches fire.
The fire-fighting spray on the ceiling of the laboratory starts, and the entire laboratory is filled instantly.
Water, the situation was not controlled until the fire brigade was dispatched
.