A. Reagents
355 mL of 10wt% NaOCl solution (0.55 mole)
47.8g of NaOH (1.20 mole)
34.1g of urea (0.57 mole)
0.47g gelatine
122 mL of 31% HCl (1.18 mole)
37.5mL of conc (92%) H2SO4 (0.64 mole)
30mL of 70% isopropyl alcohol
15mL of anhydrous isopropyl alcohol
water
B. Equipment
fume hood
1 quart jar with threaded lid
1-liter mL Erlenmeyer flask
250 mL pressure-equalizing (P-E) dropping funnel
24/40 to 19/22 reducing adaptor
24/40 Keck clamp
#9 rubber stopper with ½” dia hole
2 quart plastic funnel
plastic plate to cover mouth of funnel
magnetic stirrer/hotplate
3” magnetic stir bar
15cm Buchner funnel with filter paper
fridge for cooling to at least 8ºC (46ºF)
freezer
thermometer
small watch glass for the 1-liter E. flask
small watch glass for P-E dropping funnel fill port
bowl for use as a cooling pan for the 1-liter E. flask
ceramic dinner plate
ringstand with clamp for P-E dropping funnel
25mL beaker
250mL beaker
stirring rod
125mL Erlenmeyer flask w/stopper
250mL Erlenmeyer flask w/stopper
C. Cautions
1. Hydrazine is highly toxic.
2. Hydrazine is an environmental hazard.
3. Hydrazine is flammable.
4. Hydrazine is destroyed by air.
D. Procedure
a. Prepare the Cold NaOCl/NaOH Solution
1. Place 355mL of 10% NaOCl solution in a 1-quart jar with screw cap and cool to at least 8°C (46°F) in a fridge (or freezer).
2. Using a magnetic stirrer mix in NaOH to the cooled NaOCl solution in two 23.9g portions, cooling in between to 8°C. Try not to let the temperature rise above 20°C. Then chill in the fridge to 5-8°C.
b. Prepare the Urea/Gelatine Solution
1. Place 3mL of water in a 25mL beaker. Sprinkle in the 0.47g of gelatine, breaking it up and dispersing it with a stirring rod. Add 15mL of boiling water and stir the gelatine until dissolved.
2. Add 20mL of hot water to a 250mL beaker. Then add 34.1g of urea and stir until dissolved.
3. Pour the gelatine solution into the urea solution and stir until mixed.
c. Form the Hydrazine Solution
This is to be done in the hood as hydrazine is toxic.
(H2N)2C=O + NaOCl + 2 NaOH → N2H4 + H2O + NaCl + Na2CO3
(Hofmann degradation)
Note: A viscous, voluminous foam will be quickly formed in the following reaction. Vigorous action by the large magnetic stir bar will help keep it beaten down.
1. Place the 3” stir bar in the 1-liter E. flask and place on the magnetic stirrer/hotplate.
Insert the plastic funnel in the one-hole stopper.
Note: The following reaction should be allowed to take place for a few minutes before supplemental heating is applied. As the foam begins to dissipate heat is to be applied to steadily drive the reaction to completion at boiling.
2. Retrieve the hypochlorite solution from the freezer.
3. When the hypochlorite solution has warmed to 5-8°C, set the stir bar at speed 3 and pour the hypochlorite solution into the E. flask. Install the plastic funnel w/stopper in the E. flask. Then quickly pour in the urea/gelatine solution through the funnel into the vortex. Immediately raise the stir bar speed as required.
4. Cover the funnel with a plastic plate. The reaction initiates immediately and a snow white foam will rise to fill the flask to about the 900mL level, but possibly may even overflow into the funnel. After a few minutes the foam will begin to subside and the solution will turn translucent orange, and heat up. Turn down the stir rate to prevent foam generation. Apply heat steadily to drive the solution to boiling. The color will fade to a pale yellow then to almost clear. The clear color indicates the endpoint of the reaction. At this point heating is stopped.
5. Remove the overflow funnel and place a small watch glass over the mouth of the flask to exclude air. The watch glass will allow any CO2 to escape and also prevent a vacuum from forming. Cool the flask well in an ice bath. This is in preparation for the neutralization, during which an exotherm will be generated.
d. Neutralization with HCl
This should be done in the hood as considerable CO2 is released.
2HCl + Na2CO3 --> 2NaCl + CO2 + H2O + heat
1. While the reaction mixture is cooling measure out 122 mL of 31% HCl into a 250 mL E. flask, stopper, and place in the freezer to cool.
2. Prepare a diluted sulfuric acid solution of 38mLs of conc sulfuric acid diluted with 33 mLs of water in a 125mL E. flask. Stopper and place in the freezer to prepare for the formation of the hydrazine sulfate.
3. Attach a 24/40 to 19/22 adaptor to a 250 mL pressure-equalizing dropping funnel using a Keck clamp. Insert the outlet of the adaptor into the #9 one-holed stopper. Support the addition funnel with a ringstand and clamp and insert the stopper in the 1-liter E. flask. Add the cooled HCl from the freezer to the P-E dropping funnel (valve closed!). Place a small watch glass over the fill port of the P-E dropping funnel. This excludes air, which destroys hydrazine, yet allows the CO2 to escape as the HCl is being added. Add the HCl at 1 drop/sec to the hydrazine solution stirred on the stirrer/hotplate. The mixture will warm up.
e. Formation of Hydrazine Sulfate
NH2-NH2 + H2SO4 --> [N2H5]HSO4
1. Close the valve on the P-E dropping funnel and add the cooled/diluted sulfuric acid.
2. To the rapidly stirring mixture add the dilute sulfuric acid at 2 drops/sec. Reduce the drip rate to control foaming if necessary.
3. Continue stirring and slow the drip rate to about 1 drop/sec as crystals of hydrazine sulfate begin to appear. Stir for one hour past the addition point.
4. Place a small watch glass on the mouth of the E. flask and set aside in a cool place overnight. CO2 may continue to vent.
5. Just prior to filtering the crystals cool the flask in an ice bath for at least an hour.
f. Filtering the Crystals
1. Set up the 15cm Buchner funnel with filter paper for vacuum filtration.
2. Stir the E. flask to loosen any CO2 bubbles and clumps of crystals.
3. Remove the stir bar from the flask.
4. Decant the supernate and save it for washing crystals out of the flask.
5. Pour the crystal slurry onto the Buchner funnel and suck the supernate from the crystals.
6. Flood the wet but drained crystals with 30 mL of 70% isopropyl alcohol, stirring with a stirring rod.
7. Use a final rinse of 15 mL of anhydrous isopropyl alcohol
8. Remove the filter paper with crystals and wick away any excess liquid on a blotter paper or paper towels.
9. Air dry the crystals on a dinner plate.
E. Expected Yield
The expected yield for Mr. A’s full scale batch is about 60% based on the amount of hypochlorite used. For this reduced scale that would be 41 to 44g (0.33 mole). MP of hydrazine sulfate is 254 °C per the Baker MSDS.
F. References
1. Improved procedure of Mr. Anonymous, posted on SM 6/7/2003.
2. SM post of garage chemist on 5/19/07 providing an improvement and a reduced scale.
3. Merck patent GB392845, upon which Mr. A’s procedure is based.
4. Wikipedia entries for “hydrazine” and “Hofmann degradation.”
http://www.sciencemadness.org/talk/viewthread.php?tid=15091
355 mL of 10wt% NaOCl solution (0.55 mole)
47.8g of NaOH (1.20 mole)
34.1g of urea (0.57 mole)
0.47g gelatine
122 mL of 31% HCl (1.18 mole)
37.5mL of conc (92%) H2SO4 (0.64 mole)
30mL of 70% isopropyl alcohol
15mL of anhydrous isopropyl alcohol
water
B. Equipment
fume hood
1 quart jar with threaded lid
1-liter mL Erlenmeyer flask
250 mL pressure-equalizing (P-E) dropping funnel
24/40 to 19/22 reducing adaptor
24/40 Keck clamp
#9 rubber stopper with ½” dia hole
2 quart plastic funnel
plastic plate to cover mouth of funnel
magnetic stirrer/hotplate
3” magnetic stir bar
15cm Buchner funnel with filter paper
fridge for cooling to at least 8ºC (46ºF)
freezer
thermometer
small watch glass for the 1-liter E. flask
small watch glass for P-E dropping funnel fill port
bowl for use as a cooling pan for the 1-liter E. flask
ceramic dinner plate
ringstand with clamp for P-E dropping funnel
25mL beaker
250mL beaker
stirring rod
125mL Erlenmeyer flask w/stopper
250mL Erlenmeyer flask w/stopper
C. Cautions
1. Hydrazine is highly toxic.
2. Hydrazine is an environmental hazard.
3. Hydrazine is flammable.
4. Hydrazine is destroyed by air.
D. Procedure
a. Prepare the Cold NaOCl/NaOH Solution
1. Place 355mL of 10% NaOCl solution in a 1-quart jar with screw cap and cool to at least 8°C (46°F) in a fridge (or freezer).
2. Using a magnetic stirrer mix in NaOH to the cooled NaOCl solution in two 23.9g portions, cooling in between to 8°C. Try not to let the temperature rise above 20°C. Then chill in the fridge to 5-8°C.
b. Prepare the Urea/Gelatine Solution
1. Place 3mL of water in a 25mL beaker. Sprinkle in the 0.47g of gelatine, breaking it up and dispersing it with a stirring rod. Add 15mL of boiling water and stir the gelatine until dissolved.
2. Add 20mL of hot water to a 250mL beaker. Then add 34.1g of urea and stir until dissolved.
3. Pour the gelatine solution into the urea solution and stir until mixed.
c. Form the Hydrazine Solution
This is to be done in the hood as hydrazine is toxic.
(H2N)2C=O + NaOCl + 2 NaOH → N2H4 + H2O + NaCl + Na2CO3
(Hofmann degradation)
Note: A viscous, voluminous foam will be quickly formed in the following reaction. Vigorous action by the large magnetic stir bar will help keep it beaten down.
1. Place the 3” stir bar in the 1-liter E. flask and place on the magnetic stirrer/hotplate.
Insert the plastic funnel in the one-hole stopper.
Note: The following reaction should be allowed to take place for a few minutes before supplemental heating is applied. As the foam begins to dissipate heat is to be applied to steadily drive the reaction to completion at boiling.
2. Retrieve the hypochlorite solution from the freezer.
3. When the hypochlorite solution has warmed to 5-8°C, set the stir bar at speed 3 and pour the hypochlorite solution into the E. flask. Install the plastic funnel w/stopper in the E. flask. Then quickly pour in the urea/gelatine solution through the funnel into the vortex. Immediately raise the stir bar speed as required.
4. Cover the funnel with a plastic plate. The reaction initiates immediately and a snow white foam will rise to fill the flask to about the 900mL level, but possibly may even overflow into the funnel. After a few minutes the foam will begin to subside and the solution will turn translucent orange, and heat up. Turn down the stir rate to prevent foam generation. Apply heat steadily to drive the solution to boiling. The color will fade to a pale yellow then to almost clear. The clear color indicates the endpoint of the reaction. At this point heating is stopped.
5. Remove the overflow funnel and place a small watch glass over the mouth of the flask to exclude air. The watch glass will allow any CO2 to escape and also prevent a vacuum from forming. Cool the flask well in an ice bath. This is in preparation for the neutralization, during which an exotherm will be generated.
d. Neutralization with HCl
This should be done in the hood as considerable CO2 is released.
2HCl + Na2CO3 --> 2NaCl + CO2 + H2O + heat
1. While the reaction mixture is cooling measure out 122 mL of 31% HCl into a 250 mL E. flask, stopper, and place in the freezer to cool.
2. Prepare a diluted sulfuric acid solution of 38mLs of conc sulfuric acid diluted with 33 mLs of water in a 125mL E. flask. Stopper and place in the freezer to prepare for the formation of the hydrazine sulfate.
3. Attach a 24/40 to 19/22 adaptor to a 250 mL pressure-equalizing dropping funnel using a Keck clamp. Insert the outlet of the adaptor into the #9 one-holed stopper. Support the addition funnel with a ringstand and clamp and insert the stopper in the 1-liter E. flask. Add the cooled HCl from the freezer to the P-E dropping funnel (valve closed!). Place a small watch glass over the fill port of the P-E dropping funnel. This excludes air, which destroys hydrazine, yet allows the CO2 to escape as the HCl is being added. Add the HCl at 1 drop/sec to the hydrazine solution stirred on the stirrer/hotplate. The mixture will warm up.
e. Formation of Hydrazine Sulfate
NH2-NH2 + H2SO4 --> [N2H5]HSO4
1. Close the valve on the P-E dropping funnel and add the cooled/diluted sulfuric acid.
2. To the rapidly stirring mixture add the dilute sulfuric acid at 2 drops/sec. Reduce the drip rate to control foaming if necessary.
3. Continue stirring and slow the drip rate to about 1 drop/sec as crystals of hydrazine sulfate begin to appear. Stir for one hour past the addition point.
4. Place a small watch glass on the mouth of the E. flask and set aside in a cool place overnight. CO2 may continue to vent.
5. Just prior to filtering the crystals cool the flask in an ice bath for at least an hour.
f. Filtering the Crystals
1. Set up the 15cm Buchner funnel with filter paper for vacuum filtration.
2. Stir the E. flask to loosen any CO2 bubbles and clumps of crystals.
3. Remove the stir bar from the flask.
4. Decant the supernate and save it for washing crystals out of the flask.
5. Pour the crystal slurry onto the Buchner funnel and suck the supernate from the crystals.
6. Flood the wet but drained crystals with 30 mL of 70% isopropyl alcohol, stirring with a stirring rod.
7. Use a final rinse of 15 mL of anhydrous isopropyl alcohol
8. Remove the filter paper with crystals and wick away any excess liquid on a blotter paper or paper towels.
9. Air dry the crystals on a dinner plate.
E. Expected Yield
The expected yield for Mr. A’s full scale batch is about 60% based on the amount of hypochlorite used. For this reduced scale that would be 41 to 44g (0.33 mole). MP of hydrazine sulfate is 254 °C per the Baker MSDS.
F. References
1. Improved procedure of Mr. Anonymous, posted on SM 6/7/2003.
2. SM post of garage chemist on 5/19/07 providing an improvement and a reduced scale.
3. Merck patent GB392845, upon which Mr. A’s procedure is based.
4. Wikipedia entries for “hydrazine” and “Hofmann degradation.”
http://www.sciencemadness.org/talk/viewthread.php?tid=15091
