GB2180835A

GB2180835A - A method for the production of sodium stearate or magnesium stearate

Info

Publication number: GB2180835A
Application number: GB08523739A
Authority: GB
Inventors: Nicholas Muraguri
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-09-26
Filing date: 1985-09-26
Publication date: 1987-04-08
Also published as: GB2180835B; GB8523739D0

Abstract

A method for the production of sodium stearate or magnesium stearate, which method comprises mixing sodium hydroxide and stearic acid, and magnesium nitrate only when the magnesium stearate is being prepared, causing the sodium stearate or the magnesium stearate to crystallise out, and obtaining the crystallised sodium stearate or the crystallised magnesium stearate.

Description

SPECIFICATION A method for the production of sodium stearate or magnesium stearate This invention relates to a method for the production of sodium stearate or magnesium stearate.

Sodium stearate and magnesium stearate are used in the coating of tablets. It is an aim of the present invention to provide a method of the production of the sodium stearate or the magnesium stearate, which method is simple and lends itself to bulk preparation of the sodium stearate or the magnesium stearate.

Accordingly, this invention provides a method for the production of sodium stearate or magnesium stearate, which method comprises mixing sodium hydroxide and stearic acid, and magnesium nitrate only when the magnesium stearate is being prepared, causing the sodium stearate or the magnesium stearate to crystallise out, and obtaining the crystallised sodium stearate or the crystallised magnesium stearate.

Preferably, the method is one in which the sodium hydroxide is in the form of sodium hydroxide pellets, and in which the sodium hydroxide pellets are dissolved in a solvent prior to admixture with the stearic acid.

The solvent is preferably a mixture of rectified spirits and toluene. The mixture of rectified spirits and toluene may be in equal mixtures by volume, and such an equal volume mixture solvent is available commercially under the trade mark Kensol. Other solvents may be employed if desired.

Usually, the magnesium nitrate will be magnesium nitrate hexahydrate.

The sodium stearate may be caused to crystallise out by cooling the mixture of sodium hydroxide and stearic acid to 35-40"C, seeding the cooled mixture with powdered crystalline sodium stearate, cooling the seeded mixture to ambient temperature, and chilling the cooled mixture to cause the sodium stearate to crystallise out.

The magnesium stearate may be caused to crystallise out by cooling the mixture of sodium hydroxide, stearic acid and magnesium nitrate to ambient temperature.

The crystallised sodium stearate or the crystallised magnesium stearate may be obtained by filtering.

The filtering will usually be effected using suction.

The filtered sodium stearate or magnesium stearate may be dried with hot air or, alternatively, air dried and then further dried in an open oven.

The present invention also provides the sodium stearate or the magnesium stearate when produced by the method of the invention.

The present invention also provides tablets whenever coated with the sodium stearate or the magnesium stearate produced by the method of the invention.

In order to facilitate a full understanding of the present invention, reference will now be made to the following Examples.

EXAMPLE I PREPARATION OF SODIUM STEARATE RA W MA TERIALS: 1. Sodium Hydroxide pellets 98%.

2. Stearic Acid 96% mp 69"-710C.

3. "Kensol" solvent. This is made from equal mixtures v/v of rectified spirits and toluene 99%. The Kensol solvent boils at 72"C, its wt. per ml. is 0.83g, and it dissolves plastics.

4. Thermolyne Type 1000 stir plate.

PRODUCTION: Place 9.0g sodium hydroxide pellets into a 5 litre beaker. Add 4.5 litres of Kensol solvent.

Warm slowly with stirring on the stir plate until the temperature reaches 50"C (15 minutes). Switch off the heater and continue stirring until the pellets dissolve completely (10 minutes). The temperature should stay below 65"C. The solution will become slightly turbid.

Add 64.0g of stearic acid in a siow stream and continue stirring. Some bubbling will occur. Continue stirring for about 2 minutes.

Turbidity disappears and the solution becomes clear.

Remove the beaker from the heater and allow to stand for 5 minutes. A small amount of particulate matter settles. Decant slowly into a 7 litre steel beaker containing 2.5 litres of Kensol so as to leave the particulate matter behind.

Allow to cool to 35 -40 C. Seed liberally with powdered crystalline sodium stearate and allow to cool to ambient. Chill overnight at -5"C. Sodium stearate crystallises out.

Filter with suction on a 33cm diameter bench top porcelain buchner using a 32cm filter paper and drain as dry as possible. Dry the product by passing hot air through it. Alternatively, allow to dry in the air on filter paper or other porous material and then in an open oven at 45"C. Kensol vapours may ignite in a closed oven. Finally, dry to constant weight at 105"C.

The dry product is in the form of shiny plates. The solvent is re-used for the next run, and may be re-used ten times before purification by distillation. The following yields were obtained in four consecutive runs: 82.7%, 85.7%, 94.6%, 96.2%. Minimum purity is 99%. The dry product may be milled to the desired particle size.

All operations with Kensol solvent should be carried out under a fume hood.

EXAMPLE II PREPARATION OF MAGNESIUM STEARATE RA W MA TERIALS: 1. Sodium Hydroxide pellets 98%.

2. Stearic Acid 96% m.p. 69"-71"C.

3. Magnesium nitrate hexahydrate 99%.

4. Kensol solvent.

PRODUCTION: Place 20.09 sodium hydroxide pellets in a 5 litre beaker. Add 3.5 litres of Kensol solvent.

Warm slowly on a stir plate until the temperature reaches 45"C. Switch off the heater and continue stirring until the pellets dissolve completely. The temperature will now have risen to 62 C.

Add 142.29. of stearic acid and stir until it dissolves. The temperature falls to 60"C.

At 60"C, add 64.0g. of magnesium nitrate hexahydrate and continue stirring until it dissolves. The solution goes turbid. Stir for 3 minutes more, remove from the stir plate and cool the solution overnight at room temperature. Magnesium stearate crystallises out.

Filter using the same apparatus as with the sodium stearate described above in Example I, but with the filter plate wrapped up with nylon cloth over the filter paper. Wash the product twice with 96% ethanol and then several times with water until it is free from sodium nitrate. The nylon cloth aids in the washing because it does not tear.

Dry initially at 60 then to constant weight at 105"C. The yield is over 99%.

All operations with Kensol solvent should be carried out under a fume hood.

It is to be appreciated that the embodiments of the invention described above in the Examples have been given for illustrative purposes only and modifications may be effected.

In particular, it will be appreciated that the described production methods in the Examples will be scaled up for commercial bulk production.

Claims

1. A method for the production of sodium stearate or magnesium stearate, which method comprises mixing sodium hydroxide and stearic acid, and magnesium nitrate only when the magnesium stearate is being prepared, causing the sodium stearate or the magnesium stearate to crystallise out, and obtaining the crystallised sodium stearate or the crystallised magnesium stearate.

2. A method according to Claim lin which the sodium hydroxide is in the form of sodium hydroxide pellets, and in which the sodium hydroxide pellets are dissolved in a solvent prior to admixture with the stearic acid.

3. A method according to Claim 2 in which the solvent is a mixture of rectified spirits and toluene.

4. A method according to Claim 3 in which the mixture of rectified spirits and toluene is in equal mixtures by volume.

5. A method according to any one of the preceeding Claims in which the magnesium nitrate is magnesium nitrate hexahydrate.

6. A method according to any one of the preceeding Claims in which the sodium stearate is caused to crystallise out by cooling the mixture of sodium hydroxide and stearic acid to 35-4O0C, seeding the cooled mixture with powdered crystalline sodium stearate, cooling the seeded mixture to ambient temperature, and chilling the cooled mixture to cause the sodium stearate to crystallise out.

7. A method according to any one of Claims 1-5 in which the magnesium stearate is caused to crystallise out by cooling the mixture of sodium hydroxide, stearic acid and magnesium nitrate to ambient temperature.

8. A method according to any one of the preceeding Claims in which the crystallised sodium stearate or the crystallised magnesium stearate is obtained by filtering.

9. A method according to Claim 8 in which the filtering is effected using suction.

10. A method according to Claim 8 or Claim 9 in which the filtered sodium stearate or magnesium stearate is dried with hot air.

11. A method according to Claim 8 or Claim 9 in which the filtered sodium stearate or magnesium stearate is air dried and then further dried in an open oven.

12. A method for the production of sodium stearate or magnesium stearate, substantially as herein described with reference to the examples.

13. Sodium stearate or magnesium stearate when produced by a method as claimed in any one of the preceeding Claims.

14. Tablets whenever coated with sodium stearate or magnesium stearate produced by the method claimed in any one of Claims 1-12.