Claims
- 1. A process for the purification of crude riboflavin, comprising
- (a) dissolving said crude riboflavin in an aqueous solution of alkali metal hydroxide,
- (b) purifying said solution of riboflavin,
- (c) introducing said solution into a mixture of water and acid which is at about 90.degree.-100.degree. C., producing an acidic reaction mixture with a pH of about 6.5-0.8, while maintaining the resulting acidic reaction mixture at a temperature of about 90.degree.-100.degree. C.,
- (d) heating said acidic reaction mixture at about 90.degree.-100.degree. C. for a further 10-80 minutes, and
- (e) cooling said heated reaction mixture and isolating the crystallized riboflavin.
- 2. The process of claim 1, wherein said dissolving step comprises
- (a) suspending said crude riboflavin in water, and
- (b) adding an aqueous solution of an alkali metal hydroxide.
- 3. The process of claim 1, wherein said dissolving step comprises dissolving said crude riboflavin in a aqueous solution of an alkali metal hydroxide which has a concentration of about 0.16-0.63 molar.
- 4. The process of claim 1, wherein said purification step comprises treating said solution of riboflavin with active carbon or a filtration aid followed by filtration.
- 5. The process of claim 1, wherein said purification step comprises extracting said solution of riboflavin with an inert solvent which is insoluble or only slightly soluble in water.
- 6. The process of claim 1, comprising conducting said heating step while stirring.
- 7. The process of claim 1, wherein said dissolving and purifying steps are conducted at about 30.degree.-45.degree. C.
- 8. The process of claim 1, comprising adding bulk materials during said cooling step, said bulk materials being selected from the group consisting of corn starch, corn cob flour, fine soybean flour, wheat bran, SiO.sub.2, calcium silicates, kieselguhr, steatite, talc and bolus alba.
- 9. The process of claim 1, wherein said acid has a pKa less than or equal to 4.76.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 3421714 |
Jun 1984 |
DEX |
|
Parent Case Info
The present invention relates to a process for producing very pure riboflavin from crude riboflavin (I; vitamin B.sub.2) by dissolving the latter in dilute aqueous alkali metal hydroxide solution, if necessary purifying this solution, and isolating the riboflavin by introducing the solution into aqueous acid solution at from 90.degree. to 100.degree. C.
It is well known (cf. for example W. H. Sebrell and R. S. Harris, The Vitamins; Chemistry, Physiology, Pathology, Methods, 2nd edition, volume V, 1982, Academic Press, page 22) that riboflavin is usually synthesized by condensation of an N-(D)-ribityl-2-arylazo-4,5-dimethylaniline (II) with barbituric acid (III). ##STR1##
Rib=D-ribityl
Ar=aryl, e.g. phenyl
This procedure gives a crude product which, in addition to about 92-96% by weight of I, also contains various impurities including, for example, barbituric acid, dibarbituric acid, lumiflavin, lumichrome and N-(D)-ribityl-6-arylazo-4,5-dimethylaniline.
The condensation of other N-(D)-ribityl-4,5-dimethylaniline derivatives with barbituric acid derivatives to give riboflavin has also been described.
Moreover, the formation of riboflavin by a biosynthetic route with the aid of microorganisms is known from the literature.
Since the recovery of pure riboflavin from the crude product by crystallization processes alone entails disproportionate expense, U.S. Pat. No. 2,324,800 describes a method in which the crude riboflavin is subjected to an oxidative treatment in an aqueous acidic medium, after which any precipitates are separated off and the remaining solution is diluted with a large amount of water. This procedure gives the riboflavin in the form of yellow needles which need only be filtered off and washed.
The disadvantages of this process are that about 15% of the riboflavin used is lost during this purification process, the procedure is time-consuming and technically troublesome, and the product I obtained still contains traces of organic compounds, such as aniline, which present problems when it is used for human nutrition.
It is an object of the present invention to provide a process for producing a very pure product I, which overcomes the disadvantages of the prior art, ie. which is technically more advantageous and in which a smaller amount of I is lost during the purification process and an even purer product I is obtained.
We have found that this object is achieved by a process for the purification of crude riboflavin, wherein
(a) the riboflavin to be purified is suspended in water and brought into solution by the addition of an aqueous solution of an alkali metal hydroxide, or the riboflavin is dissolved in about 0.16-0.63 molar aqueous alkali metal hydroxide solution,
(b) if necessary, the resulting alkaline riboflavin solution is purified by treatment with active carbon or a filtration aid followed by filtration, or by extraction with an inert solvent which is insoluble or only slightly soluble in water,
(c) while a temperature of from 40.degree. to 100.degree. C., preferably about 97.degree.-99.degree. C., is maintained, the alkaline riboflavin solution obtained is introduced into water which is at about 90.degree.-100.degree. C. and to which an acid has been added in an amount such that the pH of the reaction mixture is brought to 6.5-0.8,
(d) the reaction mixture is heated at about 90.degree.-100.degree. C. for about a further 10-80, preferably 20-60, minutes, if necessary while stirring, and
(e) the reaction mixture is cooled and the riboflavin which has crystallized out is isolated.
In a particularly advantageous embodiment of the process, the temperature of the alkaline riboflavin solution in reaction steps (a) and (b) is about 10.degree.-50.degree. C., preferably about 30.degree.-45.degree. C., or the temperature exceeds 50.degree. C. for only a short time, if at all.
Losses of I in the novel purification process are substantially lower than in the case of a purification in acidic solution. This is very surprising since the literature relating to I, even the most recent literature (cf. Fermente - Hormone - Vitamine, volume III/1, Georg Thieme Verlag Stuttgart, 1974, page 631 and Ullmanns Encyklopadie der technischen Chemie, volume 23, Verlag Chemie, Weinheim, 1983, page 664), states that I readily decomposes in alkaline solution.
Although U.S. Pat. No. 2,603,633 discloses a process for the preparation of 3 different types of crystals I, in which these crystals are obtained by the addition of an acid to an alkaline solution of I at from 10.degree. to 25.degree. C., attempts to use the crystallization processes described for the purification of I on an industrial scale did not give acceptable results.
In contrast, the novel process gives riboflavin in a yield of from 90 to 92% of theory and with a purity of more than 99.5% (determined according to the European Pharmacopeia).
The novel process is suitable for producing a very pure product from crude I containing about 10-99.5% of I, as obtained in the microbiological preparation procedure or in the synthesis.
To carry out the novel process, the crude I is first suspended in water, the amount of water generally used being about 1130-6580 g, preferably about 1880-3760 g, per mole of I. Advantageously, the water used is at from 25.degree. to 50.degree. C. or preferably from 35.degree. to 45.degree. C.
An aqueous solution of an alkali metal hydroxide is added to this aqueous suspension of I in an amount such that the suspended I goes completely into solution. Preferably, aqueous KOH or NaOH, in particular the industrially very readily available and cheap NaOH in the form of about 25% strength solution, is used as the aqueous solution of an alkali metal hydroxide. About 1-1.25 moles of alkali metal hydroxide per mole of I are required to dissolve the latter; for 25% strength NaOH, this means about 0.5 kg per kg of I. However, the riboflavin can also be dissolved directly in dilute aqueous alkali metal hydroxide solution. For this purpose, about 0.16-0.63, preferably about 0.28-0.32, molar aqueous KOH or NaOH is used in amounts of about 17.5-5, preferably from 10 to 9, kg per kg of I, depending on the concentration of the alkali metal hydroxide solution used.
I is generally dissolved at from about 10.degree. to 50.degree. C., preferably from 25.degree. to 50.degree. C., in particular from 30.degree. to 45.degree. C. If I is in contact with the aqueous alkaline solution for only a short time, as is the case in a continuous procedure, temperatures higher than 50.degree. C., e.g. from 50.degree. to 60.degree. C., may also be used.
The resulting aqueous alkaline solution of I can then be purified. This can be done by treatment with active carbon followed by filtration, or by extraction with an inert solvent which is immiscible or only poorly miscible with water. The active carbon used may be virtually any commercially available grade.
Examples of suitable solvents for the extraction are ethyl acetate, chloroform and petroleum ether, in particular isobutyl acetate and n-butyl acetate.
In the purification of crude I prepared by a microbiological route, the aqueous alkaline solution of I is preferably purified by treatment with a filtration aid followed by filtration. The type of filtration aid used is not critical, it only being important to ensure that the rate of filtration is sufficiently high. For example Celite.RTM. from Johns-Manville, USA, has proven useful.
The resulting I solution, which may or may not have been purified, is then introduced into water which is at from 96.degree. to 100.degree. C., preferably from 96.degree. to 99.degree. C., and to which an acid has been added in an amount such that the pH of the reaction mixture is brought to 6.5-0.8, preferably 6-1, the temperature being maintained at from 90.degree. to 100.degree. C., preferably from 96.degree. to 99.degree. C. In special cases, particularly where riboflavin prepared by a microbial route is being purified, it is also possible for the purified or unpurified solution of I to be introduced into the acidified hot water while maintaining somewhat lower temperatures, ie. about 40.degree.-100.degree. C.
The amount of water is such that the reaction mixture contains about 18-30, preferably about 20-25, kg of water per kg of I after the addition of the alkaline solution.
Acids which are added to the water are any acids which are as strong as or stronger than acetic acid, ie. those which have a pK.sub.a of 4.76 or lower and do not attack the riboflavin under the reaction conditions. Advantageously, the conventional mineral acids, such as HCl (pK.sub.a -6), H.sub.2 SO.sub.4 (pK.sub.a -3), HNO.sub.3 (pK.sub.a -1.32) or H.sub.3 PO.sub.4 (pK.sub.a 2.09), are used, but organic acids, such as formic acid (pK.sub.a 3.77) and acetic acid (pK.sub.a 4.76), may also be employed. The use of nitric acid has proven particularly advantageous since it apparently has a mild oxidizing effect on the by-products in I, even in very dilute aqueous solution. When HNO.sub.3 is used, pure I is obtained in a color which, in its brilliance, differs substantially from the color obtained using the other acids.
The mineral acid is used in an amount such that, on the one hand, the alkali metal hydroxide solution used is completely neutralized and, on the other hand, the solution becomes acidic so that the I is advantageously and completely precipitated. Where mixtures are purified without intermediate treatment with active carbon or an extracting agent, it is advisable to acidify the mixture to a pH below 3 in order that any by-products present are more readily destroyed during heating.
In general, about 1.06-3.5 moles of acid per mole of I are required for this purpose, depending on the amount of alkali metal hydroxide solution used.
The effective yield of I in the purification process can be further improved if bulk materials permitted for the particular intended use in animal nutrition or the pharmaceutical industry are added to the aqueous acidic solution obtained according to the invention in reaction step (e).
The advantageous effect can probably be explained by the fact that, in this procedure, the adsorption behavior of I is utilized in such a way that the 4-7% of by-products adsorbed onto the crude I is replaced by insoluble additives permitted in animal nutrition and the pharmaceutical industry.
Examples of bulk materials permitted in the pharmaceutical industry are corn starch, corn cob flour, fine soybean flour and wheat bran. Examples of additives permitted in animal nutrition are SiO.sub.2, calcium silicates, kieselguhr, steatite, talc and bolus alba (white clay). The additives are used in general in amounts of from 1 to 500 g per kg of I.
US Referenced Citations (8)
Non-Patent Literature Citations (2)
| Entry |
| Fermente Hormone-Vitamine, vol. III/1, Georg Thieme Verlag Stuttgart, 1974, p. 631. |
| Ullmanns Encyclopedia of Technischen Chemie, vol. 23, Verlap Chemie, Weinheim, 1983, p. 664. |
Patent Grant
4687847
