JPH057388B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to 2-ketogulonic acid ester (KGAE)
A novel method for producing ascorbic acid from. Ketogulonic acid or its ester, which is produced in the penultimate step of normal ascorbic acid synthesis, is
It must be rearranged to ascorbic acid. Certain problems always arise with this rearrangement carried out under acidic or alkaline conditions. That is, on the one hand, in the case of acidic rearrangement, there is an inherent problem that the yield obtained is not particularly satisfactory, and also that the quality of the ascorbic acid obtained is far from what is desired. Moreover, reaction times are generally quite long in the case of acidic rearrangements. On the other hand, in the case of alkaline rearrangement, the base used for the rearrangement forms a salt with ascorbic acid, which has to be cleaved again by addition of acid for the purpose of isolating pure ascorbic acid. There is an essential problem. This cleavage again gives the salt, from which it is not easy to isolate the ascorbic acid, and the salt can only be used further, at least to a certain extent. Therefore, there is a need for a method in which ascorbic acid can be obtained from ketogulonic acid ester in a simple manner and in good yield, and in which the base required for rearrangement can be easily recovered and reused in the process. The problems now mentioned above can be eliminated by the method provided by the present invention. In other words, it has been found that when certain amines are used in the rearrangement of KGAE, the above-mentioned problems do not occur. Therefore, the method of the present invention is based on the general formula [In the formula, R means lower alkyl] is reacted with an amine having 12 to 38 carbon atoms in a suitable organic solvent to obtain the general formula [wherein X represents the ammonium ion of the C ₁₂ -C ₃₈ amine used] An ascorbic acid amine salt of the formula is formed, and by cleaving the ascorbic acid amine salt of the formula without neutralization, the formula and the ascorbic acid of the above formula and _{the optionally used C12-C38 amine are isolated} . Within the scope of the present invention, the term "lower alkyl" means alkyl groups having 1 to 5 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl and the like. Alkyl radicals having 1 to 3 carbon atoms, especially methyl and ethyl, are preferred. As amines, primary, secondary and tertiary amines having 12 to 38 carbon atoms come into consideration within the scope of the invention. The lower limit of the number of carbon atoms is determined, among other things, by whether the ascorbic acid amine salt of formula is soluble in the organic solvent used for cleavage.
On the other hand, the upper limit on the number of carbon atoms is determined by the solubility in the solvent used for the reaction between KGAE and the amine. The amines that can be used are preferably in the following order: tertiary amines>secondary amines>primary amines. Primary amines include not only linear amines but also branched amines, with branched amines being preferred. More particularly preferred are those having 12 to 24 carbon atoms. Additionally, primary amines include certain liquid basic ion exchangers such as Primene JMT (trialkyl-methylamine,
Amberlite LA-3 (a high molecular weight oil-soluble primary amine with a highly branched aliphatic chain)
It should be understood that this includes Secondary amines include not only linear but also branched alkylamines and aromatic amines. Suitable secondary amines are branched alkylamines, especially those having 16 to 25 carbon atoms. Dibenzylamine is a preferred aromatic secondary amine. Further secondary amines include certain liquid basic ion exchangers such as Amberlite FA-1 (N-dodecenyl-N-trialkyl-methylamine, a mixture of 24 to 27 carbon atoms). ) or Amberlite LA-2 (a mixture of N-lauryl-N-trialkyl-methylamines having 24 to 27 carbon atoms). Tertiary amines include in particular linear, partially branched aliphatic amines, linear alkylamines and especially those having 15 to 30 carbon atoms are preferred. The secondary amine and the tertiary amine can contain the same alkyl chain or different alkyl chains. The following are examples of amines and suitable amines for use in the present invention. Primene JMT, Amberlite LA-3, α-amino-diphenylmethane, 1,2-diphenylethylamine, bis(2-ethylhexyl)amine, Amberlite LA-1, Amberlite LA-2, dibenzylamine, dioctylamine, tripentylamine , triisopentylamine, N,N-dioctylmethylamine, trihexylamine, triheptylamine, trioctylamine and tridodecylamine. The reaction of a ketogulonic acid ester of the formula, which can also exist in pyranoid or furanoid form, with an amine is
It is carried out in a suitable organic solvent or in a solvent mixture in which the KGAE and/or the amine used are at least partially soluble. The solvent can be a protic or aprotic dipolar solvent. Examples of protic solvents are lower alcohols having 1 to 5 carbon atoms, such as methanol, ethanol, propanol, isopropanol, and the like. Examples of aprotic dipolar solvents are acetonitrile, dimethylformamide, dioxane, monoglyme, methyl cellosolve (ethylene glycol monomethyl ether), and the like. Alcohols, especially methanol, are preferred solvents. The KGAE of the formula used as starting material is a known compound or a homologue of a known compound. These can be used as such in the reaction or can also be prepared in situ from 2-ketogulonic acid by transesterification with the corresponding alcohol. The amount of solvent used is not critical per se, but is conveniently about 1:1 based on the KGAE and amine used.
The ratio is ~10:1 (ml/g). The amount of amine used in the method provided by the present invention is conveniently from about 0.1 to about 1.5, preferably from about 0.5 to about 1.1 per mole of ketogulonic acid ester.
Particularly amounts from about 0.9 to about 1 mole. In the method of the invention, the temperature, pressure and reaction period are not critical. Temperature is the factor that determines the rate. The upper temperature limit is determined by the stability of the reaction partners. The reaction is conveniently carried out at a temperature of up to about 90°C, preferably from about 50°C to about 75°C.
℃, especially about 65℃. The pressure at which the method of the present invention is carried out is not critical, and the reaction can be easily carried out under normal pressure. However, the reaction can be carried out under pressure under certain circumstances, and correspondingly elevated temperatures and short reaction times are used. The reaction time depends on the reaction temperature and is approximately 2 to 7 hours, especially approximately 3 to 5 hours at optimum temperatures. The reaction of KGAE and amine can be carried out in the presence or absence of air. However, it is preferably carried out with the exclusion of air, ie under an inert gas such as nitrogen, argon, etc. The decomposition of the ascorbic acid amine salt obtained can be carried out according to the invention without neutralization, ie without addition of acids or bases. This decomposition and isolation of pure ascorbic acid and preferably the amine used is carried out by liquid-liquid extraction. In this case, free ascorbic acid enters the polar phase and free amine enters the non-polar phase. Additionally, in some circumstances, decomposition and isolation can also be accomplished by simple digestion, ie, heating with a suitable organic solvent. Suitable non-polar solvents for extraction are those in which the amine used is well dissolved. Neutral non-polar solvents such as aliphatic or aromatic hydrocarbons (e.g. hexane,
Petroleum ether, benzene, toluene, xylene, etc.) are conveniently used. Suitable polar solvents or solvent mixtures are those in which ascorbic acid is well dissolved and is immiscible with the non-polar solvents mentioned above. water,
Methanol, ethanol, acetonitrile, acetone, etc. or mixtures thereof are conveniently used. The presence of at least a small amount of water has been found to be particularly advantageous. Water or water-methanol mixtures are particularly suitable. The temperature at which the extraction is carried out is not critical per se; the extraction can be carried out at room temperature or at elevated temperature. Extraction is preferably carried out at about room temperature.
After the extraction, ascorbic acid as well as the amine used can be easily isolated from the phases containing them by methods known per se. For digestion, essentially the same non-polar solvents as mentioned above for extraction are suitable. Heating is conveniently carried out at a temperature from about 50°C to the reflux temperature of the solvent used. Digestion is preferably carried out at reflux temperature. The ascorbic acid amine salt decomposes during this digestion, pure ascorbic acid precipitates, and the amine enters the organic phase. The amine can be easily isolated therefrom by methods known per se. All the above-mentioned operations can be carried out not only continuously but also batchwise. The following examples illustrate the invention in more detail and are not intended to limit the invention. Example 1 In a 500 ml sulfonation flask equipped with a stirrer, thermometer, reflux condenser and 50 ml dropping funnel, 26.8 g (128.7 mmol) of ketogulonic acid methyl ester and 125 ml of methanol were added under argon. The mixture was then heated to 65°C (reflux) with stirring to dissolve the ester. Then 38 g (109 mole %) of trihexylamine (99.9%) was added dropwise from the addition funnel over a period of 15 minutes. Towards the end of the trihexylamine addition, the mixture became slightly cloudy, but the solution became clear again after 5 minutes. The mixture was stirred at reflux for a further 4 3/4 hours. As a result, the mixture turned yellow. After a total of 5 hours, the mixture was washed with methanol in a 500 ml round bottom flask and concentrated in a rotary evaporator at 45° C./20 mbar. A yellow viscous oil was obtained as a residue. Dissolve the previously obtained oil in 50 ml of deionized water,
Water in a rotating perforator that is aerated with nitrogen is approx.
It was washed out with 20ml. The mixture was then continuously extracted with approximately 500 ml of n-hexane for 20 hours. As a result, the aqueous phase became almost colorless and the organic phase became yellow. After the extraction was completed, the two phases remaining in the extractor were separated using a separatory funnel. Combine the organic phases and add approx.
Dry with 30g and dry at 45℃/100~20 in a rotary evaporator.
Evaporated at mbar. As a result, the content is 97.6%
37.8g of yellow trihexylamine remained. This corresponded to a trihexylamine yield of 97.2%. The aqueous phase obtained after extraction of trihexylamine contained 21.9 g of ascorbic acid, corresponding to a yield of 96.4%. Example 2 The reaction of ketogulonic acid methyl ester with trihexylamine was carried out in a similar manner to Example 1 in different solvents. The results are summarized in the following table.

[Table] Example 3 500ml with stirrer, thermometer and reflux condenser
26.8 g (128.7 mmol) of ketogulonic acid methyl ester and 125 ml of methanol were added to a sulfonated flask under argon. The mixture was then heated to 65°C (reflux) with stirring to dissolve the ester. Then 17.5 g (50 mole %) of trihexylamine (99.9%) was added over 15 minutes. The mixture was stirred under reflux for a further 24 hours. As a result, the mixture turned yellow. continue,
The mixture was washed with methanol in a 500 ml round bottom flask and concentrated on a rotary evaporator at 45° C./20 mbar. A yellow viscous oil was obtained as a residue. Dissolve the previously obtained oil in 50 ml of deionized water,
It was flushed with about 20 ml of water into a Kutscher-Steudel extractor which was flushed with nitrogen. The mixture was then diluted with n-hexane for 20 hours.
Extracted continuously with 500 ml. After the extraction was completed, the two phases remaining in the extractor were separated using a separatory funnel. The organic phases were combined, dried with about 30 g of sodium sulfate and evaporated in a rotary evaporator at 45° C./100-20 mbar.
As a result, 17.5 g of yellow trihexylamine with a content of 99.0% remained. This corresponded to a trihexylamine yield of 99.6%. The aqueous phase obtained after extraction of trihexylamine contained 21.2 g of ascorbic acid, corresponding to a yield of 93.5%. Example 4 In a 100 ml sulfonation flask equipped with a stirrer, thermometer, reflux condenser and 50 ml dropping funnel, 26.8 g (128.7 mmol) of ketogulonic acid methyl ester and 10 ml of methanol were added under argon. The mixture was then heated to 65°C (reflux) with stirring and then trihexylamine (99.9%)
34.7 g (100 mole %) was added dropwise from the addition funnel over 15 minutes. Everything was dissolved after about 4 hours, but the mixture was slightly cloudy by the end.
The mixture was stirred under reflux for a further 4 3/4 hours.
As a result, the mixture turned yellow. After a total of 5 hours, the mixture was washed with methanol in a 500 ml round bottom flask and concentrated in a rotary evaporator at 45° C./20 mbar. A yellow viscous oil was obtained as a residue. Dissolve the previously obtained oil in 50 ml of deionized water,
Approximately water is pumped into a rotating perforator that is aerated with nitrogen.
It was washed out with 20ml. The mixture was then continuously extracted with approximately 500 ml of n-hexane for 20 hours. After the extraction was completed, the two phases remaining in the extractor were separated using a separatory funnel.
Combine the organic phases and dry with about 30 g of sodium sulfate.
Evaporated in a rotary evaporator at 45° C./100-20 mbar. As a result, 4.4 g of yellow trihexylamine with a content of 98.3% remained. This corresponded to a yield of trihexylamine of 97.5%. The aqueous phase obtained after extraction of trihexylamine contained 21.0 g of ascorbic acid, corresponding to a yield of 92.7%. Example 5 In a 500 ml sulfonation flask equipped with a stirrer, thermometer, reflux condenser and 50 ml dropping funnel, 26.8 g (128.7 mmol) of ketogulonic acid methyl ester and 125 ml of methanol were added under argon. The mixture was then heated to 65°C (reflux) with stirring to dissolve the ester. Then 33.1g of bis(2-ethylhexyl)amine (100%)
(106.5 mol%) while maintaining a PH value of approximately 6.5
Addition was made via a dropping funnel over a period of 40 minutes. The mixture was then stirred under reflux for a further 3 1/2 hours. The methanol was then distilled off in a rotary evaporator at 45° C./20 mbar. Yellow crystalline ascorbic acid amine salt was obtained. The crystals obtained in advance were suspended in 400 ml of water and 400 ml of n-hexane, and the suspension was vigorously stirred for 1 hour to completely dissolve the salt. Then add the aqueous phase to n
-Extracted twice with 100ml each of hexane. This hexane phase was backwashed twice with 100 ml of water each, dried over about 40 g of sodium sulfate, and heated to 45 °C/
Evaporated at 100-20 mbar. This results in a content of
29.2 g (86.5%) of 98% pale yellow bis(2-ethylhexyl)amine was obtained. The combined aqueous phases were concentrated to about 100 ml and back-extracted continuously with about 300 ml of n-hexane for 20 hours in a Kutscher-Steudel extractor. The organic phase was dried with about 20 g of sodium sulfate and evaporated in a rotary evaporator.
Evaporated at 45°C/100-20 mbar. A further 3.55 g (10.3%) of yellow bis(2-ethylhexyl)amine with a content of 96.1% were thus obtained.
This corresponded to an overall yield of amine of 96.8%. The combined aqueous phase obtained after extraction of the amine is the yield
It contained 21.3 g of acorbic acid, corresponding to 94.1%. Example 6 In a 200 ml sulfonation flask equipped with a stirrer, thermometer, reflux condenser and 500 ml dropping funnel,
26.8 g (128.7 mmol) of ketogulonic acid methyl ester and 25 ml of methanol were added under argon. The mixture was then heated to 65°C (reflux) with stirring and then tripentylamine (98.3%)
29.8 g (100 mole %) was added dropwise from the dropping funnel over 15 minutes. Everything went into solution after about 1 hour. The mixture was stirred under reflux for a further 4 3/4 hours. As a result, the mixture turned yellow. After a total of 5 hours, the mixture was washed with methanol in a 500 ml round bottom flask and evaporated to 45°C/20°C on a rotary evaporator.
Concentrated at mbar. A yellow viscous oil was obtained as a residue. Dissolve the previously obtained oil in 50 ml of deionized water,
Approximately water is pumped into a rotating perforator that is aerated with nitrogen.
It was washed out with 20ml. The mixture was then continuously extracted with approximately 500 ml of n-hexane for 20 hours. After the extraction was completed, the two phases remaining in the extractor were separated using a separatory funnel.
Combine the organic phases and dry with about 30 g of sodium sulfate.
Evaporated in a rotary evaporator at 45° C./100-20 mbar. As a result, 29.3 g of yellow tripentylamine with a content of 98.7% remained. This corresponded to a yield of tripentylamine of 98.9%. The aqueous phase obtained after extraction of tripentylamine contained 21.9 g of ascorbic acid, corresponding to a yield of 96.5%. Example 7 Different amines were used in a similar manner to the methods described in Examples 1-6. The results are summarized in the table below.

[Table] Example 8 In a 500 ml sulfonation flask equipped with a stirrer, thermometer, reflux condenser and 100 ml dropping funnel,
26.8 g (128.7 mmol) of ketogulonic acid methyl ester and 125 ml of methanol were added under argon. The mixture was then heated to 65°C (reflux) with stirring.
to dissolve the ester. Then, 46.2 g (100 mol %) of trioctylamine was added dropwise from the dropping funnel over a period of 15 minutes. The mixture was heated under reflux for a further 43/4 hours. This resulted in a yellow color to the mixture. After a total of 5 hours, it was concentrated in a rotary evaporator at 45° C./20 mbar. viscous 2
Some oil remained. Dissolve the oil obtained in advance in 150ml of toluene,
The solution was heated to reflux temperature while stirring.
Upon heating, ascorbic acid began to crystallize quite rapidly. The mixture was stirred for a further 1 hour at reflux temperature and the precipitate was filtered off hot with suction. Toluene the residue 15
ml and then with 15 ml hexane and dried overnight in a vacuum drying oven at room temperature/20 mbar. 20.75 g (91.5%) of pure ascorbic acid was obtained. The resulting liquid was completely evaporated using a rotary evaporator to obtain 50.8 g (110 g) of crude trioctylamine.
%) was obtained. Example 9 In a 500 ml sulfonation flask equipped with a stirrer, thermometer, reflux condenser and 50 ml dropping funnel, 26.8 g (128.7 mmol) of ketogulonic acid mer ester
and 125 ml of methanol were added under argon.
The mixture was then heated to 65°C (reflux) with stirring to dissolve the ester. Then, 46.2 g (100 mole %) of trioctylamine (98.3%) was added dropwise from the dropping funnel over a period of 15 minutes. The mixture was stirred under reflux for a further 4 3/4 hours. As a result, the mixture turned yellow. After a total of 5 hours, the mixture was washed with methanol in a 500 ml round bottom flask and concentrated in a rotary evaporator at 45° C./20 mbar. A viscous two-phase oil was obtained as a residue. Treat the previously obtained oil with 150 ml of hexane,
The mixture was heated to reflux temperature (57°C) while stirring. The yellowish ascorbic acid began to crystallize quite rapidly. After 1 1/2 hours under reflux, the crystals were filtered off hot, washed twice with 15 ml each of hexane and dried overnight at room temperature/20 mbar in a vacuum drying oven.
As a result, the content of ascorbic acid is 90.6%,
23.6 g was obtained, corresponding to a yield of 94.3%. The resulting liquid was completely evaporated using a rotary evaporator to obtain 44.8 g of 97.1% trioctylamine.
I got it. This corresponded to a yield of 95.7%. Example 10 In a 500 ml sulfonation flask equipped with a stirrer, thermometer, reflux condenser and 50 ml dropping funnel, 30.4 g (128.7 mmol) of ketogulonic acid isopropyl ester and 125 ml of methanol are added under argon to dissolve the ester. Dissolved. The mixture was then heated to 65°C (reflux) with stirring. Then trihexylamine (99.9%) 34.7g (100 mol%)
was added dropwise from the dropping funnel over a period of 15 minutes.
Towards the end of the trihexylamine addition, the mixture became slightly cloudy, but the solution became clear again after 5 minutes. The mixture was stirred under reflux for a further 6 3/4 hours. As a result, the mixture turned yellow. After a total of 7 hours, the mixture was washed with methanol in a 500 ml round bottom flask and concentrated in a rotary evaporator at 45° C./20 mbar. A yellow viscous oil was obtained as a residue. Dissolve the previously obtained oil in 50 ml of deionized water,
Approximately water is pumped into a rotating perforator that is aerated with nitrogen.
It was washed out with 20ml. The mixture was then continuously extracted with approximately 500 ml of n-hexane for 20 hours. After the extraction was completed, the two phases remaining in the extractor were separated using a separatory funnel.
Combine the organic phases and dry with about 30 g of sodium sulfate.
Evaporated in a rotary evaporator at 45° C./100-20 mbar. As a result, 36.4 g of yellow trihexylamine with a content of 95.6% remained. This corresponded to a 100% yield of trihexylamine. The aqueous phase obtained after extraction of trihexylamine contained 16.1 g of ascorbic acid, corresponding to a yield of 70.8%. Example 11 In a 750 ml sulfonation flask equipped with a stirrer, thermometer, reflux condenser and 250 ml dropping funnel,
Ketogulonic acid ethyl ester 111.1g (91% content)
and 100 ml of ethanol were added under argon.
The mixture was then heated to 65° C. with stirring to dissolve the ester. Then 134.8 g of trihexylamine (99.9%) was added dropwise from a dropping funnel over a period of 25 minutes. Stir this mixture for another 4 1/2 hours65
Stir at ℃. The mixture turned reddish-brown. 5 in total
After an hour, the mixture was washed with ethanol in a 1000 ml round-bottomed flask and concentrated on a rotary evaporator at 45° C./20 mbar. A brown viscous oil was obtained as a residue. Dissolve the previously obtained oil in 250 ml of deionized water,
The solution was extracted twice with 150 ml portions of n-hexane.
The hexane phase was backwashed with 50 ml of water and the combined aqueous phases were washed with n-hexane for 20 hours in a rotating perfluorator.
Continuous back extraction was performed with 800 ml. After the extraction was completed, the two phases remaining in the extractor were separated using a separatory funnel. The organic phases were combined, dried with about 50 g of sodium sulfate and evaporated in a rotary evaporator at 45° C./100-20 mbar. As a result, 136.7 g of yellow trihexylamine with a content of 98.6% remained. This corresponded to a 100% yield of trihexylamine. The aqueous phase obtained after extraction of trihexylamine contained 63.1 g of ascorbic acid, corresponding to a yield of 78.5%, and 14.8 g of ketogulonic acid ethyl ester, corresponding to a recovery of 14.7%. Example 12 The reaction of ketogulonic acid methyl ester with trihexylamine was carried out in the same manner as in Example 1, except that the extraction was performed with a different solvent. The results are summarized in the table below.

Table: Example 13 In a 500 ml sulfonation flask equipped with a stirrer, a thermometer, a reflux condenser and a 50 ml dropping funnel, 26.8 g (128.7 mmol) of ketogulonic acid chilluryl ester were added.
and 125 ml of acetonitrile were added under argon. The mixture was then heated to 78°C (reflux) with stirring. Then trihexylamine (99.4
%) was added dropwise from the dropping funnel over 15 minutes. After a reaction time of about 1 hour, the ester completely went into solution. After stirring for a total of 2 1/2 hours at room temperature, the orange-brown mixture was added to a rotating perfluorator that was flushed with nitrogen. The mixture was then heated with approximately 500 ml of n-hexane for 20 hours.
was extracted continuously. One hour after the start of the extraction, ascorbic acid crystallized out from the acetonitrile phase. After the extraction was completed, the extracted contents were filtered off with suction. The yellowish crystals were washed with hexane and acetonitrile and dried in a desiccator overnight. 20.6 g of ascorbic acid with a crystal content of 99.5% was obtained, corresponding to a yield of 90.4%. The mother liquor obtained after the filtration was separated using a separatory funnel. The two hexane phases were combined, dried with about 30 g of sodium sulfate and evaporated in a rotary evaporator at 45° C./100-20 mbar. As a result, 34.9 g of yellow trihexylamine with a content of 98.2% remained. This corresponded to a trihexylamine yield of 99.4%. The orange acetonitrile phase contained an additional 0.8 g of ascorbic acid. This corresponded to a yield of 93.7% when combined with crystallized ascorbic acid.

Claims (1)

[Claims] 1. General formula [In the formula, R means lower alkyl] A ketogulonic acid ester of the following formula is reacted with an amine having 12 to 38 carbon atoms in a suitable organic solvent to obtain the general formula [In the formula, X represents the ammonium ion of the C ₁₂ -C ₃₈ amine used] An ascorbic acid amine salt of the formula is generated, and the ascorbic acid amine salt of the formula is decomposed without neutralization to form the formula 1. A process for producing ascorbic acid, which comprises producing ascorbic acid of the above formula and a C ₁₂ -C ₃₈ amine, and isolating the ascorbic acid of the above formula and the optionally used C ₁₂ -C ₃₈ amine. 2. The method according to claim 1, wherein a linear tertiary alkylamine having 15 to 30 carbon atoms is used as the amine. 3. The method according to claim 1, wherein a branched secondary alkylamine having 16 to 25 carbon atoms is used as the amine. 4. The method according to claim 1, wherein a branched primary alkylamine having 12 to 24 carbon atoms is used as the amine. 5. The method according to claim 1 or 2, wherein tripentylamine, triisopentylamine, N,N-dioctylmethylamine, trihexylamine, triheptylamine, trioctylamine or tridodecylamine is used as the amine. 6 Bis(2-ethylhexyl)amine, dibenzylamine, dioctylamine, N-dodecenyl-N-trialkyl-methylamine (number of carbon atoms
mixture of 24 to 27) or N-lauryl-N
-Trialkyl-methylamine (from 24 carbon atoms)
4. The method according to claim 1 or 3, wherein a mixture of 27 amines) is used as the amine. 7 Trialkyl-methylamine (18 carbon atoms
~24), a high molecular weight oil-soluble primary amine with a highly branched aliphatic chain, α-amino-diphenylmethane or 1,2-diphenylethylamine as the amine. Or the method described in Section 4. 8. The method according to any one of claims 1 to 7, wherein a lower alcohol having 1 to 5 carbon atoms is used as an organic solvent. 9. The method according to claim 8, wherein the lower alcohol is methanol. 10 Claim 1 in which the amine is used in an amount of 0.1 to 1.5 mol per mol of ketogulonic acid ester
9. The method according to any one of items 9 to 9. 11 Claim 1 in which the amine is used in an amount of 0.5 to 1.1 mol per mol of ketogulonic acid ester
9. The method according to any one of items 9 to 9. 12 Claim 1 in which the amine is used in an amount of 0.9 to 1 mole per mole of ketogulonic acid ester
9. The method according to any one of items 9 to 9. 13. A process according to any of claims 1 to 12, wherein the reaction of ketogulonic acid and amine is carried out at a temperature of up to 90°C. 14 Reaction between ketogulonic acid and amine at 50-75°
13. The method according to any one of claims 1 to 12, which is carried out at a temperature of . 15. The method according to any one of claims 1 to 12, wherein the reaction between ketogulonic acid and an amine is carried out at a temperature of 65°C. 16. The method according to any one of claims 1 to 15, wherein the ascorbic acid amine salt is decomposed by liquid-liquid extraction. 17. A process according to any of claims 1 to 15, wherein the decomposition of the ascorbic acid amine salt is carried out by digestion with a suitable organic solvent.