Patent Application
20080064905
In accordance with the invention a process is provided for preparing 1,2-diols by a) firstly reacting a carbonyl compound of the general formula (I)
in which
R1 and R2 are each, independently, H, an optionally substituted straight-chain or branched C1-C18-alkyl radical, an optionally substituted phenyl or C5-C6-cycloalkyl radical, with hydrocyanic acid to give the corresponding cyanohydrin,
b) subjecting the cyanohydrin obtained from process step a) to an acidic hydrolysis, and
c) catalytically hydrogenating the 2-hydroxycarboxylic acid obtained from process step b) with the aid of a noble metal catalyst based on ruthenium and rhenium.
It has been found, surprisingly, that it is possible in this way to prepare 1,2-diols in good yields and in a technically simple manner (i.e. without special apparatus). Moreover, the 1,2-diols prepared in accordance with the invention have a very high purity, which was likewise not foreseeable.
The process according to the present invention comprises the three reaction stages a), b) and c). In the first reaction stage a), a carbonyl compound of the general formula (I)
is reacted with hydrocyanic acid to give the corresponding cyanohydrin. In the general formula (I), R1 and R2 are each independently H, an optionally substituted straight-chain or branched C1-C18-alkyl radical or else an optionally substituted phenyl or C5-C6-cycloalkyl radical. In the case of alkyl or cycloalkyl radicals, the carbonyl compound may also have at least one substituent from the group of OH, NH2 or OR3 where R3 is a C1-C8-alkyl radical. In the case of phenyl radicals, the carbonyl compound of the general formula (I) may also have at least one OH or NH2 substituent.
In one embodiment, the carbonyl compounds are aldehydes and especially butyraldehyde.
The temperatures in reaction stage a) can be varied within wide limits, but it has been found to be particularly advantageous for reasons of economic viability to perform this reaction at temperatures of 0 to 100° C. and especially 0 to 30° C. The reaction temperature includes all values and subvalues therebetween, especially including 10, 20, 30, 40, 50, 60, 70, 80 and 90° C. It is particularly advantageous to perform reaction stage a) without solvent or in the presence of a solvent selected from the group of water, alcohols, ethers or mixtures thereof, preference being given to using C1-C4 alcohols among the alcohols, and diethyl ether and THF among the ethers.
Moreover, process stage a) can be performed in the presence of a basic catalyst, and organic amines, for example triethylamine, can preferably be employed. The basic catalyst is preferably used in an amount of 0.1 to 10 mol % based on the carbonyl compound. The amount of basic catalyst includes all values and subvalues therebetween, especially including 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 mol %.
In one embodiment, a 0.1 to 10% molar excess of hydrocyanic acid is employed in reaction stage a), based on the carbonyl compound used. The molar excess of hydrocyanic acid includes all values and subvalues therebetween, especially including 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 mol %.
On completion of reaction stage a), it is the cyanohydrin formed can be stabilized by adjusting the pH of the reaction mixture to 1.0 to 6.0 with the aid of acids, for example hydrochloric acid. The pH includes all values and subvalues therebetween, especially including 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 and 5.5.
In the subsequent second reaction stage b), the cyanohydrin obtained from process step a) is subjected to an acidic hydrolysis. The acidic hydrolysis is preferably performed with the aid of a mineral acid, especially in the form of an aqueous solution, or in the presence of an acidic ion exchanger.
A useful mineral acid here has been found in particular to be 20 to 37% hydrochloric acid or 50 to 80% sulphuric acid. The ratio of mineral acid to cyanohydrin is relatively uncritical, but it has been found to be particularly advantageous to use the mineral acid in an acid equivalent ratio to the cyanohydrin of 1.0 to 10.0:1 and more preferably of 1.2 to 2.0:1.
The hydrolysis step b) is performed preferably at elevated temperatures of 30 to 130° C. and in particular of 60 to 110° C. The temperature includes all values and subvalues therebetween, especially including 40, 50, 60, 70, 80, 90, 100, 110 and 120° C.
It is immediately possible in the context of the present invention to perform the hydrolysis under elevated pressures, preference being given to boiling conditions under standard pressure.
On completion of the acidic hydrolysis, in one embodiment, the pH of the reaction mixture is adjusted in aqueous sodium hydroxide solution to a pH of 0 to 4, the solvent is removed and the 2-hydroxycarboxylic acid is obtained by crystallization or extraction with an organic solvent. The pH includes all values and subvalues therebetween, especially including 0.5, 1, 1.5, 2, 2.5, 3, 3.5. In the case of extraction, the 2-hydroxycarboxylic acid is preferably subsequently purified by distillation under reduced pressure at 0.1 to 100 mbar. The pressure includes all values and subvalues therebetween, especially including 0.5, 1, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 mbar.
In the third reaction stage c), the 2-hydroxycarboxylic acid obtained from process step b) is catalytically hydrogenated with the aid of a noble metal catalyst based on ruthenium and rhenium. In this case, the noble metal catalyst in stage c) has a preferred noble metal content of 1 to 10% by weight, the support material used preferably being activated carbon. The noble metal content includes all values and subvalues therebetween, especially including 2, 3, 4, 5, 6, 7, 8, 9% by weight.
Moreover, the ruthenium/rhenium catalyst used in the hydrogenation step c) has a preferred content of ruthenium and rhenium, in each case, of 1 to 10% by weight. The content of ruthenium and rhenium, in each case, includes all values and subvalues therebetween, especially including 2, 3, 4, 5, 6, 7, 8, 9% by weight.
The reaction conditions in the hydrogenation step c) can likewise be varied within wide limits. Particularly advantageous conditions have been found to be temperatures of 100 to 300° C. and more preferably of 180 to 200° C., and hydrogen pressures of 50 to 300 bar and more preferably of 200 to 250 bar. The temperature includes all values and subvalues therebetween, especially including 150, 200, 250° C. The pressure includes all values and subvalues therebetween, especially including 100, 150, 200, 250 bar.
In one embodiment, the hydrogenation stage c) can also be undertaken in two steps. The amount of the catalyst used is generally 0.1 to 7.5% by weight and especially 2 to 5% by weight, based in each case on the amount of 2-hydroxycarboxylic acid used. The amount of the catalyst includes all values and subvalues therebetween, especially including 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5 and 7% by weight
Depending on the reaction conditions, the hydrogenation in reaction stage c) has ended after at most 20 hours, preferably after 1 to 12 hours and more preferably after 7 to 10 hours.
On completion of reaction stage c), the ruthenium/rhenium catalyst is removed from the crude product by filtration and can, in one embodiment, be recycled.
The resulting reaction product comprising the corresponding 1,2-diol can, for example, be isolated or purified by distillation. In the process of the present invention, the 1,2-diol is obtained in good yields of >60% and very high purities of >98%. The yield includes all values and subvalues therebetween, especially including 65, 70, 75, 80, 85, 90, 95, 97, 98, 99 and 99.5%. The purity includes all values and subvalues therebetween, especially including 98.5, 99, 99.5%.
In the process according to the invention, 1,2-pentanediol is preferably obtained.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only, and are not intended to be limiting unless otherwise specified.
A glass flask was initially charged with 72 g (1.0 mol) of butyraldehyde at room temperature and mixed with 0.5 g of triethylamine as a catalyst. 27.5 g (1.02 mol) of hydrocyanic acid were then metered in at 15-20° C. under temperature control and stirred at room temperature for about 1 hour. Hydrochloric acid was used to establish a pH of 2-4 in order to stabilize the cyanohydrin formed.
A second flask was initially charged with 243 g (2.0 mol) of 30% hydrochloric acid at 50° C., and the cyanohydrin from flask 1 was metered in within 30 minutes. During the addition, the temperature was increased up to reflux (at 106° C.). Thereafter, the mixture was stirred under reflux for another 1 hour. The acid excess was then neutralized with 40% aqueous sodium hydroxide solution up to pH 2.
The resulting reaction mixture was admixed with 200 ml of methyl tert-butyl ether and the aqueous phase was removed. In the organic phase, 2-hydroxypentanoic acid was present in a yield of >90% which, after the solvent had been distilled off, was distilled at 140-150° C. under a reduced pressure of 1 mbar. The yield was 73.8 g (71% of theory).
29.5 g (0.25 mol) of the 2-hydroxypentanoic acid thus obtained were dissolved in 470.5 g of water and this mixture, after adding 5.0 of water-moist catalyst on activated carbon (coating: 3% Ru and 2% Re), was hydrogenated exhaustively in a 11 autoclave at a hydrogen pressure of 250 bar and at a reaction temperature of 190° C. within 8 hours.
After the end of the reaction and cooling, the catalyst was filtered off and the filtrate was freed of water by distillation under reduced pressure using a rotary evaporator with a column attachment.
The resulting residue was then, using a short-path evaporator with a short column, subjected to a fractional high-vacuum distillation.
This afforded 16.8 g of 1,2-pentanediol with a GC purity (after silylation) of 98.7%, which corresponds to a yield of 64.6% of theory based on 2-hydroxypentanoic acid used.
A glass flask was initially charged with 360 g (5.0 mol) of butyraldehyde and 300 ml of water at room temperature, and mixed with 2.5 g of triethylamine as a catalyst. 137 g (5.1 mol) of hydrocyanic acid were then metered in at 15-20° C. under temperature control and the mixture was stirred at room temperature for about 1 hour. 80% sulphuric acid was used to establish a pH of 2-4 in order to stabilize the cyanohydrin formed.
A second flask was initially charged with 980 g (8.0 mol) of 80% sulphuric acid at 90° C., and the cyanohydrin from flask 1 was metered in within 60 minutes. During the addition, the temperature was increased to 105-110° C. Thereafter, the mixture was stirred at this temperature for another 3 hours. After cooling, the acid excess was neutralized with 40% aqueous sodium hydroxide solution up to pH 2.
The resulting reaction mixture was admixed with 1000 ml of methyl tert-butyl ether and the aqueous phase was removed. In the organic phase, 2-hydroxypentanoic acid was present together with approx. 10% unhydrolyzed butyraldehyde cyanohydrin.
After the solvent had been distilled off, the product was distilled together with the cyanohydrin at 140-150° C. under a reduced pressure of 1 mbar. The yield was 338.0 g (51.5% of theory based on a purity of 90%).
A 1 l autoclave was charged with a suspension consisting of 400 g of water and 5.0 g of water-moist catalyst (coating: 8% Ru and 1% Re) and prehydrogenated at 190° C. and 250 bar of hydrogen for the period of 2 hours.
Subsequently, after cooling and decompression, 156.0 g of 2-hydroxypentanoic acid—which still contains a proportion of approx. 10% of butyraldehyde cyanohydrin—were added to the catalyst suspension and the reaction mixture was subsequently hydrogenated at a reaction temperature of 190° C. and a hydrogen pressure of 250 bar over the course of 14 hours until the hydrogen uptake had ended.
After catalyst removal, the conversion of the hydrogenation was determined to be 96% by acidimetric titration; the further distillative workup of the filtrate was effected analogously to Example 1.
This afforded 89.2 g of 1,2-pentanediol with a purity of 98.1%; this corresponds—based on 2-hydroxypentanoic acid used—to a yield of 72.1% of theory.
A glass flask was initially charged with 72 g (1.0 mol) of butyraldehyde at room temperature and mixed with 0.5 g of triethylamine as a catalyst. 27.5 g (1.02 mol) of hydrocyanic acid were then metered in at 15-20° C. under temperature control and stirred at room temperature for about 1 hour. Hydrochloric acid was used to establish a pH of 2-4 in order to stabilize the cyanohydrin formed.
A second flask was initially charged with 243 g (2.0 mol) of 30% hydrochloric acid at 50° C. and the cyanohydrin from flask 1 was metered in within 30 minutes. During the addition, the temperature was increased up to reflux (at 106° C.). Thereafter, the mixture was stirred under reflux for another 1 hour. The acid excess was then neutralized with 40% aqueous sodium hydroxide solution up to pH 2.
The resulting reaction mixture was admixed with 200 ml of methyl tert-butyl ether and the aqueous phase was removed. The organic phase was extracted by shaking with 200 ml of water and removed from the water phase. It contained 2-hydroxypentanoic acid in a yield of >90%. The organic solvent was removed by distillation and the residue was subjected to hydrogenation (stage c).
To this end, a 1 l autoclave was charged with a suspension consisting of 400 g of water and 5.0 g of water-moist catalyst (coating: 8% Ru and 1% Re) and prehydrogenated at 190° C. and 250 bar of hydrogen for a period of 2 hours.
Subsequently, after cooling and decompression, the crude 2-hydroxypentanoic acid was added to the catalyst suspension and the reaction mixture was subsequently hydrogenated at a reaction temperature of 190° C. and a hydrogen pressure of 250 bar over the course of 14 hours until the hydrogen uptake had ended.
After catalyst removal, the conversion of the hydrogenation was determined to be 96% in the filtrate by acidimetric titration; the further distillative workup of the filtrate was effected analogously to Example 1.
This afforded 68.6 g of 1,2-pentanediol with a purity of 98.1%; this corresponds—based on butyraldehyde used—to a yield of 66.0% of theory.
German patent application 10 2006 041 941.3-43 filed Sep. 7, 2006, is incorporated herein by reference.
Numerous modifications and variations on the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102006041941.3-43 | Sep 2006 | DE | national |
