Panthenol, especially its d (+) isomer, is a valuable agent for the treatment of dermatoses, burns and infectious ulcers as well as a valuable additive in shampoos and other cosmetics.

Various methods for the production of 3-hydroxypropionitrile are known from the literature, e. g. , the reaction of 2-chloroethanol with an alkali cyanide to give 3- hydroxypropionitrile as described e. g. in US 2,311, 636. The production of 3- hydroxypropionitrile by the addition of hydrocyanic acid to ethylene oxide was reported, e. g. in US 2,653, 162 and US 5,268, 499.3-hydroxypropionitrile as the addition product of water and acrylonitrile is described, e. g. in US 2,579, 580 and US 3,024, 267.

EP 1,120, 404 describes a process for the production of 3-hydroxypropionitrile which comprises the reaction of water with acrylonitrile to give a mixture of the desired product and bis (cyanoethyl) ether and subsequent pyrolysis of the bis (cyanoethyl) ether in the mixture to additional 3-hydroxypropionitrile in an overall multi-EP process. The steps of this process are: (a) reacting acrylonitrile with water in the presence of a weak base in order to obtain a two-phase organic-aqueous mixture; (b) separating off the aqueous phase in the mixture obtained in (a); (c) distilling off the acrylonitrile from the organic phase remaining after (b) in order to obtain a mixture consisting mainly of bis (cyanoethyl) ether and 3-hydroxypropionitrile; (d) subjecting the mixture obtained in (c) to a pyrolysis in the presence of a basic catalyst; and (e) isolating the desired 3-hydroxypropionitrile by fractional distillation from the mixture consisting mainly of 3-hydroxypropionitrile and acrylonitrile obtained in (d).

However, when running this reaction in a continuous manner at a large scale the yields would significantly be decreased on the one hand because of the formation of by-

products such as acrylamide and of the crystallisation of the catalyst which plugs the reactors during the addition reaction (a) and on the other hand because of considerable decomposition of the 3-hydroxypropionitrile during the fragmentation (pyrolysis) reaction.

It has been found that the reaction can be carried out in a fully continuous manner in two steps. In the first step acrylonitrile and water are continuously reacted in a staged, pressurized column reactor in the presence of a weak base. Then, the reaction mixture of the addition reaction is transferred continuously under simultaneous neutralisation of the catalyst to a reactive distillation as a second step where the fragmentation of the addition product is catalysed by the salts formed by the neutralisation of the weak base.

The reactive distillation is performed in an evaporator wherein the fragmentation reaction proceeds rapidly and with low decomposition of the products. Preferably, the evaporator is a thin film evaporator.

Ideally the conditions of the addition reaction are chosen in order to obtain a single phase solution at the end of the addition reaction which facilitates the continuous transfer of the reaction mixture with simultaneous neutralisation of the catalyst.

The present invention thus provides a process for the preparation of 3-hydroxypropio- nitrile in a fully continuous large scale process consisting of only two operations without break, according to the reaction Scheme below >.-,--"CN + H20 + base stepa) recycling of step a) acrylonitrile - + HO CN + NC~ CN - transfer and neutralisation step b) of the reaction mixture - fragmentation CN + HO CN + salt

The process consists (a) of an addition reaction in a first step where acrylonitrile and water are reacted in the presence of a weak base to form a reaction mixture of 3-hydroxypropionitrile, bis (cyano- ethyl) ether, unreacted acrylonitrile and water, which mixture is continuously neutralised during the transfer to the second process step; and (b) of a reactive distillation in a second step where the bis (cyanoethyl) ether contained in the reaction mixture is fragmented into 3-hydroxypropionitrile and acrylonitrile and the 3-hydroxypropionitrile subsequently separated and isolated.

The addition of the acrylonitrile with the water is effected in process step (a) generally at a temperature in the range of 80°C to 150°C, preferably at temperatures in the range of 100°C to 130°C, and generally at a pressure of 0.1 MPa to 0.8 MPa, preferably of 0.2 MPa to 0.6 MPa. The ratio acrylonitrile/water is 1: 1 to 1: 4, preferably 1 : 2. The water con- tains from 0.05 to 2.5 mol-%, preferably 0.15 mol-% catalyst salts. Ideally, the reaction conditions are chosen in order to obtain a single phase reaction mixture at the end of the addition reaction.

According to the invention the reaction mixture of the addition reaction (a) which con- tains 4-hydroxypropionitrile, bis (cyanoethyl) ether, unreacted acrylonitrile and water is continuously neutralised by addition of an aqueous solution of a weak acid during the transfer to the second reaction step (b) which is a distillative reaction for the fragmentation of the bis (cyanoethyl) ether to 3-hydroxypropionitrile and acrylonitrile.

The reaction temperature of the fragmentation reaction is from 140°C to 180°C, preferably from 160°C to 170°C under a pressure of 0.5 kPa to 50 kPa, preferably of 1 kPa to 10 kPa. The 3-hydroxypropionitrile is separated continuously together with the acrylonitrile formed and water; the acrylonitrile and water are then separated from the desired product (3-hydroxypropionitrile) by condensation in three consecutive stages; the high-boiling by-products formed during the entire process, as well as the catalyst are collected at the bottom of the evaporator.

If desired, the excess of water and the unreacted acrylonitrile of the addition reaction (a) may be distilled off during the transfer of the reaction mixture to the second process step.

This may for example be done in a falling-film evaporator with a distillation column mounted between the two reactors.

According to the invention the reactive distillation step (b) is operated with one single thin-film evaporator. However, if desired the reaction can also be distributed over two, or even more, smaller evaporators connected in series with the same results. Furthermore, the unreacted acrylonitrile and the acrylonitrile formed in the fragmentation process can be recycled by re-feeding it into the addition reaction.

Under the term"weak base"and"catalyst salts"in the addition reaction (a) there is to be understood an inorganic base, the pKa value of which is 8 to 12. The inorganic base is conveniently an alkali metal carbonate, e. g. sodium or potassium carbonate, an alkali metal bicarbonate, e. g. sodium or potassium bicarbonate, or a mixture of two or more of these inorganic bases, e. g. a mixture of sodium carbonate and sodium bicarbonate.

Sodium carbonate, potassium carbonate, a mixture of sodium carbonate and sodium bicarbonate or a mixture of potassium carbonate and potassium bicarbonate is preferably used as the weak base.

The term"weak acid"as used herein means a lower (Cl 3) carboxylic acid, e. g. formic acid, acetic acid or propionic acid, preferably acetic acid.

The term"neutralisation"means the direct addition of an aqueous solution of the weak acid during the transfer from the addition step (a) to the reactive distillation step (b). The reaction solution is preferably neutralised by the addition of a lower (Cl 3) carboxylic acid, e. g. formic acid, acetic acid or propionic acid. For example, when sodium carbonate or sodium bicarbonate is used as the weak base and acetic acid is used as the weak acid, the base sodium acetate is formed by the neutralisation. Preferably, a mixture of sodium carbonate and sodium bicarbonate is used as the weak base and acetic acid is used as the weak acid in the process in accordance with this aspect of the present invention.

The term"catalyst"in the reaction step (b) stands for the salts formed during neutralisa- tion of the weak base with the weak acid, especially for the sodium acetate formed by neutralisation of the sodium carbonate and bicarbonate with acetic acid.

In a preferred aspect of the invention the addition reaction (a) is carried out by feeding acrylonitrile and water in a molar ratio of 1: 1 to 1: 3, preferably in a ratio of 1: 2 into a column reactor. The reaction is carried out at a temperature of 100°C to 130°C, preferably at about 110°C and under a pressure of 0.4 MPa. The water contains from 0.05 to 2.5 mol-%, preferably 0.15 mol-% catalyst salts. The catalyst salts consists in a 75: 25 to 50: 50 mixture, preferably in a 65: 35 mixture of sodium carbonate and sodium

bicarbonate. Under these reaction conditions about 56% of the acrylonitrile are converted to bis (cyanoethyl) ether and about 21% are converted to 3- hydroxypropionitrile. The reaction mixture at the reactor exit consists in a single phase.

The reaction mixture, which consists mainly of bis (cyanoethyl) ether, 3-hydroxypropio- nitrile, water, unreacted acrylonitrile and the weak base is continuously neutralised by direct mixing of the reaction mixture with at least 0.5 to 1.5 equivalents, preferably 1 equivalent of a 20-50% aqueous weak acid solution, preferably of an acetic acid solution during the transfer to the reactive distillation step (b), where the formed salt acts as a catalyst in the fragmentation. In case of neutralisation with acetic acid the catalyst salt in step (b) is sodium acetate.

In a further preferred aspect of the invention the reactive distillation step is carried out in a thin film evaporator. The neutralised reaction mixture of step (a) is fed directly and continuously in mid-height into a distillation column mounted on a thin-film evaporator. The fragmentation of the bis (cyano ethyl) ether takes place at an evaporator temperature of 140-180°C, preferably at 160-170°C and a pressure of 0.5 kPa to 50 kPa, preferably from 1 kPa to 10 kPa. At least 95% of the bis (cyanoethyl) ether are fragmented to 3-hydroxypropionitrile in one pass. The reaction time is short, it varies from 1 to 15 minutes and depends of course on the reaction temperature. Simultaneously, the 3- hydroxypropionitrile is separated continuously at the top of the distillation column together with water and the acrylonitrile formed. Acrylonitrile and water are then separated from the 3-hydroxypropionitrile by condensation in three consecutive stages.

The high-boiling by-products formed in the entire process, as well as the catalyst salts are collected at the bottom of the evaporator.

According to the invention, 3-hydroxypropionitrile can be obtained in a fully continuous manner in high purity and high overall yield. The invention is illustrated by the following Examples: Examples Addition Reaction <BR> <BR> For all examples described below, the first reaction step (addition reaction (a) ) was per- formed in a pressurised column reactor. Acrylonitrile and water in a molar ratio of 1: 2 were fed into a double-jacketed, pressurised column reactor with 25 stirred stages. The water contained 0.15 mol-% catalyst salts based on water. The catalyst consisted in a

65: 35 mixture of sodium carbonate and sodium bicarbonate. After a reaction time of 75 minutes at 110°C and 0.4 MPa (4 bar) 56% of the acrylonitrile were converted to bis (cyanoethyl) ether and 21% to 3-hydroxypropionitrile. The clear reaction solution at the reactor exit consisted in a single light yellow phase.

The catalyst salts were continuously neutralised by direct mixing of the reaction solution with 1 equivalent of a 20 % aqueous acetic acid solution during the transfer to the second reaction step.

For example 1 the excess of acrylonitrile and water was not removed during the transfer to the second reaction step. For examples 2 and 3 the excess of acrylonitrile and water was removed during the transfer. For example 4 the non-converted bis (cyanoethyl) ether in the bottom product of the thin film evaporator was fragmented in a second pass in order to increase the overall 3-hydroxypropionitrile yield.

The neutralised solution was fed directly and continuously into the next process step.

Example 1 describes the fragmentation reaction starting from the neutralised reaction solution fed in mid-height into a distillation column mounted on a thin-film evaporator (without previous removal of the excess of water and acrylonitrile).

The reaction solution from the addition reaction consists of : 28.0 % water 17.3 % acrylonitrile 2. 3 % acrylamide 13.8 % 3-hydroxypropionitrile 38.6 % bis (cyanoethyl) ether neutralisation salts Operation parameters: evaporator size 0. 12m2 column (height/diameter) 1 m/30 mm column packing Sulzer BX feed position mid-height of the column Heating temperature of the evaporator 170°C vapor temperature at the top of the evaporator 145°C vapor temperature at the top of the column 103°C Operation pressure (vacuum) 5.5 kPa (55mbar) reflux ratio (reflux : overhead product) 1: 6 addition rate 25g/min Result:

fragmentation 98. 6 % decomposition 7. 2 % 3-hydroxypropionitrile at the top of the column in one pass 77. 7 % 3-hydroxypropionitrile loss in the bottom product 5. 2 % 3-hydroxypropionitrile recycling in the acrylonitrile/H2O-distillate 9. 9 % The 3-hydroxypropionitrile yield may be increased with a second pass by recycling of the bottom product of the distillation in an additional thin-film evaporator. As a result the maximum 3-hydroxypropionitrile yield in the continuous process was 89.4 % calculated on the 3-hydroxynitrile content of the feed solution (presuming 100 % theoretical frag- mentation).

Composition of the product 3-hydroxypropionitrile distillate 85.6 % 3-hydroxypropionitrile 6.7 % acrylamide 0.7 % acrylonitrile 7.0 % water bottom product 26.6 % 3-hydroxypropionitrile 7.7 % bis (cyanoethyl) ether 1.8 % acrylamide 0.0 % acrylonitrile 2.3 % water and decomposition products acrylonitrile condensate 87.5 % acrylonitrile 7.9 % water 0.2 % acrylamide 4.4 % 3-hydroxypropionitrile water condensate 7.9 % acrylonitrile 84.8 % water 0.6 % acrylamide 6.7 % 3-3-hydroxypropionitrile Example 2

describes the fragmentation reaction starting from the reaction solution from which excess water and unreacted acrylonitrile were distilled off during neutralisation in an falling film evaporator with a distillation column mounted as an intermediate between the column reactor and the fragmentation reactor.

The reaction solution from the addition reaction consists of : 8.7 % water 2.1 % acrylonitrile 4.4 % acrylamide 23.5 % 3-hydroxypropionitrile 61.3 % bis (cyanoethyl) ether and neutralisation salts Operation parameters: evaporator size 0. 12m2 column (height/diameter) 1 m/30 mm column packing Sulzer BX feed position mid-height of the column Heating temperature of the evaporator 167. 5°C vapor temperature at the top of the evaporator 143°C vapor temperature at the top of the column 120°C operation vacuum (pressure) 5.5 kPa (55mbar) reflux ratio (reflux : overhead product) 1: 25 addition rate 20g/min Results: fragmentation 96. 6 % decomposition 10. 3 % 3-hydroxypropionitrile yield at the top of the column without recycling 71. 6 % 3-hydroxypropionitrile loss in bottom product 8. 8 % 3-hydroxypropionitrile recycling in the acrylonitrile/H2O distillate 9. 3 % The maximum 3-hydroxypropionitrile yield in this continuous process was 85.4% calculated on the 3-hydroxypropionitrile content of the feed solution (presuming a 100% theoretical fragmentation) The 3-hydroxypropionitrile yield may be increased by recycling the evaporated mixture and by additional recycling of the bottom product of the distillation.

Composition of the product 3-hydroxypropionitrile-distillate 90.2 % 3-hydroxypropionitrile

7.8 % acrylamide 0.8 % acrylonitrile 1. 2 % water bottom product 34.1 % 3-hydroxypropionitrile 13.7 % bis (cyanoethyl) ether 2.2 % acrylamide 3.0 % acrylonitrile 1.5 % water and decomposition products acrylonitrile condensate 81.2 % acrylonitrile 7.9 % water 0.7 % acrylamide 10.2 % 3-hydroxypropionitrile water condensate 10.6 % acrylonitrile 73.3 % water 1.8 % acrylamide 14.3 % 3-hydroxypropionitrile Example 3 The reaction solution from the addition reaction consists of 10. 8 % water 2.2 % acrylonitrile 3.7 % acrylamide 21.5 % 3-hydroxypropionitrile 61.8 % bis (cyanoethyl) ether and salts from the neutralisation operation parameters evaporator size 0. 12m2 column size (height/diameter) 1 m/30 mm column packing Sulzer BX feed location mid height of the column Heating temperature of the evaporator 167. 5°C vapor temperature at the top of the evaporator 142°C vapor temperature at the top of the column 121°C operation pressure (vacuum) 5.5 kPa (55mbar)

reflux ratio (reflux : overhead product) 1: 15 addition rate 16.6g/min Results fragmentation 93. 6 % decomposition 7. 9 % 3-hydroxypropionitrile yield at the top of the column without recycling 77. 7 % 3-hydroxypropionitrile loss in bottom product 9. 7 % 3-hydroxypropionitrile recycling in the acrylonitrile/H2O-Destillat 4. 7 % The maximum 3-hydroxypropionitrile yield in this continuous process was 89.4 % calculated on the 3-hydroxypropionitrile content of the feed solution (presuming a 100% theoretical fragmentation) The 3-hydroxypropionitrile yield may be increased by recycling the evaporated mixture and by additional recycling of the bottom product of the distillation.

In a further evaporation step of the bottom product additional 8.2 % product (of the 9.7% loss) was be recovered.

Composition of the product solutions 3-hydroxypropionitrile distillate 91.3 % 3-hydroxypropionitrile 7.4 % acrylamide 0.7 % acrylonitrile 0.6 % water bottom product 30.6 % 3-hydroxypropionitrile 21.9 % bis (cyanoethyl) ether 1.3 % acrylamide 0.6 % acrylonitrile 0.4 % water and decomposition products acrylonitrile condensate 95.9 % acrylonitrile 3. 2 % water 0.1 % acrylamide 0. 8 % 3-hydroxypropionitrile water condensate 7.6 % acrylonitrile

88.2 % water 0.5 % acrylamide 3.7 % 3-hydroxypropionitrile Example 4 The bottom product from the first fragmentation reaction was transferred to a second thin-film evaporator for further fragmentation of the unreacted bis (cyanoethyl) ether.

The fragmentation product was transferred directly into the first thin-film evaporator for isolation of the 3-hydroxypropionitrile. This two-pass process increased the overall 3- hydroxypropionitrile yield.

Composition of the feed solution (bottom product of fragmentation Example 1) : 2.1 % water 0.1 % acrylonitrile 2.0 % acrylamide 31.4 % 3-hydroxypropionitrile 32.3 % bis (cyanoethyl) ether and decomposition products Operation parameters evaporator size 0. 12m2 place of feed directly into the top of the evaporator Heating temperature of the evaporator 1705°C vapor temperature at the top of the evaporator 123°C operational pressure (vacuum) 5.5 kPa (55mbar) addition rate lOg/min Results fragmentation 86. 7 % decomposition 2. 0 % 3-hydroxypropionitrile yield 86. 4 % 3-hydroxypropionitrile loss in bottom product 2 6. 4 % All values refer to the total feed amount Composition of the product solutions 3-hydroxypropionitrile crude distillate 74.4 % 3-hydroxypropionitrile 7.4 % bis (cyanoethyl) ether 3.7 % acrylamide

12.3 % acrylonitrile 2.2 % water bottom product 9.3 % 3-hydroxypropionitrile 0.3 % bis (cyanoethyl) ether 2.7 % acrylamide 0.2 % acrylonitrile 0. 0 % water and decomposition products