Patent EA-004252-B1 (EA)
Title: Method for preparing hydroxymethylthiobutyric acid
Inventor: GARRAIT MICHEL
IPC: C07C323/52
Filed: 1999-07-07
Abstract: 1. Process for hydrolyzing 2-hydroxy-4-methylthiobutyronitrile with sulphuric acid, characterized in that a molar quantity of sulphuric acid of between 0.6 and 0.88 relative to the 2-hydroxy-4-methylthiobutyronitrile is used, wherein in a first step, the hydration of 2-hydroxy-4-methy1thiobutyronitrile to 2-hydroxy-4-methylthiobutyramide is carried out with concentrated sulphuric acid in the presence of a water to 2-hydroxy-4-methylthiobutyronitrile molar ratio of between 1 and 3 and at a temperature of less than or equal to 60 degree C, in a second step, the hydrolysis of 2-hydroxy-4-methylthiobutyramide to 2-hydroxy-4-methylthiobutyric acid is carried out in the presence of an additional quantity of water. 2. Process according to claim 1, characterized in that the molar ratio between the sulphuric acid and 2-hydroxy-4-methylthiobutyronitrile is between 0.7 and 0.35. 3. Process according to claim 1, characterized in that the hydration of 2-hydroxy-4-methylthiobutyronitrile to 2-hydroxy-4-methylthiobutyramide is carried out at a temperature of between 0 and 50 degree C, continuously during the time period from 15 minute to 2 hours and at a pressure of between 0.01 bar and 3 bar to produce the medium derived from the first step contains less than 5% by weight of 2-hyrdoxy-4-methylthiobutyric acid and preferably less than 2% by weight. 4. Process according to claim 1, characterized in that the hydration of 2-hydroxy-4-methylthiobutyronitrile to 2-hydroxy-4-methylthiobutyramide is carried out at a temperature of between 0 and 50 degree C, continuously during the time period from 15 minute to 2 hours and at a pressure of between 0.01 bar and 3 bar to produce the medium derived from the first step contains more than 95% by weight of 2-hydroxy-4-methylthiobutyramide and preferably more than 98% by weight. 5. Process according to claim 1, characterized in that during the first step, the molar quantity of water relative to 2-hydroxy-4-methylthiobutyronitrile is between 1 and 2.5 mol. 6. Process according to claim 1, characterized in that the first step is carried out at a temperature of between 0 and 50 degree C. 7. Process according to claim 1, characterized in that the first step is carried out at a pressure of between 0.01 bar and 3 bar. 8. Process according to claim 1, characterized in that during the second step, a sufficient quantity of water is added in order to maintain the medium in a homogeneous form. 9. Process according to claim 8, characterized in that the minimum quantity of water during the second step is 28% by weight relative to the whole reaction medium. 10. Process according to claim 1, characterized in that the second step is carried out at a temperature of between 90 and 130 degree C. 11. Process according to claim 1, characterized in that the second step is carried out at a pressure of between 0.5 bar and 5 bar. 12. Process according to claim 1 or 5, characterized in that in the first step, a concentrated solution of 2-hydroxy-4-methylthiobutyronitrile is used. 13. Process according to claim 1 or 5, characterized in that in the first step, an aqueous solution of 2-hydroxy-4-methylthiobutyronitrile is used which is concentrated during the first step by evaporation of water. 14. Process according to claim 13, characterized in that the water evaporated is recycled to the second step.