CH636591A5 - Process for preparing methoxyacetic acid - Google Patents

Description

636591

Claims (3)

PATENT CLAIMS 1. Process for the preparation of methoxyacetic acid, characterized in that 2-methoxyethanol is oxidized with nitric acid, the reaction being started at temperatures not higher than 90°C and the reaction being completed at temperatures of 40 to 60°C. 2. The method according to claim 1, characterized in that the oxidation is carried out in the presence of a vanadium catalyst. 3. Process according to claims 1 and 2, characterized in that only part of the educt is introduced with the nitric acid and that after reaching the initial temperature of 90 °C it is cooled to 40 to 60 °C and the remaining part of the educt is metered into the reaction mixture becomes. The present invention relates to a process for the production of methoxyacetic acid. It is known that methoxyacetic acid can be produced from 2-methoxyethanol, namely indirectly via methoxyacetaldehyde, the 2-methoxyethanol being dehydrogenated in the gas phase with the aid of a suitable catalyst (Ag or Cu catalyst) and then the aldehyde thus obtained is oxidized again with the aid of other suitable catalysts (Mn or Co acetate) in the liquid phase to give the end product, methoxyacetic acid (US Pat. Nos. 2,170,854; US Pat. No. 2,286,034; US Pat 604). The present invention now relates to a process for the production of methoxyacetic acid from 2-methoxyethanol in a direct way. According to the invention, this is achieved by a method according to patent claims 1 to 3. A preferred embodiment of the invention is the following: The amount of concentrated, preferably about 65% nitric acid used for the oxidation is introduced together with part of the starting material, i.e. the 2-methoxyethanol, suitably 3 to 5%, and briefly heated to 90°C. This is to start the reaction that leads to the formation of methoxyacetic acid. It is then immediately cooled to 40 to 60° C., preferably to 60° C., and the remaining main amount of 2-methoxyethanol is added dropwise to the reaction mixture within 90 minutes in such a way that the reaction rate can be controlled well. The reaction is then allowed to continue at 40 to 60° C., preferably at 60° C., until the total oxidation time (dropping time+after-reaction) is about 3 to 7 hours, preferably 3 to 4 hours. is The molar ratio of the amount used of concentrated, preferably 65% HNO3 to the amount of starting material, resp. 2-Methoxyethanol is 3 to 1 to 5 to 1, preferably 4 to 1. The process is preferably carried out in the presence of a vanadium catalyst, expediently 1 to 2 mmol of V 2 O per mole of starting material (2-methoxyethanol), in which case the induction time for igniting the oxidation at 90° C. can be reduced. To isolate the methoxyacetic acid, most of the unreacted nitric acid is expediently distilled off in vacuo at 15 to 20 Torr, the residue, which contains about 60 to 70% methoxyacetic acid and 20 to 40% nitric acid, can be worked up as follows : a) High vacuum fractional distillation at 1 to 2 30 torr. b) Reduction of the nitric acid still present with 40% aqueous formaldehyde and/or paraformaldehyde, with any nitrous acid or nitrogen oxides still present being eliminated at the end of the reaction by addition of urea 35 can be reduced. The crude methoxyacetic acid obtained in this way is then redistilled in a vacuum at 15 torr. examples Example educt ENTa 65% catalyst temp Time Reaction Prod.: Content (%) yield (mole) (mole) cq (H) MES h2o hno3 (%) 1 2 8th — 60 3.5 97.5 _ 1.2 78.2* 2 1 4 v2os 60 3.5 97.5 1 0.3 85.7 3 1 4 v2o5 60 3 99.3 0.1 <0.01 84.8 4 1 4 - 60 3.5 99.2 0.5 0.1 88.0 5 1 4 - 60 6 98.3 0.5 0.05 88.7 6 1 5 - 60 5.5 99.2 0.5 0.05 88.0 7 1 5 - 60 3.5 99.0 0.4 0.1 89.2 * Worked up by high vacuum fractional distillation