Process for making esters of 2-acetoxyalkanoic acids using an α-hydroxyalkanoic acid ester and an acetate ester as starting materials
2-Acetoxyalkanoic acid esters are made in a reaction of an α-hydroxyalkanoic acid ester and an acetate ester in the presence of a transesterification catalyst. Unlike previous methods for making 2-acetoxyalkanoic acid esters, this process proceeds in high yield and high selectivity to the desired product.
1. A process for making a 2-acetoxyalkanoic acid ester comprising heating a mixture of an α-hydroxyalkanoic acid ester and at least one mole of an alkyl acetate ester per mole of the α-hydroxyalkanoic acid ester in a reaction vessel to a temperature of at least 150° C. under superatmospheric pressure in the presence of a transesterification catalyst to convert at least a portion of the α-hydroxyalkanoic acid ester and alkyl acetate ester to a 2-acetoxyalkanoic acid ester and at least one alkanol or phenolic compound, wherein a water content in the reaction vessel during the reaction is maintained at below 0.15% by weight, the process being characterized by a selectivity of at least 80% to the 2-acetoxyalkanonic acid ester and a yield of 2-acetoxyalkanoic acid ester is 50 to 75%, based on the starting amount of the α-hydroxyalkanoic acid ester.
2. The process of claim 1 , wherein the ester of the α-hydroxyalkanoic acid is represented by the structure:
wherein R 1 is hydrogen, linear alkyl, branched alkyl or cycloalkyl and R 2 is linear alkyl or branched alkyl.
3. The process of claim 2 , wherein the acetate ester is represented by the structure:
wherein R 3 is linear alkyl or branched alkyl.
4. The process of claim 3 , wherein R 2 and R 3 each are independently methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl or t-butyl and R 1 is methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl or t-butyl.
5. The process of claim 4 , wherein R 2 and R 3 are the same.
6. The process of claim 5 , wherein R 2 and R 3 each are methyl.
7. The process of claim 5 , wherein R 2 and R 3 each are n-butyl.
8. The process of claim 5 , wherein R 1 is methyl.
9. The process of claim 1 , further comprising recovering the 2-acetoxyalkanoic acid ester.
10. The process of claim 9 , wherein the 2-acetoxyalkanoic acid ester is recovered by crystallization or distillation.
11. The process of claim 1 , wherein the conversion of the α-hydroxyalkanoic acid ester is 50 to 80%.
12. The process of claim 1 , wherein the selectivity to the 2-acetoxyalkanoic acid ester is at least 90%.