Process for preparing alpha-hydroxy esters by esterification of alpha-hydroxy acids
An alkyl and methyl technology, which is applied in the technical field of preparing α-hydroxy ester by esterifying α-hydroxy acid, can solve the problems of insufficient methionine content and the like
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Embodiment 1-12
[0262] For Examples 1-12, HMBA (minimum 95% purity) containing monomeric HMBA (possibly containing a mixture of dimers and / or oligomers) or a mixture containing monomers, dimers and / or oligomers HMBA (88% purity) and 12% water were used as starting materials as indicated.
[0263] General scheme 1: transesterification.
[0264]
Embodiment 1
[0265] Example 1. Screening scale synthesis of HMBi by transesterification of HMBA and various isopropyl esters.
[0266]
[0267]HMBA (95.6%; 1.70 g, 1.0 equiv) was added to a 100 mL reaction vessel containing 10 equiv of isopropyl formate (10 g). No acid catalyst was used in this reaction. The reaction mixture was stirred well, then heated to 100°C (or 150°C) for 7 hours. Reactions at elevated temperature were performed in sealed tubes. The reaction mixture was sampled before and after the reaction and subjected to HPLC analysis. HMBi conversion was monitored by HPLC. Reactions with other isopropyl reagents were performed similarly on a 1 to 2 g scale at the indicated temperatures for 7 hours. The reaction can also be run at the reflux temperature of the isopropyl reagent.
[0268] Table 1 presents the results from a screening experiment using six forms of isopropyl esters reacted with HMBA without catalyst transesterification. The results showed that HMBi was gener...
Embodiment 2
[0272] Example 2. Transesterification of HMBA by catalytic transesterification with isopropyl acetate.
[0273]
[0274] HMBA (95%, 247g) was diluted in dichloromethane and washed with MgSO 4 Dried, filtered and concentrated in vacuo to provide dry HMBA which was treated with isopropyl acetate (500 mL). The reaction mixture was heated and reacted at reflux (~80°C) for 12 hours. Reactions were repeated N=3 times (N=number of experiments). The reaction conversion was monitored by gas chromatography during the reaction period to observe the conversion to HMBi. After the reaction was complete, the reaction mixture was cooled to room temperature and partitioned between 250 mL ethyl acetate and 250 mL water (2x). Sat. NaHCO with 300 mL 3 (2x) and the collected organic phase was further washed with 300 mL of saturated NaCl solution. The organic layer was washed with Na 2 SO 4 Dry, filter, and concentrate under reduced pressure to give crude HMBi (210 g, 75%). The crude pro...
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