The aliphatic esters and polyesters of substituted sterically hindered hydroxyhydrocinnamic acid are well-known as effective antioxidants for a wide variety of organic materials protecting them from oxidative and thermal degradation. Many of these esters have gained wide commercial acceptance as phenolic antioxidants.
Some transesterification catalysts which may be used to prepare the instant compounds include lithium amide, aluminum isopropylate and dibutyltin oxide. U.S. Pat. No. 4,594,444 (Orban) teaches a process for the preparation of sterically hindered hydroxyphenylcarboxylic acid esters by the transesterification of the corresponding methyl or ethyl ester with a higher aliphatic alcohol using an oxide or an organometallic compound of a metal of the fourth main group or subgroup of the periodic table as catalyst in an amount between 0.05 and 1.0 mol percent based on the methyl or ethyl ester. Higher dialkyltin oxides, particularly dibutyltin oxides, are taught as the preferred catalyst for this process.
However, if the amount of tin residue in the product is too high, ultimate product stability is compromised and efforts must be taken to remove such residues. If the amount of tin catalyst can be reduced well below that seen in the Orban process, such residue removal efforts may be unnecessary and process economies would be evident. That is the case in the instant process where the amount of tin catalyst required is so small that its removal from the final product by distillation of said product is often unnecessary.
The instant process differs from this Orban process by running the transesterification process at much lower concentrations of tin catalyst and also at lower temperature.