Patent Watch

April 7, 2008

Produce precursors for lactate esters and 1,3-propanediol simultaneously. Lactate esters are of interest as environmentally friendly biodegradable solvents. 1,3-Propanediol is being investigated as a monomer for making a new type of polyester fiber, which is useful as a spandex substitute and in carpet manufacturing. However, commercialization of these materials has been hindered by high production costs. Lactic acid and 1,3-propanediol can be produced by fermentation technology or chemical synthesis.

Synthetic lactic acid can be manufactured via several routes. Three that have operated commercially include acetaldehyde via a lactonitrile intermediate, vinyl acetate carbonylation, and acetaldehyde carbonylation. Any chemistry that avoids the use of HCN is preferable in these processes—hence the interest in carbonylation. Other routes have also been tried, for example, propylene nitration with N₂O₄ followed by acid hydrolysis. Propionic acid also has been used as a feedstock; it is first chlorinated and subsequently converted to lactic acid via acid hydrolysis.

G. D. Eastham, A. J. Rucklidge, and D. Cole-Hamilton have developed improved catalysts and operating conditions for synthesizing lactate ester precursors via carbonylation of vinyl acetate. The catalyst system for their process is based on 1,2-bis(di-tert-butylphosphinomethyl)benzene and 1,2-bis(di-tert-butylphosphinomethyl)ferrocene ligands complexed to Pd(II). Two isomers are produced: the branched methyl 2-acetoxypropanoate and the linear methyl 3-acetoxypropanoate. The branched isomer can be converted to lactate esters, and the linear isomer can be converted to 1,3-propanediol. Both ligands produced in a branched/linear ratio of 2:1–3:1, with comparable rates. At 80 °C, vinyl acetate conversion was 73%, and the products were produced at a turnover number of 14,892 mol product/(mol Pd·hr). (Lucite International U.K. [Southampton, U.K.]. Eur. Pat. 1 565 425; Feb 02, 2008; Jeffrey S. Plotkin)

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