Process for the manufacture of hydroxycarbonyl compounds

Details Process for the manufacture of hydroxycarbonyl compounds Process for the manufacture of hydroxycarbonyl compounds

1998-10-26

2000-08-22

Padmanabhan, Sreeni

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

568489, 568591, 562589, C07C 4527

Patent

active

061075256

DESCRIPTION:

BRIEF SUMMARY
This is the U.S. National Stage Application of PCT/EP97/02125 filed Apr. 23, 1997.
This invention relates to a process for the manufacture of a hydroxycarbonyl compound, more especially to the manufacture of lactic acid, 2-hydroxypropionic acid, and to a process for the manufacture of intermediates useful for syntheses of that and other compounds.
Lactic acid and its derivatives, especially salts and esters, have many industrial uses, primarily in the food industry but also increasingly in the manufacture of biodegradable polymers. Much of the product has long been obtained by fermentation of hexoses or hexose-producing raw materials, a procedure from which much unwanted by-product and effluent result; known synthetic methods have grown in commercial importance but they too present some environmental problems, and yields admit of improvement.
A synthetic route of present interest involves the selective oxidation of a propene ether in the presence of an aldehyde-group protecting or masking reagent to form 2-hydroxypropanal in which the aldehyde group is protected. This intermediate may then be deprotected and further oxidized to the desired lactic acid.
In Synthesis, August 1977, p 578, Frimer describes the preparation of an .alpha.-hydroxyacetal by epoxidation of an enol ether in an alcoholic solvent. The oxidizing agent used is m-chloroperbenzoic acid or MoO.sub.5 HMPA.
There remains a need, however, for a method of oxidation in which the oxidizing agent is more readily available or in which its conversion rate is high.
The present invention provides a process for the manufacture of a protected 2-hydroxy propanal in which a 1-propenyl ether is oxidized by hydrogen peroxide or an organic hydroperoxide in the presence of an aldehyde group-protecting reagent and a metal-containing oxidation catalyst.
The ether oxygen of the starting material, the propene ether, is advantageously linked to a hydrocarbyl, e.g., a saturated aliphatic or araliphatic, radical, advantageously a lower alkyl radical, e.g., one having at most four carbon atoms, preferably methyl, ethyl, or n-propyl. The radical may be substituted by non-hydrocarbyl groups, for example by a hydroxy group, as in, e.g., 2-hydroxyethyl, but is advantageously unsubstituted.
Reaction of the propene ether, to introduce a hydroxy group on the ethylenically bound carbon atom remote from the ether oxygen, is effected in the presence of an aldehyde group protecting reagent, a compound that forms a bond with the ethylenically bound carbon atom linked to the ether oxygen and provides a proton to the molecule. Such a protic masking or protecting compound may be, for example, an acid, especially a carboxylic acid, or, advantageously, an alcohol., in which case the resulting product is an a-hydroxy acetal, i.e., an acetal of 2-hydroxypropanal. The alcohol is advantageously an aliphatic alcohol, and may conveniently be an alcohol having a hydrocarbyl group corresponding to that of the ether starting material. It is advantageously a low-boiling alcohol, e.g., ethanol or methanol. The alcohol is advantageously present in at least a stoichiometric quantity, advantageously in a molar ratio to the propene ether of at least 5:1, preferably at least 10:1, and if desired up to 40:1. Ultimately, the reaction may be carried out in solution, in which case an excess of alcohol reactant may conveniently act as solvent.
As oxidizing agent, there may be mentioned, as indicated above, hydrogen peroxide, and an organic hydroperoxide, for example tert-butyl hydroperoxide (TBHP), ethylbenzene hydroperoxide, and cumene hydroperoxide. As oxidation catalyst is employed either a homogeneous or, preferably, a heterogeneous, catalyst. For example, there may be mentioned a metal oxide, for example TiO.sub.2, deposited on an amorphous support, e.g., silica, or a metal aerogel or xerogel. A heteropolyanionic acid catalyst is also suitable, for example, a polyoxometallate of the general formula XM.sub.12 O.sub.40.sup.x-8 wherein M represents a metal ion, e.g., Mo(VI), W(V), or V(V), and X repres

REFERENCES:
patent: 5025101 (1991-06-01), Gorun et al.
patent: 5504266 (1996-04-01), Tirtowidjojo et al.
Synthesis, Aug. 1977, pp. 578-579, A. A. Frimer: "Synthesis of Alpha-Hydroxyacetals".
Cat. Rev. Sci. Eng. (1995) 37(2), 311 to 352 "Heteropoly Acids and Related Compounds as Catalysts for Fine Chemical Synthesis".
A. Wohl, Berichte, 1908, 3599 at 3609, "Zur Kenntnis der Dreikohlenstoffreihe".

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