Process for the manufacture of oxygenates

Details Process for the manufacture of oxygenates Process for the manufacture of oxygenates

1999-08-17

2001-02-20

Padmanabhan, Sreeni (Department: 1621)

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

Organic compounds

Carboxylic acids and salts thereof

C562S589000, C568S405000, C568S470000, C568S475000

Reexamination Certificate

active

06191308

ABSTRACT:

This Application is the U.S. National Stage Application of PCT/EP97/02124 filed Apr. 23, 1997.
This invention relates to processes for the manufacture of organic compounds, and more especially to the manufacture of oxygenates of hydrocarbons.
In the industrial preparation of functional organic compounds, it is desirable that a given reaction proceeds in good yield and high specificity. There are numerous routes to organic molecules containing a hydroxy group. The yield resulting from a number of such routes is, however, not high, and environmentally acceptable effluent disposal and separation of the product from by-products add to costs.
The need for an improvement in manufacturing processes is exemplified by lactic acid production.
Lactic acid, 2-hydroxypropionic 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, for example using acetaldehyde, propene, or propionic acid, as starting materials, have grown in commercial importance but they too present some environmental problems, and yields admit of improvement.
As discussed in Chemistry in Britain, December 1996, 45, the lactic acid produced by fermentation is neutralized as it is produced by calcium carbonate and, to keep the salt in solution so that it may be separated from residues by filtration, its concentration has to be kept low, resulting in high plant capacity requirements and hence costs. The workup, including carbon treatment, evaporation and sulphuric acid treatment, produces stoichiometric quantities of calcium sulphate, and the resulting lactic acid is only of technical grade. Purification entails esterification, distillation and hydrolysis, with their associated waste production. If chemical synthesis is used, acetaldehyde is treated with HCN to give lactonitrile, which is hydrolysed using sulphuric acid resulting in the low value product ammonium sulphate. Again, for purification, the crude acid has to be esterified and the ester hydrolysed. Both commercial procedures are therefore costly in energy and, inter alia, waste disposal.
There are also numerous synthetic routes by which a hydroxy group may be introduced into a ketone. For example, hydroxyacetone, a molecule with numerous uses as an intermediate in food, fine chemicals and pharmaceutical preparation and elsewhere, for example, as a solvent, is typically made by bromination of acetone and nucleophilic replacement of the bromine substituent by a hydroxy group. Environmentally acceptable effluent disposal and separation of the desired product from by-products (which here include the aldol condensate typically resulting in the alkaline environment prevailing) again add to costs.
There clearly remains a need for a better synthetic route to many hydroxy-substituted carbonyl compounds.
In “Zeolites: A Refined Tool for Designing Catalytic Sites”, edited by Bonneviot and Kaliaguine (Elsevier, 1995) Yang and Wang describe the elimination of methanol from dimethylacetal, forming methyl vinyl ether, over aluminophosphate molecular sieves and zeolites.
In Synthesis, August 1977, p 578, Frimer describes the preparation of an &agr;-hydroxy acetal by peracid epoxidation of the corresponding enol ether in an alcoholic solvent.
In U.S. Pat. No. 5,354,875 there is disclosed the epoxidation of olefins, including vinyl ethers, using a mixture of titanium silicalite and titania.
In this specification, the term “vinyl ether” is used to denote a compound in which one of two carbon atoms joined by an olefinic bond is linked to the ether oxygen.
The present invention provides a process for the manufacture of an &agr;-hydroxy aldehyde or ketone in which the carbonyl group is protected which comprises (a) forming an acetal or ketal by reaction of an aldehyde or ketone and an alcohol or an ortho-ester, (b) decomposing the acetal or ketal to form a vinyl ether, and (c) oxidizing the vinyl ether in the presence of a carbonyl group-protective reagent to form the &agr;-hydroxy aldehyde or ketone with the carbonyl group protected.
The reaction, step (a), between the aldehyde or ketone and the alcohol is desirably carried out with the alcohol in molar excess, advantageously in at least twice molar proportions for a monohydroxy alcohol, preferably in a molar proportion of aldehyde:alcohol within the range of from 1:2 to 1:10 and more preferably from 1:2 to 1:6. Although not at present preferred, a dihydroxy alcohol may be used, in which case equimolar proportions suffice. While an elevated temperature facilitates rapid reaction and good conversion, any temperature within the range of from room temperature to 120° C., preferably about 100° C., may be used, advantageously at autogenous pressure.
As aldehyde, there may be mentioned, more especially, an aliphatic aldehyde, for example, acetaldehyde, propanal, a butanal, a pentanal or a hexanal, or an araliphatic aldehyde, e.g., phenylacetaldehyde. As ketone, there may be mentioned, more especially, an aromatic ketone, for example, acetophenone.
As the alcohol there may be mentioned more especially aliphatic alcohols, preferably saturated aliphatic alcohols, for example, methanol, ethanol, 1-propanol, as monohydroxy alcohols, and ethylene glycol as a dihydroxy alcohol. Alcohols having more than two hydroxy groups may be used, but are not at present preferred.
For ketal formation, the use of an ortho-ester is preferred to the use of an alcohol, e.g., ethyl orthoformate, CH(OC
2
H
5
)
3
may be used with good results.
The formation of the acetal or ketal is desirably carried out in the presence of a metallic halide, e.g., an alkaline earth halide, e.g., calcium chloride, or an acid catalyst, either heterogeneous or homogeneous e.g., a mineral acid, a Lewis acid, or a molecular sieve in acid form. Advantageously, a heterogeneous catalyst is used; as examples there may be mentioned a molecular sieve, for example, a silicon aluminophosphate, e.g., SAPO-5, 11 or 34, or, preferably, a zeolite, e.g., H-&bgr;, HMCM-41, H-Mordenite, H-Faujasite, or H-ZSM-5. A molecular sieve of the higher acidity represented by the zeolite examples is preferred, as is one that, like the zeolites, is relatively hydrophobic.
The molecular sieve may be used on a support, e.g., of silica or alumina, and dry silica gel and alumina may themselves be active catalysts in this reaction, as described by Kamitori, et al, Tetrahedron Letters, 26, 39, 4767 (1985).
The reaction may be carried out at room temperature or, preferably, an elevated temperature, advantageously of at least 80° C., preferably at least 100° C., in the liquid or gaseous phase, the liquid phase reaction being preferred, giving high conversion and selectivity.
The resulting acetal or ketal may readily be decomposed, step (b), by elimination of one molecule of alcohol to form a vinyl ether or by ring opening if the acetal is formed by a dihydric alcohol. Decomposition may be effected by pyrolysis, for example, by heating in an inert atmosphere at a temperature within the range of from 150 to 500° C., more especially from 250 to 400° C. A WHSV within the range of from 0.1 to 100, if desired or required using a catalyst, may conveniently be used. As catalysts there may be mentioned a supported noble metal catalyst, e.g., silver or platinum on silica or alumina, an acid catalyst, e.g., phosphorus pentoxide or p-tosyl acid, or, preferably, a molecular sieve catalyst. As molecular sieve, a weakly acid, medium or small pore material is preferred, e.g., Na-Mordenite, SAPO-34 and AlPO
4
-11. U.S. Pat. Nos. 4,891,451, 5,100,852, and 5,105,022, the disclosures of which are incorporated herein by reference, propose various catalysts (e.g., Mordenite, ZSM-5, borosilicate and iron silicate zeolites, and phosphate molecular sieves) for a reaction of this type.
If desired, steps (a) and (b) may be com

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