Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1999-09-08
2001-11-13
Solola, Taofiq A. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S541000
Reexamination Certificate
active
06316641
ABSTRACT:
The invention concerns a method for preparing an epoxide of the formula:
where R is a hydroxyl OH group for glycidol,
or an alkoxide radical O—R′ with R′=alkyl or acyl for glycidyl compounds,
or a hydrogen H or an alkyl group for alkylene oxides.
The invention applies in particular to the preparation of glycidol:
or glycidyl compounds (in which the hydrogen of hydroxyl is replaced by an alkyl or acyl radical).
Epoxides have many applications as adhesives, coatings, intermediate products for the preparation of polyurethanes etc. Glycidol and its glycidyl derivatives are one of the important epoxide families and are used to a considerable extent in the textile, plastics, pharmaceutical, cosmetics and photochemical industries, in the detergents industry, and in building and public works by reason of their properties as stabilizers, plastics modifiers, surfactants and fire retardants etc. Since the start of the 1970s, glycidol has been produced industrially by oxidizing allyl alcohol by means of hydrogen peroxide in the presence of a catalyst based on tungsten oxide. The essential defect in this method lies in the large number of steps necessary for obtaining the aforementioned oxidation, for extracting glycidol from the homogeneous aqueous medium (containing the starting reagent and several byproducts: glycerol, acrolein, betahydroxy-propionaldehyde, glycerol allyl ether and decomposition products of the catalyst) and for then purifying the glycidol obtained in the aqueous medium. Moreover, the catalyst based on tungsten oxide is decomposed during the reaction and its consumption is a factor in increasing the cost (DE-OS 2 037 703, U.S. Pat. No. 3,625,981).
It should be noted that, before this method of preparation from allyl alcohol, other methods had been proposed for preparing glycidol, either from glycerol and ethylene carbonate, propylene carbonate or butylene carbonate (U.S. Pat. No. 2,636,040), or from glycerol carbonate (U.S. Pat. No. 2,856,413). If such preparations could be transposed onto the industrial scale, they would be particularly interesting since the starting products can easily be obtained from oleaginous plant materials, thus offering an outlet for these materials. However, the method proposed in the first patent (U.S. Pat. No. 2,636,040) which consists of preparing an intermediate complex from ethylene carbonate, propylene carbonate or butylene carbonate, and decomposing this, has the drawback of requiring a succession of steps with different operating conditions, certain of these at very low pressures; moreover, the effective yield from the method is relatively low (63%). The method dealt with in the second patent (U.S. Pat. No. 2,856,413) which consists of decomposing glycerol carbonate and then synthesizing glycidol in the presence of a metal salt dissolved in the glycerol carbonate, also has the drawback of requiring successive steps with different operating conditions (decomposition at a very low pressure, synthesis of glycidol and distillation); the same comments may be formulated as previously. In addition, the inventors of the present invention have carried out tests under the conditions of this patent and have found that, during the reaction, a very adherent solid polymer is formed which is deposited on the walls of the reactor and gradually blocks it.
The object of the invention is to provide a method for preparing glycidol or a glycidyl compound, or in a more general manner an epoxide of the formula previously indicated from a cyclic organic carbonate, in particular glycerol carbonate or a derivative of this compound, which can be employed in a single step, in particular continuously, and which is able to operate at pressures above the reduced pressures called for in the methods described above.
Another objective is to obtain a high effective yield (the effective yield being defined by the number of moles of epoxide recovered to the number of moles of cyclic organic carbonate used).
Another objective is to isolate the epoxide directly, in particular glycidol or glycidyl compound, and to anticipate a high purity for this compound.
To this end, the method with which the invention is concerned uses as the starting compound a cyclic organic carbonate with 5 links having the formula:
where
R=OH (for glycerol carbonate)
R=H for propylene carbonate,
R=alkyl for alkylene carbonates,
R=O—R′ with R′=alkyl or acyl for other cyclic organic carbonates.
The method concerned is of the type in which the cyclic organic carbonate is heated under reduced pressure to a temperature at least equal to 165° C. so as to carry out a contraction reaction of the carbonate ring:
into an apoxy ring
The method of the invention is characterized in that the reaction is carried out in a solid/liquid system in the presence of a polyol and a solid catalyst consisting of a type A zeolite or &ggr;-alumina.
In the process of the invention, the reaction used makes it possible to form, in a single step (and therefore with a single set of operating conditions), the epoxide, in particular glycidol or a glycidyl derivative, which is exhausted in the form of vapor and which only has to be extracted and separated from the carbon dioxide formed (simply by condensation). An epoxide is obtained directly in this way with good purity (greater than 92%). This reaction may be easily employed continuously by continuous extraction of the gaseous phase and continuous separation by condensation. Experiments showed, particularly in the case of the preparation of glycidol, that the reaction did not require very stringent low pressures and could in particular be carried out at pressures substantially between 3×10
3
and 10×10
3
Pascals at temperatures substantially between 170° C. and 210° C.; in particular, a pressure range of between 3.3×10
3
and 6×10
3
Pascals gave excellent performances while leading to moderate industrial operating costs. Tests have shown that the effective yield of epoxide was of the order of 75% to 90%.
The method of the invention is accordingly characterized by the presence in the reaction medium of:
on the one hand, a polyol which can advantageously consist of glycerol or a polyglycerol,
on the other hand, a specific solid catalyst: A-type zeolite, preferably in the H (wherein cation is replaced by H
f
) form or containing an alkali metal or alkaline earth cation, or &ggr;-alumina.
The mechanisms which lead to the epoxide under the operating conditions of the method of the invention are novel in the type of reaction concerned. First of all, the polyol fulfils a first function of being a carrier for the organic carbonate, preventing decomposition of this compound at the temperature of the medium and enabling it to diffuse and access the catalytic sites of the zeolite or &ggr;-alumina ; the organic carbonate may thus be adsorbed on the catalytic sites of the zeolite or of the &ggr;-alumina. Once the organic carbonate is adsorbed on these catalytic sites it is able to open, taking into account the pressure and temperature of the medium, and the polyol then fulfils a second function of a proton donor enabling this opening and contraction of the carbonate ring into an epoxy ring to occur. The epoxide thus formed is gaseous at the pressure and temperature of the medium and diffuses outside the catalytic site. Moreover, no tarry deposit is observed during or at the end of the process and it seems that it is the polyol which avoids these deposits (third function of the polyol) and it thus contributes to increasing the yield. Studies seem to show that the three abovementioned functions of the polyol are fulfilled in an optimum manner when substantially between 0.1 and 0.4 mole of polyol are available per mole of cyclic organic carbonate.
The zeolite used is preferably a powder with a mean particle size of between 3 and 5 microns. It is possible advantageously to use between 3.5 and 10.5 g of zeolite per mole of cyclic organic carbonate so that the medium contains a number of catalytic sites w
Gaset Antoine
Mouloungui Zephirin
Yoo Jeong-Woo
Organisation Nationale Interprofessionelle des Oleagineux (O.N.I
Solola Taofiq A.
Young & Thompson
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