Process for preparing hydroxy-containing compounds from...

Details Process for preparing hydroxy-containing compounds from... Process for preparing hydroxy-containing compounds from...

1998-05-08

2001-11-13

Geist, Gary (Department: 1623)

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

Organic compounds

Carboxylic acid esters

C560S231000, C560S234000, C560S239000

Reexamination Certificate

active

06316664

ABSTRACT:

The invention relates to a process for preparing hydroxyl-containing compounds (1), in particular alcohols, and formic esters of a hydroxyl containing compound (2) by transesterification of a formic ester (also “formate” hereinafter) of a hydroxyl containing compound (1) with a hydroxyl-containing compound (2), in particular alcohol, in the presence of a tertiary amine.
It is known to prepare esters R
1
COOR
3
and/or hydroxyl-containing compound, in particular alcohol R
2
OH, by transesterification of esters R
1
COOR
2
with hydroxyl-containing compound, in particular alcohol R
3
OH, according to the following scheme:
R
1
COOR
2
+R
3
OH&rlarr2;R
1
COOR
3
+R
2
OH  (Equation 1).
Transesterification reactions of this type are described, for example, in The Chemistry of Carboxylic Acids and Esters, Ed. S. Patai, 1969, page 103 et seq.; Methoden der organischen Chemie (Houben-Weyl), Volume E5, Georg-Thieme Verlag, Stuttgart 1985, page 702 et seq. In the case where R
1
is H, the esters are of formic acid.
HCOOR
2
+R
3
OH&rlarr2;HCOOR
3
+R
2
OH  (Equation 2).
Some selected reactions in which formic esters are produced or result in industrial processes and are subsequently transesterified in accordance with Equation 2 are listed below.
1. Formic esters are employed as protective group for alcohols in synthetic chemistry. To obtain the unprotected alcohol it is subsequently necessary to remove the protective group quantitatively.
2. Formic esters occur in industrial processes in which formic acid is used as acidic catalyst, and in which alcohols are produced or are present. Particularly in the case of high-boiling compounds or polymers, these esters are often difficult to remove from the required alcohols by a physical purification process such as recrystallization, extraction or distillation, because their physical properties are very similar to those of the free alcohols. This is why the chemical method of transesterification is used, for example, for purification. The transesterification must take place quantitatively, and catalyst residues must not remain in the product.
a) For example, polyoxybutylene glycol formate (polyTHF formate) is formed in the cationic polymerization of tetrahydrofuran (THF) in the presence of formic acid (EP-A-503 386). In order to obtain pure polyoxybutylene glycol (polyTHF), the formate group must be removed quantitatively.
b) Another use in polymer chemistry is the polymerization of vinyl formate to poly(vinyl formate). In order to obtain the industrial product poly(vinyl alcohol), the formate groups, which are present in equimolar amounts, must be removed quantitatively.
c) In the Prins reaction of olefins with formaldehyde, which is catalyzed by formic acid, large amounts of the formates of the alcohols which are formed are produced (D.R. Adams, S. P. Bhatnagar, Synthesis (1977) 661-672; J. S. Bajorek, R. Battaglia, G. Pratt, J. K. Sutherland, J. Chem. Soc. Perkin I (1974) 1243-1245). In order to obtain the alcohols, the ester must be cleaved during the workup.
3. In reactions which are carried out in the presence of formaldehyde there is frequently formation, by Cannizzaro reaction of two equivalents of formaldehyde, of one equivalent of methanol and one equivalent of formic acid. Formic acid is also produced by crossed Cannizzaro reaction of aldehydes with formaldehyde. Formic acid produced in this way readily forms, under the reaction conditions, unwanted formic esters as byproduct. In this case too it is necessary to remove the formates either by physical separation methods or by chemical reaction.
The reactions according to Equation 1 and Equation 2 are equilibrium reactions. Starting from the ester R
1
COOR
2
, the equilibrium can be shifted in favor of the required product, the ester R
1
COOR
3
or the alcohol R
2
OH, by either using one initial component in excess or, more preferably, removing one reaction component, the alcohol R
2
OH or ester R
1
COOR
3
produced, for example by distillation or by crystallization, from the equilibrium.
It is known that addition of a catalyst is necessary to carry out the transesterification according to Equation 1 or Equation 2. Typical transesterification catalysts used in industry include sulfuric acid, p-toluenesulfonic acid, sodium hydroxide solution, sodium alcoholates, aluminum alcoholates, potassium cyanide as well as acidic or basic ion exchangers. However, these catalysts have a number of disadvantages (see: The Chemistry of Carboxylic Acids and Esters, Ed. S. Patai, 1969, page 103 et seq.; Methoden der organischen Chemie (Houben-Weyl), Volume E5, Georg-Thieme Verlag, Stuttgart 1985, page 702 et seq.).
1. The strong bases and acids used as catalyst may lead to numerous unwanted side reactions such as elimination, C-alkylation or polymerization.
2. If the required product is the alcohol R
2
OH, when strongly basic inorganic compounds like sodium methanolate are used as catalyst there are losses of yield, since part of the alcohol remains bound as alcoholate.
3. Neutralization is necessary for removal of the catalyst and liberation of alcohols from their alcoholates. This produces inorganic salts which have to be removed from the required product. This leads to decomposition of the catalyst. The inorganic salt must be disposed of.
4. Isolation of the required product is particularly difficult when the required alcohol or ester is high-boiling, crystalline or a polymer. The resulting inorganic salt cannot always be removed without difficulty in this case. Distillation in the presence of an inorganic salt results in decomposition of the required alcohol or ester.
5. If acidic or basic ion exchangers are employed as catalyst, the reaction cannot be carried out at elevated temperatures because ion exchangers are, as a rule, decomposed at temperatures above 60-100° C. On the other hand, in this case too, one reaction component, eg. the alcohol R
2
OH, may remain bound to the solid support, resulting in losses of yield. The useful life of ion exchangers is limited. Another disadvantage of heterogeneous catalysts is that they are unsuitable for reaction with compounds of low solubility, especially polymers.
6. If the transesterification is carried out in the presence of water, a competing reaction is observed in the form of hydrolysis of the ester to form alcohol and inorganic salt of the acid, eg. sodium formate in the case of formic acid. Removal of alcohols by distillation in the presence of formic esters is known to lead to losses of yield due to decomposition. In addition, when inorganic alcoholates are used as catalyst, water leads to formation of the free base and thus inactivation of the actual catalyst. For example, sodium hydroxide solution is formed from sodium alcoholate and water and is a far less effective catalyst.
EP-A-0 289 921 describes for example the transesterification of trimethylolalkane formate with methanol. It is possible to use as catalysts alkali metal or alkaline earth metal alcoholates. To obtain the required alcohol TMP it is necessary to remove the catalyst before further workup, either by ion exchanger or by neutralization with an acid. This results in decomposition of the catalyst, and the workup process becomes more costly. An inorganic salt, eg. sodium acetate or chloride, results as byproduct and must be disposed of.
The use of tertiary amines as transesterification catalysts is known for specific reactions.
DE-A 24 60 039 describes the transesterification of acetoxymethylpyridines with methanol to hydroxymethylpyridines and methyl acetate in the presence of the tertiary amine triethylamine. The alcohol which is formed, hydroxymethylpyridine, is stabilized by electron-attracting groups. The transesterification disclosed in DE-A 24 60 039 is restricted by the fact that only a selected acfivated acetic ester with primary alcohol functionality and pyridine substituents can be reacted with methanol.
The low reactivity of non-activated acetates on transesterification with methanol using tertiary amine bases as catalyst has been confir

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