Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Patent
1992-07-31
1994-03-08
Dees, Jose G.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
560 8, 560100, 560103, 560106, 560110, 560111, 560112, 560113, 560124, 560227, 560228, 560116, 560117, 560119, 562400, 562405, 562493, 562497, 562512, 562602, 562606, C07C 6976, C07C 6963, C07C 5300
Patent
active
052929280
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the environmentally friendly reaction of a low-molecular hydroxyl compound with an aliphatic carboxylic acid halide, especially of alcohols with acid chlorides.
In the preparation of esters from acid chlorides and hydroxyl compounds, the alcohol component is conventionally introduced into the reaction vessel first and the acid chloride is metered in according to the permissible temperature and pressure relationships. HCl gas is produced in this procedure and initially dissolves in the alcohol component with the evolution of heat. HCl gas is not released until saturation has been reached. The advantage of this procedure is that an uncontrollable reaction of the acid chloride with undesired hydroxyl compounds, for example water in the event of a condenser fracture, can be excluded. The essential disadvantage of this procedure is that the HCl gas formed in the reaction is absorbed in the alcohol initially introduced, with the evolution of a substantial heat of solution, and undergoes undesired secondary reactions with the alcohol component. In the case of the preparation of methyl dichloroacetate from methanol initially introduced and dichloroacetyl chloride metered in, methyl chloride and water are formed in a temperature-dependent secondary reaction. At a temperature of only a little above 40.degree. C., considerable amounts of methyl chloride are formed, which is undesired on account of its polluting properties. Methyl chloride can even be detected in the released HCl gas in the temperature region below 40.degree. C., creating the need for a special purification of the effluent gas.
In the working-up of such a reaction mixture, especially in the presence of readily saponifiable esters such as e.g. methyl dichloroacetate, the water which is also formed in this secondary reaction results in an undesired saponification, i.e. in a possibly substantial reduction of the ester yield.
It has now been found that the above-described disadvantages in the preparation of esters from acid halides and low-molecular hydroxyl compounds can be avoided by a procedure in which the acid halide is initially introduced and the hydroxyl compound is metered in.
The invention thus relates to the process described in the claims.
In the process according to the invention, low-molecular hydroxyl compounds are reacted with acid halides. Suitable hydroxyl compounds are water, aliphatic C.sub.1 -C.sub.12 alcohols, cycloaliphatic C.sub.6 -C.sub.12 alcohols and aromatic alcohols. It is preferred to use water, aliphatic C.sub.1 -C.sub.12 alcohols and cycloaliphatic C.sub.6 -C.sub.12 alcohols, especially water and aliphatic C.sub.1 -C.sub.4 alcohols, for example methanol, ethanol, n- and i-propanol and butanols.
Suitable carboxylic acid halides are the fluorides, chlorides and bromides, preferably bromides and chlorides, of aliphatic C.sub.2 -C.sub.6 carboxylic acids, cycloaliphatic C.sub.6 -C.sub.12 carboxylic acids and aromatic carboxylic acids. It is preferred to use the chlorides of lower aliphatic C.sub.2 -C.sub.6 halogenocarboxylic acids such as, for example, chloroacetic acids or chloropropionic acids.
The reactants are reacted in such a way that the carboxylic acid halide is maintained in excess during the reaction and the hydroxyl compound is added to the acid halide. For this purpose, 5 to 20 mol % of the total amount of acid halide intended for the reaction is initially introduced into the reaction vessel and the remaining acid halide and the hydroxyl compound are then introduced gradually, in approximately stoichiometric proportions, at a rate which depends on the removal of the hydrogen halide and the heat of reaction. At the end, when the amount of acid halide to be added has been consumed, the acid halide remaining in the reaction vessel is also reacted. The hydroxyl compound is introduced into the reaction vessel in an amount of 105 to 120 mol % based on the total acid halide.
If the reactants are liquid, they are preferably brought together in undiluted form in the absence of a solvent.
Dees Jos,e G.
Hoechst Aktiengesellschaft
MacMillan Keith
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