GB1595231A

GB1595231A - Process for the manufacture of glycolic acid esters

Info

Publication number: GB1595231A
Application number: GB4728577A
Authority: GB
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1976-11-15
Filing date: 1977-11-14
Publication date: 1981-08-12
Also published as: BE860878A; JPS5398924A; CA1105486A; DE2652072A1; NL7712392A; IT1088881B; FR2370716A1

Description

(54) PROCESS FOR THE MANUFACTURE OF GLYCOLIC ACID ESTERS (71) We, HOECHST AKTIEN GESELLSCHAFT a body corporate organised according td the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Postfach 80 03 20, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a process for the manufacture of glycolic acid esters.

A solution of formaldehyde or one of its linear or cyclic polymers especially paraformaldehyde or trioxane, may be reacted with carbon monoxide in the presence of an alcohol to obtain a glycolic acid ester. Because of the low reactivity of carbon monoxide, this reaction is generally carried out at a temperature of approximately 2000C under a pressure of about 400 bars.

The high pressure and the use of a gaseous reactant which, especially with other disadvantages of carbon monoxide, requires considerable expenditure on apparatus, is a serious technological and economic disadvantage of this process compared to processes carried out in the liquid phase.

The present invention provides a process for the preparation of a glycolic acid ester which comprises reacting paraformaldehyde or trioxane or a mixture thereof, with a formic acid ester in the liquid phase, preferably at a temperature in the range of from 70 to 2000 C, in the presence of an organic sulphonic acid catalyst.

The use of a formic acid ester in the process of the invention permits the process to be carried out at atmospheric pressure, or, if the reaction is carried out at a temperature above the boiling point of the formic acid ester, at a relatively low excess pressure, generally of from 20 to 30 bars. A still higher pressure of, for example, 200 bars, is also possible, but in general does not offer any advantage. Thus expensive investments necessary for a high pressure process are not required to perform the process of the invention. The extensive safety measures required in a process using carbon monoxide can also be dispensed with.

The rate of the reaction

depends on the acid strength of the catalyst.

Especially suitable as organic sulphonic acid catalysts are for example, ptoluenesulphonic acid, benzenesulphonic acid, a- or ,B-naphthalenesulphonic acid, methanesulphonic acid, ethanesulphonic acid, hexanesulphonic acid or trifluoromethanesulphonic acid. Mixtures of organic sulphonic acid and sulphuric acid catalysts are also suitable.

The amount of catalyst to be used may vary within wide limits; in general it is in the range of from 0.1 to 100 mole %, preferably 5 to 50 mole %, calculated on the formic acid ester used.

The molar ratio of paraformaldehyde and/or trioxane (calculated on their formaldehyde content) to the formic acid ester is not critical. Preferably, a ratio in the range of from 0.5:1 to 2:1 is chosen.

The reaction is preferably carried out at a temperature of from 70 to 2000 C, more preferably 90 to 1800C.

In the process of the invention, in principle any formic acid ester HCOOR is suitable. Especially suitable groups represented by R are alkyl, cycloalkyl, aryl, aralkyl and alkaryl groups having up to 8 carbon atoms, for example methyl, ethyl, propyl, i-propyl, n-butyl, isobutyl, tert.butyl, cyclohexyl, benzyl, n-octyl or 2-ethylhexyl.

To carry out the process of the invention, the mixture of paraformaldehyde and/or trioxane, formic acid ester and catalyst is suitably heated at atmospheric pressure or slight excess pressure. At a reaction temperature above the boiling point of the formic acid ester, an excess pressure of up to 50 bars has proved to be advantageous to prevent the ester from evaporating from the liquid phase. An inert gas, for example nitrogen, may be present.

The process of the invention may be carried out in any apparatus suitable for reactions in the liquid phase with or without the application of excess pressure, for example in an enamelled autoclave.

The reaction mixture may be worked up by any suitable method; for example, the glycolic acid ester formed may be directly distilled off from the reaction mixture. The catalyst can be separated from the reaction mixture and may be used again without neutralisation.

Glycolic acid esters have many technological applications. By hydrolysis of the esters, glycolic acid may be obtained in very pure form.

The hydrogenolysis of glycolic acid methyl ester is used in industry to produce glycol. Glycolic acid n-butyl ester is a commercial varnish improving agent.

Generally, glycolic acid esters are excellent solvents for polymers, copolymers, nitrocellulose, cellulose ethers, celluloid, chlorinated rubber and resins.

The following Examples illustrate the invention.

EXAMPLE 1: In a glass tube sealed by melting, 0.6 g of paraformaldehyde, 1.2 g of methyl formate and 0.9 ml of trifluoromethanesulphonic acid were heated for 1 hour at 1200C. The reaction mixture contained 1.1 g of the methyl ester of glycolic acid, corresponding to a yield of 61 mole % calculated on the starting materials used.

EXAMPLE 2: In an enamelled autoclave, 12 g of trioxane (0.4 mol of CH2O), 41 g (0.4 mol) of n-butyl formate and 1.2 ml methanesulphonic acid were heated for 1 hour to 157"C. The reaction mixture contained 17.5 g of the n-butyl ester of glycolic acid, corresponding to a yield of 33 mole %.

WHAT WE CLAIM IS: 1. A process for the preparation of a glycolic acid ester, which comprises reacting paraformaldehyde or trioxane or a mixture thereof with a formic acid ester, in the liquid phase, in the presence of an organic sulphonic acid catalyst.

2. A process as claimed in claim 1, carried out at a temperature in the range of from 70 to 200"C.

3. A process as claimed in claim 2, carried out at a temperature in the range of from 90 to 1800C.

4. A process as claimed in any one of claims 1 to 3, wherein there is prepared an ester of the general formula HO-CH2-COOR wherein R represents an alkyl, cyclo-alkyl, aryl, alkaryl or aralkyl group having up to 8 carbon atoms.

5. A process as claimed in claim 1, carried out substantially as described in either of the Examples herein.

6. A glycolic acid ester whenever prepared by a process as claimed in any one of claims 1 to 5.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. temperature above the boiling point of the formic acid ester, an excess pressure of up to 50 bars has proved to be advantageous to prevent the ester from evaporating from the liquid phase. An inert gas, for example nitrogen, may be present. The process of the invention may be carried out in any apparatus suitable for reactions in the liquid phase with or without the application of excess pressure, for example in an enamelled autoclave. The reaction mixture may be worked up by any suitable method; for example, the glycolic acid ester formed may be directly distilled off from the reaction mixture. The catalyst can be separated from the reaction mixture and may be used again without neutralisation. Glycolic acid esters have many technological applications. By hydrolysis of the esters, glycolic acid may be obtained in very pure form. The hydrogenolysis of glycolic acid methyl ester is used in industry to produce glycol. Glycolic acid n-butyl ester is a commercial varnish improving agent. Generally, glycolic acid esters are excellent solvents for polymers, copolymers, nitrocellulose, cellulose ethers, celluloid, chlorinated rubber and resins. The following Examples illustrate the invention. EXAMPLE 1: In a glass tube sealed by melting, 0.6 g of paraformaldehyde, 1.2 g of methyl formate and 0.9 ml of trifluoromethanesulphonic acid were heated for 1 hour at 1200C. The reaction mixture contained 1.1 g of the methyl ester of glycolic acid, corresponding to a yield of 61 mole % calculated on the starting materials used. EXAMPLE 2: In an enamelled autoclave, 12 g of trioxane (0.4 mol of CH2O), 41 g (0.4 mol) of n-butyl formate and 1.2 ml methanesulphonic acid were heated for 1 hour to 157"C. The reaction mixture contained 17.5 g of the n-butyl ester of glycolic acid, corresponding to a yield of 33 mole %. WHAT WE CLAIM IS:

1. A process for the preparation of a glycolic acid ester, which comprises reacting paraformaldehyde or trioxane or a mixture thereof with a formic acid ester, in the liquid phase, in the presence of an organic sulphonic acid catalyst.