DD298775A5 - PROCESS FOR THE PREPARATION OF ALKYLVINYL ETHERS - Google Patents

Abstract

The invention relates to a process for the preparation of alkyl vinyl ethers by addition of alcohols to acetylene in an aliphatic, cycloaliphatic or aromatic hydrocarbon or a halohydrocarbon or an ether or an acetal or a mixture of these substances as a solvent in the presence of an alkaline alkali metal compound and a cocatalyst. As cocatalysts crown ethers are used to increase the reaction rate under mild conditions. alkanol; Acetylene; Catalyst, alkaline; cocatalyst; Responsiveness; Reaction condition; Solvent; Hydrocarbon; crown ethers; 18-crown-6; Dibenzo-18-crown-6}

Description

Field of application of the invention

The invention relates to a process for the preparation of alkyl vinyl ethers from acetylene and alcohols. Alkyl vinyl ethers with their high synthetic potential are valuable intermediates in the chemical industry and are used in particular for the production of acetaldehyde, of polymers and of acetals and as solvents.

Characteristic of the known state of the art

The addition of alcohols to acetylene to alkyl vinyl ethers in the liquid phase can be catalyzed by compounds of some subgroup metals, in particular by mercury (cf., for example, DRP 338 281), or alkaline (cf., for example, DRP 584840 and DRP 640510, Ulimanns Encyklopadie der technischen Chemie, Bd.23, p.608, Verlag Chemie, Weinheim 1983; W. Reppe: "Chemistry and Technology of Acetylene Pressure Reactions" Verlag Chemie, Weinheim 1952; W. Reppe: "Recent Developments in the Field the chemistry of acetylene and carbon oxide ", Springer-Verlag, Berlin 1949). In the case of the alkali-catalyzed reaction in the liquid phase, preference is given to using alkali metal hydroxides or alcoholates as catalysts, the most favorable reaction temperatures being 150 ° C. to 10 ° C. If the boiling points of the alcohols to be vinylated are lower than the reaction temperature, work must be carried out under pressure (up to 2.5 MPa). The vinylation can be carried out in high-boiling solvents (cf., for example, DRP 726547) and also in high-boiling alcohols or with the addition of polyhydric alcohols, which are vinylated in the course of the reaction (cf., for example, British Patent 717051, SU 481 589 ). It is also known that the alkali-catalyzed addition of alcohols to acetylene can also be carried out in dipolar aprotic solvents such as dimethyl sulfoxide (see, for example, BZ Chem., 26 (1986141; Usp. Khim. 50 [1981] 248) known processes are in particular the relatively high reaction temperatures and the high reaction pressures required for low-boiling alcohols, which when working with acetylene requires special safety precautions and the use of said solvents their limited stability under the reaction conditions and / or the formation of by-products.

Object of the invention

The object of the invention is the synthesis of alkyl vinyl ethers from alcohols and acetylene by an environmentally compatible process to effectively industrialize the synthetic potential of the alkyl vinyl ethers and, in particular, to realize a substantial substep for a mercury-free acetylene based acetaldehyde production process.

Explanation of the essence of the invention

The invention has for its object to develop a process for the preparation of alkyl vinyl ethers by addition of alcohols to acetylene by alcohols ROH (R = alkyl radical up to 16 carbon atoms) with acetylene in an aliphatic, cycloaliphatic or aromatic hydrocarbon or a halohydrocarbon or an ether or an acetal or a mixture of these substances as a solvent (preferably in a high-boiling aliphatic or aromatic hydrocarbon or mixture) in the presence of an alkaline alkali metal compound (eg, hydroxides, alcoholates, amides, organyls, preferably potassium hydroxide or alcoholate) which allows vinylation under relatively mild reaction conditions with a relatively high reaction rate.

According to the invention, a crown ether is used as cocatalyst. Unsubstituted or substituted crown ethers are suitable, in particular 18-crown-6 or dibenzo-18-crown-e when using potassium hydroxide or alkoxide as catalyst. Heterocrown ethers also show a catalytic effect.

The concentration of crown ether and the molar ratio of alkali metal compound to crown compound can be varied within wide limits (0.1... 5OgZIOOmI solvent preferably 5... 15 g / 100 rnl of solvent or 20: 1 to 1: 1). An excess of relatively expensive crown ether or an even higher excess of alkali metal compound brings no advantage. The reaction is carried out at a pressure of 0.05 ... 0.3 MPa preferably ₁ bsi normal pressure and at a temperature of 2O ... 2OO ° C. Preference is given to temperatures of 70 to 110 ° C, in which a sufficient reaction rate is present and a high stability of the catalyst system is given.

Acetylene and alcohol are fed into the reactor in a molar ratio of 1: 1 to 20: 1; in the case of low-boiling A. alcohols, the alcohol is expediently carried along with the acetylene stream. The reaction is conducted so as to constantly maintain a low alcohol concentration in the reaction mixture. Larger amounts of alcohol reduce the reaction rate, too small amounts lead to a possible rapid decomposition of the catalyst mixture and / or solvent, recognizable by an increasing dark color and the decline in sales. The optimum concentration of alcohol depends in particular on the reaction temperature, the solvent and the alcohol used. In the case of the vinylation of n-butanol in xylene at 70 ⁰ C with KOBu / 18-crown-6 as the catalyst system preferably keeps a one butanol concentration of 0.1 ... 18Vol .-% in the reaction mixture upright. Above 15 vol .-% occurs a significant reduction in the reaction rate.

Low-boiling vinyl ethers are expediently distilled off continuously from the reaction mixture. Unreacted starting compounds can be recycled.

AusfQhrungsbelsplele example 1

In a stirred reactor (150 ml volume) with jacket heating and attached reflux condenser, a mixture of 100 ml of p-xylene, 14.04 g (0.2 mol) of potassium methoxide and 10.56 g (0.04 mol) of crown ether 18-crown-6 with exclusion of Humidity filled. With good stirring is heated to 7O ⁰ C and passed a mixture of acetylene and methanol (molar ratio 9: 1) at a flow rate of 3.5-4.0l / h from below into the reactor. The methyl vinyl ether formed is continuously distilled off and condensed. At the reactor outlet after the reflux condenser, the content of methyl vinyl ether formed is determined by gas chromatography.

The methanol supplied to the reactor is metered so that only small amounts are not reacted. If an accumulation of methanol in the reactor, recognizable by an increasing methanol content in the reaction mixture MeOCH = CH ₂ / HCsCH and a decreasing reaction rate, the methanol metering is temporarily interrupted or reduced until the optimum methanol concentration in the reactor is restored. Turnover of about 201 acetylene per hour and mole of crown ether is achieved.

Example 2

The procedure is analogous to Example 1 but using 2.96 g (0.042 mol) of potassium methoxide and 10.56 (0.04 mol) of crown ether 18-crown-6 at a reaction temperature of 70.90 and 110 ° C. There are reacted 19-27.35 or 421 acetylene per hour and moles of base corresponding to 20-28.37 and 441 acetylene per hour and moles of crown ether, cf. Tab. 1.

Examples 3-7

All examples are carried out analogously to Example 1, cf. Tab. 1. In Examples 3 and 4, instead of xylene, chlorobenzene or n-butyl ether was used as the solvent. KOH as a catalyst shows only about half the activity of potassium methoxide, cf. Example 1 with 5-butanol reacts much faster than methanol (Example 6). Dibenzo-18-crown-6 shows less activity than 18-crown-6 (see example 1 at 7).

Examples 8-12 (Comparative Examples) "

The procedure is analogous to Example 1; in Examples 9-12, in which methanol or methanol / xylene as a solvent

is used, there is no additional dosage of alcohol in the reactor, cf. Tab. 1.

Example 8 shows that virtually no conversion to methyl vinyl ether takes place under the same reaction conditions as in Example 1 but without the addition of crown ether, even with a larger amount of potassium methoxide. If methanol is used as the solvent, there is little conversion to methyl vinyl ether (Example 9 or 11). Although addition of crown ether leads to an increase in the conversion (Examples 10 and 12), the achievable conversions are far below those of the invention

implemented implementations.

Ex. catalyst COM (28,2) g) cocatalyst - solvent Tempe Molver Sales m b) ι COME (35.1 g) - ture relationship a) ω COME (35.1 g) 18-crown-6 (26.4 g) in ⁰ C C _z H ₂ / ROH 5 I 1 COM (14.0 g) COME (35.1 g) 18-crown D (10.6 g) _ Xylene (100 ml) 70 1.9 20 19-27 2 COM (2.96 g) 18-crown-6 (10.6) g) Xylene (100 ml) 70 7.5 / 1 20-28 35 90 1.6 37 42 110 4.5 / 1 44 8th 3 COM (14.0 g) 18-crown-6 (10.6 g) Chlorobenzene (100 ml) 70 5.5 / 1 40 3.2 4 COM (14.0 g) 18-crown-6 (10.6 g) n-3-butyl ether (100 ml) 70 1.10 15 2.6 5 KOH (5.7 g) 18-crown-6 (5.3 g) Xylene (100 ml) 70 1.12 13 70 6 KOBu (8.0 g) 18-crown-6 (12.6 g) Xylene (100 ml) 70 c) 105 0.9 7 COM (5,7 g) Dibenzo-18-crown-6 Xylene (100 ml) 70 5 (5.5 g) Comparative Examples: 0.001 8th Xylene (100 ml) 70 1.15 0.02 9 Methanol (100 ml) 70 d) 0.04 10 Methanol (100 ml) 70 d) 0.2 0.02 11 Methanol (100 ml) / 70 d)

COME (35.1 g) 18-crown-6 (26.4 g)

Xylene (100 ml)

Methanol (100 ml) / xylene (100 ml)

d)

0.4

Table 1:

Overview of the exemplary embodiments (Me-methyl)

^a ^ 1 acetylene / mol crown.h. 1 acetylene / mol Base.h.

c)

0.08

20 ml n-butanol / h. dropped into the reaction mixture at a flow rate of 3.5 - 4.0 1 acetylene / h. 'Flow rate acetylene 3.5 4.0 l / h.

Claims (4)

1. A process for the preparation of alkyl vinyl ethers by addition of alcohols to acetylene, by alcohols ROH with R = alkyl radical having up to 16 carbon atoms with acetylene in an aliphatic, cycloaliphatic or aromatic hydrocarbon, a halohydrocarbon or an ether or an acetal or a mixture these substances as solvent preferably in a high-boiling aliphatic or aromatic hydrocarbon or mixture in the presence of an alkaline alkali metal compound preferably potassium alkoxide or hydroxide are reacted, characterized in that in the presence of a crown ether as a cocatalyst at a molar ratio of acetylene to alcohol of 1: 1 to 20: 1 is worked. 2. The method according to claim 1, characterized in that the use of potassium alkoxides or hydroxide is used as a catalyst with 18-crown-6 or dibenzo-18-crown-6 as Kronether. 3. The method according to claim 1, characterized in that the supplied amount of alcohol is so dimensioned that in the reaction mixture or in low-boiling alcohols in the exhaust gas, an alcohol concentration between 0.1-10% is maintained constantly. 4. The method according to claim 1, characterized in that low-boiling alkyl vinyl ethers are continuously distilled off from the reaction mixture.