DD298776A5 - 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 mixture of these substances as a solvent in the presence of an alkaline-reacting alkali metal compound and a cocatalyst. As cocatalysts to increase the reaction rate under mild conditions, compounds from the class of polyethylene glycols or polypropylene glycols or their mixed oligomers having molecular weights between 600 and 1000 g / mol are used. alkanol; Acetylene; Catalyst, alkaline; cocatalyst; polyethylene glycol; polypropylene glycol; Responsiveness; Reaction condition; Solvent; Hydrocarbon}

Description

According to the invention, compounds of the general formula I are used as catalysts

with R ', R ² = H, alkyl, cycloalkyl, aryl, alkylaryl; R ³ = methyl, ethyl (n, m = 0 ... 30). Preference is given to liquid polyethylene glycols, polypropylene glycols or its mixed oligomers having molecular weights between 600 and 10OOg / mol. The molar ratio of alkali metal compound to cocatalyst can be varied between 10: 1 and 1: 1. A higher excess of cocatalyst or an even higher excess of alkali metal compound brings no advantage. The ratio of solvent to cocatalyst is chosen so that the proportion of cocatalyst does not exceed 40 vol .-%. The reaction is carried out at a pressure of 0.05 ... 0.3 MPa, preferably at normal pressure and at a temperature of 20 ... 200 ^0C. Preference is given to temperatures of 70 .. 12O ⁰ C, in which a sufficient reaction rate is present and a high stability of the catalyst system is given.

Alcohol and acetylene are fed into the reactor in a molar ratio of 1: 1 to 1:20; in low-boiling alcohols, the alcohol is conveniently carried along with the acetylene stream. The reaction is carried out so that the vinyl ether formed is removed continuously from the R9aktionsgemisch by distillation and in the Reaktionsgenvsch constantly a low alcohol concentration is maintained. Large amounts of alcohol reduce 'i'.i responsiveness to small amounts of lead to any early decomposition of the catalyst mixture and / or solvent, recognizable by an increasing darkening and the decrease in sales. The optimum concentration of alcohol depends in particular on the reaction temperature, the solvent and the alcohol used. For example, in the case of vinylation of methanol, it is preferable to maintain a methanol concentration of 5% by volume.

embodiments example 1

In a stirred reactor (150 ml volume) with jacket heating and attached reflux condenser, a mixture of 100mi p-xylene, 14.04 g (0.2 mol) of potassium methoxide and 24g (0.04 mol) of polyethylene glycol having the average molecular weight of 600 g / mol with exclusion introduced by humidity. With good stirring is heated to 70 ⁰ C and passed a mixture of acetylene and methanol (molar ratio 8.5: 1) at a flow rate of 3.5-4.0l / h from below into the reactor. When vinylation of the dihydric polyether alcohol is complete, methyl vinyl ether formation begins. The gebi ended methyl vinyl ether is distilled off continuously 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 / HC = CH and a decreasing reaction rate, the dia methanol feed is temporarily interrupted or reduced until the optimum methanol concentration in the reactor is restored. Revenues of about 6 liters of acetylene per hour and mole of polyether alcohol are achieved.

Examples 2 and 3 As described in Example 1, but using polyethylene glycol having a molecular weight of 1000 or 400 g / mol, cf.

Table 1.

Examples 4 to 7 (Comparative Examples) The procedure is analogous to Example 1; in Examples 5 and 7, in which methanol is used as solvent,

There is no additional dosage of methanol in the reactor, see. Tab. 1.

Example 4 shows that under the same reaction & conditions as in Example 1 but without the addition of polyethylene glycol, even at

a larger amount of potassium methoxide, virtually no conversion to methyl vinyl ether takes place. Is used in methanol as

Solvent worked, there is a low conversion to methyl vinyl ether (Example 5). An addition of polyethylene glycol leads

Although an increase in the conversion (Example 6), the achievable conversions are below those of the inventively carried out. If one works in polyethylene glycol as a solvent (Example 7) sets the

Methyl vinyl ether formation only after vinylation of the polyethylene glycol (under the Reaktionsbedingungert - in Example 7

after 2 hours); the conversions of methyl vinyl ether are below those of the reactions carried out according to the invention.

Table 1 Overview of the embodiments

Ex. catalyst COM (28.10g) cocatalyst solvent molar ratio Sales in IC ₂ H ₂ / COME (35.10g) C ₂ H ₂ / MeOH IC ₂ H ₂ / mol COMM h COM (28.78g) mol PEG h 1.1 1 COM (14.04g) COM (26,55g) PEG 600 (24.0 g) Xylene (100ml) 8.5 / 1 6.0 1.0 2 COM (14.04g) PEG 1000 (40,0g) Xylene (100ml) 9.0 / 1 5.0 0.9 3 COM (14.04g) PEG 400 (16.0 g) Xylene (100ml) 1.10 4.5 Comparative Examples: 0.001 4 - Xylene (100ml) 1.15 0.02 5 - Methanol (100ml) a) 0.03 6 PEG 600 (59.4 g) Methanol (100ml) a) 0.1 0.06 7 - PEG 600 (93 g) 1.11 1.8

PEG - polyethylene glycol; the number indicates the average molar mass in g / mol;

Me-methyl

a) flow rate acetylene 3.5-4.0l / 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 4 carbon atoms with acetylene in an aliphatic, cycloaliphatic or aromatic hydrocarbon or a 3m mixture of these substances as a solvent in the presence einor alkaline reacting Aikalimetallverbindung preferably potassium alcoholate or hydroxide are reacted, characterized in that in the presence of a compound of general formula ^ CMCHz-CHr-Ota-iCHR ^ CHr-O ^ -R ² (D. with R ¹ , R ² = H, alkyl, cycloalkyl, aryl, alkylaryl; R ³ = methyl, ethyl; η, m = 0 ... 30 is used as a cocatalyst at a molar ratio of acetylene to alcohol of 1: 1 to 20: 1. 2. The method according to claim 1, characterized in that are preferably used as cocatalysts liquid polyethylene glycols having molecular weights between 600 and 10OOg / mol. 3. The method according to claim 1, characterized in that the supplied amount of alcohol is so dimensioned that a concentration between 0.1 and 10VoI .-% is maintained in the reaction mixture constantly. 4. The method according to claim 1, characterized in that the formed alkyl vinyl ether is distilled off continuously from the reaction mixture. 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 mercury (cf B. DRP 338 281), or alkaline (cf., for example, DRP 584840 and DRP 640510; Ullmanns Encyklopadie of the technical chemistry, Bd. 23, P. 608, publishing house chemistry, Weinheim 1983; W.Reppe: "chemistry and technology of the acetylene pressure reactions", publishing house chemistry, Weinheim 1952; W.Reppe: "new developments in the field the chemistry of acetylene and carbon monoxide ", Springer-Verlag, Berlin 1949). In 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 are 150-18O ⁰ C. If the boiling points of the alcohols to be vinylated are lower than the reaction temperature, it is necessary to work 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, Brit. Pat., 717,051 SU 481589). 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 (cf, for example, BZ Chem., 26 (1986) 41, Usp Khim, 50 [19811248] The known processes are, in particular, the relatively high reaction temperatures and the high reaction pressures required for low-boiling alcohols, which requires special safety precautions when working with acetylene and their limited stability under the reaction conditions and / or the formation of by-products when using the solvents mentioned. Object of the invention The object of the invention is the synthesis of alkyl vinyl ethers from alcohols and acetylene under relatively mild reaction conditions 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 4 C-atoms) with acetylene in an aliphatic, cycloaliphatic or aromatic hydrocarbon or in a mixture of these substances as a solvent in the presence of an alkaline metal compound (e.g., hydroxides, alcoholates, amides, organyls, preferably potassium hydroxide or alcoholate) that permits vinylation under relatively mild reaction conditions at a relatively high reaction rate.