DD260277A1 - METHOD FOR CONTINUOUS PRODUCTION OF ALKYL MAGNESIUM HALOGENIDES - Google Patents

Abstract

The invention relates to a process for the preparation of alkyl and iso-Alkylmagnesiumhalogeniden characterized in that the reaction takes place in a zone of high turbulence and a relative excess of magnesium in the reactor is maintained. The preparation of the organic magnesium halides is carried out continuously in a tubular reactor provided with static mixers, whose column of liquid is pulsed.

Description

Dazui page drawing

Field of application of the invention

The invention relates to a process for the continuous production of alkylmagnesium halides, which also bear the general name Grignard compounds. They are important reactive intermediates for the synthesis of organoelement compounds, in particular of tin, silicon and phosphorus, as well as for the preparation of organic intermediates, dyes, pharmaceuticals and active ingredients.

Characteristic of the known state of the art

For the preparation of alkyl and iso-alkylmagnesium compounds, also referred to below as Grignard compounds, one starts from metallic magnesium and alkyl or iso-alkyl halides, which are reacted in a suitable solvent with donor properties, preferably ethers, according to equation I.

RX + Mg - »RMgX I

(R = alkyl, iso-alkyl, X = halogen)

In general, the discontinuous operation in a stirred reactor under air and moisture exclusion is preferred.

(Kirk / Othmer, Encycl.Chem.Technol., 3rd Bd., 1980, 12, pp. 30-40)

The start-up phase of the strongly exothermic Grignard reaction often causes considerable difficulties in the batchwise process due to the inevitable under or overdosing of the organic halide. In particular, by a delayed start of reaction or by a too high reaction rate occur large heat dissipation problems. This risk is reduced if there is always a sufficiently large amount of Grignard reagent in the reactor, as is the case in particular in the continuous operation. From the point of view of the continuous production of Grignard compounds, various technical solutions are described.

According to US-PS 2414505 and 2464685 is worked in stirred tanks. In this procedure, however, the heat removal is difficult because of the low specific surface area of the cooling system. In addition, the large reaction volume brings with it hazards.

According to US Pat. No. 2,066,198, DE-AS 1293767 and CS-PS 161 568 and CS-PS 169418, the Grignard reaction is carried out in vertically arranged reaction columns. By settling sludges containing magnesium oxide, especially when the apparatus is at a standstill, there is a risk of blockage. This leads to considerable difficulties when starting the reactor and also brings with it hazards. Basically, it has to be criticized that only unsatisfactory space-time yields can be achieved with the existing methods. According to CS-PS 160418, 540 ml of ethyl bromide are reacted per hour and liter of reactor volume or 353 ml of butyl iodide per hour and liter of reactor volume.

Object of the invention

The aim of the invention is to produce Grignard compounds by means of a process which allows the use of small, safety-acceptable reaction volumes and at the same time provides a large amount of Grignard reagent per unit time for further reactions.

Explanation of the essence of the invention

The invention has for its object to produce alkyl magnesium halides without the problems of heat dissipation inherent in the prior art.

It has now been found that Alkylmagnesiumhalogenide of organic halides of the general formula RX, wherein R = N-alkyl (C ₂ to C ₁₀ ) or iso-alkyl (C ₃ to Ci ₀ ) and X = halogen, preferably Cl or Br, mean and magnesium can be continuously made in a suitable solvent having donor properties when the reactants are reacted in a zone of high shear and shear forces and with the exception of total backmixing, and a permanent supply of magnesium is maintained, in part by recirculation. The reaction is carried out in a tubular reactor provided with static mixers whose reaction volume is pulsed. This method can be carried out in a device as shown as a possible embodiment in FIG. The reactor consists of a thermostattable tube 4, which is placed at an angle between 0 ° and 90 ° to the horizontal and equipped with static mixers 8 suitable design. These may contain individual elements of both identical and different types. The liquid column in the reaction tube is then pulsed by a drive (eg piston, eccentric), the transfer to the liquid column being effected by an elastic, hermetically sealing connection (eg bellows, membrane). The frequency may be between 20min " ¹ and 30oMJn" ¹ , preferably between 30min " ¹ and 150min" ¹ . The pulation is superimposed on the linear flow resulting from the dosage. The amplitude of the pulsation is between 0.2 and twice, suitably between 0.5 and simple of the reaction tube diameter. A particular advantage of the method is that due to the pulsation of the liquid through the elements of the static mixer, a high turbulence arises whose strong shear and shear forces accelerate transport processes on the magnesium surface such that a surprisingly high space-time yield results. The partial backmixing of the reaction components precludes reaction delays. Clogging and deposits occur neither in continuous operation nor when starting, stopping and restarting the apparatus. The removal of the heat of reaction is completely unproblematic because of the large specific surface area of the reaction tube and because of the high turbulence of the heterogeneous reactants. As a result, no local overheating occur, so that an accurate and almost constant temperature control can be achieved.

The reactor leaving the reaction mixture is passed through a settling tank 7, sedimented in the entrained metallic magnesium and recycled by means of a controlled closure member into the reactor. The amount of magnesium to be returned depends on different influencing variables, eg. From the level of excess magnesium that is to be maintained in the reactor; the particle size and nature of the magnesium; the metering rate of the solvent and the organic halide; from the pulsation frequency. The closure member (solenoid valve, flap) has the task to reclaim the unreacted magnesium again into the entrance of the reactor and to prevent a liquid flow from the reactor inlet into the settling tank. It has proved to be advantageous to carry out the control of the closure member as a function of the pulsation and to exploit the periodically occurring negative pressure phases. In this way, a continuous magnesium supply of 10 to 300 g, preferably 50 to 100 g of magnesium per liter of reaction volume can be maintained in the reactor.

In detail, the organic halide and the solvent by means of conventional metering devices 1 and 3 is separated or fed in a continuous mixture to the reactor. The magnesium is metered by means of the device 2 in equimolar amount to the organic halide. It is used in the form of powder or chips with a grain size of 0.05 to 20 mm, preferably in the form of chips of 0.1 to 2 mm. The magnesium must have such a grain shape that agglomeration or entanglement of the particles is excluded.

The reacted organic halides may be alkyl or iso-alkyl compounds.

Suitable solvents are, as is known, aliphatic and cyclic ethers, mixtures of hydrocarbons and these ethers, or other complexing agents, such as. As amines or phosphines, which contribute to the stabilization of the Grignard compounds.

The Grignard reagent produced in the reactor leaves the reactor via the settling tank 7 and can then be used in further reactions for application and stored under inert gas. Gas chromatographic analyzes show that the solutions obtained from Grignard reagents no longer contain unreacted organic halide.

embodiment

A lying tubular reactor of 1 liter capacity, equipped with static mixers is filled with 60 g of magnesium turnings (particle sizes 0.5) and with a solution of butylmagnesium chloride in di-n-butyl ether (1.2 mol / l). The reactor is heated to 50 ° C. The liquid column in the reactor is pulsed at a frequency of 80 min ^-1 . Subsequently, 1.71 l / h of butyl chloride and 10.3 l / h of di-n-butyl ether are added by means of metering pumps and 341 g / h of magnesium by means of a metering screw The reacted reaction mixture leaves the reactor via the settling vessel, in which entrained magnesium sediments and is periodically returned to the reactor by utilizing the negative pressure phase with the aid of a controlled valve Di-n-butyl ether with a concentration of 1.18 mol / l (97% yield).

The procedure was analogous to other examples, which are summarized in the form of a table. The examples are also related to a reactor of 1 liter capacity. It was worked in a concentration range of 0.5 to 4 mol / l, preferably 1.5 to 2.5 mol / l. The content of the resulting solution was determined by titration and by gas chromatography after a protolysis reaction.

RX RX temperature solvent yield (L / h) ( ⁰ C) (%) 1. C ₄ H ₉ CI 2.4 50 (C ₄ H ₉ J ₂ O 95.2 Second C ₄ H ₉ CI 1.47 30 (C ₄ H ₉ J ₂ O 90.2 Third C ₂ H ₅ Br 2.01 30 (C ₂ H ₅ ) 2O / toluene 94.3 4th C ₈ H ₁₇ CI 1.53 60 (C ₂ H ₅ ) ₂ O / toluene 93.7 5th C ₈ H ₁₇ Br 2.4 50 (C ₄ H ₉ ) ₂ O / toluene 94.4 6th (CHs) ₂ CHCl 2.0 40 (C ₂ H ₅ ) ₂ O / toluene 93.8 7th C ₄ H ₉ Br 2.9 40 (CH ₃ ) ₃ CO-CH ₃ 96.1

Claims (4)

claims: 1. A process for the continuous production of alkylmagnesium halides from organic halides of the general formula RX, where R = n-alkyl (C ₂ to C ₁₀ ) or iso-alkyl (C ₃ to C ₁₀ ) and X = halogen, preferably Cl or Br, and magnesium, characterized in that the reactants are reacted in a zone of high shear and gravitational forces and excluding total backmixing and a permanent supply of magnesium is maintained, in part by recycling the magnesium. 2. The method according to claim 1, characterized in that the reaction is carried out in a tubular reactor provided with static mixer whose reaction volume is pulsed. 3. The method according to claim 1, characterized in that comminuted magnesium having a particle size of 0.05 to 20 mm, preferably from 0.1 to 2 mm, any geometric, non-entangled form used and that in the reactor, a magnesium excess of 10 to 200g / l, preferably 50 to 100g / l, is maintained. 4. Process according to claims 1 to 3, characterized in that the unreacted magnesium is recycled via a controlled by utilizing the negative pressure phase of the pulsation closure member in the reactor.