IL23411A - A process for preparing tetramethyltin - Google Patents

Description

23411/2 A process for preparing tetramethyltiii M & 1 CHEMICALS IHC* C, 22538 (507)EG - D252 NOVEL PROCESS This invention relates to a process for preparing organotin compounds . More particularly it relates to a novel process for the isolation of tetra-alkylated tin compounds .

As is well known to those skilled-in-the-art , tetra-alkylated tin compounds such as tetramethyltin may be prepared by the reaction of tin tetrahalide e.g. tin tetrachloride and a methyl Grignard reagent e.g. methyl magnesium chloride as follows t CH3MgCl + SnCl« → (CH3)4Sn + MgCl2 (1) Preparation of the Grignard reagent and the reaction thereof with tin tetrachloride by Equation 1 are commonly carried out in the presence of a solvent-complexing agent such as ethyl ether, either alone or together with hydrocarbon such as toluene. In the presence of such solvents, the yields of tetra-alkylated tin attained in practice may be as low as 35% or less.

During the work-up of product from prior art reaction mixtures, the product in ether solution may, after hydrolysis, separate from the aqueous salt-saturated liquor. The organic layer is commonly then dried and distilled to yield ether, usually as a fore-run, and thereafter the desired product together with other organotin by-products which may be formed during the course of the reaction.

Most commonly, the distillation-separation may be carried out in steps wherein in the first step a distillate containing tetramethyltin and e.g. ethyl ether may be obtained. (The proximity of the boiling point of e.g. tetrahydrofuran (68°C), or the peculiar difficulties inherent in the distillation-separation, have made tetramethyltin a difficult and expensive product to prepare.) Tetramethyltin and ethyl ether co-distill and cannot readily be separated by distillation? separation of these two components and recovery of desired product tetramethyl in in pure form may be effected by a second distillation in a distillation column having 35- O plates and typically as many as 50-60 plates.

It is an object of this invention to prepare tetra-alkylated tin compounds in high yield. Other objects will be apparent to those skilled-in-the-art from inspection of the following description.

In accordance with certain of its aspects, the process of this invention for separating tetramethyltin from a solution containing at least one material selected from the group consisting of water-soluble ethers and methyltin halides may comprise contacting said solution with water thereby forming a tetramethyltin phase and a water phase containing at least one material selected from the group consisting of water-soluble ethers and methyltin halides, and separating said tetramethyltin phase from said water phase.

In accordance with certain of its specific aspects, the process of this invention for preparing tetramethyltin may comprise reacting methyl magnesium halide with tin tetrahalide in the presence of a water-soluble ether thereby forming tetramethyltin in a reaction mixture? hydrolyzing said reaction mixture thereby separating an a ueous hase and an or anic hase containin said e her and said tetramethyltinj extracting said organic phase with water thereby separating a water-ether phase and a tetramethyltin phases and withdrawing said tetramethyltin phas .

In practice of the process of this invention according to certain of its aspects, preparation of tetramethyltin may be effected from methyl halide as a starting material. The halide may preferably be an active halide i.e. a halide selected from the group consisting of bromide, iodide, and chloride; and the preferred methyl halide may be methyl chloride. Methyl halide may be reacted with magnesium in the first step of the process to form the Grignard reagent, methyl magnesium halide, in accordance with the following reactions CH3X + Mg → CH3MgX (2) This reaction may preferably be carried out under an inert atmosphere, e.g. nitrogen gas, in the presence of a water-soluble ether. Various well-known initiators may be present to facilitate formation of the Grignard reagent.

The water-soluble ethers which may be used in preparation of the Grignard reagents in practice of this invention may include ethers having a substantially high solubility in or miscibility with water at extraction temperature (15°G-50°C) , typically including tetrahydrofuran, N-methyl morpholine, the diethyl ether of diethylene glycol, the methyl ethyl ether of diethylene glycol, and N-ethyl morpholine. 2-methyl tetrahydrofuran may also be used.

The preferred ethers may be infinitely iyniscible with water at extraction temperature including tetrahydro-furan, N-methyl ntorphoLine, diethyl ether of diethylene glycol, methyl ethyl ether of diethylene glycol, N-ethyl morpholine. Preferably the ether may be an ether selected from the group consisting of tetrahydrofuran and N-methyl morpholine.

The Grignard reagent prepared by reacting the methyl halide and magnesium in the presence of appropriate initiators may be formed as and used as its complex with the ether in an excess of the ether. For convenience, reference may be made to the Grignard reagent without referring to the ether present in the complex.

In practice of the process of this invention, the reaction between tin tetrahalide SnX4 and the Grignard reagent CH3MgX may be; 4CH3MgX + SnX4 → (CH3)4Sn + **MgX2 (3) This reaction may be carried out by adding Grignard reagent CH3MgX and tin tetrahalide SnX4 to a reaction vessel. Preferably the tin tetrahalide may be added to a body of Grignard reagent contained in the reaction vessel. The reaction may be carried out in the presence of appropriate solvent^complexing agent, preferably a water-soluble ether as noted supra.

In the preferred embodiment, the Grignard reagent may be added in amount of moles per mole of tin tetrahalide. Reaction may preferably be carried out with a high degree of agitation which ensures that the reaction mixture is maintained substantially uniform.

Preferably the exothermic reaction mixture may be maintained at 35-95*0, preferably less than about 75°C. The reaction may, if desired,, be carried out at 40°C„ Typically the tin tetrahalide may be added to the reaction mixture over 60-210 minutes, say 120 minutes.

At the completion of the addition of tin tetrahalide in the preferred embodiment , the reaction mixture may be allowed to rise to and be maintained at gentle reflux, typically at 75-85°C when the reflux liquid includes tetrahydrofuran, for 30-2¾0 minutes, say 120 minutes .

The reaction mixture may then be hydrolyzed to liberate product tetramethyltin. Typically this may be effected by diluting the mixture at 30eC-40^C, say 30°C, with water, preferably containing electrolyte such as sulfuric acid in amount of 1=15%, say 10% by weight.

Typically hydrolysis may be effected by hydrolyzing the reaction mass, at 30oG-^0®G9 by mixing with 500-7^0, say 600 parts by weight of water, preferably followed by addition of electrolyte, such as 10% sulfuric acid, in an amount of 300-600, say 500 parts. The organic layer which separates may be decanted. This organic layer may contain water-soluble ether and tetramethyltin together with any by-product meth ltin chlorides which may have been formed, by-products , methyltin trichloride, dimethyltin dichloride, and trimethyltin chloride are water-soluble.

Tetramethyltin may be recovered from a solution containing at least- one material selected from the group consisting of methyltin halides and water-soluble ethers. Typically it may be recovered from a solution thereof which consists essentially of tetramethyltin and a water-soluble ether such as tetrahydrofuran - this solution commonly containing methyltin halides.

In accordance with certain aspects of this invention, typically an organic layer recovered from a process such as that supra„ which may contain 8-11, say parts of tetramethyltin per 100 parts of total organic layer, may be washed by contact with an aqueous medium, preferably water. In the preferred embodiment, 100 parts of the organic layer containing water-soluble ether and the tetramethyltin, may typically be mixed preferably in several steps with 50=500 or more parts, say 250 parts by weight of aqueous medium, preferably water. The water may contain minor amounts of e.g. water-soluble ether; but preferably it will be substantially pure water. This amount of water will preferably be added to the organic layer in several aliquots , typically equal aliquots .

The water and the organic layer may be typically maintained in contact for 10-60 minutes, say 20 minutes, at temperature of 15®C-50®C, typically 25°C. During this fsontact, which is preferably effected with vigorous agitation, the water-soluble ether may be extracted from the organic layer and thus separated from the tetramethyltin. B the use of a continuous extraction techni ue lesser It is a particular feature of this invention that the novel process permits production of pure tetramethyltin? during the extraction by aqueous medium, any trimethyltin halid©, dimethyltin dihalide, or methyltin trihalide may be simultaneously extracted from the organic phase into the aqueous phase. Since these are the commonly occurring by-products produced during production of tetramethyltin, their removal together with the removal of water-soluble ether leaves substantially pure tetramethyltin.

The aqueous phase or layer containing the water-soluble ether together with by-product organotin compounds, may be separated from the tetramethyltin phase containing the desired product tetramethyltin as by decantation. The product tetramethyl in so obtained may be found to be substantially pure, typical purity approaching 99%. The yield of the product tetramethyltin attained at this point is typically greater than 75% and frequently as high as 85%.

If desired;, the water-soluble ether and , by-products may be separated from the product tetramethyltin by the process of this invention using a counter-current, continuous, liquid-liquid extraction technique characterized by intimate contact over minimum time with minimum amount of aqueous extraction medium.

The water-soluble ether, typically tetrahydrofur n, ma be recovered from the aqueous medium as by distillation? and the so-recovered tetrahydrofuran may be dried and reused in the process. The aqueous residue may be treated with e.g. alkali if desired to separate methyltin values as water- It is a particular feature of this invention that the tetramethyltin prepared as hereinbefore set forth may be found to be high purity material attained in yields approaching the stoichiometric;,, Ho ever9 if desired, the tetramethyltin may be redistilled to permit attainment of substantially 100% pure material„ Because of the substantially high purity of the material directly obtained by the extraction process of this inventionp subsequent distillation if desired at all may be conducted in normal processing equipment without the need for large columns containing many plates or operating at high efficiencyo Although this process has been described in connection with the preparation of tetramethyltin, it will be apparent to those skilled-in-the-art that other products such as tetraethyltin may be similarly prepared. However, the problems arising during recovery of product tetra-alkylated tins containing longer chain hydrocarbons are not particularly severe and may be characteristically different from those present in the case of the meth ltins ; and accordingly the maximum advantages of the instant in-vfe^ on may be most fully recognized in connection with the recovery of tetramethyltin,, Practice of this invention may be observed by reference to the following illustrative examples wherein all parts aoted are parts by weight unless otherwise specified.

EXAMPLE 1 In this illustrative example which represents practice of the invention, methyl magnesium chloride Grignard reagent may be prepared by charging 91.3 parts of magnesium turnings to a reaction vessel which may be purged with nitrogen gas. An initiation mixture containing 25 parts of ethyl bromide in 50 parts of tetrahydrofuran may be added „ The reaction mixture may then be heated slightly and when the initiation reaction subsides, 906 parts of tetrahydrofuran and 30 parts of methyl chloride may be added slowly over 85 minutes. The reaction vessel may then be cooled to 65®C and 239 parts of methyl chloride added over 6 hours with cooling to maintain temperature constant o The reaction mixture may then be allowed to stand overnight for 15 hours .

The reaction mixture may then be refluxed at 75°C pot temperature, cooled to 35®C, and 196 parts of tin tetrachloride added thereto over 2 hours.

During this time the pot temperature may rise to 62S'C. The mixture may then be refluxed for 15 minutes, then cooled to room temperature, and then agitated for 2 hours. 950 parts of water may then be added to effect hydrolysis over 1 hour during which the temperature may rise to 68®C. After cooling to room temperature, 6<&tparts of a Isl mixture of sulfuric acid and water may be added thereby forming an aqueous phase and an organic phase. 1510 parts of aqueous phase may be separated from the organic phase. The organic phase may be mixed with 970 parts of water at 25®C9 agitated for 15 minutes s and allowed to settle β The aqueous phase may be found to contain 970 parts of water a d 410 parts of tetrahydro-furan. The organic phase contained 508 parts by weight. 161 parts of the organic phase may then be placed in a separate reaction vessel containing an air stirrer suitable for highly efficient agitation. This organic layer may be subjected to a series of extractions with water wherein in each extraction 50 parts of water are added to the reaction vessel. The mixture of water and organic phase may then be agitated at room temperature of 25°G for 10-15 minutes , the phases allowed to separate,, and the aqueous phase separated. The separated aqueous phase may be withdrawn and measured. At the end of the first batch extraction^ it may be found that the 50 parts of water originally added had increased to 80 parts of aqueous phasep the increase arising because of the water-soluble ether and any soluble products extracted from the organic layer.

Subsequent batch extractions may be carried out with aliquots of 50 parts of water until the amount of aqueous liquid recovered from the reaction vessel is substantially the same as the amount of water added.

This indicates that no more water-soluble ether was present in the reaction vessel.

The product tetraraethyl in remaining in the reaction vessel may be found to be substantially pure material .

Distillation of this material using a simple distillation apparatus may be found to give the following four fractions? Distillate Temperatur Parts by Weight at 77®C 8.2 77®C - 77.5^C 10 77„5¾C - 78°C 6.4 78®C - 78β5®0 8.1 32.7 Total Each of the four fractions may be submitted for analysis and found to be substantially pure tetramethyltin containing respectively 65.45% Sns 65.5% Sn, 65.8% Sn.P and 66.45% Sn (theoretical 66.37% Sn) and no trace of halide. Accordingly„ each of the four fractions were substantially pure tetramethyltin. Analyses of these four fractions by Vapor Phase Chromatography indicated that each was greater than 99.9 mole percent tetramethyl in. The total yield of tetramethyltin may be 78%.

EXAMPLE 2 In this example, the reaction was run essentially as in Example 1. An aliquot of product tetramethyltin from the extraction step was analysed without distillation. The pale yellow liquid contained 65.5% Sn (66.37% theoretical). Analysis by Vapor Phase Chromatography showed the product to be 99.7 mole percent pure.

The high degree of purity of the tetramethyltin made in this example was confirmed by converting this product to dimethyltin dichloride by reaction with tin tetrachloride in accordance with known standard procedures. It was found that dimethyltxn dichlorid was attained in a high yield of 90.5% of a product which was 99„ 7% pure, as determined by Vapor Phase Chromatographic analysis (m.p. 107°C - 108.6°C)„ Although this invention has been illustrated by reference to specific examples 9 numerous changes and modifications thereof which clearly fall within the scope of the invention will be apparent to those skilled-in-thearto

Claims (2)

1. NOW particularly described and ascertained the nature of our said invention and in what manner the same is to be we declare that what we claim f A process recovering tetramethyltin from a solution thereof in a water soluble ether possibly containing also one or more wherein the solution is contacted with water to a tetramethyltin phase and a water phase containing the ether if presents the A process according to Claim wherein the solution contains a methyltin dihalide and process according to Claim 1 or wherein the water soluble is or A process according to

2. Claim 2 or wherein the ether is the product of in a ether of a methyl magnesium halide with a ti and subsequent hydrolysis and removal of the resultant aqueous A prooess according to any of preceding wherein the ether solution is contacted with the water at a temperature between and A process for recovering tetramethyltin from a solution thereof in a water soluble ether possibly containing also one or more methyltin substantially described heroin with reference to the Tetramethyltin when recovered by the prooess according to any of the preceding Dated this 20th day of insufficientOCRQuality