US3211769A - Process for producing alkyltin compounds - Google Patents

Description

United States atent O 3,211,769 PROCESS FOR PRODUCING ALKYLTIN COMPOUNDS 1 Lloyd H. Brown, Crystal Lake, Ill., and Jimmy W. Hill, Olean, N.Y., assignors to The Quaker Oats Company, Chicago, 11]., a corporation of New Jersey N Drawing. Filed Sept. 4, 1962, Ser. No. 221,338 11 Claims. '(Cl. 260-429.7)

This invention relates to a new and improved process of preparing alkyltin compounds by reacting an alkyl halide and a magnesium-tin alloy in the presence of a cyclic ether solvent.

Heretofore, commercial processes for producing alkyltins have involved the use of the conventional Grignard process which required three or four operations under rather strenuous processing conditions, such as high temperatures, thus resulting in high processing costs. Also, in some of these processes, raw material costs have been higher than is desirable. One particular prior art process has overcome some of these disadvantages by reacting alkyl halides and a magnesium-tin alloy in the presence of inert reaction solvents such as cyclohexane. However, the latter process has the disadvantage that it is not suitable for the preparation of higher alkyltin compounds such as butyltin compounds.

It is an object of this invention to provide a process for producing higher alkyltin compounds such as butyltin as well as the lower alkyltin compounds.

Another object of the invention is to provide a process for converting relatively low cost raw materials into alkyltin compounds with a resulting relatively small amount of unconverted raw materials.

A further object of the invention is to provide a process for producing alkyltin compounds at relatively low temperatures of reaction and with a minimum of processing steps.

In accordance with the invention these objects are accomplished by reacting an alkyl halide with a magnesiumtin alloy, preferably Mg Sn, in the presence of a special coordinating reaction solvent to produce halogen-free alkyltin compounds.

We have found that by use of a cyclic ether solvent selected from the group consisting of tetrahydrofuran, tetrahydropyran, and certain substituted derivatives or mixtures thereof, the reaction between alkyl halides and magnesium-tin alloys proceeds under relatively mild conditions. The product obtained, depending upon the proportions of reactants, is a mixture of alkyltin compounds which are useful for a variety of purposes.

While we do not wish to be bound by any theoretical explanation of our discovery, we believe, based on experimental observations, that the special cyclic ether solvents coordinate with and remove from the magnesiumtin alloys, certain intermediate products which are believed to prevent a satisfactory reaction between the alloys and the alkyl halides. The cyclic ether solvents employed in this invention have been found to be unique in promoting reaction between the alkyl halides and the magnesiumtin alloys and particularly with respect to reaction of higher alkyl halides such as butyl chloride. Other commonly used solvents such as cyclohexane and other hydrocarbons have been employed as an inert medium for reaction of lower alkyl halides such as ethyl bromide and magnesium-tin alloys. The products produced with the use of these solvents are principally alkyl tin halides together with appreciable amounts of tetraalkyltin compounds. Reaction of higher alkyl halides such as butyl chloride with magnesium-tin alloys to form. butyl tin compounds cannot be accomplished with these inert solvents. In contrast, the cyclic ether solvents employed in the present invention promote reaction between the magnesiurn-tin alloys and higher alkyl halides such as butyl chloride as well as the lower alkyl halides. Moreover, with the use of the cyclic ether solvents of this invention the principal products produced from the reaction are polymeric type alkyltin compounds substantially free of halogens. The tin compounds produced in accordance with the invention can be represented by the formula:

wherein R is an' alkyl radical having from 2 to 8 carbon atoms and n is zero or a positive integer.

Only relatively small amounts, if any, of tetraalkyl tin compounds are produced in the process of this invention.

The unique suitability of the specified cyclic ether solvents for the purpose of the invention is apparent also when compared with other coordinating solvents of more highly basic nature than the cyclic ether solvents. Thus, for example, pyridine and similar highly basic coordinating solvents, when employed in carrying out the process of the invention, generally lead to the formation of unknown, colored products which do not yield the desired useful alkyltin compounds.

The cyclic other solvents which have been found unique in promoting reaction between the alkyl halides and the magnesium-tin alloys to form compounds of the type designated in the above formula include tetrahydropyran, tetrahydrofuran, alkyl substituted tetrahydrofurans and tetrahydropyrans in which the alkyl substituent is attached to a carbon atom not adjacent to the oxygen atom, and mixtures of the foregoing. The alkyl substituent can be an alkyl radical containing from 2 to 8 carbon atoms.

Reaction of the alkyl halides and the magnesium-tin alloys is preferably conducted at approximately the reflux temperature of the solvent employed which in the case of tetrahydrofuran is 66 C. and tetrahydropyran 83 C. Lower temperatures can be employed for the reaction but are less preferred since the reaction rate is slower necessitating longer reaction times. Higher reaction temperatures can likewise be employed particularly when it is desired to produce larger amounts of the dimer tin compounds (n=0 in Formula I) since higher temperatures favor the production of these compounds. In general, the reaction can be carried out over a very wide range of temperatures such as from about 60 to about C.

It is preferred, but not essential, to employ catalysts in the reaction. Suitable catalysts include metallic mercury and the halides such as the chlorides, bromides and iodides of mercury or cobalt. A particularly preferred catalyst is mercuric chloride.

Suitable alkyl halide reactants include alkyl chlorides, bromides or iodides. The alkyl group can range from ethyl to octyl or higher.

In a preferred embodiment of the invention a molar excess of the alkyl halide is reacted with the magnesiumtin alloy by mixing the alkyl halide with an excess of the special reaction solvent and adding the mixture incrementally to a reaction vessel containing the alloy and metal catalyst in finely ground form and protected by a nitrogen atmosphere. The amount of reaction solvent must be suflicient to keep the reaction mixture fluid throughout the reaction. The reaction mixture is heated at a refluxing temperature until the reaction is complete as evidenced by the absence of unreacted alloy. The time of reaction ranges from about an hour to about 24 hours depending on the temperature applied to the reaction and the mole ratio of alkyl halide to' the alloy. The reaction mixture is then washed with a dilute aqueous mineral acid to remove magnesium halides, and the resulting aqueous phase containing magnesium halide and the resulting organic phase containing the alkyltin compounds are separated by conventional means. The product of the reaction of the invention is generally a mixture of alkyltin compounds which are useful intermediates in the preparation of highly valuable tin compounds.

With the use of low molar ratios of alkyl halide to magnesium-tin alloy, i.e. 5:1 or lower, the n in Formula I approaches zero so that the principal products obtained are dimer compounds, bis-(trialkyltin). With the use of high molar ratios of alkyl halide to magnesium-tin alloy the principal products are polymers wherein n in Formula I is a positive integer. Molar ratios of alkyl halide to magnesium-tin alloy can range from 2:1 to 8:1 or more.

The bis-(trialkyltin) compound can be reacted with hydrochloric acid by conventional means to form the chloride which can then be hydrolyzed, if desired, to form trialkyltin oxide. One such compound, namely tributyltin oxide, finds widespread use in fungicides, bacteriostats and germicides.

The polymer tin products (nzpositive integer in Formula I) can be directly oxidized with atmospheric oxygen and at room temperature to form dibutyltin oxide. This material is useful as an intermediate in the preparation by conventional means of such compounds as dialkyltin diacetate, dilaurate, maleate, sulfide, dichloride, and mercapto esters, as well as tetraalkyltin, etc. Such means of preparation of the derivatives and their applications are described in Chemical Engineering, vol. 65, No. 16, pages 78-82.

The invention will be further illustrated but is not limited by the following examples in which the quantities are stated in parts by weight unless otherwise indicated:

Example 1 The magnesium-tin alloy, Mg Sn, was prepared by heating with agitation 72 parts of tin shot and 28 parts of magnesium turnings at 800 C. for 15 minutes in an iron crucible and nitrogen atmosphere. A mixture of 265 parts of anhydrous tetrahydropyran and 333 parts of butyl chloride was prepared. About 22 parts of the mixture and about 2 parts of ethyl bromide (hastens initiation of reaction but is not essential) was introduced into a reaction vessel having a nitrogen atmosphere and containing a finely ground mixture of 74.3 parts of the Mg Sn alloy and 1.5 parts of mercuric chloride. Heat was applied to the vessel to effect refluxing at a temperature of about 8386 C. and when the reaction had begun, as evidenced by turbulence and the formation of gray particles, the remaining tetrahydropyran-butyl chloride mixture was added dropwise over a period of about one hour. The refluxing was continued for an additional 6 hours and 45 minutes after which the mixture was cooled to about 5 C. Three hundred parts of 3% aqueous hydrochloric acid were then added to the reaction vessel, dropwise at first, with agitation. The aqueous and organic phases which formed were separated. The organic part was washed three additional times with 300 parts of 3% aqueous hydrochloric acid to insure complete removal of magnesium chloride. The aqueous part was washed once with Skellysolve F (a hydrocarbon product of the Skelly Oil Company of El Dorado, Kansas) to recover additional organic product which was combined with the original washed organic portion. The organic portion was distilled, at atmospheric pressure at first and then with vacuum gradually applied, to remove all traces of low boiling impurities. The final distillation temperature was 100 C. and the final pressure was 18 mm. of mercury. The product residue was 114.1 parts of a pale green, slightly viscous liquid having a tin analysis of 45.94% by weight using the analytical method of Gilman and King, J.A.C.S., vol. 51, page 1213. The tin analysis of 45.9% indicates that the principal product was a polymeric product. A conversion of 98.2% by weight based on the weight of tin in the alloy, was obtained in this example in which the mole ratio of butyl chloride to the magnesium-tin aly was 8: 1.

Example 2 The procedure of Example 1 was essentially repeated with the exception that the reaction was carried out in a Parr bomb, the reaction time was eight hours and the reaction temperature was in the range 105-145" C. The product had a tin analysis of 41.50% by weight and the conversion was 92.3% by weight. The tin analysis indicates that the principal product was the dimer, bis-(tributyltin).

Example 3 The procedure of Example 1 was essentially repeated with the exception that the reaction time was two hours and the refluxing temperature was in the range 83-86 C. The product had a tin analysis of 45.40% by weight and the conversion was 74.8% by weight.

Example 4 The procedure of Example 1 was essentially repeated with the exception that the mole ratio of butyl chloride to Mg Sn was 5:1, the reaction time was 24 hours, and the refluxing temperature was in the range 8391 C. The product had a tin analysis of 41.76% by weight and the conversion was 88.9% by weight.

Example 5 The procedure of Example 1 was essentially repeated with the exception that the reaction solvent was tetrahydrofuran instead of tetrahydropyran, the mole ratio of butyl chloride to Mg Sn was 3:1, the reaction time was 12 hours, and the refluxing temperature was in the range 66-77 C. The product had a tin analysis of 38.99% by weight and the conversion was 50.3% by weight.

Example 6 The procedure of Example 1 was essentially repeated with the exception that the mole ratio of butyl chloride to Mg Sn was 2:1, the reaction time was 24 hours, and refluxing temperature was in the range 83-92 C. The product had a tin analysis of 37.24% by weight and the conversion was 38.0% by weight.

Example 7 The procedure of Example 1 was essentially repeated with the exception that the reaction solvent was a mixture of 60 parts tetrahydropyran and 40 parts tetrahydofuran, the reaction time was four hours, and the refluxing temperature was in the range 78-83 C. The product had a tin analysis of 45.48% by weight and the conversion was by weight.

Example 8 The product mixture of Example 7 was oxidized to dibutyltin oxide. Air was blown very slowly into a mixture of 37.08 grams of the Example 7 product and milliliters of Skellysolve B for 24 hours. A white precipitate of butyltin oxide (21.62 grams) was separated by filtration, washed, and then dried at 60 C. in a vacuum oven. The product had a tin analysis of 47.05% by weight which compared favorably with the 47.68% theoretical tin content of dibutyltin oxide. Further proof that the product was dibutyltin oxide was demonstrated by its known reaction with hydrochloric acid to form dibutyltin dichloride, Bu SnCl To 12.48 grams of the above dibutyltin oxide in a beaker, there was added an excess of concentrated hydrochloric acid at room temperature. After 15 minutes, the oily material which separated was extracted with Skellysolve B. After separation, washing and drying, the solvent was stripped. There remained 13.9 grams of crude Bu SnCI which had a melting point of 3538 C. When recrystallized from Skellysolve B, it had a melting point of 41.0- 41.5" C. The melting point was not depressed when mixed with an equal weight of pure known dibutyltin dichloride. An infrared curve of the product compared favorably with the infrared curve of pure dibutyltin dichloride. The product analyzed 39.28% by weight of tin and 23.35% by weight of chlorine as compared respectively to the theoretical values of 39.07% and 23.34% of Bu SnCl Example 9 The procedure of Example 1 was essentially repeated with the exception that 300 parts of pyridine replaced the tetrahydropyran as reaction solvent. After eight hours at 85 C., the reaction system was found to be a black, tarry mass from which no useful products were obtained.

Example 10 The procedure of Example 1 was essentially repeated with the exception that 300 parts of 3-methyltetrahydrofuran replaced the tetrahydropyran as reaction solvent. The results obtained were similar to those of Example 1.

Example 11 The procedure of Example 1 was essentially repeated with the exception that 300 parts of S-butyltetrahydropyran replaced the tetrahydropyran as reaction solvent. The results obtained were similar to those of Example 1.

The present invention provides an improved process for producing useful alkyltin compounds. A critical feature of the invention is the use of the specified cyclic ether solvents which have been found unique in promoting the formation of alkyltin compounds. As indicated, the cyclic ether solvents of the invention permit the production of alkyltin compounds of the type designated by Formula I by reaction of magnesium-tin alloys with alkyl halides including higher alkyl halides such as butyl chloride and the like. This is in contrast to other inert solvents known in the art which do not permit reaction between the higher alkyl halides and magnesium-tin alloys and which in the case of the lower alkyl halides favor the production of alkyltin halides. The process of the invention can be carried out using relatively mild reaction conditions with the obtainment of high yields of desired tin compounds.

Those modifications and equivalents which fall within the spirit of the invention and the scope of the appended claims are to be considered part of the invention.

We claim:

1. A process for producing halogen-free alkyltin compounds which comprises reacting at a temperature not substantially above 150 C. an alkyl halide with a magnesium-tin alloy in the presence of a reaction solvent selected from the group consisting of tetrahydrofuran, tetrahydropyran, alkyl substituted tetrahydrofuran and tetrahydropyran in which the alkyl substituent is attached to a carbon atom not adjacent to the oxygen atom, and mixtures thereof.

2. A process according to claim 1 wherein said halide is a chloride.

3. A process according to claim 1 wherein there is employed a catalyst selected from the group consisting of metallic mercury, the inorganic halides of mercury and the inorganic halides of cobalt.

4. A process according to claim 1 wherein the alkyl halide is a butyl halide.

5. A process according to claim 1 wherein the molar ratio of alkyl halide to magnesium-tin alloy is within the range from 2:1 to 8:1.

6. A process for producing halogen-free butyltin compounds which comprises reacting at a temperature not substantially above C. butyl chloride with a magnesiurn-tin alloy in the presence of mercuric chloride and a reaction solvent selected from the group consisting of tetrahydrofuran, tetrahydropyran, alkyl substituted tetrahydrofuran and tetrahydropyran in which the alkyl substituent is attached to a carbon atom not adjacent to the oxygen atom, and mixtures thereof.

7. A process of producing halogen-free alkyltin compounds which comprises reacting at a temperature not substantially above 150 C. an alkyl halide with a magnesium-tin alloy in the presence of the reaction solvent tetrahydrofuran.

8. A process of producing halogen-free alkyltin compounds which comprises reacting at a temperature not substantially above 150 C. an alkyl halide with a magnesium-tin alloy in the presence of the reaction solvent tetrahydropyran.

9. A process of producing halogen-free alkyltin compounds which comprises reacting at a temperature not substantially above 150 C. an alkyl halide with a magnesium-tin alloy in the presence of the reaction solvent consisting of a mixture of tetrahydrofuran and tetrahydropyran.

10. A process of producing halogen-free alkyltin compounds which comprises reacting at a temperature not substantially above 150 C. an alkyl halide with a magnesium-tin alloy in the presence of a reaction solvent consisting of an alkyl substituted tetrahydrofuran in which the alkyl substituent is attached to a carbon atom not adjacent to the oxygen atom.

11. A process of producing halogen-free alkyltin compounds which comprises reacting at a temperature not substantially above 150 C. an alkyl halide with a magnesium-tin alloy in the presence of a reaction solvent consisting of an alkyl substituted tetrahydropyran in which the alkyl substituent is attached to a carbon atom not adjacent to the oxygen atom.

References Cited by the Examiner UNITED STATES PATENTS 3,085,102 4/63 Yatagai et a1. 260429.7

FOREIGN PATENTS 713,727 8/54 Great Britain. 878,958 10/61 Great Britain.

TOBIAS E. LEVOW, Primary Examiner.

Claims (1)

1. A PROCESS FOR LPRODUCING HALOGEN-FREE ALKYLTIN COMPOUNDS WHICH COMPRISES REACTING AT A TEMPERATURE NOT SUBSTANTIALLY ABOVE 150*C. AN ALKYL HALIDE WITH A MAGNESIUM-TIN ALLOY IN THE PRESENCE OF A REACTION SOLVENT SELECTED FROM THE GROUP CONSISTING OF TETRAHYDROFURAN, TETRAHYDROPYRAN, ALKYL SUBSTITUTED TETRAHYDROFURAN AND TETRAHYDROPYRAN IN WHICH THE ALKYL SUBSTITUENT IS ATTACHED TO A CARBON ATOM NOT ADJACENT TO THE OXYGEN ATOM AND MIXTURES THEREOF.