CA1069129A - Method for preparing alkyltin trihalides - Google Patents

Abstract

NOVEL METHOD FOR PREPARING ALKYLTIN TRIHALIDES

Abstract of the Disclosure - Alkyltin trihalides are prepared by reacting a stannous halide with the corresponding alkyl halide in the presence of specific catalysts. By conducting the reaction under superatmospheric pressure the amount of catalyst required is significantly reduced. Recycling the catalyst decreases process costs and improves the yield of organotin trihalide.

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Description

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BACKGROUND OF THE INVENTION
This invention relates to a method for preparing alkyltin trihalides.
This invention further relates to an improved method for preparing alkyltin trihalides by the catalyzed reactlon between a stannous halide and an alkyl halide. ~
United States Patent 3,340,283 whichissued May 9, 1967 to Gloskey -discloses preparing organotin trihalides, RSnX3, wherein X represents chlorine, bromine or iodine, by reacting a stannous halide, SnX2, with the corresponding hydrocarbon halide, RX. The reaction is carried out under autogenous pressure and in the presence of an amine catalyst. The desired organotin trihalide is isolated using conventional techniques, which include selective extraction and distillation. The process as disclosed in the aforementioned patent makes no provision for recovery and recycling of the catalyst, which may represent a significant economic investment, particularly for a commercial scale process employing relatively large amounts of cata-lysts for a single reaction. In addition, the catalyst may be present as -; a complex that contains as much` as 6% by weight of organotin compounds, including the desired product. These complexes are relatively stable under the condltions employed to prepare and isolate the organotin trihalide.
These complexes can reportedly be decomposed by the addition of water. While hydrolysis of the complex could result in higher yields of the organotin trihalide, it may also introduce undesirable water-soluble impurities into the organotin product, including antimony and iron compounds. This is particularly true for the ,, ' - - . . . , , ' `

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water-soluble organotin trihalides such as methyltin trichloride and butyltin trichloride. In addition, some end uses require that the water employed to decompose the complex be removed by distillation or other suitable means. This separation step significantly increases processing costs.
United States Patent 3,519,667 whichissue~July 7, 1970 to Molt et al describes the preparation of alkyltin trichlorides by the reaction between stannous chloride and either methyl chloride or ethyl chloride.
The reaction is preferably conducted under atmospheric pressure and in the presence of a phosphonium chloride or a thiocyanate catalyst. The con-centration of catalyst required is between 0.4 and 0.7 mole per mole of stannous chloride. This relatively high catalyst concentration appears necessary to achieve a useful reaction rate under atmospheric pressure.
Whatever the reason may be, the large amount of catalyst required signifi-cantly reduces volume efficiency and increases production costs.
~ ne objective of this invention is to reduce the concentration of catalyst required to prepare alkyltin trihalides. A second objective is to more effectively utilize the catalyst together with any organotin compounds that may have complexed with the catalyst in the reaction mix-ture. Surprisingly it has now been found that yield and volume efficacycan be increased and the amount of catalyst reduced if the reaction be-tween a stannous halide and a lower alkyl halide is carried out under a pressure of between 50 and about 500 p.s.i. (3500 and about 35,000 g./cm.2) and in the presence of a diluent consisting at least in part of the catalyst-containing residue from a previous distillation of a lower alkyltin trihalide prepared in accordance with the present method.

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069lZ9 This invention provides in an improved method for preparing an alkyltin trihalide, wherein the alkyl group contains between one and five carbon atoms and the halogen, represented by X, is chlorine, bromine or~iodine, by reacting the corresponding alkyl halide, RX, with a stannous halide SnX2 at a temperature of between 150 and 250C., and isolating the resultant alkyltin trihalide by distillation, the reaction between said alkyl halide and stannous halide being conducted in the presence of a diluent and a catalyst selected from the group consisting of amines and . phosphines of the general formulaeR3N and R3P, respectively, and the onium salts of said amines and phosphines wherein each Rl is individually select-ed from the group consisting of hydrogen atoms and alkyl radicals containing ~ .
between 1 and 20 carbon atoms, cycloalkyl, aryl, alkaryl and aralkyl radicals wherein the alkyl residue of said alkaryl or aralkyl radical contains between 1 and 20 carbon atoms, the improvement which resides in (a) conducting said reaction under a pressure of between 50 and 500 p.s.i. and in the presence of a diluent consisting, at least in part, of the residue remaining following a previous distillation for the recovery of said alkyltin trihalide, said diluent being a solvent or dispersant for the catalyst and a solvent for the alkyltin trihalide, and . .
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Ib) maintaining the catalyst concentration in ¦said ~esidue at between 0.005 and about 0.15 mole of catalyst per gram at~m of tin present ¦in the reaction mixture.
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~0691Z9 DETAILED DESCRIPTION OF THE INVENTION

¦ The present method for preparing lower alkyltin ¦ trihalides employs Iess catalyst than heretobefore disciosed in the prior art and, more importantly, I
improves product yield by recycling the catalyst, thereby . .
utilizing the organotin compounds which are complexed with the catalyst.
The aforementioned U. S. Patent 3,519,667 teaches using 1 mole of catalyst for every two moles of stannous halide, since the amount o~ stannous chloride converted to organotin trichloride is allegedly never greater than the amount of catalyst, on a molar basis. The disclosure contained :~ ln this patent indicates that the reaction between stannous chloride and methyl chloride can be conducted at higher than . atmospheric pressures using less catalyst than required at atmospheric pressure due to the higher concentration of methyl chlorlde present, in the liquid phase. Since stannous chloride does not have a significant vapor pressure under the ~ ' .
. ,~onditions o~ the reaction, only the methyl chloride : dissolved in the liquid phase would be expected to react.
In accordance with Henry's law, there 1s a linear relationship between the concentration o~ methyl chloride in , the solution and the partial pressure of this gas. Henry's ., law can pe expressed as P=kX where P represents the pressure of the gas, X the mole ~raction of the gas present in the 25 ' solvent, which in the present invention is the reaction medium containing the stannous halide, and k is an experimentally ¦¦ determine constant, whlch for most gasses has a value Or ~ l I

between 10 and 10 . Assuming that methyl chloride or I other alkyl halide exists as a gas under the conditions of the ¦ present reaction and obeys Henry's law, if the pressure were ¦ increased to ten times atmospheric pressure, the concentration ¦ of the gas in solution would be expected to be ten times the value at atmospheric pressure. The amount of catalyst required I to provide an equivalent reaction rate at the higher pressure ; ¦ should there~ore be proportionately lower. Specifically, a ¦ 10 fold increase in pressure should allow about a 10 fold 10 ¦ decrease ln catalyst concentration without affecting the reaction rate to any significant extent. Surprisingly the ¦ present method employs between 0.005 and 0.15 mole of catalyst, preferably less than 0.05 mole of catalyst per gram atom of tin present in the reactlon mixture under pressures khat are between 3 and 20 times atmospheric. In accordance with prior art teachings, one would expect to employ more than 0~025 mole of catalyst.
m e catalysts of the present invention are ammonia, primary, secondary and tertiary amines, phosphines and onium salts of these compounds. The amines and phosphines are of the general formula R3N and R3P, respectively, wherein each R is a hydrogen atom or a hydrocarbon radical, as previously defined. Preferably the three R radicals are identical.
i~ Typical primary amines which can be employed in the practice of this invention include: methyl amine, ethyl ', amine, n-propyl amine, n-butyl amine, i-butyl amine, n-amyl amine, hexyl amine, octyl amine, allyl amine, cyclohexyl amine, benzyl amine, p-toluidine, aniline, p-methyl aniline, ~-pheny hyl-amine, ethylene diamine and p-ch~oro aniline.

t Il : . . , 1 J.069129 The secondary amines include dimethyl amine, diethyl amine, di-n-butyl amine, di-n-amyl amine, dihexyl amine, dioctyl amine, diallyl -amine, dicyclohexyl amine, dibenzyl amine, N-methyl ethyl amine, N-methyl aniline, N-ethyl aniline, hexamethylene tetramine and N-methyl naphthyl-amine.
Useful tertiary amines include trimethyl amine, triethyl amine, tri-n-propyl amine,tri-n-butyl amine, trihexyl amine, triallyl amine and tricyclohexyl amine.
Other amines include aniline, p-toluidine, o-toluidine, m-toluidine, benzyl amine, pyridine, 2-methyl pyridine, 3-methyl pyridine, 2-ethyl pyridine, 3-ethyl pyridine, quinoline, 6-methoxy quinoline, ~-picoline, ~picoline and gamma picoline. ' Inertly substitutedamines such as p-chloro aniline can also be employed.
The phosphines corresponding to each of the foregoing amines can also be used as catalysts for the present methot. Preferred catalysts include trimethylamine, tributylamine, tributylphosphine and triphenyl-phosphine.
In the presence of the alkyl halide all of the catalysts, including ammonia and phosphine, are converted to the corresponding quaternary ammonium halide or phosphonium halide. If desired, the catalyst can be added to the reaction mixture as the corresponding quaternary onium salt, RlR ZX, wherein R is selected from the same group as Rl, X is a monovalent anionic radical, preferably chlorine, bromine or iodine and Z is nitrogen or phosphorus. Inorganic ammonium salts such as ammonium chloride are also suitable. Other useful onium type catalysts are disclosed in United States Patent 3,415,857 which issued October 12, 1968 to Hoye.

1~91~9 The reaction between the stannous halide and alkyl halide is conducted in the presence of a diluent that conslsts, at least in part, of the residue from a previous distillation of alkyltin trihalide prepared in accordance with the present method and which contains an effective amount of one of the present catalysts. Since the boiling points of the present catalysts in the form of their onium salts are considerably higher than that of the desired monoalkyltin trihalide, substantially all o-f the catalyst employed for the reaction is contained ln the residue, and can be recycled virtually indefinitely. In many instances the residue is an adequate diluent in which to carry out the reaction between the stannous halide and alkyl halide. Should additional diluent be required, for example, to reduce the viscosity of the reaction mixture, one can employ any inert organic solvent.
Typical solvents include ethers such as diethylene glycol dimethyl ether, diethyl ether, dibutyl ether, tetrahydrofuran and aliphatic hydrocarbons, such as hexane, heptane, octane, cyclohexane and those mixtures of hydrocarbons available as mlneral oils, liquid paraffins or petroleum ethers. Preferably the diluent consists, at least in part, of an alkyltin tri-halide, usually the one to be prepared using the present method.
The diluent should be a solvent or dispersant for the reactants and a solvent for both the alkyltin trihalide product and the catalyst. The relative volumes of diluent and reactant will vary somewhat depending upon process conditions. The volume of diluent should always be sufficient to completely ?
disperse or dissolve the reactants and provide a fluid reaction medium t tùe ~emperature o~ the reactlon, whlch 1s ~etween ., `, Il 1'.' ,, - - : . - , , ~ - , . - : . .

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150 and 250C., pre~erably between 170 and 200C. The mixture ¦ should be sufficiently fluid to permit trans~erral of the ¦ reaction mixture to a distillation apparatus for recovery of ¦ the alkyltin trihalide from the reaction mixture.
m e distillation residue employed as the diluent preferably contains between 0.005 and 0.15 mole of catalyst per mole o~ stannous halide to be reacted and more than 0.5 mole of organotin trihalide per mole of catalyst. If less than the required concentration of organotin trihalide is present, the volume of diluent should be increased by the addition of an inert organic liquid or additional alkyltin trihalide as previously defined, until the volume of diluent ls at least equal to the combined volumes of the stannic halide and alkyl halide.
The alkyl halide and stannous halide are reacted under a pressure of between 50 and 300 p.s.i. The pressure is controlled by ad~usting the rate at which the alkyl halide i8 added to the reaction vessel containing a stannous halide and a diluent as descrlbed hereinbefore. Under the conditions of the present method the reaction is substantially complete ,~ in from about 4 to 10 hours. Longer times may be desirable to ensure substantially complete conversion, particvlarly in large commercial scale reactors. me resultant mixture is then distilled under reduced pressure to lower the boiling point of the alkyltin trihalide, thereby reducing the amount 1~ of heat input required to isolate the product which is usually obtained in yields of 90% or greater. The present method is therefore limited to those alkyltin trihalides that boil below , _g_ . .

11 .. - -- ..... , ~ ,. - . ~ . ~, - . , ` ~1 10691Z9 about 300C. under reduced pressures. Suitable alkyltin trihalides contain between 1 and 5 carbon atoms and the halogen is chlorine, bromine or iodine.
It is desirable to recover between about 50 and 100% of the total alkyltin trihalide by distillation. Any remainder, together with the catalyst, is recycled by being used as the diluent for a subsequent reaction.
The present method usually employs a stoichiometric excesæ of alkyl halide relative to stannous halide. Preferably this ratio is between 1.03 and 2.0 moles of alkyl halide for every mole of stannous halide.
¦ The following non-limiting examples demonstrate ¦ preferred embodiments of the present method for preparing I alkyltin trihalides. All parts and percentages are by weight l unless otherwise indicated.
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¦ EXAMPLE 1 An autoclave was charged with molten monomethyltin trichloride (1153g.; 4.80 moles) and anhydrous stannous chloride (9lOg.; 9.79 moles). The autoclave was then sealed and purged with methyl chloride to remove residual air, after which it was cooled in dry ice and charged with trimethylamine (16g.). The autoclave was then sealed and the contents heated to 175-180!C. with agitation. Methyl chloride (440g.; 8.71 moles) was then pumped into the autoclave at a rate which maintained a pressure of between 250 and 300 p.s.i.g.
Following completion of-the methyl chloride addition, the f ; mixture was stirred for 2 hours while being heated to 175-180C. The total reaction time was about 6 hours. The reaction mass was then cooled to about 60C. and transferred to a distillation apparatus.
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¦ The distillate (1019g.), collected at 142-145C.
l (406-432 mm. of Hg.) was found to contain in excess of 90% by ¦ weight of monomethyltin trichloride.
¦ The residue (1219g.), consisting primarily of ¦ methyltin trichloride and catalyst, was transferred to the autoclave for use in the reaction described in the following example.
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The molten residue (1219g.) from the preceding Example 1 and stannous chlorlde (9lOg.) were charged into an autoclave, which was then purged with methyl chloride. No additional catalyst was charged. The contents of the autoclave were heated to 175-180C. The reaction and subsequent dis-tillatlon were carried out as described in Example 1, yielding a distillate (1081g.) and a residue (119Og.).
. . ~' The procedure of Example 2 was repeated using the distillation residue (119Og.) of Example 2 as a solvent. No addltional catalyst was used. The distillate weighed 1161g.
and the residue (1116g.) was suitable for recycling.
The combined distillates from Examples 1, 2 and 3 contained 97% monomethyltin trichloride, 2% dimethyltin ¦ dlchlor e, and 1% tin ( IV) chloride .

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. i, 106gl29 An autoclave was charged with mineral oil (636g.), triphenylphosphine (39g.; 0.149 mole), and stannous chloride (lOOOg.; 5.27 mole). The autoclave was then sealed and the air within the autoclave displaced by methyl chloride;
Agitation was continued while the contents Or the autoclave were heated to 175-190C. Methyl chloride (372g.; 7.37 moles) was then metered into the reactor pump at a rate that maintaine a pressure of 250-300 p.s.i.g. within the reactor. After all of the methyl chloride had been added the reaction mixture was agltated while being heated to a temperature of 170-190C.
~ - ~or 4.5 hours, during which time the pressure remained i relatively constant. The total reaction time was 9.5 hours.
The resultant mixture was cooled to about 148C. and then dlstilled, yielding a nearly colorless distillate (1168g.) boiling at 110-140C. (406-711 mm. of mercury). The distillat~
contained 97% methyltin trichloride and 3~ dimethyltin dichloride. The distillatlon residue (732g.), consisting o~
mineral oil and catalyst plus associated methyltin halides, was subsequently used to prepare additional methyltin trichloride.
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; An autoclave was charged with methyltin trichloride . (1153g.; 4.80 moles), stannous chloride (9lOg.; 4.79 moles), and triphenylphosphine (69.7g.; 0.266 moles). The autoclave was then sealed and the entrapped air displaced by methyl chloride. The mixture was stirred and heated to between 175 and 190C. Methyl chloride (440g.; 8.71 moles) was then ~ ' ' .
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i9Z9 ¦ metered into the autoclave at a rate which maintained the pressure at between 250 and 300 p.s.i.g. The slight excess of methyl chloride was required to maintain the pressure l within the autoclave at 250-300 p.s.i.g. throughout the 4.5 ¦ hour-long reaction period. After all of the methyl chloride ¦ had been added, the mixture was stirred for an additional 2 hours while the temperature was maintained between 175 and l 190C. Approximately 50% of the resultant mixture was ¦ distilled at 142-145C. (406-432 mm. of mercury). The ¦ distillate (1019g.) was found to contain 98% methyltin tri-chloride, 1.9% dimethyltin dichloride, and traces of tin (IV) chloride. The residue (1350g.), containing the catalyst, was ¦ reused in a subsequent reaction.
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¦ EXAMPLE 6 . .
l The catalyst-containing residue (1325g.j of Example ¦ 5 and stannous chloride (9lOg.; 4.79 moles) was charged to an autoclave. No additional catalyst was added. The mixture was reacted with methyl chloride as described in Example 5, and approximately 50% of the reaction mass was discilled.
The distill~te (1081g.) contained 97% methyltin trichloride, 2.5% dimethyltin dichloride, and traces of tin (IV) ch ride.

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Claims (10)

WHAT IS CLAIMED IS:

1. In an improved method for preparing an alkyltin trihalide, wherein the alkyl group contains between one and five carbon atoms and the halogen, represented by X, is chlorine, bromine or iodine, by reacting the corresponding alkyl halide, RX, with a stannous halide SnX2 at a temperature of between 150 and 250°C., and isolating the resultant alkyltin trihalide by distillation, the reaction between said alkyl halide and stannous halide being conducted in the presence of a diluent and a catalyst selected from the group consisting of amines and phosphines of the general formula R?N and R?P, respectively, and the onium salts of said amines and phosphines wherein each R1 is individually selected from the group consisting of hydrogen atoms and alkyl radicals containing between 1 and 20 carbon atoms, cycloalkyl, aryl, alkaryl and aralkyl radicals wherein the alkyl residue of said alkaryl or aralkyl residue contains between 1 and 20 carbon atoms, the improvement which resides in a) conducting said reaction under a pressure of between 50 and 500 p.s.i. and in the presence of a diluent consisting, at least in part, of the residue remaining following a previous distillation for the recovery of said alkyltin trihalide, said diluent being a solvent or dispersant for the catalyst and a solvent for the alkyltin trihalide, and b) maintaining the catalyst concentration in said residue at between 0.005 and about 0.15 mole of catalyst per gram of tin present in the reaction mixture.

2. The improved method of Claim 1 wherein the alkyltin trihalide is selected from the group consisting of methyltin trihalides and butyltin trihalides.

3. me improved method of Claim 1 wherein the alkyltin trihalide is methyltin trichloride or butyltin trichloride.

4. The improved method of Claim 1 wherein the concentration of catalyst is between 0.005 and 0.15 mole of catalyst per gram atom of tin present in the reaction mixture.

5. The improved method of Claim 1 wherein the catalyst is a trialkyl amine.

6. The improved process of Claim 5 wherein the catalyst is trimethylamine or tributylamine and the alkyl halide is methyl chloride.

7. The improved method of Claim 1 wherein the catalyst is tributylphosphine.

8. The improved method of Claim 1 wherein the catalyst is triphenylphosphine.

9. The improved method of Claim 1 wherein the reaction between the stannous halide and alkyl halide is carried out in the presence of an inert hydrocarbon diluent.

10. The improved method of Claim 9 wherein said diluent is a mineral oil.