A method for preparing methyltin compounds

A METHOD FOR PREPARING METHYLTIN

COMPOUNDS

ABSTRACT OF THE DISCLOSURE

Methyltin compounds having a structure represented by the formula» <^CH3>4.n ״⁸ ־*η in which X is a halogen and n is an integer from 0 to 3 are produced in high yields by a process in which a stannic halide is transmeth^ated with tetramethyllead at a temperature below about 90° C following which the reaction product is heated to a temperature above about 100°C for a period of time sufficient to produce the desired methyltin compound by exhaustive transmethylation. These methyltin compounds or their derivatives (such as methyltin oxides) are important for the preparation of many biocides polymer stabilizers glass strengthening agents and catalysts.

BACKGROUND OF THE INVENTION

A number of procedures for the preparation of alkyltin compounds are known. One of the known methods involves the reaction of a stannic halide with an appropriate Grignard reagent. If an excess of Grignard reagent is used, a tetramethyltin will be the primary product; however, stoichiometric or less amounts of Grignard refvgent will yield two or more of the various alkyltin halides depending upon the reaction conditions employed. Alternatively, a stannic halide may be reacted with aluminum, sodium or lithium alkyls to form alkyltin halides. A third process of limited value is the direct reaction of an alkyl halide with metallic tin, preferably conducted in the presence of metallic copper or zinc. None of these procedures has been found commerically feasible.

1Recently, consideration has been given to the possibility of the use of tetramethyllead as a methylating agent in various processes. One process I considered was the methylation of stannic halides with tetramethyllead to form methyltin compounds. The simple mixture of a stannic halide, particularly stannic chloride, with tetramethyllead without temperature control results in a violently exothermic reaction. The reaction product

Jn_ of this reaction is a solid containing unpredictable proporti^ of various methyl tin compounds. Due to the violence of the exothermic reaction and the unpredictability of the product /Tn *x in &lt;3 distribution, the simple mixturc of a stannic halide and tetramcthyllcad is an impractical and dangerous route for the synthesis of methyl tin compounds.

OuZZ-ine of, the. Invention

It has now been discovered that by application of certain temperature controls to the reaction between a stannic halide and tetramethyllead, a safe, relatively simple, economical ly practicable commercial synthesis of methyltin compounds is available using a stannic halide and tetramethyllead as the reactants. This invention thus provides a commercial process for the preparation of methyltin compounds by the transmethylation of a stannic halide with tetramethyllead. More particularly, the invention relates to the preparation of methyltin

In which compounds of the formula (CH2)4-_n SnX_n wke-p&amp;i-H X is a halogen and n is an integer of from 0 to by the transmethylation of a stannic halide with tetramethyllead at less than about 90°C followed by the heating of the transmethylation reaction product to above 100°C for a time sufficient to produce bfy^zredistribut-ioF transmethylation _ץ. ־

X)T_li^Ju1aj1s±er.ced_meikyl_gj־£u4LS a product containing a major amount of a single mcthyltin compound. As indicated, the final reaction product will contain at least a major portion, i.e., more than 50* by weight, based upon the amount of 811־X4 reactant converted, and preferably more than 75״ by weight, of a single mcthyltin compound. Additionally, the process of this invention provides for high conversion of 811X4 to the mcthyltin compounds;

in many cases almost quantitative conversions to mcthyltin compelnc are recoverable. Recoverable amounts of lead halides arc also . . . .. ., b formed during the process of this invention.

The transmethylation of stannic halides by tetramethy^ lead by the process 0Γ this invention is believed to occur by the following reactions:

(1) (C₄(₃״Pb + 3SnX₄3 ׳—־CII₃SnX₃ + C1I₃X + PbX₂ (2) 2 (Cll₃)₄Pb + 3 SnX₄ 3־(CII₃) ₂SnX₂ + 2 CII3X +21’bX₂ (3) (CII₃)₄Pb + SnX₄ ׳(CII₃)₃SnX + CII3X + PbX₂ (4) 2 (ClI₃)₄Pb + SnX₄ . (Cll₃)₄Sn + 2 (Cll₃)₂PbX₂

The process of this invention actually provides major portions of these specific products by utilizing molar ratios of reactants roughly approximating the theoretical of these equations and the described temperature controls and the after-heating step. Thus the process of this invention provides a high conversion of SnX₄ to methyltin compounds with a high yield of a particular methyltin compound.

BazZc PflAumeZeflA the InvcnZZon

The transmethylation reaction of this invention must be conducted at controlled temperatures below the boiling point of the tetramethyllead reactant (i.e. about 110°C). The reduced temperature must be maintained below about 90°C to provide the optimal methyl transfer provided by the process of this inventior. Preferably, the temperature of the methylation step should be and may even be carried below abou^ 40°C, e.g. about 15°C to 35°C, hut-above-0-Cout below 0 C,

The transmethylation reaction may be conducted in the presence or absence of an inert organic solvent. If the transmethylation is carried out in the absence of a solvent, a solid reaction product normally results. When an inert organic solvent is utilized, the product of the transmethylation may be cither a solid-solvent slurry or a solution depending upon the solubility characteristics of the products in the particular solvent

־ .

ut i1ized.

’^,Inert organic solvents contemplate only those organic solvents which do not interfere with the transmethylation reaction by reaction or complex formation with either reactant.

The presence of a solvent also is helpful in achieving the required temperature control during the transmethylation stage. Among the solvents found to be useful in this invention arc aliphatic, cycloaliphatic and aromatic hydrocarbons such as hexane, petroleum ether fractions, benzene or xylenes; chlorinated hydrocarbons such as chloroform, methylene chloride, or chloro־ benzene and lower aliphatic alcohols such as ethanol, propanol or butanol.

The temperature control of the transmethylation should normally be continued while the exothermic nature of the reaction persists. Normally, the transmethylation should therefore be continued under controlled temperature conditions for at least about one-half hour and preferably from 1 to about 10 hours. The actual reaction temperature, however, is a primary factor in the determination of the duration of the transmethylation reaction Additionally, sub or superatmospheric pressure may be employed, although atmospheric pressure is advantageously used. The pressure and temperature at which the reaction is maintained, therefore, affect the duration of the transmethylation reaction.

The molar ratio of stannic halide to tetramethyllead in the transmethylation reaction should be between about 0.2 to ^IQ: 1 in order to provide a major portion of a single mcthyltin compound as the final product. NLot-o-flint 1 קי’xamplc VII the only !X ;imp 10 in whi ch-i-ho molar ratio of tho rnnrt nnts-41i-uaj-go&lt;: S frlys-t-.»! t i ,-11 1 y f rom-th i s range nf nml.ar r;1tins₎ .a major norti Ο Π e-f a single mothyltin compound,-basod upon-tho amount qX-SjiX^

... ft' yciict u1rt jimwHtt .rs ηο4^Γο1ί11α>4. .

After the transmcthylatjon reaction has been completed, the solvent, if present , may he removed, for example by distillotion, prior to the after-heating of the transmethylation product. Additionally, if a solvent is utilized in the transmethyl a tion stage, the I’bX2 product will normally be insoluble therein. The PbX2 product can, therefore, normally be recovered prior to the after-heating stage when a solvent is utilized. The solvent, however, need not be removed prior to the aftor-heating stage. The volatile methyl halide product may also be recovered as it is accumulated during the transmethylation.

ihitial

The after-heating of the/ transmethylation product is conducted at a temperature above about 100°C but normally not above about 200°C. The upper limit of practicable temperature : i for the after-heating is, however, in actuality only determined by the temperature at which degradation of the methyltin products occurs. It is preferred, however, to carry out the after-heating treatment at about 125 to 164°C, advantageously in a two-step !

sequence, first at about 125° to 135°C and then about 145° to 165°C. Again, sub or superatmospheric pressure might be utilized, but no particular advantage arises therefrom.

During this stage/interreaction between the already formed transmethylated tiu compounds occurs/ thereby providing by redistribution of the transferred meLnyl groups a product containing at least a/ major portion 0/ a single mcthyltin compound depending /pon which molar/ratio of reactants in cquations (1) through/(/!) was most cPoscly approximated. Generally, the more closely one of these theoretical molar ratios is approximated, /he higher thc/pcrccntagc of the single mcthyltin compound in /he final product will be. As an example, it is

The after-heating treatment should advantageously be carried out in a moisture-free environment. A moisture-free environment is desirable since the methyltin halide products react with water at these temperatures to form methyltin hydroxides with the liberation of undesirable gaseous hydrogen halides.

The duration of the after-heating step may vary considerably. The major portion is based upon the total amount of SnX^ converted during the reaction. The duration of the after-heating stage may vary from about one hour to ten hours under normal circumstances. However, periods of as little as a few minutes might be sufficient under certain circumstances.

It has been found that thft after-heating stage proceeds more successfully if carried out in the absence of a solvent. If a solvent is utilized in the initial transmethylation reaction which occurs below about 90°C then the solvent should be sufficiently volatile to be easily removable prior to the after-heating.

Upon completion of the after-heating procedure, the methyltin compounds are normally recovered by the separation thereof from any other remaining by-products such as lead halides or dimethyllead halides. The separation can be accomplished, for example* by simple distillation procedures or solvent extraction methods. By using the proper molar ratio of stannic halide and tetramethyllead (as shown in the applicable foregoing equation) and by following both the temperature controlled mixing of the reactants below about 90°C and after heating of the reaction product above about 100°C it is possible to produce the desired methyltin compound in exceptionally high yields. By way of illustration trimethyltin chloride may be produced in almost quantitative yields using equimolar amounts of stannic chloride and tetramethyllead as shown in equation (3).

Methyltin compounds produced in accordance with this invention are widely recognized as being useful as biocides* particularly insecticides* stabilizers for polymers such as PVC resins* catalysts for polymerizations such as olefin polymerization* glass strengthening aids* and as chemical intermediates for the preparation of dimethyltin oxide* which in turn is a useful intermediate in the preparation of silicone and urethane curing

<td> catalysts.</td><td> More particularly, (CH^)^SnX is useful as an</td>

<td> Intermediate</td><td> in the preparation of (CH^JgSUg* a known</td>

<td> insecticide.</td><td> Compounds of the formula (CH^J^SnX^ have</td>

<td> been used to</td><td> strengthen glass by decomposing them at</td>

relatively high temperatures upon glass surfaces. The decomposition products fill any cracks or scratches in the glass surface, thereby strengthening the glass. Also compounds of the formula (CH״)_SnX_P can be reacted with caustic solutions to form dimethyltin oxide.

SPECIAL EXAMPLES

The following specific examples represent nonlimitative, preferred embodiments of this invention. Although stannic chloride and stannic bromide are the only stannic halides specifically exemplified, all the stannic halides, i»e. fluoride, chloride, bromide and iodide are contemplated as being usefu^lin this invention. In these examples the yields are calculated on the basis of the amount of SnX/j reactant present in the Initial reaction medium, unless otherwise indicated.

Example J

5.2 grams of S11CI4 (0.02 mol) were slowly added to 0.04 mol of (CllJ.I’b (9.0 cc of a 75 by weight solution in עי *I toluene) at ambient t empcratueasW i th constant stirring accompanied by external cooling. Tlie mixture was kept at ambient temperature for 4 hours and then heated for 3 hours at 130 to 140°C. Direct distillation from the vessel yielded 85% of (CHjJ^Sn. Another 5% of (Cllj^Sn was obtained by extraction of the solid residue with diethyl ether. Total.yield of (CH₃)4Sn was 90%.

Example 11

5. 2 grams (0.02 mol) of SnC14 were added drop-wise to 0.02 mol (CH₃)₄Pb (4.3 cc of an 80% by weight solution of (CH₃)₄Pb in toluene) while being stirred. The mixture was held at ambient temperature by external cooling. After stirring for 2 hours at ambient temperature the solid reaction mass was heated for 5 hours at 100°C. After extraction with diethyl ether, (CH₃)₃SnCl was obtained in a yield of almost 100%.

Example ΊΊΊ

When example II was repeated with heating for 6 hours at then

140°C instead of for 5 hours at 100°C/88% of (CHj)jSnCl and 10% of (ClIj)2SnC12 were obtained.

Example IV

A solution of 5.2 grains (0.02 mol) of S11CI4 in 20 cc of ethanol were added drop-wise to a solution of 0.02 mol of (CII₅)₄Pb (4.5 cc of a 75% by weight solution in toluene) in 20 cc of ethanol. Ambient temperature was maintained by external cooling. After stirring for 4 hours the alcohol was distilled off at atmospheric pressure and the solid residue was heated for 3 hours at 130 to 140°C. Upon extraction with diethyl ether _9^

60“ of (Cllj) jSuCJ ;!nd .35“ of (Cll-j) ^SnCl 2 ^W('* ^c obtained, ExanipCc V , , 0-5 ־

130.3 grams of SnCJ(־th 0!» mo)) were added drop-wise with constant stirring to 0.33 mol of (ClipPh (70.3 cc of an 80“ by weight solution in toluene). Λ semi-solid mass was formed. After stirring for 2 hours at ambient temperature, the mixture was heated for 2 hours at 130°C and then for 4 hours at ISO to 169*0. Extraction with diethyl ether yielded 103 grams (95¾) of (CH₃)₂SnC12 (melting point about 110°C). Rocrystallization from a light petroleum fraction (boiling range 100 to 120°C) yielded 83.1 grams (76¾) of pure (CIh) ?SnCl־> (melting • liquor point 107 to 108°C). From the mother W-q+H-d another 4.5 grams (4¾) of a mixture of (CH^SnClj and of (CHj)jSnCl was obtained. Example FT

A solution of 78.4 grams (0.3 mol) of SnCl^ in 200 cc of ethanol was slowly added to 0.2 mol of (CH^Pb (42.2 cc of an ! 80¾ by weight solution in toluene) in 200 cc of ethanol at minus * 20^DC. The clear solution obtained was stirred for 2 hours at ambient temperature. Then the alcohol was distilled off and the: solid residue was heated for 2 hours at 130°C and then for 4 hours at 150 to 160°C. By extraction with diethyl ether, 100¾ of (Cl־l₅)SnC12 (melting point about 110°C) was obtained. Recrystallization from petroleum ether (boiling range 100 to 120°C) yielded 54 grams (83¾) of pure (Cllj) 2S11C12 (melting point 107 to 108°C) and 6.4 grams (10¾) of a product with a melting range of 50 to 60°C.

Example VIZ

A solution of 0.01 mol (Clljip’b (2.25 cc of a 75“ by weight solution in toluene) in 10 cc of ethanol was slowly added at ambient temperature, to a solution of 15.6 grams (0.06 mol) • /:

of SnCljj in 60 cc of ethanol. After stirr ing for 2 hours a# V ,11(11(־ i on t temperature the alcohol was distilled off and the residue was heated for 6 hours at 140°C. Extraction with diethyl ether yielded 48:, of (CII3)SnCl3, 6¾ of (ClI3) _2>SnC 1₂ and 47¾ of SnCl₄.

Example. VJJJ

A solution of 13.1 grains (0.03 mol) of SnBr₄ in 20 cc of ethanol was slowly added to a solution of 0.02 mol of (013)4!'! (4.5 cc of a 75¾ by weight solution in toluene) in 20 cc of ethanol. The mixture was kept at ambient temperature by external cooling. Following the description of Example VI, 87¾ of (CHj)2SnBr2 and 13¾ of (CH3)3SnBr were obtained.

Example IX

Following the procedure of Example III, 8.8 grains (0.02 mol) of SnBr₄ in 20 cc of ethanol and 0.02 mol of (CH3)₄Pb (4.5 cm^ of a 75¾ by weight solution in toluene) were combined, 78¾ of (CH3)3SnBr and 10¾ of (CH3)₂SnBr₂ were obtained.