CA1051444A - Method for preparing organotin compounds - Google Patents

Abstract

NOVEL METHOD FOR PREPARING ORGANOTIN COMPOUNDS

ABSTRACT OF THE DISCLOSURE - Triorganotin derivatives of polymerizable ethylenically unsaturated carboxylic acids are prepared either in the presence or absence of solvent by reacting the acid or a suitable derivative thereof with a triorganotin hydroxide or a bis(triorganotin)oxide.
Polymerization of the acid or the triorganotin derivative thereof is avoided by using a dehydrating agent to remove the water formed as a by-product of the reaction.

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Description

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This invention relates to the preparation of triorganotin compounds. This invention further relates to the preparation of polymerizable triorganotin derivatives of unsaturated carboxylic acids. --Polymers derived from triorganotin derivatives of unsaturated monocarboxylic acids, particularly acrylic and methacrylic acids, have been recognized as effective toxicants for numerous applications, including antifouling paints. The use of these polymers for protecting a variety of materials-against the growth of harmful organisms is disclosed in U.S. Patent 3,167,473.
Monomeric precursors of the aforementioned polymers are prepared by reacting an ethylenically unsaturated acid, such as acrylic acid, or a suitable derivative thereof, such as the corresponding acid anhydride, with a triorganotin hydroxide or a bis (triorganotin) oxide. The water formed as a by-product of the reaction is conventionally removed by distillation which is conducted under either atmospheric or reduced pressure~ The reaction of an acid with a triorganotin hydroxide can be expressed by the following equation:
O O
R3SnOH + R C ~ R2C~ H20 OH OSnRl In the foregoing equation R represents a hydrocarbon radical containing from 1 to 20 carbon atoms and R2 represents an ethylenically unsaturated hydrocarbon radical.

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i The reaction mixture usually includes an inert li~uid il diluent such as an aromat;c hydrocarbon, which fonms an ll azeotropic mixture with water. The acid and triorganotin ¦¦ compound are usually heated to the boiling point of the ! 1 reaction mixture and a distillation apparatus is employed to remove the water together with a portion of the hydro- ¦
carbon diluent. In addition to facilitating removal of the relatively small amount of water formed during the reaction, the diluent lowers the concentration of unsaturated acid and the triorganotin derivative thereof, thereby reducing the likelihood of a spontaneous polymerization. This type of polymerization is undesirable in those instances when the organotin derivative is to be subsequently reacted with other I ethylenically unsaturated compounds to form copolymers such lS as those disclosed in U. S, Patent 3,167,473.
The distillation of hydrocarbon diluent and water is often conducted under reduced pressure to minimize heating f the reaction mixture.
The use of an organic diluent and distillation to remove the diluent and by-product water may be satisfactory when the total volume of reagents and diluent does not exceed about 500 c.c. As the volume of the reaction mixture increases, it becomes more difficult t~ evenly distribute heat from the walls o~ the reactor throughout the reaction mixture. Localized overheating may occur, particularly in areas adjacent to that ¦~ portion of ths reaction vessel where heat is being applied The heat input required to maintain a distillation wherein the vapor phase remains at ambient temperature is significant. If the ~ heat is not rapidly dissipated within the reaction mixture, the ! resultant localized overheating could ini~iate a spontaneous ¦ polymerization,, i -2-An objective of this invention is to provide a method for preparing relatively large amounts of triorganotin carboxylates derived from ethylenically unsaturated acids with or without any organic diluent and in the absence of significant polymer formation.
It has now been found that this objective can be realized by replacing the conventional distillation step for the removal of water by the use of certain chemicals which will effectively remove the water from the liquid phase of the reaction mixture. - -This invention provides an improvement in the method for preparing triorganotin derivatives of ethylenically un-saturated acids by (1) reacting an ethylenically unsaturated mono- or dicarboxylic acid or suitable derivative thereof, such as an ester or anhydride, witha triorganotin hydroxide or bis (triorganotin) oxide and (2) removing the water formed as a by-product of said reaction. The reaction mixture may optionally include a liquid diluent. The improvement provided by this invention resides in removing the by-product water by maintaining the reaction mixture in contact with an amount of a solid, chemically inert dehydrating agent sufficient to remove substantially all of the water. The reaction mixture is maintained in contact with the dehydrating agent for a period of time sufficient to the dehydrating agent to react with or absorb between 95 and 100% of the water present. Stoichiometric amounts of the reactants are generally employed since no advantage is achieved by employing an excess of either reactant.

L~51444 DE~ILED DESCRIPl~ION QF I~E INVENTION
_ _ . __ The present class of dehydrating agents include l anhydrous salts which react with water to form stable hydrates ¦ or particulate materials such as activated aluminum ~nd ¦ molecular sieves that are insoLuble in the reaction mixture ¦ and selectively absorb water on the surface of the particles, ¦ within the particles or both. Preferred salts yielding stable hydra~es include the anhydrous forms of magnesium sulfa~e, calcium sulfate, the calcium halides (fluoride, chloride, bromide and iodide), potassium carbonate and sodium sulfate. Other anhydrou~ saLts are suitable if they are competitive in cost and per~ormance with ~he preferred species and are chemically inert, in tha~ they are not polymerization catalysts for the unsaturated Il acid and do not ~ender the resultant reaction mixture so acidic l or baæic a~ to initiate a polymerization of the unsaturated acid or the triorganotin derivative thereof. Drying agents which-are too acidic or basic can aLso decompose the organotin ester. It i8 this criterion of chemical inertness that excludes both alkali I
metal or aLkaline earth metal hydroxides and phosphorus pentoxide !
from the class of useful dehydrating agents.
Preferred drying agents which remove water by ~bsorption include activated alumina, silica gel and molecular ~ieves, particularly ~e types designated 4A and 5A.
m e amount of de~ydrating agent employed in the method !~ of this invention is at lea~t suficient to remove between 95 and 100~ of the theoretical amount of water formed during the ~i reac~ion. The number of moles of water is eclual to the number ¦' f ~quivalents o~ carboxylic acid reacted with the triorgano'in ¦¦ compo~nd~ It is preferabl~ to u~e between a 10 and 50~ exces~
¦1 o~ de~ydrating agent over this theoretical amount. Using any 1~ i Il I
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I larger exces~ would add to the cost of the procesx without any ¦l ~ignificant corresponding increase in efficiency or rate of the dehydration step I The reaction be~ween the acid and the triorganotin ~ compound can be conducted in any organic liquid wherein the reactants and product are soluble. It is often desirable to prepare the monomer in the soLvent in which it will subsequently be polymerized. If the polymer i8 to be incorporated into a paint, it is often desirable to prepare the monomer in mineral spirits, a mixture of liquid hydrocarbons.
An unexpected advantage resulting from use of the present dehydrating agents is that triorganotin derivatives of unsaturated acids can be prepared without any solvent or diluent ¦ Heretoore, it has usually been necessary to include a liquid ¦ hydrocarbon that formis an aæeotropic mixture with water in order to remove the water and dissipate the heat input required to effect a continuous distillation. The operability of the 3 present method in the absence of a solvent make~ it possible to decrease the volume of material required to react a given ~mcunt of acid with a triorganotin compound, thereby increasing volume efficiency and reducing processing costs. Moreover, certain organic liquids such as mineral spirits, in which it m~y b~ desired to subsequently polymerize the present tri-organotin compounds~ may be unsuitable for preparing the monomer 1l using prior art methods requiring removal of water by distillation, since the hydrocarbon will not form an azeotropic mixture with water In these instances the monomer must be separated from the 801vent in which it is prepared and subsequently combined with the polymerization medium Usually the a~orementioned separation entails distilling the reaction mixture solvent.

The prolonged heating required to effect such a distillation may initiate a spontaneOus exothermic polymerization of the monomeric triorganotin compound.
In accordance with a generally preferred method of this invention, one or more unsaturated mono- or polycarboxylic acids are combined with a stoichiometric amount of one or more triorganotin hydroxides of the formula RlSnOH or the corresponding bis (triorganotin) oxides of the formula (R3Sn)20, wherein Rl represents an alkyl radical containing from 1 to 20 carbon atoms, or a cycloalkyl, aryl, aIkaryl or aralkyl radical containing up to 20 carbon atoms. The reaction can optionaIly be conducted in the presence of a suitable organic solvent, as discussed hereinbefore.
When the unsaturated acid is acrylic or methacrylic acid, the reaction between the acid and the triorganotin compound is often exothermic and may not require external heating. If desired the reaction vessel can be cooled by placing it in an ice-water mixture or other suitable low temperature environment to maintain the reacting mixture at a temperature of between 0C. and ambient temperature.
Cooling is considered optional, since neither the quality or yield of product w~ere adversely affected when the temperature of the reaction mixture spontaneously rose to as high as 57C. due to heat generated by the exothermic reaction.
The ethylenically unsaturated acid that is reacted with a triorganotin compound in accordance with the method of this in~ention is advantageously of the general formula R2(COOH)n wherein R is a monovalent or divalent hydrocarbon radical containing from

2 to 20 carbon atoms and a double bond between 2 adjacent carbon atoms that do not form part of an aromatic ring s~ructure, such as a phenyl ring. The subscript n represents the integer 1 or 2, and is also equal to the valence of R O In a preferred 51~
embodiment of the present method n is 1, i.e. the acid is a mono-carboxylic acid, and R is a radical of the formula H2C=CH- or H2G=C(CH3)-, which corresponds to acrylic acid dnd methacrylic acid, respectively. Other suitable ethylenically unsaturated monocarboxylic acids include crotonic, isocrotonic, 3-butenoic, oleic, l-cyclohexene-l-carboxylic, and cinamic acids, in addition to unsaturated acids such as abietic acid that are extracted from rosin and other natural products.
Dicarboxylic acids containing ethylenic unsaturation include maleic, fumaric, citraconic, itaconic and the isomeric tetrahydrophthalic acids, among others.
The reaction between the triorganotin compound and un-saturated acids other than acrylic, methacrylic, maleic or fumaric acids may be relatively slow, particularly if the acid is sterically hindered. In these instances it may be necessary to heat the mixture slightly, i.e. to a temperature between 30 and 50 & ., to achieve a useful reaction rate while avoiding polymerization of the unsaturated acid.
Using the preferred acrylic or methacrylic acid, the re-action with the triorganotin compound is substantially complete after only several minutes at ambient temperature. The yield of desired product is usually greater than 90% of the theoretical value.
The triorganotin reagent employed in the method of this invention is a triorganotin hydroxide or a bis (triorgano-tin) oxide wherein the three hydrocarbon radicals bonded to the tin atom contain from 1 to 20 carbon atoms. The radicals can advantageously each be alkyl, cycloalkyl, aryl, alkaryl or aralkyl.
If the polymer which is ultimately prepared from the monomeric products of the present method is to be employed to ~5~4~ ~

I control undesirable organisms às taught in U.S. Patent ¦l 3,167,473, the radicals represented by R are preferably propyl, butyl, cyclohexyl or phenyl radicals. The choice of Ij radicals for R will be in large measure determined by the ¦I desired end use for the ultimate polymer.
i Polymers wherein the R radicals are other than propyl, butyl, cyclohexyl or phenyl are useful in numerous applications, including catalysts for many types of reactions, ¦ antioxidants for rubber, and as additives for oils and other products.
The three R radicals are preferably identical, but need not be so. Synthetic methods for preparing both sym-metrically and asymmetrically substituted triorganotin oxides Il and hydroxides are sufficiently disclosed in the chemical and li patent literature that a detailed discussion of this subject ¦ is not required as part of the present specification.
, The dehydrating agent is preferably added following completion of the reaction between the unsaturated acid and the triorganotin compound. If the dehydrating agent is present during this reaction, product yleld may be decreased due to adsorptlon or absorption of the reagents by the solid de-hydrating agent. The contact time between the drying agent and reaction mixture should be at least several minutes to ¦ ensure that most, if not all, of the water reacts with or is ! adsorbed by the dehydrating agent. Agitating the mixture of , dehydrating agent and reaction product together with a liquid organic diluent, if present, is desirable since this maximizes ~i -the area of contact between the solid dëhydrating agent and the ~i liquid reaction mixture, thereby accelerating the rate at which ¦I water is removed from the liquid phase by the dehydrating agent.
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The following examples disclose preferred embodiments of the present invention and should not be regarded as limit-ing the scope of the method defined in the accompanying Claims. All parts and percentages are by weight.
S ll EXAMPLE l 1i This example demonstrates the effect of reaction ¦l temperature on the yield of tributyltin methacrylate prepared using the method of this invention.
~ A). An 86.l g. portion of methacrylic acid contain-j ing lO0 parts per million of p~methoxy phenol as a polymeri-zation inhibitor was gradually added over a lO minute period ¦ to 298 g. of bis-tri-n-butyltin oxide (TBT0). Prior to addition of the acid, the TBT0 was cooled to 5C. by im-ll mersing the reaction vessel in an ice-water mixture. The lS 1~ reaction mixture was stirred and cooled during addition of the acid, and the temperature of the reaction mixture increased to 20C. Stirring was continued for five minutes following completion of the acid addition, at which time 25 g. of anhydrous magnesium sulfate were added to the reaction mixture.
The resultant two phase mixture was stirred ~or lO minutes 1 and filtered to separate the solid and liquid phases. The ¦ latter was a slightly off-white mobile oil equivalent to a 90% yield, based on TBT0. It was assumed that additional 1~l product was entrapped by the solid phase.
,1 A potentiometric titration of the reaction product , revealed no free TBT0 and 0.65% of free methacrylic acid.
, The product was found to contain 0.33% water, as determined b~
¦ Karl Fisher analysis, and 31.2% tin (calculated tin content !~ _9_ !l I
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i. l ~C~S~4 for tri-n-butyltin methacrylate = 31.7%). The acid number of the product was 148 (calculated value = 149.5). The product dissolved in methanol to yield a clear solution, j, indlcating that no polymer was present.
5 ' B). The procedure described in part A of this example was repeated using the same amounts of TBT0 and Il methacrylic acid. The temperature of the reaction mixture il was allowed to reach a maximum of 28C. during the addition I of the methacrylic acid, following which 20 g. of anllydrous l~l magnesium sulfate were added. After being stirred for 30 ¦~ minutes, the liquid phase was separated ~rom the resultant mixture to yield 353.4 g. (94.2% yield) of an off-white oil ¦ that upon analysis was found to contain 31.05% tin, 0.35%
I water, 0.90% free methacrylic acid and no free TBT0. The l acid nurnber of the product was 148.57.
C). Tributyltin methacrylate was prepared using the general procedure described in part A of this example using twice the amounts of TBT0 and methacrylic acid specified in part A. The reaction vessel was not cooled either prior to or during the addition of methacrylic acid, which was added in two portions of approximately 100 cc. each. The ¦I temperature of the reaction mixture increased to 49C.
t following addition of the first portion of acid and reached i a maximum of 57C. during addition of the second portion.
A 40 g. portion of anhydrous magnesium sulfate was then added, the resultant two-phase mixture stirred for one hour and the solid phase removed by filtration to yield 723 g.
1 ~96.4% yield) of an off-white oil which was completely miscible ¦I with methanol. The reaction product contained 30.2% tin, l; ;
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o .21% water and no free TBT0 or methacrylic acid. The acid number of the product was 152.6.

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Il This example demonstrates the use of anhydrous calcium sulfate. Although this salt does not have the same water capacity for a given weight as anhydrous magnesium sulfate, it is more effective in reducing the water content ! of the product.
A). A 172.2 g. portion of methacrylic acid was 1l gradually added over a five minute period~with stirring, to ' 596 g. of TBT0 which had been cooled to 10C. The temperature ¦ of the reaction mixture increased to 36 C . during the addition ¦ of the acid. When the addition was completed, 20 g. of an- !
l hydrous magnesium sulfate were added and stlrring continued I for 15 minutes. The mobile oil obtained following separation ¦¦ of the solid phase weighed 737.7 g. (equivalent to a yield of ~! 98.3%, based on TBT0) and contained 0. 75% water. The relatively high water content indicated that 20 g. of an-hydrous magnesium sulfate was insufficient to absorb all of the water present in the tributyltin methacrylate. When this product was combined with 20 g. of anhydrous calcium jl sulfate and the mixture stirred for30 minutes, the water content was reduced to 0.44%.
I B). A reaction vessel equipped with a thermometer~
' nitrogen inlet, agitator and condenser was charged with 225 g.
of mineral spirits and 596 g. of TBT0. The solution was ~, purged with nitrogen for 15 minutes following which 17.0 cc.
,~ of methacrylic acid were added dropwise over a 30 minute period, ¦¦ durlng which time the temperature rose from 23C to 27C.

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The cloudy reaction mixture was then agitated for an additional 30 minutes after which 9 g. of anhydrous magnesium sulfate was added. After agitating for an additional ~j 30 minutes, the mixture was filtered.
S ` The liquid phase weighed 289 g. and was found to Il contain 0.2% water. An aliquot of the solution was then ¦~ stirred with 10 g. of anhydrous calcium sulfate for 2 hours, refiltered and analyzed for water content.
l! Found - 0.02% water !l %Free TBT0 - none found ¦ %Free Methacrylic Acid - none found This example illustrates the problems that can occur when triorganotin derivatives of unsaturated acids lS are prepared using a prior art method.
A reaction vessel was charged with 5961 g. (10 moles) Or TBT0, 1722 g. (20 moles) of methacrylic acid containing 100 parts per million of p-methoxy phenol as a polymerization inhibitor, and 8 liters of heptane. The contents of the reaction vessel were stirred while under a partial vacuum (39-65 mm. of mercury) to remove the water formed as a by-product of the reaction. An azeotropic mixture of water and heptane was collected in a trap which permitted return of the heptane to the reaction vessel. The contents of the vessel were heated to maintain the liquid phase at a tem-perature of 34C. throughout the distillation, which was continued until the theoretical amount of water collected ,1 in the trap. The solution in the reaction vessel was miscible Il with methanol to yield a clear solution, indicative of no ~ ollgomer or polymer formation. An attempt to separate the ~ -12-' 11 , "~ I
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I tributyltin methacrylate from the heptane by distillation ,~ yielded a rubbery polymer, even though the temperature of ' the mixture did not exceed 23C. during the distillation.
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Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In an improved method for preparing a triorganotin derivative of an ethylenically unsaturated mono- or dicarboxylic acid, the method consisting essentially of 1) reacting said mono- dicarboxylic acid or a derivative thereof with a triorganotin hydroxide or a bis (triorganotin) oxide;
2) removing the water formed as a by-product of the reaction from the reaction mixture; and 3) isolating said triorganotin derivative, wherein the improvement resides in removing the water by maintaining the triorganotin derivative in contact with an amount of a solid, chemically inert dehydrating agent suffi-cient to remove substantially all of the water present in the reaction mix-ture, and separating said triorganotin derivative from the dehydrating agent.

2. An improved method as defined in Claim 1 wherein the triorganotin hydroxide exhibits the formula R13SnOH wherein each R1 is individually selec-ted from the group consisting of alkyl radicals containing from 1 to 20 carbon atoms, or cycloalkyl, aryl, alkaryl and aralkyl radicals containing up to 20 carbon atoms.

3. An improved method as defined in Claim 1 wherein the bis (triorgano-tin) oxide exhibits the formula (R13Sn)2O, wherein each R1 is individually selected from the group consisting of alkyl radicals containing from 1 to 20 carbon atoms, or cycloalkyl, aryl, alkaryl and aralkyl radicals containing up to 20 carbon atoms.

4. An improved method as defined in Claim 1 wherein the ethylenically unsaturated carboxylic acid exhibits the formula R2 wherein R2 represents a hydrocarbon radical with a valence of n and containing from 2 to 20 carbon atoms inclusive, and a double bond between 2 adjacent carbon atoms that do not form part of an aromatic ring structure, and n is 1 or 2.

5. An improved method as defined in Claim 3 wherein n is 1 and R2 represents the radical CH2=CH- or CH2=C(CH3)- .

6. An improved method as defined in Claim 1 wherein the bis (triorga-notin) oxide is bis (tri-n-butyltin) oxide.

7. An improved method as defined in Claim 1 wherein the dehydrating agent is selected from the group consisting of anhydrous magnesium sulfate, anhydrous calcium sulfate, the anhydrous calcium halides, anhydrous potassium carbonate, anhydrous sodium sulfate, activated alumina, silica gel and type 4A and 5A molecular sieves.

8. An improved method as defined in Claim 1 wherein the reaction bet-ween the ethylenically unsaturated acid and the triorganotin hydroxide or bis (triorganotin) oxide is conducted in the absence of a solvent or diluent.

9. An improved method as defined in Claim 1 wherein the reaction bet-ween the ethylenically unsaturated acid and the triorganotin hydroxide or bis (triorganotin) oxide is conducted in the presence of a liquid hydrocarbon wherein both the reactants and the product are soluble.

10. An improved method as defined in Claim 1, wherein a stoichiometric amount of triorganotin derivative is employed.