US3523961A

US3523961A - Process for preparing dioctyltin maleate

Info

Publication number: US3523961A
Application number: US694836A
Authority: US
Inventors: Justin L Hirshman; Edward J Breza
Original assignee: M&T Chemicals Inc
Current assignee: M&T Chemicals Inc
Priority date: 1968-01-02
Filing date: 1968-01-02
Publication date: 1970-08-11
Anticipated expiration: 1987-08-11
Also published as: NL6818790A; CH508664A; DE1900171A1; GB1249679A

Description

United States Patent 3,523,961 PROCESS FOR PREPARING DIOCTYLTIN MALEATE Justin L. Hirshman, East Brunswick, and Edward J. Breza, Fords, N.J., assignors to M & T Chemicals Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Jan. 2, 1968, Ser. No. 694,836 Int. Cl. C0715 7/22 US. Cl. 260-429.7 19 Claims ABSTRACT OF THE DISCLOSURE In accordance with certain of its aspects, the process of this invention for preparing dioctyltin dicarboxylate may comprise reacting substantially stoichiometric amounts of dioctyltin oxide and dicarboxylic acid or dicarboxylic anhydride in the presence of an inert aliphatic hydrocarbon solvent as reaction medium thereby forming dioctyltin dicarboxylate; cooling said reaction medium after completion of said reaction thereby crystallizing said dioctyltin dicarboxylate; recovering said crystallized dioctyltin dicarboxylate as product; and maintaining said inert aliphatic hydrocarbon solvent in liquid phase during said recovery.

This invention relates to a novel process for preparing organotin compounds. More specifically it relates to a novel process for preparing these compounds particularly characterized by the ease of obtaining desired compounds in high purity.

In accordance with certain of its aspects, the process of this invention for preparing dioctyltin dicarboxylate may comprise reacting substantially stoichiometric amounts of dioctyltin oxide and dicarboxylic acid or dicarboxylic anhydride in the presence of an inert aliphatic hydrocarbon solvent as reaction medium thereby forming dioctyltin dicarboxylate; cooling said reaction medium after completion of said reaction thereby crystallizing said dioctyltin dicarboxylate; recovering said crystallized dioctyltin dicarboxylate as product; and maintaining said inert aliphatic hydrocarbon solvent in liquid phase during said recovery.

The dicarboxylic acids which may typically be employed in practice of this invention may include alkylene dicarboxylic acids such as adipic acid or succinic acid or alkenylene dicarboxylic acids such as maleic acid. The corresponding acid anhydride may be employed vis. succinic anhydride, adipic anhydride, maleic anhydride, etc.

The preferred maleic anhydride which may be employed in practice of this invention may be that commercially obtainable. If desired, maleic acid may be employed in place of and as the equivalent of maleic anhydride.

The diocyltin oxide which may be employed in practice of this invention may be di-n-octyltin oxide, or di-i-octyltin oxide, di-2-ethylhexyltin oxide, etc. The preferred reactant in practice of the process of this invention may be di-n-octyltin oxide. This oxide may be typically obtainable in purity of at least 95% having a water content of less than 1%.

The inert aliphatic hydrocarbon solvent which may be employed in practice of this invention as the reaction medium may include those having 5-16 and preferably 6-8, say 7 carbon atoms in the molecule. Typical of these straight-chain or branched chain inert aliphatic solvents may be alkanes including hexane, heptane, octane, nonane, decane, etc. Cycloaliphatic solvents including cyclohex- Patented Aug. 11, 1970 ane, cyclohexene, methylcyclohexane, ethylcyclohexane, 1,2-dimethylcyclohexane, etc., may also be employed. In practice of the preferred aspects of this invention, saturated aliphatic straight chain hydrocarbon solvents may be employed. Preferably the inert aliphatic hydrocarbon solvent may be one having a boiling point of at least about C. (and preferably above the melting point of the anhydride employed) and less than about 150 C. The preferred solvent may be one having a boiling point about C., preferably about C., and preferably heptane. Various isomers or mixtures of these solvents may be employed. Commercially obtainable mixtures such as commercial heptane (i.e. a commercial heptane having a boiling point of about 99 C.); commercial isoparaifinic mixtures having a boiling range of 126 C.l43 C. (such as Isopar E solvent) may be used. Inert aliphatic hydrocarbon solvent containing small amounts of other solvents may also be employed, but for attainment of the maximum advantages of the process of this invention, it is preferred to use substantially pure inert aliphatic hydrocarbon solvent preferably in anhydrous form. Aromatic solvents such as benzene, toluene, etc., should preferably be present, if at all, in amount less than 5%, and more preferably less than 1%.

In carrying out the process of this invention according to certain of its aspects, 70 to parts, preferably 100 parts, of inert aliphatic hydrocarbon solvent, preferably heptane may be added to a reaction vessel. 27.2-27.8, preferably 27.6 parts, of maleic anhydride (or equivalent molar amounts of other dicarboxylic acids or anhydrides) may then be added to the reaction vessel. The ratio of solvent to dicarboxylic acid or anhydride may be such as to permit solubility of the reaction product in the solvent at elevated temperature and crystallization at recovery temperature. The preferred ratio of solvent to maleic anhydride may be maintained at 2.5 :1 to 5 :1, preferably 2.7 :1 by weight as this permits proper solubility of the product in the solvent at elevated temperatures and maximum crystallization at recovery temperatures. This ensures maintenance of the desired ratio of solvent to product of 0.55:1 to 2:1, say 0.6:1.

The reaction mixture may be heated to above the melting point of the acid or anhydride. When the acid is used, the system may be heated to reflux to remove the water formed. The reaction mixture may preferably be heated above the melting point of the anhydride-in the case of maleic anhydride, to 60 C.70 0, preferably 65 C., at which point the maleic anhydride may become molten. Agitation may be provided preferably when the melting point (60 C.) is reached.

After the dicarboxylic acid, e.g. the maleic anhydride, is substantially completely melted, the dioctyltin oxide in amount of 100-105 parts, say 100 parts, may be added to the reaction vessel.

The amount of the dioctyltin oxide to be employed may preferably be substantially stoichiometrically equivalent to the dicarboxylic acid or anhydride, e.g. in the case of maleic anhydride in accordance with the following reaction:

wherein n is 2-4.

In the case of maleic acid, the reaction may be:

OCO-CH wherein n is 2-4.

Preferably the dioctyltin oxide may be added to the reaction vessel in aliquots of 5%-10%, say 5% of the total amount to be added. When the reaction is with acid, it may preferably be added all at the beginning of the reaction. During addition, the temperature of the reaction mixture may be maintained at about the melting point of the anhydride, typically 70'' C.75 0., preferably 75 C. for maleic anhydride. Addition of the aliquots of ioctyltin oxide may be carried out over 20 minutes-40 minutes, preferably 30 minutes. After the completion of the addition to the reaction mixture of the dioctyltin oxide, the reaction mixture may be maintained at reflux temperatures below about 130 C. and preferably at 70 C.l30 C., say 85 C., for 30 minutes-90 minutes, typically 60 minutes, for the reaction mixture containing maleic anhydride and di-n-octyltin oxide. During the reaction, the resulting solution may be very turbid and amber colored. When maleic acid is employed, the byproduct water may be removed by azeotropic distillation during this period.

At the end of this reaction, there may preferably be added to the reaction mixture filter medium such as diatomaceous earth; and the mixture may be agitated for 5 min.l5 min., preferably 5 min., and cooled (depending on the solvent) to temperature of 45 C.l C., preferably about C.-2S C. above the crystallization point. The so-cooled mixture may then be filtered at this temperature through a filter, e.g. a pressure filter, the temperature in which may preferably be controlled during filtration to be about 20 C. C. above the point of crystal lization-typically 60 C.-l00 C.

The filtrate may thereafter be cooled slowly to room temperature over min. 120 min., preferably 90 min. with agitation. At the end of this period, the temperature of the reaction mixture may be 20 C.-30 C., say 25 C. As the reaction mixture temperature passes through the region C.-65 C., crystallization may occur; and a thick slurry may be obtained which may be optionally thinned with solvent. The slurry may then be further cooled to 15 C.-25 C., preferably 20 C. and held at that temperature for 30 min-90 min., say 60 min. After crystallization, 20-60 parts of additional solvent may be added to the slurry to obtain a more fluid consistency. Cooling of the reaction mixture unexpectedly permits crystallization of the dioctyltin carboxylate product in pure form as a slurry of finely-divided, rod-shaped (when viewed under a microscope) crystals which may be recovered as by filtration or decantation. During recovery of the product, the inert aliphatic hydrocarbon solvent is maintained in liquid form and the crystals are not subjected to the deteriorative or disaggregative forces which would undesirably be present at higher temperatures characteristic of e.g. distillation. The formation of distinct individual crystals is desirable and important for effective and rapid filtration.

The crystalline product may then be separated, e.g. decanted or preferably centrifuged, from the solvent to recover substantially pure crystalline filter cake which may be washed with fresh inert aliphatic hydrocarbon solvent and thereafter spin dried. The cake may preferably be broken up and dried at 50 C.60 C., preferably 60 C.

The product dioctyltin dicarboxylate may be obtained as off-white to cream colored crystalline powders in yields normally greater than 95% and typically approaching stoichiometric. Commonly, the yields may be 90%- 98%. Analysis of typical products may indicate that they contain substantially the calculated amount of tin and that they have an acid number which is essentially that calculated. These products also have melting points which fall within sharp narrowly defined ranges.

The preferred product dioctyltin maleate may be obtained as an off-white to cream colored crystalline powder in yields normally greater than and typically approaching stoichiometric. Commonly the yields may be %98%. Analysis of a typical product so prepared may indicate that it may contain 24.95%26.4%, say 25.9% tin (calc. 25.96%). The saponification (i.e. acid) number may be 234-250, say 245 (calc. 244). The product may be found to have (for di-n-octyltin maleate) a melting point of 93 C.96 C.

The novel dioctyltin dicarboxylates of this invention may typically be obtained as substantially pure, freeflowing materials having an off-white to cream color. superficially the product may be in the form of a powder.

Observation under a microscope may reveal the presence of crystals which are typically orthorhombic prisms. In the case of the novel di-n-octyltin maleate, the product may, depending upon the solvent, be observed in the form of hexagonal prisms. The prisms are characterized by an X-ray diffraction pattern which indicates characteristic peaks. In the case of the preferred di-n-octyltin maleate, the peaks may be found at 13.6 A., 6.86 A. and 4.6 A. in a wide variety of solvents, including cyclohexane, Isopar-E, or Solvent 210. In the case of di-n-octyltin adipate, the X-ray spectrum may have peaks at 12.4, 4.12, 6.31, 3.51, 8.05, and 4.56 A. (in order of decreasing intensity). In the case of dioctyltin succinate, the X-ray peaks in order of decreasing intensity may be 13.7, 6.69, 4.48, 4.74, 4.27, 8.3, 7.89, and 3.37 A.

These products may typically have a sharp melting point over a narrow range. In the case of di-n-octyltin maleate, the melting point may be 93.5 C.95.5 C.

The solubility of these materials may vary. Typical is that of the di-n-octyltin maleate which may be soluble in warm aromatic hydrocarbons, hot aliphatic solvents such as heptane, and cold ketones such as methyl ethyl ketone.

Determination of the molecular weight of these novel compositions may be carried out by osmometric technique wherein the compositions may be dissolved in benzene. It is unexpected to find that these materials may have molecular Weights which are 2-4 times that of the formula weight. Commonly, they may typically possess molecular weights which may vary on recrystallization. In one instance, for example, molecular weight changed from 3.65 formula weights to 2.67 formula weights after recrystallization from heptaue.

Practice of the process of this invention will be ap parent from the following examples wherein, unless otherwise indicated, all parts are parts by weight.

EXAMPLE 1 In this example, which represents practice of a preferred embodiment of the process of this invention, 2,200 parts by weight of commercially available heptane low in aromatic hydrocarbon may be added to a reaction vessel together with 810 parts 8.25 moles) of maleic anhydride. The reaction mixture may be heated to 60 C.65 C. and stirring started as soon as the maleic anhydride is sufiicien'tly molten to' be stirred. After the maleic anhydride is almost completely molten, there may be added to the reaction vessel 2,980 parts (8.25 M) of dinoctyltin oxide. Preferably the di-n-octyltin oxide is added in aliquots of 5% of the totalt.he typical aliquot being 180-200 parts by Weight. Addition of this material may be controlled in manner to keep the temperature at 70 C.75 C. Preferably addition may be carried out over 20-40 minutes. Addition of di-n-octyltin oxide at this rate over this period of time may be sufficient to permit 1naintenance of the reaction mixture in fluid condition. After the oxide has been completely added to the reaction mixture, the reaction mixture may be further agitated for an additional hour at 80 C.-85 C. During this time, the reaction mixture may become amber colored and very turbid.

At the end of 60 minutes, diatomaceous earth filter aid in amount of 0.2 part by Weight, may be added to the reaction mixture which may thereafter be agitated for 5 minutes more while being allowed to cool to 65 C. The reaction mixture may then be filtered through a preheated pressure filter maintained at temperature of 60 C.70 C.

The filtered solution may be slowly cooled to room temperature over 90 minutes with agitation. As the filtrate cools to 35 C.-40 C. crystallization may occur (with a mild exotherm) and the reaction mixture may become thick at 30 C. An additional 688-800 parts of solvent may be added at this point to thin the slurry to a more fluid consistency. Further cooling may then be carried out to C. at which temperature, the mixture may be held for one hour. The so-cooled mixture may be filtered and the filter cake washed with 300 parts by weight of solvent and thereafter spun dry.

The filter cake which may easily be broken up may be recovered and then dried at 50 C.-60 C. The product so obtained may be 3,411 parts by Weight (90.6% yield) of a product di-n-octyltin maleate having a melting point of 93 C.96 C. and a tin content of 26.15% (theory 25.86%). The acid number may be 245 (theory 244).

EXAMPLE 2 In this example, which represents practice of an alternative embodiment of the process of this invention, 2,930 parts by weight of Isopar E solvent (commercially available mixture of C isoparaflins) may be added to a reaction vessel together With 817 parts (8.33 moles) of maleic anhydride. The reaction mixture may be heated to 60 C.65 C. and stirring started as soon as the maleic anhydride is sufficiently molten to be stirred. After the maleic anhydride is almost completely molten, there may be added to the reaction vessel 2,980 parts (8.25 moles) of di-n-octyltin oxide. Preferably the di-n-octyltin oxide is added in aliquots of 5% of the total-the typical aliquot being 180-200 parts by weight. Addition of this material may be controlled in manner to keep the temperature at 70 C.-75 C. Preferably addition may be carried out over -40 minutes. Addition of di-n-octyltin oxide at this rate over this period of time may be sufficient to permit maintenance of the reaction mixture in fluid condition. After the oxide has been completely added to the reaction mixture, the reaction mixture may be further agitated for an additional hour at 85 C.95 C. During this time, the reaction mixture may become amber colored and very turbid.

At the end of 60 minutes, diatomaceous earth filter aid in amount of 0.2 part by weight may be added to the reaction mixture which may thereafter be agitated for 5 minutes more while being allowed to cool at 65 C. The reaction mixture may then be filtered through a preheated pressure filter maintained at temperature of 60 C.- 70 C.

The filtered solution may be slowly cooled to room temperature over 90 minutes with agitation. As the filtrate cools to 35 C.-40 C., crystallization may occur and the reaction mixture may become thick at 30 C. An additional 200-400 parts of solvent may be added to thin the slurry to a more fluid consistency. Further cooling may then be carried out to 15 C. at which temperature, the mixture may be held for one hour. The so-cooled mixture may be filtered and the filter cake washed with 300 parts by weight of solvent and thereafter spun dry.

The filter cake which may easily be broken up may be recovered and then dried at 50 C.-60 C. The product so obtained may be 3,690 parts by weight (98.5% yield) 6 of a product di-n-octyltin maleate having a melting point of 93 C.-95 C., and a tin content of 25.8% (theory 25.86% The acid number may be 249 (theory 244).

EXAMPLE 3 In this example which represents practice of an alternative embodiment of the process of this invention, 2,200 parts by weight of cyclohexane may be added to a reaction vessel together with 817 parts (8.33 moles) of maleic anhydride. The reaction mixture may be heated to 60 C.-65 C. and stirring started as soon as the maleic anhydride is sufficiently molten to be stirred. After the maleic anhydride is almost completely molten, there may be added to the reaction vessel 2,980 parts (8.25 moles) of dioctyltin oxide. Preferably the dioctyltin oxide is added in aliquots of 5% of the tota1the typical aliquot being 180-200 parts by weight. Addition of this material may be controlled in manner to keep the temperature at 70 C.-75 C. Preferably addition may be carried out of 20-40 minutes. Addition of oxide at this rate over this period of time may be sufficient to permit maintenance of the reaction mixture in fluid condition. After the oxide has been completely added to the reaction mixture, the reaction mixture may be further agitated for an additional hour at C. During this time, the reaction mixture may become amber colored and very turbid.

The filtered solution may be slowly cooled to room temperature over minutes with agitation. As the filtrate cools to 35 C.-40 C., crystallization may occur and the reaction mixture may become thick at 30 C. An additional 600-800 parts of solvent may be added to thin the solvent to a more fluid consistency. Further cooling may then be carried out to 15 C. at which temperature, the mixture may be filtered and the filter cake washed with 300 parts by weight of solvent and thereafter spun dry.

The filter cake which may easily be broken up may be recovered and then dried at 50 C.60 C. The product so obtained may be 3,560 parts by weight (90.6% yield) of a product dioctyltin maleate, having a melting point of 93 C.-95 C. and a tin content of 25.54% (theory 25.86% The acid number may be 246.7 (theory 244).

From the above examples, it will be apparent that it is possible by practice of this novel process to obtain pure dioctyltin maleates directly from a reaction mixture by crystallization. It is not necessary either to distill off solvent or to age the product for extended period of time or to redistill the product in order to obtain the desired purity-as is typical of the prior art processes heretofore employed to produce this material.

EXAMPLE 4 In this example, which represents the practice of a preferred embodiment of the process of this invention, 150 parts by weight of a commercial heptane may be added to a reaction vessel together with 40.4 parts (0.277 M) of adipic acid. parts of di-n-octyltin oxide may be added. The reaction mixture may be heated to reflux (85 C.). The water of reaction may be removed over 200 minutes by condensation in a Dean Stark apparatus. Temperature of reaction then rose to 97 C. after 5 parts was collected. A clear yellow solution was obtained. The solution was cooled to 75 C. and 0.2 part of diatomaceous earth was added. The solution was filtered and cooled slowly. Crystallization occurred at 43 C.

An exotherm occurred raising the temperature to 52 C. 50 parts of heptane may be added and the mixture cooled to ambient temperature over one hour. The socooled mixture may be filtered and the filter cake washed with a small amount of solvent and thereafter dried.

The filter cake which may easily be broken up may be recovered and dried at 50 C.60 C. The product so obtained may be 129.4 parts by weight (95.6% yield) of a product having a melting point of 75 C. and a tin con tent of 24.26% (theor 24.26%). The acid number may be 240 (theory 229).

The molecular weight (osmometric in chloroform) was 692.

EXAMPLE In this example, which represents practice of a preferred embodiment of the process of this invention, 75 parts by weight of Isopar E (a commercially available mixture of iso-octanes) may he added to a reaction vessel together with 28.2 parts (0.28 M) of succinic anhydride. The reaction mixture may be heated to 120 C. and stirring started as soon as the anhydride is sufliciently molten to be stirred. After the anhydride is almost completely molten, there may be added to the reaction vessel 100 parts (0.28 M) of di-n-octyltin oxide. Preferably the di-noctyltin oxide is added in aliquots of of the total over 30 minutes. Addition of dioctyltin oxide at this rate over this period of time may be sufiicient to permit main tenance of the reaction mixture in fluid condition. After the oxide has been completely added to the reaction mixture, the reaction mixture may be further agitated for an additional hour at reflux temperature of 135 C., which temperature was reached after 90 minutes. At this time, the reaction mixture may become clear.

The mixture may be cooled to 120 C.-l25 C. and dicalite filter aid in amount of 0.2 part by weight may be added to the reaction mixture which may thereafter be filtered through a preheated pressure filter maintained at temperature of 125 C.

The filtered solution may be slowly cooled over 30 minutes with agitation. As the filtrate cools to 106 C., crystallization may occur. 100 parts of additional solvent may be added. Further cooling may then be carried out to C. at which temperature, the mixture may be filtered and the filter cake washed with a small amount of solvent Isopar E and thereafter dried.

The filter cake which may easily be broken up may be recovered and dried at 50 C. The product so obtained may be 123.6 parts by weight (97% yield) of a product having a melting point of 140 C., and a tin content of 25.71% (theory 25.74%). The acid number may be 240 (theory 243).

The molecular weight (osmometric in chloroform) was 954.

Although this invention has been illustrated by reference to specific examples, changes therein which clearly fall within the scope of this invention will be apparent to those skilled-in-the-art.

What is claimed is:

1. The process for preparing dioctyltin dicarboxylate which comprises reacting substantially stoichiometric amounts of dioctyltin oxide and dicarboxylic acid or dicarboxylic anhydride in the presence of an inert aliphatic hydrocarbon solvent in which said dioctyltin oxide, said dicarboxylic acid, and said dicarboxylic anhydride are insoluble and in which dioctyltin carboxylate is soluble as reaction medium thereby forming a solution of dioctyltin dicarboxylate in said solvent; cooling said reaction medium after completion of said reaction thereby crystalliz ing said dioctyltin dicarboxylate; recovering said crystallized dioctyltin dicarboxylate as product; and maintaining said inert aliphatic hydrocarbon solvent in liquid phase during said recovery.

2. The process for preparing dioctyltin maleate which comprises reacting substantially stoichiometric amounts of maleic anhydride and dioctyltin oxide in the presence of an inert aliphatic hydrocarbon solvent in which said dioctyltin oxide and said maleic anhydride are insoluble and in which dioctyltin maleate is soluble as reaction medium thereby forming a solution of dioctyltin maleate in said solvent; cooling said solution after completion of said reaction thereby crystallizing said dioctyltin maleate; filtering said crystallized dioctyltin maleate; and maintaining said inert aliphatic hydrocarbon solvent in liquid phase during said filtration.

3. The process of claim 2 wherein said doctyltin oxide and maleic anhydride are reacted at a temperature above the boiling point of the solvent and between about 60 C. and C. in a solvent selected from the group consisting of heptane, and isoparafiinic hydrocarbon solvent having a boiling point above the reaction temperature and below about C.; the ratio of said solvent to the product dioctyltin maleate being between 0.55:1 and 2:1; and cooling said solution of dioctyltin maleate at a temperature between about 15 C. and 40 C. to crystallize said product dioctyltin maleate.

4. The process of claim 3 wherein said solvent is heptane.

5. The process for preparing dioctyltin dicarboxylate which comprises reacting dicarboxylic acid or dicarboxylic anhydride and dioctyltin oxide in the presence of an inert aliphatic hydrocarbon solvent, in which said dioctyltin oxide and the dicarboxylic reactant are insoluble and in which dioctyltin dicarboxylate is soluble, as reaction medium thereby forming a solution of dioctyltin dicarboxylate in said solvent; filtering said solution to remove any unreacted dioctyltin oxide and dicarboxylate reactant; then cooling said solution thereby crystallizing said dioctyltin dicarboxylate, and recovering said crystalline dioctyltin dicarboxylate from said liquid solvent which is maintained in liquid phase during said recovery.

6. The process for preparing dioctyltin maleate which comprises reacting maleic anhydride and dioctyltin oxide in the presence of an inert aliphatic hydrocarbon solvent in which maleic anhydride and dioctyltin oxide are insoluble and in which dioctyltin maleate is soluble as reaction medium thereby forming a solution of dioctyltin maleate in said solution; filtering said solution to remove any unreacted dioctyltin oxide and maleic anhydride; then cooling said solution thereby crystallizing said dioctyltin maleate; and recovering the crystalline dioctyltin maleate from said liquid solvent which is maintained in liquid phase during said recovery.

7. The process of claim 6 wherein said dioctyltin oxide and maleic anhydride are reacted at a temperature above the boiling point of the solvent and between about 60 C. and 100 C. in a solvent selected from the group consisting of heptane, and isoparaflinic hydrocarbon solvent having a boiling point above the reaction temperature and below about 150 C.; the ratio of said solvent to the product dioctyltin maleate being between 0.55 :1 and 2:1; and cooling said solution of dioctyltin maleate to a temperature between about 15 C. and 40 C. to crystallize said product dioctyltin maleate.

8. The process for preparing anhydrous dioctyltin maleate as claimed in claim 6 wherein, after completion of reaction, said reaction medium is cooled to 15 C.-40 C. at which temperature said dioctyltin maleate may be removed in crystalline form.

9. The process of claim 7 wherein said solvent is heptane.

10. The process for preparing anhydrous dioctyltin maleate as claimed in claim 6 wherein said inert aliphatic hydrocarbon solvent contains 5-16 carbon atoms.

11. The process for preparing anhydrous dioctyltin maleate as claimed in claim 6 wherein said inert aliphatic hydrocarbon solvent contains 6-8 carbon atoms.

'12. The process for preparing anhydrous dioctyltin maleate as claimed in claim 6 wherein said inert aliphatic hydrocarbon solvent is a straight chain aliphatic hydrocarbon solvent.

13. The process for preparing anhydrous dioctyltin maleate as claimed in claim 6 wherein said inert aliphatic hydrocarbon solvent is heptane.

14. The process for preparing anhydrous dioctyltin maleate as claimed in claim 6 wherein said inert aliphatic 9 hydrocarbon solvent 'has a boiling point of less than 150 C.

15. The process for preparing anhydrous dioctyltin maleate as claimed in claim 6 wherein said inert aliphatic hydrocarbon solvent is an isoparatfinic hydrocarbon.

16. The process for preparing anhydrous dioctyltin maleate as claimed in claim 6 wherein the temperature of reaction is maintained at about 60 C.

17. The process for preparing anhydrous dioctyltin maleate as claimed in claim 6 wherein the temperature of reaction is maintained below 130 C.

18. The process for preparing anhydrous dioctyltin maleate as claimed in claim 6 wherein the temperature of reaction is maintained at 60 C.-100 C.

19. The process for preparing anhydrous dioctyltin maleate as claimed in claim 6 wherein the ratio of solvent to product is maintained at 0.55 :1 to 2:1.

References Cited UNITED STATES PATENTS Weisfeld et al. 260429.7 Oakes 260429.7 Katsumura et al. 260429.7 Gloskey 260429.7 Duyfjes et al. 260429.7 X Crauland 260429.7 X Anderson et al. 260429.7 Anderson et al. 260429.7 X Robins 260429.7 X Kelso 260429.7 X 'Kelso 260429.7 X

15 HELEN M. McCARTHY, Primary Examiner W. F. W. BELLAMY, Assistant Examiner