IL31403A - Process for preparing thiolcarboxylic acid anhydrides - Google Patents

Description

Prooesa for preparing thiol carboxylic acid anhydrides STAUFFER CHEMICAL COMPANY O t29680 - la This invention relates to organic acid thloanhydrldes and more particularly to a process for preparing aliphatic carboxylic acid thioariydrides by the reaction of aliphatio carboxylic aoid halides with aliphatio thiocarboxylic acids in the presence o an inert gas* Organic thioanhydrides are known. For example, processes for preparing thioanhydrides of aromatic carboxylic acids are disclosed in US Patents 2,331*650 and 2,854,325.

The thioanhydrides of aliphatic .carboxylic acids have not been extensively investigated accept as to the lowest member of the series, thioacetyl anhydride. For example, Bonner JACS 72, 4270 (1950) prepared thioacetyl anhydride by refluxing thiolacetic acid and acetyl ohlorlde. While this process is a useful laboratory procedure, it does not lend itself to large scale commercial production by reason of the highly corrosive hydrogen chloride by-product.

It has now been discovered that the fatty carboxylic aoid thioanhydrides can be prepared in good yield by reacting an aliphatic acid hallde with an llphatlo thioacid in the presence of an inert gas. In accordance with this invention, the hydrogen hallde by-product is removed f om the reaction mixture by the inert gas as it is formed so that there is no decomposition of the thioanhydrlde product or damage to the process apparatus* In a preferred embodiment a solvent Is employed in order to provide more intimate mixture, but none is required.

The reaction can be illustrated by the followin and Rr reaction diagram wherein the groups represented by R/are aliphatic hydrocarbon radicals of from 4 to 23 carbon atoms whl0h Can be 31403/2 v - 2 - the same or different and X is a halogen having an atomic weight above 0: R- Examples of suitable radicals represented by the and R' < R/groups in the above diagram inolude butyl, sec. butyl, pentyl, isohexyl, hexyl, heptyl, isoootyl, octyl, nonyl, isodecyl* deoyl, undeoyl, dodeoyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, ootadecyl, hondeoyl, eicosyl and heneicosyl, 2-ethylhexyl and 2-dimethylpropyl. Examples of suitable unsaturated radicals include ethenyl, propenyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, hexadecenyl and elcosenyl.

Solvents which can b e employed include the lower saturated alkanes of from 3 to 20 carbon atoms, halogenated saturated alkanes of f rom 1 to 10 carbon atoms and aromatic hydrocarbons of from 6 to 20 oarbon atoms. Examples of suitable solvents include alkane solvents such as propane, butane, pentane heptane, hexane, nonan , decane and dodeoane, alicyclio hydrocarbons such as cyclopropane, cyclobutane, cyclopentane and cyclohexane as well as halogenated alkanes such as ethyl chloride and diohlorodifluoromethane. Examples of aromatic hydrocarbons include benzene, toluene, xylene, mesitylene, ethyl benzene and ethyl toluene. Examples of ethers include diethyl, diisopropyl, dibutyl, anlsole and phenetole.

By this invention, the hydrogen halide by-produot 31403/2 ί - 3 action laixture in order to remove the hydrogen hallde gaseous by-product as it is formed. By this method the reaction is driven to completion without any decomposition of the thioanhydride product. Moreover, the product is produced in yields in excess of 90$. Examples of inert gases which can be employed are those which are normally gaseous and include nitrogen, carbon monoxide, carbon dioxide, neon, argon, xenon and the lower alkanes such as methane, ethane, propane and butane or natural gas* Acid halides which can be employed in the invention process are the chlorides, bromides and iodides of medium chain aliphatic carboxylic acids having from 5 to 24 carbon atoms.

For economic reasons the Chlorides are, of course, preferred. Representative examples inolude: Isovaleroyl doLoride, caproyl chloride, neo-heptanoyl ohloride, -heptanoyl chloride, pelargonic acid chloride, undecylenic acid ohloride, lauroyl ohloride, palmitoyl chloride, stearoyl chloride, oleoyl chloride, behenic acid chloride. Also mixtures of aliphatic acid chlorides can be used. Acetylenlc unsaturated oarboxylic acid halides can also be employed in the process of the invention, such as, for example, the chlorides of amylpropiolic acid, palmitolic aoid, stearolic aoid and behenolic acid.

Thio acids which can be employed are the medium chain aliphatic carboxylic thio acids having from 5 to 31 carbon atoms. Exemplary of the thio acids are the unsubstltuted and substituted hydrocarbon moieties enumerated in the previous > paragraph** ! i 31403/2 The reaction can he convenientl conduoted batchwise or continuously at atmospheric pressure at temperature between abou 25° C. and 150°C. A preferred t emperature range is between from about 55°C. and about 100°C. Reaction temperatures are not, however, a critical aspect of the invention.

Generally the reactants are present in stoichiometric amounts, although a slight excess of eitherraactant is not detrimental. The quantity of solvent should be sufficient to contain the reactants in solutio so as to provide intimate contac When the reaction is complete as evidenced by o further hydrogen halide evolution, the product can be recovered by the conventional ans such as filtration and can be further purified, if desired, by crystallization, distillation ad the like.

According to a further embodiment of this invention, it has been found that the fatty thio acids can be prepared inexpensively. in good yield by reacting an aliphatic acid halide of from 5 to 24 carbon atoms wifti hydrogen eulfide in the presence of an inert gas. By this method the corrosive hydrogen halide by-product is removed from the reaction mixture as it is formed so as to prevent the decomposition of the product and damage to the process apparatus. Moreover, no hydrogen halide aoceptor need be employed which effects a considerable reduction in cost by eliminating both the amine recovery step and the use of the amine. If desired a solvent ca be employed, but none is required* The process is not as useful for the preparation of the thioacids of less than about 5 carbon atoms, however, because of their higher volatilities. 31403/2 - The reaction can be illustrated by the following reaction diagram vfherein R* is an aliphatic hydrooarbon radical of from 4 to 23 carbon atoms and X is a halogen having an atomic weight about 30. 0 0 i> ¾ inert gas . ι· fi †v R-C-X+HgS · · R-C-SH+HX I The aliphatic hydrocarbon radicals represented by R*, the acid chlorides and the optional solvents which can advantageously j be employed are the same as those mentioned above as being suitable for the reaction of the aliphatic thiocarboxylic acids with the aliphatic oarboxylic acid halides.

The hydrogen halide by-product is removed by intro- " ducing a dry, inert gas into the reaction mixture at a rate sufficient to remove the hydrogen halide by-product as it is formed. The same inert gases oan be employed as were mentioned hereinbefore.

The proportions of reaotants are not critical* It is preferred, however, that an excess of hydrogen sulfide be employed of from about ^ OO^ to about 1000?ί by weight in order to obtain a quick reaction. Excess hydrogen sulfide can be recycled for reuse in the reaction. * · The temperature of the reaction should be sufficiently high to prevent the reaction mixture from becoming viscous and will generally be from about 50°0. to about 200°0, It is preferred, however, that the temperature be maintained between about 60°C. and about 125°C. Although the reaction can be convenientl conducted at atmos heric ressure su eratmos herio or 31403/2 - 6 - subatmospheric pressures csn be employed to advantage especially with lower alkane solvents such as propane and butane. Sub-atmospheric pressure is advantageous as it facilitates the quick removal of the hydrogen halide gas by-products.

In order to obtain complete reaction, the reaction mixture is agitated and preferably a a vigorous, turbulent rate. When the reaction is complete, as evidenced by no further hydrogen halide evolution or hydrogen silfide absorption, the product can be recovered by the conventional means, such as filtration or distillation, and can be furtherjpurified, if desired, b . ^crystallization, distillation and the like* The aliphatic carboxylic acid thioanhydrides can be employed to protect a number of polymers against degradation and discoloration due to heating. They are particularly effective in stabilizing the halogen containing hydrocarbon polymerB such as polyvinyl chloride, and polyvinylidene chloride. The presence of between about 0.01^ and about 10$ by weight of the stabilizer compound will be sufficient for most applications, although the preferable range is between about 1$ and about 5$ on a weight basis.

The following examples will serve to illustrate the. process of the invention and its preferred embodiments.

BXAMPEB 1 Preparation of thioletearlc acid To a 1-litET, 3-necked flask equipped with gas inlet tube, stirrer, thermometer and an 18 inch packed distillation column, is added 200 co. of benzene. The column is open at the 31403/2 £ - 7 - top and connected to a dropping funnel and gas outlet tube.

The flask containing 200 oo. of "benzene is heated to refluxlng temperature and hydrogen sulfide is introduced into the reaction flask by paasing it through the benzene layer at a rate of two thirds of a mole per hour. Through the dropping funnel at the top of the distillation column is added 50 grams of stearoyl -chloride over a period of three hours. Nitrogen is introduced into the reaction mixture at a rate sufficient to remove the hydrogen chloride by-product as formed and the reaction is continued for three hours. After the reaction is complete, as evidenced by no further hydrogen chloride evolution, the reaction is terminated and the reaction mixture allowed to cool to room temperature. The impurities are removed by filtration and the reaction mixture is distilled at reduced pressure to remove the benzene solvent. Thirty-three grams of pure thiolstearic acid is recovered as residue for a yield of 66%.

EXAMPLE 2 PREPARATION OF THIOLLAURIC ACID In accordance with the procedure of Example 1, thiol-lauric acid is prepared from lauroyl chloride and hydrogen sulfide.

EXAMPLE 3 PREPARATION OF THIOLCAPROIC ACID In accordance with the procedure of Example 1, thiol-caproic acid is prepared from caproyl chloride and hydrogen sulfide.

The thiolcarboxylic acids can be employed to.protect a number of polymers against degradation and discoloration due to heating. They are particularly effective in stabilizing the halogen-containing hydrocarbon polymers such as polyvinyl chloride and polyvinylidene chloride. The presence. of between about 0.017o and about 107. by weight of the stabilizer compound following examples illustrate the employment of the thio-anhydrides as stabilizers .

EXAMPLES 4 - 7 The compounds of .1, 2 and 3 (3 grams each) are blended respectively with 100 grams of polyvinyl chloride resin and 30 grams of dioctyl phthalate plasticizer. Each blend is milled at a temperature of 325°F. Samples of resin are removed from the hot mill at ten minute intervals and examined. All of the samples are white and clear at the end of 50 minutes milling time .

EXAMPLE 8 PREPARATION OF THIOSTEARIC ANHYDRIDE To a 1 liter 3-necked reaction flask fitted with a gas dispersion tube, agitator, thermometer and water cooled reflux condenser were added 104 grams (0.312 mol) of thiostearic acid dissolved in 250 milliliters of benzene. To this mixture was then added 94.4 grams (0.312 mol) of stearoyl chloride with agitation. The temperature of the exothermic reaction rose to 35°C. Nitrogen gas was introduced by way of the gas dispersion tube and the mixture was brought to reflux temperature and maintained at this temperature for four hours until the evolution of hydrogen chloride terminated. The reaction mixture was allowed to cool to 25°G . , filtered and the precipitate washed with benzene. The precipitate was washed a second time with acetone, filtered and air dried to produce 163 grams of .31403/2 - 10 - ' ' ■ ..„.._. - EXAMPLE 9'"'" ~~ ·"··'"" PREPARATION OF THIOLAURIC ANHYDRIDE .

In accordance with the procedure of Example 8 , thiolauric anhydride, is prepared from thiolauric acid and lauryl chloride.

. · ' EXAMPLE 10 ' * PREPARATION OF THIOCAPRYLIC ANHYDRIDE In accordance with the procedure of Example 8, thiocaprylic anhydride is prepared from thiocaprylic acid and caproyl chloride.

' ' EXAMPLE 11 ! The compounds of Examples 8 and 9 (3 grams each) are blended respectively with 100 grams of polyvinyl chloride resin and 30 grams of dioctyl phthalate plasticizer. Each blend is ' milled at a temperature of 325°F. Samples of resin are removed from the hot mill at ten minute intervals and examined. All of the samples are white and clear at the end of 50 minutes milling time. 31403/2

Claims (15)

1. A process for preparing aliphatic carboxylic acid thioanhydrides of the general formula 0 0 H II , and R' wherein the groups represented by R/may be the same or different aliphatic hydrocarbon radicals of from 4 to 23 carbon atoms, which comprises reacting an aliphatic acid halide of the formula Q II R-C-X wherein R is as defined above and is a halogen having an atomic weight above 30, with an aliphatic tbJblcarboxyllo acid of the formula 0 R-C-SH wherein R* is as defined above, in the presence of an inert gas which is passed through the reaction mixture at a rate sufficient to remove the hydrogen halide by-product.

2. · ihe process of Claim 1, wherein the reaction Is conducted in the presence of a solvent.

3. The process of Claim 1, wherein the temperature of the reaction is maintained between about 25°C and about 150°C.

4. · The process of Claim 1, wherein the thioaold is thiostearlo acid and the acid halide is stearoyl chloride. 31403/2 , φ - 12 -

5. The process of Claim 1, wherein the temperature of the reaction is maintained between about 39°0. and about 100°C.

6. The process of Claim 1, wherein the inert g B is nitrogen,

7. A process according to any one of Claims 1 to 6, wherein the aliphatic thiolcarboxyiic acid is prepared by reacting an aliphatic carboxyllc acid halide of the formula 0 R-C-X wherein R' and X are as defined in Claim 1, with hydrogen sulfide in the presence of an inert gas added at a rate sufficient to remove the hydrogen halide by-product as it is formed*

8. The process of Claim 7» wherein the reaction is conducted in the presence of an inert solvent.

9. The process of Claim 7, wherein the exoess of hydrogen sulfide is present of from about 100$ to &>out 1000J5.

10. The process of Claim wherein the reactants are vigorously agitated.

11. · The process of Claim 7» wherein the temperature of the reaction is maintained between about 50°C. and about 200°C.

12. · The process of Claim 7» wherein the temperature of the reaction is maintained betweenabout 60°C. and about 125°C

13. The process of Claim 7» wherein the acid halide is stearoyl chloride.

14. The process of Claim 7, wherein the acid hallde is la royl chloride.

15. The process of Claim 7» wherein the acid halide ia caproic chloride. For the Applicants RS r