Method for the synthesis of asymmetric polysulfides

Abstract

The present invention is directed to a method of making an asymmetric polysulfide, comprising the step of simultaneously reacting an olefinically unsaturated compound, elemental sulfur, and a thiol in the presence of a catalytic amount of a base to produce the asymmetric polysulfide.

Description

BACKGROUND

Soybean oil that is silylated through di- or polysulfide connectivity is of interest for use in rubber and tire compounds. The only method available for generating these types of materials is multi-step and not commercially viable, so development an alternative method is desirable.

Previous methods to produce polysulfides include vulcanization of olefins to create symmetric R—Sx-R polysulfides, using thiols to create symmetric R—Sx-R polysulfides, and using olefins to generate hydropersulfides (or hydropolysulfides). Methods for the synthesis of asymmetric polysulfides are not widely available and those that exist are typically multi-step and/or not commercially-viable.

SUMMARY

The present invention is directed to a method of making an asymmetric polysulfide, comprising the step of simultaneously reacting an olefinically unsaturated compound, elemental sulfur, and a thiol in the presence of a catalytic amount of a base to produce the asymmetric polysulfide.

DESCRIPTION

There is disclosed a method of making an asymmetric polysulfide, comprising the step of simultaneously reacting an olefinically unsaturated compound, elemental sulfur, and a thiol in the presence of a catalytic amount of a base to produce the asymmetric polysulfide.

An asymmetric polysulfide is a polysulfide that includes substitutent groups on opposite ends of the —S_x— polysulfide group that are different from each other, for example, in an asymmetric polysulfide such as Q1-S_x-Q2 the groups Q1 and Q2 are not the same.

The present invention is directed to a novel reaction that can generate asymmetric polysulfides in high yield and purity in a single step using a “one-pot” method under commercially accessible conditions. It is now found that if a mixture of olefin, elemental sulfur, thiol, and catalytic amount of base is heated at 170° C. for approximately 1 hour, the olefin can be functionalized to give a mixture of mono- and polysulfide products. The utility of this methodology is demonstrated on methyl oleate, high oleic soybean oil, commodity soybean oil, cis-cyclooctene, and squalene. The application to oils gives a new route to a wide variety of previously-unreported soybean oil derivatives. The application to squalene demonstrates the possible use of this method for functionalizing polymer backbones with polysulfides.

More broadly, the reaction mixture may be heated to a temperature range of 150 to 200° C., for a time ranging from 30 minutes to 2 hours.

By thiol, it is meant a compound including an —S—H group pendant from the compound. Such compounds may include other functional groups.

Most broadly then, in one embodiment the method of making an asymmetric polysulfide includes the step of simultaneously reacting an olefinically unsaturated organic compound, elemental sulfur, and a thiol in the presence of a catalytic amount of a base to produce the asymmetric poly sulfide.

The olefinically unsaturated organic compound may be derived from petroleum or from biological sources such as plants or microorganisms, or synthetically produced.

In one embodiment, the olefinically unsaturated organic compound is selected from the group consisting of alkenes, cycloalkenes, unsaturated fatty acid alkyl esters, and unsaturated fatty acid triglycerides.

In one embodiment, the olefinically unsaturated organic compound is a vegetable oil.

In one embodiment, the vegetable oil is soybean oil.

In one embodiment, the base is an amine. In one embodiment, the base is a tertiary amine, including but not limited to amines substituted with any combination of alkyl or aromatic substituents, amines contained within aromatic heterocycles, and fused ring amines such as bicycles (i.e. 1,4-diazabicyclo[2.2.2]octane). In one embodiment, the base is triethylamine.

In one embodiment, the asymmetric polysulfide is of formula 1

where R¹, R² and R³ are independently C15-C20 alkenyl, C15-C20 alkyl, and optionally containing aromatic groups; R is —S_x—R⁴ where x is an integer from 2 to 9, R⁴ is a monovalent organic group; each R is covalently bonded to a carbon atom of one of R¹, R² or R³; and m is the number of R groups. Each of the R⁴ may be derived from a corresponding thiol R⁴—S—H and such thiols may be used generally with an olefinically unsaturated organic compound, elemental sulfur in the presence of a catalytic amount of a base to produce the asymmetric polysulfide.

In one embodiment, R⁴ is —R⁵—Si—(OR⁶)₃ where R⁵ is C1 to C8 alkane diyl, and R⁶ are independently C1 to C8 alkyl. In one embodiment, R⁴ is —CH₃—Si—(OCH₂CH₃)₃ derivable from mercaptopropyltriethoxysilane.

In one embodiment, R⁴ is selected from the following structures

where Z is a group that helps control the reactivity of the thiocarbonylthio moiety;

where X=0-2 carbon atoms; R⁶, R⁷ can be independently hydrogen, alkyl chains, or aromatic moieties;

where R⁸, R⁹ can be independently alkyl or aromatic functionalities;R¹⁰—where R¹⁰ is a substituted or non-substituted alkyl or aromatic group optionally containing ether, carboxyl, ester, amine, or amide functionalities;

where X=0-2 carbon atoms; R¹¹, R¹² can be symmetric or asymmetric and independently be an alkyl, aromatic, or ethereal substituents;

where X=0-2 carbon atoms; R¹³, R¹⁴ can be symmetric or asymmetric and are independently hydrogen, an alkyl chain, aromatic containing functional group;

where R¹⁵, R¹⁶ can be independently hydrogen, alkyl chains, or aromatic moieties; and

where R¹⁷, R¹⁸, and R¹⁹ are independently substituted or non-substituted alkyl or aromatic groups or substituted or non-substituted heteroatom-containing groups and Y is a substituted or non-substituted alkane diyl or aromatic group optionally containing ether, carboxyl, ester, amine, or amide functionalities. In one embodiment, at least one of R¹⁷, R¹⁸, and R¹⁹ is —N(R²⁰)₂ where R²⁰ is C1 to C8 alkyl. In one embodiment, at least one of R¹⁷, R¹⁸, and R¹⁹ is —OR²¹ where R²¹ is C1 to C8 alkyl.

The following non-limiting examples further illustrate the method.

EXAMPLES

General Experimental

Soybean oil and high oleic soybean oil were generously supplied by Archer Daniels Midland. Elemental sulfur was obtained from Sigma Aldrich. 3-Mercaptopropyltriethoxysilane (MPTES) was purchased from TCI America, and triethylamine was purchased from Sigma Aldrich. Reactions were performed neat. NMR experiments were performed with a 400 MHz Varian instrument.

Example 1: Synthesis of Soy-Silane Polysulfide (Method A)

Soybean oil (1 eq, 3.0 g), elemental sulfur (2 eq vs olefins, 900 mg), and 3-mercaptopropyltriethoxysilane (1.2 eq vs olefins, 4.3 mL) were added to a 20 mL glass vial. The vial was sealed and stirred vigorously while heating to 170° C. Time was started when the bath temperature reached 120° C. The reaction was stirred for 40 minutes, at which point a deep red/orange transparent oil was obtained. NMR analysis confirmed the desired product, with a small amount of residual MPTES, which can be removed via vacuum distillation if desired.

Example 2: Synthesis of Soy-Silane Polysulfide (Method B)

Soybean oil (1 eq of olefins, 3.0 g), elemental sulfur (2 eq vs olefins, 900 mg), 3-mercaptopropyltriethoxysilane (1.2 eq vs olefins, 4.3 mL), and triethylamine (0.025 eq vs olefins, 47.1 μL) were added to a 20 mL glass vial. The vial was sealed and stirred vigorously while heating to 170° C. The reaction was stirred for 40 minutes at 170° C., at which point a dark red/orange oil was obtained. NMR analysis confirmed the desired product, with no residual MPTES detected.

Example 3: Synthesis of High Oleic Soy-Silane Polysulfide

High oleic soybean oil (1 eq of olefins, 5.147 g), elemental sulfur (2 eq vs olefins, 1.033 g), 3-mercaptopropyltriethoxysilane (1.2 eq vs olefins, 4.9 mL), and triethylamine (0.025 eq vs olefins, 55.8 μL) were added to a 20 mL glass vial. The vial was sealed and stirred vigorously while heating to 170° C. The reaction was stirred for 40 minutes at 170° C., at which point a bright orange oil was obtained. NMR analysis confirmed the desired product, with no residual MPTES detected.

Example 4: Synthesis of Methyl Oleate-Silane Polysulfide

Methyl oleate (1 eq, 5.0 g), elemental sulfur (2 eq, 1.033 g), 3-mercaptopropyltriethoxysilane (1.2 eq, 4.9 mL), and triethylamine (0.025 eq, 55.8 μL) were added to a 20 mL glass vial. The vial was sealed and stirred vigorously while heating to 170° C. Time was started when the bath temperature reached 120° C. The reaction was stirred for 40 minutes, at which point a bright orange oil was obtained. NMR analysis confirmed the desired product, with no residual MPTES detected.

Example 5: Synthesis of Cyclooctene-Silane Poly Sulfide

Cis-cyclooctene (1 eq, 1.77 g), elemental sulfur (2 eq, 1.033 g), 3-mercaptopropyltriethoxysilane (1.2 eq, 4.9 mL), and triethylamine (0.025 eq, 55.8 μL) were added to a 20 mL glass vial. The vial was sealed and stirred vigorously while heating to 170° C. Time was started when the bath temperature reached 120° C. The reaction was stirred for 40 minutes, at which point a bright orange oil was obtained. NMR analysis confirmed the desired product, with no residual MPTES detected.

Example 6: Synthesis of Squalene-Silane Polysulfide

Squalene (1 eq, 1.10 g), elemental sulfur (2 eq, 1.033 g), 3-mercaptopropyltriethoxysilane (1.2 eq, 4.9 mL), and triethylamine (0.025 eq, 55.8 μL) were added to a 20 mL glass vial. The vial was sealed and stirred vigorously while heating to 170° C. Time was started when the bath temperature reached 120° C. The reaction was stirred for 40 minutes, at which point a bright orange oil was obtained. NMR analysis confirmed the desired product, with no residual MPTES detected.

Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.

Claims

1. A method of making an asymmetric polysulfide, comprising the step of simultaneously reacting an olefinically unsaturated organic compound, elemental sulfur, and a thiol in the presence of a catalytic amount of a base to produce the asymmetric polysulfide; the thiol being a compound including an —S—H group pendant from the compound.

2. The method of claim 1, wherein the olefinically unsaturated organic compound is selected from the group consisting of alkenes, cycloalkenes, unsaturated fatty acid alkyl esters, and unsaturated fatty acid triglycerides.

3. The method of claim 1, wherein the olefinically unsaturated organic compound is a vegetable oil.

4. The method of claim 1, wherein the olefinically unsaturated organic compound is soybean oil.

5. The method of claim 1, wherein the thiol is H—S—R5-Si—(OR6)3 where R5 is C1 to C8 alkane diyl, and R6 are independently C1 to C8 alkyl.

6. The method of claim 1, wherein the thiol is a mercaptopropyltriethoxysilane.

7. The method of claim 1, wherein the base is an amine.

8. The method of claim 1, wherein the base is a tertiary amine.

9. The method of claim 1, wherein the base is 1,4-diazabicyclo[2.2.2]octane.

10. The method of claim 1, wherein the asymmetric polysulfide is of formula 1

11. The method of claim 10, wherein R4 is —R5-Si—(OR6)3 where R5 is C1 to C8 alkane diyl, and R6 are independently C1 to C8 alkyl.

12. The method of claim 10, where R4 is selected from the following structures