Patent Application
20240279170
The present invention relates to a process for preparing thiuram disulfides, to the thiuram disulfides obtainable by said process, and to the uses thereof, in particular as vulcanization accelerators and/or as sulfur donors. Tetrabenzylthiuram disulfide (referred to hereinafter as TBzTD) is particularly preferred in the context of the present invention.
Thiuram disulfides are known as vulcanization accelerating agents, particularly for the vulcanization of various types of rubber such as tires or industrial rubbers. They are also known to be sulfur donors which confer good heat resistance due to the mono- or disulfide sulfur bridges that they create. They are particularly useful in the vulcanization of natural rubber, butadiene rubbers, butyl rubbers, EPDM (for ethylene-propylene-diene monomer), latex, butadiene-acrylonitrile copolymer (or nitrile rubber or NBR for Nitrile Butadiene Rubber) or styrene-butadiene copolymer (or SBR for Styrene Butadiene Rubber). Their use makes it possible to improve the efficiency and/or the speed of the vulcanization process, without affecting the properties of the final rubber.
However, one of the problems associated with their use in vulcanization is the generation of volatile nitrosamines when they are prepared from light secondary amines such as diethylamine or dibutylamine. Specifically, volatile nitrosamines are degradation products of these accelerators that it is desired to avoid since they are carcinogenic. Thus, some thiuram disulfides are prepared from heavier amines and therefore generate nitrosamines that are not volatile (they are called “nitrosamine-safe”). In particular, they enable effective acceleration of the vulcanization process while being more environmentally friendly and without risk compared to thiuram disulfides derived from light amines. Among the “nitrosamine-safe” thiuram disulfides, mention may be made of tetrabenzylthiuram disulfide (TBzTD), tetrakis(2-ethylhexyl)thiuram disulfide (TOTD) or tetraisobutylthiuram disulfide (TiBTD).
Thiuram disulfides, whether “nitrosamine-safe” or not, must meet precise specifications with a view to their use as vulcanization accelerating agents. Good purity is thus sought in order to guarantee good activity of these products. In the case of thiuram disulfides that are solid at ambient temperature, such as TBzTD, a controlled melting point is also sought.
There is therefore a need for a process for preparing thiuram disulfides which makes it possible to obtain a product with a yield and quality that are satisfactory, or even improved compared to the known processes. There is also a need for a process for preparing thiuram disulfides which is simple to implement industrially.
There is also a need for thiuram disulfides which are as pure as possible, and/or which have controlled physicochemical properties.
One objective of the present invention is to provide a process for preparing thiuram disulfides which is easy to implement and/or has a good yield, preferably an improved yield compared to the known processes.
One objective of the present invention is also to provide thiuram disulfides having a satisfactory purity, or even a purity greater than the thiuram disulfides produced to date, preferably at least 99%.
Another objective of the present invention is to provide thiuram disulfides with a controlled melting point, preferably a TBzTD having a final melting point of greater than or equal to 135° C., preferably strictly greater than 135° C.
The present invention meets all or part of the above objectives.
Thus, the present invention relates to a process for preparing a thiuram disulfide, comprising a step of simultaneously adding an oxidizing composition and a composition comprising a dithiocarbamate salt to a reactor, said reactor already comprising a solvent S1.
The synthesis of thiuram disulfides conventionally comprises the following steps:
Said synthesis can be illustrated by that of TBzTD according to the scheme below:
In the case of the TBzTD schematized above, the sodium salt of dibenzyldithiocarbamate (2) (referred to as NaBEC) is prepared from dibenzylamine (1) and carbon disulfide, in the presence of a base, preferably in the presence of sodium hydroxide. The NaBEC obtained is then oxidized to form TBzTD (3), which precipitates at the end of the reaction.
This conventional synthesis route is described for example in documents U.S. Pat. No. 6,465,691B1 and U.S. Pat. No. 4,468,526. Document CN 1827596A describes a preparation process characterized by an oxidation step with simultaneous addition of hydrogen peroxide and sulfuric acid to a reactor comprising NaBEC. The TBzTD obtained is in the form of a slightly yellow solid have a degree of purity of 97%. No melting point of the TBzTD obtained is given.
The present inventors have surprisingly discovered that a particular implementation of the step of oxidizing the dithiocarbamate salt makes it possible to obtain a thiuram disulfide with a high purity, in particular with a purity of greater than or equal to 99% (% by mass); the purity being able to be determined in a conventional manner by HPLC.
Such a purity notably enables controlled physicochemical properties of the thiuram disulfide, such as the melting point, preferably the final melting point.
In particular, the TBzTD obtained with the process according to the invention has a melting point, preferably a final melting point, of greater than or equal to 135° C., and preferentially strictly greater than 135° C. “Final melting point” in particular means the temperature at which the melting of the thiuram disulfide is complete (when there is no longer any solid form). The, in particular final, melting point may be measured in a conventional manner by DSC (Differential Scan Calorimetry). The melting point, more specifically the final melting point, is in particular determined at atmospheric pressure (or around 1013.25 hPa).
In particular, the TBzTD obtained according to the invention is white in color, without yellowing. It may be easy to recover and to use: it is easy to filter and does not compact.
The process as according to the invention also makes it possible to obtain a yield of greater than or equal to 90%, preferably greater than or equal to 95%, or even greater than or equal to 97%.
The process according to the invention may be implemented in a simple manner, at mild temperatures, and preferably with water as solvent. It is therefore economically viable and environmentally friendly. It may be performed batchwise or continuously, preferably batchwise.
The term “—(C1-C15)alkyl” in particular denotes monovalent saturated aliphatic hydrocarbons which may be linear or branched and which comprise from 1 to 15 carbon atoms. Preferably, the alkyls comprise from 1 to 8 carbon atoms. Mention may for example be made of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl. “Branched” means that an alkyl group is substituted on the main alkyl chain.
The term “—(C6-C10)aryl” in particular denotes monocyclic, bicyclic or tricyclic monovalent aromatic hydrocarbon compounds comprising from 6 to 10 carbon atoms, in particular phenyl and naphthyl.
The term “—(C3-C10)cycloalkyl” in particular denotes monocyclic or bicyclic monovalent saturated aliphatic hydrocarbons comprising from 3 to 10 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl.
“—(C4-C10)heteroaryl” in particular means an aryl as defined above, comprising between 4 and 10 carbon atoms and comprising at least one heteroatom; for example a furanyl or a pyridinyl.
“—(C1-C15)alkylene” in particular means an alkyl radical as defined above but divalent.
“Heteroatom” in particular means an atom chosen from O, N, S, Si, P and halogens, preferably O, N or S.
“Unsaturation” in particular means a double or triple bond between two carbon atoms.
The present invention therefore relates to a process for preparing a thiuram disulfide, comprising a step of simultaneously adding an oxidizing composition and a composition comprising a dithiocarbamate salt to a reactor, said reactor already comprising a solvent S1. Said addition step enables the oxidation of the dithiocarbamate salt to thiuram disulfide.
More particularly, the present invention relates to a process for preparing a thiuram disulfide of general formula (I) below:
Preferably, the oxidizing composition and the composition comprising a dithiocarbamate salt are simultaneously introduced into the reactor above the surface of the solvent S1 present. More particularly, said compositions are introduced at the top of the reactor (that is to say through the top of the reactor), whereas the solvent S1 is placed at the bottom of the reactor.
The oxidizing composition and the composition comprising a dithiocarbamate salt may each be introduced separately or be mixed beforehand before introduction into the reactor. They are preferably introduced separately. Said introduction may take place by injection.
“Reaction medium” in particular means the medium contained in said reactor and preferably comprising said oxidizing composition, said dithiocarbamate salt composition and said solvent S1.
The addition step may be carried out at a temperature of between 5° C. and 60° C., preferably between 15° C. and 25° C., for example between 18° C. and 20° C.
During said addition step, the reaction medium may be stirred, for example using blades in the reactor. If necessary, the stirring may continue after the addition step.
During the addition step, the pH of the reaction medium may be neutral or basic. It may therefore be between 7 and 14. It is preferably greater than 7 and even more preferentially between 8 and 12, for example between 8 and 10. The pH may be monitored in a conventional manner by a pH meter.
The pH of the reaction medium may advantageously be kept constant throughout the addition step, particularly by controlling the [dithiocarbamate salt/oxidizer] molar ratios introduced. Specifically, the dithiocarbamate salt composition and the oxidizing composition may be introduced into the reactor at different molar flow rates, particularly with a dithiocarbamate salt molar flow rate greater than that of the oxidizer. In particular, the [dithiocarbamate salt/oxidizer] molar ratio introduced into the reactor is between 1 and 4, preferably between 1.5 and 3, more preferentially between 1.5 and 2.5. Preferably, the [dithiocarbamate salt/oxidizer] molar ratio introduced into the reactor is greater than or equal to 2.
In particular, the addition of the dithiocarbamate salt composition may end at the same time or before the end of the addition of the oxidizing composition. Advantageously, even though the addition of the oxidizing and dithiocarbamate salt compositions is simultaneous, the addition of the dithiocarbamate salt composition may end before the end of the addition of the oxidizing composition. In other words, the pouring of the dithiocarbamate salt composition may end before the pouring of the oxidizing composition. In this case, it is understood that the pouring of the two compositions is simultaneous until the end of the pouring of the dithiocarbamate salt composition. This may for example be obtained by virtue of a [dithiocarbamate salt/oxidizer] molar ratio introduced into the reactor of strictly greater than 2, for example between strictly greater than 2 and 4.
The addition step lasts for example between 3 h and 10 h, preferably between 4 h and 6 h.
According to one embodiment, the addition step is carried out without a catalyst.
At the end of the addition step, in the reaction medium, the [dithiocarbamate salt/oxidizer] molar ratio may be between 1.5 and 3, preferably between 1.8 and 2.5. At the end of the addition step, the pH may be acidic, for example between 2 and 5, preferably between 3 and 4.
According to one embodiment, said thiuram disulfide (in particular the TBzTD) thus obtained precipitates in said solvent S1. It is then possible to recover it by filtration, then optionally wash it with water and dry it.
Preferably, the thiuram disulfides are of general formula (I) as defined above.
Preferably, R1 and R2 are chosen from —(C1-C5)alkyls and —(C1-C5)alkylene-(C6-C10)aryls. In particular, R1 and R2 are chosen from —(C1-C10)alkyls and —(C1-C10)alkylene-(C6-C10)aryls.
According to one embodiment, R1 and R2 may be different or identical; preferably, they are identical.
In particular, the thiuram disulfide is chosen from the group consisting of:
Preferably, the thiuram disulfide is the tetrabenzylthiuram disulfide (TBzTD) of the formula below:
The dithiocarbamate salts are preferentially of general formula (II) as defined above, where R1 and R2 are as defined for the general formula (I) and X is chosen from the group consisting of alkali metals, alkaline-earth metals and ammoniums.
“Alkali metals” in particular means lithium, sodium, potassium, rubidium and cesium. Particular preference is given to sodium and potassium and most preferred is sodium.
“Alkaline-earth metals” in particular means beryllium, magnesium, calcium, strontium, barium and radium, preferably magnesium and calcium.
“Ammoniums” in particular means the NH4+ ions originating from gaseous ammonia (NH3) or aqueous ammonia (NH4OH).
Most preferably, X is sodium.
Preferably, the dithiocarbamate salt used is chosen from the group consisting of:
Most particularly preferably, the dithiocarbamate salt is NaBec.
Said dithiocarbamate salt is in particular in solution in order to carry out said process according to the invention. Thus, the dithiocarbamate salt composition may be a solution, preferably an aqueous, alcoholic or aqueous/alcoholic solution. The solvent may be chosen from water; alcohols such as methanol, ethanol, isopropanol, n-propanol, n-butanol, tert-butanol and amyl alcohol; or mixtures thereof. Preferably, the solvent is water.
Preferentially, the dithiocarbamate salt composition comprises from 15% to 95%, preferably from 50% to 90%, preferentially from 70% to 90%, by weight of solvent relative to the total weight of said composition.
Preferentially, the dithiocarbamate salt composition comprises from 5% to 85% by weight, preferably from 10% to 50%, preferentially from 10% to 30%, by weight of dithiocarbamate salt relative to the total weight of said composition.
Preferably, said composition is an aqueous solution of dithiocarbamate salt, preferably of NaBEC, comprising, or even consisting of:
“Oxidizing composition” means any composition comprising at least one oxidizer (or oxidizing agent) which makes it possible to oxidize the dithiocarbamate salt so as to obtain a thiuram disulfide. Such an oxidizer is preferentially hydrogen peroxide or a peroxide derivative originating from hydrogen peroxide. It may be a derivative resulting from the mixing of hydrogen peroxide with an acid. Said acid may be of any type, mineral or organic. Mention may for example be made of sulfuric acid (H2SO4), hydrochloric acid (HCl), carboxylic acids such as acetic acid or any other acid which is soluble in a hydrogen peroxide solution. Particular preference is given to sulfuric acid.
Thus, for example, mixing hydrogen peroxide with sulfuric acid forms peroxymonosulfuric acid.
Said composition may be a solution, preferably an aqueous solution and more preferentially an aqueous solution of hydrogen peroxide.
Said composition may be a composition comprising hydrogen peroxide, water and optionally an acid (in particular as defined above). It is possible to pour the acid separately into said reactor. However, when the acid is present, preference is given to preparing an oxidizing composition comprising said acid before addition to the reactor.
Preferably, the oxidizing composition is an aqueous solution of hydrogen peroxide and sulfuric acid (or an aqueous solution of peroxymonosulfuric acid).
In particular, the oxidizer is not oxygen (O2).
Preferentially, said oxidizing composition comprises, or even consists of, per one molar equivalent of said dithiocarbamate salt:
In particular, the amount of hydrogen peroxide is between 0.5% and 20% by weight, preferably between 1% and 10% by weight, more preferentially between 1% and 5% by weight, relative to the total weight of said oxidizing composition.
In particular, the amount of acid is between 2% and 40% by weight, preferably between 5% and 20% by weight, more preferentially between 5% and 10% by weight, relative to the total weight of said oxidizing composition.
In particular, the amount of solvent, preferably water, is between 0 and 95% by weight, preferably between 60% and 80% by weight, relative to the total weight of said oxidizing composition.
The oxidizing composition may be prepared in a conventional manner, for example by mixing the ingredients in a tank, or continuously by means of a static mixer.
The fact that “the reactor already comprises a solvent S1” in particular means that when the oxidizing composition and the dithiocarbamate salt composition are simultaneously added to the reactor, the latter already comprises the solvent S1 (this is also referred to as “a solvent bottom”). The solvent S1 may be the same or different from the solvent(s) used for the oxidizing composition and/or the dithiocarbamate salt composition. In particular, the solvent S1, that of the oxidizing composition and that of the dithiocarbamate salt composition is water.
Said solvent S1 may be an aqueous, alcoholic, aqueous/alcoholic or organic solvent. Thus, the solvent S1 may be chosen from water; alcohols such as methanol, ethanol, isopropanol, n-propanol, n-butanol, tert-butanol and amyl alcohol; organic solvents such as toluene and dichloromethane; and mixtures thereof, in particular mixtures of water and alcohol(s). Preferably, the solvent S1 is water.
In particular, the amount by weight of solvent S1 already present in the reactor is between 5% and 50% by weight, preferably between 10% and 40% by weight, more preferentially between 20% and 40% by weight, for example between 20% and 30% by weight, relative to the total weight of the oxidizing and dithiocarbamate salt compositions which are poured into the reactor.
Said solvent S1 may also comprise a surfactant, preferably a nonionic surfactant. Examples of nonionic surfactants that may be mentioned are alkoxylated fatty acids, in particular ethoxylated fatty acids, ethoxylated alcohols, ethoxylated sorbitan esters, and castor oil ethoxylates. In particular, mention may be made of the following surfactants: Tergitol®15-S-5, Tergitol®15-S-7, Tergitol®15-S-9, Tergitol®15-S-12, Ecosurf®SA-4, Ecosurf®SA-7, Ecosurf®SA-9, Rhodasurf® 870H20, Synative® RPE 2520, Breox® 50 A 20, Breox® 50 A 50, Breox® 50 A 140 or Breox® 43 A 1000.
The surfactant may in particular be added to the solvent S1 before the step of simultaneously adding the oxidizing and dithiocarbamate salt compositions.
Preferably, the amount of surfactant in said solvent S1 is between 0.005% and 1%, preferably between 0.01% and 0.5%, more preferentially between 0.05% and 0.5%, by weight relative to the theoretical total weight of thiuram to be obtained at the end of the addition step.
The process for synthesizing the thiuram disulfide may comprise the following steps:
Step i) may be carried out by reacting an amine, preferably a secondary amine corresponding to the desired thiuram disulfide, and CS2, preferably in the presence of a base. The base is in particular a base of type X—OH, where X is chosen from alkali metals, alkaline-earth metals or NH4; in particular, X is sodium or lithium.
The dithiocarbamate salts are thus obtained from a conventional and widely described synthesis using for example one molar equivalent of the amine, one molar equivalent of CS2 and one molar equivalent of sodium hydroxide (50% by mass). In particular, the dithiocarbamate salt is obtained by adding CS2 to the mixture of the amine and the base, preferably at a temperature of between 20° C. and 40° C. A composition comprising a dithiocarbamate salt is thus obtained.
Step ii) corresponds to the simultaneous addition step as according to the invention and defined above.
Preferably, steps i) and ii) do not take place in the same reactor, but in two different reactors. Use may be made of reactors of batch type or tubular reactors of continuous mixer type for step i) and/or ii). Step ii) is preferentially carried out in a batch reactor.
Step iii) of recovering the thiuram disulfide may be effected by any known means, and in particular by filtration when said thiuram disulfide precipitates in the solvent S1. It is then optionally possible to wash it with water and dry it.
The present invention also relates to a thiuram disulfide, preferably of general formula (I) as defined above, obtainable by the preparation process as according to the invention. The present invention also relates to a thiuram disulfide, preferably of general formula (I) as defined above, obtained or directly obtained by the preparation process as according to the invention. Preferably, said thiuram disulfide is TBzTD.
The present invention relates to a TBzTD having a melting point, in particular a final melting point, of between 134° C. and 137° C., preferably between 135.5° C. and 137° C., and/or a purity of greater than or equal to 99% (% by mass). Preferably, said TBzTD has a melting point, in particular a final melting point, of strictly greater than 135° C., more preferentially strictly greater than 135.5° C., and/or a purity of greater than or equal to 99% (% by mass). In particular, the TBzTD has a final melting point of greater than or equal to 136° C., for example of 137° C. Said TBzTD is notably obtainable (or obtained or directly obtained) by the process as according to the invention.
The present invention also relates to a composition comprising at least 99% by weight of TBzTD, said TBzTD having a melting point, in particular a final melting point, of strictly greater than 135° C., more preferentially strictly greater than 135.5° C. In particular, the TBzTD has a final melting point of greater than or equal to 136° C. Said TBzTD is notably obtainable (or obtained or directly obtained) by the process as according to the invention.
The present invention also relates to the use of thiuram disulfide as according to the invention as a vulcanization accelerator or an additive for lubricants, preferably an accelerator for the vulcanization of natural rubber, butadiene rubbers, butyl rubbers, EPDM (ethylene-propylene-diene monomer), latex, butadiene-acrylonitrile copolymer (or nitrile rubber or NBR for Nitrile Butadiene Rubber) or styrene-butadiene copolymer (or SBR for Styrene Butadiene Rubber).
The expression “between X and X” includes the stated endpoints, unless mentioned otherwise.
The examples below are given for illustrative purposes and do not limit the present invention.
139.2 g of water is introduced into a 500 ml flask. 35.1 g (0.15 mol, 1 eq.) of 43% by mass sulfuric acid is added. 15.3 g (0.16 mol, 1.05 eq.) of 35% by mass hydrogen peroxide is then added. Homogenization is performed at ambient temperature. 367.2 g (0.3 mol, 2 eq.) of around 24.8% by mass NaBEC is introduced into another 500 ml flask.
The reactor already contains 197 g of water stirred at 18° C. and containing 0.1% by mass of the surfactant RHODASURFO 870 H 20.
Using a first pump, the NaBEC composition is injected into the reactor.
Using a second pump, the oxidizing composition is simultaneously injected into the reactor.
The flow rate at which the NaBEC composition is introduced into the reactor is 1.31 g/min, or a molar flow rate of pure NaBEC of 1.1 mmol/min.
The flow rate at which the oxidizing composition is introduced into the reactor is 0.63 g/min, or a molar flow rate of pure oxidizer of 0.5 mmol/min. This flow rate being calculated by theoretically assuming the formation of 0.15 mol of peroxymonosulfuric acid oxidizer in the mixture prepared here from 0.15 mol of sulfuric acid and 0.16 mol of hydrogen peroxide.
The ratio of the [NaBEC/ox] molar flow rates is therefore 2.2, and the pH is between 8 and 10 until the end of the injection of the NaBEC.
At the end of the addition step, the reactor is held at 18° C. for 5 min with stirring, then is drained.
The suspension obtained is filtered on a frit, then washed with water.
The TBzTD is obtained in the form of a wet white solid, which has precipitated. It is recovered and placed in an oven overnight at 40° C.
The results obtained are as follows:
179.3 g of water is introduced into a 500 ml flask. 28.3 g (0.12 mol, 1 eq.) of 43% by mass sulfuric acid is added. 11.7 g (0.12 mol, 1 eq.) of 35% by mass hydrogen peroxide is then added. Homogenization is performed at ambient temperature.
288.4 g (0.24 mol, 2 eq.) of around 24.8% by mass NaBEC is introduced into a reactor. 76.56 g of water and 0.1% (0.07 g) by mass of the surfactant RHODASURFO 870 H 20 are then added at 18° C. and with stirring.
Using a peristaltic pump, the oxidizing composition is introduced into the reactor, already containing the NaBEC, at a flow rate of 0.61 g/min.
At the end of the step of adding the oxidizing composition, the reactor is held at 18° C. for 5 min with stirring, then is drained.
The suspension obtained is filtered on a frit, then washed with water.
The TBzTD is obtained in the form of a wet white solid, which has precipitated. It is recovered and placed in an oven overnight at 40° C.
The results obtained are as follows:
| Number | Date | Country | Kind |
|---|---|---|---|
| 2105743 | Jun 2021 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/064820 | 5/31/2022 | WO |
