MXPA00012418A - Improved process for the preparation of mercaptomethylphenols - Google Patents

Abstract

There is disclosed an improved process for the preparation of a compound of the formula I wherein n is 0 or 1, R1 is C1-C12alkyl or -CH2SR3, R2 is C1-C12alkyl, C7-C9phenylalkyl, C7-C9-phenylalkyl substituted on the phenyl radical by from 1 to 3 C1-C4alkyl groups;or -CH2SR3, R3 is C6-C18alkyl, phenyl or benzyl, R4 is hydrogen or methyl, R5 is hydrogen or methyl, with the proviso that R4 and R5 are not simultaneously methyl, by reacting a compound of the formula II wherein n, R4 and R5 are as previously defined, R11 is hydrogen or C1-C12alkyl;and R12 is hydrogen, C1-C12alkyl, C7-C9phenylalkyl, C7-C9phenylalkyl substituted on the phenyl radical by from 1 to 3 C1-C4alkyl groups;with formaldehyde or a compound that liberates formaldehyde under the reaction conditions and with at least one compound of the formula III R3SH wherein R3 is as previously defined, in the presence of a base, said base being mono- or dimethylamine or mono- or diethylamine, which process comprises treating afterwards the reaction product with a reducing agent.

Description

IMPROVED PROCESS FOR THE PREPARATION OF ERCAPTOMETI FENOLES The present invention relates to a new improved process for the preparation of mercaptomethylphenols from phenols by reaction with formaldehyde and mercaptans and the process comprising further treating the reaction product with a reducing agent. Mercaptomethylphenols are valuable antioxidants for plastics, mineral oils of elastomers and synthetic lubricants. U.S. Patent No. 4,857,572 discloses mercaptomethylphenols as antioxidants for plastics, elastomers, thickener resins, mineral oils and lubricants. The patent of the United States of America No.

No. 4,874,885 describes a process for the preparation of mercaptomethylphenols from phenols by reaction with formaldehyde and mercaptans in the presence of mono-, di- or trimethylamine or mono- or diethylamine. The patent of the United States of America No. ,276,258 discloses that the stabilizing properties of the mercaptomethylphenols in elastomers can be improved by the additional use of an epoxidized fatty acid or fatty acid ester.

The mercaptomethylphenols prepared according to the known processes have the disadvantages that they possess for example an unwanted odor and discoloration in the presence of lithium catalysts or alkaline medium mainly due to the presence of unwanted byproducts or impurities. The object of the present invention is therefore to find an improved process for the synthesis of mercaptomethylphenols with lower odor and discoloration in the presence of for example lithium catalysts and alkaline medium, and with excellent storage stability. Surprisingly, it has now been found that by treating the crude mercaptomethylphenols prepared in accordance with the process discovered in US Pat. No. 4,874,885 afterwards with a reducing agent, the stabilization quality of the mercaptomethylphenols is improved. The present invention therefore relates to an improved process for the preparation of a compound of the formula I (I) wherein Ii is 0 or 1, Ri is alkyl with 1 to 12 carbon atoms or -CH2SR3, R is alkyl with 1 to 12 carbon atoms, phenylalkyl with 7 to 9 carbon atoms, phenylalkyl with to 9 carbon atoms substituted on the phenyl radical by 1 to 3 alkyl groups with 1 to 4 carbon atoms; or -CH2SR3, R3 is alkyl having from 6 to 18 carbon atoms, phenyl or benzyl, R is hydrogen or methyl, R5 is hydrogen or methyl, with the proviso that R4 and R5 are not simultaneously methyl, by the reaction of a composed of formula II wherein n, R4 and R5 are as previously defined, Rii is hydrogen or alkyl having from 1 to 12 carbon atoms; and R 2 is hydrogen, alkyl of 1 to 12 carbon atoms, phenylalkyl of 7 to 9 carbon atoms, phenylalkyl of 7 to 9 carbon atoms substituted on the phenyl radical by 1 to 3 alkyl groups with 1 to 4 carbon atoms, with formaldehyde or a compound that releases formaldehyde under the reaction conditions and with at least one compound of formula III R3SH (lili wherein R3 is as previously defined, in the presence of a base, the base being mono- or dimethylamine or mono- or diethylamine, the process comprises further treating the reaction product with a reducing agent. The alkyl having up to 18 carbon atoms is a branched or unreacted radical, for example methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, 2-ethylbutyl, n-pentyl, isopentyl, 1-methylpentyl, 1,3-dimethylbutyl, n-hexyl, 1-methylhexyl, n-heptyl, isoheptyl, 1,3, 3-tetramethylbutyl, 1-methylheptyl, 3-methylheptyl, n-octyl, ter- octyl, 2-ethylhexyl, 1, 1,3-trimethylhexyl, 1,1,3,3-tetramethylpentyl, nonyl, decyl, undecyl, 1-methylundecyl, dodecyl, tridecyl, 1, 1,3,3,5,5-hexamethylhexyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl or octadecyl. One of the preferred definitions for Ri, R2, Rp and R? 2 is alkyl with 1 to 12 carbon atoms, especially preferred is alkyl with 1 to 4 carbon atoms, for example methyl. A preferred definition for R3 is alkyl with 8 to 12 carbon atoms, for example, n-octyl or n-dodecyl. Phenylalkyl with 7 to 9 carbon atoms unsubstituted or substituted on the phenyl radical by 1 to 3 alkyl groups with 1 to 4 carbon atoms is, for example, benzyl, α-methylbenzyl, α, α-dimethylbenzyl, 2- phenylethyl, 2-methylbenzyl, 3-methylbenzyl, 4-methylbenzyl, 2,4-dimethylbenzyl, 2,6-dimethylbenzyl or 4-tert-butylbenzyl. Preference is given to benzyl, -methylbenzyl or, -dimethylbenzyl. Of interest is a process for the preparation of a compound of formula I in which, n is 0 or 1, Ri is alkyl with 1 to 4 carbon atoms or -CH2SR3, R2 is alkyl with 1 to 4 carbon atoms , phenylalkyl with 7 to 9 carbon atoms, phenylalkyl with 7 to 9 carbon atoms substituted on the phenyl radical by a methyl group, R3 is alkyl with 6 to 12 carbon atoms, R is hydrogen or methyl, R5 is hydrogen, R11 is hydrogen or alkyl with 1 to 4 carbon atoms; and R 2 is alkyl with 1 to 4 carbon atoms, phenylalkyl with 7 to 9 carbon atoms, phenylalkyl with 7 to 9 carbon atoms substituted on the phenyl radical by a methyl group. Also of interest is a process for the preparation of a compound of formula I in which n is 0, Ri is -CH2SR3, R2 is alkyl with 1 to 4 carbon atoms, R3 is alkyl with 8 to 12 carbon atoms , R4 is hydrogen, R5 is hydrogen, R11 is hydrogen; and R12 is alkyl with 1 to 4 carbon atoms. Of special interest is a process for the preparation of 2,4-bis (n-octylthiomethyl) -6-methylphenol [Irganox 1520 (RTM), Ciba Specialty Chemicals] and 2,4-bis (n-dodecylthiomethyl) -6- methylphenol.

The reaction of the compound of formula II with formaldehyde and a compound of formula III is carried out in the presence of mono- or dimethylamine or mono- or diethylamine as the base. It is preferred to use dimethylamine as the base. The base may be, for example, in the form of a solution of 10-35% by weight in ethanol, methanol or other lower alcohol or in pure form. Dimethylamine in gaseous form can also be used. The base can be used for example in an amount of 1 to 50 mol% and, more preferably, 5-20 mol%, based on the compound of the formula III. The reaction of the compound of the formula II with the formaldehyde and a compound of the formula III can be carried out in the presence of a solvent. Examples of suitable solvents are alcohols of 1 to & carbon atoms, for example methanol, ethanol, propanol, butanol, pentanol or hexanol. However, it is also possible to use diols, polyols and ethers thereof, for example glycol, glycerol and polyethylene glycol. The reaction can be carried out in a polar aprotic solvent such as dimethylformamide or dimethyl sulfoxide, or a high-boiling aliphatic or aromatic hydrocarbon or a chlorinated hydrocarbon such as toluene, ligroin or chlorobenzene. The preferred solvent is dimethylformamide which is diluted with one of the lower alcohols or chlorinated hydrocarbons mentioned above. It is preferred, however, to carry out the process in the absence of a solvent. The reaction of the compound of formula II with formaldehyde and a compound of formula III can conveniently be carried out on the temperature scale of 80 ° C to 160 ° C, preferably 90 ° C to 150 ° C, and more preferably, of 90 ° C to 130 ° C, and at normal pressure or under pressure (for example from 0.01 to 5 bar). In the absence of a solvent, the reaction is preferably carried out under overpressure. Depending on the specific compound of the formula II and the compound of the formula III used, the reaction times may vary and may be, for example, from 1 to 24 hours, and preferably from 1 to 6 hours. The reaction mixture is conveniently heated in a nitrogen atmosphere under reflux. After cooling to room temperature, the reaction mixture is worked by conventional separation and purification methods. Most of the compounds of formula I, II and III are known and some are commercially available or can be prepared by known methods. Formaldehyde or a compound that releases formaldehyde under the reaction conditions, for example para-formaldehyde or hexamethylenetetramine, is used for the reaction. It is preferred to use formaldehyde, but para-formaldehyde is particularly preferred. A preferred reducing agent is a hydride or hydrogen with a catalyst. Preferred catalysts for hydrogenation are for example Pt, Pd, Rh, Ru, Ni as for example Raney-nickel, or Cu-Cr systems. The metals are supported on inert supports such as carbon, alumina, barium sulfate. Especially preferred catalysts are Pt, Ru, Ni and Cu-Cr. Of special interest is a process for the preparation of a compound of formula I wherein the reducing agent is a hydride. Hydrides of special interest are, for example, sodium hydride, potassium hydride, calcium hydride, lithium aluminum hydride, aluminum hydride, sodium cyanoborohydride, sodium borohydride or diisobutylaluminum hydride. Preferred hydrides are sodium borohydride, sodium cyanoborohydride and diisobutylaluminum hydride. Of special interest is a process for the preparation of a compound of formula I wherein the reducing agent is sodium borohydride.

Advantageously, the reducing agent is used in an amount of 0.02 to 10% by weight, especially 0.02 to 1% by weight, for example 0.07 to 0.5% by weight, based on the weight of the compound of formula I. The reaction step with a reducing agent can conveniently be carried out on the temperature scale of 20 ° C to 200 ° C, preferably from 40 ° C to 150 ° C, and more preferably, from 60 ° C to 100 ° C. The reaction step with a reducing agent can be carried out in the presence of a solvent. Examples of suitable solvents are the same as those mentioned above for the reaction of the compound of formula II with formaldehyde and a compound of formula III. It is preferred, however, to carry out the reduction step with a reducing agent in the absence of a solvent. After cooling to room temperature, the reaction mixture is worked by conventional separation and purification methods. Compounds of formula I prepared by the process of this invention can be used as stabilizers to protect organic materials from damage by the action of oxygen, heat, light or high-energy radiation. The preferred utility of these compounds is as antioxidants in organic polymers and in elastomers, or in mineral oils or synthetic lubricants.

The stabilizers are usually added to the organic materials in a concentration of 0.01 to 10% by weight, preferably 0.05 to 5.0% by weight, more preferably 0.1 to 2.0% by weight based on the organic material to be stabilized. The incorporation of the compounds of the formula I can be effected, for example, by mixing them with the material to be stabilized together with additional optional additives by methods conventionally employed in the medium, before or during the manufacture of shaped articles of the polymer, or also by applying the compound dissolved or dispersed to the polymer, with or without subsequent evaporation of the solvent. The compounds of the formula I can also be added to the materials to be stabilized in the form of a masterbatch containing the compounds, for example, in a concentration of 2.5 to % by weight. In the case of crosslinkable polyethylene, the compounds are added before crosslinking. In practice, the compounds of the formula I are added together with other stabilizers. The compounds of formula I are preferably added to a rubber or latex cement after polymerization but before coagulation. The lubricant formulations may also contain extra additives that are added to improve certain usage properties, for example additional antioxidants, metal deactivators, corrosion inhibitors, viscosity index improvers, pour point depressants, dispersants / surfactants and antiwear additives. The following examples illustrate the invention in more detail. Parts or percentages refer to weight.

Example 1: Preparation of 2,4-bis (n-octylthiomethyl) -6-methylphenol. a) In a 1 liter reactor, 84.2 g (2.81 mol) of para-formaldehyde, 134.9 g (1.25 mol) of o-cresol and 369.3 g (2.52 mol) of octantiol were charged. "Then 9.9 g (0.22 mol) of dimethylamine were added in. The temperature was then increased to 130 ° C before one hour, the temperature was maintained at 130 ° C for 3.5 hours, the volatile components were then removed at a bath temperature. 90-95 ° C under reduced pressure to give crude 2, 4-bis (n-octylthiomethyl) -6-methylphenol b) In a 500 ml flask, 390 g (0.92 mol) of 2-4 were mixed crude bis (n-octylthiomethyl) -6-methylphenol prepared according to the example with 3.25 g of a caustic solution containing 12% sodium borohydride, corresponding to 0.39 g (0.01 mol) of sodium borohydride. The mixture was heated at 90 ° C for 7 hours, then the reaction mixture was extracted with acetic acid and water.The volatile components were then removed at a bath temperature of 90-95 ° C under reduced pressure to give 380 g of 2, 4. bis (n-octylthiomethyl) -6-methylphenol.

Example 2: Preparation of 2,4-bis (n-octylthiomethyl) -6-methylphenol Into a 500 ml flask, 410 g (0.97 mol) of crude 2,4-bis (n-octylthiomethyl) -6-methylphenol prepared according to the example were mixed with 17 g of a caustic solution containing 12 g. % sodium borohydride; which corresponds to 2.04 g (0.05 mol) of sodium borohydride. The mixture was heated at 90 ° C for 7 hours. Then, the reaction mixture was extracted with acetic acid and water. The volatile components were then removed at a bath temperature of 90-95 ° C under reduced pressure to give 400 g of 2,4-bis (n-octylthiomethyl) -6-methylphenol.

Example 3: Preparation of 2,4-bis (n-octylthiomethyl) -6-methylphenol Into a 500 ml flask, 390 g (0.92 mol) of crude 2,4-bis (n-octylthiomethyl) -6-methylphenol prepared in accordance with Example 1 were mixed with 1 g (0.026 mol) of sodium borohydride. sodium. The mixture was heated at 90 ° C for 7 hours. Then, the reaction mixture was filtered and extracted with acetic acid and water. The volatile components were then removed at a bath temperature of 90-95 ° C under reduced pressure to give 380 g of 2,4-bis (n-octylthiomethyl) -6-methylphenol.

Example 4: Discoloration of mercaptomethylphenols in an alkaline environment.

Several rubbers were polymerized in aliphatic organic solvents using n-butyl lithium as a catalyst / initiator (anionic polymerization). After decomposition of the catalyst by means of water, lithium hydroxide is formed as the transition product. Thus the rubber cement is very alkaline as well as the water of the rubber coagulation system. The phenolic antioxidants are partially transformed under such conditions into the corresponding phenolates. Some of these phenolates or phenolate derivatives have a yellow or orange color. This discoloration leads to a yellow colored rubber instead of white colorless water. The tendency to discoloration can be determined by a direct reaction of the phenolic antioxidant with the butyl-lithium polymerization initiator. For this purpose 0.1 mmol of n-butyl lithium in the form of a 10% solution in n-hexane was added to an equivalent amount of 2,4-bis (n-octylthiomethyl) -6-methylphenol dissolved in 100 ml of n-hexane.

As an alternative method, a sodium methylate treatment can be used to avoid the use of lithium butyl. 0.5 g of 2,4-bis (n-octylthiomethyl) -6-methylphenol were dissolved according to examples la, Ib, 2 and 3 in 50 ml of methanol; 0.5 g of a 10% solution of NaOCH3 in methanol was added. The transmission of these solutions was measured at 300-500 nm using the Shimadzu UV-2100 UV-visible recording spectrophotometer. the greater the transmission in%, the better the quality of the stabilizer. The results are summarized in table 1. The discoloration can also be determined by measuring the yellowness index. In this case, the sodium methoxide method with an amount of 2.5 g 2, 4-bis (n-octylthiomethyl) -6-methylphenol was used instead of 0.5 g. The yellowness index (Yl) of the samples was determined in accordance with ASTM D 1925-70. Low Yl values denote little discoloration, high values of Yl denote severe discoloration of the samples. The lower the discoloration, the more effective the stabilizer. The results are compiled in table 1.

Table 1; a) Example of comparison. b) Examples of this invention.

Claims (9)

1. An improved process for the preparation of a compound of the formula I characterized in that n is 0 or 1, Ri is alkyl with 1 to 12 carbon atoms or -CH2SR3, R2 is alkyl with 1 to 12 carbon atoms, phenylalkyl with 7 to 9 carbon atoms, phenylalkyl with 7 to 9 carbon atoms substituted on the phenyl radical by 1 to 3 alkyl groups with 1 to 4 carbon atoms; or -CH2SR3, R3 is alkyl having from 6 to 18 carbon atoms, phenyl or benzyl, R4 is hydrogen or methyl, R5 is hydrogen or methyl, with the proviso that R4 and R5 are not simultaneously methyl, reacting a compound of the formula II wherein n, R 4 and R 5 are as previously defined, R n is hydrogen or alkyl having from 1 to 12 carbon atoms; and R12 is hydrogen, alkyl having from 1 to 12 carbon atoms, phenylalkyl having from 7 to 9 carbon atoms, phenylalkyl having from 7 to 9 carbon atoms substituted on the phenyl radical with from 1 to 3 alkyl groups with from 1 to 4 carbon atoms, with formaldehyde or a compound that releases formaldehyde under the reaction conditions and with at least one compound of formula III R3SH (III) wherein R3 is as previously defined, in the presence of a base, the base being mono- or dimethylamine or mono- or diethylamine, wherein the process comprises treating the reaction product then with a reducing agent.

2. A process according to claim 1, characterized in that n is 0 or 1, Ri is alkyl with 1 to 4 carbon atoms or -CH2SR3, R2 is alkyl with 1 to 4 carbon atoms, phenylalkyl with 7 to 9 carbon atoms, phenylalkyl with 7 to 9 carbon atoms substituted on the phenyl radical by a methyl group, R3 is alkyl with 6 to 12 carbon atoms, R is hydrogen or methyl, R5 is hydrogen, R11 is hydrogen or alkyl with 1 to 4 carbon atoms; and R 2 is alkyl with 1 to 4 carbon atoms, phenylalkyl with 7 to 9 carbon atoms, phenylalkyl with 7 to 9 carbon atoms substituted on the phenyl radical by a methyl group.

3. A process according to claim 1, characterized in that, n is 0, Ri is -CH2SR3, R2 is alkyl with 1 to 4 carbon atoms, R3 is alkyl with 8 to 12 carbon atoms, R4 is hydrogen , Rs is hydrogen, Rn is hydrogen; and R 2 is alkyl with 1 to 4 carbon atoms.

4. A process according to claim 1, characterized in that the base is dimethylamine.

5. A process according to claim 1, characterized in that 1 to 50 mol% base is used, based on the compound of formula III.

6. A process according to claim 1, characterized in that the reducing agent is a hydride.

7. A process according to claim 6, characterized in that the hydride is sodium borohydride.

8. A process according to claim 1, characterized in that the amount of reducing agent is 0.02 to 10% by weight based on the weight of the compound of the formula I.

9. A process according to claim 1, characterized in that the reaction is carried out in the absence of a solvent.