GB1596594A

GB1596594A - Substituted diphenylamines

Info

Publication number: GB1596594A
Application number: GB15849/78A
Authority: GB
Original assignee: Goodyear Tire and Rubber Co
Current assignee: Goodyear Tire and Rubber Co
Priority date: 1977-06-06
Filing date: 1978-04-21
Publication date: 1981-08-26
Also published as: IT7849424A0; IT1104836B; CA1098542A; BR7803543A; DE2820949A1; JPS543028A; FR2393790A1

Description

(54) SUBSTITUTED DIPHENYLAMINES (71) We, THE GOODYEAR TIRE & RUBBER COMPANY, a Corporation organised under the laws of the State of Ohio, United States of America, of 1144 East Market Street, Akron, Ohio, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to new antioxidants which are derivatives of diphenylamine. It also relates to methods for preparation and use of these materials and to the compositions formed by mixing these materials with polymers.

Disubstituted diphenylamines are the subject of several United States patents: 3,368,975: 3,781,361; and 3,925,215. These patents discuss their usefulness as antioxidants in polymers having low olefinic unsaturation, such as polypropylene and in lubricants.

The preparation of mono- and di-alkyl-diphenylamines by reacting diphenylamine with an alkene under reflux conditions in the presence of a Friedel Crafts condensation catalyst at atmospheric pressure is disclosed in British Patent 1,143,250.

The one-step acid catalyzed reaction between thiols, formaldehyde, and aromatic amines is shown in the prior art, see Lau and Grillot, J. Org. Chem., 28, 2763-2765 (1963): J. Org. Chem., 30, 28-33 (1965); and Grillot and Schaffrath, J.

Org. Chem., 24, 1035-1038 (1959).

The present invention has as its objects; (1) to provide a new type of diphenylamine for the protection of polymers against degradation by oxygen; (2) to provide polymers stabilized against oxygen attack; and (3) to provide a process of preparing said diphenylamines.

Other objects will become apparent as the description proceeds.

The invention pertains to compounds having the following formula:

wherein R' is selected from normal alkyl radicals having 1 to 24 carbon atoms (124 C), aryl radicals (6-10 C), monosubstituted normal alkyl radicals (1--24 C), monosubstituted aryl radicals (6-10 C), and aralkyl radicals (7-11 C); R2 and R3 are selected from H, alkyl radicals (1--6 C), aralkyl (7-11 C) radicals, halogen radicals and acyl radicals (2-10 C); and R4 is selected from H and (-CH2-S- Era).

The term "monosubstituted" as used herein means having attached thereto a radical selected from Cl, Br, OH, CN, carbomethoxy and carboethoxy. R', when it is a substituted alkyl radical, can be, for example, (2-cyano) ethyl, 2-hydroxyethyl, carbomethoxyethyl or carboethoxvmethvl. Rh R2 and R3. when thev are aralkyl radicals, can be, for example, benzyl, p-chlorobenzyl, p-vinyl-benzyl, pcarbomethoxybenzyl, p-hydroxybenzyl, or p-n-hexoxybenzyl. R1, when it is an aryl radical, may for example be p-tolyl or p-tert.butylphenyl. R', when it is a F substituted aryl radical, can be, for example, p-bromophenyl, p-hydroxyphenyl, pmethoxyphenyl, p-ethoxyphenyl, chlorophenyl (e.g. p-chlorophenyl) or carboethoxyphenyl.

The compounds of this invention are useful for the protection of polymers against oxidative degradation. They are unusually persistent because of their low volatility.

The compounds as shown in the previously given structural formula may be prepared by the acid catalyzed reaction between a suitable thiol, formaldehyde and a suitable diphenylamine in an alcohol solution. Since a diphenylamine has two equivalent aromatic rings, substitution can occur at either or both 4 or 4' positions.

The reaction product can therefore be either mono or di-substituted. If equivalent mole amounts of thiol, formaldehyde, and diphenylamine are used, then monsubstitution predominates. If disubstitution is desired, then the molar ratio of formaldehyde to thiol to diphenylamine should be 2:2:1. If other mixtures of mono and di-substitution are desired, then other mole ratios may be used.

The ingredients are mixed and refluxed for a certain period normally varying between five minutes to 24 hours. The best reflux times are normally from 20 to 24 hours.

After sufficient refluxing. the reaction mixture is cooled and rendered alkaline under which conditions the product may be separated and thereafter purified.

The three reactants and acid may be mixed at the same time or the acid may be added some time after refluxing of the reaction mixture has started. A preferred method is that in which the acid is added after refluxing has been in progress. The preferred time for refluxing prior to acid addition is approximately 1 to 3 hours.

Examples of the thiols which can be used in this preparation are: n-octane thiol, n-dodecane thiol, p-(chloro)thiophenol, thiophenol, n-hexanethiol, p-(tert.butyl)thiophenol, p-(methyl)thiophenol, benzyl mercaptan, 2-cyanoethanethiol.

The acids which may be used are those having an available hydrogen and are illustrated by but not limited to hydrochloric acid, sulfuric acid and hydrobromic acid. The preferred amount of acid is an amount equimolar with the diphenylamine. However, the molar ratio of acid to diphenylamine can range from 1/1 or less to 5/1 or more. The criteria is that the reaction media is acidic.

The alcohols which have been used, along with the reflux temperature for each is given in Table 2.

TABLE 2 Reflux Temperature Alcohol in "C Methanol 64.9 Ethanol 78.5 l-Propanol 97.1 l-Butanol 117.5 The following list of compounds illustrates but does not limit the compounds of this invention: 1. 4-(n-octylthiomethyl) diphenylamine; 2. 4-(n-dodecylthiomethyl) diphenylamine; 3. 4-(p-chlorophenylthiomethyl) diphenylamine; 4. 4-(phenylthiomethyl) diphenylamine; 5. 4,4'-bis(para-chlorophenylthiomethyl) diphenylamine; 6. 4,4'-bis(phenylthiomethyl) diphenylamine; 7. 4,4'-bis(n-dodecylthiomethyl) diphenylamine; and 8. 4,4'-bis(n-octylthiomethyl) diphenylamine.

All of the above compounds 1 through 8 have been synthesized.

The following working examples illustrate but do not limit the process for preparation of the compounds of this invention. Unless otherwise stated, percentages are weight percent and parts are parts by weight.

Had no antioxidant been present, the SB R would have absorbed 1.0 ,ö O2 in 5 to 10 hours.

WHAT WE CLAIM IS: 1. A compound having the following structural formula:

wherein R' is selected from normal alkyl radicals having 1 to 24 carbon atoms (124 C), aryl radicals (6-10 C), mono-substituted normal alkyl radicals (1--24 mono-substituted aryl radicals (6-10 C), and aralkyl radicals (7oil C); R2 and R3 are selected from H, alkyl radicals (1--6 C), aralkyl radicals (7-11 C), halogen radicals, and acyl radicals (2-10 C); and R4 is selected from H and -CH2-S- R1.

2. The compound of Claim 1, wherein R' is selected from n-octyl, n-dodecyl, p-chlorophenyl, and phenyl; and R4 is selected from hydrogen, 4-(pchlorophenylthiomethyl), 4-phenylthiomethyl, 4-(n-dodecylthiomethyl) and 4-(noctylthiomethyl).

3. A process for making the compound of Claim 1, said process comprising: mixing a thiol, formaldehyde, a diphenylamine and an acid in an alcohol solvent, refluxing, cooling the mixture and rendering it alkaline to permit the separation of the reaction product for purification where the thiol has the structure R'SH and the diphenylamine has the structure

4. The process of Claim 3 in which the solvent is selected from methanol, ethanol, I-propanol, and l-butanol, and the reflux time is 20 to 24 hours.

5. The process of Claim 4 in which the acid is added after refluxing has been in progress for approximately 1 to 3 hours.

6. The process of Claim 5 in which equivalent mole amounts of thiol, formaldehyde and a diphenylamine are used.

7. The process of Claim 4 in which the amount of acid used is equimolar with the diphenylamine.

8. A polymer selected from natural rubber, polyisoprene rubber, and styrene butadiene rubber having incorporated therein a compound of Claim 1.

9. The polymer of Claim 8 having incorporated therein I to 4 parts by weight of a compound of Claim 1 per 100 parts of rubber.

10. The polymer of Claim 9 having incorporated therein a compound of Claim 2.

EXAMPLE I 4-(Phenylthiomethyl) Diphenylamine A mixture of 169 grams (1 mole) diphenylamine, 110 grams (1.0 mole) of benzenethiol, and 81 grams of 37 percent formalin (1 mole) was prepared in 400 milliliters of 95 percent ethanol. This was refluxed for two hours. At the end of this period, 90 milliliters of concentrated HCI was added. The reflux was continued for 22 hours, and then the mixture was cooled in ice. A saturated solution of potassium hydroxide in water was added until the reaction mixture was rendered basic. An oil formed and this was extracted with 300 milliliters of chloroform. The chloroform solution was collected and dried over sodium sulfate. This was then flashed in vacuo and 258 grams dark oil remained. This amounted to 88.7 percent of theoretical yield and was used as is without further purification.

EXAMPLE II 4-(n-Octylthiomethyl) Diphenylamine A mixture of 146 grams (1 mole) of n-octanethiol, 169 grams (1 mole) of diphenylamine, and 81 grams of 37 percent formalin (1 mole) was prepared in 500 milliliters of 95 percent ethanol. To this was added 90 milliliters of concentrated HCI. The resulting solution was refluxed for 24 hours. This was cooled to room temperature and saturated KOH solution added until basic. An oil formed which was extracted with 200 milliliters of chloroform. This was collected and dried over sodium sulfate. After flash evaporation, there remained 313 grams of product as an oil (95.7 percent of theoretical yield).

EXAMPLE III 4,4'-bis-(Phenylthiomethyl) Diphenylamine A mixture of 110 grams (1 mole) of benzenethiol, 84.5 grams (0.5 mole) of diphenylamine, 40.5 milliliters of 37 percent formalin (1 mole) was prepared in 300 milliliters of 95 percent ethanol. To this was added 45 milliliters of concentrated HCI. The resulting mixture was refluxed for 24 hours. This was then cooled in ice and rendered basic by the addition of KOH solution. A gum formed. The aqueous layer was decanted from the gum. Chloroform was added to dissolve the gum. The chloroform solution was extracted with KOH (10 percent) 500 milliliters and then washed with water (1000 milliliters). The chloroform was then dried over sodium sulfated and flashed off in vacuo. A thick brown tar remained and amounted to 183 grams (88.4 percent of theoretical yield).

Polymers that may be protected by the compounds described herein are vulcanized and unvulcanized polymers susceptible to degradation by oxygen, such as natural rubber, balata, gutta percha, and rubbery synthetic polymers such as polyisoprene and styrene-butadiene rubber.

Although the precise amount of antioxidant to be used depends upon the particular polymer and conditions to which it is exposed, generally the amount employed for antioxidant and antiozonantpurposes varies between 0.1 and 10 parts per 100 parts of polymer. The preferred range for use is 1 to 4 parts per 100 parts of rubber.

The following experimental data is presented to illustrate and not to limit the use of the compounds of the present invention.

Compounds 1 through 7 were each used to stabilize an SBR polymer (1006) by addition to a benzene solution of SB R- 1006 at a concentration of one part per 100 parts rubber. Oxygen absorption tests were made on the films obtained by evaporation of the benzene. The testing procedure is of the type described in further detail in Industrial and Engineering Chemistrv, Vol. 43, page 456 (1951) and Industrial and Engineering Chemistry, Vol. 45, p. 392 (1953).

Hours to Absorb 1% Oxygen at 1000C Compound SBR-1006 1 358 2 263 3 612 4 631.5 5 710 6 632 7 480 Commercial Antioxidant &num;1 384 Commercial Antioxidant &num;2 366

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

EXAMPLE I

4-(Phenylthiomethyl) Diphenylamine A mixture of 169 grams (1 mole) diphenylamine, 110 grams (1.0 mole) of benzenethiol, and 81 grams of 37 percent formalin (1 mole) was prepared in 400 milliliters of 95 percent ethanol. This was refluxed for two hours. At the end of this period, 90 milliliters of concentrated HCI was added. The reflux was continued for 22 hours, and then the mixture was cooled in ice. A saturated solution of potassium hydroxide in water was added until the reaction mixture was rendered basic. An oil formed and this was extracted with 300 milliliters of chloroform. The chloroform solution was collected and dried over sodium sulfate. This was then flashed in vacuo and 258 grams dark oil remained. This amounted to 88.7 percent of theoretical yield and was used as is without further purification.

EXAMPLE II

4-(n-Octylthiomethyl) Diphenylamine A mixture of 146 grams (1 mole) of n-octanethiol, 169 grams (1 mole) of diphenylamine, and 81 grams of 37 percent formalin (1 mole) was prepared in 500 milliliters of 95 percent ethanol. To this was added 90 milliliters of concentrated HCI. The resulting solution was refluxed for 24 hours. This was cooled to room temperature and saturated KOH solution added until basic. An oil formed which was extracted with 200 milliliters of chloroform. This was collected and dried over sodium sulfate. After flash evaporation, there remained 313 grams of product as an oil (95.7 percent of theoretical yield).

EXAMPLE III 4,4'-bis-(Phenylthiomethyl) Diphenylamine A mixture of 110 grams (1 mole) of benzenethiol, 84.5 grams (0.5 mole) of diphenylamine, 40.5 milliliters of 37 percent formalin (1 mole) was prepared in 300 milliliters of 95 percent ethanol. To this was added 45 milliliters of concentrated HCI. The resulting mixture was refluxed for 24 hours. This was then cooled in ice and rendered basic by the addition of KOH solution. A gum formed. The aqueous layer was decanted from the gum. Chloroform was added to dissolve the gum. The chloroform solution was extracted with KOH (10 percent) 500 milliliters and then washed with water (1000 milliliters). The chloroform was then dried over sodium sulfated and flashed off in vacuo. A thick brown tar remained and amounted to 183 grams (88.4 percent of theoretical yield).

Polymers that may be protected by the compounds described herein are vulcanized and unvulcanized polymers susceptible to degradation by oxygen, such as natural rubber, balata, gutta percha, and rubbery synthetic polymers such as polyisoprene and styrene-butadiene rubber.

Although the precise amount of antioxidant to be used depends upon the particular polymer and conditions to which it is exposed, generally the amount employed for antioxidant and antiozonantpurposes varies between 0.1 and 10 parts per 100 parts of polymer. The preferred range for use is 1 to 4 parts per 100 parts of rubber.

The following experimental data is presented to illustrate and not to limit the use of the compounds of the present invention.

Compounds 1 through 7 were each used to stabilize an SBR polymer (1006) by addition to a benzene solution of SB R- 1006 at a concentration of one part per 100 parts rubber. Oxygen absorption tests were made on the films obtained by evaporation of the benzene. The testing procedure is of the type described in further detail in Industrial and Engineering Chemistrv, Vol. 43, page 456 (1951) and Industrial and Engineering Chemistry, Vol. 45, p. 392 (1953).

Hours to Absorb 1% Oxygen at 1000C Compound SBR-1006 1 358 2 263 3 612 4 631.5 5 710 6 632 7 480 Commercial Antioxidant &num;1 384 Commercial Antioxidant &num;2 366