CA1098542A - Substituted diphenylamines - Google Patents

Abstract

Abstract of the Disclosure Mono and disubstituted diphenylamines, wherein one or both of the substituents are an R-thiomethyl moiety, are produced by a reaction of thiols, formaldehyde, and a di-phenylamine in the presence of an acid. These compounds are antioxidants in rubber compounds.

Description

BACKGROUND OF THE INVENTION
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 compo-sitions formed by mixing these materials with polymers.
Disubsti-tuted diphenylamines are the subject of several United States patents: 3,368,975; 3,781,361; and 31925,215. These patents discuss their usefulness as anti-oxidants 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 condi-tions in the presence of a Friedel-Crafts condensation cata-lyst at atmospheric pressure is disclosed in British Pa-tent 1,143,250.
The one-s-tep acid catalyzed reaction between thiols, formaldehyde, and aromatic amines is shown in the prior art, see Lau and Grillot~ J. Or~. Chem., 28, 2763-2765 (1963);
J. Or~. Chem., 30, 28-33 (1965); and Grillot and Schaffrath, ~ _5~ , 24, 1035-1038 (1959).
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SUMMARY OF THE INVENTION
The present in~ention has as its objects: (1) to provide a new type of diphenylamine for the protection of polymers against degradation b~y oxygen; (2) to provide poly-mers stabilized against oxygen attack; and (3) to provide a process of preparing said diphenylamines.
Other ob~ects will become apparent as the descrip-tion proceeds.
The invention pertalns to compounds having the fol---1- ~

lowing for]nula;
~ R2 R -S-CH2 ~ ~ ~ NH ~ ~ = R

R R
wherein Rl is selected from the group consisting o~ n-octyl, n-dodecyl, chloro-phenyl, and phenyl; R2 and R3 are selected from the group consisting of H, alkyl radicals (1-6C) 9 aralkyl radicals (7-llC), halogen radicals, and acyl radicals (2-lOC); and R is selected from the group consisting of H, 4-(p-chlorophenylthiomethyl), 4-phenyl-thiomethyl, 4-(n dodecylthiomethyl) and 4-(n-octylthiomethyl). R2 and R3, when they are aralkyl radicals, can be, for example, benzyl, p-chloro-benzyl, p-vinyl-benzyl, p-carbomethoxybenzyl, p-hydroxy-benzyl, or p-n-hexoxybenzyl.
In another aspect, the present invention provides a process for making the compound defined above, said process comprising: mixing a thiol, formal-dehyde, a diphenylamine and an acid in an alcohol solvent, refluxing, cooling the mixture and adjusting its pH to permit t:he separation of the reaction pro-duct for purification where the thiol is se]ected from the group consisting of n-octene thiol, n-dodecene thiol, p-(chloro) thiophenol, and thiophenol, and the diphenylamine has the structure ~ ~ - NH -Preferably the solvent is selected from the group consisting of methanol, ethanol, l-propanol, and l~butanol, and the reflux ~ime is 20 to 24 hours.
The acid may be added after refluxing has been in progress for ap~
proximately 1 to 3 hours.
Preferably equivalent mole amounts o thiol, ~ormaldehyde and a diphenylamine are used and the amount of acid used is equimolar with the diphenylamine.

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

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DESCRIPTION OF THE PREFERRED EMBODIMENTS
The compounds as shown in the previously given structural formula may be prepared by the acid catal~zed reaction between a suitable thiol, formaldehyde and di-phenylamine in an alcohol solution. Since diphenylamine has two equivalent aroma-tic rings, substitution can occur at either or both 4 or 4' positions~ The reaction product can therefore be either mono or di-substi-tuted. If equiva-lent mole amounts of thiol, formaldehyde, and diphenylamine are used, then mono-substitution predominates. If disub-stitution is desired, then the molar ratio of formaldehyde to thiol to diphenylamine should be 2:2~ other mix-tures of mono and di-substitution are desired, then other mole ratios may be used.
The ingredients are mixed and refluxed for a cer-tain period normally varying between five minutes to 24 hoursO The best reflux times are normally from 20 to 24 hours.
A~ter sufficient refluxing, the reaction mixture is cooled and its pH is ad~justed to basic under which condi-tions the product m~y be separa-ted and thereafter purified.
The three reactants and acid may be mixed at the same time or the acid may be added some time after reflux-:
ing of the reaction mixture has started. A preferred me-thod 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:

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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 di-phenylamine 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 re~lux -temperature for each is given in Table 2.
Table 2 AlcoholReflux Temperature 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 in~ention: -1. 4- n-octylthiomethyl~ diphenylamine;
2.~4- n-dodecylthiomethyl) diphenylamine;

3. 4- p-chlorophenylthiomethyl) diphenylamine;

4. 4- phenylthiomethyl) diphenylamine;

5. 4, '-bis(para-chlorophenylthiomethyl) diphenyl-amine;

6. 4~4'-bis~phenylthiomethyl) diphenylamine;

7. 4,4'-bis~n-dodecylthiometh~l) diphenylamine; and &. 4,4'-bis(n-octylthiomethyl) diphenylamine.
All o~ the above compounds l through 8 have been synthesized.
The following working examples illustrate but do f~

not limit the process for preparation of -the compounds of this invention. Unless otherwise stated, percentages are weight percen-t and parts are parts by weightO
EXAMPLE I
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A mixture of 16~ grams (1 mole) diphenylamine, 110 grams (1.0 mole) of benzenethiol, and 81 grams of 37 percent ~ormalin (1 mole) was prepared in 400 milliliters of 95 per-cent ethanol. This was re~luxed ~or two hours. At the end of this period, 90 millili-ters of concentrated HCl was added.
me reflux was continued for 22 hours, and then the mixture was cooled in ice, A saturated solution of potassium hydro-xide in water was added until the reaction mixture was ren-dered basic. An oil formed and -this was extracted with 300 milliliters of chloroform. The chloro~orm solution was col-lected and dried over sodium sul:Eate. This was then ~lashed in vacuo and 258 grams dark oil remained. This amounted to 88.7 percent o~ theoretical yield and was used as is without ~urther puri~ication~
EXAMPLE II
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A mixture o~ 146 gr~ms (1 mole) of n-octanethlol, 169 grams (1 mole) o~ diphenylamine, and 81 grams o~ 37 per-cent formalin (1 mole) was prepared in 500 milliliters o~ 95 percent ethanol. To this was added 90 milliliters of concen-trated HCl. The resulting solution was refluxed ~or 24 hours~
This was cooled to room temperature and saturated KOH solu- -tion 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 ~13 grams of product as an oil (95.7 percen-t of theoretical yield).
EXAMPLE III
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A mixture of 110 grams (1 mole) of benzene-thiol, 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 o~
concentrated HCl. me resulting mixture was reMuxed 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 chloro~orm solution was extracted with KOH
(10 percent) 500 millili-ters and 1;hen washed with water (1000 milliliters). The chloroform was then dried over sodium sul-~ated and ~lashed off in vacuo. A thick brown tar remained and amounted to 183 grams (88.4 percent o~ theoretical yield)~
Polymers that may be protected by the compounds des-cribed herein are vulcanized and unvulcanized polymers sus-ceptible 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 o~ antioxidant to be used depends upon the particular polymer and conditlons to which it - is exposed, generally the amount employed for antioxidant and antiozonant purposes ~aries between 0.1 and 10 parts per 100 parts of polymer. The pre~erred range for use is 1 to 4 parts per 100 parts o~ rubber.

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The following experimental data is presented to illus-trate and not to limit the use of the compounds of the present in~ention.
Compounds 1 through 7 were each used to stabilize an SBR polymer (1006) by addition to a benzene solution of SBR-1006 at a concentration of one par-t 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 ~urther detail in Industrlal and Engineer-ing Chemistry, Vol. 43, page 456 (1951) and Industrial and En ne r~ Chemistr~, Vol. 45, p. 392 (1953).
Hours to Absorb 1% Oxygen at 100C.
Compound _ SBR-1006 4 631.5 Commercial Antioxidant ~1 ~84 Commercial Antioxidant #2 366 Had no antioxidant been present, the SBR would have absorbed 1.0% 2 in 5 to 10 hours.
While certain representative embodiments and de-tails have been shown for the purpose of illustrating the in-vention, it will be apparent to -those skilled in -this art that various changes and modi~ications may be made therein - without departing from the spirit or scope of the invention~

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Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A compound having the following structural wherein R1 is selected from the group consisting of n-octyl, n-dodecyl, chlorophenyl, and phenyl; R2 and R3 are selected from the group consisting of H, alkyl radicals (1-6C), aralkyl radicals (7-11C), halogen radicals, and acyl radicals (2-10C); and R4 is selected from the group consisting of H, 4-(p-chlorophenylthiomethyl), 4-phenyl-thiomethyl, 4-(n-dodecylthiomethyl) and 4-(n-octylthio- .
methyl).

2. A process for making the compound of claim l, said process comprising: mixing a thiol, formaldehyde, a diphenylamine and an acid in an alcohol solvent, refluxing, cooling the mixture and adjusting its pH to permit the separation of the reaction product for purification where the thoil is selected from the group consisting of n-octene thiol, n-dodecene thiol, p-(chloro) thiophenol, and thiophenol, and the diphenylamine has the structure .

3. The process of claim 2 in which the solvent is selected from the group consisting of methanol, ethanol, l-propanol, and l-butanol, and the reflux time is 20 to 24 hours.

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

5. The process of claim 4 in which equivalent mole amounts of thiol, formaldehyde and a diphenylamine are used.

6. The process of claim 3 in which the amount of acid used is equimolar with the diphenylamine.

7. The compound of claim 1 which is 4,4'-bis-(parachlorophenylthiomethyl) diphenylamine.