LIQUID HYDROQUINOLINE-TYPE ANTIOXYDANTS

Abstract: Condensation of acetone with a mixture comprising aniline and a C₃₋₁₅ alkylaniline and/or a C₁₋₁₂ alkoxyaniline produces a novel antioxidant for rubber. The antioxidant is in liquid form for convenience of handling.

Description: LIQUID HYDROQUINOLINE-TYPE ANTIOXIDANTS BACKGROUND OF THE INVENTION This invention relates to antioxidants for rubber, of the type known generally as hydroquinolines, which antioxidants are usually prepared, in part, by the condensation with acetone of aniline or a substituted aniline. Typical of the known materials of this type are oligomers of 1,2-dihydro-2,2,4-trimethylquinoline, produced and sold under a number of tradenames. Such oligomers are usually prepared by first condensing acetone and aniline and then subjecting the condensate to polymerization conditions. Typically, the final product is a solid mixture of dimer, trimer and tetramer, together with small amounts of monomer and higher polymers. Another similar known antioxidant material is 6-dodecyl-1,2-didydro-2,2,4-trimethylquinoline, which can be prepared by condensation of acetone with 4-dodecylaniline. The condensate is a liquid, and does not tend to polymerize. Still another similar known hydroquinoline antioxidant material is 6-ethoxy-1,2-dihydro-2,2,4trimethylquinoline, which can be prepared by condensation of acetone with p-phenetidine (4-ethoxyaniline). This condensate is also a liquid, with little tendency to polymerize. While the oligomerized product of the condensation of acetone and aniline is an effective and widely used product, its form has caused difficulties in use. Handling of solid ingredients in the preparation of rubber compounds can be a problem if the solid ingredients tend to dust, to cake, to pack, or to present other handling difficulties. In many instances, liquid forms of compounding ingredients are preferred, since liquids can be directly and automatically metered into an internal mixer, thus enabling precise control of amounts and avoiding the handling problems often associated with solid ingredients. If, in the preparation of acetone-aniline condensates, the oligomerization step, above, is omitted, a liquid "monomeric" material can be obtained, but this material is usually too volatile to be an effective antioxidant. SUMMARY OF THE INVENTION It is an object of this invention to provide an improved rubber antioxidant of the hydroquinoline type, which antioxidant is in a stable liquid form at normal storage and handling temperatures, is not excessively volatile and provides antioxidant protection to the rubber equivalent to that obt'ained using solid, oligomeric l,2-dihydro-2 , 2 ,4-trimethyl- quinoline. This object is obtained using an antioxidant which is the product of the condensation of acetone with a mixture comprising aniline and a C3 15 alkylaniline and/or a C1-12 alkoxyaniline. The mixture of aniline and substituted aniline can contain from 1 to 99 mole percent of aniline, but at 99% aniline the product is relatively volatile unless it is polymerized, and the polymerized product is too viscous to be easily handled. At 1% aniline, the properties of the antioxidant are difficult to differentiate from those of the known alkyl-substituted or alkoxy-substituted hydroquinoline antioxidants. Preferred is a material made from 25 to 75 mole percent aniline, the remainder being an alkylaniline or an alkoxyaniline as defined above, condensed with acetone. Materials within these limits exhibit good antioxidant activity and are fluid at room temperature. Preferred alkylanilines are either single compounds, such as E-dodecylaniline, or mixtures of alkyl-substituted aniline compounds within the three-to-fifteen carbon range. The alkyl substituents can be straight chain or branched chain, and can be in the ortho, meta or para position. More preferred are the para-alkylanilines. Preferred alkoxyanilines are ortho-, meta-, or para-substituted lower alkoxy anilines. By "lower" is meant that the alkoxy groups have 1-3 carbon atoms. Especially preferred are para-alkoxy compounds, most especially -phenetidine and E-anisidine. The condensation reaction is performed at any suitable temperature, depending on the desired speed of the reaction, but is preferably performed at from 1000 to 1800C. An appropriate catalyst can be employed to promote the condensation, and an acid, such as toluene sulfonic acid or HCl is most effective for this purpose. In view of the fact that simple blends of the oligomeric 1, 2-dihydro-2 , 2, 4-trimethylquinoline with 6-dodecyl-1,2-dihydro-2,2,4-trimethylquinoline or 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline set up solid after a short time it was quite unexpected that the materials of the invention remained fluid and easy to handle. DETAILED DESCRIPTION EXAMPLE I To a three-neck round-bottom flask having a thermometer well and fitted with a distillation column are charged 32.7 g (0.125 mole) dodecylaniline, 11.6 g (0.125 mole) aniline and 2.4 g (0.025 mole, 10 mole %) concentrated hydrochloric acid. (The dodecyl aniline is actually a mixtue of C8 15 alkylated anilines which contains 45% C12, 15% C11 and 12% C13 anilines.) This mixture is heated to 1400C, and acetone is introduced below the liquid surface at the rate of about 10 ml/min. The temperature is maintained at 1400 i 2 and addition is continued for 12 hours. At the end of this period, heating is continued for 15 minutes to drive off any remaining acetone. The contents of the flask are diluted with about 100 ml toluene, then washed with dilute NaHCO3 until the pH of the aqueous layer is 8.5. The organic layer is then separated and dried (with Na2SO4), and concentrated by driving off the toluene. A viscous brown oil is recovered. G. C. analysis of the oil indicates 58% 6-dodecyl-1,2-dihydro-2,2,4-trimethyl- quinoline and 6% dodecyl aniline; the remainder is presumed to be monomeric or oligomeric 1,2-dihydro-2,2,4-trimethylquinoline. EXAMPLE II The product of Example I is tested for its activity as an antioxidant in rubber, using a truck tire carcass stock based on the following masterbatch: MATERIAL PARTS BY WEIGHT Natural Rubber - SMR 5 CV 80.0 Polybutadiene - Cis-4 BR 1203 20.0 Carbon Black - N550 50.0 Processing Oil - Sundex 790 12.0 Zinc Oxide 3.0 Stearic Acid 2.0 Resin - Piccopale 100 SF 5.0 TOTAL 172.0 This masterbatch is then mill-mixed, adding sulfur, accelerator (N-2-bxydiethylene-2-benzothiazylsulfenamide) and antioxidant as shown in Table I. Compared are commercial antioxidants FLECTOLE H (polymerized 1,2-dihydro-2,2,4-trimethylquinoline) and SANTOFLEXe DD (6-dodecyl-1,2-dihydro-2,2,4trimethylquinoline). The stocks, containing varying types and amounts of antioxidants are tested for physical properties, as shown in Table I. The tensile and elongation measurements are made in the conventional manner. Fatigue-to-failure tests are made using the Monsanto Fatigue-to-Failure Tester, with dumbbell samples flexed at 100 cycles per minute at an extension of 90%. The physical test data in Table I show that the antioxidant of the invention has activity comparable to the known antioxidants. EXAMPLE III To investigate the properties of a simple blend of dihydroquinoline antioxidants, two mixtures are made.. Blend A contains equal parts by weight of polymerized 1 ,2-dihydro-2 , 2, 4-trimethylquinoline and 6-dodecyl-1,2-dihydro-2,2,4-trimethylquinoline. Blend B contains two parts by weight of the former per 1 part of the latter. Each blend is physically combined, then heated to 1600-1700C with stirring, to form a homogeneous liquid mixture. The blends are cooled to room temperature, and are found to have solidified after a week. STOCK A B C D E F G H Masterbatch 172.0 # Insoluble Sulfur 60 2.2 # Accelerator 1.2 # FLECTOL# H - 1.5 - - 3.0 - - 1.5 SANTOFLEX# DD - - 1.5 - - 3.0 - 1.5 Antioxidant of Example I - - - 1.5 - - 3.0 Physical Properties Aged 72 Hours # 100 C %Retention of Tensile 58 78 77 69 81 78 79 81 %Retention of Elongation 49 63 63 57 66 68 64 70 Aged 15 Days # 70 C %Retention of Tensile 91 95 98 99 95 97 95 100 %Retention of Elongation 82 83 83 89 81 84 82 90 Fatigue-to-Failure, Kilocycles to Failure . Unaged 71 92 86 84 93 105 98 99 Aged 24 Hrs. # 100 C 41 55 61 57 70 64 71 81 EXAMPLE IV In a manner similar to that of Example I, equimolar amounts of aniline and p-phenetiline are condensed with acetone. The resultant dark brown oily liquid remains fluid on standing. G. C. analysis gave the following: 33.2% Oligomeric 1,2-dihydro-2,2,4-trimethylquinoline 33.6% 6-Ethoxy-1,2-dihydro-2,2,4-trimethylquinoline 11.8% p-Phenetidine 8.7% Monomeric 1,2-dihydro-2,2,4-trimethylquinoline Although the invention has been illustrated by typical examples, it is not limited thereto. Changes and modifications of the examples of the invention herein chosen for purposes of disclosure can be made which do not constitute departure from the spirit apt scope of the invention.

Claims: CLAIMS 1. The product of the condensation of acetone with a mixture comprising aniline and A) a C3-15 alkylaniline or B) a c112 alkoxyaniline. 2. The product of Claim 1 wherein the mixture contains from 25 to 75 mole percent aniline. 3. The product of Claim 2 wherein the mixture is aniline and dodecylaniline. 4. The product of Claim 2 wherein the mixture is aniline and phenetidine. 5. The product of Claim 1 wherein the condensation is performed in the presence of an acidic catalyst at a temperature of from 1000 to 1800C. 6. The product of Claim 5 which is further heated to form oligomers. 7. The product of Claim 5 wherein the catalyst is hydrochloric acid or toluenesulfonic acid. 8. The product of Claim 1 wherein the mixture contains both a C3¯15 alkylaniline and a Cl¯l2 alkoxyaniline. 9. The product of the condensation, in the presence of HCl at a temperature of from 1000 to 1800C, of acetone with a mixture of aniline and a C3-15 alkylaniline, wherein the mixture contains from 25 to 75 mole percent aniline.

Inventors: EVANS, DAVID LANE, MERTEN, HELMUT LUDWIG
Applicants: MONSANTO COMPANY
Application year: 1984
Main classification: C08K5
IPC codes: C08K5, C07D215