Liquid Antioxidant Produced by Alkylating Diphenylamine With a Molar Excess of Diisobutylene

The present invention relates to a process for the production of a liquid antioxidant composition; the product so produced and its use as a stabiliser in organic material.

It is known to produce a dark-coloured solid antioxidant composition by reacting diphenylamine with diisobutylene in the presence of aluminium chloride, as catalyst. The product so obtained contains approximately 90% by weight of di-t-octyl-diphenylamine and a total of about 10% by weight of mono-t-octyl- and mixed t-butyl-t-octyl diphenylamines.

Such solid antioxidant compositions are disadvantageous in terms of ease of handling and transportation, and readiness of incorporation into the substrate to be stabilised.

Liquid antioxidant compositions which are easily handled and incorporated, and derived from diphenylamine and olefines are also known e.g. from GB patent specification No. 1,332,201.

We have now found that, by reacting diphenylamine and diisobutylene under specific reaction conditions, we can produce a liquid antioxidant composition having outstanding antioxidant properties.

Accordingly, the present invention provides a process for the production of a liquid antioxidant composition, which process comprises reacting diphenylamine with a molar excess of diisobutylene in the presence of an activated earth catalyst, while ensuring that the concentration of diisobutylene remains substantially constant throughout the reaction period, at a reaction temperature of at least 160.degree. C., the reaction being effected for such a period that the content of 4,4'-di-t-octyl-di-phenydiphenylamine in the reaction mass, excluding catalyst, is below 25%; and removing catalyst and unreacted diisobutylene. When used in the present specification and claims, the term "t-octyl" is derived from 2,2,4-trimethyl-1-pentene and denotes 1,1,3,3-tetramethylbutyl. The reaction may be conveniently effected by charging the diphenylamine and catalyst into the reaction vessel and heating the mixture to a temperature of at least 160.degree. C., preferably at least 165.degree. C., preferably with stirring. Then the diisobutylene may be added to the hot mixture of diphenylamine and catalyst at such a rate that the temperature of the mixture does not fall below 160.degree. C., preferably not below 165.degree. C. Heating and stirring may be continued at a temperature of at least 160.degree. C., with frequent sampling, until the product, excluding catalyst, contains less than 25% by weight of 4,4'-dioctyldiphenylamine.

Experiments have shown that if the reaction is stopped at points at which the amount of 4,4-dioctyldiphenylamine in the reaction mixture is above 25% by weight, then crystals form in the product on standing. The diphenylamine content of the reaction mixture quickly falls to below 10% by weight, moreover below 5% by weight and remains at this low level during the course of the reaction. Any conventional technique may be employed for effecting contact between a hot liquid reaction mixture and a liquid reactant boiling below the temperature of the hot liquid reaction mixture. Although conventional methods such as gravity feed of the diisobutylene below or close to the surface of the reaction mixture is a satisfactory technique, it is preferred to use a temperature-regulated metering pump in order to introduce the diisobutylene reactant. The temperature at which the process of the invention is effected is at least 160.degree. C. and may be considerably higher e.g. up to 250.degree. C. To reduce degradation risks, the maximum temperature used is usually about 190.degree. C.

The time over which the diisobutylene reactant may be added to the hot mixture of diphenylamine and catalyst can vary over a wide range depending on the reaction temperature but is usually within the limits of 3 to 30 hours.

The molar ratio of diphenylamine to diisobutylene can also vary widely but is kept within the range of from 1:1.11 to 1:2.5 preferably from 1:1.3 to 1:1.75 in order to reduce raw material costs, and to minimise the addition times of diisobutylene.

The catalyst may be removed from the reaction mixture using any known method for separating a solid from a liquid, in particular any known filtration or centrifugation method. Catalyst recovery is conveniently carried out by vacuum filtration of the hot reaction mass. Likewise excess diisobutylene may be removed from the reaction mixture by any convenient method for separating liquids of different boiling points, in particular by fractional distillation. Recovery of excess diisobutylene reactant is readily accomplished by vacuum distillation of the reaction mixture.

The activated earth catalyst used in the process of the present invention preferably has a free moisture content below 10%, more preferably below 5% by weight.

Commercially-available catalysts which have proved effective include Fulcat.RTM.14, Fulmont.RTM.700C, Fulmont.RTM.237, Katalysator K10 (Sud-Chemie) and, especially Fulcat.RTM.22B (a sulphuric acid-activated Fullers Earth). The Fulcat and Fulmont catalysts are commercially-available from Laporte Industries.

Activated earth catalysts used according to the present process are advantageous over the known aluminium chloride catalysts in that:

(a) catalyst removal can be effected by simple filtration; and

(b) activated earths, having bleaching properties, provide end products which are much lighter in colour than those obtained using aluminium chloride catalysts.

The amount of catalyst used in the process of the present invention may vary widely without detriment to the course of the reaction. For practical purposes, however, we prefer to use catalyst amounts within the range of from 5% to 25%, more preferably from 5% to 15% by weight, based on the weight of diphenylamine reactant.

The products of the process of the present invention are believed to contain at least the following components:

(i) t-butylated diphenylamines;

(ii) t-octylated diphenylamines; and

(iii) higher alkylated diphenylamines.

The liquid antioxidants produced by the process of the present invention are useful as antioxidants in a wide range of organic materials.

Accordingly, the present invention further provides a composition comprising an organic material susceptible to oxidative degradation and, as stabiliser, a stabilising amount of a liquid product produced according to the process of the invention.

A particular class of organic materials susceptible to oxidative deterioration for which the products of the process of the invention are valuable as antioxidants, is that consisting of lubricants and functional fluids of mineral oil origin or synthetic lubricants or functional fluids, especially those derived from carboxylic esters and intended for use at temperatures at, or above 200.degree. C.

Examples of synthetic lubricants include lubricants based on a diester of a dibasic acid and a monohydric alcohol, for instance dioctyl sebacate or dinonyl adipate; on a triester of trimethylol propane and a monobasic acid or mixture of such acids, for instance trimethylol propane tripelargonate, trimethylol propane tricaprylate or mixtures thereof; on a tetraester of pentaerythritol and a monobasic acid or mixture of such acids, for instance pentaerythritol tetracaprylate; or on complex esters derived from monobasic acids, dibasic acids and polyhydric alcohols, for instance a complex ester derived from trimethylol propane, caprylic acid and sebacic acid; or of mixture thereof.

Other synthetic lubricants are those known to the art-skilled and described e.g. in "Schmiermittel-Taschenbuch" (Huethig Verlag, Heidelberg 1974). Especially suitable, apart from the preferred mineral oils are e.g. phosphates, glycols, polyglycols, polyalkylene glycols and poly-alpha olefines.

Other organic materials susceptible to oxidative degradation for which the products of the process of the present invention are particularly valuable antioxidants, include, for instance, substances falling within the following groups:

(a) natural and synthetic polymeric materials, for instance natural rubber; synthetic addition polymers such as homopolymers and co-polymers of vinyl and vinylidene monomers, including ethylene, propylene, styrene, butadiene, isoprene, acrylonitrile, vinyl chloride or vinyl acetate; synthetic polymers derived from condensation reactions and containing ether, ester (ex carboxylic, sulphuric or carbonic acids) amide or urethane groupings, for instance alkyd and polyamide resins; in the case of these polymers, the liquid antioxidant may be incorporated during a polymer processing step, for instance during the compounding of rubber;

(b) non-polymeric oxygen-containing substances, for instance aldehydes such as n-heptaldehyde; and unsaturated fatty acids or esters thereof for instance methyl oleate and ricinoleic acid;

With regard to these other organic materials mentioned above, the antioxidants produced by the process of the invention are effective in the stabilisation of rubbers. They may be used in natural or synthetic rubbers. An example of a synthetic rubber is SBR (styrenebutadiene rubber).

Alternatively, the products may be used to stabilise a mixture of natural and synthetic rubber, for instance a blend of natural and styrene-butadiene rubber.

The antioxidant products of the process of the present invention may be employed in multi-ingredient compositions, that is compositions containing at least one organic substance susceptible to oxidative deterioration or a mixture thereof and one or more organic or inorganic compounds, for instance an alcoholic or aqueous emulsion of an organic material susceptible to oxidative deterioration.

The compositions of the present invention preferably contain a proportion of the liquid antioxidant produced according to the present invention within the range of from 0.05% to 5.0% by weight based on the weight of the organic material. More preferably, the compositions contain a proportion of the liquid antioxidant within the range of from 0.1% to 4.0% by weight based on the weight of the organic material. The amount of antioxidant product employed in any particular organic material will depend not only on the nature of the organic material but also on the external conditions under which the material is to be used. Thus organic materials to be used at normal temperatures will usually require a smaller proportion of the liquid antioxidant product than organic materials, such as synthetic lubricants designed for use at elevated temperatures.

In addition to the liquid antioxidant, a lubricant may also contain, in order to iprove certain applicational properties, other additive such as further antioxidants, metal passivators, rust inhibitors, viscosity index improvers, pour-point depressors, dispersants/surfactants or anti-wear additives.

2,6-Di-tert.-butylphenol

2-tert.-butyl-4,6-dimethylphenol

2,6-Di-tert.-butyl-4-ethylphenol

2,6-Di-tert.-butyl-4-n-butylphenol

2,6-Di-tert.-butyl-4-i-butylphenol

2,6-Di-cyclopentyl-4-methylphenol

2-(.alpha.-Methylcyclohexyl)-4,6-dimethylphenol

2,6-Di-octadecyl-4-methylphenol

2,4,6Tri-cyclohexylphenol

2,6-Di-tert.-butyl-4-methoxymethylphenol

2,6-Di-tert.-butyl-4-methoxyphenol

2,5-Di-tert.-butyl-hydroquinone

2,5-Di-tert.-amyl-hydroquinone

2,6-Diphenyl-4-octadecyloxyphenol

2,2'-Thio-bis-(6-tert.-butyl-4-methylphenol)

2,2'-Thio-bis-(4-octylphenol)

4,4'-Thio-bis-(6-tert.-butyl-3-methylphenol)

4,4'-Thio-bis-(6-tert.-butyl-2-methylphenol)

2,2'-Methylene-bis-(6-tert.-butyl-4-methylphenol)

2,2'-Methylene-bis-(6-tert.-butyl-4-ethylphenol)

2,2'-Methylene-bis-[4-methyl-6-(.alpha.-methylcyclohexyl)-phenol]

2,2'-Methylene-bis-(4-methyl-6-cyclohexylphenol)

2,2'-Methylene-bis-(6-nonyl-4-methylphenol)

2,2'-Methylene-bis-(4,6-di-tert.-butylphenol)

2,2'-Ethylidene-bis-(4,6-di-tert.-butylphenol)

2,2'-Ethylidene-bis-(6-tert.-butyl-4-isobutylphenol)

2,2'-Methylene-bis-[6-(.alpha.-methylbenzyl)-4-nonylphenol]

4,4'-Methylene-bis-(6-tert.-butyl-2-methylphenol)

1,1-Bis-(5-tert.-butyl-4-hydroxy-2-methylphenol)-butane

2,6-Di-(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-methylphenol

1,1,3-Tris-5-tert.-butyl-4-hydroxy-2-methylphenyl)-3-n-dodecyl-mercaptobuta ne

Ethyleneglycol-bis[3,3-bis-(3'-tert.-butyl-4'-hydroxyphenyl)-butyrate]

Di-(3-tert.-butyl-4-hydroxy-5-methylphenyl)-dicyclopentadiene

Di-[3'-tert.-butyl-2'-hydroxy-5'-methyl-benzyl)-6-tert.-butyl-4-methyl-phen yl]-terephthalate

1,3,5-Tri-(3,5-di-tert.-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene

Di-(3,5-di-tert.-butyl-4-hydroxybenzyl)-sulfide

Bis-(4-tert.-butyl-3-hydroxy-2,6-dimethylbenzyl)dithiol-terephthalate

1,3,5-Tris-(3,5-di-tert.-butyl-4-hydroxybenzyl)-isocyanate

1,3,5-Tris-(4-tert.-butyl-3-hydroxy-2,6-dimethylbenzyl)-isocyanurate

3,5-Di-tert.-butyl-4-hydroxybenzyl-phosphonic acid-dioctadecylester

3,5-Di-tert.-butyl-4-hydroxybenzyl-phosphonic acid-monoethylester Calcium-salt

4-Hydroxy-lauric acid anilide

4-Hydroxy-stearic acid anilide

2,4-Bis-octylmercapto-6-(3,5-di-tert.-butyl-4-hydroxyanilino)-s-triazine

N-(3,5-di-tert.-butyl-4-hydroxyphenyl)-carbamic acid octyl ester

N,N'-Di-(3,5-di-tert.-butyl-4-hydroxyphenylpropionyl)-hexamethylene-diamine

N,N'-Di-(3,5-di-tert.-butyl-4-hydroxyphenylpropionyl)-trimethylene-diamine

N,N'-Di-(3,5-di-tert.-butyl-4-hydroxyphenylpropionyl)-hydrazine

N,N'-Di-isopropyl-p-phenylenediamine

N,N'-Di-sec.-butyl-p-phenylenediamine

N,N'-Bis(1,4-dimethyl-pentyl)-p-phenylenediamine

N,N'-Bis(1-ethyl-3-methyl-pentyl)-p-phenylenediamine

N,N'-Bis(1-methyl-heptyl)-p-phenylenediamine

N,N'-Dicyclohexyl-p-phenylenediamine

N,N'-Diphenyl-p-phenylenediamine

N,N'-Di-(naphthyl-2-)-p-phenylenediamine

N-Isopropyl-N'-phenyl-p-phenylenediamine

N-(1,3-Dimethyl-butyl)-N'-phenyl-p-phenylenediamine

N-(1-Methyl-heptyl)-N'-phenyl-p-phenylenediamine

N-Cyclohexyl-N'-phenyl-p-phenylenediamine

4-(p-Toluene-sulfonamido)-diphenylamine

N,N'Dimethyl-N,N'-di-sec.-butyl-p-phenylenediamine Diphenylamine

4-Isopropoxy-diphenylamine

N-Phenyl-1-naphthylamine

N-Phenyl-2-naphthylamine

octylated Diphenylamine

4-n-Butylaminophenol

4-Butyrylamino-phenol

4-Nonanoylamino-phenol

4-Iodecanoylamino-phenol

4-Octadecanoylamino-phenol

Di-(4-methoxy-phenyl)-amine

2,6-Di-tert.-butyl-4-dimethylamino-methyl-phenol

2,4'-Diamino-diphenylmethane

4,4'-Diamino-diphenylmethane

N,N,N,N'-Tetramethyl-4,4'-diamino-diphenylmethane

1,2-Di-(phenylamino)-ethane

1,2-Di-[(2-methyl-phenyl)-amino]-ethane

1,3-Di-(phenylamino)-propane

(o-tolyl)-biguanide

Di-[4-(1',3'-dimethyl-butyl)-phenyl]amine

for copper e.g.

Benztriazole and derivatives thereof, Tetrahydrobenztriazole,

2-Mercaptobenzthiazole, 2,5-Dimercaptothiadiazole, Salicylidenepropylenediamine,

Salts of Salicylaminoguanidine.

(a) Organic acids, their esters, metal salts and anhydrides e.g. N-Oleoyl-sarcosine, Sorbitan-mono-oleate, lead-naphthenate, Dodecenyl-succinic anhydride, 4-Nonyl-phenoxy-acetic acid.

(b) nitrogen-containing compounds e.g.

I. Primary, secondary or tertiary aliphatic or cycloaliphatic amines and amine-salts of organic and inorganic acids e.g. oil-soluble alkylammonium carboxylates

II. Heterocyclic compounds e.g. Substituted Imidazolines and Oxazolines

(c) Phosphorus-containing compounds e.g.

Amine salts of phosphonic acid partial esters

(d) Sulfur-containing compounds e.g.

Barium-dinonylnaphthalene-n-sulfonates, calcium petroleum sulfonates

Polymethacrylates, Vinylpyrrolidone/Methacrylate-Copolymers,

Polybutenes, Olefin-Copolymers, Styrene/Acrylat-Copolymers

Polymethacrylates, or alkylated Naphthalene derivatives.

Polybutenylsuccinic acid-imides, Polybutenylphosphonic acid derivatives, basic Magnesium-, Calcium-, and Bariumsulfonates and -phenolates.

Sulfur and/or Phosphorus and/or Halogen containing compounds e.g. sulfurised vegetable oils, zinc dialkyldithiophosphates, Tritolylphosphate, chlorinated Paraffins, Alkyl- and Aryldisulfides.

The following Examples illustrate the invention in more detail.

169.2 g Diphenylamine and 33.8 g of an activated earth (Fulcat.RTM. 22B from Laporte Industries) are charged into a reaction vessel equipped with stirring- and temperature detecting means, and the mixture is heated to 165.degree. C. Once the mixture is sufficiently mobile, the stirrer is put into operation. 196.4 g diisobutylene is then added gradually, at such a rate that the temperature of the reaction mixture does not drop below 165.degree. C. The addition requires 5 hours for completion. Reflux commences soon after the start of the addition. Heating and stirring is continued at 165.degree. C. with frequent sampling until gas/liquid chromatographic analysis shows that the content of 4,4'-dioctyldiphenylamine is below 25% (excluding catalyst).

The reaction mass is cooled to 60.degree. C. and the catalyst is removed by vacuum filtration. The filtrate is transferred to a distillation apparatus and heating and stirring are commenced and the pressure is reduced to 26 mbar. Throughout the distillation, the internal temperature is slowly allowed to rise to 165.degree. C. and is held at this temperature for two hours, during which distillation ceases. 300 g of a viscous, dark liquid are obtained having flash point 210.degree. C.

The reaction conditions employed in Example 1 are varied in terms of temperature range and ratio used of diphenylamine (DPA) to diisobutylene (DIB).

The results are set out in the following Table 1.