US2267337A - Extreme pressure lubricant - Google Patents

Description

Patented 1941 :Netherlands. assignorsto Shell Development Company, San corporation of Delaware No. Drawing orlgincl applieation August .2,

1937, Serial N0; 158,958.: .Dlvlded'and this-applloation January In the NethcrlandslAugust g9, v

. "loamy crass-w ll t bnir'elates to lubricants suitable 'Iherelative-pos'ition bi its for lubrication under-very high prwsures and at elevated temperatures; and-is .a division ofpour copending application, No. 156,958; Kflled August "2, 1937;" Patent No. 2,194,418; issued- March 26. 1940.

It has already v catingoils and greasessubstances known as exe treme pressuresubstances, which prevent seizure and scoring of metals which are in motion we; tive to each other under very high pressures. Most of the substances heretofore suggested contain halogen, sulfur or phosphorus in a'form conducive to corrosion. The thought generally prevailed that these elements give rise to a. chemical reaction to form products which keep the metals separated when the ofl film gives way under excessive pressures; It was reasoned that since a chemical reaction essential to the working of an extreme pressure lubricant, a certain amount of corrosionfisQ-indispensable for. the activity of extreme pressure substances.

been proposedf to add to lubri molecule to have little-1f. any. influence,-

corrosive properties, particularlyso if they possess two or more carboxyl radicals; It, furthermore, the i compounds are structurally compact. they are also highly resistant tqjthermal decomposition at the elevated temperatures normally encountered in the'lubrication of internal com- It has further been proposed "to use oxyhydrocarbons such as fatty acids, cresols, phthalic acid,

etc., for the purpose ofenhancing the power of exteme pressure substances. However, these oxyhydrocarbons, when used by themselves, have little, if any, effect in the matter of inducing extreme pressure properties in mineral oils.

It is the p se ofthis invention to provide. extreme pressure lubricants which are free from corrosiveness andwhich for their effectiveness} apparently do not rely, orrely only partialimon and the a chemical reaction between the metals extreme pressure substances.

We have discovered that aromatic compounds built up of at leasttwo 6,-carbon rings and said' compound containing at least'two hydroxyl-con taining radicals havingjnot' more thanone carbon atom between the hydroxyl groups and the rin substituted in the same or different ary'l rings, 1. e. the hydroxy'groups may be attached directly tothe ring as in phenols or may be part.

bustion' engines and are therefore especially valprovided they a e presentin'theirf form and not bound as esters,-salts,,etc. l Thecompounds'of our invention -areinon-feorw; rosivetowardssteel, bronze-and va'r1ous bearing nrieta'ls and in many instances'havfe-positive anti;-

uable for use in" crankcase lubricants for internal:

combustion engines.

Due to the fact that our compounds possess two or more hydroxyl or carboxyl radicals they havehigh. boilingjtemperatures, and most of them are substantially non-volatile. This is of obvious advantage in lubricating oils to be'used in internal combustion engines.

The solubility of our compounds in hydrocarbon oils is quite low and therefore they are usually used in the form for suspensions rather than solutions. Suspensionsmay be prepared'in any suitable manner, as by'dispersing the coincolloid mill, or by dissolving them, in aiiuitualsolvent, etc. Substances having a stabilizing feet onthe suspension so produced, such as "-quantities. ofv fattyacids of the-type of stearic acid,':may'be-added toadvantage. Owing-to their power to"preserve the suspension, such subs i stances have frequently theadditional eflect of, enhancing the extreme pressure properties ofour compounds, particularly atelevated temperatures, when the suspensions tend to become unof a carbo-hydroxyl' group as in benzoic acid or benzyl alcohol show good extreme pressure qualities when added to lubricating oils in quantities 1 substantially above 1%. While the presence of two of the hydroxyl radicals is suflicient 'toimpart iothe polycyclic.- compounds extreme pressure properties, additional hydroxyl radicals'improve this property.

Thus between two substances of equal molecular structure but differing in the number of attached hydroxyl radicals, those containing the larger number of hydroxyls are in general more active.

stable. I a t It has been stated hereinbefore that-the two or more fi-carbon rings ofour eompoundswshould stand in' close proximity of each other. By this a we mean that the earbocyclic rings should preferably be separated from each other by a chain or chains of notmorethan two atoms oian element normally capable of firmly linking 6-carbon rings to produce stable compounds, said element having an atomic number below 17. Thus compounds containing two or more G-carbon rings which are separated by'two or less carbon or nitrogen atoms, or by}; single atom of the group consisting of oxygen, sulfur and phosphorus, not forming part of the ring, or which are advantageously linked directly without an intermedipounds in the lubricating oil witlrthe aid-feta ate atom as in diphenyl, vor by common carbon.

atoms as in naphthalene. are known to be very stable in the absence or other unstable linkages or radicals. While many. compounds are known in which the rings are separated by other elements, having atomic numbers above 16 capable oi linking 6-carbon rings, such as As, Sb. Hg. Pb, etc., we have found that such compounds, although sumciently stable for many purposes are not suflicientiy stable to be of practical use in lubrication, particularly at high temperatures or in the presence oi moisture, notwithstanding that all of them exhibit extreme pressure properties,

provided they have the necessary hydroxyl radicals; and still other compounds in which the link is formed by elements having atomic numbers below 17, other than those enumerated above, such as Mg, Al, Si, are known to be extremely unstable, some of them igniting in contact with air, and others rapidly hydrolyzing in contact with water.

Derivatives containing the necessary hydroxyl radicals of diphenylethane, diphenylmethane, triphenylmethane, diphenyl, naphthalene, tetraline, anthracene, phenanthrene, picene, chrysene, acridine, phenacine, diphenyloxide, dinaphthyloxide, diphenylsuliide, dinaphthylsulflde, carba-.

zol, azobenzol, triphenylphosphine. or homologues of these compounds are examples of suitable compounds.

In addition. the rings may contain short aliphatic side chains. relatively long side chains of more than 2 carbon atoms being very undesirable as they greatly lower the thermal stability of our compounds.

The presence of polar radicals other than hydroxyl of the type described in our compounds may be permissible but is usually of little advantage and in many instances of decided disadvantage. For instance, amino radicals frequently reduce the resistance our compounds toward oxidation, halogens tend to make them corrosive, nitro radicals lower the thermal stability, etc.

The quantity of our compounds required to impart to mineral lubricatingoils high pressure resisting properties normally varies between about 1 to 10%. r

In the following examples, which illustrate our invention. results are shown of tests, made in the Boerlage four-ball apparatus described in Engineering. July 14, 1933, with a straight mineral lubricating oil and blends thereof with various compounds of the group herein described.

Example I A 4% suspension of a methylene dibetanaphthol in a Venezuelan bright-stock gave a welding pressure of 300 kg., whereas the unblended oil permitted welding at 150 kg.

Example II The family of diphenyl methane derivatives provides a large number of suitable compounds which may be obtained by condensing polyphenols, as hydroquinone, resorcine, pyrocatechin, phloroglucine, pyrogallol; or carboxyl phenols as salicylic acid, cresotic acid, gallic acid,

or naphthols, naphthoic acids, hydroxy anthracene, alizarine, etc.; with a lower aldehyde such as formaldehyde or acetaldehyde. Also mixtures of various phenols may be condensed.

For instance, a mixture of 3 parts of resorcine, 1 part of a 40% aqueous solution of formaldehyde and 20 parts of an 8% aqueous hydrochloric acid is allowed to stand for several hours, during which time a precipitate of methylene diresorcine is formed, which is filtered of! and recrystallized from ethyl alcohol. The product obtained consists of microscopic crystals. A 4% suspension thereof in the brightstock of Example I raised the welding pressure to 500 kg. All parts are by weight.

Example 111 180 grams of salicylic acid are heated on a steam bath for. 40 hours with grams of a 30% aqueous formaldehyde solution and 640 milliliters concentrated hydrochloric acid. The crystalline salicylic acid is slowly converted to a sandy powder containing methylene disalicylic acid, which is washed with water to remove the free hydrochloric acid, dissolved in dilute ammonia, filtered and reprecipitated with dilute sulfuric acid. A 4% suspension of the product in the lubricating oil oi Example I gave a welding pressure of 600 kg.

Example 1v Methylene digallic acid, obtained in a manner similar to the procedure described in Example IV, in a 4% suspension in the lubricating oil of Example I gave a welding pressure of 500 kg.

Example V Another large class of suitable compounds known as the rosolic acids or aurines, which are derivatives of triphenyl methane, may be obtained by condensing phenols or carboxyl phenols with oxalic acid in the presence of a condensing agent such as sulfuric acid, zinc chloride, etc. A 4% suspension of aurine or pararosolic acid raised the welding pressure in the lubricating oil of Example I to 400 kg.

Example VI