US3398165A - Diesters containing adamantane nuclei - Google Patents

Description

United States Patent 3,398,165 DIESTERS CONTAINING ADAMANTANE NUCLEI Irl N. Duling, West Chester, and Abraham Schneider, Over-brook Hills, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey N0 Drawing. Filed Mar. 2, 1966, Ser. No. 531,059 13 Claims. (Cl. 260-410) This invention relates to novel diesters containing one or two adamantane nuclei per molecule. Each adamantane nucleus contains not more than one unsubstituted bridgehead carbon atom or in other words has not more than one tertiary hydrogen atom attached thereto. The diesters are either oily liquids or waxy solids. They are characterized by good hydrolytic stability, oxidative stability and thermal stability and have particular utility as lubricants or as components in lubricating oil and grease compositions.

The diesters of the present invention comprise two types as follows:

(I) Diesters of alkyl-substituted adamantane 1,3-diols with alkanoic or cycloalkanoic acids.

(II) Diesters of alkyl-substituted adamantane l-mono- 01s with alkanedioic or cycloalkanedioic acids.

These two types of diesters are represented by structural formulas as hereinafter shown. They are both characterized as being derived from the esterification of the specified monoor di-acids by alcohols in which the hydroxy group or groups are located at bridgehead positions of the adamantane nucleus.

The use of certain types of diesters as synthetic lubricating oils and greases for special applications is well known and is described, for example, in Synthetic Lubricants by Gunderson and Hart (Reinhold Publishing Corp, 1962), pages 39-43 and 151-245. These synthetic ester lubricants comprise di-esters made from aliphatic monoalcohols and aliphatic dibasic acids such as glutaric, adipic, azelaic and sebacic acids, as well as the reverse type of diesters made from glycols and aliphatic monocarboxylic acids. Those made from the aliphatic monools and diacids have been used widely as aircraft lubricants for turboprop and turbojet engines, usually being formulated with suitable additives to meet United States Military Specification MlL-L-7808. Lubricants for this purpose are required to have low temperature fluidity characteristics as well as good stability at high temperature operating conditions. The specific diester used perhaps most widely for gas turbine engine lubrication is the di(2-ethylhexyl)sebacate. Besides being used for aircraft engine lubrication, synthetic diesters have also been employed as gear oils, instrument oils, machine gun lubricants, hydraulic fluids and greases.

In the prior art monoesters of l-adamantane carboxylic acid and several aliphatic alcohols have been prepared and testified for suitability as lubricating oils. This Work has been described by Spengler et al., Erdol und Kohle- 'Erdgas-Petrochemie, vol. 15, pages 702-707 (September, 1962). The alcohols used ranged from propanol to tetradecanol. The monoester products were oils but they did not prove to be attractive as special lubricants. Each molecule of these esters contained three unsubstituted bridgehead carbon atoms in the adamantane nucleus or,

in other words, three tertiary hydrogen atoms which provide relatively reactive sites in the molecule. While their thermal stability was considered good, the resistance to oxidation in the presence of metals was reported to be poor as also was the lubricating quality of the esters. These authors also reported preparing a diester of 1- adamantane carboxylic acid and hexamethylene-l,6-glycol but this product was a high melting solid (M.P.=l01 C.) rather than an oil.

The present invention is directed to diesters containing either one or two adamantane nuclei and in which each ester group is the reverse of that in the prior art referred to above. In other words the adamantane nucleus (A) is attached to an oxygen atom of the carboxyl group in tlns fashion,

rather than to the carbon atom in .the linkage The present structural arrangement,

resulting from the adamantane-derived reactant being an alcohol instead of an acid, imparts greater stability to the ester product for reasons as hereinafter explained.

The diester products provided by the present invention conform in structure either to Formula I or Formula II as follows:

R3-C-O o-c-R H II R o-c-R -c-o R In these formulas the R groups are as follows:

R a radical having 0-20 carbon atoms selected from the class of hydrogen, alkyl and cycloalkyl,

R and R alkyl or cycloalkyl radicals having 1-20 carbon atoms each,

R an alkylene or cycloalkylene radical having 1-20 carbon atoms.

It should be noted that of the specified substituents at the bridgehead positions of the adamantane nuclei only R can be a hydrogen atom. Hence only one tertiary hydrogen atom can be attached to each adamantane nucleus. Embodiments of the invention which may often be preferred for either type of diester will have an alkyl substituent at the R position and hence will contain'no tertiary hydrogen on the adamantane nucleus. For both types of diesters it is usually preferable that the various bridgehead substituents (R R and, in Formula 11, R be methyl or ethyl groups or both, as the substituted adamantanes corresponding thereto can be more readily obtained as starting material for preparing the corresponding products in accordance with the invention.

Both of the above-specified types of diesters have high stabilities against thermal and oxidative degradation and good hydrolytic stability. As compared to the prior art esters mentioned above, the present diesters have better thermal stability by virtue of the fact that a double bond cannot form in an adamantane nucleus. Awell known decomposition route for conventional types of esters depends upon their ability, under appropriate conditions, to transfer a hydrogen atom from the beta position of the alcohol-derived moiety in the following manner:

This decomposition results, as shown, in the conversion of the ester into an acid and an olefin. The occurrence of this in a lubricant under conditions of use, of course, would be highly undesirable. While the prior art esters can undergo this type of decomposition at high temperature, the present ester cannot as this would require the formation of a double bond in the adamantane nucleus which will not occur. In contrast the reverse type of esters made from l-adamantane carboxylic acid and an aliphatic alcohol or glycol can undergo this type of thermal decomposition.

Another reason for the overall better stability of the present products as compared to the prior art esters made from 1 adamantane carboxylic acid is the fact that the present products have at most only one tertiary hydrogen attached at each adamantane nucleus and preferably may have none. In comparison the prior art esters have three bridgehead tertiary hydrogen sites on each adamantane nucleus. These are reactive sites constituting spots in the molecule where oxidation and peroxide formation can occur.

Still another reason for the better stability of the present products is that the ester structure represented by will less readily undergo hydrolysis under non-acidic conditions than the reverse structure Since contamination of the lubricant by water may occur in some lubrication systems, this improved hydrolytic stability provides still another desirable stability feature of the present products.

As starting material for preparing the diesters, bridgehead mono-, dior tri-alkylated adamantanes corresponding to the desired alkyl or cycloalkyl adamantane moiety of the product can be used. For making the products of Formula I only the monoand di-alkylated ada- I! OH ER CCI mantanes can be used, whereas for those of Formula 11 trialkylated adamantanes can also be employed. While the number of carbon atoms in each alkyl or cycloalkyl group can vary widely ranging say up to 20, it is usually preferable that the R groups be methyl and/or ethyl since the parent hydrocarbons corresponding thereto are more readily obtainable. Thus l-ethyladamantane, 1,3-dimethyladamantane, l-ethy1-3-methyladamantane, 1,3,5- trimethyladamantane and 1,3-dimethyl-5-ethyladamantane can be prepared by aluminum halide catalyzed isomerization of C C tricyclic perhydroaromatics, as disclosed by Schneider et al., JACS, vol. 86, pp. 5365-5367. Higher alkyl or cycloalkyl groups can be substituted on the adamantane nucleus by a Wurtz snythesis involving reacting bridgehead chloro or bromo adamantanes with alkali metal alkyls or cycloalkyls in the manner disclosed in the aforesaid Spengler et al. reference. The alkylated adamantanes can, for the present purpose, have either nonbranched or branched alkyl groups and can have one or more cycloalkyl radicals in the alkylation moiety with the total number of carbon atoms in each R group ranging up to twenty. Preferably the R groups contain no tertiary hydrogen atoms.

The starting alkylated adamantane hydrocarbon is first converted to a 1,3-diol if esters according to Formula I are desired, or to a l-monool if Formula II products are the kind to be prepared. One manner of effecting such conversions is by air oxidation of the parent hydrocarbons at, for example, 160 C. in the presence of a metal salt oxidation catalyst, as disclosed in Schneider United States applications Ser. No. 395,557, now U.S. Patent 3,356,740 and Ser. No. 395,580, now US. Patent 3,356,- 741 each filed Sept. 10, 1964. In the oxidation monools form first and these will subsequently convert to diols if the reaction is allowed to continue sufficiently. Some amounts of ketones are also formed during the oxidation. Production of the monools can be maximized by stopping the oxidation before conversion has been reached, while production of diols can be maximized by oxidizing to higher conversion levels.

Another way of preparing either l-monools or 1,3-diols of the alkyladamantanes is by reacting the latter with an acetic acid solution of chromic acid, as disclosed in Moore United States application Ser. No. 421,614, filed Dec. 28, 1964, now abandoned. By using a relatively low mole ratio of Cr to hydrocarbon such as 3 :2 good yields of the monool can be obtained, whereas using a higher ratio such as 6:1 results in good yields of the diol.

The preparation of diesters utilizing these bridgehead monools or diols of alkyladamantanes is not as readily accomplished as When aliphatic alcohols or glycols are employed. Attachment of the hydroxyl group at a bridgehead carbon of the adamantane nucleus makes the group relatively inactive. This is especially true when two bridgehead hydroxyl groups are attached to the nucleus. Hence many of the known methods of esterification may not be suitable for making products of the present invention or at least for obtaining these products in good yield. For example, conventional esterification of the l-monools or 1,3-diols with aliphatic diacids or monoacids by means of an acidic catalyst generally is not a good way of preparing these diester products.

A preferred procedure for making the diesters is by reacting the hydroxy-containing adamantane compound with aliphatic or cycloaliphatic acid chlorides. Thus, for producing the Type I diesters, the procedure involves the following reaction:

This reaction takes place too slowly at room temperature and hence an elevated temperature should be employed, e.g., 100-150 C. A solvent such as pyridine can be used so that the hydrogen chloride will be neutralized as it is formed. While this is not essential, it is advantageous for inhibiting side reaction particularly in cases where R is a hydrogen atom.

The preferred esterification procedure for making Type II diesters involves reaction as follows:

This esterification reaction takes place more readily than that of the preceding equation and can be carried out at room temperature simply by mixing the two reactants. The reaction is exothermic and hence it is desirable to add the monool slowly to the alkane dioyl chloride while stirring the mixture. Again a solvent such as pyridine can be used to avoid side reaction and is particularly desirable in case R is a hydrogen rather than an alkyl substituent.

In carrying out the first shown esterification wherein dihydroxyadamantanes are used, stoichiometric proportions of the reactants can be used but it is generally preferable to employ an excess of the acyl chloride. An excess of the diol would lead to the formation of hydroxy monoesters which should be avoided. An excess of the acyl chloride, however, helps to insure complete esterification of the diols. Furthermore the excess acyl chloride can be readily removed from the reaction product by treatment with an aqueous solution of sodium carbonate or other alkali, whereas any excess of the hydroxy-containing component cannot be removed in this manner. Generally a molar ratio of acyl chloride to the dihydroxyadamantane reactant in the range of 2:1 to :1 will be used in carrying out this reaction.

In effecting the other esterification in which monohydroxyadamantanes are employed, the use of a stoichiometric excess of the alcohol helps to insure complete esterification of the alkane dioyl chloride. However removal of the excess alcohol is not readily effected, as this requires the use of such separation procedures as chromatography, distillation and/or fractional crystallization. It is generally desirable to use at least a stoichiometric amount of the dioyl chloride and preferably a small excess. For example, the molar ratio of the dioyl chloride to the monool may be in the range of 0.5 :l to 0.7: 1. Any resulting half-ester can be removed by washing the product with aqueous sodium carbonate.

After the esterification reaction has been completed, any conventional or suitable procedure can be used for working up the product. The mixture can be diluted with a solvent such as ether, pentane or benzene and then washed with aqueous sodium carbonate solution or other mild alkali to remove any acid chlorides. The diester product can be recovered in relatively pure form by distillation and/ or chromatography. In cases where highly pure product is desired, hydrogenation using Raney nickel catalyst (which does not affect the ester group) and contact with decolorizing adsorbents can be utilized. The diesters of both types when highly pure are colorless, while the less pure products usually have a pale yellow color. These products are generally viscous oils, except that increasing the sizes of the various R groups in the molecules causes the produces to become waxy solids and particularly so when the R group are unbranched chains. Preferred products of the invention wherein the R groups attached to the adamantane nuclei are methyl and/or ethyl are oils at ordinary temperature.

For preparing Type I diesters the acyl chlorides of any alkyl or cycloalkyl monocarboxylic acids having 2-21 carbon atoms are suitable for contributing the moieties to the molecules, and fatty acids are inexpensive sources of this component. Acyl chlorides having 6-12 carbon atoms and a straight chain R group are preferred for making lubricant oils. Specific examples are the chlorides corresponding to the following acids: caproic, nheptylic, caprylic, pelargonic, capric, n-undecylic and lauric. However, lower and higher members can also be used such as the chlorides corresponding to the following carboxylic acids: acetic, propionic, butyric, isovaleric, myristic, palmitic, stearic, arachidic and the like. Also chlorides corresponding to acids containing naphthene rings can be used, for example, corresponding to cyclohexane carboxylic acid or Decalin carboxylic acids.

For the Type II diesters the dioyl chlorides of any alkylene or cycloalkylene dicarboxylic acids having 3-22 carbon atoms can be employed as the source of the o 0 labillinkage. Those corresponding to straight chain diacids having 6-12 atoms are preferred for making lubricant oils namely, the following diterminal diacids: adipic, pimelic, suberic, azelaic, sebacic, undecanedioic and dodecanedioic. However, dichlorides of diacids having less or more carbon atoms also can be used including those of malonic, succinic and glutaric acids, as also can the dichlorides of diacids containing naphthene rings such as cyclohexane dicarboxylic acids or Decalin dicarboxylic acids.

Any of the foregoing acid chlorides can be made from the corresponding monoacid or diacid by reacting the same in known manner with suitable chloride reagents such as phosgene, thionyl chloride, oxalyl chloride, PCl or PCl The following examples are specific illustrations of the invention:

Example 1.-Preparation of 1,3-(5,7-dimethyl)adamantyl dipelargonate This example shows preparation of the above designated Type I diester from pelargonic acid (R =8 carbons) and 1,3-dihydr0xy-5,7-dimethyladamantane. Oxalyl chloride was used to convert the pelargonic acid to its acyl chloride. Specifically, g. of oxalyl chloride were slowly added to g. of pelargonic acid and the mixture was refluxed for 2 hours. Excess oxalyl chloride was removed under aspirator vacuum at room temperature. The resulting acid chloride was heated to 105-1 10 C. and 70 g. of 1,3-dihydroxy-5,7-dimethyladamantane were cautiously added in small portions to the well stirred mixture. The oil was then stirred and heated at C. for one-half hour to complete the reaction. After this a solution of 50 g. sodium carbonate in 300 ml. water was added and the mixture was stirred for 2-3 days, then diluted to 1200 ml. with water and extracted with 500 ml. ether. The ether layer was washed twice with sodium chloride solution, stirred with anhydrous magnesium sulfate and charcoal, and filtered to give a light yellow solution. Evaporation of the ether gave g. of the 1,3-(5,7-dimethyl)adamantyl dipelargonate. Identification was accomplished by infrared, NMR, and mass spectra of the broad VPC peak. The diester product was a pale yellow oil and its properties are listed in Table 1 infra.

Examples 2-5 For Examples 2, 3, 4 and 5 other Type I diesters were made from 1,3-dihydroxy-5,7-dimethyladamantane in subadamantyl)dodecancdicarboxylate. This oil had prop erties as shown in Table 2 infra.

Examples 7-8 In these examples two other Type II diesters were prepared in substantially the same manner as described in TABLE 1.PROPERTIES OF TYPE I DIESTERS Density, R.I., Kv. at Kv. at ASTM Glass Melting Acid Used No. of O g./l. at 20 0. 100 F., 210 F., D-567, Transi- Point,

1n R 20 C. es. es. V.I. tion Temp. OJ

1 T and M.P. obtained by diflerential thermal analysis. 2 At C.

3 None. 4 Higher glass transition temperature for the dilaurate due to erystallluity.

The data in Table 1 show that a variety of Type I diester oils can be made of different viscosities and varying widely in viscosity index. Some of the oils will have Example 6 except that the diacids used were, respectively, adipic acid (R =4 C) and azelaic acid (R =7 C). These products likewise were oils having the properties relatively high V.I. values, as shown by the dipelargonate 25 shown in Table 2.

TABLE 2.-PROPERTIES OF TYPE II DIESTERS Density, R.I., ASTM Glass Melting Dlaeld Used N o. of G g./l. at 20 0. EV. at 100 Kmat 210 D-567, Transition Point,

in R4 20 0. F., es. F., cs. V.I. Temp. 0.

D ('IQ, (3.

Adlpie 4 32. 6 9. 76 62 Azelaic 7 1. 036 1 4977 245.1 15.3 -64 Dodeeanedioie 10 1.008 1 4944 370 6 23.6 88 67 2 None.

Example 6.Preparation of bis-(3,5-dimethyladamanty l)dodecanedicarboxylate In this example the above-specified Type II diester was prepared from the diterminal diacid, dodecanedicarboxylic acid (R =l0 C), and 1,3-dihydroxy-5,7-dimethyladamantane. The diacid was first convented to the alkane dioyl chloride by means of oxalyl chloride. Specifically 10 ml. of oxalyl chloride were added dropwise to 5. g. of the diacid in a 100 ml. flask fitted with a reflux condenser and a dropping funnel. Vigorous reaction and evolution of gas occurred. The mixture was gently reiluxed tior two hours and allowed to cool to room temperature. Excess oxalyl chloride was removed at room temperature by maintaining the flask under aspirator vacuum for two hours. Then l-hydroxy-3,S-dimethyladamantane (7.6 g.) was added in three portions, an aspirator vacuum being maintained between additions to facilitate removal of by-product 'HCl. The mixture was stirred for one-half hour with gentle heating, then cautiously added to 10% sodium carbonate solution (500 ml.). The mixture was stirred overnight and extracted twice with a total of 500 ml. ether. The combined ether layers were washed three times with water (sodium chloride sometimes was added to break up an emulsion), then stirred with anhydrous magnesium sulfate and decolo-rizing carbon. Filtration and evaporation of the ether gave 11.5 g. of a clear yellow oil. This oil was chromatographed on alumina. Combination of center fractions gave 6.5 g. of a colorless viscous oil after removal of the elution solvent (5% ether in hexane). Characterization of the single broad VPC peak by infrared, NMR and mass spectra identified the product as bis-(3,5-dimethyl- As shown in Table 2 the three representative oils of Type II were more viscous than those of Table I. The data for both types of diester's show that V.I. increases as the length of the linear chains derived from the aliphatic acid increases.

Products of the invention have better low temperature properties than would be predicted from the A.S.T.M. viscosity-temperature slope between F. and 210 F. This is shown, for example, by data listed in Table 3 for the dipelargonate product of Example 1. Table 3 shows measured values of kinematic viscosities at various temperatures compared with values predicted from the A.S.T.M. slope. It also shows flash point, T and pour point values for this product.

TABLE 3.PROPERTIES OF DIPELARGONATE EXAMPLE 1 Predicted Measured Viscosity properties:

K at 500 Kv. at 210 F- 7. O5 Ky. at 100 F. 54.1 Ky. at 0 F. 2, 924 Kv. at -30 22, 076 Pour point, F. 90 O F Flash point, F 480 As shown here, viscosities at temperature below 0 F. are considerably less than the values that would be predicted from the A.S.T.M. slope.

Example 9' solution (one liter). The mixture was filtered through diatomaceous earth, pentane being used to wash the oil therefrom. The pentane layer was separated from the green aqueous layer and washed three times with water. Most of the pentane was stripped OE and anhydrous sodium carbonate added to the oil to make a thick paste. This was maintained for 2 hours at 70 C. under nitrogen. The sodium carbonate was filtered from the oil and washed with pentane. Alumina (5 g.) was added to the pentane solution and the mixture was stirred two hours at 70 C. under nitrogen. The pentane was stripped oif and the oil was distilled. The first 5% and the last 7% of distillate were discarded. A small amount of dark residue was obtained and also discarded. The product boiled at 212.5 C. at .12 mm. Hg. The oil was filtered through a 0.8 fiberglass filter covered with /2 inch of alumina. The resulting clear, colorless product had a faint pleasant ester odor, acid number .2 and iodine number 1.

The highly purified dipelargonate product was subjected to two kinds of stability tests. One was a thermal stability test involving subjecting the oil in a nitrogen atmosphere to 600 F. for 6 hours. For comparison, the conventional ester lubricant, di (2 ethylhexyl)sebacate, was also tested by this procedure. The other was a bench scale test for corrosion and oxidation stability substantially like that described in WAD Tech. Rep. 60-794 (Wright Air Development Center). This involved contacting a ml. sample in the presence of a copper washer for 24 hours at 400 F. with air at a rate of 20 l./hr. Again for comparison, di 2 ethylhexyl)sebacate was tested in the same manner. For these corrosion and oxidation stability tests both oils contained added inhibitors in conventional amounts.

TABLE 4.THERMAL STABILITY (600 F.) TESTS The foregoing specific examples are illustrative of the two types of diester products within the scope of the invention. Many other specific examples conforming to either Formula I or Formula 11 could be enumerated. When any one of the R groups in the molecule is straight chain and becomes long enough, the product tends to be a waxy solid instead of an oil. However these waxes can also be used for lubricant purposes, for example, as components of greases.

We claim:

1. A diester having 1-2 adamantane nuclei and corresponding to one of the following formulas:

E? 1 -0-0 o-c-R 1 1. 0 o R n II R 3 o-c am-c-o 3 an wherein R is a radical having 0-20 carbon atoms selected from the group consisting of hydrogen, alkyl and cycloalkyl, R and R are alkyl or cycloalkyl radicals having 1-20 carbon atoms, and R is an alkylene or cycloalkene radical having 1-20 carbon atoms.

2. A diester according to claim 1 corresponding to Formula I.

3. A diester according to claim 2 wherein R and R have 1-2 carbon atoms each.

1,8-(5,7-dimethyl)- adamantyl dipelargonate di-(2-ethy1hexyl)- sebacate 1 Mainly solid.

4. A diester according to claim 3 wherein R is an alkyl group having 5-41 carbon atoms.

5. A diester according to claim 2 which is a diester Results of the comparative corrosion and oxidation of 1,3-dihydroxy-5,7-dimethyladamantane and an alkanoic stability tests are set forth in Table 5.

acid.

TABLE 5.CORROSION AND OXIDATION STABILITY TESTS 1,3-(5,7-dimethyD-adamantyl di-(2-ethylhexyl) dipelargonate (inhibited) sebacate (inhibited) KV. at F.:

Before test After test Percent increase.

Percent increase Evaporation Loss, wt. percent Appearance after test Percent Insolubles Efiect on Copper:

Weight loss, mgJsq. cm

A.S.T.M. D-l30 rating Brown; no precipitation.

2 Brown; moderate precipitation: 3 S1. tarnish.

l Corrosion.

6. A diester according to claim 5 wherein said alkanoic acid is selected from the group consisting of caproic, n-heptylic, caprylic, pelargonic, capric, undecyclic and lauric acids.

7. A diester according to claim 1 corresponding to 13. A diester according to claim 12 wherein said al- Formula II. kanedioic acid is selected from the group consisting of 8. A diester according to claim 7 wherein R is hydroadipic, pirnelic, suberic, azelaic, sebacic, undecanedioic gen and R and R have 1-2 carbon atoms each. and dodecanedioic acids.

9. A diester according to claim 8 wherein R is an 5 alkyl group having 4-10 carbon atoms. References Cited 10. A diester according to claim 7 wherein R R FOREIGN PATENTS and R have 1-2 carbon atoms each.

11. A diester according to claim 10 wherein R is an M105 2/1961 France alkyl group having 4-10 carbon atoms. 10 i 12. A diester according to claim 7 which is a diester HENRY HLESPjzmary i of 1-hydroxy-3,5-dimethy1adamantane and an alkanedioic NIELSEN, Asslsfam Examllleracid.

Claims (1)

1. A DIESTER HAVING 1-2 ADAMANTANE NUCLEI AND CORRESPONDING TO ONE OF THE FOLLOWING FORMULAS: