US 2575196 A
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Patented Nov. 13, 1951 T OFFICE MIXED EST] BIS F POLYHYDRIC ALCOHOLS -.\ND DIBASIC ACIDS Paul V. Smith, In, Westileld, N. 3., minor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application October 1, 1948,
Serial No. 52,4
This invention relates to a new class of compounds which have been particularly suitable for use as synthetic lubricants because of their low pour points and high viscosity indices.
In the lubricant art, considerable progress .has beenrealized in recent years in the production of lubricants characterized by one or morespecific properties and adapted for particular uses. In the main, this progress can be attributed to two developments: the first, new refining procedures, and the second, addition agents capable of imparting particular properties to available lubricants. Thus, viscosity index improvers and pour depressants are added to automotive lubricants to render the lubricants more adaptable to wide changes in temperature conditions, while other agents are added to improve the load-carrying properties of a lubricant which is to be employed, from example, under extreme pressure conditions.
Recently, in an efiort to obtain superior lubricants endowed with specific and superior characteristics, a new field has been explored, namely the synthesis of lubricants from various materials. Esters represent one class of materials which have attracted unusual interests as synthetic lubricants. In general, they are characterized by higher viscosity indices and lower pour points than mineral oils of corresponding viscosity. The esters described in the present specification have. been found to exhibit very low pour points, and high viscosity indices. Lubricants possessing such properties are of special value in the lubrication of engines which are subjected to high temperatures such as combustion turbine engines, particularly those of the prop-jet type. Mineral oil lubricants containing added viscosity index improvers, thickeners or other highly nonvolatile additives are undesirable for use in such engines because of the tendency to leave a residue which accumulates and interferes with the operation of the engine. A synthetic lubricant of the type described in the present specification is especially adapted to use under such conditions, since the lubricant contains no additives and thus tends to leave no residue upon volatilization.
The new compounds of the present invention which have been found to be particularly suitable for use as lubricating oils are complex esters prepared by reacting one molecular proportion of a monobasic aliphatic acid with one molecular proportion of a glycol, thereby forming a half ester of-the glycol, after which two molecular proportions of such half ester are reacted with one molecular proportion of a dibasic aliphatic acid. The esters are formed by simple reaction of the component parts, without heating or otherwise treating the product to form 0, polymerized or resinous material. It is usually desirable to employ an esterification catalyst such as p-toluenesulfonic acid. The reactions are conducted by the usual esterification methods, removing water as formed, as by means of a water trap attached to a refluxing condenser. A reaction medium or water-entraining medium, such as naphtha, benzene, toluene, or the like, is go usually employed.
The new class of compounds may be broadly defined by the following general formula:
1 OOC R OOC Ra where R1 and R1 are glycol radicals which may consist of saturated aliphatic hydrocarbon groups, straight chain or branched, containing 2 to 20 carbon atoms each, or they may each represent a series of saturated aliphatic hydrocarbon radicals interlinked by one or more oxygen or sulfur atoms, or both oxygen and sulfur atoms, provided there are at least two carbon atoms between each carboxyl group and the nearest oxygen 0r sulfur atom and at least two carbon atoms between each pair of oxygen and/or sulfur atoms in the chain, and provided further that the total number of carbon, oxygen and sulfur atoms in each radical is from 5 to 80 and the number of sulfur atoms in each radical is not greater than two. R2 and R2 of the formula each represent 3 an aliphatic hydrocarbon radical, straight chain or branched, saturated or unsaturated, containing 1 to 22 carbon atoms, or they may represent organic radicals consisting of groups of short aliphatic hydrocarbon radicals interlinked by oxygen atoms, provided that the number of oxygen atoms in each radical is not greater than 5 and provided that there is at least one carbon atom between the carboxyl group and the first oxygen atom and at least two carbon atoms between each pair of oxygen atoms, the total number of carbon and oxygen atoms in the radical being from 3 to 22, or the radicals R2 and R2 containing up to 20 carbon atoms. These may include, for example, ethylene. glycol, propylene glycol, butylene glycols; pinacone, trimethylene glycol, tetramethylene glycol, pentamethylene.
HO CH2CH2OMCH2CH=OH where'n is 1 to 26, and the polypropylene glycols of the general formula may represent organic radicals eachconsisting of an aliphatic hydrocarbon chain containing a single interlinking sulfur atom. such sulfur atom being separated from the carboxyl group by at least one carbon atom, the total number of carbon and sulfur atoms in the radical being from 3 to 22, R3 of the formula is an aliphatic hydrocarbon radical, straight chain or branched, saturated or unsaturated, containing 0 to 30 carbon atoms, or it may be an organic radical consisting of a series of saturated aliphatic hydrocarbon radicals interlinked by one or more atoms of oxygen or sulfur, or both oxygen and sulfur, provided there are at least two carbon atoms between each pair of oxygen or sulfur atoms, provided there are not more than two sulfur atoms in each chain, provided there is at least one carbon atom between the carboxyl group and the first oxygen or sulfur atom, and provided that the total number of carbon, oxygen, and sulfur atoms in the entire radical R3 is from 3 to 80. The molecular weight of the entire ester should be at least 300 and the viscosity at 210 F. should not be greater than 150 seconds (Saybolt) to provide a product having lubricating properties.
Among the various components of the complex esters of the present invention, certain preferences may be pointed out as giving the optimum of desired properties from the standpoint of service as a lubricant. The preferred glycols are the polyethylene glycols of the formula H0 (CH2C'H2O) nCH2CH2OH where n i to 26. The preferred monobasic acids are e fatty acids containing 2 to 10 carbon atoms per molecule. The preferred dibasic acids are the straight chain dibasic acids of the parafifinic group having from 6 to 10 carbon atoms per molecule.
Among the monobasic acids which may be employed in the preparation of the esters of the present invention the following may be listed as illustrative:
Acetic acid Propionic acid Butyric acid Valeric acid ,Caproic acid 1 R1 Br Br fimcn-cnoblnkcnon where R1 or R2 is a methyl group and the other is hydrogen, and where n is l to 20, maylikewise be employed. Glycols containing sulfur atoms in thioether linkages may also be employed, and these include such compounds as thiodiglycol and l,2-bis(2 hydroxyethylmercapto) ethane. There also may be used glycols containing both oxygen and sulfur in similar linkages; such a compound is bis- [2- (2-hydroxyethoxy) ethyl] sulfide.
Illustrative examples of the dibasic acids-which may be employed in the synthesis of the complex esters of the present invention are the following: Oxalic acid Malonic acid Succinic acid Glutaric acid Adipic acid Pimelic acid Suberic acid Azeiaio acid Sebacic acid Brassylic acid Pentadecanedicarboxylic acid Tetracosanedicarboxylic acid C4C24 Alkenylsuccinic acids Diglycolic acid Thiodiglycolic acid The C4--Czi alkenyl succinic acids listed above are prepared by condensing olefins or mixtures of r olefins with maleic anhydride.
If desired, various addition agents may be incorporated in the esters of the present invention for the purpose of improving their properties with respect to their usefulness as lubricants. For example, antioxidants, viscosity index improvers, thickeners, dyes, etc., may be added.
Data will be given below showing the preparation of severalexarnples of complex esters within the scope of the present invention, indicating the adaptability of these esters to lubricating service. All of these esters were Prepared by a general esterification method which may be described in detail as follows: In a 1-liter round bottom reaction flask, fitted with a reflux condenser and water trap, were placed one mol of monobasic acid, one mol of glycol, 2.5 grams of p-toluenesuifonic acid monohydrate (catalyst), and ml. toluene. The mixture was refluxed until no more Water collected in the water trap. After cooling, 0.5 mol of dibasic acid was added and the refluxing process resumed until again no more water collected in the trap. The mixture was washed with three 100 ml. portions of saturated aqueous sodium carbonate solution and one 100 ml. portion of water. After drying with Drierite (anhydrous calcium sulfate) the material was filtered and stripped at a pressure of about 5 mm. to a bath temperature of about 225 C.
The results of tests of various properties of esters prepared by the above general method are shown in the table of data as follows:
2. A composition according to claim 1 in which R1 and R1 represent radicals of the formula Flash Kinematic Viscosity A i t A STM seos our Component of Ester 31 Slope Index m;
,Valerlc acid Adi c 435 42. 480 8. 487 0. 588" v 153 -35 475 43. 335 8. 678 0. 583 153 -35 Adfp acid... 470 37. 240 7. 493 0. 610 152 Triethylene glycol Acetic i Sebaclc acid 440 82- m 13.409 0. 567 141 35 Tetraethylene glycol Propionic acid.
baclc acid 415 51. 846 9. 922 0. 573 150 -35 Tetraethylene glycol Butyric acid Bebacic acid 435 54. 56 10. 60 0. 559 152 35 Tetraethylene gly Valerie acid 1 Sebacic acid 445 58. 852 11.576 0. 542 152 -35 Tetraethylene glycol Caproic acid I Sebaeie acid 465 56. 150 10. 995 0. 651 152 -35 Tetraethylene glycol--- But ic acid Thlodipropionic acid 375 37. 330 7. 111 0. 636 150 -35 'xlahito l l u Thiodipro ionic acid 390 42. 470 7.734 0. 633 144 -40 'ietraethy ene glycol. 13% i th"? 1 e an mo sebgcie acid (0 25 mol) an 37.840 7. 493 0.614 151 4a Tetraethylene glycol- Acetic acid Adipic acid 395 116.3 14030 0.631 121 15 gthylene glycol ut 10 ac Adigi c acid i 435 62. 155 11. 476 0. 560 148 --35 Polyethylene glycol (300 mol wt.)
where R1 and R1 are radicals of the formula -(CH2CH2X)nCH2CH2-in whichX is a member of the group consisting of oxygen and sulfur and n is an integer from 1 to 7; where R: and R2 are alkyl groups containing 1 to 7 carbon atoms each; and where R3 is a radical selected from a group consisting of (1) radicals of the formula -(CH2)m-- where m is an integer from 4 to 8,
. (2) radicals of the formula -(CH2)nO(CH2)n where n is an integer from 2 to 4, and (3) radicals of the formula -(CH2)pS(CH2)p where p is an integer from 2 to 4.
(CH1CH2O) nCH2CH2- where n is an integer from 2 to 3.
3. A composition according to claim l in which R: is a radical of the formula (CH2)m where m is an integer from 4 to 8.
4. A compositionaccording to claim 3 in which m is 4.
5. As a new composition of matter a compound according to claim 1 in which R1 and R1 of the formula each represent the radical R: and R2 of the formula each represent the radical -(CH1):CH3 and R: of the formula represents CH2CH2S-CH:CH2
6. A composition according to claim 1 in which 2 R1 and R1 of the formula represent radicals of the formula in which R2 and R2 of the formula represent methyl radicals, and in which R3 of the formula represents the radical 7. A composition according to claim 1 in which R1 and R1 of the formula represent the radical (CH2CH2O 3CH2CH2- in which R: and R2 of the formula represent (CH2):CHz
6 Name Date Roberts Dec. 10, 1935 PAUL SMITH 2,234,722 Dickey et a1. Mar. 11, 1941 2,384,119 Muskat Sept. 4, 1945 REFERENCES CITED The following references are of record in the file of this patent: