April 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
491
coYcLusIoss
ACKNOWLEDGMENT
A rlumber of diester fluids have been found with a combination of properties desirable in lubricants for use a t low temperatures. T h e most suitable compounds are long-chain diesters with two or more short aliphatic side chains suitably positioned. Although these compounds contain two ester groups (and in some cases also ether-oxygen linkages), they are dominantly hydrocarbon in composition. They are found t o resemble in viscometric, thermometric, and volatility properties the geometrically analogous hydrocarbons, particularly a t high molecular weights. T h e most promising fluids have molecular weights ranging from 300 t o 600 and freezing and pour points from -40" t o lese than - 100" F. They have maximum evaporation rates at 150" F. of 0.5% by weight, decreasing t o values of less than 0 . 1 5 for those of t h e higher molecular weights. T h e flash and fire points ranged from 300" t o 500" F., t h e spontaneous ignition temperature from 700" t o 800" F., and t h e spray flammability from 13 t o 45% oxygen, increasing with t h e viscosity of the fluid. T h e fluids can be grouped in four classes according t o their viscosities a t 100" and -40" F., respectively: ( a ) 5 t o 10 and 300 t o 1300 centistokes: ( b ) 10 t o 14 and 1200 t o 3000 centistokes: (c) 15 t o 25 and 6700 t o 8300 centistokes: ((1) 30 t o 60 and 7000 t o G6,OOO centistokes. The best combination of viscometric properties are found for several types of diesters: (1) glutarates, adipates, azelates, and sebacates made with sec-amy1 alcohol, 3-methylbutanol, 2-ethylbutanol, 2-ethylhexanol, and the branched-chain secondary alcohols, undecanol and tetradecanol; (2) those made by reacting the above acids with 2-(2'-ethylbutoxy) ethanol; (3) those made by reacting hexamethylene glycol or decamethylene glycol with a branched-chain acid such as 2-ethylhexanoic acid: and (4)those made by reacting triethylene glycol or a polyethylene glycol with 2-ethylhexanoic acid. The somewhat inferior viscometric properties of type 3 diesters, as compared t o type 1, coupled n.ith their lesser availability make t h e type 3 fluids of little present interest for lubrication. T h e higher specific gravities and the ability of class 2 and 4 diesters to dissolve more water than those of class 1 of t h e same molecular weight makes them less desirable for some applications. It is concluded t h a t specially selected diesters of classes 1, 2, and 4 are good base fluids for the development of lnbricant compositions, those of cl 1 being most suitable for the greatest variety of uses. Also a comparative study is decirable of the oxidation stabilities and t,he effectiveness with which these fluids can he inhibited agiinst oxidation and rusting hy tlir nction of chemical addition agents.
T h e authors gratefully acknowledge the cooperation received from their co-workers, especially from Charles Saunders who supplied t'he d a t a relating to solubility and hydrolysis, Miles V. Sullivan who made the measurements of spontaneous ignition temperature and spray flammabilit'y, and Paula Taylor and Charles Saundcrs who obtained the data on flash and fire points. LlTERATURE CITED
Aepli, 0 . T., and McCarter, I T , S.,ISD. ENQ.CHEM.,AX. I . R . , and eo--workers. 0 . S . R . D . R ~ p t 1894 . 1943). Fischer, Karl, A n g e w . Chem., 48, 394 (1933), Helmore, W., in "Science of Petroleum" (Dunstan rt ( I ! . ) , Val. IT, p. 297'0, Oxford Univ. Press. 1938. Hickman, K. C., J . Franklin Inst., 221, 215 (1%36). I b i d . , 221, 383 (1938). Hickman, K. C., and Sanford, C. It,, Ret. Sci. I m t i , m i p r r / a . 1, 140~~~~, 11930).
Mikeska, L. A , , IND.ESG.CHEM.,28, 97'0 (1936~. Natl. Bur. of Standards, Supplement to C'irc. C410 (1937). Nissan, -1.H., Clark, L. V. W., and Nash, A. IT., J . I m / . F'-I, phenosyphenyl, xenyl, and dodecylphenyl), of phenylhendecThe pure diesters resemble highly refined petroleum oils in anoic acid, and of the available naphthenic and petroleum their inahility t o prevent the displacement of the oil from iron or steel surfaces hy drops of mater: hence they do not have rust sulfonic acids having molecular weights from 300 t o 600, were all able to inhibit the rusting of steel in this test when used in conpreventive properties. .I few samples of commercially availcentrations of 0.2 t o 0.5% b y m i g h t . T h e salts of t h e acids able diesters were found t o have some rust preventive value, having the highest molecular n-eights Tere those required in the b u t this was found t o tie due t o the presence of an adsorbable lowest concentration. Thus, zinc di-(phenylhendecanoate), impuritv. -1common and often adequatelv effective met,hod of imparting rust, preventive propertie? t o oils is by dissolving or zinc di-(phenyletearate), and zinc di-(dodecylphenylstearate) dispersing in them a small amount of a polar and hydrophilic \\-ere needed in weight concentrations of 0.5, 0.35, and 0 . 2 5 5 , compound of suitahle itruetiire. .in investipation on the mode respectively. Sorbitan mono-oleate and also any one of the of action o f such additives, the relation of organic structure t o animoniuni compounds made from cyclohexylamine or dicyclorust inhilitive value, and the significance of the various empirical hexylamine and either lauric or sylylstearic acid !yere satisfactory in inhibiting rusting a t neight concentration of 0.5$. test methods was completed during the war, and a preliminary For many applications a greater degree of rust inhibition was report rvas made (1). This background n ' a ~used as a guide i n the t election of riiqt in hi hi to^ and of the niethods of testing the desired than could be made evident n-ith the turbine oil rusting oils for rust preventive value. I t n-ne concluded t h a t the rust teat. The various inhibited oils found satisfactory in the turinhibitor5 found efcectire in hydrocarbons should also be effecbine oil corroqion test r e r e therefore esposed t o the static water drop t e 4 ( 1 ) using distilled 11-ater a t 140' F. .I11 of the inhihitors Ithough differences in the solubilities of the compounds in the two types of fluids might affect their relative by iveight, were mentioned, in coiicentrntions of 0.2 t o 0.5', ratings as rust inhibitors. wtkfactory after 168 hour3 of esposure except the sortlitan Since the most promising application of diehters is in the mono-oleate and the ammonium compounds ~ l i i c hirere required del-elopnient of l o n temperature luhricants, only tho.se rust inin :i concentration of 1.OC;. 0
T ~ B L111. E
EFFECT
Intioxidant
- ........
.
diphenyl;^ II i i ii e S - ( p - f e r / - a i r i v l p h e i i v l ) ethanolamine
O F VARIOCS I X H I B I T O R S O N OXID.\TIOS
10
:1 10 o-Cyclohesyiphenof 10 p-Cyclohex?li)henol 20 p-Phenylphennl 0 20 4-te~.t-Ruty1-2-phenylphenol 0 10 4-teri-Butyl-o-crerol 0 10 p-lert-hniylpheiiol 0 10 6-Isoprop?l-ni-cresol 0.10 4-id-Butylcatechol 0 10 a Using oxygen a t 125 pounds jnitial pressure b n.c. = no change,
OF
DI-(z-ETHYLHEXYL) S E B i C i T E
Appearance after Oaida-ion Te-t h .___ T'iscositp at 100" F. yellIra1iza2481' Initial, tinn S o I)ur?lcentistokes Increase Increase Fluid C w ~ p ~ r uniin Steel 12.6 0.8 16 6 Cloudy Clxidized. c n r r oded 11.r. 11.c. 12 6 -0 8 0 21 nr. 11'. .\mber, -light sedinient Oxidized 1 0 12 6 0.0 2 6 n a r k green Oxidized iic. ii.(?. 2 5 12.6 0 0 0 33 Clear, slightly yellow Oxidized n.c. 11 r . 0 5 12 6 0 0 0.07 n.r III'. Clear, slightly yellow Oxidized 0 5 12 6 -0.8 2.6 I.ight green Xnne present I1.C 1I.C. 0 12.6 0.0 2 6 Zieht e r w n Oxidized n.r. 11 c . 0 12.6 0.0 0 07 Clk.r,':lightly yellow n . r . n.c. i1.c. 0 12.6 0.0 0.10 Clear Oridized n.c. n c. 0 5 12 6 0 0 0 20 Clear, slightly yello\v Oxidized 11.c 11.1'. 0 12.6 0.0 0.07 Clear. pale yellow (Ixidized n,r. i1.c. 12.6 0.5 0 0 0.32 Clear, slightly green Oxidized 11.r. 11.c. a n d bomb maintained a t 212" F. for 168 hours.
C'oncn . W t . no 0 0 0 0 0
3T.IBILITY"
AP, 1.h. 33 0
INDUSTRIAL AND ENGINEERING CHEMISTRY
494
Vol. 39, No. 4
limitation of the available rust-inhitititig compounds. \\
r
POLYIIER THlCKENERS A N D V . 1 . IIlPROVERS
I.
