Oxidatively stable esters derived from diamondoids totally hydroxylated at the bridgeheads

#This invention relates to carboxyric acid per-esters of perhyroxy diamondoids. More particularly, the invention relates to per-esterified diamondoids including alkyl substituted and unsubstituted adamantanes, and lubricant compositions containing the same.

#Efforts to improve upon the performance of natural mineral oil based lubricants by the synthesis of oligomeric hydrocarbon fluids have been the subject of important research and development in the petroleum industry for at least fifty years and have led to the relatively recent market introduction of a number of superior synthetic lubricants, for example, polyalphaolefins. In terms of lubricant property improvement, the thrust of the industrial research effort on synthetic lubricants has been toward fluids exhibiting useful viscosities over a wide range of temperature, i.e., improved viscosity index, while also showing lubricity, thermal and oxidative stability and pour point equal to or better than mineral oil. Viscosity index (VI) is the most common measure that is applied to the decrease in viscosity of petroleum oils with increasing temperature. A series of Pennsylvania oils exhibiting relatively small change in viscosity with changing temperature is arbitrarily assigned a VI of 100, whereas a series of Gulf Cost oils whose viscosities change relatively greatly is assigned a VI of 0. From the viscosity measurements at 40.degree. and 100.degree. C., the VI of any oil sample can be obtained from detailed tables published by the ASTM (ASTM D-2270). 14 Kirk-Othmer Encyclopedia of Chemical Technology 489 (Wiley, 1981). U.S. Pat. No. 4,913,794 to Le et al. teaches a method for improving the viscosity index of a lubricant stock and is incorporated herein by reference for its discussions of viscosity index and lubricant upgrading processes.

#U.S. Pat. No. 3,671,598 to Moore relates to the isomerization of adamantane-containing compounds in the presence of sulfuric acid to provide useful traction fluids.

#FIG. 1 is a GC trace of the starting diamondoid mixture used as feedstock for the distillation of Example 1.

#FIG. 2 is a GC trace of the adamantanes-enriched mixture recovered from the distillation of Example 1.

#FIG. 3 is a GC trace of the hydroxylated adamantanes product of Example 2.

#This invention provides novel per-esterified diamondoid compounds, mixtures of diamondoid esters containing per-esterified diamondoids, and a two-step method for making the per-esters and the mixed esters. The per-esterified diamondoid compounds and the mixed esters are useful as lubricant stocks due to their lubricity as well as their thermal/oxidative stability.

#Feedstocks useful in the present invention include substituted or unsubstituted adamantane, and a mixture of alkyl-substituted adamantane compounds is preferred. Examples of particularly preferred substituted adamantane starting materials include adamantane, methyladamantane, dimethyladamantane, trimethyladamantane, and the following adamantanes with at least one bridgehead position unsubstituted: tetra-, penta-, hexa-, hepta-, and octa-methyladamantanes.

#The first step of the two-step synthesis method of the present invention hydroxylates the tertiary adamantane bridgehead positions as well as the other tertiary carbons in the molecule. For example, 2-methyladamantane has four bridgehead tertiary carbons and one nonbridgehead tertiary carbon at the 2-position. Suitable oxygen donors include the inorganic persulfates, and OXONE brand monopersulfate compound (formula: 2KHSO.sub.5.KHSO.sub.4.K.sub.2 SO.sub.4, commercially available from E. I. Du Pont de Nemours and Company, 1007 Market Street, Wilmington, Del., 19898) is particularly preferred.