Sulfur and Fatty Esters in Multicomponent Additives

The work of Dorinson [63] on the relation between the basic chemistry and the additive action of sulfurized fatty materials deals with one of the most widely used multicomponent lubricant additives in industry. There are two aspects to the multicomponent nature of products of the sulfurization of ethenoid fatty esters. One is the consequence of the complexity of the sulfurization reaction, so that even if the starting material is a pure fatty ester, the ultimate sulfurized product is a mixture of several species. But the most important aspect of the structure of the sulfurized fatty product is the fact that even were it a single-component substance, it would still be intrinsically multifunctional. For instance, Dorinson [63] reported that the product of the sulfurization of methyl u-undecenoate can be shown to contain at least 50% of the following compounds  

The long-chain structure by itself, as exemplified by n-aliphatic hydrocarbons, shows no extreme-pressure lubricant functionality. Evidently the additive action is connected with the carboxylate ester and the sulfide structures. To demonstrate this, Dorinson isolated an ester/ sulfide component from sulfurized methyl undecylenate, identified its structure, synthesized an organosulfide-ester with this structure, and showed that the lubricant additive activity was the same for the fraction separated from sulfurized methyl undecylenate end for the synthetic material. The data, summarized ib Fig. 11-15, were obtained tiy pin-and-disk wear tests with hardened steel rubbing specimens and show the effect of contact pressure on the depth-rate of wear. The significant feature is the change from a low rate of wear, relatively insensitive to increase of pressure in the range 0.276-1.724 GPa (40,000-250,000 Ib/in ), to pressure-sensitive increase of wear rate at 1.724 GPa and higher. 

The separate action of the organosulfur component and the ester component in the organosulfide-ester structure was studied with di-sec-octyl disulfide and methyl laurate respectively. The results are given by the curves I and II of Fig. 11-16. Up to the limit of the load capacity of the apparatus, the solution of di-sec-octyl disulfide shows no ameliorating effect relative to the course of wear with uncompounded base oil. Methyl laurate has an inhibitory effect on the wear rate up to a contact pressure of 1.379 GPa (200,000 lb/in2), after which the wear rate increases drastically on further loading and the test terminates with 

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