Patent GB-561898-A (GB)
Title: Improvements in or relating to lubricating oils
Filed: 1942-04-02
Abstract: An extreme pressure lubricant comprises a lubricating oil having dispersed therein an aromatic hydroxy - substituted polysulphide having a carboxyl or ester substituent.  Preferably compounds having two aromatic radicals with the hydroxyl substituent in the para position to the polysulphide group are employed, mixtures of the di, tri, and tetrasulphides of such compounds being generally used.  The polysulphides may be associated with the corresponding thioethers, free sulphur, and halogenated organic compounds such as chlorinated paraffin wax, halogenated quinones, or nitro-polychlor-benzenes.  The mixtures of polysulphides are produced by reacting aromatic hydroxy-substituted esters such as methyl salicylate with sulphur monochloride or mixtures thereof with sulphur in the presence of a catalyst such as finely-divided copper or other metal or a compound such as anhydrous ferric chloride.  The nature of the product is varied by varying the proportion of sulphur monochloride used; when excess is employed, the di(3 - carbomethoxy - 4 - hydroxyphenyl) disulphide initially formed reacts with further molecules of sulphur monochloride to form dimers or higher polymers.  According to one example, a mixture of 15.2 grams of methyl salicylate acid 6.75 grams of sulphur monochloride is gently heated with 0.1 grams copper dust till the evolution of hydrogen chloride has ceased after which the mixture is heated to 120 DEG  C. for 10 minutes.  A shiny yellow solid consisting of di(3-carbomethoxy-4-hydroxyphenyl) disulphide 45-50 per cent, elementary sulphur 2 per cent, "loosely held" sulphur 5.6 per cent, di(3 - carbomethoxy - 4 - hydroxyphenyl) tri and tetrasulphide 20-30 per cent and di(3 - carbomethoxy - 4 - hydroxyphenyl) thioether 20-30 per cent is formed.  With rather more sulphur monochloride, a proportion of the dimer of di(3-carbomethoxy-4-hydroxyphenyl) disulphide is produced.  If flowers of sulphur are added to the reaction mixture an increase in the amount of tri and tetrasulphides and of elementary sulphur occurs.  A varying degree of chlorination also takes place.  In another example a mixture of amyl salicylate and sulphur chloride is heated with sulphur monochloride and a few iron filings and a stream of dry chlorine then passed at 80 DEG  to 100 DEG  C. for 2 hours through the viscous liquid produced.  A product containing 12.9 per cent chlorine and 8.9 per cent elementary sulphur is obtained. To prepare pure products free from mixtures, methyl salicylate is stirred with chlorsulphonic acid first below 35 DEG  C. and then at 70 DEG  C. and the mixture poured into concentrated HCl and alcohol. The 6-chlorosulphonyl methyl salicylate produced is then refluxed with zinc dust to form methyl 5-mercaptosalicylate, which on oxidation with ferric chloride gives di(3 - carbomethoxy - 4 - hydroxyphenyl) disulphide.  Upon warming with dilute alkali this material hydrolyses to di(3 - carboxy - 4 - hydroxyphenyl) disulphide.  From methyl - 5 - mercaptosalicylate the corresponding acid can be formed by hydrolysis and upon suspending this product in dry chloroform and adding sulphur monochloride gradually a white compound di(3-carboxy-4-hydroxyphenyl) tetrasulphide can be obtained. This compound on refluxing with absolute alcohol previously treated with dry HCl yields di(3-carbothoxy - 4 - hydroxyphenyl) tetrasulphide.  Tests made with this compound show that only negligible quantities of sulphur were removed by heating with copper powder for half an hour at 100 DEG  C., which was the test applied for determining elementary sulphur (as distinguished from "loosely held" sulphur) in the other tests.  For preparing extreme pressure lubricating oils by means of the above materials, from 0.5 to 2 per cent may be added. Tables are given showing the results of film rupture tests on oils containing materials produced according to the examples.  The proportion of "loosely held" sulphur should be as high as possible and that of free (elementary) sulphur as low as possible. In any case free sulphur should not exceed 15 per cent.  The p materials may be used in admixture with known addition agents for improving the properties of lubricating oils.  Specifications 291,100 [Class 2 (iii)], 455,235 and 498,046 are referred to.