Patent GB-866502-A (GB)
Title: Manufacture of metal salts of dialkyl dithiophosphoric acids
IPC: C07F9/17
Filed: 1958-12-16
Abstract: Metal salts of dialkyl (or dicycloalkyl) dithiophosphoric acid suitable for use us additives for lubricants (see Group III) are obtained by reacting phosphorus pentasulphide with at least one alkanol or cycloalkanol having up to 14 carbon atoms at a temperature in the range of 160 DEG  to 200 DEG F. for a time in the range of 1 to 6 hours while maintaining the specific gravity of the reaction mixture in the range of 1,015 to 1,035 at 78 DEG F. to obtain a dark coloured reaction mixture and separating solids therefrom, neutralising the purified dark product with a basic inorganic metal compound at a temperature in the range of 140 to 200 DEG F., heat soaking the dialkyl (or dicycloalkyl) dithiophosphoric acid salt so obtained at a temperature in the range of 150 DEG  to 200 DEG F. for 1 to 4 hours, while maintaining the water content thereof at from 0,5 to 4 weight per cent and the pH at from 6,0 to 6,6 then separating substantially completely inorganic solids from the heat soaked acid salt by filtering while maintaining the water content at from 0,5 to 4 weight per cent., and drying the purified acid salt to a water content not exceeding one weight per cent.  Specified alcohols are methanol, ethanol, butanol, isobutanol, isopropanol, cyclohexanol, methyl isobutyl carbinol, 2-ethyl hexanol, methyl cyclohexanol and primary branched chain alkanols such as C5, C7 or C13 "Oxo" alcohols and mixtures of alkanols having from 3 to 14 carbon atoms may be used and especially a mixture of two alkanols having from 3 to 6 carbon atoms.  Suitable mixtures are isopropanol-methyl isobutyl carbinol, and isobutyl alcohol-primary amyl alcohol.  The neutralising agent is preferably an oxide or hydroxide of a suitable metal, e.g. zinc, magnesium, calcium, aluminium, manganese, iron, cobalt, nickel, copper, barium, or lead.  A diluent oil e.g. a hydrocarbon distillate oil is preferably used after the neutralisition and heat soaking steps and prior to the filtration to remove inorganic solids.  An example is given for the production of a zinc dialkyl dithiophosphate from a mixture of methyl isobutyl carbinol (70% wt.) and isopropanol (30% wt.) using zinc oxide as the neutralising agent.  The final drying step may be effected by stripping with an inert gas e.g. nitrogen, by azeotroping with benzene or isobutyl alcohol or by entrainment with a light hydrocarbon, e.g. hexane.ALSO:An additive for lubricating oils comprises a metal salt of a dialkyl or dicycloalkyl dithiophosphoric acid obtained by reacting phosphorus pentasulphide with at least one alkanol or cycloalkanol having up to 14 carbon atoms at a temperature in the range of 160 DEG  to 200 DEG F. for a time of 1 to 6 hours while maintaining the specific gravity of the reaction mixture in the range of 1.015 to 1.035 at 78 DEG F. to obtain a dark coloured reaction mixture, cooling the latter and separating solids therefrom, neutralising the purified dark product with a basic inorganic metal compound at from 140 DEG  to 200 DEG F., heat soaking the dialkyl dithiophosphoric acid salt at from 150 DEG to 200 DEG F. for 1 to 4 hours while maintaining its water content at from 0.5 to 4% weight and the pH in the range of 6.0 to 6.6 then separating substantially completely inorganic solids from the heat soaked acid salt by filtering, preferably after the addition of a diluent oil, e.g. a hydrocarbon diluent oil, while maintaining the water content at from 0.5 to 4% weight and drying the purified salt to a water content not exceeding 1% weight (see Group IV(b)). Specified alkanols and cycloalkanols are methanol, ethanol, butanol, isobutanol, isopropanol, cyclohexanol, methyl isobutyl carbinol, 2-ethyl hexanol, methyl cyclohexanol and C5, C7 and C13 oxo alcohols. Mixtures of C3-C14 alkanols and especially a mixture of two alkanols having from 3 to 6 carbon atoms may also be used.  The neutralising agent is preferably an oxide or hydroxide of a suitable metal, e.g. zinc, magnesium, calcium, aluminium, manganese, iron, cobalt, nickel copper, barium or lead.  In an example a concentrate of a zinc dialkyl dithiophosphate in a hydrocarbon distillate oil, said concentrate being obtained as above from a mixture of methyl isobutyl carbinol (70% wt.) and isopropanol (30% wt.) is added to a hydrocarbon lubricating oil (derived from a mid-continent crude by solvent extraction) and a methacrylate type viscosity index improver, a barium-calcium sulphurised phenate, calcium sulphate and a phosphosulphurised pinene are also added.  In another example the zinc dialkyl dithiophosphate is added to a mixed hydrocarbon lubricating oil and a polybutylene type viscosity index improver, a phosphosulphurised polybutylene neutralised with a basic barium nonyl phenol sulphide-sulphonate mixture and a chlorinated wax-naphthalene condensate also added.