Process for the preparation of dithiophosphoric acids

Details Process for the preparation of dithiophosphoric acids Process for the preparation of dithiophosphoric acids

1993-04-06

1997-12-30

Ambrose, Michael G.

Organic compounds -- part of the class 532-570 series

Organic compounds

Phosphorus esters

558123, C07F 918, C07F 917, C07F 9165

Patent

active

057032629

DESCRIPTION:

BRIEF SUMMARY
This invention relates to the preparation of dithiophosphoric acids.
Dithiophosphoric acids, which are important intermediates in the production of lubricant and oil additives, are generally made by reaction of phosphorus(V) sulphide (also called tetraphosphorus decasulphide, P.sub.4 S.sub.10) with an appropriate alcohol or phenol. The reaction proceeds in accordance with the equation:
According to U.S. Pat. No. 3,274,300 (Van Wazer et al) improved yields of dialkyldithiophosphoric acids (called in this specification O,O-dialkylphosphorodithioates) are obtained if the alcohol is reacted with a phosphorus sulphide and an excess of sulphur. According to this specification, it is essential to use sufficient sulphur to provide a sulphur to phosphorus atomic ratio of at least 2.6, i.e. more sulphur than that required to form phosphorus(V) sulphide, and this excess sulphur must be in solution or chemical combination with the phosphorus in the phosphorus sulphide composition. A mechanical mixture of sulphur with phosphorus(V) sulphide gives an inferior result and according to a comparative example, reaction of phosphorus(V) sulphide with n-butanol at the reflux temperature (about 114.degree. C.) in the presence of additional sulphur to provide an overall atomic ratio of sulphur to additional sulphur to provide an overall atomic ratio of sulphur to phosphorus of 3.5, gives a yield of dibutyldithiophosphoric acid (O,O-dibutylphosphorodithioate) of only about 60%.
We have now surprisingly discovered that excellent yields of dithiophosphoric acids may be obtained by reaction of phosphorus sesquisulphide (P.sub.4 S.sub.3) with elemental sulphur and the required alcohol or phenol at elevated temperature. The reaction apparently proceeds in accordance with the equation: overall stoichiometry as the reaction of phosphorus(V) sulphide with an alcohol, but it is totally unexpected that phosphorus sesquisulphide would react with sulphur at the relatively low temperatures which are used in the new process, and indeed it is not clear that the new process proceeds via phosphorus(V) sulphide as intermediate.
The present invention accordingly provides a process for the preparation of a dithiophosphoric acid which comprises reacting phosphorus sesquisulphide with sulphur and an alcohol or phenol at elevated temperature, the overall atomic ratio of sulphur to phosphorus being at least 2.5 to 1.
The process is preferably performed at a temperature from about 85.degree. C. to 150.degree. C., and most conveniently at the reflux temperature of the alcohol or phenol used. A solvent may be included in the reaction mixture, but is usually unnecessary unless the boiling point of the alcohol or phenol used is above the decomposition temperature of the starting materials or reaction products.
A wide variety of alcohols or phenols can be used in the new process including more particularly mono- and polyhydric, straight or branched aliphatic alcohols of up to 20, preferably 3 to 10, carbon atoms, which may be substituted, eg. by a mercapto radical of formula R'-S- where R' is a substituted or unsubstituted aliphatic radical of up to 12 carbon atoms or by an acyloxy radical of up to 20 carbon atoms, and alkyphenols having up to 20 carbon atoms in the alkyl residue. Specific examples of alcohol and phenols which can be used in the new process are n-butanol, 2-ethyl-hexan-1-ol, isobutanol, glycerol, glycerylmonooleate, p-nonyl-phenol and p-dodecylphenol. Mixtures of alcohols and phenols can also be used, eg. isopropanol and sec-hexanol, sec-butanol and iso-butanol, sec-butanol and 2-ethyl-hexanol, and isobutanol and isopentanol. Since for practical reasons a liquid product may be preferable to a solid crystalline product, use of mixtures of alcohols and/or phenols is often preferred.
The proportion of sulphur in relation to the phosphorus sesquisulphide should be at least sufficient for the stoichiometry of the reaction as set out above. Both the phosphorus sesquisulphide and the sulphur can be of ordinary reagent grade and in finely divided for

REFERENCES:
patent: 3274300 (1966-09-01), Wazer et al.

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