Ashless Phosphorus-Containing Lubricating Oil Additives 73
where R is an alkyl group, typically C 8 −C 22. It is also possible to use secondary and tertiary amines,
R 2 NH and R 3 N in the production of these salts.
3.3.4 NEUTRAL PHOSPHITE ESTERS
As with phosphate esters, it is possible to produce both neutral and acid phosphite esters. The neu-
tral triaryl phosphites are produced by reacting phosphorus trichloride with a phenol or substituted
phenol (reaction 3.14).
PCl 33 3ArOH (ArO) P 3HCl
triaryl phosphite→ (3.14)This is also a stepwise process occurring through the production of the monoaryl and diaryl hydro-
gen phosphite intermediates.
The production of neutral trialkyl phosphites using PCl 3 requires the addition of a tertiary
amine base to neutralize the acid formed (reaction 3.15). Unless the HCl is removed quickly, it can
cause the process to reverse with the production of an alkyl halide and the dialkyl acid phosphite
(reaction 3.16).
PCl 333 3ROH 3R N P(OR) 3R NHCl
trialkyl phosphite→ (^3) (3.15)
P(OR) HCl RCl (RO) POH 2
dialkyl acid phosphite
3 → (3.16)
The use of mixtures of different alcohols or different phenols can result in the production of mixed
alkyl or aryl phosphites. Mixed alkylaryl phosphites can be produced by reacting triaryl phosphite
with alcohols to give a mixture of aryldialkyl- and alkyldiaryl phosphites (reaction 3.17). A com-
mercial example of such a product promoted as an oil additive is decyldiphenyl phosphite.
(ArO) P 32 ROH (ArO) POR ArOH ArOP
alkyldiaryl phosphite
→ROH→((OR) 2 2ArOH
aryldialkyl phosphite
(3.17)
Because of their widespread use in the plastics industry as stabilizers for polyvinylchloride, etc.,
many different neutral phosphites are commercially available. These range from C 2 to C 18 alkyl
(normally saturated) and from C1–9 alkaryl. In lubricant applications, the most common products
are those with alkyl chains of C 8 −C 18 and C 10 −C 15 alkaryl, for example, trioctyl phosphite and tris-
(2,4-ditertiarybutylphenyl) phosphite. The last type is increasingly important in view of its better
hydrolytic stability.
3.3.5 ALKYL AND ARYL ACID PHOSPHITES
Alkyl and aryl acid phosphites are manufactured by reacting together phosphorus trichloride, an
alcohol (or phenol), and water (reaction 3.18):
PCl ROH H O RO POH HCl
dialkyl acid phosphite
322 ^23 →() (3.18)
Mixtures of alcohols, as indicated earlier, may also be used to produce di-mixedalkyl phosphites.
The commercially available dialkyl acid phosphites vary from C 1 to C 18 with use as oil additives
falling mainly in the range of C 8 −C 18.