Lubricant Additives

70 Lubricant Additives: Chemistry and Applications

composition, has little impact on AW properties. Of greater importance are the actual phosphorus
content and the level of impurities present, particularly those that are acidic.
In the past, the tri-o-cresyl phosphate content was a source of much concern in view of the high
neurotoxicity of the material (see Section 3.19). However, the feedstock that is most widely used
today in the production of TCP, is predominantly a mixture of m- and p-cresol, and o-cresol levels
are extremely low.

3.3.1.2 Synthetic Phosphates from Isopropylphenols

In this case, phenol is alkylated with propylene to produce a mixture of isomers of isopropylated
phenol (Figure 3.4). Depending on the reaction conditions and the degree of alkylation, it is pos-
sible to produce a range of isopropylphenyl phosphates (IPPPs) with viscosities varying from ISO
VG 22 to VG 100. In seeking an alternative product to TCP (an ISO 32 viscosity-grade fl uid), the
products with the closest phosphorus contents and viscosities (IPPP/22 and IPPP/32) are most
widely used.

3.3.1.3 Synthetic Phosphates from Tertiarybutylphenols

In a similar fashion to the manufacture of isopropyphenyl phosphates, it is possible to produce a
range of phosphates from butylated phenols prepared by the reaction of isobutylene with phenol
(Figure 3.4). The tertiarybutyl substituent is larger in size than the isopropyl substituent, and this

O P O

O

O

CH 3

CH 3

CH 3

Tricresyl phosphate

O P O

O

O

CH 3

CH 3

CH 3

CH 3

CH 3

CH 3

Trixylyl phosphate

FIGURE 3.3 The structures of tricresyl and trixylyl phosphate.

C CH 2

CH 2

H

CH 3 OH OH OH OH

+++

C

CH 3

CH 3

OH OH OH

++

Propylene Phenol ortho- meta-

meta-para-

para-

Isomers of isopropyl phenol

Isomers of tertiarybutyl phenol

Butylene Phenol

FIGURE 3.4 Process for the production of feedstocks used in the manufacture of synthetic phosphates.