Lubricant Additives

152 Lubricant Additives: Chemistry and Applications

the reaction will stop at this stage. This is shown in reaction 5.3 of Figure 5.6. If the new double
bond is external, the reaction with another molecule of maleic anhydride is possible [45]. This is
shown in reaction 5.4.
For dispersants, polyisobutylphenol is the alkylphenol of choice. It is synthesized by reacting
polyisobutylenes with phenol in the presence of an acid catalyst [56–58]. Lewis acid catalysts, such
as aluminum chloride and boron trifl uoride, are often employed. Boron trifl uoride is preferred over
aluminum chloride because the reaction can be carried out at low temperatures, which minimizes
acid-mediated breakdown of polyisobutylene [58]. This is desired because dispersants derived from
low-molecular-weight phenols are not very effective. Other catalysts, such as sulfuric acid, meth-
anesulfonic acid, and porous acid catalysts of Amberlyst® type, can also be used to make alkylphe-
nols [59,60]. Polyisobutylene also reacts with phosphorus pentasulfi de through an ene reaction, as
described in Chapter 4. The resulting adduct is hydrolyzed by the use of steam to alkenylphosphonic
and alkenylthiophosphonic acids [2,3]. The methods to synthesize alkylphenols and alkenylphos-
phonic acids are shown in Figure 5.7.
A new carboxylate moiety derived from glyoxylic acid to make dispersants has been reported in
the literature [61–65]. However, at present, no commercial products appear to be based on this
chemistry.

5.6.3 THE POLAR MOIETY

The two common polar moieties in dispersants are based on polyamines and polyhydric alco-
hols. The structures of common amines and alcohols used to make dispersants are shown in
Figure 5.8.
The polyamines are manufactured from ethylene through chlorination, followed by the
reaction with ammonia [66]. The reaction scheme is given in Figure 5.9. As shown, polyamines

R

(^432)
H 3 C
H 3 C
H 3 C
CH H^3 C
3
CH 3 CH 3 CH 3
H 3 C CH 3
CH 2
CH 2
CH 3 CH 3
CH 3
CH 2 CH 2
CH 3
CH 2
CH 3 CH^3
CH 3 CH 3
CH 2
CH 3
CH 3
CH 2 CH 3
1
R
(^432)
1
I
VI

• CI 2 −CI

−H•

−H• (From C 5 )

CI H

II

R 4

1

3 2

H

III

• transfer

H•transfer

R

4

3

2

1

(From C 4 )

H

(^432)
C^1
H
H
H

• 5

V

VII

IV

R R^43

2

H^1

H

R

(^432)
1
FIGURE 5.5 Mechanism of chlorine-assisted diene formation.