Lubricant Additives

Dispersants 153

contain piperazines as a by-product. Examining the structures of various amines, one can see
that they contain primary, secondary, and tertiary amino groups. Each type of amino group has
different reactivity toward alkenylsuccinic anhydride. The primary amino group reacts with
the anhydride to form a cyclic imide, the secondary amino group reacts with the anhydride to
form an amide/carboxylic acid, and the tertiary amino group does not react with the anhydride
at all [67].
However, it can make a salt if a free carboxylic acid functionality is present in the molecule,
as is the case in amide/carboxylic acid. These reactions are shown in Figure 5.10. New high-
molecular-weight amines derived from phosphoric acid–catalyzed condensation of polyhydroxy
compounds, such as pentaerythritol, and polyalkylene polyamines, such as triethylenetetramine,
are known [68]. These amines are claimed to form high total base number (TBN) dispersants with

Diels−Alder reaction

Ene reaction

O

H

H O

O

H 3 C

R

H

H 3 C

H 3 C

R

H

H 3 C

CH 2

CH 2

O

O

O

H 3 C

H 3 C CH 2

C

O

R

O

CH O

3

O

H 3 C

H 3 C

CH 3

H

H O

O

R

R

H 3 C

O

CH 2

H 3 CCH 3

O

O

H H

R

H 3 C

H

O

O

O

H 3 C CH 3

C

H

R

H

O

O

O

CH 2

H 3 C

H 3 C

H

H H

H

C

H H

O

R

H

O

O

H 3 C

H 3 C

(5.1)

(5.2)

(5.3)

(5.4)

FIGURE 5.6 Mechanism of alkenylsuccinic anhydride formation.