Lubricant Additives

Detergents 129

With naphthalene, however, steric factors are not as important because of its bicyclic nature.
The alkyl groups are likely to be attached to different aryl rings, except for very highly alkylated
naphthalenes. Commercial NA-SUL® products are based on alkylnaphthalene chemistry.
During petroleum refi ning, crude mineral oil is washed with a sulfonating agent such as sul-
fur trioxide or oleum [36]. Crude mineral oil contains reactive unsaturated compounds containing
multiple bonds and alkylaromatics. These react with sulfur trioxide to form sulfonic acids. This is a
desirable step because oils containing unsaturates and aromatics have a greater susceptibility toward
oxidative breakdown, which could lead to the formation of increased deposits. If this occurs, it is
likely to lead to equipment malfunction [5,23,37–42]. An analogous process is used to manufacture
medicinal-quality white oil from petroleum. In the subsequent reaction, the sulfonic acid fraction is
reacted with sodium hydroxide to convert the acids into sodium salts. These salts are washed with
water to extract green acid soaps, which are used in many consumer products. The residual water-
insoluble material is then extracted with alcohol. This results in the isolation of mahogany acid
soaps, which are useful in making detergent additives. The process is summarized in Figure 4.5.
Alkylphenols are made in a manner analogous to alkylbenzenes, that is, by alkylating phenol
with an olefi n in the presence of an acid catalyst. The preferred catalysts are sulfuric acid, alumi-
num chloride, and boron trifl uoride [39–42]. The alkylphenols can be either converted directly into
their neutral or basic salts or further reacted with sulfur or sulfur dichloride to form sulfur-bridged
alkylphenols and with formaldehyde to form methylene-bridged alkylphenols. This is shown in
Figure 4.6.
Alkylsalicylic acids are prepared from alkylphenols by reacting the alkali metal, especially
potassium, phenates with carbon dioxide. The reaction is known as the Kolbe–Schmitt reaction [43].
Like the natural sulfonate process, this process yields alkali metal salts.
These must be either neutralized with a mineral acid to free acids to use them to make deter-
gents or reacted directly with a metal halide, such as calcium chloride or magnesium chloride, to
make the calcium or magnesium soaps [44].
Alkenylphosphonic and alkenylthiophosphonic acid detergents are only rarely used. The acids
are prepared by reacting polyisobutylene of varying molecular weights with phosphorus pentasul-
fi de and the subsequent hydrolysis of the resulting adduct [45,46]. The adduct is believed to result
from an ene-type addition of phosphorus pentasulfi de to polyolefi n. This type of addition does not
result in the loss of the double bond, but it shifts the double bond down the carbon chain. Unless
steric factors hinder the reaction, at least theoretically, the ene product can react with another mol-
ecule of phosphorus pentasulfi de. This process can extend further. The adduct is hydrolyzed by the
use of steam. One obtains a complex mixture of acids that include fully hydrolyzed (sulfur-free)

FIGURE 4.5 Isolation of natural sodium sulfonates.

Mineral oil + SO 3 Sulfonated unsaturated

and aromatic compounds

+ NaOH

Green acid soaps Water extraction

Alcohol extraction

Largely paraffinic

mineral oil

Mahogany acid soaps

Natural detergent

substrates