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124 Lubricant Additives: Chemistry and Applications

Oxidation inhibitors, detergents, and dispersants make up the general class of additives called

stabilizers and deposit control agents. These additives are designed to control deposit formation,

either by inhibiting the oxidative breakdown of the lubricant or by suspending the harmful products

already formed in the bulk lubricant. Oxidation inhibitors intercept the oxidation mechanism, and

dispersants and detergents perform the suspending part [3,4]. Detergents are the topic of this chap-

ter, and dispersants are the topic of the subsequent chapter. Detergents are metal salts of organic

acids that frequently contain associated excess base, usually in the form of carbonate. Dispersants

are metal-free and are of higher molecular weights than detergents. The two types of additives work

in conjunction with one another.

The  nal products of combustion and lubricant decomposition include organic and inor-

ganic acids, aldehydes, ketones, and other oxygenated materials [4,5]. The acids have the

propensity to attack metal surfaces and cause corrosive wear. Detergents, especially basic deter-

gents, contain reserve base that will neutralize the acids to form salts. Although this decreases

the corrosive tendency of the acids, the solubility of the salts in the bulk lubricant is still low.

The organic portion of the detergent, commonly called soap, has the ability to associate with

the salts to keep them suspended in the bulk lubricant. However, in this regard, detergents are

not as effective as dispersants because of their lower molecular weight. The soap in detergents

and dispersants also has the ability to suspend nonacidic oxygenated products such as alcohols,

aldehydes, and resinous oxygenates [4]. The mechanism by which this occurs is depicted in

Figure 4.1.

Dispersants and detergents together make up the bulk, ∼45 to 50%, of the total volume of the

lubricant additives manufactured. This is a consequence of their major use in engine oils, transmis-

sion  uids, and tractor hydraulic  uids; all of which are high-volume lubricants [6].

As mentioned earlier, detergents neutralize oxidation-derived acids as well as help suspend

polar oxidation products in the bulk lubricant. Because of this, these additives control rust, corro-

sion, and resinous buildup in the engine. Like most additives, detergents contain a surface-active

polar functionality and an oleophilic hydrocarbon group, with an appropriate number of carbon

atoms to ensure good oil solubility [2]. Sulfonate, phenate, and carboxylate [7] are the common

polar groups present in detergent molecules. However, additives containing salicylate and thiophos-

phonate functional groups are also sometimes used.

FIGURE 4.1 Oil suspension of polar oxidation products.

Oil

Polar

oxidation

product

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Detergents 125

4.2 DETERGENT TYPES

Detergents are the metal salts of organic acids. The acids normally used to synthesize these com-

pounds include arylsulfonic acids such as alkylbenzenesulfonic acids and alkylnaphthalenesulfonic

acids [8–11]; alkylphenols [12–16]; carboxylic acids such as fatty carboxylic acids, naphthenic acids,

and petroleum oxidates [17–20]; and alkenylphosphonic and alkenylthiophosphonic acids [21–23].

Sometimes, a mixture of different types of acids is also employed [24]. The reaction of these acids

with inorganic bases, such as metal oxides, metal hydroxides, and metal carbonates, results in the

formation of salts [7]. The quantity of the metal used may be equal to (stoichiometric amount) or

in excess of the exact amount necessary to completely neutralize the acid functionality. The pres-

ence of metal in stoichiometric amount results in the formation of the neutral salt, often referred

to as a neutral detergent or soap. If the metal is present in excess, the detergents are called basic,

overbased, or superbased [7,25]. It is important to note that basic detergents appear as clear homo-

geneous  uids, the same as neutral detergents, because the excess metal is present in a colloidal

form [26]. The general formulas for metal sulfonates, metal phenates, and metal carboxylates are

presented in Figure 4.2.

The excess base in basic detergents may be present as metal hydroxide, metal carbonate, or

both. For neutral detergents, x and y in the formulas in Figure 4.2 are zero. For low overbased

detergents, such as those with a base number of about 50 or less, x may be zero and y may be a low

number, or both x and y may be low numbers. This implies that slightly overbased detergents are

either carbonate-free or contain a mixture of both the hydroxide and the carbonate. Highly over-

based detergents invariably have a large amount of carbonate as the reserve base. That is, in their

case, y is low and x is very high. In some cases, x can be as high as 20, or more. In summary, the

excess base per equivalent of acid in metal hydroxide–containing detergents is generally lower than

that in metal carbonate–containing detergents.

4.3 DETERGENT PARAMETERS

Detergents are described chemically in terms of their metal ratio, percent sulfated ash, degree of

overbasing or conversion, soap content, and total base number (TBN) [7].

The metal ratio is de ned as the total equivalents of metal per equivalent of acid. The percent

sulfated ash is the ash produced when the detergent is treated with sulfuric acid and burned. All

organic material in the detergent burns, leaving behind the metal sulfate ash. Sulfate ash results

from the reaction of metal compound with sulfuric acid either directly, as with metal hydroxide and

metal carbonate, or through the oxidative degradation of the metal sulfonate. Detergents are not the

only additives that result in sulfate ash. Other metal-containing additives in the lubricant also con-

tribute toward it. Such additives include metal carboxylates and metal dialkyldithiophosphates such

as zinc dialkyldithiophosphate. The former compounds are sometimes used as friction modi ers

and corrosion inhibitors, and the latter compounds are commonly used as oxidation inhibitors and

antiwear agents. Because the metal compounds can lead to the formation of the inorganic material

FIGURE 4.2 General formulas for detergents. (Adapted from Rizvi, S.Q.A., Additives and additive chemistry.,

ASTM Manual on Fuels and Lubricants.)

(RSO

)

yM(OH)

(RCOO)

yM(OH)

(RPhO)

yM(OH)

Basic sulfonate

a and c = 1 and b = 2, if the metal M is monovalent; a and c = 2 and b =1, if the metal M is divalent

Basic carboxylate

Basic phenate

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126 Lubricant Additives: Chemistry and Applications

(ash) on combustion, a formulator must know the metal content of a formulation to offset any prob-

lem that might occur. This is because the lubricant travels past piston rings into areas that experi-

ence  ame and high temperatures, such as the top land and the groove behind the top ring; it burns

to produce ash. Ash is undesired because it is believed to initiate deposit formation. Sulfated ash is

one of the methods used to assess the metal content of a lubricant, and the methods to determine

this are described in the ASTM Standards D 482 and D 874 [27].

The degree of overbasing is the number of equivalents of the metal base per equivalent of the

acid substrate. This is usually expressed as conversion, which indicates the amount of inorganic

material relative to that of organic material. Conversion is expressed as the number of equivalents of

base per equivalent of acid times 100 [7]. The soap content is the amount of neutral salt as a percent

of detergent composition.

The TBN of the detergent re ects its ability to neutralize acids. For basic sulfonate and phos-

phonate detergents, only the overbased portion of the detergent, that is, the carbonate and the

hydroxide (see Figure 4.2), possesses this capability. The neutral metal sulfonates and phospho-

nates, that is, soaps, lack this ability. However, for basic carboxylates, salicylates, and phenates,

soaps also possess the acid-neutralizing ability. This is because, unlike sulfonates and phospho-

nates that are strong acid–strong base salts, metal carboxylates, metal salicylates, and metal phe-

nates are strong base–weak acid salts. This makes them Lewis bases, hence the acid-neutralizing

ability.

Let us try to calculate the detergent parameters for a detergent of a hypothetical molecular

formula (RSO

)

(CO

)

(OH)

.* In this formula, v, w, x, and y denote the number of sulfonate

groups, the number of calcium atoms, the number of carbonate groups, and the number of hydroxyl

groups, respectively. The metal ratio, the total equivalents of metal per equivalent of acid, for such

a detergent equals to 2w/v. The coef cient 2 signi es the divalent nature of calcium. For metals

such as sodium and potassium, which are monovalent, the ratio equals to w/v. The degree of over-

basing or conversion, which is metal ratio times 100, is (w × 100)/v for monovalent metals and

(2w × 100)/v for divalent metals. Neutral detergents, or soaps, have a conversion of 100 because the

ratio of equivalents of base to the equivalents of acid is 1. Soap content for such a detergent can be

calculated using the following equation:

Percent soap

formula weight [(RSO Ca] 100

effective form

⫽

⫻)

uula weight

(4.1)

The effective formula weight is the weight of all the atoms that make up the formula (RSO

)

(CO

)

(OH)

plus the diluent, if present. The diluent can be the incidental alkylate that does not

get sulfonated or the diluent oil that is intentionally added. If one must add oil, most of it is added

to reactants at the beginning of the reaction, especially during the manufacture of basic detergents.

The presence of diluent is believed to facilitate micelle formation, thereby making the process more

ef cient. Adding oil after the reaction is not as effective.

The TBN indicates a detergent’s ability to neutralize acids. In additives and formulated lubri-

cants, the TBN is expressed as mg KOH/g of additive [27]. The method to determine base numbers

is described in the ASTM Standard D 974 [28]. For sulfonate and phosphonate detergents, it can be

calculated by using the number of equivalents of excess metal after salting the acid, that is (2w – v),

according to Equation 4.2.

TBN (mg KOH/g)

effective formula weight

⫽

⫻()2 56 100wv ,⫺

(4.2)

* The correct formula for such a detergent is (RSO

)Ca.xCaCO

.yCa(OH)

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Detergents 127

To calculate the base number of monovalent metal-derived sulfonates, one must use only (w – v) in

Equation 4.2. For divalent metal-derived carboxylate, salicylate, and phenate detergents, Equation 4.3

is to be used.

TBN (mg KOH/g)

()

effective formula weight

⫽

⫻2 56 100w ,

(4.3)

For monovalent metal salt of this type, the numerator will be w × 56,100. As mentioned earlier, the

percent sulfated ash is the quantity of solid metal sulfate that results when the detergent is treated

with sulfuric acid and the mixture ignited. Theoretical sulfated ash for divalent and monovalent

metals can be calculated using the following equations. Equation 4.4 is for divalent metals, and

Equation 4.5 is for monovalent metals.

Percent sulfated ash

molecular weight of M SO 100

atom

⫽

⫻⫻w

iic weight of metal M effective formula weight⫻

(4.4)

Percent sulfated ash

molecular weight of M SO 100

ato

⫽

⫻⫻05.w

mmic weight of metal M effective formula weight⫻

(4.5)

4.4 DETERGENT SUBSTRATES

Various organic acids are used to synthesize detergents. These include alkylaromatic sulfonic acids,

alkylphenols, alkylsalicylic acids, fatty carboxylic acids, and alkenylphosphonic acids. Alkylaro-

matic sulfonic acids, such as alkylbenzenesulfonic acids and alkylnaphthalenesulfonic acids, are

made by reacting the respective alkylbenzenes and alkylnaphthalenes with a sulfonating agent. The

alkylaromatic starting materials are made through alkylation of aromatics—benzene and naph-

thalene [29–33]. To make synthetic sulfonates, benzene or naphthalene is  rst alkylated and then

sulfonated. The alkylating agent is either an alkyl halide or an ole n. The ole ns can be α-ole ns,

internal ole ns, or ole n oligomers such as polypropylene and polyisobutylene. An acid catalyst is

usually required. One may choose from many acids. These include mineral acids such as sulfuric

acid and phosphoric acid, Lewis acids such as aluminum chloride and boron tri uoride, organic

acids such as methanesulfonic acid, and mixtures thereof [32,33]. Some of the inorganic acids such

as sulfuric acid are also available on a solid support, such as Fuller’s earth or silica. Unlike other

catalysts that require neutralization at the end of the reaction, these catalysts just require  ltration

to remove them. Zeolites and related mixed-metal oxides also enjoy the same advantage as the solid

alkylation catalysts [30,31]. Another class of catalysts, exempli ed by Amberlysts

, is aromatic

polymer-derived sulfonic acids [31,34]. Although they have the advantages of being insoluble, hence

easier to remove, and of multiple use, they have the disadvantage of being expensive. It is important

to note that not all catalysts have equal effectiveness in all alkylations.

Alkylaromatic sulfonic acids are derived either from the sulfonation of alkylaromatics, such as

alkylbenzenes and alkylnaphthalenes, or from petroleum re ning. The alkylbenzenes and alkyl-

naphthalenes are converted into respective sulfonic acids by reacting them with a sulfonating agent.

The acids thus obtained are called synthetic sulfonic acids. Alkylbenzenesulfonic acids are also

available from petroleum re ning. These are referred to as natural sulfonic acids. Detergents made

from synthetic sulfonic acids are called synthetic sulfonates and those made from natural sulfonic

acids are called natural or petroleum sulfonates.

The steps involved in making synthetic sulfonic acids are shown in Figure 4.3. The degree of

branching in alkylbenzenes and alkylnaphthalenes, commonly called the alkylate, increases as we

go from α-ole ns to internal ole ns to ole n oligomers. More branching of the alkylate implies

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128 Lubricant Additives: Chemistry and Applications

somewhat less-ef cient sulfonation but better oil solubility of the  nal sulfonate detergent. The com-

mon reagents used to sulfonate alkylaromatics are sulfur trioxide, fuming sulfuric acid or oleum,

and chlorosulfonic acid [35]. Oleum is 15–30% sulfur trioxide dissolved in concentrated sulfuric

acid. In general, the alkylate is dissolved in a hydrocarbon solvent, such as hexane or heptane, and

reacted with the sulfonating reagent. One obtains a mixture of a monosulfonic acid and disulfonic

or higher sulfonic acids. The latter must be removed because of the high polarity of their metal salts,

hence potentially lower oil solubility. This can be easily achieved by water washing. The disulfonic

and higher sulfonic acids are also undesired because, when reacted with polyvalent metals, they

have the tendency to make polymeric salts that are usually of low lubricant solubility as well.

Not all components of the alkylate are sulfonatable. In the case of alkylbenzenes, the spe-

cies that do not sulfonate easily include polyalkylated benzenes, such as trialkylbenzene, or highly

branched dialkylbenzenes. Their sulfonation dif culty is primarily a consequence of the steric

crowding of the sulfonatable positions. Monoalkylbenzenes do not suffer from this drawback and

hence sulfonate easily. In general, the sulfonation of branched alkylbenzenes is slower than linear

alkylbenzenes. In the case of alkylbenzenes, Figure 4.4 shows structures that are sulfonatable and

those that are not.

FIGURE 4.3 Synthesis of sulfonic acid substrates.

+ Olefin or alkyl halide

Acid

Benzene Alkylbenzene

+ Olefin

Naphthalene Alkylnaphthalene

+ SO

or oleum

Alkylbenzene Alkylbenzenesulfonic acid

FIGURE 4.4 Alkylbenzene structures.

Monoalkyl

Sulfonatable

Dialkyl Trialkyl

Not sulfonatable if R group

is highly branched

Not sulfonatable

Alk

lbenzene constituents

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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 re 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 ole n in the presence of an acid catalyst. The preferred catalysts are sulfuric acid, alumi-

num chloride, and boron tri 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-

 de and the subsequent hydrolysis of the resulting adduct [45,46]. The adduct is believed to result

from an ene-type addition of phosphorus pentasul de to polyole 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 pentasul 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

Sulfonated unsaturated

and aromatic compounds

+ NaOH

Green acid soaps

Water extraction

Alcohol extraction

Largely paraffinic

mineral oil

Mahogany acid soaps

Natural detergent

substrates

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130 Lubricant Additives: Chemistry and Applications

alkenylphosphonic acids and partially hydrolyzed (contain residual sulfur) alkenylthiophosphonic

acids. The reactions to synthesize alkylsalicylic acids and alkenylphosphonic and thiophosphonic

acids are shown in Figure 4.7.

Recently, the development of basic detergents that are not derived from organic acids has been

reported [47,48]. Substrates that can be overbased include organic amines and polyamines, ethers,

and organic sul des (sulfurized ole ns). Only alkali metal–derived overbased materials have

been reported.

4.5 SYNTHESIS OF NEUTRAL AND BASIC DETERGENTS

To make detergents, the organic acids are reacted with a metal base, such as a metal oxide or a

metal hydroxide. In general, the reaction between the organic acid and the inorganic base is not

good because of poor contact between the two reactants. A number of compounds, called pro-

moters, are used to facilitate salt formation and the subsequent carbonation or a related reaction.

Common promoters include ammonium hydroxide; low-molecular-weight carboxylic acids, such as

formic acid and acetic acid; low-molecular-weight alkylphenols; and other polar compounds, such

as nitroalkanes and imidazolines. A comprehensive list of such agents is provided elsewhere [49].

Most of these reagents are used in combination with water, except for high-temperature overbasing

reactions where water will not stay in. In such cases, alcohols, such as 2-ethylhexanol or iso-octyl

alcohol, and alkylphenols that have high boiling points are used. When water is present as part of

the promoter system, it either is added or results from the neutralization reaction. The promoters

are surfactants, that is, they contain a hydrophilic moiety, such as a hydroxyl group or a carboxylic

acid functionality and a reasonably sized alkyl group to impart a somewhat hydrophobic character

to the molecule.

FIGURE 4.6 Synthesis of alkylphenol substrates.

Alkylphenol

OH OH

Phenol

+ Olefin

Acid

Alkylphenol

(S)

Sulfur-coupled alkylphenol or phenol sulfide

S or SCI

Methylene-coupled

alkylphenol

R = alkyl group, typically C

−C

X = 1−3

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Detergents 131

Not all promoters are effective for all overbasing reactions, and one has to experiment to select

the right promoter system. For low-temperature overbasing (≤100°C), alcohol–water mixtures are

commonly used; for high-temperature overbasing (≥100°C), low-molecular-weight alkylphenols

are used. The structure of the  nal detergent from the two processes is believed to be different

and hence the performance in certain tests. The role of promoters in the overbasing reaction is not

well understood. One explanation regarding their role is based on their preferential reaction with

the base to form an alkoxide or a phenoxide. This species then transfers the metal to the substrate,

thereby facilitating salt formation and overbasing. The other explanation is based on their acting as

a surfactant and a wetting agent. This improves contact between the base and the substrate, thereby

assisting the reaction to occur. The second explanation is de nitely more plausible than the  rst.

However, in high-temperature overbasing reactions, usually carried out under anhydrous condi-

tions, the  rst explanation may have merit.

Although a number of metals can be used to make neutral salts (soaps), only a fewer metals have

the ability to result in oil-soluble basic detergents. The common metals that can be used for this

purpose include lithium, sodium, and potassium in group I and magnesium, calcium, strontium, and

barium in group II of the periodic table. Aluminum is the only overbasable metal in group III. Over-

based salts of transition metals such as zinc, copper, cadmium, molybdenum, copper, manganese,

cobalt, nickel, and iron, from sulfonic acids, alkylphenols, and naphthenic acids are also reported in

the patent literature [19,50,51]. The ability to overbase relates to a metal’s base strength: the higher

the basic character, the easier it is to overbase. For group I metals, where basic character increases

from lithium to sodium to potassium, it is easier to overbase potassium than lithium. In group II

metals, the basic character increases from magnesium to calcium to strontium to barium; hence, it

is easier to overbase barium than magnesium.

FIGURE 4.7 Synthesis of alkylsalicylic acids and alkenylphosphonic acids.

Alkylphenol

Potassium alkylsalicylate

COOK

Alkylsalicylic acid

COOH

KCI

KOH

HCI

Phosphorus pentasulfide

Polyisobutylene P

adduct

∆

Polyisobutenylphosphonic acid

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132 Lubricant Additives: Chemistry and Applications

Various detergents derived from metal anions other than hydroxide and carbonate are reported

in the patent literature. The anions include sul tes, sulfates, thiosulfates, borates, and phosphates

[32,49,52–55]. These detergents are obtained either from the carbonate detergent by displacing the

carbonate anion with the alternative anion or by using the anion precursor during overbasing. For

example, one can obtain metal sul te overbased detergent either by blowing sulfur dioxide during

overbasing or by displacing carbon dioxide in a carbonate detergent with sulfur dioxide. The result-

ing metal sul te detergent can be oxidized to a sulfate detergent by using an oxygen source, such as

oxygen gas or peroxide, or to a thiosulfate detergent by reacting it with elemental sulfur [49,52,53].

Borate and phosphate overbased compositions can be made using boric acid or phosphoric acid

during the reaction [54,55].

Common commercial detergents are derived from calcium, magnesium, sodium, and barium.

The metals are listed in order of preference. As mentioned, neutral detergents are made by react-

ing the acid substrate with a stoichiometric amount of the metal base, and overbased detergents are

made by reacting the substrate with an excess amount of base in the presence of carbon dioxide. To

make calcium and magnesium salts from natural sulfonic acids and alkylsalicylic acids, one must

convert commercially available alkali metal (sodium and potassium) salts (see Figures 4.5 and 4.7)

into free acids by reacting them with a mineral acid and then reacting the acids with magnesium

oxide or calcium hydroxide. Alternatively, alkali metal salts can be converted directly into magne-

sium and calcium salts through a double-decomposition reaction with a metal halide, as shown in

Figure 4.8. To make the natural sulfonate detergent, one must react the mahogany acid soap with

a metal halide such as calcium chloride. The reaction converts the sodium sulfonate soap into cal-

cium sulfonate, which can be overbased if desired. Because of the extensive branching, petroleum-

derived sulfonates have better oil solubility than synthetic sulfonates of similar molecular weight.

Figure 4.9 presents the idealized structures of neutral detergents.

To make overbased detergents, one can use either a two-step process or a one-step process.

Generally, the one-step process is preferred over the two-step process. In the two-step process,

the neutral salt or the soap is made  rst, which is subsequently overbased. In the one-step pro-

cess, the excess metal base is charged to the reaction; once the neutral salt formation is complete,

carbon dioxide blowing (carbonation) of the reaction is initiated. When carbon dioxide uptake

stops, the reaction is considered complete and it is worked up to isolate the product. Figure 4.10

summarizes the two processes. For making overbased natural sulfonates and alkylsalicylates,

one can double-decompose alkali metal salts in situ by reacting with a metal halide and overbasing.

The alkali metal halide by-product need not be removed until the overbasing is complete. It comes

out during the  nal  ltration, which is employed to remove any unreacted excess base and other

particulate materials.

FIGURE 4.8 Double-decomposition reaction.

CaCl

Ca + 2NaCl

CaCl

Ca + 2KCl

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Detergents 133

FIGURE 4.9 Idealized structures of neutral salts (soaps).

)

Metal salt of alkylbenzenesulfonic acid Metal salt of alkylnapthalenesulfonic acid Metal salt of alkylphenol

Metal salt of alkylsalicylic acid

Sulfur and methylene-bridged phenates

X = 1 or 2

Y = S or CH

M = Na, Mg, Ca

R R

Metal thiophosphonateMetal phosphonate Metal thiopyrophosphonate

FIGURE 4.10 Processes to make basic detergents.

Substrate + metal oxide or hydroxide

O M(OH)y

Base

Stoichiometric amount

Neutral salt

Base

or no CO

Basic or overbased salt

One-step process:

Two-step process:

Substrate + metal oxide or hydroxide

or no CO

O M(OH)

Excess base

Basic salts = neutral salts M

O, M(OH)

, or M

M = Na, Mg, Ca, or Ba

x = 1 and y = 2 for Mg, Ca, and Ba (divalent metals)

x = 2 and y = 1 for Na (monovalent metal)

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