Sulfating-Sulfonating agents

Applications
Chemical and physical factors in sulfonation and sulfation

Concentration of SO3

Chemical Structure of the organic compound

Time temperature reagent strength

Catalysts
Solvents
Kinetics
Thermodynamics
Industrial Equipment and techniques
Sulfamic Acid Sulfation Equipment
Figure illustrates the equipment used for sulfamic acid sulfation. This batch process is run in a stainless
steel or glass lined, air tight, stirred tank reactor. The reactor has heating and cooling coils and provision
for weighing in the organic reactant and the sulfamic acid. Before the reaction starts, air is purged from
the reactor with dry nitrogen and the reaction is run under a blanket of nitrogen. The organic is weighed
into the reactor and a 5% molar excess of sulfamic acid is then added. The reactor is purged and
blanketed with dry nitrogen to remove oxygen. The reactants are heated to 110–160°C and held at this
temperature for approximately 90 minutes. The products are then cooled to 70°C and water or alcohol
are added to dilute the product.

Chlorosulfonic Acid Sulfation Equipment

Chlorosulfuric acid can be used to sulfonate in either a batch or continuous process. For the batch
process, illustrated in Figure, the equipment is a glass lined, stirred, sealed reactor with heating and
cooling jackets. The reactor must be fitted with a glass lined absorber to remove the HCl gas evolved in
the reaction. A slight vacuum is usually pulled on the reaction vessel to enhance HCl removal. The
liberated HCl gas is absorbed into water to make a dilute HCl solution. In operation, the alcohol or ethoxy
alcohol feedstock is charged to the reactor and chlorosulfuric acid is gradually added. A good
refrigeration system is required for heat removal because the reaction is exothermic. The reaction mass
must be kept at approximately 25°C to avoid side reactions and color body formation and to minimize
foaming. The rate of addition of chlorosulfuric acid is adjusted to ensure that this temperature is not
exceeded. Immediate neutralization is required once the reaction is complete.
Oleum and Sulfuric Acid Sulfonation Equipment

Oleum and sulfuric acid can be used to sulfonate aromatics and alcohols in either batch or continuous
equipment. For detergent alkylates, the batch equipment is very similar to other processes. As shown in
Figure 14, the required equipment is a stirred, sealed, glass lined or stainless steel kettle with a provision
for heating and cooling. The detergent alkylate is first added to the reaction vessel then the oleum is
slowly added over a period of several hours. The reaction is highly exothermic and the oleum addition
rate is determined by the ability to remove the heat of reaction. The temperature should be maintained
below 35°C for optimum product quality. Frequently the heat of reaction is removed by pumping the
reaction mixture through an external heat exchanger. Because it is an equilibrium reaction, except for
the special case of azeotropic sulfonation of hydrotropes with sulfuric acid, a large surplus of sulfuric acid
forms. When the sulfonation reaction is complete, the sulfuric acid may be separated from the
sulfonated detergent alkylate by adding water. The water addition (typically about 10% by weight of the
reaction mixture) causes a phase separation to occur between the sulfonic acid and the diluted sulfuric
acid. The separation usually takes place in a separate, glass lined vessel and occurs over a period of
about 10 hours. Materials of construction are crucial because the dilution process makes sulfuric acid
which is in a very corrosive temperature and concentration range. After separation, the sulfonic acid may
be neutralized with aqueous sodium hydroxide, usually in a separate neutralization vessel. Including
neutralization, total batch time is 15 to 20 hours. The product contains about 15% sodium sulfate after
neutralization if the acid is separated, and about 60% sodium sulfate if not. Without separation, the
product's application is limited to low active, traditional detergent powders where the large content of
sodium sulfate is used as a filler.
Air/SO3 Sulfonation Equipment

Four possible sources of SO3 gas used for an air/SO3 sulfonation system are:

• Sulfuric acid plant converter gas

• SO3 from boiling concentrated oleum

• Liquid SO3

• Sulfur burning in equipment specifically designed to produce SO3 gas for sulfonation

Converter gas from a sulfuric acid plant contains 10–12% SO3 and appears to be a potential SO3 source
for sulfonation. There are three other more subtle difficulties when using a sulfuric acid plant as an SO3
source for sulfonation. First, the SO3 gas at approximately 18% concentration must be diluted to the
normal range for sulfonation (typically 4–7%). An auxiliary air supply must be installed, which adds
expense and complexity. Second, because sulfuric acid absorption towers are used for air drying, the
air/SO3 from a sulfuric acid plant has a higher dew point (typically –35°C) than that required in a
sulfonation plant (typically –60°C to –80°C). The high dew point causes product quality problems in the
sulfonation process and accelerates corrosion of the process equipment. Third, the pressure of the
air/SO3 from the sulfuric acid plant is usually not sufficient to overcome the pressure drop of the
sulfonation system. Compressing the air/SO3 from the converter is not trivial as it requires a high alloy
compressor to withstand the corrosive environment created by the wet air/SO3 stream.

Another possible source of SO3 for sulfonation is produced by boiling oleum to produce gaseous SO3
which is then blended with dry air.
Sulfonation equipment based on liquid SO3 has become increasingly undesirable for the following
reasons: Safety concerns • Liquid SO3 is unavailable in many parts of the world • Sulfur is readily
available worldwide • Sulfur is relatively inexpensive.

The basic plant package for a sulfur burning, air/SO3 sulfonation installation includes a sulfur supply
system, air supply system, SO3 gas plant system, SO3 absorber system, sulfonator, neutralizer, effluent
gas clean-up system, control system and motor control center.
Sulphonation of benzene
Sulfonation of benzene

It is sulfonation, also known as Sulphonation, that produces sulfonic acids in any one of various ways. An important
sulfonation technique is the reaction of aromatic hydrocarbons with sulfuric acid, chlorosulfonic acid, or sulphur trioxide; the
reaction of organic halogen compounds with inorganic sulfites; and the oxidation of disulfides and thiols.

Sulfonation of benzene is the process of forming benzenesulfonic acid by heating benzene with fuming sulphuric
acid (H SO + SO ). This reaction is reversible.
2 4 3

Sulfonation of benzene mechanism

Electrophilic substitution happens between sulfuric acid and benzene during the sulfonation of benzene. There are two
sulfonation methods for benzene. Both methods of sulfonating benzene are equally effective.

At 40°C for several hours, benzene is heated under the reflux of intense fuming sulfuric acid. Benzenesulfonic acid is the
end product. Sulphur trioxide (SO ) is the electrophile in this case. Based on the type of acid being utilised, there are two
3

approaches to making sulphur trioxide electrophile. Dissociation of concentrated sulfuric acid with traces of SO can yield it.
3

Because it is a solution of SO in sulfuric acid (H S O ). Fuming sulfuric acid, or H S O is a much richer source of sulfuric
3 2 2 7 2 2 7

acid. Due to its polarity and positive charge on the sulphur atom, sulphur trioxide is electrophilic. This is what attracts the
electrons of the ring.
2H₂SO₄ → H O + SO₃ + HSO
3
+
4
–

Reverse sulfonation of benzene

Benzene sulfonation is a chemical process that can be undone. In the presence of water, sulphur trioxide quickly produces
sulfuric acid and heat. The reaction is reversed by heating benzenesulfonic acid in a solution of sulfuric acid diluted in water.
It is possible to make deuterated benzene because the sulfonation reaction is so reversible. To better understand reaction
pathways, because the C-D bond is more powerful than the C-H bond, isotopically labelled reagents can be helpful.

Sulfonation of aniline
An electrophile refers to an electron-seeking species. Thus, electrophilic substitution reaction refers to the
reaction in which an electrophile substitutes another electrophile in an organic compound. Anilines undergo the
usual electrophilic reactions such as halogenation, nitration and sulphonation. We will discuss them
one-by-one, but let’s first understand the behaviour of anilines towards the attack of an electrophile:

1. The functional group (-NH2) associated with aniline is an electron donating group and hence is very activating
towards the electrophilic substitution reaction.
2. Due to its various resonating structures, there’s an excess of electron or negative charge over ortho- and para-
positions of the benzene ring than the meta- position. Thus, anilines are o- and p- directive towards electrophilic
substitution reaction.

Sulphuric acid reacts vigorously with aniline to form anilinium hydrogen sulphate which on heating produces
sulphanilic acid which in turn also has a resonating structure with zwitterion as shown in the above figure.
Zwitterion basically refers to a dipolar ion in which both positive and negative charges exist and the molecule
as a whole is neutral. It is also called inner salt sometimes. It differs from amphoteric ions in the sense that it
has negative and positive charges simultaneously while amphoteric ions are either cationic or anionic at a time.

Anilines don’t undergo Freidel crafts reaction because they react with ferric chloride of the reaction mixture
which acts as catalyst for the reaction.