What are the side reactions and by products of sulfonation reactions

A reaction in which the hydrogen atom in an aromatic hydrocarbon compound, such as a benzene molecule, is replaced by a sulfonic acid group (—SO3H) in a sulfuric acid molecule. Sulfonation reaction process A reaction process in which a sulfonic acid group (—SO3H) or a sulfonyl chloride group (—SO3Cl) is introduced into an organic molecule. The sulfonic acid group substitution of hydrogen on the carbon atom during sulfonation is called direct sulfonation; The sulfonic acid group replaces the halogen or nitro group on the carbon atom, which is called indirect sulfonation.

Sulfonating agents are usually made with concentrated sulfuric acid.

or oleum as a sulfonating agent, sometimes sulfur trioxide, chlorosulfonic acid, sulfur dioxide.

Chlorine, sulfur dioxide, oxygenation and sodium sulfite.

and so on as a sulfonating agent.

The reaction in which the hydrogen atom in the organic compound is replaced by the sulfonic acid group (—SO3H) in the sulfuric acid molecule is called sulfonation. But since the reaction is mainly in aromatic compounds.

, so it is often referred to as a sulfonation reaction on aromatic compounds. The reaction principle of this section The sulfonation reaction of aromatic compounds belongs to the electrophilic substitution reaction in terms of mechanism.

There are roughly three reaction conditions: aqueous sulfuric acid, sulfur trioxide and oleum sulfuric acid. Some of them [1] proved experimentally:

When benzene reacts with sulfur trioxide in an aprotic solvent, the attacking electrophile is sulfur trioxide; When sulfonated in aqueous sulfuric acid, the electrophile is a hydrogenital cation of sulfate (which can be understood as hydrated protons.

sulfur trioxide); In oleum, the electrophiles are pyrosulfate hydronium ions (i.e., protonated pyrosulfuric acid) and H2S4O13 (which can be understood as one molecule of sulfuric acid + three molecules of sulfur trioxide). Therefore, the reaction mechanism of sulfonation is slightly different under different conditions.

The main thing is the reaction to produce sulfone, which also produces sulfone.

1. Indirect sulfonation: when the halogen or nitro group on the carbon atom in the organic compound molecule is relatively active, it can be replaced by the sulfo group if it reacts with sodium sulfite;

2. The sulfonation reactor uses sulfuric acid, chlorosulfonic acid or sulfur trioxide in the liquid phase sulfonation, and the membrane reactor is used to sulfonize dodecylbenzene with gaseous sulfur trioxide. When alkane sulfonate chlorination or sulfonation oxidation with SO2+Cl2 or SO2+O2, the gas-liquid bubbling reactor is used;

3. Product use: The introduction of sulfonic acid group into organic molecules can increase the water solubility and acidity of the product. Most water-soluble dyes contain sulfonic acid groups.

Some sulfonates are anionic surfactants, such as detergents, wetting agents, penetrants, emulsifiers, solubilizers, etc., polymer sulfonates include dispersants, strong acid ion exchange resins, elastomers, water-soluble synthetic gums and thickeners, etc., the sulfo groups on the aromatic ring can also be converted into hydroxyl groups, amino groups, chlorinated mountains, cyano groups, etc., so as to prepare a series of intermediates, sometimes, in order to locate or facilitate the progress of other reactions, the sulfonic acid group can be temporarily introduced on the aromatic ring first, and then the sulfonic acid group hydrolysis is carried out after completing the specific reaction, sulfonyl chloride group is an active group, from which a series of products such as aryl sulfonamide and aryl sulfonate can be prepared.

Excessive sulfuric acid sulfonation This method is used for the sulfonation of most aromatic compounds. When sulfonated with concentrated sulfuric acid, the general formula of the reaction is:

where ar stands for aryl group. The water produced by the reaction decreases the concentration of sulfuric acid and slows down the reaction rate, so a large amount of sulfonating agent is used. Refractory aromatic hydrocarbons should be sulfonated with oleum acid. At this time, the free sulfur trioxide in it is mainly used, so a large amount of sulfonating agent is also used.

ar－h+so3—→ar－so3h

The advantage of sulfur trioxide sulfonation is that no water is generated during sulfonation, and the amount of sulfur trioxide can be close to the theoretical amount, and the reaction is fast and the waste liquid is less. However, sulfur trioxide is too reactive and is prone to produce by-products such as sulfones during sulfonation, so it is often diluted with air or solvents. It is mainly used in the sulfonation process of surfactants such as sodium dodecylbenzene sulfonate from dodecylbenzene.

From the above description, it can be seen that sulfur trioxide is too active, so the reaction that occurs is different from that of concentrated sulfuric acid, and the temperature is different, and the products are also different. Naphthalene is sulfonated with concentrated sulfuric acid at low temperature, mainly to produce naphthalene-1-sulfonic acid that is easily hydrolyzed, and high-temperature sulfonation mainly produces naphthalene-2-sulfonic acid that is difficult to hydrolyze.

Sulfonation is an important step in the synthesis of a variety of organic products, and is widely used in pharmaceutical, pesticide, fuel, detergent and petroleum industries. Some drugs have some problems in clinical application due to poor water solubility, such as low bioavailability, large dosage, and slow absorption in tablets or capsules. Sulfonation of such compounds can enhance not only their water solubility, but also their biological activity.

Sulfonation: A reaction in which a hydrogen atom is replaced by a sulfonic acid group in a sulfuric acid molecule.

Sulfonation: A reaction in which a hydrogen atom is replaced by a sulfonic acid group in a sulfuric acid molecule.

Indirect sulfonation When the halogen or nitro group on the carbon atom in the organic compound molecule is relatively active, it can be replaced by the sulfo group if it reacts with sodium sulfite;

Sulfonation reactors are generally used in kettle reactors for sulfuric acid, chlorosulfonic acid or sulfur trioxide in liquid phase sulfonation. A membrane reactor is used to sulfonate dodecylbenzene with gaseous sulfur trioxide. When alkane sulfonate chlorination or sulfonation oxidation with SO2+Cl2 or SO2+O2, the gas-liquid bubbling reactor is used;

Product Use: The introduction of sulfonic acid groups into organic molecules can increase the water solubility and acidity of the product. Most water-soluble dyes (e.g., direct dyes, acid dyes, and reactive dyes) contain sulfonic acid groups. Some sulfonates are anionic surfactants, such as detergents, wetting agents, penetrants, emulsifiers, solubilizers, etc.

Sulfonates of polymers include dispersants, strongly acidic ion exchange resins, elastomers, water-soluble synthetic adhesives and thickeners. The sulfo group on the aromatic ring can also be converted into hydroxyl group, amino group, chlorine group, cyano group, etc., so as to prepare a series of intermediates. Sometimes, in order to localize or facilitate the progress of other reactions, sulfonic acid groups can be temporarily introduced into the aromatic ring, and then the sulfonic acid groups can be hydrolyzed after the specific reaction is completed.

Sulfonyl chloride group is an active group, from which a series of products such as aryl sulfonamide and aryl sulfonate can be prepared.

The reaction of introducing a sulfo group (-SO3H) into an organic molecule is called sulfonation. Aliphatic compounds are usually sulfonated by indirect methods.

Aromatic compounds are mainly directly sulfonated (electrophilic substitution reaction). Commonly used sulfonating agents are concentrated sulfuric acid, oleum sulfuric acid, etc. The sulfonation reaction is generally carried out according to the following process.