Salt refers to a kind of compound composed of metal ion or ammonium ion (NH4+) and acid ion (or non-metal ion). In chemical reactions, salts are generally the products of metathesis reactions. There are other reactions that can form salts, such as displacement reactions. Salt and salt react to form new salts, for example, sodium chloride and silver nitrate react to form silver chloride and sodium nitrate. The salt reacts with a base to form a new salt and a new base, such as ferric chloride and sodium hydroxide react to form sodium chloride and iron hydroxide. Salt and acid react to form new salt and new acid, such as sulfuric acid and barium chloride react to form barium sulfate and hydrochloric acid. Solutions of soluble salts are conductive.
Because of its advantages such as simple synthesis methods, abundant species, and different physical and chemical properties, salt has a wide range of applications in many fields such as chemistry, biomedicine, and so on.
- Chemistry: Salt is widely used in chemistry. On the one hand, many salts are the reactants of chemical reactions, and the products of many chemical reactions are also salts. On the other hand, many kinds of salts can be used as catalysts to catalyze chemical reactions. Heteropoly acid salt, as a kind of relatively oxidizing multi-electron oxidation catalysts, has an anion structure that remains stable after gaining 6 or more electrons. It easily oxidizes various substrates, so it is often used as a catalyst in the chemical field to catalyze oxidation reactions. Some heteropoly acid salts have microporous or even ultramicroporous structures, which can be modified by the introduction of functional metals to achieve bifunctionality and shape selectivity. Some inorganic salts can also be used as catalysts to catalyze organic reactions. For example, potassium ferricyanide can catalyze the cyclization of phenolnitroalkanes to form cycloheptatrienone compounds.
Figure 1. Cyclization reaction catalyzed by potassium ferricyanide
- Biomedicine: Salt is also widely used in the field of biomedicine. The main ingredient of milk mineral salt is calcium phosphate, which has the functions of enhancing bone density, controlling weight, improving bioavailability and reducing the incidence of other diseases, so it is widely used in health products. Hypertonic saline solution can not only restore the content of blood vessels and maintain circulation stability in a short time, but also reduce the systemic destructive inflammatory response, so it has unique advantages in the process of cardiopulmonary and cerebral resuscitation. Therefore, hypertonic saline is often used in the clinic to assist patients with cardiac arrest.
Figure 2. Calcium phosphate
- Other fields: In addition to the above fields, salt has a wide range of applications in many other fields. For example, the inorganic polymer aluminum salt has strong electric neutralization ability, large molecular weight, strong adsorption performance and considerable stability, and can be used as a flocculant in water treatment. The sulfonic acid group of lignin sulfonate has strong hydrogen ion exchange capacity, so it can be used to make ion exchange resin.
According to the degree of solubility in water, salts can be divided into soluble salts and insoluble salts. Depending on the composition of the salt, salts can be divided into single salt and combined salt, which is also the most common classification method. In addition, single salts can be divided into normal salts, acid salts, and basic salts, while combined salts can be divided into double salts and complex salts.
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