What Is an Amide?

Amide is a chemical substance. In structure, amide can be regarded as a compound in which the hydroxyl group in the carboxyl group of the carboxylic acid molecule is substituted with amino or hydrocarbon amino (-NHR or -NR2); it can also be considered as ammonia or amine A compound in which a hydrogen on a nitrogen atom of a molecule is replaced by an acyl group.

Compounds containing amide bonds are called amides. Amides can be regarded as both nitrogen-containing derivatives of carboxylic acids and ammonia or amine derivatives. Amides can be classified according to their structure: amides, imides, lactams and N-substituted amides. The product in which the two hydrogen atoms in the ammonia molecule are replaced by an acyl group is called an imide, and the amide structure containing an amide bond is called a lactam; the product in which the hydrogen atom on the nitrogen atom of the amide molecule is replaced by a hydrocarbon group is called an N-substituted amide . ^[1]

Amide names are often referred to as "ceramic amides" based on the names of acyl and amino groups. The lactams are usually named , , , etc. to indicate the relative positions of amino and carbonyl groups. If there is a substituent on the nitrogen, prefix the name with "N" to indicate that the substituent is on the nitrogen atom, for example: ^[2]

In the amide molecule, the nitrogen atom is sp ² hybridized, and the p-orbital of the lone pair electron and the carbonyl group form a P- conjugate. As a result of the conjugation, not only the electron cloud density and bond length in the amide molecule tend to be equalized, but also the rotation of the CN single bond is hindered. C, N and the four atoms connected to C and N are all on the same plane. . The planar configuration of the amide greatly affects the physical and chemical properties of the amide and the spatial structure of the protein. ^[1]

Except for formamide being liquid, other amides are mostly colorless crystals, and aliphatic N-alkyl substituted amides are often liquid. Because of the strong hydrogen bonding ability between amide molecules and the greater polarity of amide molecules, their melting points are even higher than those of carboxylic acids with similar molecular weights. When the hydrogen atom on the amino group is replaced by a hydrocarbyl group, its molecular hydrogen bonding association is reduced, and its melting point is also reduced. For example, the melting point of acetic acid (relative molecular weight 60) is 16.6 ° C and the boiling point is 118 ° C; the melting point of acetamide (relative molecular weight 59) is 81 ° C and the boiling point is 222 ° C;

Liquid amide can dissolve not only organic compounds, but also many inorganic compounds. It is a good solvent. For example, N, N-dimethylformamide (DMF) and N, N-dimethylacetamide can be mixed with water and most organic solvents as well as many inorganic liquids at any ratio. They are very good aprotic polar solvents.

Lower amides are soluble in water, and their solubility decreases with increasing molecular weight. The melting and boiling point constants of some common amides are shown in the table. ^[1]

Amide is a very weak base that can interact with

Mainly used as industrial solvents, used in the pharmaceutical industry for production

(1) Urea

Urea, also known as urea, is a diamide of carbonic acid. Urea is the final product of protein metabolism in mammals and is found in the urine of animals. The ammonia released by many nitrogen-containing compounds during metabolism is toxic, and the concentration of ammonia is reduced by converting it into urea and excreting it from the urine. The urine excreted by normal adults every day contains about 30g of urea. Urea is a colorless crystal with a melting point of 133 ° C. It is easily soluble in water and ethanol and hardly soluble in ether. Urea is a very important substance and has a wide range of uses. It is used as an efficient solid nitrogen fertilizer in agriculture and an important raw material for organic synthesis. For synthetic drugs, plastics, etc. Urea itself is a drug, which has a significant effect on reducing intracranial pressure and intraocular pressure. Urea has an amide structure and has the general chemical properties of an amide. But because two amino groups are linked to a carbonyl group, it shows some special properties.

a. There are two amino groups in the weakly basic urea molecule, one of which can form a salt with a strong acid, so it is weakly basic. Nitrate and oxalate of urea are difficult to dissolve in water and easily crystallize. Utilizing this property, urea can be extracted from urine.

b. The hydrolysis reaction urea is an amide compound, which is easily hydrolyzed under the action of acid, alkali or urease.

c. Biuret formation and biuret reaction urea is a special amide. Its two amino groups are connected to the same carbonyl group, so it has different properties from ordinary amides. If urea is heated slightly above its melting point, bimolecular condensation occurs, and two molecules of urea remove one molecule of ammonia to form biuret. Biuret is a colorless needle-like crystal with a melting point of 190 ° C. It is hardly soluble in water and can be dissolved in lye. It reacts with a small amount of copper sulfate (CuSO4) solution in alkaline solution, that is, it is purple-red. This color reaction is called biuret reaction. This color reaction can occur in compounds containing two or more amide bonds (peptide bonds) in the molecule, such as peptides and proteins.

(2) Malonyl urea

Urea reacts with acid chloride, anhydride or ester to form the corresponding ureide. For example, urea reacts with malonyl chloride to form malonyl urea. Malonyl urea is a colorless crystal with a melting point of 245 ° C and is slightly soluble in water. Its molecule contains a structure that can undergo keto-enol tautomerism: Since malonyl urea is acidified from keto to enol, it is also called barbitur acid. Barbituric acid itself does not have a pharmacological effect, but its two hydrogen atoms on the C-5 methylene group are substituted by a hydrocarbon group (5,5-disubstituted). Many of the substitutes are a type of important sedative hypnosis Drugs, collectively known as barbiturates. Its general formula is: there are many barbiturates, the main ones are barbiturate, phenobarbital (lumina), pentobarbital, isoprenebarbital and so on. They are crystalline or crystalline powders, hardly soluble in water, and soluble in general organic solvents. Sodium salts of barbiturates can be used for injection.

(3) sulfa drugs and chloramine drugs

A compound in which a hydrogen atom in a hydrocarbon molecule is replaced by a sulfo group (-SO3H) is called a sulfonic acid. Aromatic sulfonic acids are the most important, such as benzenesulfonic acid. The chemical properties of sulfonic acids are similar to those of carboxylic acids, but they are much more acidic than carboxylic acids. Phenylsulfonyl chloride can react with ammonia or amine to form sulfonamide. In medicine, important sulfonamides include sulfa drugs and chloramines.

a. Sulfonamides: Sulfonamides are excellent chemotherapeutic agents, beginning to be used in the 1930s. They can inhibit the growth and reproduction of a variety of bacteria, such as streptococcus, staphylococcus, pneumococcus, meningococcus, dysentery, etc., and are therefore commonly used to treat diseases caused by the above-mentioned bacteria. The simplest sulfa drug is p-aminobenzenesulfonamide, or sulfa (SN) for short. Sulfa is a colorless crystal with a melting point of 163 ° C. It has a slightly bitter taste and is slightly soluble in water. Sulfonamide can be dissolved in a strong acid or a strong alkali solution. This is because it has an amino group attached to the benzene ring, so it can react with an acid to form a salt; at the same time. The hydrogen atom on the amino group bonded to the sulfonyl group is acidic due to the influence of the sulfonyl group, so it can interact with the base. Sulfonamide has great side effects when taken orally and is only used externally to treat purulent trauma. In order to reduce the side effects of sulfonamide, other atomic groups are generally used to replace the hydrogen atom on the sulfonylamino group, which has less side effects and is called sulfa drugs. Sulfonamides have a broad antibacterial spectrum, stable properties, good oral absorption, and convenient use. Table 18-2 is some common sulfa drugs. Trimethoprim (TMP) does not belong to sulfa drugs in its chemical structure, but it can strengthen the effect of sulfa drugs and also enhance the efficacy of various antibiotics. It is called sulfa synergists and is often used with sulfa drugs or antibiotics. Wu used. Trimethoprim (TMP) Common sulfa drugs

b. Chloramines: Compounds in which the hydrogen atom of the amino group is replaced by a chlorine atom in the benzenesulfonamide molecule are called chloramines. For example: Chloramines are white or yellow crystalline powders with a slight odor of chlorine. Soluble in water and ethanol, difficult to dissolve in organic solvents such as ether. Chloramines are oxidants. They react with water to form hypochlorous acid or sodium hypochlorite. They have bactericidal and disinfectant effects on chemical poisons, so they are of great significance in military medicine.