An organic substance in which the hydroxyl group in a carboxylic acid is replaced by an amino group or an amino group.It is mainly used as industrial solvent.In structure, amide can be regarded ascarboxylic acidIn moleculecarboxylOfhydroxylcoveraminoOr hydrocarbon amino (- NHR or - NRtwo）Substituted compounds;It can also be regarded asammoniaOr hydrogen coating on nitrogen atom in amine moleculeacylA compound formed by substitution.
Liquid amide is an excellent solvent for organic and inorganic substances.The boiling point of amide is higher than that of corresponding carboxylic acid.
Compounds with acyl groups linked to nitrogen atoms are called amides.Amides can be regarded as nitrogen-containing derivatives of carboxylic acids, as well as ammonia or amine derivatives.
When naming, the acid word of carboxylic acid should be changed to amide.In English, the suffix of carboxylic acid is changed to amide.There are three hydrogen attached to the nitrogen atom of ammonia. One hydrogen is replaced by an acyl group, which is called a monoamide, and the other two or three hydrogen are replaced, which is called a diamide or a triamide.In English, di and tri are used to indicate two or three additions before the English name of carboxylic acid.
A dicarboxylic acid is called a diamine if two carboxyl hydroxyl groups are replaced by one amino group respectively.In English, the suffix of dicarboxylic acid is changed to diamide.If two carboxyl hydroxyl groups are replaced by the same amino group, the ring compound obtained is called a diimide.Imide is used to replace the end of corresponding carboxylic acid in English.If one carboxyl group is retained and another carboxyl hydroxyl group is replaced by amino group, the main functional group is carboxyl group, the parent compound is carboxylic acid, and the amide is treated as a substituent group, which is called carbamoyl group.The cyclic amide containing CONH in the ring is called a lactam.English name in the correspondingAdd lactam after hydrocarbon name.[2]
Structure of amide
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In amide molecule, the nitrogen atom adopts sptwoHybridization, the p orbital of the lone pair electrons and the carbonyl group form p - π conjugation.As a result of conjugation, not only the electron cloud density and bond length in the amide molecule tend to be averaged, but also the rotation of the C-N single bond is blocked. C, N and the four atoms connected with C and N are all on the same plane.This planar configuration of amide has a great influence on the physical and chemical properties of amide and the spatial structure of protein.[1]
physical property
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Except formamide, which is liquid, other amides are mostly colorless crystals, and monoalkyl substituted amides are often liquid.Because of amideIntermolecular hydrogen bondThe association ability is strong, and the polarity of amide molecule is large, so its melting and boiling point is even higher than that of carboxylic acid with similar molecular weight.When the hydrogen atom on the amino group is replaced by the alkyl group, its melting and boiling points also decrease due to the reduction of the hydrogen bond association between its molecules.
Liquid amide can not only dissolve organic compounds, but also many inorganic compounds. It is a good solvent.For example, N, N-dimethylformamide and N, N-dimethylacetamide can be mixed with water, most organic solvents and many inorganic liquids in any proportion. They are good aprotic polar solvents.
chemical property
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Amides are compatible withstrong acidAlcoholysis reaction occurs, and the adduct formed by the reaction, such as CHthreeCONHtwo·HCl, very unstable, complete in case of waterhydrolysis。Amides can also formMetal saltMost metal salts are completely hydrolyzed when they meet with water, but (CHthreeCONH)twoHg is quite stable.Amide can be hydrolyzed intocarboxylic acidAnd ammonia (or amine).Amide in dehydrating agentPhosphorus pentoxideHeat carefully in the presence of, that is, change intonitrile。Amides are catalysed or hydrogenated withLithium aluminum hydrideReaction, can be reduced to amine.Amides can also react with hypohalides to form a primary amine with one less carbon atom.
Amides can be partially dehydrated by ammonium carboxylate, orAcyl halide、Acid anhydride、esterAmmonia hydrolysis;Nitrile can also be partially hydrolyzed and stopped at amide stage.
Low molecular liquid amide such asN. N-Dimethylformamide、N. N-DimethylacetamideIt is an excellent nonprotonPolar solventIt can also be used as plasticizer, lubricant additive and organic synthetic reagent.Long chain fatty acid amide, such asStearamideIt can be used as waterproof agent for fiber fabrics,ErucamideIt is a lubricant for polyethylene and polypropylene extrusion.N. N-dihydroxyethyl long-chain fatty acid amide is a non-ionic surfactantVinyl chloride vinyl acetate copolymerOfPlasticizer。N-sulfonyl substituted long-chain fatty acid amides are synthetic fibersSoftener。Dicarboxylic acidPolycondensation with diaminepolyamideIt has excellent performanceSynthetic fibre。
Acidity and alkalinity: Amides are generally near neutral compounds, but under certain conditions they can show weak acid or weak alkalinity.Amides are acyl derivatives of ammonia or amine. There are amino or hydrocarbon amino groups in the molecule, but their alkalinity is much weaker than that of ammonia or amine.Amide alkalinity is very weak, becauseAmino nitrogenUnshared pair on andcarbonylOfπ electronformationConjugate systemThe density of the electron cloud on nitrogen decreases, so the ability to accept protons decreases.At this time, C-N bond has a certain degree of double bonding.However, the decrease of electron cloud density on nitrogen makes thePolarityIncrease, thus showing weak acidity.If there are two ammonia moleculeshydrogen atomBy adiprotic acidA cyclic imino compound (imide) is formed by the substitution of an acyl group of.Due to the electron absorption of the two carbonylsImino groupThe polarity of N-H bond of N is significantly increased, and the hydrogen atom on nitrogen is more likely to become proton, and is weakly acidic.For example:
Hydrolysis: Amide is difficult to hydrolyze under normal circumstances.When heated in the presence of acid or base, the reaction can be accelerated, but it is much slower than the hydrolysis of carboxylic acid ester.N-substituted amides can also be hydrolyzed to form carboxylic acids and amines.
React with nitrous acid: amide reacts with nitrous acid to generate corresponding carboxylic acid and releasenitrogen。
Main purpose
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Mainly used as industrial solvent, and used in production in pharmaceutical industryvitamin、hormone, also used for manufacturingChlordimeform。In organic reactions,DimethylformamideIt is not only widely used as reaction solvent, but also important for organic synthesisintermediate。
