Карбодиимидтер: құрылымы, қасиеттері және қолданылуы

1=Class of organic compounds with general structure RN=C=NR'

In organic chemistry, a carbodiimide (systematic IUPAC name: methanediimine) is a functional group with the formula RN=C=NR. On Earth they are exclusively synthetic, but in interstellar space the parent compound HN=C=NH has been detected by its maser emissions. A well known carbodiimide is dicyclohexylcarbodiimide, which is used in peptide synthesis. Dialkylcarbodiimides are stable. Some diaryl derivatives tend to convert to dimers and polymers upon standing at room temperature, though this mostly occurs with low melting point carbodiimides that are liquids at room temperature. The C=N distances are short, nearly 120 pm, as is characteristic of double bonds. Carbodiimides are chiral, possessing C2 symmetry and therefore axial chirality. However, due to the low energy barrier to the molecule rotating and thereby converting quickly between its isomers, the actual isolation of one optical isomer of a carbodiimide is extremely difficult. It has been demonstrated at least once, in the case of conformationally restricted cyclic carbodiimides; though there are other reports of one handed axially chiral carbodiimides, their validity has since been called into question on experimental and computational grounds. The parent compound, methanediimine, (HN=C=NH), is a tautomer of cyanamide.

In organic synthesis, compounds containing the carbodiimide functionality are used as dehydration agents. Specifically they are often used to convert carboxylic acids to amides or esters. Additives, such as N hydroxybenzotriazole or N hydroxysuccinimide, are often added to increase yields and decrease side reactions. Polycarbodiimides can also be used as crosslinkers for aqueous resins, such as polyurethane dispersions or acrylic dispersion. Here the polycarbodiimide reacts with carboxylic acids, whose functional groups are often present in such aqueous resins, to form N acyl urea. The result is the formation of covalent bonds between the polymer chains, making them crosslinked.

The formation of an amide using a carbodiimide is a common reaction, but carries the risk of several side reactions. The acid 1 will react with the carbodiimide to produce the key intermediate: the O acylisourea 2, which can be viewed as a carboxylic ester with an activated leaving group. The O acylisourea will react with amines to give the desired amide 3 and urea 4. The possible reactions of the O acylisourea 2 produce both desired and undesired products. The O acylisourea 2 can react with an additional carboxylic acid 1 to give an acid anhydride 5, which can react further to give the amide 3. The main undesired reaction pathway involves the rearrangement of the O acylisourea 2 to the stable N acylurea 6. The use of solvents with low dielectric constants such as dichloromethane or chloroform can minimize this side reaction.

In contrast to DCC, DIC (N,N diisopropylcarbodiimide) is a liquid. Its hydrolysis product, N,N' diisopropylurea, is soluble in organic solvents.

EDC is a water soluble carbodiimide reagent used for a wide range of purposes. Apart from uses similar to those of DCC and DIC, it is also used for various biochemical purposes as a crosslinker or chemical probe.

1 cyclohexyl (2 morpholinoethyl)carbodiimide metho p toluene sulfonate is a carbodiimide developed for the chemical probing of RNA structure in biochemistry.