condensation in chemistry

From Big Medical Encyclopedia

CONDENSATION in chemistry — big group of various synthetic reactions of organic and biological chemistry. Biosynthetic reactions To., catalyzed by enzymes, lead to formation of many important connections. These are synthesis lemon to - you from oxalacetic to - you in a cycle Tricarboxylic to - t, glucose — from pyroracemic to - you, biosynthesis saturated fat to - t and steroids, creation of porphobilinogen and many other transformations. Reactions To. are widely applied in organic synthesis (laboratory and industrial), including during the receiving many medicinal substances and natural biologically active compounds (e.g., carotinoids).

Examples To. can serve aldol condensation (see), reactions of S-alkylation, including chlorine methylation of aromatic compounds, etc.

Reactions To. lead to formation of new carbon-to-carbon linkages therefore as a result To. there is a complication of a carbon skeleton of a molecule. These reactions can be intermolecular and intramolecular (reactions of cyclization). In most cases they are followed by eliminating of any simple inorganic or organic molecule (hydrogen, water, halogen hydride, ammonia, alcohol, etc.); in certain cases To. proceeds as addition reaction, i.e. without eliminating of any particles (a diene synthesis, benzoinovy To., etc.). To reactions To. refer also formation of heterocycles, at Krom there is an emergence not only of carbon-to-carbon linkages, but also bonds between carbon and heteroatoms (N, O, S etc.) and heteroatoms with each other. Formation of bonds With — O, C — N, etc., not connected with creation of heterocycles (e.g., receiving esters, amides, etc.), does not join in the concept «condensation».

To reactions To. polycondensation, i.e. education adjoins high-molecular compounds (see) from bi-or multifunctional organic compounds, also followed by eliminating of low-molecular products; polyreactions, unlike reactions actually To., can pass by education ester, amide and another similar to them bonds. Biopolymers belong to natural polycondensates (proteins, polynucleotides, polysaccharides, etc.). Polyreactions are very important for receiving polymeric materials.

Usually reactions To. proceed under the influence of so-called condensation agents (agents) which role can be various (a catalysis, formation of reactive intermediate compounds, binding of the chipping-off particles). Agents To. can be proton and aprotic to - you (H 2 SO 4 , HCl, HF, AlCl 3 , ZnCl 2 ), the bases — alkalis, alcoholates, amides of alkali metals (see. Acids and bases ), metals (sodium, copper, etc.), various oxidizers, etc. Types K. and their mechanisms are various and cannot be reduced to one scheme. Many reactions To. carry own names (Klayzen's condensation, Vyurtts's reaction, Dikman's cyclization and so forth).

Bibliography: Vorozhtsov H. H. Bases of synthesis of intermediate products and dyes, page 682, M., 1955, bibliogr.; Short chemical encyclopedia, t. 2, Art. 682, M., 1963; Lenindzher A. Biochemistry, the lane with English, M., 1976; M and y about-f and with JT. S. Himiya and technology of chemical pharmaceuticals, L., 1964.

A. I. Tochilkin.