Chemical Condensation

CHEMICAL CONDENSATION, one of the principal methods for the synthesis of organic substances. The term "condensation" should be understood as the formation of new bonds between carbon atoms either within the same molecule, e.g., the conversion of diphenylmethane into fluorene, C₁₃H₁₀,

as well as in different molecules, a typical example of which is the formation of aldol from aldehyde: CH₃.CO.H + CH₃.CO.H = CH₃.C(OH)H.CH₂.CO.H. Sometimes chemical condensation is understood in a broader sense, meaning by it the formation of new bonds not only between carbon atoms, but also between carbon and other elements (nitrogen, oxygen, sulfur, etc.), which leads to the merging of the concept of chemical condensation with the broader concept of organic synthesis. Sometimes chemical condensation proceeds without the action of any reagents (autocondensation) upon heating, distillation, or passing the vapors of a given substance through red-hot tubes (pyrogenetic chemical condensation). In some cases, light serves as the condensing agent. In the majority of cases, chemical condensation requires the action of specific reagents (condensing agents) depending on the nature of the reacting bodies. Condensing agents can be oxidizing agents in cases where chemical condensation is associated with the removal of hydrogen, or metals (sodium, zinc, tin, silver, copper) when chemical condensation is caused by the elimination of a halogen (2RCl + Zn = ZnCl₂ + R-R). In cases where chemical condensation is associated with the elimination of water, dehydrating agents are used (sulfuric acid, zinc chloride, phosphorus pentoxide, etc.). Upon the elimination of hydrogen chloride, the condensing agents can be sodium hydroxide, calcium carbonate, sodium acetate, etc. In the Friedel-Crafts synthesis, during the introduction of alkyls into the benzene ring, chemical condensation proceeds under the influence of aluminum chloride (C₆H₆ + RCl + AlCl₃ = C₆H₅.R + HCl + AlCl₃). There are condensing agents whose mode of action remains completely unclear so far. In some cases, an insignificant amount of a condensing agent acting as a catalyst is sufficient to reproduce the reaction; such are many metal salts. In many cases, the action of condensers reduces to the preliminary isomerization of the starting materials. Chemical condensation is also significant in biological processes. An example of chemical condensation can be the action of carboligase (see), the synthesis of sugars in plants, and others.