Acid condensation
The term is used in technology and chemistry for two different things:
- Condensation of acids and
- Condensation with acids
Condensation of acids
As acid condensation, the deposition, d. H. Called condensation of gaseous acids on cold surfaces. It can occur primarily during combustion processes (exhaust gases, in chimneys and technical systems). This creates the risk of corrosion.
If the material to be burned contains sulfur or chlorine compounds , sulfur dioxide (SO 2 ) or hydrogen chloride (HCl) can be produced. These gases combine with water vapor to form sulphurous acid or hydrochloric acid . Sulfurous acid can be obtained by atmospheric oxygen to form sulfuric acid are oxidized.
If nitrous gases (NO x ) are produced during combustion , these can ultimately be oxidized to nitric acid.
Acid condensates can also form in the atmosphere, which can be reflected in water droplets (aerosols, rain) or on ice crystals.
Condensation with acids
Acids are often used as catalysts in organic chemical synthesis . In the early days of chemistry, however, little was known about its function. For a long time , concentrated sulfuric acid or phosphoric acid was considered to be "dehydrating agents" which made certain condensation reactions possible in the first place. The term “acid condensation” comes from the chemical laboratories; it means that reactions were carried out in the presence of (mostly inorganic, strong) acids. Sulfuric acid and phosphoric acid sometimes served (undiluted) as solvents at the same time. Gaseous hydrogen chloride can be introduced into a mixture of reacting substances.
Now that the (catalytic) function of acids has been clarified in most cases, the term “acid condensation” appears somewhat antiquated.
Examples
Aldol condensations are usually catalyzed by bases. However, the "acidic aldol condensation" has also been known for a long time. In condensation reactions of aromatic compounds, especially phenols , or pyrrole derivatives with carbonyl compounds , acids often serve as “condensation agents”; the starting materials are thus converted into the products “by acid condensation”.
Individual evidence
- ^ BZ Ahn, F. Gstirner: Obtaining catechin dimers by acid condensation. Arch. Pharm. Pharm. Med. Chem., 303, 720-724 (1970), doi: 10.1002 / ardp.19703030904
- ^ JA Joule, GF Smith: Heterocyclic Chemistry. 2nd edit., P. 199, Van Nostrand Reinhold Company, London, 1978, ISBN 0-442-30212-6