Aldehydes are substances that are part of the great Organic Chemistry , having a general formula RCHO . Together with the Ketones, which are RRCO-shaped, they are called Carbonyl Compounds .
The functional group of aldehydes is the carbonyl group C = O . In an Aldehyde there is at least one Hydrogen atom attached to the carbon of the Carbonyl group. Formaldehyde, the simplest aldehyde, has two hydrogens bound to the Carbonyl group, its final formula being: H 2 C = O. It also has the commercial name of Formol.
Also linked to the Carbon of the Carbonyl group, is the radical R , which may be an aliphatic hydrocarbon chain or an aromatic ring .
The simplest Aldehyde, Formaldehyde (H 2 C = O) tends to polymerize , that is, the individual molecules join together to form a compound of high molecular mass. In this polymerization, much heat is released and is often explosive, so formaldehyde is usually prepared and stored in aqueous solution, to reduce its concentration.
Formaldehyde, a very unpleasant odor liquid is a raw material in the polymer industry. In the laboratory, it is used as a preservative for dead animals. Aldehydes of higher molecular mass, such as cinnamic aldehyde or butyraldehyde, have a pleasant smell and are used in the manufacture of perfumes.
Aldehydes are more reactive than ketones due to the fact that the carbonyl functional group is at the end of the chain of these. Ketones have the carbonyl group closed by the two radicals R.
Nomenclature of the Aldehydes
The common names of the aldehydes are derived from the corresponding carboxylic acids . Only the ending “ico” is replaced by aldehyde, and the word acid is eliminated.
The aldehydes that have a branched chain in their R, will take the name of the longest chain formed. The rest will be a substituent.
The IUPAC names of the aldehydes follow a common pattern: the longest chain containing the carbonyl group -CHO is considered as the parent structure and is named after replacing the “or” ending of the alkane with “al”. The position of a radical or substituent is indicated by a number, the carbonyl carbon always remaining as Carbon 1.
Properties of Aldehydes
The polarized Carbonyl group converts the aldehydes into polar substances , so they have higher boiling points than the non-polar compounds of similar molecular weight. This results in that they will have to be heated more to make them boil.
The short chain aldehydes are soluble in water, probably because of the hydrogen bonds that can be established between the solvent molecules and the solute molecules. The limit solubility is reached around five carbons. The aldehydes and ketones are soluble in the usual organic solvents.
Formaldehyde , the simplest, is a gas in its pure state, so it is used as an aqueous solution, called Formalin; in the form of one of its solid polymers called Paraformaldehyde, of form (CH 2 O) n ; or Trioxane (CH 2 O) 3 . When dry formaldehyde is needed, for example for a reaction, it is obtained by heating Paraformaldehyde or Trioxane.
Salicylaldehyde , called IUPAC ortho-hydroxybenzaldehyde, is one of the raw materials of aspirin, a drug commercially called Aspirin.
Benzaldehyde is a benzene ring together with a carbonyl group. It is a liquid with a transparent color that tends to pale yellow, and has a powerful fruity smell, cherries and bitter almonds. It is slightly soluble in water, but dissolves well in Alcohol or Ether. Since it oxidizes very easily in the presence of air, it must be protected from sunlight, in dry and ventilated places. Benzaldehyde is found in almonds, and can be obtained from seeds of fruits such as plums, cherries, peaches.
Butyraldehyde or Butanal has a characteristic apple aroma, so it is used as synthetic flavor in foods. In addition, it is used for the production of rubber accelerators. It also acts as an intermediate reagent in the manufacture of plasticizers, solvents and alcohols.
Acetaldehyde serves as raw material to oxidize and produce acetic acid. In addition, he is involved in production processes of perfumes, dyes, plastics and synthetic rubber.
Examples of aldehydes
- Formaldehyde or Formal
- Acetaldehyde or Etanal
- Propionaldehyde or Propanal
- Butiraldehyde or Butanal