Difference Between Aldehyde and Formaldehyde

Aldehyde vs Formaldehyde

Both aldehyde and formaldehyde are organic compounds, which possess a carbonyl functional group. Formaldehyde is also come under the category of aldehyde, but it differs from the general aldehydes in certain ways.

Aldehyde

Aldehydes have a carbonyl group. This carbonyl group is bonded to another carbon from one side, and from the other end it is connected to hydrogen. Therefore, aldehydes can be characterized with the –CHO group, following is the general formula of an aldehyde.

In a carbonyl group, carbon atom has a double bond to oxygen. The carbonyl carbon atom is sp² hybridized.  So aldehydes have a trigonal planar arrangement around the carbonyl carbon atom. The carbonyl group is a polar group, thus, aldehydes have higher boiling points compared to the hydrocarbons having the same weight. But, these cannot make stronger hydrogen bonds like alcohols resulting lower boiling points than the corresponding alcohols. Because of the hydrogen bond formation ability, low molecular weight aldehydes are soluble in water. But, when the molecular weight increases, they become hydrophobic. The carbonyl carbon atom is partially positive charged, hence can act as an electrophile. Therefore, these molecules are easily subjected to nucleophilic substitution reactions. The hydrogens attached to the carbon next to the carbonyl group has acidic nature, which accounts for various reactions of aldehydes.

In the nomenclature of aldehyde, according to the IUPAC system “al” is used to denote an aldehyde. For aliphatic aldehydes, the “e” of the corresponding alkane is replaced with “al”. For example, CH₃CHO is named as ethanal, and CH₃CH₂CHO is named as propanal. Aldehydes with ring systems, where the aldehyde group is directly attached to the ring, “carbaldehyde” term is used as a suffix to name them. But, C₆H₆CHO is commonly known as benzaldehyde rather than using benzenecarbaldehyde.  Aldehydes can be synthesized by various methods. One method is by oxidizing primary alcohols. Moreover, aldehydes can be synthesized by reducing esters, nitriles and acyl chlorides.

Formaldehyde

The simplest aldehyde is formaldehyde. However, this is deviated from the general formula of an aldehyde by having a hydrogen atom instead of a R group. So, formaldehyde has the following structural formula.

Formaldehyde is a colorless gas at room temperature, which is also flammable. Its IUPAC name is methanal, with the suffix –al, which shows that it is an aldehyde.  Formaldehyde has a strong odor, and it is highly toxic to the human body. It is naturally synthesized in the body as a by-product of metabolism pathways. For example, methanol breaks down in liver producing formaldehyde. But, this does not accumulate inside as it is quickly converted into formic acid. Formaldehyde can also be naturally produced in the atmosphere when oxygen, methane, and other hydrocarbons react together under sunlight. Formaldehyde is a widely used chemical in industries. It is used to produce disinfectants, fertilizer, automobiles, paper, cosmetics, wood preservation, etc.

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