Difference Between Aldehyde and Formaldehyde

The key difference between aldehyde and formaldehyde is that the aldehyde contains an R group attached to a –CHO group but, the formaldehyde doesn’t have an R group as other aldehydes.

The major difference between aldehyde and formaldehyde lies upon the chemical structure of those compounds. Both these are organic compounds containing carbon, hydrogen and oxygen atoms. Furthermore, they possess a carbonyl functional group, which is a –CHO group. As its name implies, formaldehyde is also a form of aldehyde.

CONTENTS

1. Overview and Key Difference
2. What is Aldehyde
3. What is Formaldehyde
4. Side by Side Comparison – Aldehyde vs Formaldehyde in Tabular Form
5. Summary

What is Aldehyde?

Aldehydes have a carbonyl group. This carbonyl group binds with another carbon from one side, and from the other end, it connects to a hydrogen atom. Moreover, in a carbonyl group, carbon atom essentially has a double bond to oxygen. Therefore, we can characterize aldehydes with the –CHO group, in which, the oxygen atom has a double bond with the carbon atom.

In the nomenclature of aldehydes, according to the IUPAC system, we use the term “al” to denote an aldehyde. For aliphatic aldehydes, the “e” of the corresponding alkane is replaced with “al”. For example, we can name the compound CH₃CHO as ethanol, and CH₃CH₂CHO as propanol. Aldehydes with ring systems, where the aldehyde group directly attaches to the ring, we can use the term “carbaldehyde” as a suffix to name them. However, C₆H₆CHO is commonly known as benzaldehyde rather than using benzenecarbaldehyde.

Furthermore, we can synthesize these organic compounds by various methods. One method is via primary oxidizing alcohols. In addition, we can synthesize them by reducing esters, nitriles and acyl chlorides.

Structure

The carbonyl carbon atom has sp² hybridization. Thus, aldehydes have a trigonal planar arrangement around the carbonyl carbon atom. A carbonyl group is a polar group; thus, these molecules have higher boiling points compared to the hydrocarbons having the same weight.

However, these compounds cannot make stronger hydrogen bonds like alcohols which results in lower boiling points than the corresponding alcohols. Because of the hydrogen bond formation ability, low molecular weight aldehydes are soluble in water. Anyway, when the molecular weight increases, they become hydrophobic.

The carbonyl carbon atom has a partial positive charge; hence, it 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.

What is Formaldehyde?

The simplest aldehyde is formaldehyde. However, the structure of this compound deviates from the general formula of an aldehyde by having a hydrogen atom instead of an R group. Therefore, formaldehyde has the general formula of H-CHO.

Moreover, formaldehyde is a colourless gas at room temperature, which is also flammable. Its IUPAC name is methanal, with the suffix –al, which shows that it is an aldehyde.  This compound has a strong odour, and it is highly toxic to the human body. However, it naturally forms in the body as a by-product of metabolism pathways. For instance, methanol breaks down in liver producing formaldehyde. Anyway, it does not accumulate inside as it quickly converts into formic acid.

Also, formaldehyde forms naturally in the atmosphere when oxygen, methane, and other hydrocarbons react together under sunlight. Formaldehyde has so many uses as a major chemical in industries. It is useful to produce disinfectants, fertilizer, automobiles, paper, cosmetics, wood preservation, etc.

What is the Difference Between Aldehyde and Formaldehyde?

Formaldehyde is the simplest form of aldehydes. But, the key difference between aldehyde and formaldehyde is that aldehydes contain an R group attached to a –CHO group but, the formaldehyde doesn’t have an R group as other aldehydes. Therefore, the general chemical formula of aldehydes is R-CHO, but for formaldehyde, it is H-CHO.

As another important difference between aldehyde and formaldehyde, we can take the phase of matter that they exist at standard temperature and pressure; aldehydes can occur in either gaseous or liquid phases while formaldehyde occurs in the gaseous phase. Furthermore, an easily observable difference between aldehyde and formaldehyde is their odour. That is; most of the aldehydes have a pleasant odour but, the formaldehyde has a pungent odour.

Summary – Aldehyde vs Formaldehyde

Aldehydes are organic compounds. Formaldehyde is the simplest aldehyde. Therefore, the key difference between aldehyde and formaldehyde is that the aldehyde contains an R group attached to a –CHO group but, the formaldehyde doesn’t have an R group as other aldehydes.

Reference:

1. Brown, William H., and Jerry March. “Aldehyde.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 31 Dec. 2015. Available here  
2. “Formaldehyde.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine. Available here  

Image Courtesy:

1.”FunktionelleGruppen Aldehyde”By MaChe (talk) – Own work, (Public Domain) via Commons Wikimedia  
2.”Formaldehyde 200″By Emeldir (talk) – Own work, (Public Domain) via Commons Wikimedia