Chemistry

Examples of Aldehydes

We explain that what are examples of aldehydes? The aldehydes are organic chemical compounds consisting of carbon, hydrogen and oxygen. They are hydrocarbon chains that have an oxygen atom at one of their ends, joined with a double bond. They result from the oxidation reaction of alcohols. In fact, its name comes from the term “dehydrogenated alcohol”, taking the syllables al-de-hi-do.

Aldehydes are characterized by carbonyl group , which is the functional group of the last carbon in the chain, joined by a double bond to oxygen: > C = O . Carbon has two single bonds to hydrogen atoms or alkyl or aryl groups. The simplest and most widely used aldehyde is formaldehyde , whose formula is HCHO, known as formaldehyde in solution.

Properties of aldehydes

The formaldehyde , HCHO, is a gas at room temperature and dissolves readily in water. In the form of a 40% solution , it is known as formalin or formalin . It is used as an embalming fluid and sometimes as a preservative for biological specimens; however, this substance is toxic.

Formaldehyde is widely used in the manufacture of adhesives and plastics . For example, it is the raw material for bakelite . Formaldehyde is prepared by oxidation of methanol, and is among the 25 chemicals with the highest annual production in the United States. This reaction is basically the same that occurs in the human body when methanol is ingested.

CH ₃ OH (oxidation) -> HCHO + H ₂

Methanol -> Formaldehyde + hydrogen gas

The formaldehyde HCHO has the following properties:

Being a gas, it is very flammable
Is colorless
Has pungent and pungent odor
Density: 820 Kg / m ³
Molecular weight: 30.03 g / mol
Melting point: -92 ° C
Boiling point: -21 ° C
It is very soluble in water

The next member of the aldehyde series is acetaldehyde, with the formula CH ₃ CHO. In linear form, the aldehyde group is written as CHO . Therefore, the formula for acetaldehyde can be written as CH ₃ CHO. Acetaldehyde is obtained by oxidation of ethanol.

CH ₃ CH ₂ OH (oxidation) -> CH ₃ CHO + H ₂

Ethanol -> Acetaldehyde + hydrogen gas

There is a premise that must be taken into account:

The oxidation of a primary alcohol produces an aldehyde.

Reduction of a carboxylic acid produces an aldehyde.

A primary alcohol is one in which the hydroxyl is attached to carbon that is only linked to hydrogens or to one carbon. For example, methanol CH ₃ OH and CH ₃ CH ₂ OH.

The acetaldehyde CH ₃ CHO has the following properties:

Has a pleasant fruity smell
Colorless
Density: 788 Kg / m ³
Molecular weight: 44 g / mol
Melting point: -122 ° C
Boiling point: 20 ° C
It is soluble in water in all proportions

The propionaldehyde CH ₃ CH ₂ CHO has the following properties:

Has an intense smell
Density: 810 Kg / m ³
Molecular weight: 58 g / mol
Melting point: -81 ° C
Boiling point: 49 ° C
It is soluble in water in a ratio of 16 grams per 100 of water.

Unsaturated aldehydes

When aldehydes have a double or triple bond at some position in their chain, they are said to be unsaturated . That is to say that, in the absence of hydrogens that complete two carbons, an additional bond is formed between them, sharing electrons so that the molecule is stable.

For example:

CH ₂ = CO Ethenal
CH ₃ CH = CO Propenal

These have a double bond, in a certain position, and therefore change the name of the compound.

On the other hand:

CH≡C-CHO Propinal
CH ₃ -C≡C-CHO Butinal

Aldehyde nomenclature

To write the IUPAC name of an aldehyde , two steps are followed:

The final “o” of the original alkane (which is the longest carbon chain containing the carbonyl group) is removed
The ending “-al” is added

For example:

HCHO comes from methane (CH ₄ , 1 carbon alkane), which is why it is called Methanal .
CH ₃ CHO comes from ethane (C ₂ H ₆ , 2-carbon alkane), which is why it is called Ethanal .
CH ₃ CH ₂ CHO comes from propane (C ₃ H ₈ , 3-carbon alkane), which is why it is called Propanal .
CH ₃ CH ₂ CH ₂ CHO comes from butane (C ₄ H ₁₀ , 4-carbon alkane), which is why it is called Butanal .

To write the common name of an aldehyde , two steps are followed:

The name of the carboxylic acid it comes from is written.
The word “aldehyde” is added.

For example:

HCHO comes from formic acid (HCOOH), which is why it is called Formaldehyde .
CH ₃ CHO comes from acetic acid (CH ₃ COOH), which is why it is called Acetaldehyde .
CH ₃ CH ₂ CHO comes from propionic acid (CH ₃ CH ₂ COOH), which is why it is called Propionaldehyde .
CH ₃ CH ₂ CH ₂ CHO comes from butyric acid (CH ₃ CH ₂ CH ₂ COOH), which is why it is called Butyraldehyde .

To write the name of an unsaturated aldehyde , there are two steps to follow:

The position of the double or triple bond (the carbon in which it is found, starting from the carbonyl group) is indicated.
The name of the aldehyde is written, placing in the middle “en” for double bonds and “in” for triple bonds.

For example:

CH ₃ -C≡C-CHO 2-butynal
CH ₃ -CH ₂ -C≡C-CHO 2-pentinal
CH ₃ -CH = CH-CHO 2-butenal
CH ₃ -CH ₂ -CH = CH-CHO 2-pentenal