Examples of Aldehydes
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
- 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.
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.
- 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
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
- 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.
- 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.
- 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
Examples of aldehydes
- Methanal or formaldehyde HCHO
- Ethanal or Acetaldehyde CH 3 CHO
- Propanal or Propionaldehyde CH 3 CH 2 CHO
- Butanal or Butyraldehyde CH 3 CH 2 CH 2 CHO
- Pentanal CH 3 CH 2 CH 2 CH 2 CHO
- Hexanal CH 3 CH 2 CH 2 CH 2 CH 2 CHO
- Heptanal CH 3 (CH 2 ) 5 CHO
- Octanal CH 3 (CH 2 ) 6 CHO
- Nonanal CH 3 (CH 2 ) 7 CHO
- Dechannel CH 3 (CH 2 ) 8 CHO
- 2-butenal CH 3 -CH = CH-CHO
- 2-pentenal CH 3 -CH 2 -CH = CH-CHO
- 2-hexenal CH 3 -CH 2 -CH 2 -CH = CH-CHO
- 3-hexenal CH 3 -CH 2 -CH = CH-CH 2 -CHO
- 3-pentenal CH 3 -CH = CH-CH 2 -CHO
- 2-butyinal CH 3 -C≡C-CHO
- 2-pentinal CH 3 -CH 2 -C≡C-CHO
- 2-hexinal CH 3 -CH 2 -CH 2 -C≡C-CHO
- 3-hexinal CH 3 -CH 2 -C≡C-CH 2 -CHO
- 3-pentinal CH 3 -C≡C-CH 2 -CHO