Ketones: Formula, Types, Properties, Nomenclature, Uses and Examples

The ketones they are organic compounds that possess a carbonyl group (-CO). They are simple compounds in which the carbon of the carbonyl group is bonded to two carbon atoms (and their substituent chains). Ketones are"simple"because they do not have reactive groups such as -OH or -Cl attached to carbon.

Recognized as polar compounds, ketones are usually soluble and volatile, which makes them good solvents and additives for perfumes. In addition, they are easy to prepare, relatively stable and have high reactivity, which has made them an almost perfect intermediate compound for preparing more complex organic compounds.

Finally, the elimination of ketones from the human body is usually associated with a low level of sugar (in diabetic cases and / or extreme fasting), which can cause serious health problems for the patient.

General formula of ketones

Ketones are carbonyl compounds in which this group is bound to two hydrocarbon groups; these may be alkyl groups, benzene ring groups or both.

A ketone can simply be represented as R- (C = O) -R ', where R and R' are any two hydrocarbon chains (alkanes, alkenes, alkynes, cycloalkanes, benzene derivatives and others). There are no ketones with a hydrogen attached to the carbonyl group.

There is a wide variety of methods for the preparation of ketones in the industrial and laboratory environment; In addition, it is important to note that ketones can be synthesized by different organisms, including humans.

In industry, the most common method for the synthesis of ketones involves the oxidation of hydrocarbons, typically with the use of air. On a small scale, ketones are usually prepared through the oxidation of secondary alcohols, which gives as products a ketone and water.

Beyond these most common methods, ketones can be synthesized through alkenes, alkynes, salts of nitrogen compounds, esters and many other compounds, which makes them easy to obtain.

Types of ketones

There are several classifications for ketones, depending mainly on the substituents in their chains R. The following are the most common classifications for these substances:

According to the structure of your chain

In this case, the ketone is classified by the way in which its chain is structured: the aliphatic ketones are those that have two radicals R and R 'that have the form of alkyl radicals (alkanes, alkenes, alkynes and cycloalkanes).

On the other hand, the aromatic ones are those that form benzene derivatives, without ceasing to be ketones. Finally, mixed ketones are those that have an R alkyl radical and an R 'aryl radical, or vice versa.

According to the symmetry of its radicals

In this case the radicals R and R 'substituents of the carbonyl group are studied; when these are equal (identical) the ketone is called symmetric; but when they are different (like most ketones), they call themselves asymmetric.

According to the saturation of its radicals

Ketones can also be classified according to the saturation of their carbon chains; If these are in the form of alkanes, the ketone is called a saturated ketone. In contrast, if the chains are found as alkenes or alkynes, the ketone is called unsaturated ketone.

Dicetones

This is a separate class of ketone, since the chains of this ketone have two carbonyl groups in their structure. Some of these ketones have unique characteristics, such as a longer bond length between carbons.

For example, diketones derived from cyclohexane are known as quinones, which are only two: ortho-benzoquinone and para-benzoquinone.

Physical and chemical properties of ketones

Ketones, like most aldehydes, are liquid molecules and have a series of physical and chemical properties that vary depending on the length of their chains. Its properties are described below:

Boiling point

Ketones are highly volatile, highly polar and can not donate hydrogen for hydrogen bonds (they do not possess hydrogen atoms attached to their carbonyl group), so they have higher boiling points than alkenes and ethers, but lower than alcohols of the same molecular weight.

The boiling point of a ketone increases as the size of the molecule increases. This is due to the intervention of van der Waals and dipole-dipole forces, which require a greater amount of energy to separate the atoms and electrons attracted within the molecule.

Solubility

The solubility of ketones has a strong influence in part on the ability of these molecules to accept hydrogens in their oxygen atom and thus form hydrogen bond with water. In addition, attractive, scattering and dipole-dipole forces are formed between ketones and water, which increase their soluble effect.

Ketones lose solubility capacity the larger their molecule, as they start to require more energy to dissolve in water. They are also soluble in organic compounds.

Acidity

Thanks to its carbonyl group, ketones have an acid nature; this happens because of the resonance stabilization capacity of this functional group, which can transfer protons from its double bond to form a conjugate base called enol.

Reactivity

Ketones are part of a large number of organic reactions; this occurs due to the susceptibility of its carbonyl carbon to the nucleophilic addition, in addition to its polarity.

As stated above, the high reactivity of ketones makes them a recognized intermediate product that serves as a basis for synthesizing other compounds.

Nomenclature

Ketones are named according to the priority or importance of the carbonyl group in the entire molecule, so when you have a molecule governed by the carbonyl group, the ketone is named by adding the suffix"-one"to the name of the hydrocarbon.

The longest chain containing the carbonyl group is taken as the main chain, and then the molecule is named. If the carbonyl group does not have priority over the other functional groups of the molecule, then it is identified with"-oxo".

For more complicated ketones, the position of the functional group can be identified by a number, and in the case of diketones (ketones with two identical R and R 'substituents), the molecule with the suffix"-dione"is named.

Finally, the word"ketone"can also be used after identifying the chains of radicals attached to the carbonyl functional group.

Difference between aldehydes and ketones

The major difference between aldehydes and ketones is the presence of a hydrogen atom attached to the carbonyl group in the aldehydes.

This atom has an important effect when it comes to involving a molecule in an oxidation reaction: an aldehyde will form a carboxylic acid or a carboxylic acid salt, depending on whether oxidation occurs under acidic or basic conditions.

On the other hand, a ketone does not have this hydrogen, so the minimum steps necessary for oxidation do not occur.

There are methods to oxidize a ketone (with oxidizing agents much more powerful than those typically used), but these break the ketone molecule, separating it first into two or more parts.

Industrial and daily life uses

In the industry ketones are often observed in perfumes and paints, taking roles of stabilizers and preservatives that prevent other components of the mixture from degrading; they also have a broad spectrum as solvents in those industries that manufacture explosives, paints and textiles, in addition to pharmaceuticals.

Acetone (the smallest and simplest ketone) is a solvent recognized worldwide, and is used as a paint remover and thinner.

In nature, ketones can appear as sugars, called ketoses. Ketoses are monosaccharides that contain one ketone per molecule. The best known ketose is fructose, the sugar found in fruits and honey.

The fatty acid biosynthesis that occurs within the cytoplasm of animal cells also occurs through the action of ketones. Finally, and as mentioned above, there may be an elevation of ketones in the blood after fasting or in diabetic cases.

Examples of ketones

Butanone (C4H ₈ OR)

Also known as MEK (or MEC), this liquid is produced on a large scale in the industry and is used as a solvent.

Cyclohexanone (C ₆ H ₁₀ OR)

Produced on an enormous scale, this ketone is used as a precursor of the synthetic nylon material.

Testosterone (C ₁₉ H ₂₂ OR ₂ )

It is the main hormone of the male sex and an anabolic steroid, found in most vertebrates.

Progesterone (C _twenty-one H ₃₀ OR ₂ )

Endogenous steroid and sex hormone involved in the menstrual cycle, pregnancy and embryogenesis in humans and other species.

References

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4. ChemGuide. (s.f.). Introducing Aldehydes and Ketones. Retrieved from chemguide.co.uk
5. Calgary, U. O. (s.f.). Ketones. Retrieved from chem.ucalgary.ca