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Ketones: types, properties, nomenclature, uses, examples

Recognized as polar compounds, ketones are often soluble and volatile, making them good solvents and additives for perfumes. Furthermore, they are easy to prepare, relatively stable, and possess high reactivity, which has made them an almost perfect intermediate for preparing more complex organic compounds.

Ketones
General formula of ketones

Finally, the elimination of ketones from the human body is often associated with a low blood sugar level (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 linked to two hydrocarbon groups; these can be alkyl groups, benzene ring groups, or both.

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

In industry, the most common method for ketone synthesis 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 yields a ketone and water as products.

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

There are several classifications for ketones, depending primarily on the substituents on their R chains. The most common classifications for these substances are listed below:

According to the structure of your chain

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

For their part, aromatic ones are those that form benzene derivatives, while still being ketones. Lastly, 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 the same (identical) the ketone is called symmetric; but when they are different (like most ketones), this is called 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 saturated ketone. Instead, if the chains are found as alkenes or alkynes, the ketone is called an unsaturated ketone.

On the left ethane, on the right acetylene. Images via wikimedia commons.

Dicetons

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 carbon bond length.

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

ortho-benzoquinone. Surachit at English Wikipedia / Public domain

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, considerably polar, and cannot donate hydrogens for hydrogen bonding (they do not have 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 the van der Waals forces and the dipole-dipole forces, which require a greater amount of energy to separate the attracted atoms and electrons within the molecule.

Solubility

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

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

Acidity

Thanks to their carbonyl group, ketones have an acid nature; This happens due to the resonance stabilization capacity of this functional group, which can give up protons from its double bond to form a conjugated base called enol.

Reactivity

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

As stated above, the great reactivity of ketones makes them a recognized intermediate product that serves as the 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 main chain is taken as the one with the longest carbonyl group, and then the molecule is named. If the carbonyl group does not take precedence over the other functional groups in the molecule, then it is identified with “-oxo”.

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

Finally, the word “ketone” can also be used after identifying the radical chains attached to the carbonyl functional group.

Ketones

Difference between aldehydes and ketones

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

This atom has an important effect on 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.

In contrast, a ketone does not have this hydrogen, so the minimum steps necessary for oxidation to occur do not occur.

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

Industrial uses and in daily life

In the industry ketones are often observed in perfumes and paints, taking roles as 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, as well as pharmaceuticals.

Acetone (the smallest and simplest ketone) is a widely recognized solvent 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.

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 O)

Butanone molecule. Source: Pixabay.

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

Cyclohexanone (C 6 H 10 O)

Cyclohexanone molecule. Benjah-bmm27 / Public domain

Produced on a huge scale, this ketone is used as a precursor to the synthetic material nylon.

Testosterone (C 19 H 22 O 2 )

Testosterone molecule. Wikimedia commons

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

Progesterone (C 21 H 30 O 2 )

Medroxyprogesterone acetate, component of cyclofemin

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

Acetone ( CH 3 (CO) CH 3 )

Composed of acetone. Benjah-bmm27 / Public domain

Also known as propanone, it is a colorless compound used for the manufacture of various industrial products such as plastics, as well as for household hygiene products and cosmetics such as nail polish remover.

Cortisone (C 21 H 28 O 5 )

Cortisone. Benjah-bmm27 / Public domain

Steroid hormone used to fight certain ailments and conditions such as inflammation, acne, allergies and other types of skin reactions, asthma or cancer, and leukemia.

Benzophenone (C 13 H 10 O)

Benzophenoma. Benjah-bmm27 / Public domain

Compound widely used in the creation of perfumes and other cosmetic or sun protection products due to its aromatic composition.

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