Organic chemistry is a very complex science, but interesting. Indeed, the connection of the same elements in different quantities and sequences promotes the formation of substances with different properties. Let's look at the compounds of the carbonyl group called "ketones" (chemical properties, physical characteristics, methods for their synthesis). And also compare them with other substances of the same genus - aldehydes.
Ketones
This word is the general name for a whole class of substances of organic nature, in the molecules of which the carbonyl group (C = O) is associated with two carbon radicals.
Ketones are close in structure to aldehydes and carboxylic acids. However, they immediately contain two C atoms (carbon or carbon) connected to C = O.
Formula
The general formula of substances of this class is as follows: R 1 -CO-R 2 .
To make it more understandable, as a rule, it is written like this.
In it, C = O is a carbonyl group. A R 1 and R 2 Are carbon radicals. In their place can be various compounds, but carbon must be in their composition.
Aldehydes and Ketones
The physical and chemical properties of these groups of substances are quite similar to each other. For this reason, they are often considered together.
The fact is that aldehydes also contain a carbonyl group in their molecules. They even have very similar formulas to ketones. However, if in the substances under consideration C = O is attached to 2 radicals, then in aldehydes it has only one, instead of the second - hydrogen atom: R-CO-H.
An example is the formula for a substance of this class - formaldehyde, better known to everyone as formalin.
Based on the formula CH 2 O, it can be seen that its carbonyl group is not bound to one, but to two atoms of H.
Physical properties
Before you deal with the chemical properties of aldehydes and ketones, it is worth considering their physical features.
- Ketones are fusible solids or volatile liquids. The lower representatives of this class dissolve perfectly in H 2 O and interact well with organic solvents .
Some representatives (for example, CH 3 COSH 3 ) are remarkably soluble in water, and in absolutely any proportions.
Unlike alcohols and carboxylic acids, ketones have greater volatility, with the same molecular weight. This is facilitated by the inability of these compounds to form bonds with H, as H-CO-R can. - Different types of aldehydes may reside in various states of aggregation. So higher R-CO-H are insoluble solids. Lower ones are liquids, some of which mix well with H 2 O, but some of them are only soluble in water, but no more.
The simplest of the substances of this type, formic aldehyde, is a gas with a pungent odor. This substance is highly soluble in H 2 O.
The most famous ketones
There are many substances R 1 -CO-R 2 , however, not so many are known. First of all, it is dimethyl ketone, which we all know as acetone.
Also, his fellow solvent is butanone or, as it is called, methyl ethyl ketone.
Among other ketones whose chemical properties are widely used in industry are acetophenone (methylphenylketone). Unlike acetone and butanone, its smell is quite pleasant, which is why it is used in perfumes.
For example, cyclohexanone belongs to typical representatives of R 1 -CO-R 2 , and is most often used in the manufacture of solvents.
It is impossible not to mention diketones. This name is R 1 -CO-R 2 , in which not one but two carbonyl groups in the composition. Thus, their formula is: R 1 -CO-CO-R 2 . One of the simplest, but widely used in the food industry, representatives of diketones is diacetyl (2,3-butanedione).
The listed substances are just a small list of ketones synthesized by scientists (chemical properties are discussed below). In fact, there are more of them, but not everyone has found application. Moreover, it is worth considering that many of them are toxic.
Chemical properties of ketones
Substances in this category are able to react with various substances. This is precisely their special chemical properties.
- Ketones are able to attach to themselves H (hydrogenation reaction). However, to produce this reaction, the presence of catalysts in the form of metal atoms of nickel, cobalt, cuprum, platinum, palladium, and others is necessary. As a result of the reaction, R 1 —CO — R 2 evolve to secondary alcohols.
Also, when interacting with hydrogen in the presence of alkali metals or Mg amalgam, glycols are obtained from ketones. - Ketones with at least one alpha-hydrogen atom, as a rule, fall under the influence of tautomerization of keto-enol. It is catalyzed not only with acids, but also with bases. Typically, the keto form is a more stable phenomenon than enol. This equilibrium makes it possible to synthesize ketones by hydration of alkynes. The relative stabilization of the enol keto form by conjugation leads to a rather strong acidity of R 1 -CO-R 2 (when compared with alkanes).
- These substances can react with ammonia. However, they proceed very slowly.
- Ketones interact with hydrocyanic acid. As a result, α-hydroxy nitriles arise, the saponification of which contributes to the appearance of α-hydroxy acids.
- Reacting with alkyl magnesium halides leads to the formation of secondary alcohols.
- Joining NaHSO 3 contributes to the emergence of hydrosulfite (bisulfite) derivatives. It is worth remembering that only methyl ketones are capable of reacting in a fatty row.
In addition to ketones, aldehydes can similarly interact with sodium hydrosulfite.
When heated with a solution of NaHCO 3 (baking soda) or mineral acid, derivatives of NaHSO 3 can decompose, accompanied by the release of free ketone. - During the reaction, R 1 —CO — R 2 ketoximes are formed with NH 2 OH (hydroxylamine) and H 2 O as a by-product
- In reactions involving hydrazine, hydrazones are formed (the ratio of the substances taken is 1: 1) or azines (1: 2).
If the resulting product (hydrazone) reacts with caustic potassium under the influence of temperature, N and saturated hydrocarbons are released. This process is called the Kizhner reaction. - As mentioned above, aldehydes and ketones have similar chemical properties and the production process. In this case, acetals R 1 -CO-R 2 are formed more complex than acetals R-CO-H. They appear as a result of the action of esters of orthoformic and orthosilicic acids on ketones.
- Under conditions with a higher concentration of alkalis (for example, when heated with concentrated H₂SO₄), R 1 -CO-R 2 undergo intermolecular dehydration with the formation of unsaturated ketones.
- If alkali is present in the reaction with R 1 —CO — R 2 , ketones undergo aldol condensation. As a result of this, β-keto alcohols are formed, which can easily lose the H 2 O molecule.
- The chemical properties of ketones are quite indicative of the example of acetone, which reacted with mesityl oxide. In this case, a new substance is formed under the name phoron.
- Also, the Leykart-Wallach reaction, which helps to restore ketones, can be attributed to the chemical properties of the organic substance under consideration.
What R1-CO-R2 is derived from
Having become acquainted with the properties of the substances under consideration, it is worth learning the most common methods for their synthesis.
- One of the best known reactions for the preparation of ketones is the alkylation and acylation of aromatic compounds in the presence of acidic catalysts (AlCl 3 , FeCI 3 , mineral acids, oxides, cation exchange resins, etc.). This method is known as the Friedel-Crafts reaction.
- Ketones are synthesized by hydrolysis of ketimines and vic diols. In the case of the latter, the presence of mineral acids as catalysts is necessary.
- Also, hydration of acetylene homologs or, as it is called, the Kucherov reaction, is used to obtain ketones.
- Guben-Gesh reactions.
- Cyclization of Ruzichki is suitable for the synthesis of cycloketones.
- These substances are also extracted from tertiary peroxoesters by means of Krieg rearrangement.
- There are several methods for the synthesis of ketones during the oxidation reactions of secondary alcohols. Four reactions are distinguished depending on the active compound: Swern, Kornblum, Corey-Kim and Wig-Dering.
Scope of application
Having dealt with the chemical properties and the preparation of ketones, it is worth knowing where these substances are used.
As mentioned above, most of them are used in the chemical industry as solvents for varnishes and enamels, as well as in the production of polymers.
In addition, some R 1 -CO-R 2 well established as fragrances. As such, ketones (benzophenone, acetophenone and others) are used in perfumes and cooking.
Acetophenone is also used as a component for the manufacture of sleeping pills.
Benzophenone, due to its ability to absorb harmful radiation, is a frequent ingredient in anti-tanning cosmetics and at the same time a preservative.
The effects of R1-CO-R2 on the body
Having learned what compounds are called ketones (chemical properties, uses, synthesis and other data about them), it is worth familiarizing yourself with the biological characteristics of these substances. In other words, find out how they act on living organisms.
Despite the fairly frequent use of R 1 -CO-R 2 in industry, it is always worth remembering that such compounds are very toxic. Many of them have carcinogenic and mutagenic properties.
Special representatives can cause irritation on the mucous membranes, up to burns. Alicyclic R 1 -CO-R 2 can affect the body like drugs.
However, not all substances of this kind are harmful. The fact is that some of them are actively involved in the metabolism of biological organisms.
Ketones are also peculiar markers of carbon metabolism disorders and insulin deficiency. In the analysis of urine and blood, the presence of R 1 -CO-R 2 indicates various metabolic disorders, including hyperglycemia and ketoacidosis.