What is the difference between aldehydes and ketones. Ketones

Aldehydes and ketones are derivatives of hydrocarbons containing a functional carbonyl group SO. In aldehydes, the carbonyl group is bonded to a hydrogen atom and one radical, and in ketones to two radicals.

General formulas:

The names of common substances of these classes are given in Table. ten.

Methanal is a colorless gas with a pungent suffocating odor, highly soluble in water (the traditional name for a 40% solution is formalin), poisonous. Subsequent members of the homologous series of aldehydes are liquids and solids.

The simplest ketone is propanone-2, better known as acetone, at room temperature - a colorless liquid with a fruity odor, t bp = 56.24 ° C. Mixes well with water.

Chemical properties aldehydes and ketones are due to the presence of a CO carbonyl group in them; they easily enter into reactions of addition, oxidation and condensation.

As a result accession hydrogen to aldehydes formed primary alcohols:

When reduced with hydrogen ketones formed secondary alcohols:

Reaction accession sodium hydrosulfite is used to isolate and purify aldehydes, since the reaction product is slightly soluble in water:

(by the action of dilute acids, such products are converted into aldehydes).

Oxidation aldehydes passes easily under the action of atmospheric oxygen (the products are the corresponding carboxylic acids). Ketones are relatively resistant to oxidation.

Aldehydes are able to participate in reactions condensation. Thus, the condensation of formaldehyde with phenol proceeds in two stages. First, an intermediate product is formed, which is a phenol and an alcohol at the same time:

The intermediate then reacts with another phenol molecule to give the product polycondensation –phenol-formaldehyde resin:

Qualitative reaction on the aldehyde group - the reaction of the "silver mirror", i.e., the oxidation of the C (H) O group with silver (I) oxide in the presence of ammonia hydrate:

The reaction with Cu (OH) 2 proceeds similarly; when heated, a red precipitate of copper oxide (I) Cu 2 O appears.

Receipt: general way for aldehydes and ketones - dehydrogenation(oxidation) of alcohols. When dehydrogenating primary alcohols are obtained aldehydes, and in the dehydrogenation of secondary alcohols - ketones. Usually, dehydrogenation proceeds when heated (300 °C) over finely divided copper:

When oxidizing primary alcohols strong oxidizing agents (potassium permanganate, potassium dichromate in acid environment) the process is difficult to stop at the stage of obtaining aldehydes; aldehydes are easily oxidized to the corresponding acids:

A more suitable oxidizing agent is copper (II) oxide:

Acetaldehyde in industry obtained by the Kucherov reaction (see 19.3).

The most widely used aldehydes are methanal and ethanal. Metanal used for the production of plastics (phenolic plastics), explosives, varnishes, paints, medicines. Ethanal- the most important intermediate in the synthesis of acetic acid and butadiene (production of synthetic rubber). The simplest ketone, acetone, is used as a solvent for various varnishes, cellulose acetates, in the production of film and explosives.

ALDEHYDES AND KETONES

Aldehydes and ketones are hydrocarbon derivatives containing a C=O carbonyl group. In the molecule of aldehydes, at least one valence of the carbonyl group is spent on the connection with the hydrogen atom, and the other - with the radical (of the limiting series in limiting aldehydes and unsaturated - in unsaturated aldehydes). General formula of aldehydes:

and R can be equal to H.

In the case of ketones, both valences of the carbonyl group are spent in connection with radicals. General formula of ketones:

Isomerism. Nomenclature.

The general formula of limiting aldehydes and ketones C n H 2 n O.

The isomerism of aldehydes is related to the structure of the radicals. So, for example, four aldehydes are known with the formula

(see below).

Aldehydes are named either by the acids into which they are converted during oxidation (with the same number of carbon atoms), or by saturated hydrocarbons with the addition of the suffix -al(systematic nomenclature).

	formic aldehyde (formaldehyde), methanal (Fig. 1 a)
	acetaldehyde, ethanal (Fig. 1 b)
	propionaldehyde, propanal
CH 3 -CH 2 -CH 2 -CHO	butyric aldehyde, butanal
	isobutyric aldehyde, 2-methylpropanal
CH 3 -CH 2 -CH 2 -CH 2 -CHO	valeric aldehyde, pentanal
	isovalernanaldehyde, 3-methylbutanal
	methylethylacetic aldehyde, 2-methylbutanal
	trimethylacetic aldehyde, 2,2-dimethylpropanal

The isomerism of ketones is associated with the structure of the radicals and with the position of the carbonyl group in the carbon chain. Ketones are named after the radicals attached to the carbonyl group. According to the systematic nomenclature, the suffix -on is added to the name of the saturated hydrocarbon and the number of the carbon atom associated with carbonyl oxygen is indicated:

How to get

Aldehydes and ketones are prepared by a number of common methods.

1. Oxidation or catalytic dehydrogenation of primary alcohols produces aldehydes, secondary - ketones. These reactions have already been cited when considering the chemical properties of alcohols.

2. Aldehydes and ketones are also conveniently obtained by pyrolysis of acids and their mixtures in the form of vapors over oxides of certain metals (ThO 2, MnO 2, CaO, ZnO) at 400-450 ° C:

R - COOH + H-COOH → R-CHO + CO 2 + H 2 0

2R-COOH → R -CO -R + C0 2 + H 2 0

R-COOH + R "- COOH → R - CO-R '+ C0 2 + H 2 0

Many textbooks indicate that aldehydes and ketones can be obtained by pyrolysis of Ca- and Ba-salts carboxylic acids. In fact, this reaction gives very low yields. However, some methyl ketones can still be obtained by pyrolysis of mixtures of barium or iron salts of acetic acid and some other acid. All these reactions have a radical mechanism.

3. Hydrolysis of geminal dihalogen derivatives results in aldehydes if both halogens are at one of the extreme carbon atoms, and ketones if the halogen atoms are at one of the middle carbon atoms. These reactions have already been mentioned in the study of the chemical properties of dihalogen derivatives of hydrocarbons.

4. Hydration of acetylene and its homologues under the conditions of the Kucherov reaction leads, respectively, to acetaldehyde or ketones:

HC≡CH + H 2 O→ CH 3 -CHO

5. Carbonyl compounds in high yields (about 80%) are formed during the oxidation of the corresponding alcohols with mixtures of dpmethyl sulfoxide with acetic anhydride or anhydrous phosphoric acid.

RCH 2 OH + (CH 3) 2 SO → RCH \u003d O + (CH 3) 2 S

6. The conversion of haloalkyls to aldehydes with chain extension by one carbon atom is achieved by treating them with sodium tetracarbonyl ferrate in the presence of triphenylphosphine and then with acetic acid:

R - Hlg + Na 2 Fe (CO) 4 RCOFe (CO 3) P (C 6 H 5) 3 R–CH \u003d O

There are several modifications of this method.

7. Ketones with good yields are obtained by reacting acid chlorides with lithium dialkyl cupratamn and cadmium alkyls:

R 2 CuLi + R "COCI → R - CO - R" + LiCI + R - Сu

8. In technology, aldehydes are obtained by direct addition of CO and H 2 to olefins (oxosynthesis) at 100-200 ° C under a pressure of 10-20 MPa (100-200 atm) in the presence of cobalt or nickel catalysts (for example, Co + ThO 2 + MgO, deposited for diatomaceous earth):

The reaction with ethylene and propylene is carried out in the gas phase, and with more complex olefins (C 4 -C 20) - in the liquid phase. As can be seen from the above scheme, oxosynthesis produces aldehydes containing one more carbon atom than the original olefins. This synthesis has importance to obtain higher primary alcohols (catalytic reduction of aldehydes). The mechanism of oxosynthesis can be represented as follows:

2Co + 8CO → Co 2 (CO) 8

Co 2 (CO) 8 + H 2 → 2HCo (CO) 4

R -CH \u003d CH 2 + HCo (CO) 4 → R - CH 2 -CH 2 - Co (CO) 4

R - CH 2 -CH 2 -Co (CO) 4 + CO → R-CH 2 -CH 2 -CO - Co (CO) 4

R-CH 2 -CH 2 -CO-Co (CO) 4 + HCo (CO) 4 → R-CH 2 -CH 2 -CHO + Co (CO ) 8

Physical properties

Formic aldehyde is a gas with a very pungent odor. Other lower aldehydes and ketones are liquids easily soluble in water; lower aldehydes have a suffocating odor, which, when strongly diluted, becomes pleasant (reminiscent of the smell of fruits). Ketones smell pretty good.

With the same composition and structure of the carbon chain, ketones boil at slightly more high temperatures than aldehydes. The boiling points of normal chain aldehydes and ketones are higher than those of isostructure compounds. For example, valeric aldehyde boils at 103.4°C, while isovaleric aldehyde boils at 92.5°C. Aldehydes and ketones boil at a temperature much lower than alcohols with the same number of carbon atoms, such as propionaldehyde, bp. 48.8 °C, for acetone 65.1 °C, for n- propyl alcohol 97.8 °C. This shows that aldehydes and ketones, unlike alcohols, are not strongly associated liquids. At the same time, the boiling points of carbonyl compounds are much higher than the boiling points of hydrocarbons with the same molecular weight, which is associated with their high polarity. The density of aldehydes and ketones is below unity.

In the IR spectra, the CO group is characterized by intense absorption at 1720 cm -1 . In the NMR spectrum, the hydrogen signal of the aldehyde group is in a very weak field.

Chemical properties

Aldehydes and ketones are highly reactive. Most of their reactions are due to the presence of an active carbonyl group. The double bond of a carbonyl group is similar in physical nature to a double bond between two carbon atoms (σ-bond + π-bond). However, while E c=c<2Е с-с, энергия связи С=О (749,4 кДж/моль) больше, чем энергия двух простых С-О-связей (2х358 кДж/моль). С другой стороны, кислород является более электро­отрицательным элементом, чем углерод, и потому электронная плотность вблизи атома кислорода больше, чем вблизи атома уг­лерода. Дипольный момент карбонильной груп­пы - около 9 10 -30 Кл/м (2,7 D). Благодаря такой поляризации углеродный атом карбонильной группы обладает электрофильными свойствами и способен реагировать с нуклеофильными реагентами. Соответ­ственно атом кислорода является нуклеофильным. В реакциях присоединения отрицательно поляризо­ванная часть присоединяющейся молекулы всегда на­правляется к углеродному атому карбонильной груп­пы, в то время как ее положительно поляризованная часть направляется к кислородному атому.

The addition reaction of nucleophilic reagents at the carbonyl bond site is a stepwise process. Schematically, the addition reaction, for example, sodium hydrosulfite to acetaldehyde, can be depicted as follows:

Radicals capable of increasing the positive charge on the carbonyl carbon atom greatly increase the reactivity of aldehydes and ketones; radicals or atoms that reduce the positive charge on that carbon atom have the opposite effect.

In addition to addition reactions at the carbonyl group, aldehydes and ketones are also characterized by reactions involving carbon radicals adjacent to the carbonyl group, due to the electron-withdrawing effect of the carbonyl group on them. These include oxidation, halogenation, and condensation reactions.

A. Hydrogenation. Hydrogen addition to aldehydes and ketones occurs in the presence of hydrogenation catalysts (Ni, Co, Cu, Pt, Pd, etc.). In this case, aldehydes are converted into primary, and ketones into secondary alcohols. One of the methods for obtaining alcohols is based on this.

Recently, nthium aluminum hydride LiA1H 4 has often been used as a reducing agent. The reaction proceeds with the transfer of a hydride ion:

The advantage of reduction with LiAlH 4 is that this reagent does not reduce carbon-carbon double bonds.

When aldehydes or ketones are reduced with hydrogen at the time of isolation (using alkali metals or amalgamated magnesium), glycols are also formed along with the corresponding alcohols:

pinacon

The ratio between the resulting alcohol and glycol depends on the nature of the carbonyl compound and the reduction conditions. During the reduction of ketones, pinacones predominate in the reaction products in aprotic solvents; in the case of aliphatic saturated aldehydes, glycols are formed in small amounts.

The reaction proceeds with the intermediate formation of free radicals:

B. Nucleophilic addition reactions.

1. The addition of magnesium haloalkyls is discussed in detail in the description of methods for obtaining alcohols.

2. The addition of hydrocyanic acid leads to the formation of α-hydroxynitriles, the saponification of which produces α-hydroxy acids:

α-hydroxypropionic acid nitrile

This reaction begins with the nucleophilic attack of the carbon atom by the CN - ion. Hydrogen cyanide is added very slowly. The addition of a drop of potassium cyanide solution greatly speeds up the reaction, while the addition of mineral acid reduces the reaction rate to near zero. This shows that the active reagent in the formation of cyanohydrin is the CN - ion:

3. The addition of sodium hydrosulfite gives crystalline substances, usually called hydrosulfite derivatives of aldehydes or ketones:

When heated with a solution of soda or mineral acids, hydrosulfite derivatives decompose with the release of free aldehyde or ketone, for example:

The reaction with sodium hydrosulfite is used for the qualitative determination of aldehydes and ketones, as well as for their isolation and purification. However, it should be noted that only methyl ketones with the CH 3 -CO - grouping enter into the reaction with sodium hydrosulfite in the fatty series.

4. Interaction with ammonia makes it possible to distinguish between aldehydes and ketones. Aldehydes release water to form aldimines:

acetaldimin, etanimi n

which are easily polymerized (cyclized into crystalline trimers - aldehyde ammonias:

aldehydeammia to

During cyclization, the double bond C = N is broken and three imine molecules are combined into a six-membered ring with alternating carbon and nitrogen atoms.

Ketones do not form similar compounds with ammonia. They react very slowly and more complex, like so:

5. With hydroxylamine, aldehydes and ketones, releasing water, form oximes (aldoximes and ketoximes):

acetaldoxime

acetone oxime

These reactions are used for the quantitative determination of carbonyl compounds.

Reaction mechanism (R=H or Alk):

6. Of particular interest are the reactions of carbonyl compounds with hydrazine and its substituted ones. Depending on the conditions, hydrazine reacts with aldehydes and ketones in a ratio of 1:1 or 1:2. In the first case, hydrazones are formed, and in the second - azines (aldazines and ketazines):

hydrazone

aldazine

ketazine

Hydrazones of ketones and aldehydes, when heated with solid KOH, release nitrogen and give saturated hydrocarbons (Kizhner reaction):

Currently, this reaction is carried out by heating the carbonyl compound with hydrazine in high-boiling polar solvents (di- and triethylene glycols) in the presence of alkali. The reaction can also be carried out at room temperature under the action of tert-butyl potassium in dimethyl sulfoxide.

Aldehydes and ketones with substituted hydrazines - with phenylhydrazine C 6 H 5 -NH-NH 2 and semicarbazide form phenylhydrazones and semicarbazones, respectively. These are crystalline substances. They serve for the qualitative and quantitative determination of carbonyl compounds, as well as for their isolation and purification.

Formation of phenylhydrazones:

Semicarbazones are formed according to the scheme:

The reactions of aldehydes and ketones with hydrazine derivatives are similar in mechanism to their reactions with ammonia and hydroxylamine. For example, for acetaldehyde and phenylhydrazine:

These reactions are characterized by acid catalysis.

7. Aldehydes and ketones are able to add water to the carbonyl group to form hydrates - geminal glycols. These compounds in many cases exist only in solutions. The equilibrium position depends on the structure of the carbonyl-containing compound:

So, formaldehyde at 20 ° C exists in an aqueous solution by 99.99% in the form of a hydrate, acetaldehyde - by 58%; in the case of acetone, the hydrate content is negligible, while chloral and trichloroacetone form stable crystalline hydrates.

Aldehydes with a higher molecular weight form solid hemihydrates that are stable at low temperatures with water:

8.

In the presence of traces of a mineral acid, acetals are formed:

Acetals are liquids with a pleasant ethereal odor. When heated with dilute mineral acids (but not alkalis), they undergo hydrolysis with the formation of alcohols and the release of aldehydes:

Acetal, derived from butyric aldehyde and polyvinyl alcohol, is used as an adhesive in the manufacture of safety glasses.

Ketone acetals are more difficult to obtain - by the action of ethyl esters of orthoformic HC (OC2H 5) 3 or orthosilicic acid on ketones:

9. Under the action of alcohols on aldehydes, hemiacetals are formed:

Aldehydes and ketones, when interacting with PCI 5, exchange an oxygen atom for two chlorine atoms, which is used to obtain geminal dichloroalkanes:

This reaction in the stage that determines the nature of the final product is also a nucleophilic addition reaction:

B. Oxidation reactions. The oxidation of aldehydes is much easier than that of ketones. In addition, the oxidation of aldehydes results in the formation of acids without changing the carbon skeleton, while ketones are oxidized to form two simpler acids, or an acid and a ketone.

Aldehydes are oxidized by atmospheric oxygen to carboxylic acids. Intermediate products are hydroperoxides:

An ammonia solution of silver hydroxide OH, when lightly heated with aldehydes (but not with ketones), oxidizes them to acids with the formation of free metallic silver. If the test tube in which the reaction is taking place was previously degreased from the inside, then silver lays down in a thin layer on it. inner surface- a silver mirror is formed:

This reaction, known as the silver mirror reaction, is used for the qualitative determination of aldehydes.

Aldehydes are also characterized by a reaction with the so-called Fehling liquid. The latter is an aqueous alkaline solution of a complex salt formed from copper hydroxide and sodium potassium salt of tartaric acid. When aldehydes are heated with Fehling's liquid, copper (II) is reduced to copper (I), and the aldehyde is oxidized to acid:

Red copper oxide Cu 2 O precipitates almost quantitatively. This reaction with ketones does not go.

Aldehydes can be oxidized to carboxylic acids by many common oxidizing agents such as potassium dichromate, potassium permanganate, by the ionic mechanism, the first step of the process usually being the addition of the oxidizing agent to the CO group.

The oxidation of ketones proceeds with a break in the carbon chain in different directions, depending on the structure of the ketones.

From the oxidation products, one can judge the structure of ketones, and since ketones are formed during the oxidation of secondary alcohols, then, consequently, the structure of these alcohols.

D. Polymerization reactions. These reactions are typical only for aldehydes. Under the action of acids on aldehydes, their trimerization occurs (partially tetramerization):

The mechanism of polymerization can be represented as follows:

D. Halogenation. Aldehydes and ketones react with bromine and iodine at the same rate, regardless of the halogen concentration. Reactions are accelerated by both acids and bases.

A detailed study of these reactions led to the conclusion that they go with the preliminary transformation of the carbonyl compound into enol:

E. Condensation reactions.

1. Aldehydes in a weakly basic medium (in the presence of acetate, carbonate or potassium sulfite) undergo aldol condensation (A.P. Borodin) with the formation of aldehydesirts (hydroxyaldehydes), abbreviated as aldols. Aldols are formed by the addition of an aldehyde to the carbonyl group of another aldehyde molecule, breaking the C-H bond at the α-position to the carbonyl, as shown in the example of acetaldehyde:

aldol

In the case of aldolizacin other aldehydes, such as propionic, only the group in the a-position to the carbonyl reacts, since only the hydrogen atoms of this group are sufficiently activated by the carbonyl group:

3-hydroxy-2-methylpentanal

If there is a quaternary carbon atom next to the carbonyl, aldolization is not possible. For example, trimethylacetic aldehyde (CH3)3C-CHO does not give an aldol.

The mechanism of the base-catalyzed aldol condensation reaction is as follows. The aldehyde exhibits the properties of a CH-acid. The hydroxyl ion (catalyst) reversibly detaches a proton from an a-carbon atom:

Aldol, when heated (without water-removing substances), splits off water with the formation of unsaturated crotonaldehyde:

Therefore, the transition from a saturated aldehyde to an unsaturated aldehyde through an aldol is called croton condensation. Dehydration occurs due to the very high mobility of hydrogen atoms in the α-position with respect to the carbonyl group (hyperconjugation), and, as in many other cases, the p-bond with respect to the carbonyl group is broken.

When aldehydes capable of aldol condensation are exposed to strong bases (alkalis), resinification occurs as a result of deep aldol (or croton) polycondensation. Aldehydes that are not capable of aldol condensation, under these conditions, enter into the Cannizzaro reaction:

2 (CH 3) 3 C-CHO + KOH → (CH 3) 3 C-COOK + (CH 3) 3 C-CH 2 OH.

Aldol condensation of ketones occurs under more stringent conditions - in the presence of bases, such as Ba(OH) 2 . In this case, P-ketoalcohols are formed, which easily lose a water molecule:

Under even more severe conditions, for example, when heated with concentrated sulfuric acid, ketones undergo intermolecular dehydration with the formation of unsaturated ketones:

mesityl oxide

Mesityl oxide can react with the new acetone molecule:

phoron

Condensation between aldehydes and ketones is also possible, for example:

3-penten-2-one

In all these reactions, aldol condensation occurs first, and then the resulting hydroxyketone is dehydrated.

2. Ester condensation of aldehydes takes place under the action of aluminum alkogolates in a non-aqueous medium (V.E. Tishchenko).

ethyl acetate

AND. Decarbonylation. Aldehydes, when heated with tris(triphenylphosphine)rhodium chloride, undergo decarbonylation to form hydrocarbons:

R-CHO + [(C 6 H 5) 3 P] 3 PhCl → R-H + [(C 6 H 5) 3 P] 3 RhCOCl.

When studying the chemical transformations of aldehydes and ketones, it is necessary to pay attention to the significant differences between them. Aldehydes are easily oxidized without changing the carbon chain (silver mirror reaction), ketones are oxidized with difficulty with chain breakage. Aldehydes polymerize under the influence of acids, form aldehyde ammonias, give acetals with alcohols in the presence of acids, enter into ester condensation, give color with fuchsine sulfuric acid. Ketones are not capable of such transformations.

individual representatives. Application

Formic aldehyde (formaldehyde) is a colorless gas with a pungent specific odor, bp. -21 °С. It is poisonous, irritating to the mucous membranes of the eyes and respiratory tract. Highly soluble in water, 40% formaldehyde aqueous solution is called formalin. In industry, formaldehyde is obtained by two methods - incomplete oxidation of methane and some of its homologues and catalytic oxidation or dehydrogenation of methanol (at 650-700 ° C over a silver catalyst):

CH 3 OH → H 2 + H 2 CO.

Due to the absence of an alkyl radical, formaldehyde has some special properties.

1. In an alkaline environment, it undergoes an oxidation-reduction reaction (Cannizzaro reaction):

2. When formaldehyde (formalin) is lightly heated with ammonia, hexamethylenetetramine (urotropine) is obtained, synthesized for the first time by A. M. Butlerov:

6H 2 C \u003d O + 4NH 3 → 6H 2 0 + (CH 2) 6 N 4

urotropin

Urotropin is used in large quantities in the production of phenol-formaldehyde resins, explosives (RDX obtained by nitration of urotropine)

hexagen

in medicine (as a diuretic, as an integral part of the anti-influenza drug Calcex, in the treatment of kidney diseases, etc.).

3. In an alkaline environment, for example, in the presence of milk of lime, as was first shown by A. M. Butlerov, formaldehyde undergoes aldolization with the formation of hydroxyaldehydes up to hexoses and even more complex sugars, for example:

hexose

In the presence of alkalis, formaldehyde can also condense with other aldehydes, forming polyhydric alcohols. Thus, the condensation of formaldehyde with acetic aldehyde produces a tetrahydric alcohol - pentaerythritol C (CH 2 OH) 4

CH 3 CHO + 3H 2 CO → (NOCH 2) 3 CCHO

(HOCH 2) 3 CCHO + H 2 CO → (NOCH 2) 4 C + HCOO -

Pentaerythritol is used to produce resins and a very strong explosive - tetranitropentaerythritol (PETN) C(CH 2 ONO 2) 4 .

4. Formaldehyde is capable of polymerization to form cyclic and linear polymers.

5. Formaldehyde is able to enter into various condensation reactions with the formation of synthetic resins that are widely used in industry. Thus, phenol-formaldehyde resins are obtained by polycondensation of formaldehyde with phenol, and carbamide resins with urea or melamine.

6. The condensation product of formaldehyde with isobutylene (in the presence of H 2 SO 4) is 4,4-dimethyl-1,3-dioxane, which, when heated to 200-240 ° C in the presence of catalysts (SiO 2 + H 4 P 2 O 7), decomposes to form isoprene.

Formalin is widely used as a disinfectant for disinfection of grain and vegetable stores, greenhouses, greenhouses, for dressing seeds, etc.

Acetic aldehyde, acetaldehyde CH 3 CHO - liquid with a sharp not pleasant smell. bp 21 °C. Vapors of acetaldehyde cause irritation of mucous membranes, suffocation, and headache. Acetaldehyde is highly soluble in water and in many organic solvents.

Industrial methods for the production of acetaldehyde have already been considered: hydration of acetylene, dehydrogenation of ethyl alcohol, isomerization of ethylene oxide, catalytic oxidation of saturated hydrocarbons with air.

Recently, acetaldehyde is produced by the oxidation of ethylene with atmospheric oxygen in the presence of a catalyst according to the scheme:

CH 2 \u003d CH 2 + H 2 O + PdCl 2 → CH 3 -CHO + 2HCl + Pd

Pd + 2CuC1 2 → 2CuCl + PdCl 2

2CuCl + 2HCI + 1/2 O 2 → 2CuCI 2 + H 2 O

2CH 2 \u003d CH 2 + O 2 → 2CH 3 CHO

Other 1-alkenes form methyl ketones in this reaction.

Acetic acid, acetic anhydride, ethyl alcohol, aldol, butyl alcohol, acetals, ethyl acetate, pentaerythritol and a number of other substances are obtained from acetaldehyde on an industrial scale.

Like formaldehyde, it condenses with phenol, amines, and other substances to form synthetic resins that are used in the production of various polymeric materials.

Under the action of a small amount of sulfuric acid, acetaldehyde polymerizes into paraldehyde (C 2 H 4 O 3) 3 and metaldehyde (C 2 H 4 O 3) 4; the quantities of the latter increase with decreasing temperature (down to -10 °C):

Paraldehyde is a liquid with bp. 124.5 °C, metaldehyde is a crystalline substance. When heated with traces of acid, both of these substances depolymerize, forming acetaldehyde. From paraldehyde and ammonia, 2-methyl-5-vinylpyridine is obtained, which is used in the synthesis of copolymers - synthetic rubbers.

Trichloroacetic aldehyde, chloral CCI 3 CHO, is obtained by chlorination of ethyl alcohol.

Chloral is a colorless liquid with a pungent odor; with water forms a crystalline hydrate - chloral hydrate. The stability of chloral hydrate is explained by the enhancement of the electron-withdrawing properties of carbonyl carbon under the influence of the strong inductive effect of chlorine:

Has a hypnotic effect. By condensation of chloral with chlorobenzene, insecticides are obtained on an industrial scale.

Under the action of alkali on chloral, chloroform is formed:

Acetone CH 3 COCH 3 - a colorless liquid with a characteristic odor; T.bp.=56.1 °C, T.pl.=0.798. Let's well dissolve in water and in many organic solvents.

Acetone is obtained:

1) from isopropyl alcohol - by oxidation or dehydrogenation;

2) oxidation of isopropylbenzene obtained by alkylation of benzene, along with phenol;

3) acetone-butanol fermentation of carbohydrates.

Acetone as a solvent is used in large quantities in the paint and varnish industry, in the production of acetate silk, film, smokeless powder (pyroxylin), for dissolving acetylene (in cylinders), etc. It serves as the starting product in the production of unbreakable organic glass, ketene, etc. d.

ALDEHYDES AND KETONES

1. Determination of aldehydes and ketones, difference in structure.

2. Nomenclature and isomerism

3. Physical properties

4. Chemical properties. The structure of the carbonyl group (electronic effects of the group).

5. Application of aldehydes and ketones.

6. Impact on human health and nature.

Aldehydes and ketones are oxygen-containing organic compounds containing carbonyl group (-C=O).

General formula of carbonyl compounds:

- alkyl radicals (CH3-. C2H5-)

Nomenclature of aldehydes and ketones

For aldehydes, the trivial, rational, and IUPAC (systematic) nomenclature is used.

Trivial names aldehydes are derived from the trivial names of those acids into which aldehydes are converted during oxidation.

According to rational nomenclature the names of aldehydes are constructed using the name of acetaldehyde as the basis. More complex aldehydes are considered as derivatives with the replacement of hydrogen atoms in the methyl group of acetaldehyde by more complex radicals.

According to IUPAC nomenclature the names of aldehydes are built from the name of the corresponding hydrocarbon and the addition of the suffix -al. The chain numbering always starts from the carbonyl carbon atom, so the group number is not put. Numbers and prefixes indicate the position and number of substituents.

Nomenclature of ketones.

For ketones trivial name used for the first representative - acetone (CH3COCH3).

According to rational nomenclature, the names of ketones are built by listing the radicals associated with the carbonyl group in ascending order of their molecular weight and adding the base "ketone".

According with IUPAC nomenclature in the ketone, the longest chain containing the -C=O group is selected, the numbering starts from the end where this group is located. The names of ketones are built from the name of hydrocarbons with the addition of the ending - HE, the number must indicate the position of the functional group. Also, numbers and prefixes indicate the position and number of deputies.

The structure of the carbonyl group C=O

The properties of aldehydes and ketones are determined by the structure of the carbonyl group >C=O.

The carbon and oxygen atoms in the carbonyl group are in the state of sp2 hybridization. Carbon with its sp2-hybrid orbitals forms 3 s-bonds (one of them is a C–O bond), which are located in the same plane at an angle of about 120° to each other. One of the three oxygen sp2 orbitals is involved in the C–O s bond, the other two contain unshared electron pairs.

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The C=O bond is strongly polarized. The electrons of the C=O multiple bond, especially the more mobile p-electrons, are shifted to the electronegative oxygen atom, which leads to the appearance of a partial negative charge. The carbonyl carbon acquires a partial positive charge.

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When oxidizing alcohols, a copper catalyst is used.

2) Another way - catalytic hydrationacetylene, the intermediate compound is vinyl alcohol (this method was considered in the first module - and is called the Kucherov reaction).

If you take methyl acetylene instead of acetylene, you get acetone.

3) Ozonolysis of alkenes was also studied in detail in the first module (topic ALKENES)

4) In industry, production is carried out by pyrolysis of carboxylic acids and their salts.

5) Hydrolysis of dihalogenated alkanes and methylarenes.

This reaction leads to aldehydes if both halogens are on the same carbon atom. If the atom is at the end of the chain, it is an aldehyde; if it is in the middle, it is a ketone.

6) Friedel-Crafts reaction (considered in acylation reactions of arenes, electrophilic substitution of aromatic hydrocarbons).

Chemical properties of aldehydes and ketones

The chemical properties are determined by the structural features of the >C=O carbonyl group, which has polarity - the electron density between the C and O atoms is unevenly distributed, shifted to the more electronegative O atom. As a result, the carbonyl group acquires an increased reactivity, which manifests itself in various addition reactions along double bond.

In addition, due to the shift in electron density, hydrogen atoms located in the α-position relative to the carbonyl group acquire mobility, this property is called CH-acidity.

In all cases, ketones are less reactive than aldehydes, in particular because of the steric hindrance created by the two organic R groups.

I. Double bond addition C=O, interaction with O-, N-, S-nucleophiles

1) When interaction with alcohols aldehydes form hemiacetals - compounds containing both alkoxy and hydroxy groups on one carbon atom. Hemiacetals can then react with another molecule of alcohol, forming full acetals - compounds where one carbon atom has two RO groups at the same time. The reaction is catalyzed by acids and bases. In the case of ketones, the addition of alcohols to the double bond in C=O is difficult.

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3) In the same way (opening the double bond C \u003d O) they react with aldehydes and ketones ammonia and amines, the addition products are unstable and condense with the release of water and the formation of a C=N double bond. This reaction makes it possible to distinguish between aldehydes and ketones.

In the case of the interaction of aldehyde and ammonia, imines are obtained, and the so-called Schiff bases are formed from amines - compounds containing the fragment >C=NR.

Ketones do not form similar compounds with ammonia. They react more slowly and difficult:

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5) Reactions with hydroxylamine are carried out with the release of water. The reaction product of an aldehyde or ketone with hydroxylamine is oxime. Such compounds are of interest for organic synthesis.

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7) Aldehydes and ketones react with halonucleophiles. As reagents, phosphorus and sulfur halides are used, but most often - phosphorus pentachloride.

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The role of the catalyst is to accelerate the enolization process (we will consider the essence of the catalyst operation below using the condensation reaction as an example).

2) Condensation reactions. For aldehydes and ketones, condensation is possible between two molecules of the same compound. With such a condensation of aldehydes, the double bond of one of the molecules opens, a compound is formed containing both an aldehyde and an OH group, called an aldol (aldehyde alcohol).

The resulting condensation is called, respectively, aldol, this reaction is catalyzed by bases. The resulting aldol can further condense to form a C=C double bond and release condensation water. The result is an unsaturated aldehyde (crotonaldehyde). Such a condensation is called crotonic, after the name of the first compound in the series of unsaturated aldehydes.

Ketones are also able to participate in aldol condensation, and the second stage, crotonic condensation, is difficult for them.

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Let's take a closer look at the reaction mechanism:

The hydroxyl ion is the initiator of the reaction; it removes a proton from the methyl group of the aldehyde (stage I). Then the methylene component attacks the carbonyl component, the second molecule of the carbonyl compound (stage II). The products of aldol condensation easily remove water in the presence of bases (stage III).

2) Condensation of aldehydes and ketones with phenols goes with the removal of the carbonyl atom O (in the form of water), and the methylene group CH2 or substituted methylene group (CHR or CR2) is inserted between two phenol molecules. This reaction is most widely used to obtain phenol-formaldehyde resins.

III Reduction and oxidation

Aldehydes and ketones are, as it were, intermediate compounds between alcohols and carboxylic acids: recovery leads to alcohols, and oxidation leads to carboxylic acids. Under the action of H2 (in the presence of a Pt or Ni catalyst), aldehydes are reduced, forming primary alcohols, and ketones - secondary alcohols (these reactions were discussed in detail in the lecture "Alcohols").

Oxidation aldehydes to carboxylic acids passes quite easily in the presence of O2 or under the action of weak oxidizing agents, such as an ammonia solution of silver hydroxide. This reaction is accompanied by the formation of a silver mirror on the inner surface of the reaction device (more often, an ordinary test tube), it is used for qualitative detection of the aldehyde group.

Aldehydes are oxidized by Fehling's liquid. Fehling's reagent is an aqueous alkaline solution formed from Cu (OH) 2 and potassium-sodium salt of tartaric acid (Rochelle salt). When the solutions are drained, a complex compound is formed (such as copper glycolate). Next, the aldehyde reduces divalent copper to monovalent. Ketones do not enter into such reactions.

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There are also for ketones qualitative reactions- for example, iodoform test. This reaction is given by methyl ketones (during the reaction, the color of iodine disappears and a precipitate of CH3I is released at the same time).

3CH3CO-R + 3I2 + 4NaOH = CH3I¯ + RCOONa + 3NaI + 3H2O

The use of aldehydes and ketones

Formaldehyde H2C=O (its aqueous solution is called formalin) is used as a leather tanning agent and a preservative for biological preparations.

Acetone (CH3)2C=O is a widely used extractant and solvent for varnishes and enamels.

Aromatic ketone benzophenone (C6H5)2C=O with a geranium scent, used in perfume compositions and for aromatizing soaps.

Some of the aldehydes were first found in the composition of essential oils of plants, and later artificially synthesized.

Aliphatic aldehyde CH3(CH2)7C(H)=O (a trivial name is pelargonic aldehyde) is found in the essential oils of citrus plants, has the smell of orange, and is used as a food flavoring.

The aromatic aldehyde vanillin is found in fruits tropical plant vanilla, synthetic vanillin is now more often used - a well-known flavoring additive in confectionery.

vanillin benzaldehyde benzophenone

Benzaldehyde, which smells of bitter almonds, is found in almond oil and in essential oil eucalyptus. Synthetic benzaldehyde is used in food fragrance essences and in perfume compositions.

Benzophenone and its derivatives are able to absorb UV rays, which has determined their use in creams and sunburn lotions, in addition, some benzophenone derivatives have antimicrobial activity and are used as preservatives. Benzophenone has a pleasant smell of geranium, and therefore it is used in perfume compositions and for flavoring soaps.

The ability of aldehydes and ketones to participate in various transformations determined their main use as starting compounds for the synthesis of various organic substances: alcohols, carboxylic acids and their anhydrides, drugs (urotropin), polymer products (phenol-formaldehyde resins, polyformaldehyde), in the production of various fragrant substances (based on benzaldehyde) and dyes.

Impact on human health and nature

Aldehydes are chemically active substances that have toxic effect(narcotic and irritating effect on mucous membranes). As the molecular weight increases, the narcotic effect of the compounds increases. Lower and unsaturated aldehydes have mutagenic and carcinogenic properties.

When the concentration of aldehydes in the reservoir exceeds 50 mg / l, fish die, and the ingress of aldehydes into wastewater inhibits their biochemical purification.

The toxic effect of ketones is manifested in the defeat of the central nervous system. They are excreted slowly from the body due to good solubility in the blood.

Aldehydes and ketones.

Aldehydes and ketones have similar chemical structure. Therefore, the story about them is combined in one chapter.

In the structure of both compounds, there is a divalent carbonyl group:

The difference between aldehydes and ketones is as follows. In aldehydes, the carbonyl group is bonded to one hydrogen atom and to a hydrocarbon radical, while in ketones it is bonded to two hydrocarbon radicals.

Chemical properties of aldehydes and ketones.

The presence of a carbonyl group in both aldehydes and ketones determines a certain similarity of their properties. However, there are also differences. This difference is explained by the presence of a hydrogen atom bonded to the carbonyl group in the aldehyde molecule. (There is no such atom in the ketone molecule).

The carbonyl group and the hydrogen atom associated with it are separated into a separate functional group. This group was named aldehyde functional group.

Due to the presence of hydrogen in the aldehyde molecule, the latter are easily oxidized (add oxygen) and turn into carboxylic acids.

For example, when acetaldehyde is oxidized, acetic acid is formed:

Due to their easy oxidizability, aldehydes are energetic reducing agents. In this they are significantly different from ketones, which are much more difficult to oxidize.

Obtaining aldehydes and ketones.

Aldehydes and ketones can be obtained by oxidation of the corresponding alcohols, having the same carbon skeleton and hydroxyl at the same carbon atom, which forms a carbonyl group in the resulting aldehyde or ketone.

If a primary alcohol is used as the alcohol to be oxidized, then the oxidation will result in an aldehyde.

Formic aldehyde (formaldehyde).

is the simplest aldehyde with the formula:

Formaldehyde is obtained from methyl alcohol, the simplest of alcohols.

In formaldehyde, the hydrogen atom acts as a radical.

Properties:

It is a gas with a pungent odor and is highly soluble in water. It has antiseptic and tanning properties.

Receipt:

receive formaldehyde from methyl alcohol by its catalytic oxidation with atmospheric oxygen or by dehydrogenation (hydrogen elimination).

Application:

Water solution formaldehyde (usually 40%) is called formalin. Formalin is widely used for disinfection and preservation of anatomical preparations. Significant amounts of formaldehyde are used to produce phenol-formaldehyde resins.

It is one of the most important aldehydes. It matches ethyl alcohol and can be obtained by its oxidation.

Acetic aldehyde widely found in nature and industrially produced in large quantities. It is present in coffee, ripe fruit, bread, and is synthesized by plants as a result of their metabolism.

Properties:

Acetic aldehyde- easily boiling colorless liquid (boiling point 21 degrees C). It has a characteristic smell of rotten apples, it is highly soluble in water.

Receipt:

In the industry acetaldehyde it turns out:

1. ethylene oxidation,
2. adding water to acetylene
3. oxidation or dehydrogenation of ethanol.

Application:

Apply acetaldehyde to obtain acetic acid, butadiene, some organic substances, aldehyde polymers.

Dimethyl ketone (acetone).

dimethyl ketone (acetone) is the simplest ketone. In its molecule, the role of hydrocarbon radicals is performed by methyl CH 3(residue of methane).

Properties:

Acetone is a colorless liquid with a characteristic odor.

Boiling temperature 56,2 degrees FROM.

Acetone miscible with water in all proportions.

It is one of the metabolites produced by the human body.

Receipt:

1. Acetone can be obtained by oxidation of propene,
2. Get methods used acetone from isopropyl alcohol and acetylene,
3. main part acetone obtained as a co-product in the production of phenol from benzene by the cumene method.

Application:

Acetone- very good solvent many organic substances. It is widely used in the paint and varnish industry, in the production of certain types of artificial fiber, unbreakable organic glass, film, smokeless powder. Acetone also used as a starting material for the synthesis of a number of organic compounds.

Aldehydes – organic matter, whose molecules contain a carbonyl group C=O, connected to a hydrogen atom and a hydrocarbon radical.
The general formula for aldehydes is:

In the simplest aldehyde, formaldehyde, the role of the hydrocarbon radical is played by another hydrogen atom:

The carbonyl group attached to the hydrogen atom is often referred to as aldehyde:

Ketones- organic substances in the molecules of which the carbonyl group is bonded to two hydrocarbon radicals. Obviously, the general formula for ketones is:

The carbonyl group of ketones is called keto group.
In the simplest ketone, acetone, the carbonyl group is bonded to two methyl radicals:

Nomenclature and isomerism of aldehydes and ketones

Depending on the structure of the hydrocarbon radical associated with the aldehyde group, limiting, unsaturated, aromatic, heterocyclic and other aldehydes are distinguished:

In accordance with the IUPAC nomenclature, the names of saturated aldehydes are formed from the name of an alkane with the same number of carbon atoms in the molecule using the suffix -al. For example:

The numbering of carbon atoms of the main chain starts from the carbon atom of the aldehyde group. Therefore, the aldehyde group is always located at the first carbon atom, and it is not necessary to indicate its position.

Along with the systematic nomenclature, trivial names of widely used aldehydes are also used. These names are usually derived from the names of carboxylic acids corresponding to aldehydes.

For the name of ketones according to the systematic nomenclature, the keto group is denoted by the suffix -he and a number that indicates the number of the carbon atom of the carbonyl group (numbering should start from the end of the chain closest to the keto group). For example:

For aldehydes, only one type of structural isomerism is characteristic - the isomerism of the carbon skeleton, which is possible from butanal, and for ketones also the isomerism of the position of the carbonyl group. In addition, they are also characterized by interclass isomerism (propanal and propanone).

Physical properties of aldehydes

In an aldehyde or ketone molecule, due to the greater electronegativity of the oxygen atom compared to the carbon atom, the bond C=O strongly polarized due to electron density shift π -bonds to oxygen:

Aldehydes and ketones are polar substances with excess electron density on the oxygen atom. The lower members of the series of aldehydes and ketones (formaldehyde, acetaldehyde, acetone) are infinitely soluble in water. Their boiling points are lower than those of the corresponding alcohols. This is due to the fact that in the molecules of aldehydes and ketones, unlike alcohols, there are no mobile hydrogen atoms and they do not form associates due to hydrogen bonds. Lower aldehydes have a pungent odor; aldehydes containing from four to six carbon atoms in the chain have an unpleasant odor; higher aldehydes and ketones have floral odors and are used in perfumery .

Chemical properties of aldehydes and ketones

The presence of an aldehyde group in a molecule determines characteristic properties aldehydes.

1. Recovery reactions.

The addition of hydrogen to aldehyde molecules occurs via a double bond in the carbonyl group. The product of hydrogenation of aldehydes are primary alcohols, ketones are secondary alcohols. So, when acetaldehyde is hydrogenated on a nickel catalyst, ethyl alcohol is formed, and when acetone is hydrogenated, propanol-2 is formed.

Hydrogenation of aldehydes- reduction reaction, in which the degree of oxidation of the carbon atom included in the carbonyl group decreases.

2. Oxidation reactions. Aldehydes are able not only to recover, but also oxidize. When oxidized, aldehydes form carboxylic acids.

Air oxygen oxidation. For example, propionic acid is formed from propionaldehyde (propanal):

Oxidation with weak oxidizing agents(ammonia solution of silver oxide).

If the surface of the vessel in which the reaction is carried out was previously degreased, then the silver formed during the reaction covers it with a thin, even film. It turns out a wonderful silver mirror. Therefore, this reaction is called the "silver mirror" reaction. It is widely used for making mirrors, silvering decorations and Christmas decorations.

3. Polymerization reaction:

n CH 2 \u003d O → (-CH 2 -O-) n paraforms n \u003d 8-12

Obtaining aldehydes and ketones

The use of aldehydes and ketones

Formaldehyde(methanal, formic aldehyde) H 2 C=O:
a) to obtain phenol-formaldehyde resins;
b) obtaining urea-formaldehyde (urea) resins;
c) polyoxymethylene polymers;
d) synthesis medicines(urotropin);
e) disinfectant;
f) preservative of biological preparations (due to the ability to fold the protein).

Acetic aldehyde(ethanal, acetaldehyde) CH 3 CH \u003d O:
a) production of acetic acid;
b) organic synthesis.

Acetone CH 3 -CO-CH 3:
a) solvent for varnishes, paints, cellulose acetates;
b) raw materials for the synthesis of various organic substances.