Plan
Introduction
Physical properties and being in nature
Chemical properties
Methods for obtaining monobasic carboxylic acids of the aromatic series
Nitrobenzoic acids
Application
Conclusion
Bibliography
Introduction
Systematic name benzoic acid
Traditional names for benzoic acid
Chemical formula C6H5COOH
Molar mass 122.12 g/mol
Physical properties
Condition (St. conditional) solid
Thermal properties
Melting point 122.4 °C
Boiling point 249.2 °C
Decomposition temperature 370 °C
Specific heat of vaporization 527 J/kg
Specific heat of fusion 18 J/kg
Chemical properties
Solubility in water 0.001 g/100 ml
Aromatic carboxylic acids are benzene derivatives containing carboxyl groups directly bonded to the carbon atoms of the benzene nucleus. Acids containing carboxyl groups in the side chain are considered to be aromatic fatty acids.
Aromatic acids can be divided according to the number of carboxyl groups into one-, two- or more basic ones. The names of acids in which the carboxyl group is directly attached to the nucleus are derived from aromatic hydrocarbons. The names of acids with a carboxyl in the side chain are usually derived from the names of the corresponding fatty acids. The acids of the first type are of the greatest importance: for example, benzoic (benzenecarboxylic) C 6 H 5 -COOH, P- toluic ( P-toluenecarboxylic), phthalic (1,2-benzenedicarboxylic), isophthalic (1,3-benzenedicarboxylic), terephthalic (1,4-benzenedicarboxylic):
Story
It was first isolated by distillation in the 16th century from benzoin resin (dewy incense), hence the name. This process was described by Nostradamus (1556) and later by Girolamo Rouchelli (1560, under the pseudonym Alexius Pedemontanus) and Blaise de Vigenère (1596).
In 1832, the German chemist Justus von Liebig determined the structure of benzoic acid. He also investigated how it related to hippuric acid.
In 1875, the German physiologist Ernst Leopold Zalkowsky investigated the antifungal properties of benzoic acid, which had long been used in fruit preservation.
Sulfosalicylic acid
2-hydroxy-5-sulphobenzoic acid
HO3S(HO)C6H3COOH 2H3O M 254.22
Description
Sulfosalicylic acid is a colorless translucent needle-shaped crystals or white crystalline powder.
Sulfosalicylic acid is easily soluble in water, alcohol and ether, insoluble in benzene and chloroform, photosensitive. Aqueous solutions are acidic.
Application
Sulfosalicylic acid is used in medicine for the qualitative determination of protein in urine, during analytical work to determine the content of nitrates in water.
In industry, sulfosalicylic acid is used as additives to the main raw materials, in the synthesis of substances.
Physical properties and being in nature
Monocarboxylic acids of the benzene series are colorless crystalline substances with a melting point above 100 °C. Acids with pair- substituent positions melt at much higher temperatures than their isomers. Aromatic acids boil at slightly higher temperatures and melt at much higher temperatures than fatty acids with the same number of carbon atoms. Monocarboxylic acids are rather poorly soluble in cold water and much better in hot water. Lower acids are volatile with water vapor. In aqueous solutions, monocarboxylic acids exhibit a greater degree of dissociation than fatty acids: the dissociation constant of benzoic acid is 6.6·10 -5, acetic acid is 1.8·10 -5. At 370C, it decomposes to benzene and CO2 (phenol and CO are formed in a small amount). When interacting with benzoyl chloride at elevated temperatures, benzoic acid is converted to benzoic anhydride. Benzoic acid and its esters are found in essential oils (for example, in clove, tolu and Peru balsams, benzoin resin). Hippuric acid, a derivative of benzoic acid and glycine, is a waste product of animals. It crystallizes in the form of colorless plates or needles, melting at 121 ° C, easily soluble in alcohol and ether, but hardly soluble in water. Currently, benzoic acid is quite widely used in the dye industry. Benzoic acid has antiseptic properties and is therefore used for food preservation. Various derivatives of benzoic acid also find considerable application.
Chemical properties
Benzene was discovered by Faraday in 1825 and its gross formula C 6 H 6 was established. In 1865, Kekule proposed its structural formula as cyclohexatriene-1,3,5. This formula is still used today, although, as will be shown later, it is imperfect - it does not fully correspond to the properties of benzene.
The most characteristic feature of chemical behavior benzene is the amazing inertness of double carbon-carbon bonds in its molecule: in contrast to those considered; previously unsaturated compounds, it is resistant to oxidizing agents (for example, potassium permanganate in acidic and alkaline media, chromic anhydride in acetic acid) and does not enter into the usual electrophilic addition reactions characteristic of alkenes, alkadienes and alkynes.
Trying to explain the properties of benzene by structural features, many scientists, following Kekule, put forward their own hypotheses on this matter. Since the unsaturation of benzene did not manifest itself clearly, it was assumed that there were no double bonds in the benzene molecule. So, Armstrong and Bayer, as well as Klaus, suggested that in the benzene molecule the fourth valencies of all six carbon atoms are directed towards the center and saturate each other, Ladenburg - that the carbon skeleton of benzene is a prism, Chichibabin - that in benzene carbon is trivalent.
Thiele, improving the Kekule formula, argued that the double bonds in the latter are not fixed, but constantly move - “oscillate”, while Dewar and Hückel proposed structural formulas of benzene with double bonds and small cycles.
At present, based on the data of numerous studies, it can be considered firmly established that the six carbon and six hydrogen atoms in the benzene molecule are in the same plane and that the clouds of π-electrons of carbon atoms are perpendicular to the plane of the molecule and, therefore, are parallel to each other and interact with each other. The cloud of each π-electron is overlapped by clouds of π-electrons of neighboring carbon atoms. A real benzene molecule with a uniform distribution of the π-electron density over the entire ring can be represented as a flat hexagon lying between two tori.
Hence it follows that it is logical to depict the benzene formula as a regular hexagon with a ring inside, thereby emphasizing the complete delocalization of π-electrons in the benzene ring and the equivalence of all carbon-carbon bonds in it. The validity of the latter conclusion is confirmed, in particular, by the results of measuring the lengths of C–C bonds in the benzene molecule; they are the same and equal to 0.139 nm (C-C bonds in the benzene ring are shorter than ordinary (3.154 nm), but longer than double (0.132 nm)). The distribution of electron density in the benzene molecule; bond lengths, bond angles
A very important derivative of benzoic acid is its acid chloride - benzoyl chloride. It is a liquid with a characteristic odor and strong lachrymatory action. Used as a benzoylating agent.
benzoyl peroxide used as an initiator for polymerization reactions, as well as a bleaching agent for edible oils, fats, flour.
Toluic acids. Methylbenzoic acids are called toluic acids. They are formed by partial oxidation of o-, m- And P-xylenes. NN -Diethyl- m-toluylmide is effective repellent- an insect repellant
n-tert-Butylbenzoic acid is produced commercially by liquid-phase oxidation tert-butyltoluene in the presence of a soluble cobalt salt as a catalyst. It is used in the production of polyester resins.
Phenylacetic acid obtained from benzyl chloride via nitrile or via organomagnesium compounds. This is a crystalline substance with so pl. 76 °C. Due to the mobility of the subatomic atoms of the methyl group, it easily enters into condensation reactions. This acid and its esters are used in perfumery.
Aromatic acids enter into all those reactions that are also characteristic of fatty acids. Various acid derivatives are obtained by reactions involving the carboxyl group. Salts are obtained by the action of acids on carbonates or alkalis. Esters - by heating a mixture of acid and alcohol in the presence of mineral (usually sulfuric) acid:
If the deputies in ortho- position is not, then the esterification of the carboxyl group occurs just as easily as in the case of aliphatic acids. If one of ortho- positions are substituted, the esterification rate is greatly reduced, and if both ortho- positions are occupied, esterification usually does not occur (spatial difficulties).
Ethers ortho-substituted benzoic acids can be obtained by the reaction of silver salts with haloalkyls (esters of sterically hindered aromatic acids are easily and quantitatively saponified in the presence of crown ethers). Due to steric hindrances, they are difficult to hydrolyze. Groups larger than hydrogen fill up the space around the carbon atom of the carboxyl group to such an extent that the formation and saponification of the ester is difficult.
Obtaining С6Н5СООН:
Main ways:
1. By oxidizing a wide variety of benzene derivatives with one side chain, for example, toluene, ethylbenzene, benzyl alcohol, etc.: С6Н5СН3 ® С6Н5СООН
2. From benzonitrile, which is hydrolyzed with acid or alkali for this: 2H2 O C6H5CN ¾¾® C6H5COOH + NH3
Benzoic (or dewy incense), Acidum benzoicum sublimatum, Flores Benzoës is a very common substance in nature of the composition C7H6O2, or C6H5-COOH; found in certain resins, balsams, in the herbaceous parts and roots of many plants (according to earlier, as yet unverified observations), as well as in the flowers of Unona odoratissima (in the essence of alan-jilan, or ylang-ylang), in the beaver stream, and mainly in benzoin resin, or dewy incense, whence its name. About the products of dry distillation of this resin, there are indications in the writings relating to the 16th century; Blaise de Vigenère, in his treatise (1608) "Traité du feu et du sel", first mentions a crystalline substance from benzoin, which was later investigated more closely and received the name Flores benzoës. Its composition was finally established by Liebig in 1832, and Kolbe suggested considering it as a phenylcarboxylic acid. B. acid can be obtained synthetically from benzene and is formed in many reactions that occur with bodies of the aromatic series. For pharmaceutical needs, they use exclusively acid obtained by sublimation of benzoin resin. It is best to take Siamese dewy incense for this purpose, since it does not contain cinnamic acid, or Calcutta, which is cheaper and also contains a lot of B. acid. The crushed resin is slightly heated in a sand bath in iron pots, during which the mass first melts and then releases heavy vapors of B. acid, which settle on the cold parts of the device in the form of crystals. To collect the substance, the pot is covered with a paper cone or a lid with a wide tube, through which the vapors are diverted into a wooden box covered with paper. At the end of the operation (and strong heating should be avoided if possible), the acid remains in the receiver or on the paper cone in the form of snow-white crystals or flakes. The preparation obtained in this way has a distinct smell of vanilla, which depends on the content of a small amount of essential oil in the resin. The best yields can be achieved by infusing finely ground resin with milk of lime or soda for a long time. The mixture is then heated until the resin melts, and the substance is isolated from the resulting benzoate salt hydrochloric acid. The acid obtained in this way has a weaker odor than that obtained by sublimation. For technical purposes, hippuric acid (see this word) contained in the urine of herbivores is taken as a starting material. The urine is quickly evaporated to ⅓ of its original volume, filtered and treated with an excess of hydrochloric acid, and hippuric acid is isolated in crystalline form. After a day, the crystals are separated from the mother liquor and purified by re-crystallization until the stubborn smell of urine almost completely disappears. Purified hippuric acid is boiled with hydrochloric acid, during which splitting into B. acid and glycocol occurs:
HOOC-CH3 + H3O = HOOC-CH3(NH3) + C6H5-COOH.
B. acid can be obtained in large quantities from C6H5-CH3 toluene by oxidizing it with nitric acid; but it is more profitable (as is practiced at factories) to take for this purpose not toluene, but benzenyl chloride С6Н5CCl3; this latter is heated with water in hermetically sealed vessels; the acid formed in this way stubbornly retains halogen-substituted products. Further, B. acid is obtained by heating the lime salt of phthalic acid with caustic lime; finally, significant amounts of it remain as a by-product during the manufacture of bitter almond oil due to the oxidation of the latter. Acid obtained in one way or another by B. is purified by recrystallization from hot water; decolorization of solutions is carried out by treatment with animal charcoal or heating with weak nitric acid. Synthetically, Kekule obtained benzoic acid by acting with carbonic acid on bromobenzene in the presence of metallic sodium:
C6H5Br + 2Na + CO2 = C6H5CO2Na + NaBr.
Friedel and Crafts prepared it directly from benzene and carbonic acid in the presence of aluminum chloride. Pure B. acid is colorless one-clinomeric needles or tablets, beats. weight 1.2 (at 21 °), which does not change in the light, while the one obtained by sublimation from dewy incense turns yellow after a while due to the decomposition of the essential oil contained in it. The substance melts at 121.4 °C, boils at 249.2 without decomposition, and sublimates below the boiling point; has no smell. Its vapors act irritatingly on the mucous membranes of the respiratory organs. With water vapor, the acid flies already below 100 °, and therefore its aqueous solutions cannot be thickened by evaporation. 1000 parts of water are dissolved at 0° 1.7 wt. hours, and at 100 ° 58.75 h. B. acids. It is also highly soluble in alcohol, ether, chloroform, essential and fatty oils. Some impurities, even in very small amounts, change its physical properties so dramatically that at one time the existence of an isomeric B. acid was recognized and it was called salic acid, but both substances turned out to be completely identical (Beilstein). When the vapor is passed through a very heated pumice stone, or, better, during dry distillation with caustic barite or slaked lime, B. acid decomposes into benzene and carbon dioxide. When fused with caustic potash, all three hydroxybenzoic acids are obtained along with other products; oxidizing agents act on it quite difficult. With sodium amalgam, benzoic aldehyde, benzyl alcohol and other products of complex composition are formed. Chlorine and bromine, as well as iodine in the presence of iodic acid, act in a substitutive manner; fuming nitric acid gives nitrobenzoic acids, and fuming sulfuric acid gives sulphobenzoic acids. In general, the hydrogens of the phenyl group in bionic acid can be replaced one after the other by various residues, and an enormous number of diverse compounds are formed, of which several isomeric forms are known for many. Of the derivatives of B. acid, formed through substitution in the carboxyl group, the simplest will be the following:
Benzoyl chloride, B. acid chloride, C6H5-COCl was first obtained by Liebig and Wöhler in 1832 by treating bitter almond oil with dry chlorine; it is also formed by the action of phosphorus pentachloride or trichloride on benzoic acid or phosphorus oxychloride on benzoicone sodium salt. Colorless liquid with a pungent odor. weight 1.324 (at 0°), boiling at 198°; solidifies in the cooling mixture into crystals (melting at -1°). Hot water quickly decomposes into hydrochloric and B. acids; easily enters into double decomposition with a number of substances; so, under the action of ammonia, Liebig and Wöhler obtained from it benzamide, or the amide of B. acid, C6H5-CONH3, a crystalline substance that melts at 128 °, sp. weight 1.341 (at 4°), soluble in hot water, alcohol and ether. Benzamide is also obtained by heating B. acid with ammonium thiocyanate. Water-removing substances easily convert it into B. acid nitrile, benzonitrile or phenyl cyanide - C6H5CN. This latter is also obtained from the potassium salt of sulphobenzoic acid and potassium cyanide. The substance is a liquid with a bitter almond odor, boiling at 190 °, sp. weight 1.023 (at 0 °), solidifying with strong cooling into a solid mass. It is difficult to dissolve in boiling water and easily in alcohol and ether.
How to getmonobasic carboxylic acids of the aromatic series
Monobasic carboxylic acids of the aromatic series can be obtained by all common ways known for fatty acids.
Oxidation of alkyl groups of benzene homologues. This is one of the most commonly used methods for obtaining aromatic acids:
Oxidation is carried out either by boiling the hydrocarbon with an alkaline solution of potassium permanganate, or by heating in sealed tubes with dilute nitric acid. As a rule, this method gives good results. Complications occur only in those cases when the action of oxidizing agents destroys the benzene ring.
Oxidation of aromatic ketones. Aromatic ketones are easily obtained by the Friedel-Crafts reaction. Oxidation is usually carried out using hypochlorites according to the scheme:
However, other oxidizing agents may also be used. Aceto derivatives are more easily oxidized than hydrocarbons.
Hydrolysis of trihalogen derivatives with halogens at one carbon atom. When toluene is chlorinated, three types of chlorine derivatives are formed: benzyl chloride (used to obtain benzyl alcohol), benzylidene chloride (to obtain benzoic aldehyde), benzotrichloride (processed into benzoic acid and benzoyl chloride). The direct hydrolysis of benzotrichloride does not go well. Therefore, benzotrichloride is converted by heating with benzoic acid to benzoyl chloride, which then easily gives benzoic acid upon hydrolysis:
Hydrolysis of nitriles:
This method is widely used in the fat series. In the aromatic series, the starting nitriles are obtained from diazo compounds, from halogen derivatives by exchange with copper cyanide in pyridine or by fusion of sulfonates with potassium cyanide. Nitriles of acids with a nitrile group in the side chain are obtained by an exchange reaction from halogen derivatives.
Reaction of aromatic hydrocarbons with halogen derivatives of carbonic acid
The carboxyl group can be introduced into the nucleus by a reaction analogous to the Friedel-Crafts synthesis of ketones. Aluminum chloride serves as a catalyst:
Reactions of organometallic compounds with CO 2 :
Lithium or organomagnesium compounds are usually used.
Acid chlorides are obtained by the action of thionyl chloride or phosphorus pentachloride on acids:
Anhydrides are obtained by distillation of a mixture of acid with acetic anhydride in the presence of phosphoric acid or by the action of acid chlorides on salts:
When benzoyl chloride reacts with sodium peroxide, crystalline benzoyl peroxide is obtained:
The action of an alcoholate on benzoyl peroxide produces a salt of perbenzoic acid (benzoyl hydroperoxide). This acid is used to obtain oxides from unsaturated compounds. (Prilezhaev's reaction):
In the absence of a catalyst, benzene does not react with bromine and chlorine, thus demonstrating the stability of the three double bonds in its molecule to the action of electrophilic agents. At the same time, the presence of the latter is confirmed by the interaction of benzene with chlorine during irradiation, leading to the formation of hexachlorocyclohexane (hexachloran):
An interesting reaction involving double bonds is observed when benzene in the liquid phase is irradiated with light with a wavelength of 253.7 nm. Under these conditions, the benzene molecule is rearranged, turning into the so-called valence isomers.
Nitrobenzoic acids
Nitration of benzoic acid results in 78%-meta-, 20% ortho- and 2% pair- nitrobenzoic acids. The last two isomers without impurities of other isomers are obtained by oxidation ortho- And pair- nitrotoluenes.
Nitrobenzoic acids are more acidic than benzoic acid. (TO= 6.6 10 -5): O- isomer - 100 times, m- isomer - 4.7 times and p-iso measures - 5.6 times. A similar regularity is also observed in the case of halogenated acids.
Application
Benzoic acid and its salts have a high bactericidal and bacteriostatic activity, which sharply increases with a decrease in the pH of the medium. Due to these properties, as well as non-toxicity, benzoic acid is used:
preservative in the food industry (addition of 0.1% acid to sauces, pickles, fruit juices, jams, minced meat, etc.)
in medicine for skin diseases as an external antiseptic (antimicrobial) and fungicidal (antifungal) agent, and its sodium salt as an expectorant.
In addition, benzoic acid and its salts are used in food preservation (food additives E210, E211, E212, E213). Esters of benzoic acid (from methyl to amyl), which have a strong odor, are used in the perfume industry. Various derivatives of benzoic acid, such as chloro- and nitrobenzoic acids, are widely used for the synthesis of dyes.
Benzoic acid is used in the production
caprolactam
benzoyl chloride
additive to alkyd varnishes that improves gloss, adhesion, hardness and chemical resistance of the coating
Salts and esters of benzoic acid (benzoates) are of great practical importance.
Sodium benzoate food preservative, polymer stabilizer, corrosion inhibitor in heat exchangers, expectorant in medicine.
Ammonium benzoate is an antiseptic, preservative in the food industry, corrosion inhibitor, stabilizer in the production of latexes and adhesives.
Transition metal benzoates are catalysts for the liquid-phase oxidation of alkylaromatic hydrocarbons to benzoic acid.
Esters of benzoic acid from methyl to isoamyl are fragrant substances. Methyl benzoate is a solvent for cellulose ethers.
Isoamyl benzoate is a component of fruit essences.
Benzyl benzoate is an odor fixative in perfumery, a solvent for fragrant substances, an antiseptic, and a moth repellant.
Precautionary measures:
Causes irritation on contact with skin.
Inhalation of the aerosol causes convulsive cough, runny nose, sometimes nausea and vomiting.
Conclusion
Latin name: Acidum benzoicum
Benzoic acid C6H5COOH is the simplest monobasic carboxylic acid of the aromatic series.
Benzoic acid - colorless crystals, poorly soluble in water, well - in ethanol and diethyl ether.
It is used mainly in the form of sodium (great solubility in water) - sodium benzonate, potassium and calcium salts.
Melting point - 122.4°С,
Boiling point - 249°C.
Easily sublimes (one of the ways to obtain is the dry distillation of benzoin resin); distilled with water vapor.
Benzoic acid (Bc) is used in medicine for skin diseases as an external antiseptic (antimicrobial) and fungicidal (antifungal) agent, and its sodium salt is used as an expectorant.
B. to. and its salts have a high bactericidal and bacteriostatic activity, which increases sharply with a decrease in the pH of the medium.
Reaction with some forms of ascorbic acid (vitamin C) is possible.
In the body, benzoic acid combines with glycine to form harmless hippuric acid, which is excreted in the urine.
The allowable dose of benzoic acid and its salt for humans is 5 mg/kg of body weight per day.
Concentration recipes: 0.2-0.5% (for 50 g of cream - 0.2 g of sodium benzoate).
The activity of benzoic acid decreases in the presence of non-ionic surfactants, proteins and glycerol.
Used in conjunction with other preservatives.
Being soluble in fats, it can be used as a preservative for fats, lipsticks, etc. The maximum concentration in cosmetic products is 0.5%.
Salts of benzoic acid - benzoates (for example, sodium benzoate) are also used as preservatives.
Other Uses: Benzoic acid esters, which have a strong odor, are used in the perfume industry.
Various derivatives of benzoic acid, such as chloro- and nitrobenzoic acids, are widely used for the synthesis of dyes.
B. to. and its esters are found in essential oils (for example, in clove), toluan and Peruvian balsams, benzoic resin (up to 20% acid and up to 40% of its esters).
Additional Information:
In practice, aqueous solutions of sodium benzoate with a concentration of 5 to 25% are most often used.
To prepare the solution, the required amount of preservative is dissolved in approximately half of the required volume of drinking water heated to 50 ... 80C. After complete dissolution of the salt, the remaining water is added to the resulting solution and mixed thoroughly. It is recommended to filter the solution through a layer of cotton fabric (calico). If the preservative is dissolved in hard water, the solution may be slightly cloudy, but this does not affect its preservative effect.
When developing a specific formulation for adding a preservative to a product, the following should be considered:
the acidity of the environment affects the effectiveness of preservatives - the more acidic the product has, the less preservative needs to be added to it;
as a rule, reduced-calorie foods have a high water content and are easily spoiled, so the amount of preservative added to them should be 30-40% more than recommended for regular products;
the addition of alcohol, a large amount of sugar, or other substance that exhibits preservative properties, reduces the required amount of preservative.
Literature
1 Zemtsova M.N. Guidelines for coursework in organic chemistry.
2. Chemical reagents and preparations Goshimizdat 1953, Pp. 241-242.
3. Karyakin Yu.V., Angelov I.I. Pure Chemicals Ed. 4th, per. and additional M.: Chemistry 1974, P. 121-122.
4. "Brief chemical encyclopedia" Ed. Soviet Encyclopedia, Vol. 4 M. 1965 Pp. 817-826.
5. Petrov A.A., Balyan H.V., Troshchenko A.T. Organic Chemistry: Textbook for High Schools. - St. Petersburg: "Ivan Fedorov", 2002, P. 421-427.
6. Gitis S.S., Glaz A.I., Ivanov A.V. Workshop on organic chemistry: - M.: Higher school, 1991. - 303.: ill.
7. Shabarov Yu.S. Organic chemistry: Textbook for universities in 2 books. - M .: Chemistry, 1996. Pp. 558-561, 626-629.
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