The benzoic acid is the simplest aromatic acid of all, having as molecular formula C6H5COOH. It owes its name to the fact that it had benzoin as its main source for a long time, a resin obtained from the bark of several trees of the genus Styrax..
It is found in many plants, especially fruits, such as apricots and blueberries. It is also produced in bacteria as a by-product of the metabolism of the amino acid phenylalanine. It is also generated in the intestine by the bacterial (oxidative) processing of the polyphenols present in some foods..
As can be seen in the image above, the C6H5COOH is, unlike many acids, a solid compound. Its solid consists of light, white and filiform crystals, which give off an almond aroma.
These needles have been known since the 16th century; for example, Nostradamus in 1556 describes its dry distillation from benzoin gum.
One of the main capacities of benzoic acid is to inhibit the growth of yeast, mold and some bacteria; for which it is used as a food preservative. This action is pH dependent.
Benzoic acid has several medicinal actions, being used as a component of pharmaceutical products that are used in the treatment of skin diseases such as ringworm and athlete's foot. It is also used as an inhalant decongestant, expectorant and pain reliever.
A high proportion of the industrially produced benzoic acid is destined for the production of phenol. Likewise, a part of it is destined to the production of glycol benzoates, used in the manufacture of plasticizers..
Although benzoic acid is not a particularly toxic compound, it has some harmful actions for health. For this reason, the WHO recommends a maximum intake dose of 5 mg / Kg of body weight / day, which is equivalent to a daily intake of 300 mg of benzoic acid..
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In the upper image the structure of benzoic acid is represented with a model of bars and spheres. If the number of black spheres is counted, it will be verified that there are six of them, that is to say, six carbon atoms; two red spheres correspond to the two oxygen atoms of the carboxyl group, -COOH; and finally, the white spheres are the hydrogen atoms.
As can be seen, on the left is the aromatic ring, whose aromaticity is illustrated by the broken lines in the center of the ring. And on the right, the -COOH group, responsible for the acidic properties of this compound.
Molecularly, the C6H5COOH has a flat structure, due to the fact that all its atoms (with the exception of hydrogens) have sp hybridizationtwo.
On the other hand, the highly polar -COOH group allows a permanent dipole to exist in the structure; dipole that could be seen at first glance if its electrostatic potential map were available.
This fact has as a consequence that the C6H5COOH can interact with itself through dipole-dipole forces; specifically, with the special hydrogen bonds.
If you look at the -COOH group you will find that the oxygen in C = O can accept a hydrogen bond; while the oxygen of the O-H, donates them.
Benzoic acid can form two hydrogen bonds: it receives and accepts one simultaneously. Therefore, it is forming dimers; that is, its molecule is "related" to another.
Are these pairs or dimers, C6H5COOH-HOOCC6H5, the structural base that defines the solid resulting from its arrangement in space.
These dimers compose a plane of molecules that, given their strong and directional interactions, manage to establish an ordered pattern in the solid. Aromatic rings also participate in this ordering through interactions by dispersal forces..
As a result, the molecules build a monoclinic crystal, the exact structural characteristics of which can be studied by instrumental techniques, such as X-ray diffraction..
It is from here then that a pair of flat molecules can be arranged in space, predominantly by hydrogen bonds, to give rise to those white and crystalline needles..
Acid:
-benzoic
-carboxylic benzene
-dracylic
-carboxybenzene
-benzeneoform
C7H6ORtwo or C6H5COOH.
122.123 g / mol.
Solid or in the form of crystals, usually white in color, but can be beige in color if it harbors certain impurities. Its crystals are scaly or needle-shaped (see first image).
It smells like almonds and is pleasant.
Tasteless or slightly bitter. Flavor detection limit is 85 ppm.
480ºF to 760mmHg (249ºC).
252.3 º F (121.5 - 123.5 ºC).
250ºF (121ºC).
It can sublimate from 100 ºC.
3.4 g / L at 25 ºC.
-1 g of benzoic acid is dissolved in a volume equal to: 2.3 mL of cold alcohol; 4.5 ml of chloroform; 3 mL of ether; 3 mL of acetone; 30 mL of carbon tetrachloride; 10 mL of benzene; 30 mL of carbon disulfide; and 2.3 mL of turpentine oil.
-It is also soluble in volatile and fixed oils.
-It is slightly soluble in petroleum ether.
-Its solubility in hexane is 0.9 g / L, in methanol 71.5 g / L, and in toluene 10.6 g / L.
1.316 g / mL at 82.4 º F, and 1.2659 g / mL at 15 ºC.
4.21 (relative to air taken as reference = 1)
1 mmHg at 205ºF and 7.0 x 10-4 mmHg at 25 ºC.
A solution with a concentration of 0.1% in water is stable for at least 8 weeks.
Decomposes on heating, emitting acrid and irritating smoke.
1.26 cPoise at 130 ºC.
3227 KJ / mol.
534 KJ / mol at 249 ºC.
About 4 in water.
31 N / m at 130 ºC.
4.19 at 25 ºC.
1.504 - 1.5397 (ηD) at 20 ºC.
-In contact with bases (NaOH, KOH, etc.) it forms benzoate salts. For example, if it reacts with NaOH, it forms sodium benzoate, C6H5COONa.
-Reacts with alcohols to form esters. For example, its reaction with ethyl alcohol gives rise to the ethyl ester. Some esters of benzoic acid serve as plasticizers.
-Reacts with phosphorus pentachloride, PCl5, to form benzoyl chloride, an acid halide. Benzoyl chloride can react with ammonium (NH3) or an amine such as methylamine (CH3NHtwo) to form benzamide.
-The reaction of benzoic acid with sulfuric acid produces the sulfonation of the aromatic ring. The functional group -SO3H replaces a hydrogen atom in the meta position of the ring.
-It can react with nitric acid, with the use of sulfuric acid as a catalyst, forming meta-nitrobenzoic acid.
-In the presence of a catalyst, such as ferric chloride, FeCl3, benzoic acid reacts with halogens; for example, reacts with chlorine to form meta-chlorobenzoic acid.
Some production methods for this compound are listed below:
-Most benzoic acid is produced industrially by oxidizing toluene with oxygen in the air. The process is catalyzed by cobalt naphthenate, at a temperature of 140-160 ºC and at a pressure of 0.2 - 0.3 MPa.
-Toluene, on the other hand, can be chlorinated to produce benzotrichloride, which is subsequently hydrolyzed to benzoic acid..
-The hydrolysis of benzonitrile and benzamide, in an acid or alkaline medium, can give rise to benzoic acid and its conjugate bases..
-Benzyl alcohol in an oxidation mediated by potassium permanganate, in an aqueous medium, produces benzoic acid. The reaction occurs by heating or reflux distillation. Once the process is finished, the mixture is filtered to eliminate manganese dioxide, while the supernatant is cooled to obtain benzoic acid..
-The benzotrichloride compound is reacted with calcium hydroxide, using iron or iron salts as catalysts, initially forming calcium benzoate, Ca (C6H5COO)two. Then this salt by reaction with hydrochloric acid is converted into benzoic acid.
-It is used in the production of phenol by oxidative decarboxylation of benzoic acid at temperatures of 300-400 ° C. For what purpose? Because phenol can be used in the synthesis of Nylon.
-From it, glycol benzoate is formed, a chemical precursor of diethylene glycol ester and triethylene glycol ester, substances used as plasticizers. Perhaps the most important application for plasticizers is adhesive formulations. Some long chain esters are used to soften plastics like PVC.
-It is used as a rubber polymerization activator. In addition, it is an intermediate in the manufacture of alkyd resins, as well as additives for applications in the recovery of crude oil..
-In addition, it is used in the production of resins, dyes, fibers, pesticides and as a modifying agent for polyamide resin for the production of polyester. It is used to maintain the aroma of tobacco.
-It is a precursor of benzoyl chloride, which is a starting material for the synthesis of compounds such as benzyl benzoate, used in the production of artificial flavors and insect repellants..
-It is a component of Whitfield ointment that is used to treat fungal skin conditions such as ringworm and athlete's foot. Whitfield's ointment is made up of 6% benzoic acid and 3% salicylic acid..
-It is an ingredient in benzoin tincture that has been used as a topical antiseptic and inhalant decongestant. Benzoic acid was used as an expectorant, analgesic and antiseptic until the beginning of the 20th century.
-Benzoic acid has been used in the experimental therapy of patients with residual nitrogen accumulation diseases.
Benzoic acid and its salts are used in the preservation of food. The compound is capable of inhibiting the growth of mold, yeast and bacteria, through a pH-dependent mechanism..
They act on these organisms when their intracellular pH falls to a pH lower than 5, almost totally inhibiting the anaerobic fermentation of glucose for the production of benzoic acid. This antimicrobial action requires a pH between 2.5 to 4 for a more effective action..
-Used to preserve foods such as fruit juices, carbonated drinks, phosphoric acid sodas, pickles, and other acidified foods.
It can react with ascorbic acid (vitamin C) present in some drinks, producing benzene, a carcinogenic compound. Because of this, we are looking for other compounds with the ability to preserve food that do not have benzoic acid problems..
-It is used in active packaging, being present in ionomer films. Benzoic acid is released from them, capable of inhibiting the growth of species of the Penicillium and Aspergillus genera in microbial media..
-It is used as a preservative agent for the aroma of fruit juice and perfume. It is also used with this application in tobacco.
-Benzoic acid is used as a selective herbicide to control broad-leaved weeds and grasses in soybeans, cucumbers, melons, peanuts, and woody ornamentals..
-In contact with the skin and eyes it can cause redness. Inhalation can cause irritation of the respiratory tract and cough. The intake of large amounts of benzoic acid can cause gastrointestinal disorders, which can lead to liver and kidney damage.
-Benzoic acid and benzoates can release histamine which can cause allergic reactions and irritation of the eyes, skin, and mucous membranes..
-It has no cumulative, mutagenic or carcinogenic effect, since it is rapidly absorbed in the intestine, being eliminated in the urine without accumulating in the body..
-The maximum dose allowed according to WHO is 5 mg / Kg of body weight / day, approximately 300 mg / day. Acute toxicity dose in man: 500 mg / kg.
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