DEFINITION

Toluene (methylbenzene)- a chemical compound of organic nature, a representative of the class of aromatic hydrocarbons, the closest homologue of benzene. Toluene is a colorless liquid, insoluble in water.

Combustible, burns with a smoky flame. It has a pungent odor, as well as a mild narcotic effect. The main physical constants of toluene are given in table. 1. Used in the production of explosives, benzoic acid, saccharin, varnishes, printing inks. It is used as an additive to motor fuel as a component of high-octane gasolines.

Table 1. Physical properties and density of toluene.

Toluene is two orders of magnitude less toxic than benzene due to the fact that it is oxidized to benzoic acid and excreted from the body. Wherever possible, benzene should be replaced with toluene.

Chemical composition and structure of the toluene molecule

The chemical composition of the toluene molecule can be reflected using the empirical formula C 6 H 5 -CH 3 . The methyl radical is directly linked to the benzene ring 7. The structural formula of toluene is as follows:

Rice. 1. The structure of the toluene molecule.

Brief description of the chemical properties and density of toluene

For toluene, as for all aromatic hydrocarbons, substitution reactions in the benzene ring are characteristic, which proceed according to the electrophilic mechanism. Due to the presence of a methyl radical in the composition of toluene, the substitution of hydrogen atoms most often occurs in the ortho- or para-position:

Halogenation (toluene interacts with chlorine and bromine in the presence of catalysts - anhydrous AlCl 3 , FeCl 3 , AlBr 3)

C 6 H 5 -CH 3 + Cl 2 \u003d C 6 H 4 Cl-CH 3 + HCl;

- nitration (toluene easily reacts with a nitrating mixture - a mixture of concentrated nitric and sulfuric acids)

— alkylation according to Friday-Crafts

C 6 H 5 -CH 3 + CH 3 -CH (CH 3) -Cl \u003d CH 3 -C 6 H 4 -CH (CH 3) -CH 3 + HCl.

Addition reactions to toluene lead to the destruction of the aromatic system and proceed only under harsh conditions:

- hydrogenation (the reaction proceeds when heated, the catalyst is Pt)

C 6 H 5 -CH 3 + 3H 2 \u003d C 6 H 11 -CH 3.

As a result of the oxidation of toluene, benzoic acid is formed:

5C 6 H 5 -CH 3 + 6KMnO 4 + 9H 2 SO 4 = 5C 6 H 5 COOH + 6MnSO 4 + 3K 2 SO 4 + 14H 2 O;

The reaction of interaction of toluene with chlorine in the light leads to substitution in the hydrocarbon radical:

C 6 H 5 -CH 3 + Cl 2 \u003d C 6 H 5 -CH 2 Cl + HCl.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Synonym - methylbenzene. Colorless mobile volatile liquid with a pungent odor. Miscible in unlimited limits with hydrocarbons, many alcohols and ethers, while mixing toluene with water is impossible. Dissolves polymers: polystyrene at room temperature, polyethylene when heated. Combustible, burns with the release of soot. Toluene was first isolated from tolu balsam, a yellowish-brown, sweet-smelling resin from the South American tree toluifera balsamum. Hence the name - toluene. This balm was used in the preparation of cough remedies and in perfumery. Currently, toluene is obtained from petroleum fractions and coal tar or in the processes of catalytic reforming of gasoline fractions and pyrolysis. It is isolated by selective extraction and subsequent rectification.
Coal toluene, formed during the coking process, is extracted from the coke oven gas as a component of crude benzene, subjected to sulfuric acid purification (to remove unsaturated and sulfur-containing compounds) and isolated by rectification.
A significant amount of toluene is obtained as a by-product in the synthesis of styrene from benzene and ethylene.
Vapors easily form explosive mixtures that ignite even from a spark of static electricity.

Application of toluene:

Toluene is a valuable raw material for organic synthesis, for the production of motor fuel components with a high octane number, for the production of explosives (trinitrotoluene), pharmaceuticals, dyes and solvents. As the main component, it is included in the composition of mixed solvents (, R-4A, R-5A, R-12) used for dissolving in the manufacture and application of epoxy, vinyl, acrylic, nitrocellulose, chlorinated rubber paints and varnishes. Oxidation reactions are of practical importance; as a result of such a reaction, benzoic acid is obtained. To obtain benzoic acid, the oxidation of toluene with air or atmospheric oxygen is used. The process is carried out either in the vapor or in the liquid phase. Liquid-phase processes in industry are used more often.

Danger to humans:

Toluene is a toxic product (hazard class - third). Toluene vapors at high concentrations have a narcotic effect on a person, causing severe hallucinations and a dissociative state. Until 1998, toluene was part of the popular Moment glue, which made it popular with drug addicts. Elevated concentrations of toluene vapor also have a harmful effect on the human nervous system, irritate the skin, as well as the mucous membranes of the eyes. Being a highly toxic poison, it affects the function of the body's hematopoiesis. The result of impaired hematopoiesis are diseases such as cyanosis, hypoxia. There is toluene substance abuse, which also has a carcinogenic effect. Vapors penetrate through the respiratory organs or intact skin, cause damage to the nervous system (there is lethargy and disruption of the vestibular apparatus. Sometimes these processes are irreversible.
In the air of the working area, regulatory documents regulate the maximum permissible content of vapors:
- maximum single concentration - 150 mg/m3;
- average shift concentration – 50 mg/m3.
Work with toluene and solvents based on it is necessary in rubber gloves resistant to their effects, always under draft and in a well-ventilated area.

Fire hazard:

Highly flammable. Toluene belongs to class 3.1 flammable liquid with a flash point of less than +23 degrees C. Avoid open flames, sparks and smoking. A mixture of toluene vapor with air is explosive.
When loading and unloading operations, the rules for protection against static electricity in the chemical, petrochemical and oil refining industries should be strictly observed. Production facilities in which work with toluene is carried out must be provided with supply and exhaust ventilation, and equipment with local suction. In rooms for the storage and use of toluene, it is prohibited to use open fire, as well as the use of tools that give a spark when struck. Electrical equipment and artificial lighting must be explosion-proof. To extinguish toluene, it is necessary to use water mist, chemical and air-mechanical foam. To extinguish small fires, hand-held foam or carbon dioxide fire extinguishers are used. In the event of a toluene spill, neutralization should be carried out by backfilling with sand and removing it to a specially designated place.

This standard applies to petroleum toluene obtained in the process of catalytic reforming of gasoline fractions, as well as in the pyrolysis of petroleum products and intended for the needs of the national economy as a raw material for organic synthesis, high-octane additives to motor fuels, a solvent and for export.

Formulas: empirical C 7 H 8

Relative molecular weight (according to international atomic masses 1985) - 92.14.

Mandatory requirements for product quality are set out in sections 1, , , .

1. TECHNICAL REQUIREMENTS

1.1. Petroleum toluene must be manufactured in accordance with the requirements of this standard according to the technological regulations approved in the prescribed manner.

(Revised edition, Rev. No. 4).

1.2. (deleted, rev. № 4).

1.3. In terms of physical and chemical parameters, petroleum toluene must comply with the requirements and standards specified in the table

Note . When supplying petroleum toluene for export, it is allowed to determine the color in accordance with GOST 29131-91 with a norm of not more than 20 Hazen units (platinum-cobalt scale)

(Changed edition, Rev. No. 2, 4, 5).

2. SAFETY REQUIREMENTS

2.1. Petroleum toluene belongs to the toxic products of the third hazard class. Toluene vapors at high concentrations have a narcotic effect, adversely affect the nervous system, and irritate the skin and mucous membranes of the eyes.

(Revised edition, Rev. No. 4).

2.2. The maximum allowable concentration of toluene vapor in the air of the working area is set at 150 mg/m 3 (maximum single) and 50 mg/m 3 (average shift).

(Revised edition, Rev. No. 6).

The analysis of the air environment is carried out in accordance with the guidelines for measuring the concentration of harmful substances in the air of the working area, approved by the Ministry of Health.

2.3. Petroleum toluene is one of the flammable, explosive products, the flash point in a closed crucible is 4 ° C, the auto-ignition temperature is 536 ° C, the concentration limits of ignition of toluene vapor in a mixture with air (by volume): lower-1.3%, upper-6 .7%.

(Revised edition, Rev. No. 5).

2.4. When working with toluene, it is necessary to use personal protective equipment: a filtering gas mask with a box of brand A and BKF, goggles, rubber gloves, overalls in accordance with standard industry standards approved in the prescribed manner, protective ointments and pastes.

(Revised edition, Rev. No. 5).

2.5. When loading and unloading operations, the rules for protection against static electricity in the chemical, petrochemical and oil refining industries should be strictly observed.

2.6. Production facilities in which work with toluene is carried out must be provided with supply and exhaust ventilation, and equipment with local suction.

2.7. In rooms for the storage and use of toluene, it is prohibited to use open fire, as well as the use of tools that give a spark when struck. Electrical equipment and artificial lighting must be explosion-proof.

2.8. To extinguish toluene, it is necessary to use water mist, chemical and air-mechanical foam.

To extinguish small fires, hand-held foam or carbon dioxide fire extinguishers are used.

(Revised edition, Rev. № 4, 5).

2.9. In the event of a toluene spill, neutralization should be carried out by backfilling with sand and removing it to a specially designated place.

3. ACCEPTANCE RULES

3.1. Petroleum toluene is taken in batches. A batch is any amount of toluene that is homogeneous in terms of quality and is accompanied by one quality document.

3.2. Sample size - according to GOST 2517-85.

3.3. If unsatisfactory test results are obtained for at least one of the indicators, repeated tests of a newly selected sample of the same sample are carried out on it.

The retest results apply to the entire lot.

3.4. The indicator of distillation limits is determined by the manufacturer once a quarter.

When supplying toluene for export - for each batch.

(Changed edition, Rev. No. 2, 4).

3.5. The mass fraction of impurities for toluene used as an additive to increase the octane number of motor fuels is not determined.

3.6. The mass fraction of sulfur is determined for the highest grade toluene intended for the production of caprolactam.

3.5; 3.6. (Introduced additionally, Rev. No. 2, 5).

4. TEST METHODS

4.1. Toluene samples are taken according to GOST 2517-85. For the combined sample take 1 dm 3 toluene.

(Changededition, rev. No. 2).

4.2. On a typical chromatogram of toluene, the peaks up to "n-nonane correspond to non-aromatic hydrocarbons, the next peak to benzene, the peaks beyond toluene correspond to aromatic hydrocarbons C 8 .

4.3. The density of toluene, determined by a hydrometer, at 20 ° C is calculated by the formula:

where is the density of the test toluene at the test temperature, g/cm 3 ;

γ - temperature correction to density, which for toluene is equal to 0.00093 g/cm 3 per 1°C in the temperature range from minus 30 to plus 30°C;

t - test temperature,° C.

(Introduced additionally, Rev. No. 4).

5. PACKAGING, LABELING, TRANSPORT AND STORAGE

5.1. Packing, marking, transportation and storage of petroleum toluene - in accordance with GOST 1510-84.

5.2. Danger sign - according to GOST 19433-88, class 3, subclass 3.2, hell. 3, classification code 3212, UN serial number 1294.

For product labeling with mandatory certification, a mark of conformity is used according to regulatory documentation. The conformity mark is affixed to the accompanying documentation.

(Revised edition, Rev. No. 5).

6. MANUFACTURER WARRANTY

6.1. The manufacturer guarantees the compliance of petroleum toluene with the requirements of this standard, subject to the conditions of transportation and storage.

6.2. Guaranteed shelf life of toluene from the date of manufacture - 6 years.

(Changed edition, Rev. No. 2, 4).

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the Ministry of Oil Refining and Petrochemical Industry of the USSR

DEVELOPERS

M.N. Yablochkin,cand. chem. sciences; F.N. Lisunov; A.V. Karaman, cand. economy sciences (topic leaders); Yu.I. Archakov, doctor of tech. sciences; V.L. Vorobyov, cand. chem. sciences; E.G. Korchunova; G.I. Kuzmin; THOSE. Kraev.

2. APPROVED AND INTRODUCED BY Decree of the USSR State Committee for Standards No. 2495 dated September 13, 1978

3. The standard complies with ST SEV 5476-86 in terms of appearance, mass fraction of toluene and benzene, color of sulfuric acid, reaction of water extract for toluene of the highest quality category and appearance, mass fraction of toluene, color of sulfuric acid, reaction of water extract for toluene of the first quality category and complies with the international standard ISO 5272-79 in terms of appearance, density, color of sulfuric acid, mass fraction of total sulfur, benzene, C 8 aromatics, non-aromatic hydrocarbons for toluene of the highest quality category and appearance, density, distillation limit, color sulfuric acid, mass fraction of benzene and tests on a copper plate for toluene of the first quality category.

4. REPLACE GOST 14710-69; GOST 5.961-71

5. REFERENCE REGULATIONS AND TECHNICAL DOCUMENTS

Number of paragraph, subparagraph, enumeration, application

Toluene, or following another nomenclature, methylbenzene, is a colorless liquid with a slightly sweet, strong aroma characteristic of varnishes and paints, insoluble in water. Belongs to the class of aromatic hydrocarbons (arenes), substances with a benzene nucleus and a special nature of chemical bonds, is its simplest representative along with benzene. Density and other properties of toluene Toluene is a combustible substance, when burned, it smokes strongly. Inhalation of toluene vapors can cause mild drug intoxication. Less toxic than benzene, as it is excreted from the body, turning into benzoic acid during the oxidation process. Like other aromatic hydrocarbons, toluene is lighter than water and does not dissolve in it. Soluble in alcohols, ether and acetone. The structure of toluene is similar to benzene, except for the replacement of one atom with a CH3 group. It enters into two types of chemical reactions: with the participation of the benzene ring or with the participation of the methyl group. Table of physical properties of toluene Density (g/cm3) Specific gravity (kg/m3) How much does 1 cubic meter of toluene weigh (t) Melting point (ºС) Boiling point (ºС) 0,86694 866,9 0,8669 -95 +110,6 The specific gravity of toluene depends on the temperature of the substance. At 20ºС Application of toluene Toluene, benzene and other aromatic hydrocarbons are used in the production of paints and varnishes, dyes. Some of them are used as physiologically active substances, for example, in the production of plant care products, in the production of medicines. Toluene is a solvent for a large number of polymers. A large percentage of toluene is in the P-4 solvent. The composition of the mixture includes, in addition to aromatic hydrocarbons (62% toluene), acetone (26%) and butyl acetate (12%). Used as an additive in high octane gasolines. May be a component of explosives. It is the main component of some solvents, a component of some types of varnishes, printing inks, a derivative of benzoic acid and saccharin. health hazard Toluene is dangerous not only for human health, but also for the environment. The substance enters the body through the pores of the skin and respiratory tract. Long-term exposure and accumulation of a harmful substance can cause serious diseases of the nervous system, such as encephalopathy. Toluene, like similar aromatic hydrocarbons, is also detrimental to the blood and blood-forming organs. Signs of poisoning with toluene: nausea, dizziness, imbalance, inhibition of consciousness and reactions. Prolonged and severe poisoning can lead to irreversible consequences and death. Toluene is flammable. Rules for working with toluene: use rubber gloves constantly ventilate the room, do not inhale vapors do not use open flames in work areas, store in a tightly closed container away from heat sources. The property of the working fluid (alcohol) in a vacuum Nomogram for determining the boiling point of substances under reduced pressure. boiling point of a substance in vacuum are found using a nomogram (Fig. 76) on the continuation of a straight line connecting the boiling point of this substance at atmospheric pressure and the value of the residual pressure. For approximate calculations, you can also use the rule of thumb: when the pressure is halved, the boiling point of substances decreases by about 15 ° C. Pressure-boiling point chart published by Maybridge Chemical Co., Ltd. To bring the boiling point at a certain pressure to 760 mm Hg. Art., connect the corresponding values ​​​​on scales A and C with a straight line. The desired boiling point value is read on scale B. If you then connect the found boiling point value with a straight line to any pressure value on the C scale, then its intersection point with scale A will give an approximate boiling point corresponding to the selected pressure. 1 mm. rt. Art. = 133.32 Pa = 1.3158 10-3 atm Source: : Gordon A., Ford R. Chemist's Companion: Physical and Chemical Properties, Methods, Bibliography. - M.: Mir, 1976 - 510 p. Boiling temperature, Boiling point The temperature at which a liquid boils under constant pressure. The boiling point corresponds to the temperature of saturated vapor above the flat surface of the boiling liquid, since the liquid itself is always somewhat overheated relative to the boiling point. According to the Clausius-Clapeyron equation, with increasing pressure, the boiling point increases, and with a decrease in pressure, the boiling point decreases accordingly: , where is the boiling point at atmospheric pressure, K, - specific heat of vaporization, J/kg, - molar mass, kg/mol, is the universal gas constant. The limiting boiling point is the critical temperature of a substance. So the boiling point of water will change on Earth depending on the altitude: from 100 ° C at sea level to 69 ° C at the top of Everest. And with an even greater increase in height, a point will arise at which it will no longer be possible to obtain liquid water: ice and steam will pass directly into each other, bypassing the liquid phase. The boiling point of water depending on the pressure can be calculated quite accurately using the formula: , , where the pressure is taken in MPa (ranging from 0.1 MPa to 22 MPa). Boiling temperature constancy The boiling point at atmospheric pressure is usually given as one of the main physicochemical characteristics of a chemically pure substance. However, data on the boiling point of ultrapure substances, in particular, organic liquids such as ether and benzene, may differ significantly from the usual tabular data. This is due to the formation of associates that can accumulate in the liquid in the absence of water as a mediator of the establishment of an equilibrium state. Thus, ultra-dried benzene can be subjected to fractional distillation in the range of 90-118 °C. Parameters of critical points of some substances Substance Units Kelvin atmospheres cm³/mol Hydrogen 33,0 12,8 61,8 Oxygen 154,8 50,1 74,4 Mercury ethanol 516,3 63,0 Carbon dioxide 304,2 72,9 94,0 Water 218,3 Nitrogen 126.25 33,5 Argon 150.86 48,1 Bromine Helium 5.19 2,24 Iodine Krypton 209.45 54,3 Xenon 289.73 Arsenic Neon 44.4 27,2 Radon Selenium Sulfur Phosphorus Fluorine 144.3 51,5 Chlorine 416.95 Heat exchange Physical properties of alcohol Density of solvents at different temperatures Densities (g/cm 3 ) of the most common solvents at different temperatures are given. Solvent Density, g/ml 0°C 10°C 20°C 30°C 40°C 50°C 60°C 70°C 80°C 90°C 100°C 1-Butanol 0.8293 0.8200 0.8105 0.8009 0.7912 0.7812 0.7712 0.7609 0.7504 0.7398 0.7289 1-Hexanol 0.8359 0.8278 0.8195 0.8111 0.8027 0.7941 0.7854 0.7766 0.7676 0.7585 0.7492 1-Decanol 0.8294 0.8229 0.8162 0.8093 0.8024 0.7955 0.7884 0.7813 0.7740 1-Propanol 0.8252 0.8151 0.8048 0.7943 0.7837 0.7729 0.7619 0.7506 0.7391 0.7273 0.7152 2-Propanol 0.8092 0.7982 0.7869 0.7755 0.7638 0.7519 0.7397 0.7272 0.7143 0.7011 0.6876 N,N-Dimethylaniline 0.9638 0.9562 0.9483 0.9401 0.9318 0.9234 0.9150 0.9064 0.8978 0.8890 N-methylaniline 1.0010 0.9933 0.9859 0.9785 0.9709 0.9633 0.9556 0.9478 0.9399 0.9319 0.9239 Aniline 1.041 1.033 1.025 1.016 1.008 1.000 0.9909 0.9823 0.9735 0.9646 0.9557 Acetone 0.8129 0.8016 0.7902 0.7785 0.7666 0.7545 0.7421 0.7293 0.7163 0.7029 0.6890 Acetonitrile 0.7825 0.7707 0.7591 0.7473 0.7353 0.7231 0.7106 0.6980 0.6851 Benzene 0.8884 0.8786 0.8686 0.8584 0.8481 0.8376 0.8269 0.8160 0.8049 0.7935 Butylamine 0.7606 0.7512 0.7417 0.7320 0.7221 0.7120 0.7017 0.6911 0.6803 0.6693 0.6579 Hexane 0.6774 0.6685 0.6594 0.6502 0.6407 0.6311 0.6212 0.6111 0.6006 0.5899 0.5789 Heptane 0.7004 0.6921 0.6837 0.6751 0.6664 0.6575 0.6485 0.6393 0.6298 0.6202 0.6102 Dean 0.7447 0.7374 0.7301 0.7226 0.7151 0.7074 0.6997 0.6919 0.6839 0.6758 0.6676 dichloromethane 1.362 1.344 1.326 1.307 1.289 1.269 1.250 1.229 1.208 1.187 1.165 diethyl ether 0.7368 0.7254 0.7137 0.7018 0.6896 0.6770 0.6639 0.6505 0.6366 0.6220 0.6068 Isopropylbenzene 0.8769 0.8696 0.8615 0.8533 0.8450 0.8366 0.8280 0.8194 0.8106 0.8017 0.7927 methanol 0.8157 0.8042 0.7925 0.7807 0.7685 0.7562 0.7435 0.7306 0.7174 0.7038 0.6898 Methyl acetate 0.9606 0.9478 0.9346 0.9211 0.9074 0.8933 0.8790 0.8643 0.8491 0.8336 0.8176 Methyl propanoate 0.9383 0.9268 0.9150 0.9030 0.8907 0.8783 0.8656 0.8526 0.8393 0.8257 0.8117 Methyl formate 1.003 0.9887 0.9739 0.9588 0.9433 0.9275 0.9112 0.8945 0.8772 0.8594 0.8409 Methylcyclohexane 0.7858 0.7776 0.7693 0.7608 0.7522 0.7435 0.7346 0.7255 0.7163 0.7069 0.6973 m-xylene 0.8813 0.8729 0.8644 0.8558 0.8470 0.8382 0.8292 0.8201 0.8109 0.8015 0.7920 Nitromethane 1.139 1.125 1.111 1.097 1.083 1.069 1.055 1.040 1.026 Nonan 0.7327 0.7252 0.7176 0.7099 0.7021 0.6941 0.6861 0.6779 0.6696 0.6611 0.6525 o-xylene 0.8801 0.8717 0.8633 0.8547 0.8460 0.8372 0.8282 0.8191 0.8099 Octane 0.7185 0.7106 0.7027 0.6945 0.6863 0.6779 0.6694 0.6608 0.6520 0.6430 0.6338 Pentanoic acid 0.9563 0.9476 0.9389 0.9301 0.9211 0.9121 0.9029 0.8937 0.8843 0.8748 0.8652 p-Xylene 0.8609 0.8523 0.8436 0.8347 0.8258 0.8167 0.8075 0.7981 0.7886 propyl acetate 0.9101 0.8994 0.8885 0.8775 0.8662 0.8548 0.8432 0.8313 0.8192 0.8069 0.7942 Propylbenzene 0.8779 0.8700 0.8619 0.8538 0.8456 0.8373 0.8289 0.8204 0.8117 0.8030 0.7943 propyl formate 0.9275 0.9166 0.9053 0.8938 0.8821 0.8702 0.8581 0.8457 0.8330 0.8201 0.8068 carbon disulfide 1.290 1.277 1.263 1.248 1.234 Carbon tetrachloride 1.629 1.611 1.593 1.575 1.557 1.538 1.518 1.499 1.479 1.458 1.437 Toluene 0.8846 0.8757 0.8667 0.8576 0.8483 0.8389 0.8294 0.8197 0.8098 0.7998 0.7896 Acetic acid 1.051 1.038 1.025 1.012 0.9993 0.9861 0.9728 0.9592 0.9454 Chlorobenzene 1.127 1.116 1.106 1.096 1.085 1.074 1.064 1.053 1.042 1.030 1.019 Chloroform 1.524 1.507 1.489 1.471 1.452 1.433 1.414 1.394 Cyclohexane 0.7872 0.7784 0.7694 0.7602 0.7509 0.7414 0.7317 0.7218 0.7117 0.7013 ethanol 0.8121 0.8014 0.7905 0.7793 0.7680 0.7564 0.7446 0.7324 0.7200 0.7073 0.6942 ethyl acetate 0.9245 0.9126 0.9006 0.8884 0.8759 0.8632 0.8503 0.8370 0.8234 0.8095 0.7952 Ethylbenzene 0.8836 0.8753 0.8668 0.8582 0.8495 0.8407 0.8318 0.8228 0.8136 0.8043 0.7948 Ethyl propanoate 0.9113 0.9005 0.8895 0.8784 0.8671 0.8556 0.8439 0.8319 0.8197 0.8072 0.7944 Ethyl formate 0.9472 0.9346 0.9218 0.9087 0.8954 0.8818 0.8678 0.8535 0.8389 0.8238 0.8082 RELATED ARTICLES Feedback site `s map About the site