DEFINITION
Under normal conditions (at 25 o C and atmospheric pressure) propane is a colorless, odorless gas (the structure of the molecule is shown in Fig. 1), which, at a vapor concentration of 1.7 - 10.9%, forms an explosive mixture with air.
Propane is practically insoluble in water, since its molecules are of low polarity and do not interact with water molecules. It dissolves well in non-polar organic solvents such as benzene, carbon tetrachloride, diethyl ether, etc.
Rice. 1. The structure of the propane molecule.
Table 1. Physical properties of propane.
Getting propane
The main sources of propane are oil and natural gas. It can be isolated by fractional distillation of natural gas or the gasoline fraction of oil.
In the laboratory, propane is obtained in the following ways:
— hydrogenation of unsaturated hydrocarbons
CH 3 -CH \u003d CH 2 + H 2 →CH 3 -CH 2 -CH 3 (kat \u003d Ni, t o);
— reduction of haloalkanes
C 3 H 7 I + HI → C 3 H 8 + I 2 (t o);
- according to the reaction of alkaline melting of salts of monobasic organic acids
C 3 H 7 -COONa + NaOH → C 3 H 8 + Na 2 CO 3 (t o);
- the interaction of haloalkanes with metallic sodium (Wurtz reaction)
C 2 H 5 Br + CH 3 Br + 2Na → CH 3 -CH 2 -CH 3 + 2NaBr.
Chemical properties of propane
Under normal conditions, propane does not react with concentrated acids, molten and concentrated alkalis, alkali metals, halogens (except fluorine), potassium permanganate and potassium dichromate in an acidic environment.
For propane, reactions proceeding according to a radical mechanism are most characteristic. The homolytic cleavage of C-H and C-C bonds is energetically more favorable than their heterolytic cleavage.
All chemical transformations of propane proceed with splitting:
- C-H bonds
- halogenation (S R)
CH 3 -CH 2 -CH 3 + Br 2 → CH 3 -CHBr-CH 3 + HBr ( hv).
- nitration (S R)
CH 3 -CH 2 -CH 3 + HONO 2 (dilute) → CH 3 -C (NO 2) H-CH 3 + H 2 O (t o).
- sulphochlorination (S R)
C 3 H 8 + SO 2 + Cl 2 → C 3 H 7 -SO 2 Cl + HCl ( hv).
- dehydrogenation
CH 3 -CH 2 -CH 3 → CH 2 \u003d CH-CH 3 + H 2 (kat \u003d Ni, t o).
- dehydrocyclization
CH 3 -CH 2 -CH 3 → C 3 H 6 + H 2 (kat \u003d Cr 2 O 3, t o).
- C-H and C-C bonds
- oxidation
C 3 H 8 + 5O 2 → 3CO 2 + 4H 2 O (t o).
Propane application
Propane is used as an automobile fuel, and is also used in everyday life (balloon gas).
Examples of problem solving
EXAMPLE 1
EXAMPLE 2
| Exercise | Calculate the volumes of chlorine and propane, reduced to normal conditions, that will be required to obtain 2,2-dichloropropane with a mass of 8.5 g. |
| Solution | We write the reaction equation for the chlorination of propane to 2,2-dichloropropane (the reaction occurs under the action of UV radiation): H 3 C-CH 2 -CH 3 + 2Cl 2 = H 3 C-CCl 2 -CH 3 + 2HCl. Calculate the amount of substance 2,2-dichloropropane (molar mass is - 113 g / mol): n (C 3 H 6 Cl 2) \u003d m (C 3 H 6 Cl 2) / M (C 3 H 6 Cl 2); n (C 3 H 6 Cl 2) \u003d 8.5 / 113 \u003d 0.07 mol. According to the reaction equation n(C 3 H 6 Cl 2): n(CH 4) = 1:1, i.e. n (C 3 H 6 Cl 2) \u003d n (C 3 H 8) \u003d 0.07 mol. Then the volume of propane will be equal to: V(C 3 H 8) = n(C 3 H 8) × V m ; V (C 3 H 8) \u003d 0.07 × 22.4 \u003d 1.568 liters. According to the reaction equation, we find the amount of chlorine substance. n(C 3 H 6 Cl 2) : n(Cl 2) = 1:2, i.e. n(Cl 2) = 2 × n(C 3 H 6 Cl 2) = 2 × 0.07 = 0.14 mol. Then the volume of chlorine will be equal to: V (Cl 2) \u003d n (Cl 2) × V m; V (Cl 2) \u003d 0.14 × 22.4 \u003d 3.136 l. |
| Answer | The volumes of chlorine and propane are 3.136 and 1.568 liters, respectively. |
Propane is an organic compound, the third representative of alkanes in the homologous series. At room temperature, it is a colorless and odorless gas. The chemical formula of propane is C 3 H 8 . Fire and explosion hazard. It has little toxicity. It has a weak effect on the nervous system and has narcotic properties.
Structure
Propane is a saturated hydrocarbon consisting of three carbon atoms. For this reason, it has a curved shape, but due to the constant rotation around the bond axes, there are several molecular conformations. The bonds in the molecule are covalent: C-C non-polar, C-H weakly polar. Because of this, they are difficult to break, and the substance is rather difficult to enter into chemical reactions. This sets all the chemical properties of propane. It has no isomers. The molar mass of propane is 44.1 g/mol.
How to get
In industry, propane is almost never synthesized artificially. It is isolated from natural gas and oil by distillation. For this, there are special production facilities.
In the laboratory, propane can be obtained by the following chemical reactions:
Physical properties of propane
As already mentioned, propane is a colorless and odorless gas. It is insoluble in water and other polar solvents. But it dissolves in some organic substances (methanol, acetone and others). At -42.1 °C it liquefies, and at -188 °C it becomes solid. It is flammable, as it forms flammable and explosive mixtures with air.
Chemical properties of propane
They are typical properties of alkanes.
The mechanism of halogenation reactions is chain. Under the action of light or high temperature, the halogen molecule decomposes into radicals. They interact with propane, taking away a hydrogen atom from it. As a result, a free cut is formed. It interacts with the halogen molecule, again breaking it into radicals.
Bromination occurs by the same mechanism. Iodization can only be carried out with special iodine-containing reagents, since propane does not interact with pure iodine. When interacting with fluorine, an explosion occurs, a polysubstituted propane derivative is formed.
Nitration can be carried out with dilute nitric acid (Konovalov's reaction) or nitric oxide (IV) at an elevated temperature (130-150 °C).
Sulfoxidation and sulfochlorination are carried out under UV light.
Propane combustion reaction: C 3 H 8 + 5O 2 → 3CO 2 + 4H 2 O.
Milder oxidation can also be carried out using certain catalysts. The combustion reaction of propane will be different. In this case, propanol, propanal or propionic acid is obtained. In addition to oxygen, peroxides (most often hydrogen peroxide), transition metal oxides, chromium (VI) and manganese (VII) compounds can be used as oxidizing agents.
Propane reacts with sulfur to form isopropyl sulfide. For this, tetrabromoethane and aluminum bromide are used as catalysts. The reaction proceeds at 20 °C for two hours. The reaction yield is 60%.
With the same catalysts, it can react with carbon monoxide (I) to form isopropyl ester of 2-methylpropanoic acid. The reaction mixture after the reaction must be treated with isopropanol. So, we examined the chemical properties of propane.
Application
Due to its good combustibility, propane is used in everyday life and industry as a fuel. It can also be used as fuel for cars. Propane burns at almost 2000°C, which is why it is used for welding and cutting metal. Propane burners heat bitumen and asphalt in road construction. But often the market does not use pure propane, but its mixture with
Oddly enough, but he found application in the food industry as an additive E944. Due to its chemical properties, propane is used there as a solvent for fragrances and also for the treatment of oils.
A mixture of propane and isobutane is used as the refrigerant R-290a. It is more efficient than older refrigerants and is also environmentally friendly as it does not deplete the ozone layer.
Propane is widely used in organic synthesis. It is used to produce polypropylene and various kinds of solvents. In oil refining, it is used for deasphalting, that is, reducing the proportion of heavy molecules in the bitumen mixture. This is necessary for the recycling of old asphalt.
A mixture of propane and butane has long been used in many areas of industry, production and everyday life, this is due to the special properties of the mixture of these gases. Propane-butane has a unique ability to change from liquid to gaseous form and vice versa. In this case, to obtain the required state, it is not required to use any cryogenic aggregates.
How to get propane-butane
Propane-butane is obtained from oil and condensate of its associated gases, another name for propane-butane is liquefied petroleum gas. Its liquid or gaseous form is determined by climatic conditions: when the temperature rises, it is converted into steam, when it decreases and the pressure simultaneously increases, it takes a liquid form.
Where and how propane-butane is used
Petroleum gas is considered an environmentally friendly type of fuel, so it is used in home heating systems, used in agriculture, other industries as fuel for boilers or vehicles, as well as in welding or cutting metals. In this case, butane acts as the fuel itself, and propane creates the necessary pressure. Propane-butane is produced in cylinders, the proportions are strictly regulated by the state, since the mixture is extremely explosive.
How gas welding work takes place in production:
For production work, the propane-butane mixture is produced in the form of special gas welding burners, into which combustible gas and oxygen are supplied from cylinders. If it is required to cut the metal, the process occurs due to its combustion in an oxygen jet and the removal of the oxides that it forms.
In the process of welding with a propane-butane mixture, the metal to be welded and its filler analogue are melted by a flame that forms petroleum gas. The edges of the products are melted, and the gap between them is filled with filler metal, which is carefully introduced into the center of the burner flame with the mixture.
Propane-butane mixture is widely used in domestic and industrial sectors for a reason. Along with its unique properties, it has a relatively low and stable cost. In addition, most boiler houses and enterprises are designed for two types of fuel - their combustion devices can alternately burn propane-butane mixture and natural gas, which gives good savings.
Published: 01/04/2017 21:21Propane is a gas with the chemical formula C 3 H 8 that is odorless and colorless. Butane is the same colorless gas as odorless propane, the formula of butane is C 4 H 10. Propane and butane belong to a number of alkanes and are used as LPG fuel components. LPG is a liquefied hydrocarbon gas, propane, like butane, has a calorific value suitable for use as a fuel. The general similarity of the physical properties of the two gases does not extend to their boiling point - for propane it is -43 o C, for butane it is much higher (-0.5 o C).
Therefore, propane can be used as a fuel at sub-zero temperatures, but butane cannot, for which a mixture of gases is used - liquefied petroleum gas or propane-butane. A mixture of gases is made so that propane (as a mixture of propane and butane is called for short) can be safely used at any temperature. Separate use of propane is impossible for the following reason - when heated, propane expands significantly, which leads to an increase in pressure on the walls of the vessel (in which gas is stored) from the inside. This property of propane leads to the formation of cracks on the inner walls of the tank and its gradual deterioration (due to the loss of the ability to hermetically contain the gas inside). A propane leak is not the worst consequence of its expansion. In the case of sudden heating, propane can explode the tank from the inside and cause significant damage to nearby people. Substances with a pungent odor are added to the mixture of propane and butane to detect leaks in a timely manner.
A mixture of propane and butane is stored inside a cylinder or gas tank in liquefied form. Liquefaction of propane-butane occurs under the influence of pressure - the compressor method, under pressure, a mixture of propane and butane is stored inside the tank. The liquefaction of propane makes it convenient for transportation and storage - in liquefied form, a mixture of propane and butane takes up 600 times less space. Storage is carried out at normal temperature, as a result of which propane partially passes from a liquid state to a gaseous state (in this state, propane-butane is used as a fuel, in a gaseous state it is supplied to a gas boiler).
How is propane-butane produced?
Propane is produced as a result of oil extraction or refining operations. During oil production, associated petroleum gas is released - a mixture of various hydrocarbon gases, including propane. Such production of propane occurs during fracking - the technology of oil production with hydraulic fracturing. Part of the propane is obtained as a by-product of oil refining at refineries. The propane is then liquefied and transported to gas filling stations.