Chemical and physical properties of alkynes
Alkynes are ternary hydrocarbons between carbon atoms that form with the formula CnH2n-2. The particles themselves under such conditions are in a state of sp-hybridization. This is the name of the process of mixing different orbitals (single-electron wave function) with the subsequent appearance of identical, equivalent in their characteristics.
The physical properties of alkynes are few, but the chemical properties are quite a number. However, both some and others deserve attention.
Similarity to alkenes
It really is. The physical properties of alkynes are similar to those characteristic of alkenes - acyclic unsaturated double bond hydrocarbons. Formula - CnH2n.
Lower alkynes are C2 – C4, they are gases. They have slightly higher boiling points than similar alkenes.
Since those and other compounds are hydrocarbons, they dissolve poorly in water. For their molecules are hydrophobic. In organic solvents such as butanol, xylene, benzene, carbon disulfide,and in many others dissolve better.
It should also be noted that alkenes and alkynes are less dense than water. Alkanes, saturated hydrocarbons with the maximum possible number of hydrogen atoms, are also included in this list.
There are a lot of them. And it is also important to note them with attention, since we are talking about the physical and chemical properties of alkynes. In short, the list looks like this:
- Alkines with a terminal triple bond are C-H acids. They form strong alkynides with strong bases.
- If they are associated with ammonium monovalent copper or silver, they form a qualitative reaction with a terminal triple bond.
- By adding sodium cyanide to silver alkynide, an alkyne can be obtained.
- Alkinides are strong nucleophiles. They can enter into various nucleophilic substitution reactions. Which, by the way, is often applicable for the synthesis of acetylene homologues - alkyne, the physical properties of which will be discussed a little later.
- Chlorination of acetylene with copper chloride produces dichloroacetylene. But only in aqueous solutions of CuCl.
- If you act on monosubstituted acetylenes with halogen (an energetic oxidizing agent), you will be able to get haloalkynes.
Also, these compounds can participate in carbonylation, ethynylation, electrophilic, radical, and nucleophilic addition, hydroboration, oxidation, isomerization, oligomerization, polymerization, cyclic formations, etc.
The physical properties of alkynes are best demonstrated with specific examples, referring to the characteristics of representatives of this group of compounds.
Etin is a colorless gas, also called acetylene. Formula - C2H2. In water, like any other alkyne, insoluble. Lighter than air. It boils at −83.8 ° C. Decomposed by compression with an explosion. Etin is stored in cylinders filled with either activated carbon impregnated with acetone or diatomaceous earth (a rock consisting of the remains of diatom algae). In such conditions, ethine is dissolved in large quantities under pressure.
This gas must not be released to the open air. It is explosive. Interestingly, particles of this compound were found on Neptune and Uranus.
Highly flammable colorless gas with CH formula.3-C≡CH. It has a very unpleasant and sharp smell. The chemical and physical properties of alkyne allow it to be used as rocket fuel.
This substance is obtained by hydrolysis of magnesium carbide. Also, propyne is a byproduct in the production of acetylene. Here are some of the physical and thermal properties of this substance:
- Molar mass - 40.06 k / mol.
- Density - 0.70 g / cm3.
- Melting point is minus 102.7 ° C.
- Boiling point - minus 23.21 ° C.
- Enthalpy of education - 185.4 kJ / mol.
If we talk about chemical properties, then it is worth noting that propine is capable of isomerizing in the presence of silicates or other catalysts into allene - the simplest representative of the class of homocumulenes, unsaturated organic compounds with cumulated carbon double bonds.
Before telling about the physical properties of alkyne, known by this name, it is important to note: it is characterized by structural isomerism. He has two isomers:
- Butin-1. Melting point is minus 125.9 ° C. It boils at + 8.1 ° C. Density - 0.678 g / cm ³.
- Butin-2. Melting point - minus 32.3 ° C. It boils at 27 ° C. Density - 0.694 g / cm ³.
Their molar mass is the same - 54.09 g / mol. But there is a butin-2 property that is not characteristic of another isomer. He breaks out. And for this we need a temperature of −49.Under these conditions, vapors above the surface of a given substance flash in the air under the influence of an ignition source. But there is no steady burning.
This compound also has two isomers:
- Pentin-1. Formula: CH = -C-CH2-CH2-CH3. Melting point - minus 90 ° C. It boils at +39.3 ° C. Density is 0.695 d204.
- Pentin-2. Formula: CH3-C- = C-CH2-SN3. Melting point - minus 101 ° C. It boils at +55 ° C. Density is 0.714 d204.
Otherwise, the properties of both isomers are identical to everything that was listed before. They have no color and smell, they burn, react to the addition, can interact with hydrogen, lighter than air.
By the way, since we are talking about the physical properties of alkenes and alkynes, it should be noted that there is still such a compound - pentene. It is an unsaturated hydrocarbon with six isomers. Pentenes are low-boiling liquids that dissolve only in organic solvents. Their melting point ranges from -168.5 ° C to -137.56 ° C. To boil penten, it is necessary from + 20,06 ° C to + 38,57 ° C.
About these compounds - finally. Considering the physical properties of alkynes and alkenes, alkanes also cannot be ignored.These are acyclic hydrocarbons with a branched or linear structure with simple bonds. Formula - CnH2n + 2.
The simplest member of this class is methane. Colorless gas with CH formula4, non-toxic and safe for health. But it becomes explosive if it accumulates indoors. Especially when the concentration is between 4.4% and 17%.
What about physical properties? Molar mass - 16.05 g / mol. Density - 0.7168 kg / m³ in the gas state. It melts at -182.49 ° C, and boils at -161.58 ° C. May self-ignite if temperature reaches 537.8 ° C.