Here are the molecular formulas and names of the first ten carbon straight chain alkynes.
Actylene is prepared by dropping water on calcium carbide (calcium dicarbide).
CaC2 +2HOH ⇒ C2H2 +Ca(OH)2
– Give Reason:Actylene gas must be firstly passes over copper sulphate solution in dilsuphuric acid?
-To remove phosophine gas(PH3) and hydrogen sulphide H2S that is due to impurities of CaC2
Ethyne burns with a smoky flame in a limited amount of air because carbon does not completely burn.
2C2H2 +3O2 ⇒ 2CO2 +2H2O+2C
Burns producing CO2 ,water vapor and heat energy (exothermic reaction)
2C2H2 +4O2 ⇒ 4CO2 +2H2O +heat
The amount of heat reaches about 3000? C, therefore oxyacetylene flame is used for welding and cutting metals.
Because ethyne contain two (Pi) bonds beside one sigma bond, it reacts by addition in two steps. The triple bond is changed to double and then to single bond. The addition reactions can be illustrated as follow.
In the presence of finely divided nickel in 2 steps
Ethyne reacts vigorously with halogens. The reaction may be accompanied by flame and light when it reacts with chlorine.
However, when ethyne is passed through bromine water dissolved in carbon tetrachloride, the red colour of bromine is discharged.
This reaction is used to detect the unsaturation of ethyne.
C2H2+Br2 → C2H2Br2 +Br2 → C2H2Br4
bromine dissolved in carbon tetrachloride
-Ethyne reacts with water by addition in the presence of a catalyst e.g. H2SO4, HgSO4 at 60? C to give acetaldehyde (ethanal).
This reaction is used to prepare ethanoic acid (acetic acid) by the oxidation of acetaldehyde (ethanal).
Ethanal(Acetaldehyde ethanoic acid(acetic acid)
Reduction of aldehydes
CH3CHO 2H reduction → CH3CH2 OH
By heating the natural gas at high temperature (1500 c) then fast cooling (rapid quenching) the product
2CH4(g) 1500c /rapid quenching→ C2H2 +3H2(g)
Draw the apparatus used in preparation of an unsaturated organic gas in which there are 2 pi bonds and one sigma bond between its two carbon atom ?
Methane reacts with chlorine in presence of ultraviolet rays (substitution reaction) and doesn’t react with bromine water
Ethene and ethyne react with bromine water (addition reaction)
Give reason: Bromine dissolved in carbon tetrachloride can not be used to differentiate between ethene and ethyne ?
-Because it reacts with both of them by addition leads to the disappearance of the red color of bromine