The purpose of this experiment is to find out how the rate of hydrolysis of an organic halogen compound depends on: a the identity of the halogen atom. b the nature of the carbon-hydrogen ‘skeleton’. Theory Experiment: In this experiment, the rate of hydrolysis of 1-chlorobutanne, 1-bomobutane, 1-iodobutane, Chlorobenzene is compared. A general equation for the hydrolysis is: R-X + H2O ???? R-OH + H+ + X- (Where R = alkyl or aryl group; X= halogen atom)
Hydrolysis of organic halogen compounds is a nucleophilic substitution reaction. In a nucleophilic substitution a lone pair of electron on a nucleophile, H2Ois attracted to a carbon atom, with a partial positive charge. The nucleophile is then substituted for the atom or group attached to the carbon atom. Since halide ions are being substituted out. By following the rate of the reaction by carrying it out in the presence of silver ions, so that any halide ions produced form a silver halide precipitate.
Ag+(aq) + X-(aq) ???? AgX(s) By comparing the time for appearance of precipitate, we can compare the rate of hydrolysis. The smaller the time needed, the faster the rate of hydrolysis. Hydrolysis is a chemical process in which a certain molecule is split into two parts by the addition of a molecule of water. One fragment of the parent molecule gains a hydrogen ion (H+) from the additional water molecule. The other group collects the remaining hydroxyl group (OH-). Types of halogen compound
Haloalkanes: organic compounds having one or more halogen atoms replacing hydrogen atoms in alkanes. The general formula of haloalkanes: CnH2n+1X. Classification of haloalkanes: Halobenzenes- organic compounds in which the halogen atom is directly attached to a benzene ring. Physical property: halogen compound has a little higher boiling point that corresponding alkane of comparable molecular mass. This is due to the dipole-dipole attraction between the molecules which is much stronger the the van der waals’ force held between alkane molecules.
They are insoluble in water due to the inability to form extensive H-bond with water molecules. Chemical properties The features of the molecules of haloganoalkanes which make them susceptible to nucleophilic substitution: Owing to the high electronegativity of halogens, the C-X bond is highly polar. The polarization of the C-X bond makes the electron deficient carbon atom susceptible to attack by a electron rich nucleophile. Halogen atom can form a stable leaving ion.