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Abstract
Azo dyes are the dominant class of commercial dyes, and the emergence of new technologies has stimulated a renewed interest in their chemistry. Interest now extends from the more traditional fields of textile dyeing and effluent degradation to areas as diverse as optical data storage, ink-jet printing, biochemical assays, and potential pharmaceutical treatments
The scope of the following work was to determination of the activity coefficient of aniline, 0-, m-, p-ethylaniline, p-ethoxyaniline, 0- and p- iodoaniline, determination of the activity coefficient quotient fH+ jfAr-NHj for the above listed amines at different temperatures and ionic strength, evaluation of the equilibrium constant for the proton ionization of listed amines under different conditions of temperature and in the presence of different salt concentrations, also evaluation of the basic dissociation constant of that amines by distribution method, determination of ~F (the free energy), ~H (the enthalpy), ~s (the entropy change) for proton ionization of the amines under consideration, at different temperatures, study of the kinetics, and mechanisms for the diazotization reaction under different conditions, determination of the overall velocity coefficient for chloride catalyzed diazotization of those amines, determination of the velocity coefficient for the rate determining step for chloride catalyzed diazotization, making use of the values of proton ionization constant K, and the activity coefficient quotient fH+jfAr-NHj obtained from the thermodynamic studies of proton ionization,
determination of ~F” (the free energy of activation), ~H” (the enthalpy of activation), ~S” (the entropy of activation), and E (the energy of activation) for the rate determining reaction, and studing of the effect of the substituent on the rate of diazotization, basicity of amino groups.
The proton ionization constant of anilinium ion was found to increase with temperature and ionic strength. However in the case of o-ethyl anilinium, p-ethyl anilinium, p-ethoxy anilinium, p-iodo anilinium and o-iodo anilinium ions it was found to decrease with the increase of the ionic strength while m-ethyl ionanilinium decreases with increasing ionic strength till reaching a minimum then increases.
The proton ionization constant of o-iodoanilinium ion is greater than those of aniline, o-ethyl anilinium, m-ethyl anilinium, p-ethyl anilinium, p-ethoxy anilinium, and p-iodo anilinium, and that of anilinium which is still greater than o-ethyl anilinium, m¬ethyl anilinium, p-ethyl anilinium. This indicates the dependence of proton ionization constants of the amines on the structure of the amine molecule.
From the obtained result it is clear that in the case of substituents which are of electron releasing properties the specific reaction rate increases. This can be due to the presence of electron releasing group that increases the electron cloud density around the nitrogen of the amino group and this facilitate the attraction of the positively charged nitosating agent while in the case of electron attracting substituent the specific reaction rate decrease due to the decrease of electron cloud density around the nitrogen atom of the amino group and accordingly decrease the attraction of the nitrosating agent and there by the specific reaction rate decrease.
Key words: Proton ionization, diazotization, substituenteffect