Organic reactions acid strength effects

These three concepts allow a quick inspection of a simple acid (HX) for its relative acid strength. Experimental analysis of the acids commonly encountered in organic reactions requires knowledge of at least three factors (1) electronic effects, (2) resonance effects, and (3) solvent effects. 

The pKg values given for all organic molecules in this chapter are based on their reaction in water, which means that water is the base in those reactions. If a different solvent is used, the pK is different. If another base is added to the water solution, the pK may be different. Remember that acid strength depends on the strength of the base, which influences the position of the equilibrium and Kg. In the reaction of acetic acid (ethanoic acid, 18) and water, the conjugate acid is HgO+ and the conjugate base is the acetate anion (24). In this reaction, water reacts as the base, but water is also the solvent and it has a profound effect on the course of the reaction. 

Fluorinated Acids. This class of compounds is characterized by the strength of the fluorocarbon acids, eg, CF COOH, approaching that of mineral acids. This property results from the strong inductive effect of fluorine and is markedly less when the fluorocarbon group is moved away from the carbonyl group. Generally, their reactions are similar to organic acids and they find apphcations, particularly trifluoroacetic acid [76-05-1] and its anhydride [407-25-0] as promotors in the preparation of esters and ketones and in nitration reactions. 

The effect of solution chemistry on the speciation of the organic contaminant 1-naphtol (1-hydroxynaphthalene) and its complexatiom with humic acid is reported by Karthikeyan and Chorover (2000). The complexation of 1-naphtol with humic acid (HA) was studied during seven days of contact, as a function of pH (4 to 11), ionic strength (0.001 and 0.1 M LiCl), and dissolved concentration (DO of 0 and 8 mg L ) using fluorescence, UV absorbance, and equilibrium dialysis techniques. In a LiCl solution, even in the absence of HA, oxidative transformation of 1-naphtol mediated by was observed. In addition, the presence of humic acid in solution, in the absence of DO, was found to promote 1-naphtol oxidation. These reactions are affected by the solution chemistry (pH, ionic strength, and cation composition). 

The section on degradation of organics deals with paints, plastics, nylon, wood, and architectural organics. The effects of acid deposition on wood and other cellulosic materials are described. Strength losses in wood may be caused by hydrolytic degradation of the hemicelluloses and a sulfonation reaction of the lignin. Thus, the fibrils and matrix structure is affected. Cotton materials can be affected similarly, and soiling will result. The effect of acid deposition of nylon is indicative of a potentially shorter serviceable lifetime for outdoor fabrics. 

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