Preface

The volume Applicative Chemistry of Tanning Metallic Heterocomplexes depicts a comprehensive picture of a new chapter in the chemistry of coordination compounds, with industrial applications in the field with the longest history, natural leather processing. The chemistry of heterocomplex compounds is a fascinating field for experts in chemical synthesis and structural analysis, and for technologists specializing in leather processing. The volume describes the vast theoretical and practical possibilities of exploiting the action synergism of metals with different collagen crosslinking capacity. The possibility of reducing chromium content from leather tanning agents by replacing it with other tanning metals has significant environmental implications and minimum changes in terms of quality and production costs of natural leather, and is a viable alternative for a safe future. The volume is intended for researchers, chemical auxiliary producers, experts in natural leather processing who are looking for clean and efficient solutions for wastewater pollutants, sludge or solid wastes while striving to preserve the known characteristics of mineral tanned natural leather. Chapter 1 provides an overview of the history of natural leather processing, which is intermingled with the eras of human civilization development and helps to understand the chemistry of processing a complex material, unmatched by any other similar synthetic material, in terms of hygienic properties and compatibility with the human body. A venture in the modern era of basic chromium salts tanning helps to understand the relationship between types of chromium compounds complexed with various organic ligands, as well as the properties of leather. The possibilities of modeling sensory and physical-mechanical characteristics of leathers by using tanning agents with various properties suggests an infinite area of creativity which carries until modern times, when the search for ways to optimize organic tanning variants is still in progress. Chapter 2 discusses the experience accumulated in the modern period regarding minimization of environmental impact of using basic chromium salts as tanning agent within the restrictions imposed by the aqueous reaction medium and the need to preserve natural properties of collagen fibers. Although scientific progresses in chromium salt management used in natural leather tanning and the long-term future of this material are acknowledged, the large chemical auxiliary companies are considering organic alternatives of collagen crosslinking. Resorting again to methods of optimizing tanning processes using metal salts is an increasingly discussed variant for restoring the known mineral character of traditional leathers. In this context, tanning metallic heterocomplexes are an intelligent, low-cost and much more versatile alternative compared to any other proposed variant. Chapter 3 summarizes the attempts of heterocomplexing various tanning metals, and of understanding the structure and correlation with the stability and properties imparted to leathers. The multiple interconnection ability of functional groups of the collagen macromolecule and the action synergism of several types of tanning metals represent the argument that supports and promotes tanning metallic heterocomplexes as an alternative for the future. Chapter 4 is a culmination of practical pilot scale experimentation activity, under industrial conditions, conducted by two authors who have decoded the complexing mechanism of three tanning metals with the potential of substantially reducing the use of chromium as tanning agent. Defining the stability boundaries of binary and ternary compositions of the new metallic heterocomplexes and the new calculation formulas to establish the synthesis reagents constitute a progress in the coordination chemistry of tanning agents. Chapter 4 can serve as a reference eBook for the synthesis of stable tanning metallic heterocomplexes within the technological limits of application in leather tanning, an original contribution in the field and a starting point for any new research endeavor. Chapter 5 deals with specific analyses for coordination complexes, for the purpose of anticipating the behaviour of tanning metallic heterocomplexes upon the interaction with natural leather. Analysis of ionic components explains the more pregnant anionic nature compared to that of the best known tanning agent, basic chromium salt, and therefore, the improved efficiency of using tanning metallic heterocomplexes in natural leather tanning.