Physical and Chemical Properties of Selected Chlorinated Solvents

1.1 Introduction

The physical and chemical properties of chlorinated solvents are well understood and documented extensively in the literature. Given their chemical and physical properties and frequency of detection, they are of special interest and use in environmental forensic investigations. While there are many chlorinated solvents encountered in forensic investigations, the focus of this chapter includes a presentation of the physical/chemical properties and degradation pathways of trichloroethylene (TCE), perchloroethylene (PCE or tetrachloroethylene), methyl chloroform [1,1,1 trichloroethane (TCA)], carbon tetrachloride (CT), and CFC-113 (trichlorotrifluoroethane, 1,1,2 trichloro-1,1,2 trifluoroethane).

Of these compounds, the nomenclature for CFC-113 (Cl2FC-CClF2) is unique. CFC compounds are encoded by four numbers: the first number refers to the number of double bonds, the second number refers to the number of carbons minus one, the third number refers to the number of hydrogen plus one, and the fourth number refers to the number of fluorine atoms. If one of the numbers equates to zero, it is not included. The letter codes a, b and c refer to isomers with progressively less evenly distributed molecular weight across the two carbon atoms (e.g., CFC-112a). The most even isomer has no letter code.

The terms methyl chloroform and 1,1,1 trichloroethane (TCA) are used interchangeably throughout these chapters to honor the original manuscripts and/or research. Methyl chloroform is the more current term.

Synonyms, including product names and in many cases, producers for the these five compounds are found in Appendix A. A knowledge of product names is of special forensic interest; for example, if the product Genklene (methyl chloroform) was used at a site, then it is known that the producer, ICI Chemicals & Polymers Limited (ICI) manufactured it from 1960 to December 31 1995, and that it was used in vapor and ultrasonic cleaning, precision cleaning, adhesive formulations and aerosol applications. If the Genklene was manufactured at the ICI Chemicals complex at Runcorn, England, the additional forensic opportunities can be explored, including stabilizer packages likely used and/or manufacturing methods and anticipated impurities unique to the Runcorn plant.

1.2 Physical and Chemical Properties

An overview of physical and chemical properties associated with the five chlorinated solvents is presented (Table 1.1). Some of the more f