Methods for the Detection of Benzenedithiols and Their Analogs by GC-MS Kirill Tretyakov 1, Roman Borisov 2, Nino Todua 1, Vladimir Zaikin 2, Stephen Stein 1, Anzor Mikaia 1. 1 National Institute of Standards and Technology, Gaithersburg, Maryland; 2 Topchiev Institute of Petrochemical Synthesis RAS, Moscow, Russia. OVERVIEW “Para-effect” leading to [C n F 2n+1 CΞS] + ions in the spectra of di(perfluoroacyl)dithiabenzenes is discovered and studied; characteristic ions for differentiation of positional isomers are determined. Figure 1. Mass spectra of isomeric di(acetyl)benzenedithiols REFERENCES 1. Zaikin V., Halket J. A. Handbook of Derivatives for Mass Spectrometry, IMPublications, Chichester, 2009, P INTRODUCTION A unique para-effect has been detected for perfluoroacyl derivatives of bifunctional anilines and the proposed fragmentation mechanism has been confirmed: METHODS Synthesis: Initial bifunctional mercapto- and hydroxybenzenes as well as derivatizing agents (acetic, trifluoro- and chlorodifluoro- acetyl, pentafluoropropionyl and heptafluorobutyryl anhydrides or chlorides) are commercially available. Selective and quantitative derivatization reactions are accomplished in the presence of pyridine 1. Acetates. Fragmentation pathways of di(acetyl)benzenedithiols are shown in Scheme 1. The peak ratios can be used for structure determination. The prominent peak at m/z 167 present only in the spectrum of ortho-isomer is not formed via a two stage process ([M - CH 2 CO - OH] + ); it is a result of a skeletal rearrangement (Scheme 1). CONCLUSIONS 1. “Para-effect” leading to [C n F 2n+1 CΞS] + ions in the spectra of di(perfluoroacyl)dithiabenzenes is discovered and studied; 2. Characteristic ions for differentiation of positional isomers are determined; 3. The preferred charge location and fragmentation is established for di(perfluoroacyl)mercaptophenols. X = NH, O, S; R = CF 3, C 2 F 5, C 3 F 7 Spectra of similar classes of compounds - diacyl derivatives of benzenediols, mercaptophenols and dimercaptobenzenes are studied. Measurements: EI mass spectra are measured on GC/MS systems with quadrupole and magnetic sector analyzers. GC/MS/MS spectra are obtained on a triple quadrupole system. High resolution mass spectra measurements are performed on the double-focusing magnetic sector analyzer. Figure 3. Mass spectra of isomeric is (trifluoroacetyl)mercaptophenols Trifluoroacetates. Two ions [M - CF 3 COS] + (m/z 205) and [M - CF 3 CO 2 ] + (m/z 221) are characteristic for the ortho-isomer (Figure 2a); they can be used for its differentiation from meta- and para- counterparts. The ion [M - CF 3 CO 2 ] + has the same origin as an ion F1 (Scheme 1) in the spectrum of ortho-diacetyl-analog. Figure 6. Mass spectra of isomeric bis(trifluoroacetyl)benzenediols RESULTS AND DISCUSSION Benzenedithiol derivativesMercaptophenol derivativesBenzenediol derivatives Figure 2. Mass spectra of isomeric di(trifluoroacetyl)benzenedithiols Scheme 1. Fragmentation mechanisms of 1,2-di(acetylthio)benzene Scheme 2. Fragmentation mechanisms of 1,2-di(acetylthio)benzene Chlorodifluoroacetyl, heptafluorobutyryl derivatives. Mass spectra of the mixed derivatives are studied to understand the mechanisms of fragmentation of the molecular ions. It is established that mainly the radicals are eliminated from the O-acyl moiety, as shown in Scheme 4. Trifluoroacetates. The spectrum of ortho-isomer (Figure 3a) exhibits similar to S-S-analog fragmentation pathways (ions at m/z 205 and 221). However peak at m/z 152 (analog of 168 in Figure 2a) becomes prominent. The mechanism of it’s formation is depicted on Scheme 3. Scheme 3. Mechanism of formation of an ion at m/z 152 The mechanism of formation of [M - 113] + ion in the case of meta- and para-mercaptophenols is different compared to the ortho-isomer: M +  → [M - COF] + (m/z 271) → [M - COF - CF 2 O] + (m/z 205). Figure 4. Mass spectra of ortho isomeric chlorodifluoroacetyl, heptafluorobutyryl mercaptophenols Figure 5. Mass spectra of para isomeric chlorodifluoroacetyl, heptafluorobutyryl mercaptophenols Mass spectra of isomeric trifluoroacetylbenzenediols reflect above discussed fragmentation pathways. In addition peaks due to the elimination of fluorine and carbon oxide become significant in the spectra (Figure 6). a) X = Y = S; b) X = S, Y = O; c) X = Y = O R, R ’ = CH 3, CF 3, C 2 F 5, C 3 F 7, CF 2 Cl Scheme 4. Mechanism of formation of [M - COR] + ions The “para-effect” leads to an ion [CF 3 CΞS] + in the case of para- di(trifluoroacetyl)benzenedithiol (Figure 2c); it’s formation proceeds similar to para-di(perfluoroacyl)diaminobenzenes with the location of the charge on thioacyl moiety (Scheme 2). The spectra of pentafluoropropionyl- and hexafluorobutyryl-derivatives exhibit similar fragmentation patterns.