In situ generation of HCN for mass spectrometric studies

Abstract

Hydrogen cyanide (HCN) for use in ion preparation can be generated in the gas phase by the neutral-neutral reaction of trimethylsilyl cyanide (Me 3 SiCN) and water in a flowing afterglow mass spectrometer. We demonstrate that the approach can be used to generate a wide range of HCN solvated ions such as F Ϫ (HCN), Cl Ϫ (HCN), CN Ϫ (HCN), PhNO 2 ·Ϫ (HCN), Me 3 SiO Ϫ (HCN),and PhSiF 4 Ϫ (HCN), many of which are otherwise difficult to generate. The bond dissociation energy of CN Ϫ (HCN), generated by using this approach, has been measured by using energy-resolved collision-induced issociation (CID) to be 0. [2,3] in both the condensed phase and the gas phase. Whereas solvated halide [4,5] and alkoxide [6] ions are readily examined, clusters of cyanide are especially of interest because CN Ϫ is a pseudohalide with an ambidentate nature. Moreover, the conjugate acid, HCN, is a weak acid (⌬H acid ϭ 350.9 Ϯ 0.2 kcal/mol) [7] with extensive positive charge character on the hydrogen, making it an attractive hydrogen-bonding moiety in the gas phase [8]. Recently, HCN has gained much interest as it has been found to be a tracer for young stellar objects, and it has been detected in the atmosphere of Titan [9].An important challenge in carrying out studies involving cyanide or hydrogen cyanide is in the safe generation of the reagents. Because of its toxicity, HCN is rarely used directly as a reagent gas. Previous studies by Larson and McMahon [8] and Meot-Ner and coworkers [10] have used the solution phase reaction of KCN and acids (HCl or H 2 SO 4 ) to produce HCN, which was directly added to the mass spectrometer. Subsequently, ion-exchange equilibria [8] and van't Hoff measurements [10] were used to determine anion-neutral binding energies of CN Ϫ and HCN containing clusters. Recent studies have utilized the reaction of CH 4 and NH 3 with Pt catalyst to generate HCN in a molecular beam apparatus [11].In this work, we describe a simple in situ approach for generation of HCN for ion clustering studies. Hydrogen cyanide is formed by the neutral-neutral reaction of trimethylsilyl cyanide, Me 3 SiCN, with water in a flowing afterglow reactor. We demonstrate that the approach can be used to generate a wide range of HCN solvated ions and report energy-resolved CID studies of the HC 2 N 2 Ϫ ion formed. From these CID studies, we report a direct measurement of the [CN-HCN] Ϫ bond dissociation energy. Throughout this paper, HC 2 N 2 Ϫ refers to the m/z 53 species that has been observed and characterized. However, this notation does not indicate a specific ion structure. The structures of the HC 2 N 2 Ϫ isomers are addressed computationally at the end of this study. ExperimentalAll experiments were carried out in a flowing afterglow triple quadrupole mass spectrometer that has been previously described [12,13]. Fluoride was prepared by 70 eV electron ionization of neutral fluorine gas (5% in He, Spectra Gases Inc., Branchburg, NJ) and carried by helium buffer gas (0.400 torr, flow (He) ϭ 190 STP cm 3 /s) through the flow tube wh...

Salts of HCN‐Cyanide Aggregates: [CN(HCN)2]− and [CN(HCN)3]−

“…In the following, we will only discuss the DFT results. In accord with other theoretical studies, there are three possible stable linear isomers of the monosolvate [CN(HCN)] − (Figure ). As shown in Figure , isomer L1 with one covalent C−H and one H⋅⋅⋅N bridge is the thermodynamically favored isomer; however, the energy difference between L1 and L2 is rather small at 0.72 kcal mol −1 .…”

“…The stepwise formation of the HCN solvates [CN(HCN) n ] − were computed to be exothermic and exergonic for n= 1–3 (Table S10); however, the larger the value of n , the less negative are the Δ n H ° 298 /Δ n G ° 298 values (Δ n H ° 298 : −23.6, −18.7, and −13.0; Δ n G ° 298 : −15.9, −11.1, and −7.0 kcal mol −1 ; cf. from mass spectrometry: Δ 1 H ° 298 =−20.1±1.6, and −20.7, as well as Δ 2 H ° 298 =−16.4, and Δ 3 H ° 298 =−12.6 kcal mol −1 ) …”

Salze von HCN‐Cyanid‐Aggregaten: [CN(HCN)2]− und [CN(HCN)3]−

“…Im Folgenden werden nur die Ergebnisse der DFT-Berechnungen besprochen. In Übereinstimmung mit anderen theoretischen Studien [61,62,[84][85][86] Bereits Meot-Ner, Scheiner und Liebman [61] zeigten durch Ab-initio-Berechnungen von [CN(HCN) n ] À -Ionen, dass sehr flache Potentiale bei geringen ¾nderungen der Struktur wie Winkel und Diederwinkel sowie für die Wanderung eines Protons angenommen werden kçnnen. Wir haben das Rotationspotential des zentralen CN À -Ions in einem flexiblen (HCN) n -System (n = 2, 3, siehe Abbildung S14 und S15) ge-Abbildung 5.…”

“…Jedoch werden die Werte für D n H8 298 / D n G8 298 umso weniger negativ, umso grçßer n ist (D n H8 298 : À23.6, À18.7, und À13.0; D n G8 298 : À15.9, À11.1, und À7.0 kcal mol À1 ; vgl. mit massenspektroskopisch ermittelten Werten: D 1 H8 298 = À20.1 AE 1.6 [84] und À20.7 [61] sowie D 2 H8 298 = À16.4 und D 3 H8 298 = À12.6 kcal mol À1 ). [61] Zusammenfassend haben wir die ersten Beispiele von HCN-Cyanid-Aggregaten, [CN(HCN) n ] À (n = 2, 3), im festen Zustand isoliert und strukturell charakterisiert.…”

“…Im Folgenden werden nur die Ergebnisse der DFT‐Berechnungen besprochen. In Übereinstimmung mit anderen theoretischen Studien gibt es drei stabile lineare Isomere des Monosolvats [CN(HCN)] − (Abbildung ). Wie in Abbildung dargestellt, ist das Isomer L1 mit einer kovalenten C‐H‐ und einer H⋅⋅⋅N‐Brücke das thermodynamisch bevorzugte Isomer, jedoch ist der Energieunterschied zwischen L1 und L2 mit 0.72 kcal mol −1 eher gering.…”