Old acid, new chemistry. Negative metal anions generated from alkali metal oxalates and others

Abstract

A brief search in Sci Finder for oxalic acid and oxalates will reward the researcher with a staggering 129,280 hits. However, the generation of alkali metal and silver anions via collision-induced dissociation of the metal oxalate anion has not been previously been reported, though Tian and coworkers recently investigated the dissociation of lithium oxalate [18]. The exothermic decomposition of alkali metal oxalate anion to carbon dioxide in the collision cell of a triple quadrupole mass spectrometer leaves no place for the electron to reside, resulting in a double electron-transfer reaction to produce an alkali metal anion. This reaction is facilitated by the negative electron affinity of carbon dioxide and, as such, the authors believe that metal oxalates are potentially unique in this respect. The observed dissociation reactions for collision with argon gas (1.7-1.8 ϫ 10 Ϫ3 mbar) for oxalic acid and various alkali metal oxalates are discussed and summarized. Silver oxalate is also included to demonstrate the propensity of this system to generate transition-metal anions, as well. (J Am Soc Mass Spectrom 2010, 21, 1944 -1946) © 2010 American Society for Mass Spectrometry T he chemical concept of metals producing positive ions (cations) and non-metals negative ions (anions) is a fundamental precept taught as early as in high school and reinforced throughout a person's university career. However, under certain conditions, metal anions can be created and, as such, their electron affinities are well characterized and calculated both experimentally and theoretically [1]. In solution, alkali metal anions (except lithium) in 'supra molecule complexes' have been prepared in THF and crown ethers. These characteristically blue solutions are now fabricated to control the amount of metal ions, including metal anions. Such solutions have been extensively studied for use in organic synthesis and elucidation of charge-transfer to solvent dynamics (CTTS) [2][3][4][5][6][7][8][9]. In the gas phase, a beam of positively charged alkali cations created from metal vapor can undergo double electron capture to generate a low density negative ion beam [10]. Other means of negative ion generation include discharge and sputter ion sources, namely Cs ϩ ions with a suitable metal cathode [11]. Studies in ion traps utilize dissociative electron attachment to create metal anions [12]. Thus, metal anions are created only via complex experimental procedures or specific experimental apparatus. This paper outlines a method for the production of metal anions requiring a simple oxalate salt solution and a commercially available triple quadrupole mass spectrometer.Oxalic acid is one of the oldest known acids, first isolated from wood sorrel (Oxalis acetosella). It is often found as salt oxalates in many biological systems; particular well known is calcium oxalate found in rhubarb root, known for both its medicinal properties and as a potential poison. Ammonium oxalate is found in guano and there is evidence for the sodium and potassium salts pres...

New Mono‐ and Dimeric Members of the Secalonic Acid Family: Blennolides A–G Isolated from the Fungus Blennoria sp.

“…We have been investigating a procedure to convert certain metal ions from their +1 oxidation state into anions by collision‐induced dissociation (CID) of the anions of metal dicarboxylic acid salts for some time 4. The formation of metal anions from the anions of oxalate salts has been independently communicated recently by the Mayer group 5. However, no details were provided about the dissociation mechanism.…”

Mild route to generate gaseous metal anions

“…[4] The formation of metal anions from the anions of oxalate salts has been independently communicated recently by the Mayer group. [5] However, no details were provided about the dissociation mechanism. In addition to oxalates, we have observed several other anions of dicarboxylic acid salts producing metal anions as dissociation products.…”

Halide anions are formed from reactions between atomic metal anions and halogenated aromatic molecules

“…CO 2 is another small molecule with negative EA. The utility of CO 2 as a leaving group was noted by Curtis et al after observing the decomposition of metal–oxalate complexes in the collision cell of a triple quadrupole mass spectrometer to produce M − , where M = Na, K and Ag . The process can be generalized as follows: where (CO 2 ) 2 represents the oxalate dianion and M is the metal center.…”

“…The process can be generalized as follows: where (CO 2 ) 2 represents the oxalate dianion and M is the metal center. It was theorized by Curtis et al that the high production of AMAs is enabled largely via the negative electron affinity of CO 2 (−0.6 eV), but is also affected by the electron affinity of the metal, the size of the metal and the strength of the bond between the carbon and metal within the complex . Attygale and co‐workers found that other dicarboxylic acid salts such as maleate, fumarate and succinate could also be used …”