The fragmentation patterns were obtained by electron-impact on 6-acetamido-, 6-amino-, 6-bromo-, 6-chloro-, 6-methoxy-, 6-methyl-, 6-nitro-, 5-carboxy-, 5-iodo-, 5-methoxy-and 5-nitro-2pyridinecarboxylic acids, as well as 2-and 3-pyridinecarboxylic acids. Most of these acids lost CO, [M -441 as their first major fragmentation. This is in direct contrast to the substituted benzoic acids which show loss of OH [M -171 or CO,H [M -451 in their first major fragmentation. Our work suggests that the ring nitrogen may determine which pathway predominates. Figures are presented to illustrate the patterns and metastable ions are indicated when found for the transitions discussed.FRAGMENTATIQN patterns by electron-impact of pyridine and some substituted derivatives can be found in the l i t e r a t~r e .~.~,~ The mass spectral data of benzoic acid and some substituted derivatives have also been r e p~r t e d , * ,~>~ but nothing has appeared concerning the pyridinecarboxylic acids. A systematic investigation was undertaken to study the mass spectral fragmentations of a number of substituted 2-pyridinecarboxylic acids. It was possible to contrast the primary fragmentations of 5and 6-substituted-2pyridinecarboxylic acids with similarly substituted benzoic acids. It was of interest to determine if the primary loss was that of the substituent (at C-6 or C-5), loss of the acid function (at C-2), or ring rupture.Not all fragmentation processes will be discussed since many are predictable from a given molecular ion. Only those that are unique or offer an interesting comparison will be mentioned in the discussion. These fragmentations are due primarily to electron bombardment because (1) five of the ten acids show metastable ions which indicate that CO, is lost after ionization and (2) the direct inlet temperature was well below the melting point of these compounds (all of these compounds decompose at or above their melting points).
Compounds tha f lose CO, as$rst major fragmentThe fragmentation patterns of 2-pyridinecarboxylic acid (la), 6-methyl-2-pyridinecarboxylic acid (Ib), 6-bromo-2-pyridinecarboxylic acid (Ic), 6-chloro-2pyridinecarboxylic acid (Id), 6-amino-2-pyridinecarboxylic acid (Ie), 5-iodo-2pyridinecarboxylic acid (IIa), 2,5-pyridinedicarboxylic acid (IIb), 5-methoxy-2-pyridinecarboxylic acid (IIc) and 5-nitro-2-pyridinecarboxylic acid (IId) are shown in Scheme 1. All of these acids had molecular ion peaks of less than 10% fractional abundance, while loss of 44 mass units [M -CO,] generated peaks of 8 % or more.This was in direct contrast to the benzoic acids which usually displayed a somewhat larger molecular ion peak and showed as their two most characteristic peaks [M -OH] or [M -C0,H].5 555 * The occurrence of this process is supported by the presence of an appropriate metastable ion in the mass spectrum.