On the solvent and counter ion-free mechanism of ketalization reactions of gaseous activated carbonyls

被引:1
作者
Beraldo Moraes, Luiz Alberto [1 ]
Meurer, Eduardo Cesar [2 ]
Eberlin, Marcos Nogueira [3 ]
机构
[1] Univ Sao Paulo, Mass Spectrometry Appl Nat Prod Lab, Dept Quim, Fac Filosofia Ciencias & Letras Ribeirao Preto, BR-14040901 Ribeirao Preto, SP, Brazil
[2] Univ Fed Parana, Dept Quim, Lab Fenn Mass Specrometry, BR-86900000 Jandaia Do Sul, PR, Brazil
[3] Univ Estadual Campinas, ThoMSon Mass Spectrometry Lab, Inst Quim, BR-13083970 Campinas, SP, Brazil
基金
巴西圣保罗研究基金会;
关键词
Ion-molecule reactions; Pentaquadrupole mass spectrometer; Ketalization; GAS-PHASE; SCANS;
D O I
10.1016/j.ijms.2017.07.003
中图分类号
O64 [物理化学(理论化学)、化学物理学]; O56 [分子物理学、原子物理学];
学科分类号
070203 ; 070304 ; 081704 ; 1406 ;
摘要
Ketalization of aldehydes and ketones is widely used in solution to protect their reactive carbonyl groups from undesired transformations. This reaction is known to be stereospecific and usually employs a diol [HOCH2CH2OH]. In acidic media, the reaction is believed to first involve the addition of OH to C=O+ H, with subsequent cyclization due to a second OH nucleophilic attack promoting intramolecular nudeophilic substitution and loss of water. To investigate the intrinsic features of such key organic reaction, gas phase reactions of mass-selected protonated and alkylated ketones [R C(R')=OH+, R-C(R')=O+-CH3 with methoxyethanol [CH3OCH2CH2OH] were performed via pentaquadrupole multiple-stage mass spectrometry. Initially, the reactions were carried out with protonated ketones. Two mechanistic routes were considered for the reaction studied in such solvent-free and counter ion-free environment: the classic reaction pathway observed in solution, and a second possibility where 5-exo-tet ring closing would occur, followed by methanol loss. Whereas protonated ketones were found to display low ketalization yields and'to react mainly by proton transfer, methylated ketones reacted mainly by ketalization. The gas phase mechanism was studied using O-18 and H-2 labeling, and via comparison with authentic ions. The findings confirmed the operation of the classical ketalization mechanism also in the gas phase, and the high yield and regioespecificity of such reactions suggest that it can be widely used as a diagnostic ion/molecule reaction for diols. (C) 2017 Elsevier B.V. All rights reserved.
引用
收藏
页码:170 / 177
页数:8
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