Synthesis of Precursors to Tetrazole Monomers by Acid-Catalyzed Alkylation
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hesis of Precursors to Tetrazole Monomers by Acid-Catalyzed Alkylation S. A. Egorova,*, M. A. Ishchenkoa, and A. S. Alikberova a
St. Petersburg State Institute of Technology, St. Petersburg, 190013 Russia *e-mail: [email protected] Received February 22, 2020; revised April 23, 2020; accepted April 23, 2020
Abstract—The alkylation of 1H-tetrazole and 5-methyl-1H-tetrazole with 2-chloro- and 2-bromoethanol in concentrated sulfuric acid gave precursors to 2-ethenyl-2H-tetrazole and 2-ethenyl-5-methyl-2H-tetrazole in preparative yields. The alkylation process in deuterated sulfuric acid was studied by 1H NMR spectroscopy. The yields of the alkylation products ranged from 14 to 76%, depending on the conditions and reactants, and the concentration of the 2-substituted isomers was no less than 99%. Keywords: tetrazole, precursors to tetrazole-containing monomers, regioselective alkylation, 2-chloroethanol, 2-bromoethanol
DOI: 10.1134/S1070428020070131 of 2-substituted isomers. If highly stabilized carbocations are generated from initial alcohols, the yield reaches 70–90%, and the reaction time ranges from one to several hours at room temperature. Despite obvious efficiency of this method, we have found only one published example of its application for the synthesis of 2-(1-halopropan-2-yl)-2H-tetrazoles as precursors to tetrazole monomers [11] (Scheme 1).
Tetrazole polymers have attracted much interest in recent years. The first publications on this class of polymers were concerned exclusively with their application as high-energy materials, in particular as gun powders [1]. Nowadays, the scope of their use covers such fields as medicine [2], energetic materials [3], catalysis [4], ion-exchange membranes [5], coordination [6] and photosensitive polymers [7], etc. The diversity of their applications is related to the unique set of properties of tetrazole ring which is characterized by high enthalpy of formation, high nitrogen content, and complexing ability. In addition, tetrazole polymers exhibit pharmacological and photochemical activities. A comprehensive review on tetrazole-containing polymers has been made in [8]. Vinyl derivatives of tetrazoles have been considered separately [9].
In the reactions with 1-bromopropan-2-ol, the yields of the target products were fairly high (58–88%). In the case of 1-chloropropan-2-ol, the yields were fairly poor (15–45%) due to electron-withdrawing effect of the chlorine atom, which destabilized intermediate carbocation. The reactions were carried out in 96% sulfuric acid for 7 days at room temperature. No further attempts were made to develop the field of synthesis of precursors to tetrazole monomers, presumably because of the low reactivity of halogen-containing alkylating agents. However, analysis of published data indicates that the most important are vinyltetrazoles obtainable from 2-(2-haloethyl)-5-R-tetrazoles; therefore, study of
A promising method of synthesis of tetrazole derivatives is based on acid-catalyzed alkylation which was reported for the first time in [10
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