Alkaloids and Selected Topics in Their Thermochemistry.

Maja Ponikvar-Svet,Diana N. Zeiger,Joel F. Liebman

doi:10.3390/molecules26216715

Abstract

Alkaloid chemistry is varied and complex. Many alkaloids attract a great deal of interest because of their physiological activity, yet surprisingly little is known about the thermochemistry of these compounds, especially in the gas phase. In this paper, we investigate the thermochemical characteristics, specifically demethoxylation enthalpies rather than those derived from trans-methoxylation reactions, of a series of biologically relevant alkaloids in their condensed phase.

Highlights

Let us start with the definition of an alkaloid
How can we study any reactions analogous to reactions R1 and R2 for condensed-phase alkaloids, and do we find thermoneutrality? An analysis of the few thermochemically characterized alkaloids, all in their condensed phase, is the theme of the present study
We start with the enthalpy of formation data for some alkaloids

Summary

Introduction

Let us start with the definition of an alkaloid. In the public/popular literature, alkaloids are defined as “any of numerous usually colorless, complex, and bitter organic bases (such as morphine or caffeine) containing nitrogen and usually oxygen that occur especially in seed plants and are typically physiologically active” [1]. Experimental studies of the energetics of virtually no alkaloids have ever been undertaken in the gas phase, given that the necessary measurements of enthalpy of vaporization or sublimation remain unreported. This is perhaps not surprising because most alkaloids are multiply substituted, impressively high molecular weight species that have high melting and boiling points. Related volatility and enhanced heat stability are found as subjects for the blossoming study of natural polycyclic hydrocarbons and nonpolar oxygen-containing derivatives These species often have structural complexity and “poetic” names that parallel those of alkaloids (e.g., [15]). Is numerically the same as that of the difference of our demethoxylation enthalpies connecting the enthalpies of formation of ROCH3 and RH with those of R’OCH3 and R’H

The Enthalpies of Formation of Brucine and Strychnine

The Enthalpies of Formation of Anisine and Amarine

Conclusions